Division of Agricultural Sciences 
 UNIVERSITY OF CALIFORNIA 
 
 
 
 
 i 
 
 ■ > 
 ■■*■■•■ * * - • -. - "■'■ 
 
 CALIFORNIA AGRICULTURAL 
 EXPERIMENT STATION 
 
 BULLETIN 773 
 
GROWERS and SHIPPERS 
 
 interested in choosing new cooling facilities and modifying existing ones 
 will find information in the first section of this bulletin on "Cooling i 
 Methods/ 7 ,, 
 
 ENGINEERS 
 
 and others desiring to design coolers will find the second section on 
 "Cooler Designs" especially useful. 
 
 RESEARCH WORKERS \ 
 
 will turn to the technical third section, "Analysis and Test Data," which 
 contains the material on which the first two sections are based. 
 
 CONTENTS 
 
 Section I: Cooling Methods 3 
 
 Introduction 3 
 
 Ice or mechanical refrigeration?.... 3 
 
 Humidity control 4 
 
 Types of Coolers 5 
 
 Room cooling 5 
 
 Fast methods of air cooling 6 
 
 Hydrocooling 9 
 
 Vacuum cooling 10 
 
 Cooling Methods in Rail Cars 13 
 
 Car cooling by ordinary spacing .... 13 
 
 Car cooling by chimney suction 14 
 
 Forced-air cooling in rail cars 15 
 
 Costs of Cooling Methods 18 
 
 Section II: Cooler Design 21 
 
 Comparing and estimating cooling rates 21 
 
 Cooling rooms 21 
 
 Forced-air coolers 22 
 
 Mechanical refrigeration capacity . . 26 
 
 Ice bunker design 29 
 
 Spray humidification 32 
 
 Insulation and vapor barrier 36 
 
 Air passages 37 
 
 Fans 38 
 
 Section III: Analyses and Test Data 39 
 
 Cooling Calculations 39 
 
 Refrigerator Load 42 
 
 Ice Bunker Performance 43 
 
 Humidity Calculations 46 
 
 Optimum Insulation 48 
 
 Forced-Air Cooling Calculations .... 50 
 
 Half-Cooling Times 55 
 
 Units and Conversion Factors 63 
 
 References 64 
 
 Acknowledgments 66 
 
Section I 
 
 COOLING METHODS 
 
 INTRODUCTION 
 
 Cooling may greatly reduce deteriora- 
 tion of fruits and vegetables between 
 harvest and consumption. Although cool- 
 ing effects on the product are important 
 and should be carefully considered in 
 planning an operation, this bulletin dis- 
 cusses only the engineering aspects of 
 cooling. 
 
 Room cooling, a method used widely, 
 relies on the heat being carried from the 
 product to the ice or refrigerated surfaces 
 chiefly by air which is circulated around 
 the containers. 
 
 Fast methods of air cooling, such as 
 ceiling-jet cooling and forced-air cooling, 
 use air that is made to flow through the 
 containers. 
 
 Hydrocooling depends on water being 
 flowed about or through containers or 
 through a bulk layer of the product, 
 carrying heat from the product to ice or 
 refrigerated surfaces. 
 
 Vacuum cooling uses equipment in 
 which heat is absorbed by evaporation 
 of water from the product. 
 
 "Body" icing relies on finely chopped 
 ice, packed inside the container and 
 mixed with the product, to absorb heat. 
 
 Cooling may be carried on in spaces 
 designed specifically for that purpose, in 
 rooms used also for storage, or in loaded 
 cars. The heat removed from the product 
 is commonly absorbed either by melting 
 
 ice or by mechanical refrigeration. Hu- 
 midity is sometimes controlled in air 
 coolers to prevent dehydration of the 
 product. 
 
 All five methods listed above, using ice 
 or mechanical refrigeration, with or with- 
 out humidity control, have their places 
 and are in profitable commercial use in 
 California. 
 
 ICE OR MECHANICAL 
 REFRIGERATION? 
 
 The initial cost of an ice bunker is a 
 small fraction of the cost of a mechanical 
 system to do the same job. On the other 
 hand, it is much cheaper to operate 
 the mechanical system than to buy ice. 
 Generally, the total annual cost for an 
 operating season of a month or two is 
 less for an ice-cooled unit, while for a 
 season of four to six months or more, a 
 mechanical system is cheaper. 
 
 A well-planned ice bunker requires 
 little maintenance and is very simple to 
 operate. A mechanical system must be 
 operated and cared for intelligently and 
 will eventually require fairly expensive 
 maintenance to insure against failure at 
 a critical time. Supplies of ice and elec- 
 tricity are local problems. An ice bunker 
 maintains higher humidity in a cooler or 
 storage than most mechanical systems do. 
 However, humidity is undesirably low 
 
 The Author: 
 
 Rene Guillou is Associate Specialist in the Experiment Station, Department of Agricultural 
 Engineering, Davis. 
 
 JULY, 1960 
 
 [3] 
 
with any system when the product is 
 warm and the containers are dry unless 
 water sprays are provided; water sprays 
 can produce satisfactory humidity in any 
 system. 
 
 Size and weight of a refrigeration 
 source are important in the case of 
 mobile equipment. The size and weight 
 of a mechanical unit are usually only a 
 fraction of the size and weight of a 
 bunker and water-ice to do the same 
 work. Dry ice compares favorably with 
 mechanical refrigeration in weight and 
 volume needed to absorb heat at a given 
 rate, though the cost per heat unit ab- 
 sorbed is about double the cost for water 
 ice. 
 
 HUMIDITY CONTROL 
 
 Some products, such as grapes, de- 
 teriorate seriously from loss of moisture 
 during cooling and storage. Other things 
 being equal, moisture loss is proportional 
 to the difference in water-vapor pressure 
 between the product and the surrounding 
 air and the time over which this differ- 
 ence exists. The time element may be 
 reduced by cooling the product as rapidly 
 as possible. Evaporation after a product 
 is cooled may be reduced by use of the 
 lowest air velocity that will prevent a rise 
 in temperature, thus allowing evapora- 
 tion from the product to raise the hu- 
 midity of the air in its immediate vicinity. 
 Probably most may be accomplished, 
 however, by raising the general level of 
 humidity of the air in a cooler or storage. 
 
 The humidity in a cooler or storage is 
 determined in part by the size and tem- 
 perature of the cooling surfaces. Large 
 cooling surfaces within a few degrees of 
 air temperature ordinarily condense out 
 less moisture than smaller surfaces that 
 must be colder in order to give the same 
 refrigerating effect. A little more mois- 
 ture condenses in brine-spray cooling 
 units than on ice or dry coils at the 
 same cooling-surface temperature. Boxes 
 and packing materials absorb moisture 
 rapidly when they are first moved from 
 
 dry outside air to a humid cooler. As 
 they become damper, they absorb mois- 
 ture more slowly, but it may take them 
 weeks to come to equilibrium. 
 
 Usually, the moisture to offset these 
 losses is evaporated from the product, 
 the air in the cooler remaining at a 
 humidity at which the losses and gains 
 balance. Use of larger cooling surfaces 
 on which there is less condensation re- 
 sults in higher air humidity and corre- 
 spondingly less evaporation from the 
 product. In a well-insulated storage con- 
 taining cold fruit in damp containers 
 and cooled by a large ice bunker, con- 
 densation on the cooling surfaces and 
 evaporation from the product may be 
 insignificant. To attain this condition 
 with mechanical refrigeration requires 
 very large and expensive cooling units, 
 and it is practically impossible to attain 
 it with warm fruit even with ice as a 
 coolant. Air humidity may be raised 
 quite easily by means of fog sprays in 
 a cooler or storage. In 1958 there were 
 several such installations in California. 
 In one case rooms cooled by brine spray 
 and humidified with fog sprays were held 
 at 91 per cent relative humidity and after 
 several months the grapes stored in them 
 were considered equal in condition to 
 those in adjacent rooms cooled by ice. 
 
 Substitution of fog spray for evapora- 
 tion from the product makes it possible 
 to have whatever humidity is desired 
 while using relatively small cooling sur- 
 faces. A spray system capable of supply- 
 ing 10 or 15 gallons of water per ton-day 
 of refrigeration or per ton of ice melted, 
 plus whatever moisture is absorbed by 
 boxes and packing material, can maintain 
 90 per cent relative humidity in the 
 return air under almost any practical 
 conditions. 
 
 Condensation in a brine-spray cooler 
 requires addition of salt to offset that 
 lost in overflow from the brine tank. 
 Moisture sprayed into a room cooled by 
 dry coils, less what is absorbed by the 
 boxes, must be removed from the coils 
 
 [4] 
 
by defrosting. At very high humidities 
 there may be trouble from collection of 
 water on walls or floor or from wetting 
 containers or product. These problems 
 
 have been anticipated in existing installa- 
 tions but so far they have not been 
 troublesome. 
 
 TYPES OF COOLERS 
 
 ROOM COOLING 
 
 Exposure of packed containers to cold 
 air in a refrigerated space is one of the 
 commonest methods of cooling. Ad- 
 vantages of this method are: 
 
 1. The product may be cooled and 
 subsequently stored in the same place 
 without rehandling and with no special 
 facilities for the cooling operation. 
 
 2. Design of the plant and its operation 
 are simple. 
 
 3. Because of the relatively slow rate 
 at which the produce is cooled, peak 
 loads on the refrigeration system are less 
 than with fast-cooling methods. 
 
 Limitations and disadvantages are: 
 
 1. When produce is cooled in prepara- 
 tion for immediate shipment, the time 
 required for room cooling sometimes 
 delays loading or results in produce be- 
 ing loaded before it is adequately cooled. 
 
 2. Deterioration of the product in the 
 
 <I00 
 
 time needed to cool it may be appreciable 
 if the product is highly perishable or is 
 initially very warm or if spaces between 
 the stacked containers are not adequate. 
 
 3. There is usually a stage in the cool- 
 ing process in which the exposed portion 
 of stacks or of individual containers is 
 considerably colder than the interior. 
 While this condition exists, air move- 
 ment from the warmer product may 
 result in condensation of moisture — 
 "sweating" — on the colder product. 
 
 4. If special cooling rooms are pro- 
 vided and the produce is rehandled, a 
 modern, fast-cooling system uses less 
 floor space and requires no more 
 handling. 
 
 5. If special cooling rooms are not 
 provided, each addition of warm pro- 
 duce raises the temperature and lowers 
 the relative humidity in the storage 
 space. This subjects stored products to 
 
 Pears in cartons 
 tight- stacked on pallet 
 
 Fig. 1. Room cooling in typical situations, average fruit pulp temperatures. 
 
 [5] 
 
continual fluctuations in temperature 
 and humidity. 
 
 6. Products which respire rapidly may 
 evolve considerable heat in the course 
 of a slow cooling operation, which uses 
 additional refrigeration and slows cool- 
 ing still further. 
 
 Room cooling appears to be well 
 adapted to apples and pears, which are 
 not highly perishable and which are 
 likely to be stored after cooling. Faster 
 cooling methods deserve consideration 
 for peaches, grapes, strawberries, and 
 for all perishable vegetables. The time 
 required for room cooling depends 
 mainly on the relation of exposed con- 
 tainer surface to the weight of the 
 product. The effect of vents in corru- 
 gated fibreboard cartons seems to be 
 proportional to the additional area which 
 they expose, with no consistent differ- 
 ences due to shape or location. 
 
 Air movement sufficient to prevent the 
 formation of warm pockets in a room 
 usually brings the exposed container 
 surfaces to near air temperature in a 
 short time. Further acceleration of cool- 
 
 ing requires velocities sufficient to actu- 
 ally drive air into or through the con- 
 tainers. It is not practicable to expose a 
 reasonable proportion of the containers 
 to such velocities in a conventional cool- 
 ing room. Special air-jets or tunnels are 
 required for this purpose, as discussed 
 in following sections. Figure 1 shows 
 rates of room cooling for some typical 
 products and containers. 
 
 FAST METHODS OF AIR COOLING 
 
 Ceiling-jet cooling 
 
 Heat may be removed from fruits or 
 vegetables faster by air flowing into the 
 containers and about the individual 
 articles than by air flowing about the 
 containers. An ingenious and economical 
 use of this principle is made by pro- 
 viding air ducts on the ceiling of a cool- 
 ing room with nozzles to direct air jets 
 vertically downward. The floor is marked 
 to show the positions in which containers 
 are to be stacked, leaving channels which 
 line up with the nozzles above. 
 
 Cooling is considerably faster than in 
 a conventional cold room, as shown in 
 figure 2. Costs for installation of the 
 ducts and nozzles and for additional fan 
 power are moderate and good use is 
 made of the floor space. 
 
 Conventional room 
 lugs exposed on 4 sides 
 
 Hours 
 
 Fig. 2. Comparative cooling of grapes by different methods, 
 average fruit pulp temperatures in lidded lugs. 
 
 [6] 
 
Forced-air cooling 
 
 The term "forced-air cooling" is used 
 here to designate the cooling of fruits or 
 vegetables by use of a difference in air 
 pressure to force air through stacked 
 containers. Heat is carried away pri- 
 marily by flow of air past the produce 
 inside the containers rather than by flow 
 past the outside of the containers as in 
 ordinary room cooling. 
 
 Advantages of forced-air cooling are: 
 
 1. Fast cooling reduces time for de- 
 terioration while the product is warm 
 and allows prompt loading without con- 
 cern for subsequent cooling in rail cars 
 or in trucks. 
 
 2. Packed containers may be cooled 
 rapidly while stacked on the floor, on 
 pallets, or on conveyors, without de- 
 ferring the lidding operation as in air- 
 blast cooling and without wetting the 
 containers and contents as in hydro- 
 cooling (see page 9). 
 
 3. Air movement is always from colder 
 fruit upstream to warmer fruit down- 
 stream, which avoids the sweating that 
 is sometimes troublesome when air moves 
 from warm fruit near the center of con- 
 tainers to cold fruit near the outside, as 
 it may in room cooling. 
 
 IOOi 
 
 £ 80 
 5i 
 
 S< 60 
 
 IE 
 
 £.* 
 
 _ 3 
 
 .si 
 
 Ec 40 
 
 — <u 
 
 o * 
 
 — « 
 
 C QQ 
 
 20 
 
 4. Fan energy, in horsepower hours to 
 accomplish a given cooling job, is less 
 than for other methods of air cooling. 
 Energy used to circulate the coolant in 
 any cooling operation is eventually con- 
 verted into heat, which must be offset 
 by additional refrigeration. The total 
 cost of this additional refrigeration is 
 usually several times the cost of operat- 
 ing the fans or pumps and is sometimes 
 a substantial part of the total cost of 
 cooling. 
 
 5. Compared with ordinary room cool- 
 ers, forced-air coolers can care for a 
 given volume of product in a fraction 
 of the space, which reduces both first 
 cost and refrigeration losses. 
 
 6. Existing room coolers can often be 
 converted for forced-air cooling at small 
 expense. The quantity of fruit in a cooler 
 at one time may be reduced by such a 
 conversion, but cooling is usually so 
 much faster that more fruit may be 
 cooled in a day. 
 
 Limitations and disadvantages are: 
 
 1. As with any fast cooling method, an 
 additional handling of the product is 
 necessary as compared with cooling in 
 storage or in a loaded rail car. 
 
 2. Containers must be vented and air- 
 flow through the pack must not be pre- 
 vented by wraps or dividers, or by the 
 nature of the product, as in the case of 
 leafy vegetables. 
 
 Conventional room 
 (cup packed lidded lugs) 
 
 I 
 
 I 
 
 Hydrocooler 
 (naked fruit) 
 
 I 
 J 
 
 Half cool 
 
 Forced air cooler 
 
 (cup packed lidded lugs) 
 
 Hours 
 
 Fig. 3. Comparative cooling of peaches by different methods, average fruit pulp temperatures. 
 
 [7] 
 
3. Cooling is increasingly uneven as 
 air is forced through several tiers of 
 containers. The upstream fruit may be 
 cooled virtually to air temperature in a 
 very short time, and this must not be so 
 cold as to cause injury in the time re- 
 quired to satisfactorily cool the down- 
 stream fruit. 
 
 4. It is not practicable to equal the 
 very short cooling times attainable by 
 hydrocooling or by vacuum cooling. 
 
 Forced-air cooling was first tested by 
 the University of California on a labora- 
 tory scale in 1955, and in a pilot model 
 in 1956. In 1958 a dozen commercial 
 units in California were cooling grapes, 
 peaches and strawberries with outputs 
 ranging from a ton per hour to over a 
 carload an hour. The product is handled 
 with hand trucks or on pallets or is 
 stacked on conveyors which run through 
 the coolers. Half-cooling times, based on 
 the warmest fruit and the ice tempera- 
 tures, range from 30 minutes to 2 hours 
 depending on product, containers, and 
 fan capacity. Refrigeration is either me- 
 chanical or from ice. 
 
 Plan No. 243, "Fruit Cooler," obtain- 
 able at cost of blueprints from Agricul- 
 tural Publications, 207 University Hall, 
 2200 University Ave., Berkeley 4, gives 
 plans and specifications for an ice-cooled 
 unit with an output of about one ton 
 per hour. Several grower-shippers have 
 planned and constructed successful small 
 forced-air coolers. Design of larger units, 
 particularly if mechanical refrigeration 
 is used, should be undertaken by a com- 
 petent engineer. 
 
 Figures 2 and 3 show cooling rates 
 commonly obtained in forced-air coolers 
 with peaches and with grapes, and by 
 other cooling methods for comparison. 
 Forced-air cooling is best adapted to 
 situations where it is desirable to cool 
 a product in a few hours but not neces- 
 sarily in minutes, where the pack is open 
 to through-air flow or can be made so 
 and where the product or the container 
 would be damaged by water. 
 
 Other methods of 
 fast air cooling 
 
 Fast cooling may be obtained by 
 directing high-velocity air-blasts into 
 open containers (20). Three coolers of 
 this type were operated in California at 
 
 ■Warmest box centers 
 •Average box centers 
 
 Fig. 4. Car cooling by ordinary spacing, wrapped pears in standard boxes. (Data from 
 1942 mimeographed report by U.S. Dept. of Agriculture and Univ. of California). 
 
 [8] 
 
one time, but two of these have been 
 dismantled. Operators have reported 
 excellent cooling. However, conveyors 
 to expose the necessary number of un- 
 lidded containers in a single layer have 
 been expensive to install and to main- 
 tain. At least one extra handling of each 
 container is necessary. Energy put into 
 the system by high-power fans — around 
 10 horsepower per ton of fruit cooled 
 per hour — and difficulty in controlling 
 air leakage, have combined to require 
 excessive refrigeration. 
 
 Air may be caused to flow into stacked 
 containers by placing them in a tunnel 
 through which air is moved at high 
 velocity. This method is used in South 
 Africa and has been tested in the Pacific 
 Northwest (25) . Around 6 horsepower of 
 fans per ton of fruit cooled per hour 
 have been used with accompanying 
 rather serious refrigeration losses. So 
 far as is known there are no installa- 
 tions in California. 
 
 HYDROCOOLING 
 
 Fruits and vegetables may be cooled 
 very rapidly by bringing them in contact 
 
 3 
 
 100 
 
 Z 80 
 
 Warmest basket centers 
 -Average basket centers 
 
 60 
 
 2 40 
 
 20 
 
 except brief stops for reicing 
 I I 
 
 J I I L_ 
 
 with moving cold water. This may be 
 accomplished in several types of equip- 
 ment and the job will be fast and uniform 
 if these requirements are met: 
 
 1. The water should move over the 
 surface of the individual fruits or vege- 
 tables. 
 
 2. The water should contact as much 
 of the surface of the individual fruits 
 or vegetables as their nature allows. 
 
 3. The water should be kept cold. 
 Water showered on a mass of fruits 
 
 or vegetables and running down through 
 it is moving satisfactorily, but if the 
 mass of material is deep — a foot or more 
 — the water may channel and come in 
 contact with only a part of the lower 
 surfaces. This may be avoided by prop- 
 erly proportioning the water flow and 
 the drainage at the bottom of the con- 
 tainers. The ideal is to have the con- 
 tainers full but overflowing only slightly, 
 most of the water running down through 
 the containers. If the product is im- 
 mersed in a tank, it should be arranged 
 so that water passes through the mass 
 of material, not merely around it or 
 under it. Figure 3 shows a typical hydro- 
 cooling curve in comparison with other 
 methods of cooling. 
 
 Hydrocooling is competitive in cost 
 with other methods and is the fastest 
 method for all products except leafy 
 vegetables, for which vacuum cooling is 
 faster and cheaper if facilities are avail- 
 able. Hydrocooled products commonly 
 gain moisture in the cooling operation 
 
 10 
 
 15 
 
 20 
 Hours 
 
 25 
 
 30 
 
 35 
 
 40 
 
 Fig. 5. Car cooling by ordinary spacing, plums in 4-baslcet crates. (Data from 1942 
 mimeographed report by U. S. Dept. of Agriculture and Univ. of California.) 
 
 [9] 
 
-6f«-l 
 
 1 
 1 
 
 -19*" 
 
 Proposed corton for peors or 
 opples. Contents 2l50cu in., I 
 US bushel about45lb.net. 
 
 Height of these cartons moy 
 be changed for other capacities 
 
 d — ± 
 
 J 
 
 Proposed corton for plums or grapes 
 Contents 1300 cu. in, about 301b. net. 
 
 Rail cor chimney load 
 3 chimneys wide 99" 
 12 chimneys long 396" 
 144 cartons per layer 
 
 Truck solid load 
 93"wide 
 
 Roil car solid load, 
 5 cartons wide 99 
 30 cartons long 398" 
 150 cartons per layer 
 
 Truck solid lood 
 86" wide 
 
 Fig. 6. Proposed design and arrangement of 
 cartons for chimney-suction cooling. 
 
 and wilt less in subsequent storage and 
 handling than if they had been cooled 
 by air or in vacuum. 
 
 The objections to hydrocooling are 
 possible damage to containers and pack- 
 ing materials from wetting and damage 
 to the product from wetting or from in- 
 fections carried by the water. The use 
 of disinfectants in the water is a problem 
 in plant physiology which is beyond the 
 scope of this publication. Damage to 
 containers and packing materials may 
 be eliminated by cooling before packing. 
 If this is done, however, any rise in 
 temperature of the product after cooling 
 must be offset by additional refrigera- 
 tion either before or after packing. Tests 
 of hydrocoolers have commonly shown 
 that less than half of the ice purchased 
 is melted by heat removed from the 
 product (30) . The rest is melted in stor- 
 age, in handling, by warm air entering 
 the cooler and by heat entering through 
 exposed or poorly insulated surfaces. 
 Power supplied to the water pump is 
 converted to heat by churning of the 
 
 water, melting about 24 pounds of ice 
 per hour per horsepower. 
 
 Portable, rented hydrocoolers allow 
 fixed charges on the equipment to be 
 spread over a number of seasonal opera- 
 tions and provide fast and effective cool- 
 ing at reasonable cost. Portability is 
 commonly attained, however, at the ex- 
 pense of best economy in the use of ice 
 and labor. Permanent, stationary units 
 can well be provided with at least 4 
 inches of insulation on outside surfaces, 
 with reduced entrance of warm air into 
 the system and with outside rehandling 
 of ice eliminated. Circulation of water 
 through a large ice bunker, built against 
 the fruit cooling unit and on a level 
 slightly below it, reduces refrigeration 
 losses and labor to a minimum. 
 
 VACUUM COOLING (12) 
 
 Leafy vegetables are cooled on a large 
 scale by pumping away the air around 
 them until moisture evaporates rapidly 
 from their surfaces. The resulting water 
 vapor is not pumped away but is con- 
 densed by refrigeration and run into a 
 sump. Evaporation and cooling depend 
 on the relation of temperature of the 
 product to the surrounding pressure and 
 are, therefore, fastest at the warmest 
 surfaces wherever located. Consequently, 
 cooling is uniform even to the center of 
 a head of lettuce in the center of a car- 
 load. 
 
 The heat to evaporate 1 per cent of a 
 quantity of water at room temperature 
 is sufficient to reduce the temperature of 
 the rest of the water by 11°F. Leafy 
 vegetables depart only slightly from this 
 behavior. A typical, large installation 
 cools two loaded refrigerator cars an 
 hour in each of two vacuum chambers, 
 using 625 horsepower of vacuum pumps 
 beside the chambers, and refrigeration 
 from a nearby ice plant. Smaller coolers 
 use ice to condense the water vapor and 
 may be moved from one shipping point 
 to another as needed. 
 
 The outstanding advantage of vacuum 
 
 [10 
 
Standard box, 4 sides exposed 
 
 Average pears 
 
 Standard box, 4 sides exposed 
 
 10 
 
 20 
 
 30 40 
 
 Hours 
 Warmest and coolest pears 
 
 50 
 
 J 
 60 
 
 Fig. 7. Car cooling pears by chimney suction. 
 
 cooling is that leafy vegetables, difficult 
 to cool by other methods, may be field- 
 packed and then cooled quickly and 
 uniformly. Because the operation is fast 
 and the walls of the chambers are not 
 cooled, there is little heat leakage into 
 the system and refrigeration is used very 
 efficiently. 
 
 On the other hand, the equipment is 
 costly and requires skilled attendance. 
 Economical, over-all operation is made 
 possible only by a large daily output. 
 There must be adequate volume to 
 operate a plant at near capacity, and in 
 
 order to be cooled quickly, the product 
 must have a large surface in proportion 
 to its weight and a surface through 
 which moisture can readily evaporate. 
 
 Reports of vacuum-cooling tests have 
 been rather conflicting and leave the 
 possibilities of the process somewhat un- 
 certain. Table 1 has been calculated from 
 data believed to be reliable and gives at 
 least an idea of what to expect. 
 
 Lettuce is, of course, outstandingly 
 adapted to vacuum cooling, as is attested 
 by the almost universal use of the process 
 for lettuce that is to be shipped any dis- 
 
 [ii] 
 
\ ^Standard lug, air 400 fpm on 2 sides 
 
 V 
 
 \ /-Chimney- vented corton 
 
 Standord crate, 4 sides exposed 
 
 10 15 
 
 Hours 
 Average grapes 
 
 10 15 
 
 Hours 
 Average plums 
 
 (posed 
 
 5 10 15 20 
 
 Hours 
 
 Warmest and coolest grapes 
 
 10 15 20 
 
 Hours 
 Warmest and coolest plums 
 
 25 
 
 Fig. 8. Car cooling grapes by chimney suction. Fig. 9. Car cooling plums by chimney suction. 
 
 tance. Apparently asparagus and sweet 
 corn must be held in vacuum about 
 twice as long as lettuce for equal cooling, 
 and celery about four times as long, at 
 correspondingly greater cost. These 
 products are well adapted to hydro- 
 
 TABLE 1 
 
 Vacuum Cooling Rates for Typical 
 
 Products 
 
 Product 
 
 Minutes in 
 vacuum to reduce 
 
 temperature 
 halfway to 32 °F 
 
 Lettuce 
 
 3 
 
 Parsley, spinach 
 
 5 
 
 Asparagus, sweet corn 
 
 Brussel sprouts, cabbage. . . 
 Celery, snap beans, cauli- 
 flower 
 
 6 
 9 
 
 12 
 
 Bell peppers, strawberries. . 
 Carrots, grapes . . . 
 
 25 
 
 80 
 
 ( ) ranges, tomatoes 
 
 100 
 
 
 
 cooling, or to forced-air cooling if in 
 packages damaged by water, and the 
 advantage of vacuum cooling them is 
 questionable. Strawberries, grapes, roots, 
 and larger fruits cool comparatively 
 slowly in vacuum and it is quicker and 
 cheaper to use either hydrocooling or 
 forced-air cooling. 
 
 Investigators report that wetting some 
 products results in faster vacuum cool- 
 ing, though the chief advantage in wet- 
 ting is apparently a reduction in weight 
 loss and wilting. Wetting followed by 
 vacuum cooling may be desirable for 
 some products, such as flowers, but in 
 most cases a single hydrocooling opera- 
 tion would seem to be cheaper and 
 equally effective. 
 
 "BODY" ICING 
 
 Finely chopped ice may be mixed with 
 some products as they are packed. Direct 
 contact of the product with the ice re- 
 
 12] 
 
suits in fast cooling and virtually all of 
 the ice is used to absorb heat from the 
 product. One pound of ice will cool four 
 pounds of product about 40°F. This 
 method is limited to products and con- 
 tainers that are not damaged by the ice 
 or by water. Considerable labor is usually 
 
 involved, water leaking from the con- 
 tainers may be troublesome, and the 
 pack shrinks in both weight and volume 
 as the ice melts. Lettuce and other leafy 
 vegetables that are now vacuum cooled 
 were formerly body iced. 
 
 COOLING METHODS IN RAIL CARS 
 
 CAR COOLING BY 
 ORDINARY SPACING 
 
 Probably the simplest and cheapest 
 method of cooling produce for rail ship- 
 ment is by loading refrigerator cars in 
 such a manner that heat is removed from 
 the product by operation of the car fans. 
 This is most commonly accomplished by 
 providing spaces between containers 
 through which air from the fans is 
 circulated. Cooling is usually commenced 
 immediately on completion of loading 
 by operating the fans with a portable 
 electric motor until the car starts on its 
 journey. The only costs are for the port- 
 able motor and for refilling the ice 
 bunkers. 
 
 Offsetting the advantage of low cost 
 is the relatively slow cooling ordinarily 
 attained as shown in figures 4 and 5. 
 Portable motors used to operate the car 
 fans must be removed before the cars 
 are expected to be moved. Cooling often 
 has not been adequate at this time. Slow 
 movement over branch lines, switching, 
 re-icing and slow movement up initial 
 mountain grades may combine to defer 
 by many hours the train speed that is 
 necessary for a resumption of full-speed 
 fan operation. 
 
 Incomplete initial cooling appears at 
 least to contribute to wetting of portions 
 of the load, which sometimes causes con- 
 siderable damage in cars loaded with 
 fibreboard cartons. When fans are not 
 operating, the air in a refrigerator car 
 circulates slowly by convection, down- 
 ward in the ice bunkers and upward 
 through the load. This would be expected 
 
 to cool the outer surfaces of the bottom 
 containers nearest the ice bunkers quite 
 rapidly but to affect the upper part of 
 the load little if at all. Surfaces of con- 
 tainers in contact with the ice bunkers 
 would also be cooled, especially those 
 near the floor. When a car is moved and 
 the fans operate, the air circulation is 
 reversed and warm, moist air from the 
 upper part of the load is forced down- 
 ward past the cold lower containers, and 
 moisture would be expected to condense 
 on them. 
 
 Railroad men and shippers differ on 
 how much damage is attributable to 
 condensation and how much to possible 
 splash of water from the melting ice. The 
 load may be shielded, both from splash 
 and from condensation, by covering the 
 lower part of the bunker wall and also 
 the floor near the bunker with corru- 
 gated fibreboard or heavy paper. 
 
 Wooden boxes are frequently held in 
 position by a frame or "brace" in the 
 center of the car. Air which passes down- 
 ward through this brace sweeps the top 
 and bottom of the load but does not pass 
 between the boxes where it is most 
 needed. While no tests of this effect seem 
 to have been reported, it is probable that 
 short-circuiting of air through the brace 
 slows cooling considerably. Auxiliary 
 fans are sometimes used to hasten cool- 
 ing before the cars are moved, but opera- 
 tion of the regular car fans at high speed 
 with the available 2-horsepower portable 
 motors, instead of the more commonly 
 used 1 or 1 V^-horsepower ones, is 
 simpler and probably equally effective. 
 
 [13] 
 
When product and containers are not 
 damaged by wetting it is a common 
 practice to blow a layer of chopped ice 
 into the car, on top of the load. Only 
 a fraction of the load is cooled by direct 
 contact with the ice, but air from the 
 car fans passes quite freely downward 
 through the chopped ice and is cooled 
 considerably below the temperature at 
 which it leaves the bunkers. Cooling is 
 hastened and the bunkers need to be re- 
 iced less often. 
 
 The effectiveness of car cooling may 
 be estimated from the ice consumption. 
 Melting a ton of ice cools a 15-ton car- 
 load from 6°F to 8°F under ordinary 
 conditions. This often gives a better 
 estimate of average load temperature 
 than inserting a thermometer in an 
 accessible container. 
 
 CAR COOLING BY 
 CHIMNEY SUCTION 
 
 Provision of air channels in fibreboard 
 box loads by means of wooden spacing 
 devices has not been satisfactory because 
 the wood tends to cut into the boxes in 
 transit. Fibreboard spacing devices re- 
 quire careful installation and have not 
 always been secure. Most important, the 
 tendency of cartons to bulge into the 
 channels may loosen the pack and expose 
 susceptible products to vibration injury 
 or roller bruising. 
 
 In chimney loading the boxes them- 
 selves provide the spacing; the load is 
 very resistant to shifting and disarrange- 
 ment; and boxes cannot bulge, because 
 of contact with each other and with the 
 car walls. However, common chimney 
 load patterns expose only a small part 
 of the surface of each box to a chimney 
 and leave some boxes with no exposed 
 surface at all, which results in slow 
 cooling. 
 
 Laboratory tests at Davis have shown 
 promise in the use of vented cartons of 
 a size to build three chimneys across a 
 rail car, giving every box access to a 
 chimney as shown in figure 6. When the 
 
 car is fully loaded, the air from the car 
 fans is forced to flow downward through * 
 the chimneys. Use is made of the physical 
 principle that pressure in a fluid stream 
 is lowest where the velocity is highest 
 and vice versa. Two vents open from 
 each box into the chimney. One vent is 
 opposite the center of the chimney where 
 the air velocity is high. The other vent 
 is in the corner of the chimney where 
 the air velocity is low. This arrangement 
 causes air to be sucked out of the box 
 through the center vent and to flow in 
 through the corner vent. 
 
 Figures 7, 8 and 9 show cooling ob- 
 tained with a single chimney in the 
 laboratory at Davis. Air movement in 
 the chimney was made equal to that 
 estimated in an actual load from car-fan 
 characteristics, allowing for resistance 
 to air flow through chimneys, floor racks 
 and ice bunkers. Carton surfaces not 
 exposed to the chimney were insulated 
 to simulate contact with adjacent cartons 
 at equal temperatures. Cooling based on 
 average fruit temperature was faster in 
 chimney-vented cartons than in standard 
 containers exposed to room air. As would 
 be expected, the fruit next to the vents 
 cooled considerably faster than the fruit 
 farthest from the vents. The curves show 
 how this difference compared with that 
 between the outside fruit and the center 
 fruit in standard containers. Pears cooled 
 by chimney venting and then ripened 
 showed no significant differences in color 
 or in pressure test between the fruit 
 nearest the vents and that farthest from 
 the vents. 
 
 Initial full-scale tests of chimney suc- 
 tion cooling in 1959 were disappointing, 
 due apparently to partial closure of the 
 vents by small irregularities in stacking 
 and by failure of vents in carton covers 
 to register accurately with vents in the 
 bodies. It seems essential that the vents 
 should be neither smaller nor farther 
 from the carton corners than those shown 
 in figure 6 and that vents in the covers 
 should be at least % inch wider than 
 
 14] 
 
Fan 
 
 
 
 Air blast 
 
 
 Return air 
 
 Floor rack 
 
 Fig. 10. Car cooling by horizontal air flow through side-vented boxes. 
 
 those in the bodies. On the other hand, 
 the proposed chimney loading pattern 
 proved to be unusually tight and stable. 
 The place of this method of cooling is 
 yet to be determined. 
 
 FORCED-AIR COOLING 
 IN RAIL CARS 
 
 By suitable loading methods the car 
 fans may be made to force air through 
 boxes in a rail car instead of around 
 them, which considerably expedites the 
 cooling. This method has been developed 
 by Fibreboard Paper Products Corpora- 
 tion for car cooling of produce in vented 
 corrugated fibreboard boxes. The spac- 
 ing devices and the name "Krisp Kool- 
 ing" are patented. 
 
 The arrangement of the load is shown 
 in figure 10. The tiers of boxes and the 
 channels between them run the full length 
 of the car. Spacing is maintained by 
 fibreboard devices, which also serve to 
 close the tops of alternate channels. The 
 remaining channels are closed at the 
 floor by strips of paper or fibreboard 
 placed before the car is loaded. Applica- 
 tion of a nonskid adhesive to the bottoms 
 of the boxes, which prevents sliding but 
 allows them to be easily lifted apart, 
 serves to further stabilize the load. Air 
 from the ice bunkers is blown by the car 
 fans into the space above the load, passes 
 down into the channels that are open at 
 their tops, is forced horizontally through 
 the side-vented boxes, passes down 
 
 [15] 
 
Warmest of 12 points in centers of boxes 
 Average of 12 points in centers of boxes 
 
 Half cool 
 
 15 
 Hours 
 
 Reiceing 
 
 at 
 Roseville 
 JJL 
 
 25 
 
 Fig. 11. Car cooling celery by horizontal air 
 flow through side-vented fibreboard boxes, 
 December 5-6, 1956. (Data Fibreboard Paper 
 Products Corporation). 
 
 through the channels that are open at 
 the bottom, and returns beneath the 
 slatted floor to the ice bunkers. Rapid 
 initial cooling melts the ice quickly, and 
 provision should be made for early re- 
 icing. 
 
 Figures 11 and 12 show some measure- 
 ments of cooling by this method. Cooling 
 is considerably faster than is commonly 
 attained by circulating air around the 
 containers and is comparable with top 
 icing. The load is not wet as it is by 
 top icing. Moisture evaporated from the 
 product has not been measured but is 
 obviously much less than in vacuum 
 cooling. Disadvantages may be the labor 
 required to arrange spacers and the 
 possibility that failure of the spacers 
 may allow disarrangement of the load. 
 A tendency of fibreboard boxes to bulge 
 into the air channels is objectionable 
 with products that depend on a tight 
 pack or fill to prevent damage from 
 vibration in transit. 
 
 Downstream melons 
 
 Average melons 
 
 Fig. 12. Car cooling cantaloupes by horizontal air flow through side-vented fibreboard 
 boxes, September 5, 1957. (Data U. S. Horticultural Fielid Station, Fresno). 
 
 [16] 
 
100 
 
 6 8 
 
 Hours 
 Warmest Point in Each 
 
 10 
 
 Load 
 
 14 
 
 16 
 
 100 
 
 Solid lines show actual cooling. 
 Dashed lines show probable result 
 if cooling had been continued. 
 
 6 8 10 
 
 Hours 
 
 Average Temperature of Each Load 
 
 12 
 
 14 
 
 16 
 
 Fig. 13. Truck loads of grapes cooled with stationary ice bunkers, Lodi, 
 September, 1955. (Data by Gordon Mitchell). 
 
 [17] 
 
COOLING IN TRUCKS 
 
 Successful cooling of produce in trucks 
 has been limited in part by the lack of 
 adequate refrigeration, and in part by 
 the general lack of false floors, requiring 
 air to pass through the load horizontally 
 from end to end, instead of through the 
 much shorter vertical distance from top 
 to bottom as in refrigerated rail cars. 
 
 Refrigeration that is ample to hold a 
 low temperature in the hottest weather 
 may be entirely inadequate to cool a 
 warm load at a satisfactory rate. To cool 
 a carload of warm produce adequately 
 in a large truck would require six-ton ice 
 bunkers and fans equivalent to those in 
 a refrigerated rail car, or corresponding 
 mechanical refrigeration. Produce trucks 
 are not provided with anything like this 
 refrigeration. If they were, charges 
 would have to be materially higher to 
 pay for the larger system and for de- 
 voting so much of the allowable gross 
 weight to it. 
 
 Stationary ice bunkers or mechanical 
 
 refrigeration systems are sometimes used 
 to cool produce in loaded trucks. Such 
 units provide ample refrigeration and 
 powerful fans, but cooling at best is only 
 comparable with that in rail cars and 
 often is not adequate at the end of an 
 eight-hour period. Figure 13 shows tem- 
 peratures in four random truck loads of 
 grapes cooled at stationary ice bunkers. 
 To provide false floors in produce 
 trucks would reduce both the space and 
 the allowable weight for pay load, and 
 long waits for loads to cool would fur- 
 ther reduce the tonnage that could be 
 moved by trucks and drivers in a ship- 
 ping season. The operators of truck pre- 
 coolers are meeting a public demand 
 and in many cases the immediate al- 
 ternative to their operations would be no 
 precooling at all. It seems, however, 
 that in the end it is more economical to 
 provide facilities for cooling produce be- 
 fore it is loaded than to use trucks as 
 coolers. 
 
 COSTS OF COOLING METHODS 
 
 Costs of cooling fruits or vegetables 
 will obviously vary widely, depending 
 on temperature reduction accomplished 
 and on cost to a particular operator for 
 refrigeration, labor and facilities. The 
 following figures are offered only to give 
 operators an idea of what to expect and 
 how to arrive at better estimates for their 
 own conditions. 
 
 The heat given up by a ton of produce 
 and its containers in cooling 36°F is 
 sufficient to melt about % ton of ice. If 
 ice costs $8 per ton, this amounts to $2 
 per ton of produce. Costs of mechanical 
 refrigeration including fixed charges are 
 comparable. Heat evolved by respiration 
 of such active products as asparagus or 
 strawberries in a slow cooling operation 
 may add 20 per cent or more to this 
 figure. These may be considered as the 
 
 only costs of cooling in storage. Labor, 
 fixed charges, and refrigeration to offset 
 heat leakage are the same for the storage 
 operation regardless of where the prod- 
 uct is cooled. 
 
 Room cooling, forced-air cooling, 
 hydrocooling, and vacuum cooling all 
 require special cooling facilities and re- 
 handling of the product. Consequently, 
 these methods are usually more costly 
 than cooling in storage or car cooling. 
 So far as is known, there have been no 
 studies of the comparative costs of these 
 methods. 
 
 Room cooling is the simplest of these 
 methods and should require the least 
 labor. But it requires the largest cooled 
 space per unit of output, with compara- 
 tively large refrigeration losses and high 
 first cost and fixed charges. 
 
 [18] 
 
Forced-air cooling requires a smaller 
 cooled space per unit of output and, with 
 reasonably good design, involves smaller 
 refrigeration losses and lower fixed 
 charges than room cooling. However, 
 somewhat more labor and considerably 
 more care are needed to operate a forced- 
 air cooler. 
 
 One grower-shipper reported that he 
 purchased the materials and had a car- 
 penter build his ice-cooled, forced-air 
 cooler, which cools one ton of cup-packed 
 peaches per hour, for approximately 
 $1,000. University economists reported 
 the following costs per ton of peaches 
 cooled in this cooler from 72°F to 40°F, 
 or to 20 per cent of the initial tempera- 
 ture difference between product and ice 
 (16). 
 
 Ice at $10 per ton delivered. . . . $2.66 
 abor: including segregating 
 sizes, stacking boxes, loading 
 them into the cooler, and un- 
 loading them into a refriger- 
 ated truck 1.72 
 
 Depreciation, interest, taxes, in- 
 surance and repairs 1.00 
 
 Electricity 03 
 
 Total cost per ton of peaches. $5.41 
 
 Another forced-air cooler, designed to 
 cool five carloads of grapes in four hours, 
 was built under contract for approxi- 
 mately $40,000, or $2,000 per ton per 
 hour of output. This cost included exca- 
 vating for ice bunkers, filling for a dock- 
 height concrete floor, high-pressure fans 
 for forcing air through three-tier stacks 
 of boxes, and an electric job to pass city 
 inspection. The owner said that he was 
 crediting the cooling operation with $8 
 per ton of fruit and would do custom 
 cooling for that rate, which he estimated 
 would pay for the cooler in five years. 
 
 Hydrocooling, if the equipment is 
 designed for economical operation, 
 should be similar to forced-air cooling 
 in its costs. The unit is smaller than a 
 
 forced-air cooler for a given output, but 
 is of a more expensive type of construc- 
 tion, so that first cost and fixed charges 
 should not be too different for these two 
 systems. Exposed storage and rehandling 
 of ice and meagre insulation of the cooler 
 itself sometimes result in excessive re- 
 frigeration losses. 
 
 A study in North Carolina reports that 
 a hydrocooler capable of cooling about 
 three tons per hour of peaches in bushel 
 baskets cost $5,500 installed in 1954, or 
 $1,830 per ton per hour of output (30) . 
 Average costs per ton for cooling 500 
 tons of peaches per year from 81 °F to 
 51 °F, or to 39 per cent of the initial 
 temperature difference between product 
 and ice, were: 
 
 Ice at $7 per ton delivered $3.30 
 
 Depreciation, interest, taxes, in- 
 surance, and repairs 1.80 
 
 Labor: icing, lifting baskets in 
 and out of cooler only, at 60 ff 
 per hour 45 
 
 Electricity and hypochlorite. . . .09 
 
 Total cost $5.64 
 
 Hydrocoolers are supplied by a Cali- 
 fornia ice company to its customers for 
 installation and rental charges that com- 
 monly amount to less than $1 per ton of 
 product. With mechanized material hand- 
 ling, this brings the total cost to under 
 $5 per ton, for cooling to 25 per cent of 
 the initial temperature difference between 
 product and ice. 
 
 Vacuum cooling virtually eliminates 
 refrigeration losses, but the equipment 
 is expensive and operators must be in- 
 telligent, careful and well trained. Fixed 
 costs per unit of output would be exces- 
 sive if they were not kept down by fast 
 operation over a long season. Charges by 
 California operators amount to from 
 $6.50 to $10 per ton, for cooling usually 
 to less than 20 per cent of the initial tem- 
 perature difference between product and 
 ice. 
 
 [19] 
 
Cooling in rail cars by operation of 
 car fans at the shipping point requires 
 a charge for labor and fan operation as 
 well as for ice. There is no charge for 
 use of the cars for this purpose, however, 
 so that cooling in rail cars is compara- 
 tively inexpensive. Charges for operating 
 car fans and for salting and re-icing 
 bunkers commonly amount to $3 to $4 
 per ton of produce. 
 
 Total and comparative costs of the 
 cooling methods obviously vary consid- 
 erably with local prices, annual use, effi- 
 
 ciency of management, and temperature 
 reduction accomplished. Estimates for 
 the 1958 season have fallen in the range 
 of $5 to $10 per ton of product with 
 roughly half of this cost for refrigera- 
 tion and % each for fixed charges and 
 for labor and supplies. Any of these cool- 
 ing costs are small when compared with 
 benefits to be expected. It seems safe to 
 say that the primary consideration in 
 choice of a cooling system is not its cost 
 but its effect on the product. 
 
 12 18 24 30 
 
 Fig. 14. Example of six hours half-cooling time. 
 
 [20] 
 
Section II 
 
 COOLER DESIGN 
 
 COMPARING AND ESTIMATING 
 COOLING RATES (10,29) 
 
 Cooling rates are measured in this pub- 
 lication by half-cooling times, as shown 
 by the example in figure 14. Half -cooling 
 time is easily measured and is the same 
 for a given set-up regardless of the in- 
 itial temperature of the product. The 
 temperature that will be reached at a 
 given time or the time to reach a given 
 temperature may be roughly estimated 
 from the number of half-cooling times as 
 follows: 
 
 Number of Remaining fraction of 
 
 half-cooling initial temperature 
 
 times difference 
 
 1 1/2 
 
 2 1/4 
 
 3 1/8 
 
 4 1/16 
 
 5 1/32 
 
 A half-cooling time may be based on the 
 temperature of the ice or other cooling 
 surface or on the temperature of the air 
 in an air cooler or of water in a hydro- 
 cooler, provided only that the base tem- 
 perature is reasonably constant. It is im- 
 portant to note the base that has been 
 used for any particular half-cooling 
 time and to use this same base in esti- 
 mates made from it or in half-cooling 
 times to be compared with it. Half-cool- 
 ing times for various products under 
 various conditions are tabulated on pages 
 55 to 63. 
 
 COOLING ROOMS (3) 
 
 Desirable air flow to cooling rooms is 
 sometimes estimated at 6,000 to 8,000 
 cubic feet per minute per carload of pro- 
 duce, or about 1 cubic foot per minute 
 for each 4 to 5 pounds of produce. For 
 a product 40°F above air-blast tempera- 
 ture and half-cooling to air temperature 
 in 12 hours, this can be calculated to 
 correspond to a 7°F to 9°F difference be- 
 tween air blast and air return. These con- 
 ditions would usually be considered satis- 
 factory. For a warmer product or for 
 faster-cooling containers, such as straw- 
 berry trays, proportionately more air is 
 needed. Less air may be satisfactory if 
 the product is initially cooler or if it cools 
 more slowly. 
 
 Satisfactory air movement and elim- 
 ination of warm pockets, in any but very 
 large rooms, may usually be obtained by 
 mounting fans in one wall near the ceil- 
 ing with air returns in the same wall near 
 the floor. Containers should be stacked 
 with their sides exposed if possible and 
 with air channels parallel to the direction 
 of air movement. Increased air circula- 
 tion hastens cooling somewhat by reduc- 
 ing the rise in temperature of the air as 
 it passes through the room but otherwise 
 has little effect except on the most ex- 
 posed containers. 
 
 Use of ceiling jets to hasten cooling 
 is discussed on page 6. Curtains dropped 
 from a false ceiling to confine the re- 
 turning air to channels through the load 
 have been used, but at this writing no 
 
 [21] 
 
2 
 6r 
 
 4- 
 
 o 
 
 3 
 
 O 
 
 k. 
 Q. 
 
 £) 
 
 •>s 
 
 E 
 
 <•- 
 o 
 
 o 
 
 .08 
 
 .06 
 
 I 2 
 
 Half-cool (hours) 
 
 8 10 
 
 .2 
 
 .8 
 
 I 2 
 
 Half-cool (hours) 
 
 8 10 
 
 Fig. 15. Forced-air cooling grapes in lidded lugs, half-cooling of downstream boxes, 
 based on constant temperature air supply. 
 
 tests are available on the air flows or 
 pressures used or on the effects on cool- 
 ing rate. It can be estimated, however, 
 that to double the cooling rate in a con- 
 ventional room by this method would 
 probably require an air velocity of 1,000 
 fpm in a channel 8 inches wide and 30 
 feet long beside each tier of boxes. A 
 
 forced-air system using the same air flow 
 and floor space would apparently cool 
 the product in a fraction of the time. 
 
 FORCED-AIR COOLERS 
 
 The first consideration in planning a 
 forced-air cooler is the relation of fan 
 capacity to cooling time. Figures 15 to 
 
 [22] 
 
z 
 
 6 r 
 
 4- 
 
 o 
 
 I ' 
 
 £ 8 
 
 1-6 
 
 .1 
 .08 
 
 .06, 
 
 .6 
 
 8 I 2 
 
 Half-cool (hours) 
 
 8 10 
 
 4 .6 .8 I 2 4 6 8 10 
 
 Ha If- cool (hours) 
 
 Fig. 16. Forced-air cooling strawberries in open cartons, half-cooling of 
 downstream cartons, based on constant temperature air supply. 
 
 24 show the air flows needed to cool 
 various products half-way to air tem- 
 perature in given times. Cooling three- 
 fourths or seven-eights or fifteen-six- 
 teenths of the way to air temperature 
 takes twice, three times or four times as 
 long. 
 
 These curves are based on a constant 
 
 temperature air blast. Estimation of 
 slower cooling due to variation in air- 
 blast temperature is described in the fol- 
 lowing section on ice-bunker size. As a 
 rough figure, half-cooling from product 
 to ice temperature may be 50 per cent 
 longer than the corresponding time based 
 on air temperature. The air flow per 
 
 [23] 
 
u 
 
 6 
 4 
 
 § 
 
 $ .8 
 
 I 6 
 
 a » 
 
 .1 
 
 .08 
 .06 
 
 2 
 6 
 4- 
 
 8 I 
 1 6 
 
 i 4 
 
 < .2 
 
 .08 
 .06, 
 
 .8 I 2 
 
 Half-cool (hours) 
 
 8 10 
 
 4 
 
 .8 I 2 
 
 Half-cool (hours) 
 
 8 10 
 
 Fig. 17. Forced-air cooling peaches in paper cups in lidded lugs, half-cooling 
 of downstream boxes, based on constant temperature air supply. 
 
 pound of product to produce a given 
 half-cooling time in the downstream pro- 
 duce is not significantly affected by the 
 thickness of the stack or layer of produce 
 through which air passes. 
 
 The static head to produce a given 
 half-cooling time is, however, drastically 
 affected by the thickness of the stack or 
 
 [ 
 
 layer, as shown by the upper curves in 
 figures 15 to 24. The static head taken 
 from one of these charts must be added 
 to the static head needed to move the air 
 through the ice bunker or cooling unit 
 and through the openings, passages and 
 turns in the system to get the head that 
 must be developed by the fans. Air-flow 
 
 24] 
 
6 8 1 2 
 
 Holf-cool (hours) 
 
 Fig. 18. Forced-air cooling plums in open 
 Sanger lugs, half-cooling of downstream box, 
 based on constant temperature air supply. 
 
 and static head in passages and ice bunk- 
 ers and choice of fans are discussed in 
 following sections. As explained there, 
 savings in floor space and labor by use of 
 stacks of four tiers or more should be 
 weighed carefully against the added cost 
 of fans and refrigeration entailed in op- 
 erating at a high static pressure. 
 
 The general arrangement of a pressure 
 cooler and the method of handling and 
 stacking the product should be coordi- 
 nated with other packing and shipping 
 activities. There are four general meth- 
 ods of getting products into the cooler 
 and out again : on pallets moved by fork 
 trucks, in stacks moved by hand trucks, 
 by moving containers on conveyors, or 
 by stacking containers in the cooler by 
 hand and removing them with hand 
 trucks. 
 
 Figure 25 illustrates movement of pal- 
 lets by fork trucks. The flexible, hinged 
 curtain has been very satisfactory. Pallets 
 may be stacked two high with a saving in 
 
 it 
 
 4-»-Tier* 
 
 06 2 
 
 
 
 
 
 Holf-cool ( 
 
 lours) 
 
 
 
 
 
 6 
 
 
 
 
 
 
 
 
 
 
 4 
 
 
 
 
 
 
 
 
 
 
 2 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 « 8 
 
 . 
 
 
 
 
 
 
 
 
 
 " 6 
 
 E 
 
 " 
 
 
 
 
 
 
 
 
 
 3. 4 
 
 - 
 
 
 
 
 
 
 
 
 
 * 
 o 
 
 
 
 
 
 
 
 
 
 
 5 2 
 
 
 
 
 
 
 
 
 
 
 08 
 
 
 
 
 
 : 
 
 i 
 
 
 1 
 
 
 Ub 
 
 2 
 
 4 
 
 .6 
 
 8 1 
 
 2 
 
 4 
 
 6 
 
 8 
 
 10 
 
 Holf-cool (hours) 
 
 Fig. 19. Forced-air cooling grapes in vented 
 cartons, half-cooling downstream carton, based 
 on constant temperature air supply. 
 
 floor space but with more work for the 
 fork truck. Pallets may also be stacked 
 two-wide with the air passing through 
 four or six tiers of boxes, though this re- 
 quires either high static pressure or a 
 slower cooling job as is shown in figures 
 15 to 24. Cooling of a multiple-tier stack 
 is fastest and most uniform if the top 
 of the stack is exposed to the air supply 
 and if the tiers are spaced slightly apart, 
 as explained in figure 26. 
 
 Movement of boxes into a cooler by 
 roller conveyor for hand stacking and 
 later removal with hand trucks is shown 
 in figure 27. Boxes may be stacked di- 
 rectly in the cooler with no more labor 
 than is needed to stack them on pallets, 
 and movement by fork truck into the 
 cooler is eliminated. This is a good ar- 
 rangement if the cooler is close to the 
 packing line and boxes are moved di- 
 rectly to nearby cars or trucks (21). 
 
 Figure 28 shows boxes being forced- 
 aircooled in U-shaped stacks against the 
 
 25 
 
s 
 
 X 
 
 £ 2 
 
 .08- 
 
 oeL- 
 
 '2 3 4~Tiers 
 
 WW 
 
 4 6 .8 I 2 4 6 8 10 
 
 Half-cool (hours) 
 
 6- 
 4 - 
 
 06 2- 
 
 6 8 1 2 
 
 Holf-cool (hours) 
 
 Fig. 20. Forced-air cooling plums in vented 
 cartons, half-cooling downstream carton, based 
 on constant temperature air supply. 
 
 air returns in a combination room and 
 pressure cooler. Cool grapes picked in 
 the morning are stacked with ordinary 
 spacing in the room area. The warm 
 afternoon picking arrives in the early 
 evening and is stacked for pressure cool- 
 ing. With hand tongue-trucks and some 
 practice, the handlers can place stacks 
 tightly end-to-end for pressure cooling. 
 It would be troublesome to do this with 
 clamp trucks. 
 
 By the next morning the fruit in the 
 room area has been cooled for three six- 
 hour half-cooling times and the warmer 
 pressure-cooled fruit has been cooled for 
 four or five two-hour half-cooling times. 
 During the morning all the fruit is loaded 
 out or moved for storage to another room 
 where the air velocity is much lower. 
 
 Running containers through a cooler 
 on a conveyor, which is loaded and un- 
 loaded outside of the cooler, makes it un- 
 necessary to provide space inside for men 
 to work. Such an operation is shown in 
 figure 29. This type of cooler is very 
 
 compact in relation to cooling capacity. 
 There is a minimum of outside surface 
 and air moves through short passages 
 and a single tier of containers, giving a 
 good cooling rate with low static head 
 and low-power fans. These features com- 
 bine to allow economical construction 
 and excellent ice economy, especially in 
 small units and during intermittent op- 
 eration. The cooler shown in the photo- 
 graph was designed and built by the 
 owner for about $1,000 and cools one ton 
 of cup-packed peaches per hour. In a 
 similar unit, 75 to 80 per cent of the ice 
 was melted by heat removed from the 
 fruit while the cooler was operating, and 
 200 pounds of ice was melted per day in 
 hot weather while the cooler was not in 
 use. Plans for the unit in the photograph 
 may be purchased at cost from Agri- 
 cultural Publications, 207 University 
 Hall, 2200 University Ave., Berkeley 4 
 (Plan No. 243, 'Fruit Cooler"). 
 
 MECHANICAL REFRIGERATION 
 CAPACITY 
 
 General design of refrigeration sys- 
 tems is beyond the scope of this publi- 
 cation, but tables for determining refrig- 
 eration capacity in relation to produce 
 temperatures and cooling rate may be 
 useful. Calculation of these tables is ex- 
 plained on pages 39 to 41. 
 
 Refrigeration capacity needed for a 
 
 TABLE 2 
 Refrigeration for Continuous Cooling 
 
 
 Fraction of refrigeration used to absorb 
 heat from product 
 
 Degrees F 
 cooled 
 
 .50 
 
 .65 
 
 .80 
 
 
 Tons refrigeration per ton of product 
 cooled per hour 
 
 70 
 
 60 
 
 50 
 
 40 
 
 30 
 
 20 
 
 22 
 19 
 16 
 12 
 9 
 6 
 
 17 
 14 
 12 
 10 
 
 7 
 5 
 
 14 
 
 12 
 
 10 
 
 8 
 
 6 
 
 4 
 
 [26] 
 
.8 I 2 
 
 Half-cool (hours) 
 
 Fig. 21. Forced-air cooling pears in vented cartons, half-cooling of downstream 
 cartons, based on constant temperature air supply. 
 
 continuous operation, such as hydro- 
 cooling, is shown in table 2. 
 
 The fraction of refrigeration used to 
 absorb heat from the product is about 
 .50 with light insulation or considerable 
 air leakage, or .80 in a well-enclosed and 
 insulated unit. Heat evolved by respira- 
 tion of the product, in the short time 
 
 ordinarily occupied by a continuous cool- 
 ing operation, is usually not significant. 
 In a batch operation, where the cool- 
 ing rate is commonly proportional to the 
 temperature difference between product 
 and coolant, the refrigeration load is 
 quite high when starting to cool a warm 
 batch, as shown in table 3. 
 
 [27 J 
 
Tiers— - 4 \ 
 
 V 
 
 X 
 
 \ 
 
 6 
 4 
 
 - 
 
 Holf-cool (hours) 
 
 
 2 
 
 a 8 
 
 € -6 
 
 E 
 
 S 4 
 
 s 
 
 - 
 
 \ 
 
 
 Lu 
 
 w .2 
 < 
 
 .1 
 
 08 
 .06 
 
 r * e- 
 
 .8 1 2 
 
 4 6 8-10 
 
 Half- cool (hours) 
 
 Fig. 22. Forced-air cooling artichokes in 
 vented cartons, half-cooling downstream car- 
 tons, based on constant temperature air supply. 
 
 6 - 
 4 - 
 
 s 2 
 
 I 
 
 I .8 
 
 J 6 
 
 E 4 
 
 .08 
 10 06 
 
 Large vents 
 
 I sq in/4 lb melons 
 Small vents 
 
 I sq in/10 lb melons 
 
 4 6 8 1 2 4 6 
 
 Half-cool (hours) 
 
 Half-cool (hours) 
 
 Fig. 23. Forced-air cooling melons in cartons, 
 half-cooling of downstream cartons, based on 
 constant temperature air supply. 
 
 Table 3 shows only the refrigeration 
 needed to absorb heat from cooling the 
 product. Additional capacity must be al- 
 lowed for losses, and in some cases, for 
 heat evolved by respiration. Conduction, 
 
 infiltration and heat from fans may be 
 estimated separately; or total losses with 
 slow cooling, light insulation, or consid- 
 erable air leakage from the outside may 
 be estimated as roughly equal to heat 
 
 TABLE 3 
 
 Refrigeration to Absorb Heat From the Cooling Product in a Batch Operation 
 
 
 Half-cooling, product to coolant 
 
 Remaining temp, 
 difference between 
 product and coolant 
 
 24 hr 
 
 12 hr 
 
 6hr 
 
 3hr 
 
 2hr 
 
 lhr 
 
 
 Tons refrigeration per ton of product in batch 
 
 degrees F 
 
 80 
 
 60 
 
 40 
 
 .36 
 .27 
 .18 
 .13 
 
 .09 
 .07 
 .04 
 .02 
 
 .71 
 .54 
 .36 
 
 .27 
 
 .18 
 .13 
 .09 
 .04 
 
 1.4 
 
 1.1 
 .71 
 .54 
 
 .36 
 
 .27 
 .18 
 .09 
 
 2.9 
 2.1 
 1.4 
 1.1 
 
 .71 
 .54 
 .36 
 
 .18 
 
 4.3 
 3.2 
 2.1 
 1.6 
 
 1.1 
 
 .80 
 .54 
 
 .27 
 
 8.6 
 6.4 
 4.3 
 3.2 
 
 2.1 
 1.6 
 1.1 
 .54 
 
 30 
 
 20 
 
 15 
 
 10 
 
 5 
 
 [28] 
 
TABLE 4 
 
 Refrigeration Capacity to Absorb Heat 
 
 of Respiration 
 
 Product 
 
 Apples 
 
 Asparagus . . . 
 Beans, snap. 
 Broccoli .... 
 
 Cantaloupes . 
 
 Carrots 
 
 Celery 
 
 Cherries .... 
 
 Corn, sweet . 
 
 Grapes 
 
 Oranges 
 
 Peaches 
 
 Pears 
 
 Strawberries 
 Tomatoes. . . 
 
 Temperature (F) 
 
 so' 
 
 70° 
 
 60° 
 
 50° 
 
 4(f 
 
 Tons refrigeration per ton product 
 
 02 
 50 
 24 
 35 
 
 08 
 08 
 
 .24 
 .02 
 .04 
 .04 
 
 .04 
 .13 
 .04 
 
 .02 
 
 .39 
 .20 
 .26 
 
 .05 
 .05 
 .05 
 .05 
 
 .20 
 .02 
 .03 
 .03 
 
 .03 
 .09 
 .03 
 
 .01 
 .24 
 .13 
 .17 
 
 .03 
 .03 
 .03 
 .03 
 
 .13 
 .01 
 .02 
 
 .02 
 
 .02 
 .06 
 
 .02 
 
 .15 
 .08 
 .10 
 
 .02 
 ,02 
 .02 
 .02 
 
 .01 
 .01 
 
 .01 
 .04 
 .01 
 
 02 
 
 from the product when half-cooled; or 
 total losses with fast cooling and a tight, 
 well-insulated unit may be estimated as 
 equal to heat from the product when 
 three-fourths cooled. 
 
 Table 4 shows the approximate tons 
 of refrigeration capacity needed to ab- 
 sorb heat evolved by respiration of vari- 
 ous products at different temperatures. 
 
 TABLE 5 
 
 Tons Ice Melted per Ton of Product 
 
 Cooled 
 
 
 Per cent of ice melted by heat 
 from product 
 
 Reduction in 
 product temp. 
 
 50 
 
 65 
 
 80 
 
 
 Tons ice per ton of product 
 
 Degrees F 
 
 60 
 
 .77 
 
 .60 
 
 .48 
 
 50 
 
 .64 
 
 .50 
 
 .40 
 
 40 
 
 .52 
 
 .40 
 
 .32 
 
 30 
 
 .39 
 
 .30 
 
 .24 
 
 20 
 
 .26 
 
 .20 
 
 .16 
 
 .8 I 2 
 
 Half-cool (hours) 
 
 Fig. 24. Forced-air cooling of oranges in 
 bulk, half-cooling of average fruit based on 
 constant temperature air supply. (Data by R. L. 
 Perry, University of California). 
 
 This must be added to the amount from 
 table 3, plus an allowance for losses, to 
 estimate the capacity that should be in- 
 stalled. 
 
 Instead of installing the large refrig- 
 erating capacity needed to maintain fast 
 cooling when starting a warm batch, it 
 may be more economical to install less 
 refrigeration and accept slower initial 
 cooling. The initial half-cooling period 
 is lengthened by 45 per cent by provision 
 of half the refrigeration that would be 
 needed for a maximum initial cooling 
 rate. This refrigeration capacity is ade- 
 quate after the product is half cooled and 
 cooling then proceeds at the rate de- 
 termined by exposure of the product. 
 Figure 30 illustrates this principle. 
 
 ICE BUNKER DESIGN 
 
 The weight of ice that will be melted 
 in a cooling operation can be estimated 
 from tables 5 and 6. A ton of ice in 
 
 [29] 
 
TABLE 6 
 
 Ice Melted by Heat of Respiration in 
 
 Cooling Various Products from 80°F to 
 
 35°F, in Air at 32°F, at Four Different 
 
 Cooling Rates 
 
 Product 
 
 Asparagus . . 
 
 Apples 
 
 Beans, snap. 
 Broccoli. . . . 
 
 Cantaloupes . 
 
 Carrots 
 
 Celery 
 
 Cherries. . . . 
 
 Corn, sweet. 
 
 Grapes 
 
 Oranges 
 
 Peaches .... 
 
 Pears 
 
 Strawberries 
 Tomatoes. . . 
 
 Half-cooling time 
 
 24 hr 12 hr 4 hr 
 
 lhr 
 
 Tons ice per ton of product 
 
 .60 
 
 .30 
 
 .10 
 
 .02 
 
 .01 
 
 
 .32 
 
 .16 
 
 .05 
 
 .42 
 
 .21 
 
 .07 
 
 .08 
 
 .04 
 
 .01 
 
 .08 
 
 .04 
 
 .01 
 
 .08 
 
 .04 
 
 .01 
 
 .08 
 
 .04 
 
 .01 
 
 .32 
 
 .16 
 
 .05 
 
 .02 
 
 .01 
 
 
 .04 
 
 .02 
 
 .01 
 
 .40 
 
 .02 
 
 .01 
 
 .04 
 
 .02 
 
 .01 
 
 .16 
 
 .08 
 
 .03 
 
 .04 
 
 .02 
 
 .01 
 
 .02 
 
 .01 
 .02 
 
 .01 
 
 01 
 
 jumbled blocks occupies about 50 cubic 
 feet; 60 cubic feet per ton will allow 
 for upper corners of the bunker that are 
 not filled. 
 
 With slow cooling or light insulation, 
 about 50 per cent of the ice is melted by 
 heat from product; with fast cooling and 
 heavy insulation, about 80 per cent of the 
 ice is melted by heat from product. 
 
 Some ice is melted also by heat evolved 
 by respiration of the product (Wright, 
 et al., 1954) . This is of small consequence 
 with fruits, but with some vegetables and 
 particularly if cooling is slow, heat of 
 respiration is important. Table 6 shows 
 the ice melted by heat of respiration while 
 cooling various products from 80°F to 
 35 °F at four different rates in air at 
 32°F. The heat evolved by respiration 
 while cooling to any particular tempera- 
 ture is directly proportional to the time 
 elapsed in reaching that temperature. The 
 
 TABLE 7 
 Relation of Half-Cooling Times in Typi- 
 cal Forced- Air Coolers and Room Coolers 
 to Ice Depth in Bunker and Static Head 
 in Bunker. Ice in 100-Pound Blocks, Air 
 Flow 100 Cubic Feet per Minute per 
 Square Foot Grate Area 
 
 
 Static 
 
 head 
 
 (inches 
 
 water) 
 
 Relative half- 
 cooling times 
 
 Ice depth 
 (feet) 
 
 Forced- 
 air 
 cooler 
 
 Room 
 cooler 
 
 20 
 
 .75 
 .60 
 .45 
 .30 
 .20 
 .15 
 .12 
 
 1.0 
 1.0 
 
 1.1 
 
 1.3 
 1.5 
 1.8 
 2.2 
 
 5.0 
 
 16 
 
 12 
 
 8 
 
 5.0 
 5.1 
 5.3 
 
 5 
 
 5.5 
 
 4 
 
 3 
 
 5.8 
 6.0 
 
 reason for this is explained in the dis- 
 cussion of refrigeration load, pages 42 
 and 43. 
 
 Figures 31 and 32 are based on tests 
 in a small bunker with 50-pound ice 
 blocks and calculations for the larger 
 sizes. For a given air flow, and cooling 
 effect, 50-pound blocks as compared with 
 300-pound blocks require half the depth 
 of ice but about the same static head, 
 leaving a question as to how much break- 
 ing of blocks is worth while. Doubling 
 the air velocity in a bunker requires a 
 40 per cent greater depth of ice and over 
 four times the static head for a given 
 cooling effect. The recommended 100 cfm 
 per square foot of grate area seems rea- 
 sonable but 200 cfm per square foot is 
 quite extravagant in use of fan power. 
 
 Table 7 shows calculated effects on 
 product cooling-times of effectiveness of 
 air cooling in the ice bunker. These re- 
 sults are in accord with the obvious prin- 
 ciple that most of the temperature differ- 
 ence and resistance to heat transfer in a 
 room cooler is between the product and 
 the air, and therefore conditions in the 
 ice bunker have comparatively little ef- 
 fect. In a forced-air cooler, on the other 
 
 [ 30 } 
 
Fig. 25. Forced-air cooling, boxes on pallets. Air supply is through opening in ceiling, return is 
 from space behind boxes, which will be enclosed by placing another pallet and closing the door. 
 
 hand, the resistance between the product 
 and the air is much less, and conditions 
 in the ice bunker are relatively impor- 
 tant. The basis of these estimates is dis- 
 cussed on pages 43 to 46. 
 
 Location of an ice bunker as close as 
 possible to the product being cooled and 
 on the same level reduces the space occu- 
 pied by air passages, and the fan power 
 needed to move the air. There is least 
 outside surface exposed to heat leakage 
 and requiring insulation if the bunker 
 is located along the side of a rectangular 
 cooling area, making the entire cooled 
 structure approximately square; and 
 also, if the bunker is on the same level 
 as the cooling operation. It is usually 
 cheaper to construct a bunker above 
 ground, and this allows water from the 
 melting ice to be drained by gravity. 
 Hatches in the top of an elevated bunker, 
 where they are not trucked over, can be 
 simply constructed and are easily made 
 air tight. 
 
 These advantages must be offset 
 against the convenience of other floor 
 plans at a particular site, the possibility 
 of using the top of a depressed bunker as 
 a loading dock, and the necessity of pro- 
 viding an elevator to ice an above-ground 
 bunker. It is important that sump pumps, 
 float switches and strainers in a depressed 
 bunker be accessible for maintenance 
 while ice is in the bunker. Failure of the 
 drainage system soon floods the bunker 
 and shuts the cooler down until repairs 
 can be made. 
 
 The conventional ice grate is made 
 with heavy wood sills, notched or blocked 
 to support 4" x 4" timbers on about 10- 
 inch centers. The 4 x 4's are turned with 
 corners upward and are capped with steel 
 angles. Blocks of falling ice are split by 
 the steel angles and impact forces are 
 absorbed by the wooden framework. 
 There is little information on air resist- 
 ance and effectiveness of air cooling in 
 ice bunkers. Air resistance and cooling 
 
 [31] 
 

 ♦ t r 
 
 / 
 / 
 
 
 
 
 
 
 
 
 
 
 ♦- 
 
 — 
 
 — •- 
 
 
 
 
 
 
 
 — ^ 
 
 
 
 
 
 
 
 ,» 
 
 
 
 
 
 
 
 — - 
 
 
 
 
 
 
 
 ._ 
 
 
 
 
 
 
 
 
 
 i 
 
 Good 
 
 
 
 
 
 
 
 
 
 U-^~~f4 i / 
 
 
 
 
 
 
 
 
 
 
 — 
 
 — »- 
 
 
 
 
 
 
 
 _»- 
 
 
 
 
 
 
 
 -*- 
 
 
 
 
 
 
 
 — *- 
 
 
 
 
 
 
 
 — »_ 
 
 
 
 
 
 
 
 
 i 
 
 ■ 
 
 Bad 
 
 Fig. 26. When several tiers are stacked for 
 pressure cooling the top of the stack should be 
 exposed to the air supply, so that the boxes 
 which receive the least air also receive the 
 coldest air. It is helpful to space the tiers W 
 or %" apart, to allow cold air that passes be- 
 tween the boxes to mix with warmer air that 
 passes through them. 
 
 effectiveness usually fall rapidly with in- 
 itial melting after a bunker has been re- 
 iced and then decline erratically as chan- 
 nels form and collapse. Disappearance of 
 ice from portions of the grate is accom- 
 panied by a second rapid fall in air re- 
 sistance and cooling effectiveness. Size 
 of ice blocks and arrangements in which 
 they fall result in different performance 
 after successive re-icings. A common rule 
 is to allow 1 square foot of grate area 
 for each 100 cfm of air that passes 
 through the bunker and to maintain the 
 ice at least 5 feet deep in 100-pound 
 blocks or 3 feet deep in 300-pound 
 blocks. The temperature of air passing 
 through such a bunker is reduced roughly 
 half-way to ice temperature with a static 
 head across the bunker of about .2 inch 
 of water. 
 
 SPRAY HUMIDIFICATION 
 
 Calculated humidities resulting from 
 net addition of different amounts of 
 moisture in a cold room or cooler are 
 shown in table 8. These figures agree well 
 with the few available tests of existing 
 installations and are believed to be a 
 
 Fig. 27. Forced-air cooling. Boxes are moved from lidder to cooler on roller conveyor and 
 stacked by hand, cooled fruit is removed with hand trucks. Air supply is through ceiling, return 
 is from space behind boxes. 
 
 [32] 
 
Fig. 28. Forced-air cooling. Boxes are placed by hand trucks in U-shaped stacks and 
 covered with canvas. Air supply is from above, return is from behind the stacks. 
 
 good basis for designing fog systems. 
 The figures for moisture added are per 
 ton of refrigeration. Under many condi- 
 tions a given cooling effect is accompa- 
 nied by about the same condensation, re- 
 gardless of cooling surface temperature. 
 The amounts of moisture shown in 
 table 3 will condense on dry coils, on ice 
 or in a brine spray. In case of dry coils 
 above freezing, or ice, this condensation 
 is easily drained away. Overflow of a 
 brine spray system consumes salt and re- 
 quires attention to the brine concentra- 
 tion. Addition of 16 gallons of water 
 per day per ton of refrigeration at tap 
 temperature and its removal at brine tern- 
 Fig. 29. Forced-air cooling. Boxes loaded and 
 unloaded outside on roller conveyor which 
 runs through the cooler. Canvas or light ply- 
 wood will cover space between stacks, air 
 supply is from above and between stacks and 
 walls, return is through the floor from space 
 between stacks, which is closed at the ends by 
 the doors. 
 
 perature adds about 1 per cent to the re- 
 frigeration load. 
 
 [33] 
 
Refrigeration capacity for maximum initial cooling rate 
 
 •Refrigeration capacity for one-half maximum initial cooling rate 
 
 Half-cooling Times 
 Fig. 30. Effect of refrigeration capacity on cooling rate. 
 
 Depth of Ice (feet) 
 
 12 16 
 
 Depth of Ice (feet) 
 
 Depth of Ice (feet) 
 
 Fig. 31 . Effect of air velocity in ice bunker, 
 ice in 100-pound blocks. 
 
 -.50 
 
 3 
 
 " 
 
 Weight 
 
 of 
 
 ice 
 
 blocks (lb)" 
 
 ~^50 
 
 - 
 
 
 
 
 
 ^too 
 
 Remaining temp. _ 
 diff. (per cent) 
 
 ~^_ , 
 
 
 
 
 
 
 
 
 
 
 " 
 
 
 
 
 
 ^^■-iOO 
 
 y^ 
 
 
 1 
 
 
 l 
 
 
 j^, 
 
 
 
 4 8 
 
 
 2 
 
 
 16 
 
 20 24 
 
 Depth of Ice (feet) 
 
 Fig. 32. Effect of ice-block size in ice bunker, 
 air flow 100 cfm per sq. ft. grate area. 
 
 [34 
 
TABLE 8 
 
 Relative Humidities Resulting from Net Addition of Moisture in a Cooler or Cold 
 
 Room and Corresponding Condensation on Cooling Surfaces 
 
 
 Return 
 
 air 
 temp. 
 
 Cooling 
 surface 
 temp. 
 
 Net moisture added 
 (gal. per day per ton refrigeration or per ton of 
 
 ice melted) 
 
 Kind of cooling surface 
 
 
 
 4 
 
 8 
 
 12 
 
 16 
 
 
 Degrees F. 
 
 Return air relative humidity 
 
 Unsalted ice or dry coils. . . . 
 
 35 
 
 32 
 
 88 
 
 91 
 
 94 
 
 98 
 
 100 
 
 
 
 25 
 
 64 
 
 72 
 
 82 
 
 95 
 
 100 
 
 
 
 18 
 
 46 
 
 60 
 
 76 
 
 95 
 
 100 
 
 
 
 10 
 
 30 
 
 50 
 
 75 
 
 95 
 
 100 
 
 Salted ice or brine spray. . . . 
 
 35 
 
 32 
 
 82 
 
 85 
 
 88 
 
 92 
 
 100 
 
 
 
 25 
 
 59 
 
 68 
 
 78 
 
 92 
 
 100 
 
 
 
 18 
 
 42 
 
 56 
 
 74 
 
 92 
 
 100 
 
 
 
 10 
 
 29 
 
 49 
 
 74 
 
 92 
 
 100 
 
 Unsalted ice or dry coils. . . . 
 
 50 
 
 32 
 
 50 
 
 58 
 
 69 
 
 81 
 
 99 
 
 
 
 25 
 
 36 
 
 47 
 
 61 
 
 81 
 
 99 
 
 
 
 18 
 
 26 
 
 40 
 
 58 
 
 81 
 
 99 
 
 
 
 10 
 
 17 
 
 35 
 
 58 
 
 81 
 
 99 
 
 Salted ice or brine spray. . . . 
 
 50 
 
 32 
 
 47 
 
 54 
 
 65 
 
 79 
 
 98 
 
 
 
 25 
 
 34 
 
 45 
 
 59 
 
 79 
 
 98 
 
 
 
 18 
 
 26 
 
 40 
 
 57 
 
 79 
 
 98 
 
 
 
 10 
 
 17 
 
 34 
 
 57 
 
 79 
 
 98 
 
 Condensation of 16 gallons of water 
 per day per ton of refrigeration as ice 
 on dry coils releases several times as 
 much heat as does cooling the water, 
 adding about 6 per cent to the refrig- 
 eration load. Part of this loss is recovered 
 by hot-gas defrosting or by defrosting 
 with warm water from the condenser. 
 Mechanics of defrosting on such a scale 
 is a consideration, however. Introduction 
 of this amount of moisture as steam 
 rather than as water spray adds over 40 
 per cent to the refrigeration load. 
 
 In order to maintain the above net ad- 
 ditions of moisture, it is necessary to 
 supply also the water absorbed by dry 
 containers. Grape boxes held in 90 per 
 cent relative humidity storage at Davis 
 gained about % per cent of their dry 
 weight per day initially, about % per 
 cent per day after 20 days, about % per 
 cent per day after 40 days, etc. 
 
 Two types of air-and-water atomizing 
 nozzles are available for spray humidifi- 
 cation. In one type water is piped to the 
 nozzle under pressure. The other type 
 uses a tank in which the float-controlled 
 level is a few inches below the nozzle and 
 the water is sucked up by the air as it 
 issues from the nozzle. The former type 
 is the simplest to install and maintain, 
 but slight variations in air or water pres- 
 sure may make the spray too coarse or 
 stop it entirely, requiring close adjust- 
 ment of pressure regulators in the air and 
 water lines. Suction feed from a float- 
 tank automatically proportions the water 
 to the air supply and a satisfactory spray 
 is obtained over a wide range of air pres- 
 sures. Electric soil-heating cable may be 
 used to keep pipes and tanks from freez- 
 ing. 
 
 Spray-humidification is analyzed in 
 more detail on pages 46 to 48. 
 
 [35] 
 
INSULATION AND VAPOR 
 BARRIER (1,8) 
 
 Inadequate insulation may double the 
 refrigeration used in a cooler, adding as 
 much as $2 per ton of product to cost of 
 a cooling operation, and may in addition 
 seriously slow the cooling by raising the 
 temperature of the air or water used. 
 Effectiveness of the materials commonly 
 used to insulate walls and ceilings — fibre- 
 glass, mineral wool, other fibrous ma- 
 terials, plastic foams, or multiple layers 
 of aluminum foil and paper — is not very 
 different, inch for inch of thickness. 
 These insulations should be chosen on a 
 basis of cost and deterioration under 
 expected conditions of service. 
 
 Wooden studding which contacts both 
 faces of a wall will conduct four or five 
 times as much heat as the same area of 
 insulation between the studs. Staggered 
 studs, each contacting only one face of 
 the wall, are worth while for a cooler 
 operating a long season. Steel fastenings 
 or pipes have 1,000 times, and aluminum 
 ones 6,000 times, the heat conductivity 
 of insulation. Metal passing through heat 
 insulation has been likened to a leak in 
 the bottom of a boat. It is a common prac- 
 tice to use 4 inches of insulation in walls 
 and 6 inches in ceilings or roofs. This 
 may be calculated to be the thickness for 
 least combined cost of insulation and re- 
 frigeration under the conditions below. 
 
 Cost of 4-inch insulation, installed 12j£ per sq. ft. 
 
 Cost of 6-inch insulation, installed 18jzf per sq. ft. 
 
 Insulation to pay for itself in five years, plus 10 per cent 
 annually of its average value during that time for in- 
 terest, insurance and taxes 
 
 Cost of ice or equivalent mechanical refrigeration $6 per ton 
 
 Time of annual operation 20 days 
 
 Average temperature difference between inside and outside 
 of insulation in walls 30°F 
 
 Average temperature difference between inside and outside 
 of insulation in roof 60°F 
 
 Heat conduction through insulation 03 Btu/ft 2 hrF/f t 
 
 Differences in any of the above figures 
 that save 20 per cent in annual insulation 
 cost, or that add 20 per cent to the an- 
 nual refrigeration cost, justify adding 10 
 per cent to the insulation thickness. It is 
 evident that 4-inch and 6-inch thicknesses 
 are a minimum and that 6-inch and 8- 
 inch insulation will pay for itself in many 
 cases. Ordinary concrete walls need as 
 much insulation as wooden ones. Twelve 
 inches of ordinary concrete have about 
 the same insulating value as % inch of 
 wood. Special aggregates can improve 
 the insulating value of concrete consid- 
 erably. Manufacturers of these products 
 can supply information on their effective- 
 ness. Concrete and styrofoam sandwiches, 
 cast flat and then tipped up into place, 
 
 have been used successfully for ice 
 bunkers. 
 
 Floors and walls against dry soil do 
 not introduce much heat after the first 
 yard or so of soil is cooled, which may 
 take several days, however. It can be 
 calculated that ice or other refrigeration 
 used in cooling the soil is worth perhaps 
 four cents per square foot of surface each 
 time the cooler is started up. Insulation 
 is seldom provided, though apparently 
 it should pay for itself. Heat can enter 
 easily through exposed edges of floors or 
 through surface soil against walls. Wall 
 insulation should be carried two feet or 
 more below the floor or below the outside 
 grade, whichever is higher. 
 
 Inadequate insulation may seriously 
 
 36 
 
impair the cooling effect of an ice AIR PASbAGta [i) 
 bunker. Air may emerge at 35°F from The cost of air passages and their ef- 
 
 the ice in a bunker and on its way to the fects on the operation should be minor 
 
 product be warmed to 40°F by contact factors in a well-designed fruit or vege- 
 
 with poorly insulated surfaces. The cover table cooler, though unfortunately this 
 
 of a poured concrete bunker is sometimes is not always the case. Ice bunkers or 
 
 not insulated at all. On a hot day its top cooling units should be located as close 
 
 surface may be too hot to touch while its as possible to the fruit that is being 
 
 under surface is being swept by the cold cooled, and so arranged that openings 
 
 air supply — conditions for serious heat through which the air passes may be of 
 
 leakage at a point where it does most to ample size. Passages may sometimes be 
 
 impair the effectiveness of the cooler, entirely eliminated, as by mounting fans 
 
 Forced-air coolers should not be designed in a wall between a cooling room and 
 
 with sheet metal or extensive, thin ply- an ice bunker, or by placing a cooling 
 
 wood surfaces separating the return and unit in a room or separated from it only 
 
 supply air. The return air in a forced- by a wall. Where passages are necessary 
 
 air cooler may sometimes be 20°F or they should be of ample size, their walls 
 
 more warmer than the supply. Heat leak- should be smooth and free from obstruc- 
 
 age from the return to the supply does tions, and there should be as few turns 
 
 not waste refrigeration but it slows cool- as possible, 
 ing of the produce. Under these conditions, a few simple 
 
 The inner part of the insulation is rules are sufficient to estimate the static 
 
 usually cold enough to condense mois- pressure that will be contributed by the 
 
 ture from any outside air that reaches air passages to the total head against 
 
 it. To prevent this there should be a which the fans must work. It is first neces- 
 
 vapor-proof barrier on the outside of the sary to estimate the air velocity, which 
 
 insulation. The insulation is then warmer is the air flow in cubic feet per minute 
 
 than the inside air which reaches it and divided by the area of the opening or 
 
 remains reasonably dry. Blanket insula- the section of the passage in square feet, 
 
 tion with a layer of metal foil on one For velocities of 500 feet per minute or 
 
 side may be used. If there is foil on both less, the pressure loss is negligible in 
 
 sides, the perforated side should be in- produce cooler operation and this is an 
 
 ward. Polyethylene sheeting is an excel- ideal condition if openings can be made 
 
 lent vapor barrier. lar g e enough. 
 
 Although opinion differs in this re- A pressure of about .02-inch is needed 
 
 spect, it is probably best to omit any to move air throu g h an opening or into 
 
 vapor barrier in a concrete floor that is a P assa S e or around a s q uar e corner if 
 
 laid on the ground. Such a floor, whether the velocit > r 1S 550 fe f P er minute ' This 
 
 insulated or not, eventually becomes con- ^XL^ UP W highei velocities 
 
 siderably colder than the soil beneath it, 
 
 with the result that vapor from the soil 7nn *,. ^ • , rvo • i. 
 
 , , i . -i * ' 00 * eet P er minute 03 inch 
 
 condenses on the underside ol any vapor -, nrkA £ . n „ . , 
 
 i . ., . . -j j /\ • . * i 1,000 feet per minute 06 inch 
 
 barrier that is provided. Omission of the -. . ™ r , . „ rt . , 
 
 i 11 .u • 1,400 feet per minute 12 inch 
 
 vapor barrier allows the moisture to n ' ~ - J . „. . , 
 
 ii i.i . 4 j 2,000 feet per minute 24 inch 
 
 come through the concrete into the room, 
 
 which does no harm in a produce cooler Pressure is needed to overcome friction 
 
 and is even of some help in regard to i n a long passage, as well as to move air 
 
 cooling the floor and to raising the into it. For a wood or concrete passage 
 
 humidity. with no projections from its walls, each 
 
 [37] 
 
length equal to 30 times the least lateral 
 dimension is about equivalent to another 
 opening or to a square corner. Friction 
 may be doubled by small offsets or pro- 
 jections, or reduced by one-half in a 
 smooth metal duct. For example, the 
 static pressure to produce an air flow 
 of 5,000 cubic feet per minute in a 
 smooth wood passage l'x 5' and 60' 
 long, with one square turn, is estimated 
 as follows: 
 
 ^OOrfm = 1000 fpm air yeIocity 
 
 1 X o 
 Pressure to move air into 
 
 entrance 06 inch 
 
 Pressure to move air around 
 
 turn 06 inch 
 
 Pressure to move air through 
 
 60' 
 
 passage 
 
 30 X 1' 
 
 x .06 inch .12 inch 
 
 Total pressure 24 inch 
 
 If such a passage as that in the example 
 above was between the stacked containers 
 and the wall in a forced-air cooler, there 
 would be a difference of .24 inch in the 
 pressures at the two ends of the stack. 
 This would result in some of the boxes 
 getting considerably less air than others, 
 or even perhaps in some boxes getting 
 no air at all. Due to eddies in the pas- 
 sages, this effect can be very erratic and 
 troublesome. It is recommended that air 
 passages beside the boxes in a forced-air 
 cooler should be large enough to keep the 
 velocity under 500 feet per minute when 
 the total pressure on the boxes is % inch, 
 and under 1,000 feet per minute when 
 the total pressure on the boxes is 2 inches. 
 
 FANS (8) 
 
 Fans for use in fruit or vegetable cool- 
 ers should be chosen on a basis of ratings 
 certified to conform to test methods of 
 one of the fan manufacturers' associa- 
 
 tions. These ratings are usually given in 
 catalogs or should be furnished by deal- 
 ers on request. To insure comparable 
 results, these tests are made under ideal 
 conditions, with straight, clear passages 
 10 fan diameters upstream and down- 
 stream. Turns or obstructions have un- 
 predictable effects on the true static head 
 against which a fan works. Discharge in 
 commercial installations is seldom more 
 than 90 per cent of that based on static 
 head in the rest of the system, and turns 
 or large obstructions near the fans may 
 reduce this figure to 75 or even 50 per 
 cent. 
 
 Ratings are usually for air delivered in 
 cubic feet per minute and for static pres- 
 sure against which the fan is working 
 in inches of water. Static pressure in a 
 cooler is the sum of the pressures needed 
 to move the air through openings, pas- 
 sages and turns; through the ice bunker 
 or cooling system; and in a forced-air 
 cooler, through the product. 
 
 Inexpensive, sheet-metal fans may be 
 used for pressures up to % or % inch. 
 More expensive high-speed propeller fans 
 are available for pressures up to 1% or 
 2 inches, above which it is necessary to 
 use still more expensive centrifugal fans 
 or special types of axial-flow fans. Fan 
 power to circulate a given flow of air is 
 in direct proportion to the static pres- 
 sure. 
 
 Power supplied to fans is converted to 
 heat by churning of the air, requiring ad- 
 ditional ice or refrigeration. A ton of 
 mechanical refrigeration, or melting of a 
 ton of ice a day, is required to offset the 
 heat introduced by 3% horsepower of 
 fans with the motors in the cooled space 
 or 4 horsepower of fans with the motors 
 outside. Coolers should be designed to 
 operate at high static pressures only after 
 considering the costs for fans and refrig- 
 eration that are involved. 
 
 [38 
 
Section III 
 
 ANALYSES AND TEST DATA 
 
 COOLING CALCULATIONS (10,29) 
 
 An object placed in surroundings at a 
 constant lower temperature, if resistance 
 to heat transfer from the object to the 
 surroundings is constant, cools according 
 to Newton's law. The process is conveni- 
 ently analyzed as follows: 
 
 Let 
 
 d 
 t 
 
 h 
 
 = time in the new surroundings. 
 
 = temperature of the object at 
 time 6. 
 
 = initial temperature of the ob- 
 ject. 
 
 = temperature of the surround- 
 ings. 
 
 F = = remaining fraction of 
 
 initial temperature differ- 
 ence between the object and 
 the surroundings. 
 
 C = the rate of cooling divided by 
 the temperature difference 
 between the object and the 
 surroundings, called the 
 "cooling coefficient." 
 
 Z = time to reduce the initial tem- 
 perature difference between 
 the object and its surround- 
 ings by one-half, called the 
 "half-cooling time." 
 
 Then 
 
 
 
 dt/dO = C(t - k 
 
 >) 
 
 
 1, I- 
 
 6 -c^u- 
 
 - U 
 
 - *0 ' 
 
 C 
 
 7 ln| 
 
 
 
 6 hiF 
 
 
 
 (1) 
 
 In a 
 
 (2) 
 
 From equation (1), C may be calcu- 
 lated from observations of time and tem- 
 perature, or when C is known it may be 
 used to calculate the time to reach a given 
 temperature or the temperature that will 
 be reached in a given time. Graphically, 
 C is the slope of a plot of InF against 0, 
 which is easily constructed on semi-log 
 paper, and which may be used to deter- 
 mine either 6, F or C when any two of 
 these quantities are known. 
 
 Equation (2) and the half-cooling time 
 Z are in some ways more convenient. 
 This equation may be solved for Z, 0, or 
 F, when any two of these quantities are 
 given, by a single setting of a log-log 
 slide rule; or either natural or common 
 logarithms may be taken from tables. Z 
 may be estimated by inspecting observa- 
 tions for the time at which the initial 
 temperature difference is reduced by one- 
 half. The time needed to cool a product 
 to l/o, % or Ys of the initial temperature 
 above its surroundings is Z, 2Z or 3Z. 
 
 [39} 
 
In the commercial cooling of fruits and 
 vegetables, the conditions for Newton's 
 law are seldom strictly satisfied. There 
 is often a considerable temperature gra- 
 dient within a container, or within indi- 
 vidual fruits or vegetables when these are 
 exposed, and resistance to heat transfer 
 to the surroundings may vary. Most im- 
 portant, the temperature of the immedi- 
 ate surroundings, such as the air among 
 stacked containers or even the tempera- 
 ture of the main air stream, may fall 
 considerably as cooling progresses. In 
 most cases, however, there is a final heat 
 sink at reasonably constant temperature, 
 such as a thermostatically controlled 
 space or the ice in a bunker. It has been 
 our experience that Newton's law applies 
 quite well if t is taken as the average 
 temperature of the product at time 6, 
 and t as the temperature of the final heat 
 sink. This application would be exact if 
 the conductance from the thermal center 
 of the product to a fixed-temperature heat 
 sink were constant, and apparently, the 
 departures from such an ideal condition 
 are small. 
 
 For cooling in variable-temperature 
 surroundings, the cooling coefficient may 
 be considered as the decrease in object 
 temperature in degrees per hour divided 
 by the average temperature difference 
 between the object and its surroundings. 
 This may be written as: 
 
 C = 
 
 (ti - t)/e 
 
 {t ~~ ^o)av 
 
 (3) 
 
 It is convenient to calculate (t— £ )av 
 as the numerical average of equally timed 
 observations. The resulting value of C 
 is a measure of the exposure of the object 
 in relation to its heat capacity, though it 
 is obviously not possible to predict the 
 cooling of an object from this coefficient 
 without having also some means of pre- 
 dicting the surroundings temperature. 
 
 Equation (3) may also be used when 
 the surroundings temperature is constant. 
 In this case determining (£-£ ) av fr° m 
 
 equally timed observations is the same as 
 calculating it as the log mean of initial 
 and final observations. For a given ob- 
 ject exposed in a given way, C is evi- 
 dently the same whether it is determined 
 in constant temperature surroundings or 
 in variable temperature surroundings, 
 and a half-cooling time Z may be calcu- 
 lated from it, though Z will have a physi- 
 cal meaning only when the surroundings 
 temperature is constant. 
 
 C will obviously not be the same, how- 
 ever, for different portions of the heat 
 circuit; for example, from product to 
 adjacent air, from product to main air 
 stream, or from product to ice bunker. 
 Cooling coefficients or half-cooling times 
 as given in references may have been 
 determined in any one of these ways, and 
 it is important to note which. A figure 
 based on a constant-temperature heat 
 sink is the only one that can be used to 
 predict cooling behavior. For this reason 
 as well as for purposes of comparison, it 
 is useful to estimate a conversion from 
 one base to another. Using primed sym- 
 bols to indicate the shorter portion of the 
 heat circuit, we may write for any time : 
 
 C = 
 
 (h - t)/e 
 
 it — to) av 
 
 and C" = (<1 
 
 t)/6 
 
 (t - $. 
 
 Hence: g_ = (t - < ') av 
 
 C (t — to)av 
 
 For air cooling systems the heat ca- 
 pacity of the coolant is usually small 
 and at any time the heat flowing through 
 the circuit is that being lost by the prod- 
 uct. Under these circumstances t - t' and 
 t - t are proportional to the heat re- 
 sistances over which they are measured. 
 The heat resistances between different 
 elements of a cooling system ordinarily 
 depend on the physical setup and do not 
 change as cooling progresses. Conse- 
 quently (t - 1' ) / (t - 1 ) , is the same at 
 whatever stage of cooling it is measured 
 and we may write simply: 
 
 [40 
 
C t - to 
 C " t- to 
 
 
 7 M 
 z ~ C 
 
 
 Z' c t - 
 Z " C ' " t - 
 
 -to 
 
 - to 
 
 Since 
 
 C 
 
 2T C_ t - to 
 
 (4) 
 
 Commonly, V Q is the temperature of an 
 air supply or a water supply and t is 
 the temperature of ice, or of refrigerant 
 in an evaporator. From measurement or 
 former experience with similar situa- 
 tions (t - Iq) / (t - 1 ) may be estimated 
 at some fraction, usually between % and 
 % . The product will then be cooled 
 half-way to ice or refrigerant tempera- 
 ture in a reciprocal fraction, usually be- 
 tween % or x %, of the time required to 
 cool it half-way to a constant surround- 
 
 ing air or water temperature, with the 
 same exposure. 
 
 Calculations of Z and Z' to allow for 
 effectiveness of air cooling in an ice 
 bunker or evaporator are more involved. 
 Continuing the above nomenclature and 
 also letting: 
 
 t r 
 
 R v = 
 
 temperature 
 product. 
 
 of air leaving 
 
 t - t r 
 t- t' 
 
 ratio of air to prod- 
 
 uct temperature differences, down- 
 stream/upstream. 
 
 R c = 
 
 V - t, 
 
 ratio of air to cold- 
 
 sink temperature differences, down- 
 stream/upstream. 
 
 From equation (4) above 
 
 Z^ 
 
 z 
 
 t - to (t - to) - (to - U) 
 
 t - to 
 
 t - t. 
 
 ^ = 1 - 
 
 £p — tp 
 
 t - u 
 
 (a) 
 
 From definitions: 
 
 (t - to) - (t r - to) = R p [(t - to) - (to - to)] 
 
 I . tp — tp 
 
 t r to — D 
 
 Combining (b) and (c) and simplifying: 
 
 = R P [(t - to) - (to - to)] 
 
 (t - to) - U ~ 
 
 R c 
 to — to R c — RcRi 
 
 t — £o 1 — R c Rp 
 
 (b) 
 (c) 
 
 (d) 
 
 Combining (a) and (d) : 
 
 Z 1 R c — R c Rp 1 — Rc 
 Z 1 — R C R P 1 — R c Rp 
 
 (5) 
 
 Z/Z' is plotted against R c for representative values of R p in figure 33, on which 
 table 7 is based. 
 
 [41] 
 
4.0 r 
 
 3.5 
 
 Typical forced air cooler- 
 Typical room cooler 
 
 3.0 
 
 2.5 
 
 2.0 
 
 Fig. 33. Effect of ice-bunker conditions on cooling. 
 
 Z/Z / is product-to-ice half-cooling time divided by product-to-air half-cooling time. 
 R c is ratio of air-to-ice temperature differences downstream and upstream. 
 R is ratio of air-to-product temperature differences downstream and upstream. 
 
 REFRIGERATION LOAD (31) 
 
 Specific heat of plant material is 
 usually estimated by assuming that the 
 average specific heat of the dry matter is 
 .2 and the specific heat of the water con- 
 tent is 1.0. On this basis the specific heats 
 of most fruits and vegetables involved in 
 cooling operations range from .85 to .95, 
 with an average value of about .9. Con- 
 tainers and packing materials may be 
 estimated to weigh y i0 as much as the 
 product and to have a specific heat of .3. 
 A specific heat of .93, based on the net 
 weight of product, takes into account the 
 heat capacity of the containers also. This 
 is well within the accuracy to which prac- 
 tical cooler performance may be pre 
 dieted and is used for calculations in this 
 publication. Complete tabulations of spe 
 cine heats, on which corrections may be 
 based if desired, are available in refer- 
 ences (3, 31). 
 
 Refrigeration load from cooling of 
 the product in a batch operation may be 
 calculated from the cooling equations de- 
 veloped in the preceding section: 
 
 dt/dO = C(t - to) 
 where 
 
 lni 
 
 (t - to) 
 
 dt/dd — cooling rate F/hr 
 
 C = cooling coefficient, F/hrF 
 
 t — to = temperature of product 
 
 minus temperature of heat sink, 
 
 F 
 In y 2 = .69 
 Z = half-cooling time, hr 
 
 Refrigeration load from cooling of the 
 product in a continuous operation is the 
 rate at which the product is passing 
 through the cooler, times the temperature 
 reduction accomplished, times the spe- 
 cific heat of the product. 
 
 < 
 
 [42 
 
The total heat evolved by respiration 
 in a given cooling operation may be cal- 
 culated by integrating the respiration 
 rate, or it may be estimated graphically 
 by plotting respiration rates against tem- 
 peratures at successive half -cooling times 
 as in figure 34. Any desired scale of time 
 in hours may be substituted for the scale 
 of half-cooling times. The total heats 
 evolved by respiration, in refrigeration 
 ton-hours, are then represented by the 
 areas under the curves. Table 4 was pro- 
 duced in this way. 
 
 The scale of areas to refrigeration ton- 
 hours is evidently directly proportional 
 to the scale of Y-axis distances to hours. 
 From this it follows that the heat evolved 
 by respiration while cooling to any par- 
 ticular temperature is directly propor- 
 tional to the time elapsed in reaching that 
 temperature. W. V. Hukill has demon- 
 strated this analytically (31). 
 
 Losses by heat conduction into a cooler 
 through the walls and ceiling may be 
 estimated with fair accuracy from tabu- 
 lated conductances of the construction 
 materials. Heat introduced by the fans 
 can be calculated from electrical input 
 at the rate of 3,413 Btu per kwh. Heat 
 pickup from a concrete floor-slab is more 
 uncertain. Infiltration of warm air from 
 the outside can only be guessed from ex- 
 perience and is usually important be- 
 cause of appreciable static pressure and 
 suction in a cooler. At least for small 
 coolers it is probably as safe to make a 
 single estimate of losses based on an 
 assumed efficiency; ranging from 50 per 
 cent for slow cooling, meagre insulation 
 or considerable infiltration ; up to 80 per 
 cent for fast cooling and tight, well- 
 insulated construction. 
 
 PERFORMANCE 
 
 u o 
 
 1 
 
 2 3 4 
 •Half-cooling Times 
 
 5 
 
 6 
 
 80 
 
 56 
 
 44 38 35 
 
 Product Temperature (°F) 
 
 34 
 
 33 
 
 Fig. 34. Refrigeration to absorb heat of 
 respiration, initial product temperature 80°F / 
 coolant temperature 32°F. 
 
 D 
 
 h 
 
 ICE BUNKER 
 
 (6, 11, 14) 
 
 Nomenclature 
 
 A = surface area of ice per unit of F 
 volume occupied. 
 
 a = surface area of ice block of effec- 
 tive mean size. 
 
 [43], 
 
 'o = 
 
 U = 
 
 = linear dimension of ice block of 
 effective mean size. 
 
 = heat conductance from fluid to 
 ice per unit surface area. 
 
 = heat conductance from fluid to 
 ice per unit of volume occu- 
 pied. 
 
 = distance in direction of fluid flow. 
 
 = number of ice blocks. 
 
 = fluid head per unit distance in 
 direction of flow. 
 
 = fluid head in distance X. 
 
 = temperature of fluid after flow- 
 ing distance L. 
 initial temperature of fluid, 
 temperature of ice. 
 t' - U 
 
 remaining fraction of 
 
 initial temperature difference 
 between fluid and ice. 
 
V = fluid velocity in gross section of 
 
 flow path. 
 W = weight of ice block of effective 
 
 mean size. 
 X = distance in direction of flow in 
 which temperature difference 
 between fluid and ice is re- 
 duced by one-half. 
 Subscripts 1 and 2 represent two con- 
 ditions being compared. 
 
 Other things remaining equal, heat 
 transfer to broken ice in a bunker from 
 air or water being forced through it 
 varies directly with the temperature dif- 
 ference between the ice and the air or 
 water. The relation of temperature dif- 
 ference to distance traveled is therefore 
 logarithmic, corresponding to the rela- 
 tion of temperature difference to time in 
 the case of a cooling body as discussed 
 previously. The distance in which the 
 temperature difference is reduced by one- 
 half is convenient for estimating the tem- 
 perature reached in a given distance or 
 the distance to reach a given temperature. 
 This might be called the "half-cooling 
 distance," corresponding to the half- 
 cooling time for a cooling body. A par- 
 allel analysis leads to the relation L/X — 
 InF/ln %, which may be used for calcu- 
 lations. 
 
 Effect of size of ice blocks. The 
 "half-cooling distance" is evidently in- 
 versely proportional to the heat conduc- 
 tance per unit volume: 
 
 X,/X 2 = tijh[ 
 
 Heat conductance per unit volume is in 
 turn directly proportional to heat con- 
 ductance per unit surface times surface 
 per unit volume: 
 
 From geometry, for blocks of similar 
 shape : 
 
 a 2 /ai = OD2/A) 2 , 
 n 2 /wi = (D 1 /D 2 y , 
 {Dx/DtY = WJW 2 
 
 Combining: 
 
 Xr/X* = (Wt/Wt) 
 
 to 
 
 (6) 
 
 Hence, the distance in which a given 
 change in fluid temperature is accom- 
 plished should vary with something be- 
 tween the square-root and the cube-root 
 of the effective weight of the ice blocks. 
 From fluid dynamics, friction from 
 flow among solids is inversely propor- 
 tional to approximately the 1.5 power 
 of the effective dimension of the solids, 
 giving: 
 
 P1/P2 = (iV^i) 1 - 5 , 
 where (Z> 2 /Z>i) 3 = W 2 /W 1 
 
 Combining: 
 
 Pi/Pt = Wz/Wt 
 
 (7) 
 
 In words, static head for flow through 
 a given distance is inversely proportional 
 to the square-root of the effective ice- 
 block weight, other things being equal. 
 Equations (6) and (7) may be com- 
 bined to find the effect of ice-block 
 weight on the static head needed to half- 
 cool the fluid, velocity remaining un- 
 changed : 
 
 P1/P2 = { V i/V2){X l /X 2 ) 
 
 = (W 2 /W 1 ) - 5 (W 1 /W 2 ) - 33 
 
 to (W2/WO - 5 (W 1 /W 2 ) - 5 
 = (W 2 /W 1 ) - 17 to (lf#i)° 
 
 KlK = {h2/h l ){a 2 /a l )(n 2 /n l ) 
 
 Apparently the static head to accomplish 
 a given change in fluid temperature 
 should be practically independent of the 
 
 From heat transfer data, depending on weight of the ice blocks. 
 
 conditions: Effect of fluid velocity among ice 
 
 blocks of a fixed size. The "half-cooling 
 hi/ hi = {Di/D 2 ) Q to (Di/D 2 )- 5 distance" with varying flow is evidently 
 
 [44] 
 
.I75r 
 
 .150 
 
 Inches water = 1.25x10 (fpm) 
 
 .125 
 
 .100 
 
 • Bunker 4'x 24'x7'deep 
 ©Bunker 3' x 4'x 4' deep 
 Ice in 50 lb blocks 
 
 .075 
 
 .050 
 
 .025 
 
 75 100 125 
 
 Velocity in Gross Section (fpm) 
 
 Fig. 35. Airflow through ice bunkers, static head related to air velocity. 
 
 200 
 
 directly proportional to velocity and in- 
 versely proportional to heat conductance 
 per unit volume: 
 
 Xi/Ti = (Vi/V i )(h' 2 /h' 1 ) 
 
 In this case the surface per unit volume 
 is fixed, so that heat conductance per 
 unit volume is directly proportional to 
 heat conductance per unit of surface, 
 and from heat transfer principles for 
 turbulent flow, approximately: 
 
 h' 2 /h[ 
 Combining: 
 
 AtAi = (V2/VO 
 
 Xi/x t = (F,/y 2 ) 
 
 (8) 
 
 Consequently, the distance to accomplish 
 a given change in fluid temperature 
 should vary directly with the .4 power 
 of the fluid velocity. 
 
 From fluid dynamics, friction from 
 
 turbulent flow through a bed of solids 
 is about proportional to the 1.8 power 
 of the velocity: 
 
 P1/P2 = (pi/p 2 )(x 1 /x 2 ; 
 
 = (Fi/V*)" 
 
 (9) 
 
 (10) 
 
 For flow through a given distance, the 
 static head should vary directly with the 
 1.8 power of the fluid velocity, and for 
 a given change in fluid temperature the 
 static head should vary directly with the 
 2.2 power of the fluid velocity. 
 
 Equations (6) through (10) should 
 apply to cooling of either air or water 
 in ice bunkers. They have been used to 
 extrapolate the inadequate available data 
 in figures 31 and 32. 
 
 Figures 35 and 36 show tests with air 
 flow through small bunkers, illustrating 
 
 [45] 
 
Q. 4 
 
 Q 
 
 .3 
 
 Depth (ft) = 0.64 (fpm) 
 
 • Bunker 4 , x24'x7'deep 
 ©Bunker 3'x4'x4'deep 
 Ice in 501b blocks 
 
 25 
 
 50 
 
 150 
 
 175 
 
 75 100 125 
 
 Velocity in Gross Section (fpm) 
 
 Fig. 36. Air flow through ice bunkers, half-cooling depth related to air velocity. 
 
 200 
 
 the erratic effects of recurrent melting 
 and collapse of the ice structure. These 
 results are consistent with conventional 
 full-scale construction. A sufficient num- 
 ber of observations at regular time inter- 
 vals might show a statistical distribution 
 on which more satisfactory design pro- 
 cedures could be based. Published data 
 on water-flow through broken ice seem 
 to be entirely lacking and time has not 
 permitted such measurements at Davis. 
 
 HUMIDITY CALCULATIONS (28) 
 
 Refrigeration texts commonly discuss 
 the graphical representation on a psy- 
 chrometric chart of changes in air tem- 
 perature, moisture content and enthalpy. 
 Such a representation of the history of 
 a pound of dry air as it circulates in a 
 closed system must evidently be a closed 
 
 figure. This is a very convenient and 
 useful way of analyzing events in produce 
 coolers and storages. 
 
 Figure 37 shows possible cycles in a 
 cooler or storage where a pound of 
 circulating air picks up 2 Btu in the 
 cooling or storage room and loses 2 Btu 
 in a cooling unit where the by-pass factor 
 is 40 per cent and the cooling surfaces 
 are at 32°F. 
 
 If no moisture is gained or lost any- 
 where in the circuit, the dewpoint of 
 the air may be at the temperature of the 
 cooling surfaces and a pound of dry air 
 may be alternately heated and cooled 
 along line A" F" . Entering air is about 
 37°F, 80RH; return air is 45.5°F, 59RH. 
 
 If produce is being cooled without 
 spray humidification, conditions may be 
 like those in the next circuit above, with 
 history of a pound of dry air as follows : 
 
 [46] 
 
13 
 
 Btu per pound dry air 
 14 15 16 
 
 32 
 
 34 36 38 40 42 44 46 48 
 
 Dry Bulb(°F) 
 
 Fig. 37. Effect of humidification on air conditions in a produce cooler. 
 
 50' 
 
 A' 
 
 A'B f 
 
 B'D' 
 
 = Enters from cooling surfaces 
 at 36°F, 90RH. 
 
 = Gains 1.8 Btu from warm pro- 
 duce and heat leakage from 
 outside. 
 
 = Gains 3.0 grains moisture by 
 evaporation from produce. 
 D'E' = Gains .2 Btu and .4 grain mois- 
 ture by mixture with .02 lb 
 air from outside, by leakage. 
 
 = Loses 1.0 grain moisture by 
 absorption in boxes. 
 
 = Returns to cooling surfaces at 
 43°F, 75RH. 
 
 = Loses 2.0 Btu and 2.4 grains 
 moisture to cooling surfaces. 
 
 The shape and position of this figure 
 evidently depend on the order and 
 magnitude of these events. However, it 
 is only by virtue of net loss of moisture 
 from the packed product or gain of 
 
 moisture from outside air that the abso- 
 lute humidity is anywhere above line 
 A" F". 
 
 Spraying water into the entering air 
 may virtually stop evaporation from the 
 product and double moisture absorption 
 by the containers, as represented in the 
 upper diagram; history of a pound of 
 dry air being as follows: 
 
 E'F' 
 
 F' 
 
 F'A' 
 
 AC 
 
 CD 
 
 DE 
 
 = Enters from cooling surfaces at 
 35.5°F, 96RH. 
 
 = Gains 5.8 grains moisture from 
 spray, of which .6 grain evap- 
 orates and 5.2 grains remain 
 as a fog. 
 
 = Gains 1.8 Btu from warm pro- 
 duce and heat leakage from 
 outside. 
 
 = Gains .2 Btu and .4 grain mois- 
 ture by mixture with .02 lb 
 from outside, by leakage. 
 
 47] 
 
EF = Loses 2.0 grains moisture by 
 absorption in boxes. 
 
 F = Returns to cooling surfaces at 
 41°F, 90RH. 
 
 FA = Loses 2.0 Btu and 4.2 grains 
 moisture to cooling surfaces. 
 
 Conditions without and with water 
 spray are summarized in table 9. Air 
 circulation, cooling surface temperature, 
 by-pass in the cooling units, and heat 
 added and removed are assumed to be 
 fixed. In this example, 5.2 grains of 
 moisture per pound of entering air re- 
 mains in suspension until the air is 
 warmed and dried by contact with the 
 produce and containers. For comparison, 
 a thick natural fog contains two grains 
 of suspended moisture per pound of air, 
 and up to 18 grains per pound has been 
 measured in dense clouds. In practice the 
 gains and losses of moisture and heat in 
 a cooling room occur more or less in 
 parallel, rather than in series as shown 
 in the diagrams. The level of humidity 
 that may be attained by use of a spray 
 system without trouble from water col- 
 lecting on floors or on produce is some- 
 thing that must apparently be determined 
 by experience. 
 
 It should be noted that the relation of 
 moisture condensed to heat given up at 
 
 the cooling surfaces depends only on 
 return air and cooling surface conditions 
 and is independent of the by-pass factor. 
 Figures 38 to 41 are constructed from a 
 psychrometric chart for a range of return 
 air and cooling-surface conditions. In 
 some cases line AF in figure 37 inter- 
 sects the saturation line at a temperature 
 above that of the cooling surfaces. This 
 indicates condensation from mixing as 
 air passes through the cooling unit. This 
 condensation or fog may impinge on 
 surfaces in the cooling unit and be re- 
 tained, or it may pass out with the air 
 blast and evaporate as mixing is com- 
 pleted. These alternatives are indicated 
 in figures 38 to 41. 
 
 OPTIMUM INSULATION (28) 
 
 Produce coolers are sometimes used 
 for shorter seasons than other insulated 
 structures but at wide differences of 
 temperature between inside and outside, 
 raising questions as to how much insula- 
 tion should be provided. The following 
 analysis assumes that temperature dif- 
 ference between outside and inside of 
 insulation is independent of insulation 
 thickness, that cost of refrigeration per 
 heat unit absorbed is fixed and that 
 annual insulation cost is directly pro- 
 portional to insulation thickness. 
 
 TABLE 9 
 Effect of Water Spray on Temperatures and Humidities in a Cooler Refrigerated 
 
 with Unsalted Ice 
 
 Air conditions 
 
 Entering air 
 
 Return air 
 
 Moisture added or removed 
 
 Spray 
 
 Evaporation from produce 
 
 Gain from air leakage 
 
 Condensation in boxes 
 
 Condensation on cooling surfaces 
 
 Without spray 
 
 With spray 
 
 36F, 90RH 
 43F, 75RH 
 
 35.5F, 96RH 
 41F, 90RH 
 
 Gal per day per ton of refrigeration 
 per ton of ice melted 
 
 vTone 
 
 14.5 
 
 7.5 
 
 None 
 
 1.0 
 
 1.0 
 
 2.5 
 
 5.0 
 
 6.0 
 
 10.5 
 
 [48] 
 
IOOi- 
 
 10 18 25 32 
 
 Cooling surface 
 temperature (°F) 
 
 Dotted lines 
 
 fog forms in cooling unit and evaporates 
 Dashed line 
 
 fog forms in cooling unit and is retained 
 
 2 4 6 8 10 12 14 16 
 
 Moisture (gallons per day per ton of refrigeration) 
 
 Fig. 38. Moisture added in a room and condensed on ice or coils, return air 35°F. 
 
 Nomenclature (any consistent units) : 
 
 Ci = annual cost of insulation per unit 
 area and thickness, 
 cost of refrigeration per heat unit 
 absorbed. 
 = annual operating season. 
 = heat conductance of insulation. 
 = temperature difference outside to 
 
 inside of insulation. 
 = insulation thickness. 
 
 C r = 
 
 Then: 
 
 Annual cost of insulation per unit area 
 
 — c* %x» 
 Annual cost of refrigeration to offset 
 
 heat leakage through a unit area of 
 
 insulation = C r kLta/x 
 
 Taking the derivative of total cost with 
 respect to x and equating to zero: 
 
 d - CrkLt d /x 2 = 
 x = (C r kLt d /Ci)i 
 
 In words, the optimum insulation thick- 
 ness is the square root of the annual cost 
 of refrigeration to offset heat leakage 
 through a unit area of unit thickness, 
 divided by the annual cost of insulation 
 of unit area and thickness. Consider for 
 example a metal hydrocooler under these 
 conditions: 
 
 Insulation cost installed S^/sq ft 1" 
 thick, annual fixed charges 33% per 
 cent, annual cost 1^/ft 2 in 
 
 [49] 
 
10 
 
 25 
 
 32 
 
 I00r 
 
 90- 
 
 80- 
 
 2. 
 
 X 70 
 
 60 
 
 50 
 
 40- 
 
 30 
 
 20. 
 
 
 # 
 # 
 
 / 
 § 
 
 ^f ^^^ 
 
 
 -^^J? 
 
 
 - 
 
 J& jf 
 
 
 
 18 / 
 
 
 y 
 
 / J°~^ Brine temperature (°F) 
 
 
 y 
 
 Dotted lines 
 
 
 
 fog forms in cooling unit 
 
 and evaporates 
 
 ,i., 
 
 Dashed line 
 
 fog forms in cooling unit and is retained 
 
 . I 1 I 1 1 i 
 
 2 4 6 8 10 12 
 
 Moisture (gallons per day per ton of refrigeration) 
 
 14 
 
 16 
 
 Fig. 39. Moisture added in a room and condensed in brine spray, return air 35°F, 
 relative humidity at brine surface 93 per cent. 
 
 Refrigeration cost $6/ton for ice, 
 .002^/Btu 
 
 Annual operating season 30 days, 720 
 hours 
 
 Heat conductance of insulation .36 
 Btu/ft 2 hr(F/in) 
 
 Temperature difference outside to in- 
 side, average, 30°F 
 
 Annual cost of refrigeration to offset 
 heat leakage through 1 sq ft of insula- 
 tion 1 inch thick: 
 
 (.002jzf/Btu)(.36 Btu/ft 2 hr F/in) 
 • (720hr)(30°F) = 15.5*! in/ft 2 
 Optimum thickness : 
 
 [(15.5^m/ft 2 )/(l^/ft 2 in)P = 4 in 
 
 FORCED-AIR COOLING 
 CALCULATIONS (5,27) 
 
 Calculation of forced-air cooling times 
 and temperatures from principles of 
 heat transfer requires constants which 
 have not been directly determined. Calcu- 
 lations from assumed constants are use- 
 ful, however, in evaluating and applying 
 existing test data. Heating or cooling of 
 a bed of solids, by a fluid passing 
 through, establishes temperature gradi- 
 ents from entrance to exit in both the 
 fluid and the solid. Calculation of the 
 initial fluid temperatures from entrance 
 to exit, and of the solid temperatures at 
 the entrance from start to finish, are not 
 
 [50] 
 
10 18 25 32 
 
 i /// 
 
 Dotted lines 
 
 fog forms in cooling unit and evaporates 
 
 Dashed line 
 
 fog forms in cooling unit and is retained 
 
 '0 2 4 6 8 10 12 14 16 
 
 Moisture (gallons per day per ton of refrigeration) 
 
 Fig. 40. Moisture added in a room and condensed on ice or coils, return air 50°F. 
 
 difficult, but fluid and solid temperatures 
 in the interior as time passes are some- 
 thing of a problem. 
 
 Figure 42 shows a graphical solution 
 published by C. C. Furnas, for air flow 
 parallel to the axis of a prismatic ar- 
 rangement of solids, with solids initially 
 at a uniform temperature and air 
 entering at a constant temperature and 
 rate (5, 27). 
 Nomenclature is as follows: 
 
 c a = Specific heat of air, Btu/lb F 
 
 c s = Specific heat of product and con- 
 tainers, Btu/lb F 
 
 hA = Heat conductance from product 
 to air, Btu/ft 3 hr F 
 
 w a = Air rate in gross section, lb/hr ft 2 
 
 w s 
 x 
 
 e 
 t 
 
 h 
 
 te 
 
 to 
 
 z 
 
 D 
 
 T 
 
 1] 
 
 Density of product and con- 
 tainers as stacked, lb/ft 3 
 Distance from air entrance, ft 
 Distance from air entrance to 
 
 air exit, ft 
 Time, hr 
 Temperature of product at x and 
 
 6, F 
 Initial temperature of product, F 
 Temperature of product at exit 
 
 at time 0, F 
 Initial temperature of air, F 
 Time to reduce (t — t ) by one- 
 half 
 
 hAx/caWa "Distance parameter' ' 
 hA6/c s w s "Time parameter" 
 
Dotted lines 
 
 fog forms in cooling unit and evaporates 
 
 Dashed line 
 
 fog forms in cooling unit and is retained 
 
 2 4 6 8 10 12 14 
 
 Moisture (gallons per day per ton of refrigeration) 
 
 Fig. 41. Moisture added in a room and condensed in brine spray, return air 50°F, 
 relative humidity at brine surface 93 per cent. 
 
 T.5,T. us Time parameters for (t — t ) 
 /(h - t ) = .5 and .125 re- 
 spectively 
 
 Tables 10 to 12 show calculated cool- 
 ing rates for downstream fruit, related 
 to heat conductance, air rate and product 
 density. It is interesting that arranging 
 a given lot of fruit in a single tier or in 
 several tiers, while the air flow in cfm/lb 
 of fruit is held constant, increases both x e 
 and w a in proportion and so has no direct 
 effect on the cooling rate of the down- 
 stream fruit. The increase in w a no doubt 
 results in some increase in hA, which 
 should in turn produce faster down- 
 stream cooling in a multiple-tier arrange- 
 
 ment. Note however that air flow among 
 the fruits is probably partly laminar, that 
 hA depends in part on resistance to heat 
 flow inside the fruits, which is not af- 
 fected by w a , and that table 10 shows 
 that cooling rate varies only with some 
 fractional power of hA. It is not surpris- 
 ing for tests to show that cooling of the 
 downstream fruit is not significantly af- 
 fected by single or multiple tier arrange- 
 ments so long as the air flow in cfm/lb 
 of fruit is not changed. 
 
 Table 11 shows that the cooling rate 
 of the downstream fruit should vary with 
 about the square-root of the air rate, 
 which is in accord with test results. Table 
 12 shows the considerable effect of prod- 
 
 [52] 
 
3 4 
 
 T= hA0/c s w 8 
 
 Fig. 42. Graphical solution for heat transfer between a moving fluid 
 and a bed of solids. (Furnas, 1930; Schumann, 1929). 
 
 uct density, so evident in the fast cooling 
 of such light products as strawberries in 
 trays. 
 
 These tables show the approximations 
 involved in considering that cooling is 
 logarithmic — in particular that a half- 
 cooling time calculated from one stage 
 in a cooling operation may be used to 
 predict conditions at some other stage. 
 Z 5 and Z. 125 represent half-cooling times 
 calculated for reduction of the initial 
 
 temperature difference to one-half and 
 one-eighth of its initial value, respec- 
 tively. For small values of D, correspond- 
 ing in general to thin stacks and high 
 air velocities, Z 5 and Z 125 agree very 
 well. For the largest value of D, in table 
 11, Z 5 is 75 per cent greater than Z 125 , 
 indicating that for thick stacks and low 
 air velocities half-cooling times provide 
 only a rough prediction of cooling be- 
 havior. 
 
 [53 
 
TABLE 10 
 
 Forced Air Cooling with Varying Product-to-air Heat Conductances 
 
 c a = .24 Btu/lb F, c s = .9 Btu/lb F, w s = 30 lb/ft 3 , air rate 1 cfm/lb product = 144 lb/hr 
 
 ft 3 , c s ws = 27 Btu/ft 3 F, x e / 
 
 CaWa = .029 ft 
 
 3 F/Btu. 
 
 
 
 
 hA 
 (Btu/ft» hr F) 
 
 hAxe/CaWa 
 
 = D 
 
 (no dimension) 
 
 T.5 
 
 from chart 
 (no dimension) 
 
 T.125 
 
 from chart 
 (no dimension) 
 
 T.sCW./hA 
 
 = Z.5 
 
 (hr) 
 
 T.uiCsW,/UA 
 
 = Z.l2b 
 
 (hr) 
 
 ^average 
 
 (hr) 
 
 10 
 
 20 
 
 40 
 
 80 
 
 .29 
 
 .58 
 
 1.16 
 
 2.32 
 
 4.64 
 
 .9 
 1.2 
 1.8 
 
 2.8 
 5.2 
 
 2.8 
 3.4 
 4.4 
 6.1 
 9.0 
 
 2.5 
 1.6 
 1.2 
 1.0 
 .9 
 
 2.5 
 1.5 
 1.0 
 
 .7 
 .5 
 
 2.5 
 1.6 
 1.1 
 
 .8 
 
 160 
 
 .7 
 
 TABLE 11 
 Forced Air Cooling with Varying Air-rate 
 
 hA = 40 Btu/ft 3 hr F, c c 
 Btu/ft 3 F. 
 
 .24 Btu/lb F, c a = .9 Btu/lb F, w s = 30 lb/ft 3 , c s w s 
 
 27 
 
 Air rate 
 (cfm/lb 
 product) 
 
 hAXe/CaWa 
 
 = D 
 (no dimension) 
 
 from chart 
 (no dimension) 
 
 T.us 
 
 from chart 
 
 (no dimension) 
 
 T.bCsWs/hA 
 
 = z. b 
 
 (hr) 
 
 T .i2bC e w,/3hA 
 
 = Z.12S 
 
 (hr) 
 
 ^average 
 
 (hr) 
 
 .25 
 
 .5 
 
 4.64 
 2.32 
 1.16 
 
 .58 
 .29 
 
 5.2 
 
 2.8 
 
 1.7 
 
 1.2 
 
 .9 
 
 9.0 
 6.1 
 4.4 
 3.4 
 
 2.8 
 
 3.5 
 1.9 
 
 1.2 
 .8 
 .6 
 
 2.0 
 
 1.4 
 
 1.0 
 
 .8 
 
 .6 
 
 2.8 
 1 6 
 
 1.0 
 
 1 l 
 
 2.0 
 
 8 
 
 4.0 
 
 .6 
 
 
 TABLE 12 
 
 Forced Air Cooling with Varying Product Density 
 
 hA = 40 Btu/ft 3 hr F, c a = .24 Btu/lb F, c s = .9 Btu/lb F, air rate 1 cfm/lb product. 
 
 (lb/ft*) 
 
 CsW» 
 
 (Btu/ft»F) 
 
 air rate 
 (lb/ft« hr) 
 
 hAXe/CaWa 
 
 = D 
 
 (no 
 
 dimension) 
 
 from chart 
 
 (no 
 dimension) 
 
 T.125 
 
 from chart 
 
 (no 
 dimension) 
 
 T.iCsWs/hA 
 (hr) 
 
 T.i2oC s w s /MA 
 
 = Z.125 
 
 (hr) 
 
 ^average 
 
 (hr) 
 
 15.... 
 30.... 
 50... 
 
 13.5 
 
 27 
 45 
 
 72 
 144 
 240 
 
 2.32 
 1.16 
 
 .70 
 
 2.85 
 1.75 
 1.30 
 
 6.1 
 4.4 
 3.5 
 
 1.0 
 1.2 
 1.4 
 
 .7 
 1.0 
 1.3 
 
 .8 
 1.1 
 
 1.4 
 
 [54] 
 
HALF-COOLING TIMES 
 
 Room cooling, 
 
 Half-cooling times based on constant air temperature, data from tests at Davis, 
 except as noted. 
 
 Half-cooling time 
 
 Artichokes packed in paper-lined apple boxes, loaded on end with 
 sides in contact with adjacent boxes, tops and bottoms exposed 
 to air in random motion, average of 10 thermocouples in centers 
 of artichokes 9 hr 
 
 Grapes in standard wooden lugs with sides and ends exposed to air 
 in random motion, average of two thermocouples in grapes in one 
 box 10 hr 
 
 Same, 400 fpm air velocity parallel to long dimension of lug, sides 
 and ends exposed, average of five thermocouples in grapes in 
 each of two boxes 8 hr 20 min 
 
 Grapes in 12 2-lb consumer cartons in master cartons, stacked with 
 sides and ends exposed to air in random motion, average of two 
 thermocouples in grapes in each of two boxes 23 hr 
 
 Pears, standard wrapped pack in wooden boxes, ends and bulged 
 top exposed to air in random motion, thermocouples in corner, 
 side and center pears, average of three tests : 
 
 Corner pear 6 hr 
 
 Average pear 16 hr 
 
 Center pear 24 hr 
 
 Pears naked in wirebound box, about 35 lb net, sides and ends ex- 
 posed to air in random motion 
 
 Of four thermocouples in pears: 
 
 Coolest 9 hr 
 
 Average 12 hr 
 
 Warmest 13 hr 
 
 Pears naked in telescope carton with hand holes in ends, about 40 lb 
 net, sides and ends exposed to room air 
 
 Of four themocouples in pears : 
 
 Coolest 9 hr 
 
 Average 18 hr 
 
 Warmest 21 hr 
 
 Same, but pears wrapped and carton ends only exposed 
 
 Of four themocouples in pears : 
 
 Coolest 15 hr 
 
 Average 25 hr 
 
 Warmest 28 hr 
 
 [55] 
 
Pears naked in telescope carton with no vents, 36 lb net, sides and 
 
 ends exposed to room air, thermocouples in corner, side and center , 
 
 pears, average of three tests Haif-cooiing time 
 
 Corner pear ^ nr 
 
 Average pear 11 hr 
 
 Center pear 17 hr 
 
 Pears in 2-lb consumer carton packed 20 in cubical master carton, 
 four sides exposed to room air, average of two tests 
 Of four thermocouples in pears: 
 
 Coolest. 8 hr I 
 
 Average 14 hr 
 
 Warmest • 18 hr 
 
 $ 
 
 Pears naked in field lug, sides and ends exposed, other lugs beneath 
 
 and on top 
 
 Of four thermocouples in pears : 
 
 Coolest 7 hr 
 
 Average 8 hr ^ j 
 
 Warmest ., ...'. .,;:." 9 hr 
 
 Half-cooling time 
 
 Pear, Single, 2%" dia., 260 grams Surface Center 
 
 Exposed to room air 52 min 1.3 hr 
 
 20 mph air blast 8 min 30 min 
 
 4 
 
 Pear, single, 2" dia., 100 grams 
 
 Exposed to room air 28 min 36 min 
 
 20 mph air blast 6 min 18 min 
 
 Pears in 36-lb cartons stacked on pallet, top and bottom vents in line 
 with vent in pallet, no lateral spacing, thermocouples in centers 
 of nine cartons, tests in Lake County Haif-cooiing time 1 
 
 Coolest carton (corner bottom) 12 hr 
 
 Average of nine cartons 24 hr 
 
 Warmest carton (center top) 48 hr 
 
 Pears in 36-lb cartons cross-stacked on pallet, with lateral 
 
 spacing, thermocouples in centers of cartons, tests in Haif-cooiing time 
 
 T olro r^rvnr-i + ir Six cartons Six cartons 
 
 i^aKe bouncy with vents wit h ut vents 
 
 Coolest carton 8 hr 17 hr 
 
 Average carton . 14 hr 18 hr 
 
 Warmest carton 21 hr 21 hr 
 
 [56] 
 
Plums in 12^" X 12}^" X 7" (inside) corrugated fibreboard box, 
 top layer in fibreboard tray, 25 lb net, average of two thermo- 
 couples in plums in each box 
 
 With polyethylene liner: Haif-cooiing time 
 
 Two sides exposed in room air 24 hr 
 
 Two sides exposed in 10 mph air 12 hr 
 
 No liner, two hand holes: 
 
 Two sides exposed in room air 16 hr 
 
 Two sides exposed in 10 mph air 4 hr 
 
 Same, but folded telescope box, sides five layers of corrugated 
 board, 
 
 Two sides exposed to room air, no vents 26 hr 
 
 Four exposed vents each Y%" X 2}^" 15 hr 
 
 Six exposed vents each %" X3" 11 hr 
 
 Same, box with projecting lids, sides two layers of corrugated 
 board, 
 
 Two sides exposed to room air, four exposed vents each 1" 
 
 X 3" 9hr 
 
 Plums in 12^" X 12^" X 7" (inside) laminated kraft-veneer box 
 with wooden frame, top layer in fibreboard tray, 25 lb net, average 
 of two thermocouples in plums, two sides exposed to room air ... . 9 hr 
 
 Plums in 12^" X 12^ ,/ X 7" (inside) corrugated fibreboard box, top 
 layer in fibreboard tray, 25 lb net, two sides exposed, average of 
 two thermocouples in plums in each box 
 
 Projecting lid, room air 11 hr 
 
 Projecting lid, air velocity 720 fpm 8 hr 
 
 Telescope box : 
 
 8 W X 2" horizontal vents, room air 10 hr 
 
 8 K" X 2" horizontal vents, 630 fpm 8 hr 
 
 8 Y2' X 2" vertical vents, room air 1 1 hr 
 
 8 y 2 " X 2" vertical vents, 520 fpm 9 hr 
 
 4 34" X 2" horizontal vents, room air 1] hr 
 
 4 l /i" X 2" horizontal vents, 630 fpm 10 hr 
 
 No vents, room air 18 hr 
 
 Plums in four-basket crate, two sides exposed, average of two ther- 
 mocouples, room air 9 hr 
 
 Same, 630 fpm 2 hr 
 
 Plums, single fruits on table : 
 
 Room air 30 min 
 
 Air blast 1750 fpm 8 min 
 
 [57] 
 
Potatoes in special boxes to test effect of vents; 11 3^" X 17 %" 
 X 8%" high; tops, bottoms and ends insulated; sides two layers 
 corrugated fibreboard exposed to air movement and with vents as 
 indicated, average of four thermocouples in potatoes in each box 
 
 Per cent of side area vented 
 
 Half-cooling time 
 
 Room air 
 
 200 f pm 
 
 No vents . . 
 
 hr 
 15.3 
 
 14.8 
 14.0 
 11.8 
 10.0 
 
 8.6 
 5.9 
 5.0 
 
 hr 
 
 14 
 
 1.3 
 
 14.1 
 
 2.6 
 
 10 3 
 
 5.2 
 
 10 9 
 
 10.4 
 
 5 7 
 
 24 
 
 5 7 
 
 52 
 
 4 
 
 100 
 
 2 7 
 
 
 
 - 
 
 (1 per cent of side vented reduces cooling time about 5 per cent) 
 
 Potatoes in experimental plastic lugs 15" X 24" X 9" outside, 64 lb TT . 
 
 . ' Half-cooling 
 
 net, 7.4 lb tare, stacked three high m room air, average of five time 
 
 thermocouples in potatoes in center lug, tight bottoms 9 hr 
 
 Same, but wood lugs 12%" X 22" X 9", 50 lb net, 9 lb tare. ... 6 hr 
 
 Strawberries in corrugated fibreboard tray containing 12 12-ounce 
 baskets, six stacks of 12 trays each on single pallet, all sides ex- 
 posed in large cold-storage room 
 
 Of four thermocouples in berries : 
 
 Average 2.2 hr 
 
 Warmest 3 nr 
 
 Forced-air cooling 
 
 Half-cooling times based on constant air temperature, data from tests at Davis, 
 except as noted. 
 
 Artichokes packed in plum cartons 123^" X l2 l / 2 " X 6J^" high 
 inside, three layers of 16 artichokes each, net wt 32.9 lb, 2 %," X 
 3" vents in each of opposite faces of cartons, axes of artichokes 
 normal to air-flow, static air head across carton J/g" water, air- 
 flow 1.5 cfm/lb product 1.2 hr 
 
 Grapes, stack of five standard lidded lugs, average net wt 28 lb each, 
 average of five thermocouples in each of two boxes, static head 
 
 across lugs .09", air flow 1.5 cfm/lb product 41 min 
 
 Same, static .005", air flow .2 cfm/lb product 3.7 hr 
 
 Same, static ("water). .07 .05 .03 .02 .01 .008 
 air-flow (cfm/lb) . . . 1.2 1.0 .74 .58 .36 .26 
 
 [58] 
 
Grapes in 123^" X 12^" X 7" plum carton, 3 %" X 3" vents in each 
 of opposite faces, 23.8 lb net, average of 10 thermocouples in car- 
 ton: 
 
 Static head, 
 inches 
 
 2.1 
 .75 
 .25 
 .10 
 
 Air flow 
 cfm/lb fruit 
 
 4.5 
 2.5 
 1.5 
 
 .84 
 
 Half-cooling time 
 
 10 min 
 15 min 
 22 min 
 34 min 
 
 Grapes in 12 2-lb consumer cartons in master carton, 6 Y%' X 1%" 
 vents in each of opposite faces of master with 34" X 13^" vents 
 in 2-lb cartons to match, average of four thermocouples in up- 
 stream 2-lb cartons and four in downstream, static on master 
 carton .2", air-flow 1.1 cfm/lb fruit, average fruit 48 min 
 
 Same, downstream fruit 
 
 80 min 
 
 Grapes in 12 2-lb consumer cartons in master cartons, 134" X 7" 
 vents in tops and bottoms of masters by shying flaps, 5 Y2' holes 
 in top and bottom of each end of 2-lb cartons, stack of five master 
 cartons with vents lined up, slatted floor, static top to bottom 
 .15", air flow .13 cfm/lb fruit, simulating solid load in rail car, 
 horizontal baffle in center of master carton to force air to sides, 
 average of two thermocouples in grapes in bottom master carton 
 
 Same, but no baffle 
 
 Same, but no holes in 2-lb cartons 
 
 Melons in cartons 14J4" X 2334" X 9M" high outside, net weight 
 58 lb, stacked four high on slatted floor rack, }/$" static head on 
 top of stack, simulating rail car loaded solid : 
 
 5hr 
 5hr 
 9hr 
 
 Vent area 
 
 Air flow 
 
 Half-cooling time 
 
 Top 
 
 Bottom 
 
 Matching 
 floor slots 
 
 Top 
 carton 
 
 Second 
 carton 
 
 Third 
 carton 
 
 Bottom 
 carton 
 
 (in*) 
 
 20 
 
 11 
 
 18 
 
 (in*) 
 
 15 
 11 
 
 18 
 
 (in*) 
 
 1.0 
 1.0 
 1.2 
 
 (cfm) 
 
 25 
 
 28 
 29 
 
 hr 
 2.2 
 
 2.6 
 2.5 
 
 hr 
 
 4.8 
 3.8 
 
 3.6 
 
 hr 
 
 6.6 
 6.1 
 5.9 
 
 hr 
 
 7.5 
 
 7.7 
 6.1 
 
 Peaches in paper cups, two layers in standard wooden box, 22 lb 
 net, horizontal air flow, average of 8 thermocouples near pits of 
 peaches 
 
 Thin pads, static head .08": Haif-cooUng time 
 
 5.0 cfm/lb fruit 50 min 
 
 4.8 cfm/lb fruit 50 min 
 
 Thick pads, static head .10": 
 
 1.3 cfm/lb fruit 51 min 
 
 [59] 
 
Peaches in naked pack, two layers in standard wooden box, 22 lb 
 net, horizontal air flow, average of eight thermocouples near pits 
 
 Of peaches Half-cooling time 
 
 Thick pads, static head .07", 5.2 cfm/lb fruit 46 min 
 
 Thick pads, static head .005", 1.3 cfm/lb fruit 1.3 hr 
 
 Peaches in 12^" X 123^" X 7" (inside) plum boxes with 3 %" X 
 3" vents in each of opposite faces, 48 peaches net weight 19 lb, 
 horizontal air flow 
 
 Half -cooling time 
 
 25 min 
 
 29 min 
 
 34 min 
 
 46 min 
 
 1.2 hr 
 
 Static head 
 inches 
 
 Air flow 
 cfm/lb fruit 
 
 2.1 
 
 7 
 
 1.2 
 
 5 
 
 .8 
 
 4 
 
 .16 
 
 2 
 
 .04 
 
 1 
 
 Pears naked in 12" X 18" X 10" cartons with side vents, 36 lb net, 
 air flow horizontal, average of 8 thermocouples in fruit 
 
 Static head 
 inches 
 
 Air flow 
 cfm/lb fruit 
 
 .50 
 
 2.4 
 
 .30 
 
 1.8 
 
 .13 
 
 1.4 
 
 .08 
 
 .86 
 
 Half -cooling time 
 
 39 min 
 46 min 
 50 min 
 1.1 hr 
 
 Pears naked in 12" X 18" X 9^" cartons, 36 lb net, stack of four 
 cartons with top and bottom vents in line, 1 thermocouple in 
 center of pear in center of each carton, static head on stack .1" 
 
 
 Air flow 
 
 cfm/lb 
 
 fruit 
 
 Half -cooling time 
 
 Arrangement 
 
 Carton 
 
 
 Top 
 
 2nd 
 
 3rd 
 
 Bottom 
 
 Bottom carton with vents exposed. . 
 
 .40 
 .30 
 
 hr 
 
 1.7 
 2.5 
 
 hr 
 4.5 
 
 5.5 
 
 hr 
 
 7.5 
 7.5 
 
 hr 
 8 2 
 
 Bottom carton in floor rack with Y^" slots on 4" 
 centers 
 
 9 
 
 
 
 Plums in Sanger lugs, 22 lb net, horizontal air flow, average of eight 
 
 thermocouples in plums in 1 lug Haif-cooiing time 
 
 Static head .10", air-flow 2.3 cfm/lb fruit 29 min 
 
 Static head .008", air-flow .6 cfm/lb fruit 78 min 
 
 Same, but vertical air-flow 
 
 Static head .09", air-flow 2.3 cfm/lb fruit 27 min 
 
 Static head .01", air-flow .7 cfm/lb fruit 59 min 
 
 [60] 
 
Plums in 12}^" X 12^" X 7" cartons with 3 %" X 3" vents in each 
 of opposite faces, 24 lb net, horizontal air flow, average of 10 
 thermocouples in plums in one carton 
 
 Static head Airflow 
 
 inches cfm/lb fruit Half-cooling time 
 
 1.4 4.0 20 min 
 
 .8 3.0 23 min 
 
 .3 1.6 32 min 
 
 .05 .6 53 min 
 
 Potatoes in 12" X 18" X 9J^" pear cartons stacked 4 high with top 
 and bottom vents in line, 40 lb net per box, static head .12" on 
 top of stack, air flow .56 cfm/lb product, two thermocouples in 
 potatoes in each box 
 
 Location of box 
 
 Half-cooling time 
 
 Top 
 
 Bottom 
 
 Average 
 
 Top 
 
 hr 
 
 .6 
 2.1 
 3.3 
 
 4.8 
 
 hr 
 2.1 
 
 3.2 
 
 4.7 
 5.8 
 
 hr 
 1.4 
 
 2nd 
 
 2.6 
 
 3rd 
 
 Bottom 
 
 4.0 
 5.3 
 
 Strawberries in corrugated fibreboard trays containing 12 12-ounce 
 baskets, six stacks of 12 trays each on single pallet against air- 
 return from large cold-storage room, static head on three tiers of 
 trays .5", air-flow estimated 3.0 cfm/lb berries, test at Watson- 
 ville 
 
 Of six thermocouples in berries: Haif-cooiing time 
 
 Average 16 min 
 
 Warmest 23 min 
 
 Strawberries in above pack but three trays in one stack in labora- 
 tory cooler, average of nine thermocouples in berries 
 
 Static head 
 inches 
 
 .05 
 .002 
 
 air flow 
 cfm/lb berries 
 
 3.0 
 
 .8 . 
 
 25 min 
 1 hr 
 
 [61] 
 
2 min 
 
 Hydrocooling (data from tests at Davis except as noted) Half-cooling time 
 
 Asparagus in bunches (data by R. L. Perry, 17), five bunches, total 
 weight 15.2 lb, immersed in trough with water flow 3 gpm, aver- 
 age of 10 thermocouples 
 
 Cantaloupes in commercial hydrocooler (data by Lipton and Stew- 
 art, 13), thermocouples % inch beneath surface, half-cool to water 
 temperature 20 min 
 
 Peaches in half-bushel baskets (data by Harris and Spigner, 9). 
 Fruit dia 2Jjj$", in different positions in baskets, water flow 8 
 gal/min sq ft, temperatures at pit. 
 
 Concentration 
 
 Calculated half-cooling time 
 
 wetting agent (ppm) 
 
 Top 
 
 Middle 
 
 Bottom 
 
 Average 
 
 
 min 
 
 min 
 
 min 
 
 min 
 
 
 
 8 
 
 22 
 
 12 
 
 12 
 
 250 
 
 9 
 
 13 
 
 10 
 
 10 
 
 500 
 
 8 
 
 11 
 
 10 
 
 10 
 
 750 
 
 9 
 
 11 
 
 9 
 
 10 
 
 1,000 
 
 8 
 
 9 
 
 10 
 
 9 
 
 Fruit dia 23^", in centers of baskets, temperatures at pit. 
 
 Water-flow 
 (gal/min sq ft) 
 
 Calculated half-cooling time 
 
 With wetting 
 agent 
 
 Without wetting 
 agent 
 
 24 
 
 min 
 
 9 
 14 
 24 
 
 min 
 
 8 
 
 18 
 
 16 
 
 8 
 
 22 
 
 3 
 
 31 
 
 1.8 
 
 
 
 
 Fruit dia 2J^", water flow 3.6 gal/min sq ft, no wetting agent: 
 
 Depth 
 
 Surface 
 
 «" 
 
 l 
 
 Half-cooling time 
 
 1 min 
 
 ie" 8 min 
 
 2 22 mm 
 
 p it 28 min 
 
 Water flow 3.6 gal/min sq ft, with wetting agent, temperatures 
 at pit: 
 
 Fruit diameter 
 inches 
 
 Half-cooling time 
 
 2 34 13 min 
 
 25 A 16 min 
 
 [62] 
 
Peaches in special test box 1 ft cube inside, 114 peaches, 34 lb net, four thermo- 
 couples at pits, water sprayed on top, drains adjusted to keep box empty or 
 full of water, tests at Davis: 
 
 Water level in box 
 
 Water flow 
 through box 
 
 Half-cooling time 
 
 Average 
 
 Warmest 
 
 min 
 
 min 
 
 22 
 
 38 
 
 14 
 
 15 
 
 15 
 
 18 
 
 18 
 
 22 
 
 21 
 
 24 
 
 Box empty 
 Box full . . . 
 
 (gpm) 
 
 5.0 
 5.7 
 2.8 
 2.0 
 1.5 
 
 Peaches in commercial hydrocoolers (Toussaint et al, 1954), half- Haif-cooiing time 
 cooling at pits based on 32°F ice, tests at 1 1 hydrocoolers, range . . 8 to 14 min 
 Average 11 min 
 
 Pears in open lug (150 size Anjou), water spray about 4 gal/min sq 
 ft, three thermocouples near cores, 
 
 Top layer 11 min 
 
 Center layer . 
 Bottom layer. 
 
 Pear, single fruit immersed in still water. 
 Core 
 
 Plum, single fruit immersed in still water, at pit , 
 
 17 min 
 13 min 
 
 6 min 
 20 min 
 
 4 min 
 
 UNITS AND CONVERSION FACTORS 
 
 One ton of refrigeration equals: 
 
 288,000 Btu/da, 12,000 Btu/hr, 200 
 Btu/min 
 
 Heat absorbed by melting water ice at 
 rate of: 
 
 1 ton/da, 83 lb/hr, 1.4 lb/min 
 
 Heat absorbed by vaporizing dry ice 
 at the rate of: 
 0.52 ton/da, 44 lb/hr, .73 lb/min 
 
 Melting 1 lb water ice absorbs 144 Btu. 
 
 Vaporizing 1 lb dry ice absorbs 274 Btu. 
 
 One kilowatt-hour converted to heat 
 equals 3,413 Btu/hr = .28 tons of re- 
 frigeration. 
 
 One horsepower converted to heat equals 
 2,540 Btu/hr = .21 tons of refrigera- 
 tion. 
 
 Specific heats: fruits and vegetables .85 
 to .95, average .90 used in this bul- 
 letin; wood and paper .30, air at 35°F 
 .24. 
 
 Specific volume of air at 35°F 12.5 ft 3 /lb. 
 
 1 lb = 7,000 grains. 
 
 1 grain moisture per Btu = 5 gal w T ater 
 per ton-da of refrigeration. 
 
 Approximate compressor horsepower per 
 ton of refrigeration (2) 
 
 Evaporator Temp. (°F) 
 
 Condenser Temp. (°F) 
 
 95 
 
 115 
 
 135 
 
 30 
 
 20 
 
 1.1 
 
 1.3 
 1.5 
 1.7 
 
 1.5 
 1.8 
 2.1 
 2.3 
 
 2.0 
 2 4 
 
 10 
 
 2 7 
 
 
 
 3 2 
 
 
 
 [63 
 
REFERENCES 
 
 1. American Society of Heating and Air-Conditioning Engineers. Heating, ventilating, air- 
 
 conditioning guide. 35th edition. American Society of Heating and Air Conditioning 
 Engineers. 1957. 
 
 2. American Society of Refrigerating Engineers. Air conditioning-refrigerating data book, 10th 
 
 edition, design. American Society of Refrigerating Engineers. 1957-58. 
 
 3. American Society of Refrigerating Engineers. Air conditioning-refrigerating data book, vol. 1, 
 
 refrigeration applications. American Society of Refrigerating Engineers. 1959. 
 
 4. Friedmann, B. A., and W. A. Radspinner. Vacuum cooling fresh vegetables and fruits. AMS- 
 
 107. USDA Agricultural Marketing Service. April, 1956. 
 
 5. Furnas, C. C. Heat transfer from a gas stream to a bed of broken solids. Industrial and 
 
 Engineering Chemistry. 22(7) : 721-31. July, 1930. 
 
 6. Giedt, Warren H. Principles of engineering heat transfer. Van Nostrand. 1957. 
 
 7. Harvey, E. M., E. P. Atrops, H. W. Hrusehka and H. R. Barber. Shipping and cooling-in-car 
 
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 Agricultural Marketing Service. November, 1954. 
 
 8. Henderson, S. M. and R. L. Perry. Agricultural process engineering. John Wiley & Sons. 1955. 
 
 9. Harris, Hubert, and R. L. Spigner. Hydrocooling peaches. Mimeograph. Alabama Polytechnic 
 
 Institute Agr. Exp. Sta. No date. 
 
 10. Hicks, E. W. Precooling of fruits and vegetables, some theoretical considerations. Paper No. 
 
 2593 (0.11) Proceedings of Ninth International Refrigeration Congress. International Insti- 
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 11. Hickson, Arthur W. and Sidney J. Baum. Heat and mass transfer coefficients in liquid-solid 
 
 systems. Industrial and Engineering Chemistry. 33(11) : 1433-39. November, 1941. 
 
 12. Isenberg, F. M. and John Hartman. Vacuum cooling vegetables. Cornell Extension Bulletin 
 
 1012. New York State College of Agriculture. June, 1958. 
 
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 Western Grower and Shipper. 30(6) June, 1959. 
 
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 December, 1957. 
 
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 shipping California asparagus. Bulletin 600 University of California Agr. Exp. Sta. April, 
 1936. 
 
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 California cantaloupes as influenced by maturity, handling and precooling. Technical Bulletin 
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 refrigeration in transit. Technical Bulletin 899. USDA October, 1945. 
 
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 Report 198. USDA Bureau of Plant Industry, Soils and Agricultural Engineering, 1948. 
 
 21. Redit, W. H., M. A. Smith and P. L. Benfield. Tests on hydrocooling and refrigeration of 
 
 peaches in transit from Georgia and South Carolina, 1954. AMS-62. USDA Agricultural 
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 23. Ryall, A. Lloyd. A study of packaging materials. Ice and Refrigeration. August, 1952. 
 
 24. Ryall, A. Lloyd. Condensed data on rate of cooling experimental plum cartons. Mimeograph. 
 
 U. S. Horticultural Field Station, Fresno. May, 1953. 
 
 25. Sainsbury, G. F. Improved fruit cooling methods. Refrigerating Engineering, 59(5) May, 1951. 
 
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26. Sainsbury, G. F. and H. A. Schomer. Influence of carton stacking patterns on pear cooling 
 
 rates. Marketing Research Report No. 171. USDA Agricultural Marketing Service. April, 
 1957. 
 
 27. Schumann, T. E. W. Heat transfer: A liquid flowing through a porous prism. Journal of the 
 
 Franklin Institute. 208 (3) September, 1929. 
 
 28. Stoecker, W. F. Refrigeration and air conditioning. McGraw-Hill. 1958. 
 
 29. Thevenot, R. Precooling. Paper No. 2592 (0.10) Proceedings of Ninth International Re- 
 
 frigeration Congress, International Institute of Refrigeration, Paris. 1955. 
 
 30. Toussaint, W. D., T. T. Hatlow and George Abshier. Hydrocooling peaches in the North 
 
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 31. Wright, R. C, Dean H. Rose and T. M. Whiteman. The commercial storage of fruits, vegetables 
 
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 [65 
 
ACKNOWLEDGMENTS 
 
 This publication presents the engineering conclusions of cooperative studies by 
 the Departments of Agricultural Economics, Agricultural Engineering, Pomology, 
 Vegetable Crops and Viticulture and of the Extension Division of the University of 
 California. Particular appreciation is due to George Giannini, Ralph Parks and 
 Russell Perry of the University of California, to Diven Meredith for his contributions 
 to forced-air cooler design, to Richard Bagdasarian, Harry Carian, Randolph Frink 
 and Glen Moody who demonstrated their confidence in University findings by con- 
 structing the first commercial forced-air coolers, and to Vincent Gessel for test data 
 on his installations of spray humidification and cooling by air jets directed down- 
 ward from the ceiling. 
 
 10m-7,'60(A7954)JF 
 
i' fcmw nmm 
 
 21 ji> *m. 
 
 \M. . . 
 
 This is probably the world's largest plow — it was built about 1910. It plowed 
 an acre in four and one-quarter minutes. A swath 60 feet wide was turned 
 under by 55 bottoms, pulled by three oil-burning tractors. The monster plow 
 was built in sections and assembled for several test runs in the midwest. 
 
 Impractical? ... no! 
 
 This "stunt" yielded new knowledge about hitches . . . knowledge that agri- 
 cultural engineers have used in designing many of today's farm implements. 
 
 For more than 40 years agricultural engineering has offered opportunity to 
 young men of mechanical bent with an interest in agriculture. And as 
 mechanization increases on farms, opportunities in agricultural engineering 
 expand . . . with the GOOD JOBS going to those who are WELL TRAINED. 
 
 Many leaders in the field were trained at the University of California at 
 Davis. The staff at Davis is recognized nationally and internationally for 
 its accomplishments in teaching and in research. The Department of Agri- 
 cultural Engineering is accredited ... a graduate is eligible for examina- 
 tion for a Professional Engineer's license, or he may continue study toward 
 a master's or doctor's degree. The growing College of Letters and Science 
 on the same campus broadens the student's educational and social back- 
 grounds. 
 
 For further information . . . 
 
 about courses and careers in agricultural engineering, write Mr. Roy Bainer, 
 Chairman, Department of Agricultural Engineering, University of California, 
 Davis. 
 
 Or . . . See the College Entrance Advisor in the office of your local Farm 
 Advisor.