Particular characteristics of transcritical CO2 refrigeration cycle with an ejector |
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| Affiliation: | 1. Department of Process Equipment and Control Engineering, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China;2. Key Laboratory for Thermal Science and Power Engineering, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China;1. Jaume I University, Dep. of Mechanical Engineering and Construction, Campus de Riu Sec s/n E-12071, Castellón, Spain;2. Polytechnic University of Valencia, Department of Applied Thermodynamics, Camino de Vera, 14, E-46022, Valencia, Spain;1. Escuela Superior de Ingeniería, Departamento de Máquinas y Motores Térmicos, Universidad de Cádiz, Avda. de la Universidad de Cádiz, 11519 Puerto Real, Spain;2. Escuela Técnica Superior de Ingeniería, Grupo de Termotecnia, Universidad de Sevilla, Camino de los Descubrimientos, s/n, 41092 Sevilla, Spain;1. Tianjin Key Laboratory of Refrigeration Technology, Tianjin University of Commerce, Tianjin, 300134, China;2. Future Energy Center, School of Sustainable Development of Society and Technology, Mälardalen University, Västerås, SE-72123, Sweden;3. Department of Human and Engineered Environmental Studies, The University of Tokyo, Chiba, 277-8563, Japan;4. Key Laboratory of Efficient Utilization of Low and Medium Grade Energy, MOE, Tianjin University, Tianjin, 300072, China;1. Institute of Thermal Technology (ITT), Silesian University of Technology (SUT), Gliwice 44-100, Poland;2. SINTEF Energy Research, Trondheim 7465, Norway;3. Norwegian University of Science and Technology, Trondheim 7465, Norway |
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| Abstract: | The present study describes a theoretical analysis of a transcritical CO2 ejector expansion refrigeration cycle (EERC) which uses an ejector as the main expansion device instead of an expansion valve. The system performance is strongly coupled to the ejector entrainment ratio which must produce the proper CO2 quality at the ejector exit. If the exit quality is not correct, either the liquid will enter the compressor or the evaporator will be filled with vapor. Thus, the ejector entrainment ratio significantly influences the refrigeration effect with an optimum ratio giving the ideal system performance. For the working conditions studied in this paper, the ejector expansion system maximum cooling COP is up to 18.6% better than the internal heat exchanger cycle (IHEC) cooling COP and 22.0% better than the conventional vapor compression refrigeration cycle (VCRC) cooling COP. At the conditions for the maximum cooling COP, the ejector expansion cycle refrigeration output is 8.2% better than the internal heat exchanger cycle refrigeration output and 11.5% better than the conventional cycle refrigeration output. An exergy analysis showed that the ejector expansion cycle greatly reduces the throttling losses. The analysis was also used to study the variations of the ejector expansion cycle cooling COP for various heat rejection pressures, refrigerant temperatures at the gas cooler exit, nozzle efficiencies and diffuser efficiencies. |
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