Energy and exergy efficiencies of different configurations of the ejector-based CO2 refrigeration systems
Carbon dioxide (CO2) is an appropriate replacement for conventional refrigerants due to its low global warming effects. However, its application within a traditional refrigeration compression cycle leads to low thermodynamic performance due to the large expansion losses in a throttling process. The application of ejectors allows reducing these losses. Many scenarios of ejector-based cycles have been proposed. Among them four different configurations may be distinguished: an expansion work recovery cycle (EERC), a liquid recirculation cycle (LRC), an increasing compressor discharge pressure cycle (CDPC) and a vapor jet refrigeration cycle (VJRC). This study deals with the comparative analysis of these cycles. In order to study the performance of the cycles, the numerical simulations are developed using EES software. Two performance criteria, energy efficiency (COP) and exergy efficiency are evaluated for each cycle. The highest values of these criteria point to the most thermodynamically efficient cycle. The results show that the EERC has the highest COP and exergy efficiency compared to other cycles. For example, the COP of the EERC is 3.618 and the exergy efficiency is 9.68%. The COP (resp. exergy efficiency) is approximately 23.3% (resp. 23.3%), 24.9% (resp. 25.5%) and 5.6 times (resp. 56.2%) higher than the corresponding energy and exergy efficiencies of LRC, CDPC and VJRC. Moreover, in comparison with a basic throttling valve cycle, the COP and exergy efficiency in EERC are higher up to 23% and 24% correspondingly. The detailed exergy analysis of EERC cycle has pinpointed the equipment where the major exergy losses take place. The largest losses occur in the evaporator (about 33% of the total exergy destruction of the cycle) followed by the compressor (25.5%) and the ejector (24.4%).
comparative analysis, COP, ejector, exergy efficiency, refrigeration systems, transcritical CO2 cycles, two-phase
 Gay, N.H., Refrigerating system. Google Patents, 1931.
 Kornhauser, A.A., The use of an ejector as a refrigerant expander. Proceedings of the 1990 USNC/IIR – Purdue Refrigeration Conference, Purdue University, West Lafayette, IN, US, pp. 10–19, 1990.
 Li, D. & Groll, E.A., Transcritical CO2 refrigeration cycle with ejector-expansion device. International Journal Refrigeration, 28(5), pp. 766–773, 2005.https://doi.org/10.1016/j.ijrefrig.2004.10.008
 Fangtian, S. & Yitai, M., Thermodynamic analysis of transcritical CO2 refrigeration cycle with an ejector. Applied Thermal Enginnering, 31(6), pp. 1184–1189, 2011. https://doi.org/10.1016/j.applthermaleng.2010.12.018
 Elbel, S. & Hrnjak, P., Ejector refrigeration: an overview of historical and present developments with an emphasis on air-conditioning applications. International Refrigeration and Air Conditioning Conference, pp. 2350-1–2350-8, 2008.
 Phillips, H.A., Refrigeration system. Google Patents, 1938.
 Lorentzen, G., Throttling, the internal haemorrhage of the refrigeration process. Proceedings of the Institute of Refrigeration, 80, pp. 39–47, 1983.
 Lawrence, N. & Elbel, S., Mathematical modeling and thermodynamic investigation of the use of two-phase ejectors for work recovery and liquid recirculation in refrigeration cycles. International Journal Refrigeration, 58, pp. 41–52, 2015.https://doi.org/10.1016/j.ijrefrig.2015.06.004
 Bergander, M.J, New regenerative cycle for vapor compression refrigeration, Final Scientific Report, DOE Award DE-FG36-04GO14327. Madison, CT, USA, 2005.
 Bergander, M., Refrigeration cycle with two-phase condensing ejector, International Refrigeration and Air Conditioning Conference, Purdue, USA, pp. R008-1-R008-8, 2006.
 Elbel, S.W. & Hrnjak, P.S., Effect of internal heat exchanger on performance of transcritical CO2 systems with ejector. International Refrigeration and Air Conditioning Conference, pp. R166-1–R166-8, 2004.
 Li, D., Investigation of an ejector-expansion device in a transcritical carbon dioxide cycle for military ECU applications [Ph. D. Dissertation]. Purdue University, West Lafayette, IN, 2006.
 Nehdi, E., Kairouani, L. & Bouzaina, M., Performance analysis of the vapour compression cycle using ejector as an expander. International Journal Energy Research, 31(4), pp. 364–375, 2007.https://doi.org/10.1002/er.1260
 Sarkar, J., Optimization of ejector-expansion transcritical CO2 heat pump cycle. Energy,33(9), pp. 1399–1406, 2008.https://doi.org/10.1016/j.energy.2008.04.007
 Ameur, K., Aidoun, Z. & Ouzzane, M., Modeling and numerical approach for the design and operation of two-phase ejectors. Applied Thermal Engineering, 109, pp. 809–818, 2016.https://doi.org/10.1016/j.applthermaleng.2014.11.022
 Smolka, J., Bulinski, Z., Fic, F., Nowak, A.J., Banasiak, K. & Hafner, A., A computational model of a transcritical R744 ejector based on a homogeneous real fluid approach. Applied Mathematical Modelling, 37(3), pp. 1208–1224, 2013.https://doi.org/10.1016/j.apm.2012.03.044
 Khalil, A., Fatouh, M. & Elgendy, E., Ejector design and theoretical study of R134a ejector refrigeration cycle. International Journal Refrigeration, 34(7), pp. 1684–1698, 2011.https://doi.org/10.1016/j.apm.2012.03.044
 Selvaraju, A. & Mani, A., Analysis of an ejector with environment friendly refrigerants. Applied Thermal Engineering, 24(5–6), pp. 827–838, 2004.https://doi.org/10.1016/j.applthermaleng.2003.08.016
 He, Y., Deng, J. & Zhang, Z., Thermodynamic study on a new transcritical CO2 ejector expansion refrigeration system with two-stage evaporation and vapor feedback. HVACR Research, 20(6), pp. 655–664, 2014.https://doi.org/10.1080/10789669.2014.929422