Experimental Study of Single Screw Expander Used in Low-medium Temperature Geothermal Power System Energy Procedia 61 ( 2014 ) 854 – 857 Available online at www.sciencedirect.com ScienceDirect 1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of ICAE2014 doi: 10.1016/j.egypro.2014.11.981 The 6th International Conference on Applied Energy – ICAE2014 Experimental study of single screw expander used in low- medium temperature geothermal power system Jingfu Wanga,b,*, Xinxin Zhanga,b, Yongzhi Zhanga,b, Yong Zhanga,b, Wei Wanga,b aKey Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry of Education, College of Environmental and Energy Engineering,Beijing University of Technology, Beijing 100124, PR China bKey Laboratory of Heat Transfer and Energy Conversion, Beijing Municipality, College of Environmental and Energy Engineering,Beijing University of Technology, Beijing 100124, PR China Abstract Research and development of renewable energy is one solution to energy crisis and its related environmental problem. Among all kinds of renewable energy, geothermal energy has good development feasibility due to its low investment and operation costs, independence to weather and climate change, and stable power generation. In China, high- temperature geothermal resource is rare; however, low-medium temperature geothermal resource is widely distributed. Therefore, small and medium sized geothermal power system based on low-medium temperature organic Rankine cycle(ORC) is a good choice for geothermal exploitation. Expander is the key device in such system. Single screw expander has proper size and good output performance. Therefore, in order to test the application of single screw expander in geothermal exploitation, compressed air was used as working fluid to conduct experimental study at different temperature. The results show that at the same rotational speed, the single screw expander at a higher air temperature has a bigger output power, a smaller gas consumption rate, a bigger expansion ratio, a bigger temperature drop, a higher thermal efficiency, and a smaller irreversible loss. Moreover, if a lubricant circle is added in the experimental system, the single screw expander with lubricant at a lower air temperature will have the same performance as the expander without lubricant at a higher air temperature. Therefore, the performance of single screw expander can be improved by adding a lubricant circle and raising compressed air temperature. © 2014 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICAE Keywords: Single screw expander; Geothermal power generation; Organic Rankine cycle; Compressed air; Lubricant circle * Corresponding author. Tel.: +86-10-6739-1612 ; fax: +86-10-6739-2774 . E-mail address: jfwang@bjut.edu.cn . © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of ICAE2014 http://crossmark.crossref.org/dialog/?doi=10.1016/j.egypro.2014.11.981&domain=pdf Jingfu Wang et al. / Energy Procedia 61 ( 2014 ) 854 – 857 855 1. Introduction With industrial development in recent years, a lot of problems caused by energy consumption are become more and more serious. Therefore, development and utilization of new energy and renewable energy is great significance. Among all kinds of renewable energy, geothermal energy has an average capacity factor of 70% and capacity factors up to 90% are considered possible[1]. Moreover, geothermal energy has good development feasibility due to its low investment and operation costs, independence to weather and climate change, and stable power generation. In China, high-temperature geothermal resource is rare; however, low-medium temperature geothermal resource is widely distributed. Therefore, small and medium sized geothermal power system based on low-medium temperature organic Rankine cycle(ORC) is a good choice for geothermal exploitation. Expander is the key device in such system. The rapid development of compressor technology makes a possible breakthrough in the manufacture of small size expander. Single screw technology has many advantages such as a good force balance, a long life, a high pressure ratio, a high volumetric efficiency, a high efficiency at part load, a simple structure, a low noise, and so on. Therefore, single screw expander becomes a promising technology in small size expander. In this paper in order to test the application of single screw expander in geothermal exploitation, compressed air was used as working fluid to conduct experimental study at different temperature. 2. Establishment of Experimental System The single screw expander used in experimental system was developed and manufactured by the lab where the authors work. Some previous research work has been conducted on single screw expander by the members in author’s research team[2-4]. In this study, expander inlet flow is 1.1 Nm3/min and power output is 10kW. Fig 1 depicts the single screw expander experimental system with heated compressed air as the working fluid. The main device consists of a single screw expander, a compressed air heating system, a lubricant system, a data acquisition system, and a dynamometer machine. Fig. 1. single screw expander experimental system 3. Experimental Result and Discussion Due to the length limitation of paper, only the performances of single screw expander with and without lubricant when inlet temperature is 80 are reported. Fig 2 to Fig 7 depict the relation between the 856 Jingfu Wang et al. / Energy Procedia 61 ( 2014 ) 854 – 857 performances of single screw expander and its rotational speed. Theses performances includes power, gas consumption rate, expansion ratio, temperature drop, thermal efficiency, and irreversible loss. Fig. 2. relation between power and rotational speed Fig. 3. relation between gas consumption rate and rotational speed Fig. 4. relation between expansion ratio and rotational speed Fig. 5. relation between temperature drop and rotational speed Fig. 6. relation between thermal efficiency and rotational speed Fig. 7. relation between irreversible loss and rotational speed Jingfu Wang et al. / Energy Procedia 61 ( 2014 ) 854 – 857 857 From the above figures, it can be seen that because of the sealing and lubricating of lubricant, At the same rotational speed, the single screw expander with lubricant has a bigger power output. At the same rotational speed, the single screw expander with lubricant has a smaller gas consumption rate. The expansion ratio of expander decreases with the increase of rotational speed. The expander with lubricant has a bigger expansion ratio at the same rotational speed. At the same rotational speed, the expander with lubricant has a bigger temperature drop. At the same rotational speed, the expander with lubricant has a bigger thermal efficiency, but the efficiency increase is not very significant. At the same rotational speed, the expander with lubricant has a smaller irreversible loss. 4. Conclusion In order to test the application of single screw expander in geothermal exploitation, compressed air was used as working fluid to conduct experimental study at different temperature. The results show that at the same rotational speed, the single screw expander at a higher air temperature has a bigger output power, a smaller gas consumption rate, a bigger expansion ratio, a bigger temperature drop, a higher thermal efficiency, and a smaller irreversible loss. Moreover, if a lubricant circle is added in the experimental system, the single screw expander with lubricant at a lower air temperature will have the same performance as the expander without lubricant at a higher air temperature. Therefore, the performance of single screw expander can be improved by adding a lubricant circle and raising compressed air temperature. Acknowledgements This work was supported by the National Key Basic Research Program of China (973 Program, No.2013CB228306). The authors gratefully acknowledge them for financial support of this work. References [1] Lenzen M. Current State of Development of Electricity Generating Technologies: A Literature Review. Energies 2010,3: 471-472. [2] Lu YW, He W, Wu YT, Ji WN, Ma CF, Guo H. Performance study on compressed air refrigeration system based on single screw expander. Energy 2013,55:762-768. [3] Wang W, Wu YT, Ma CF, Xia GD, Wang JF. Experimental study on the performance of single screw expanders by gap adjustment. Energy 2013,62:379-384. Biography Prof. Jingfu Wang got this doctor degree from Tohoku University, Japan. Now he works in Beijing University of Technology and his research interest is utilization technology of renewable energy and basic theory of combustion and pollution control mechanism.