Energy and Exergy Analyses of Different Transcritical CO2 Refrigeration Cycles

Öz

Carbon dioxide has received increasing attention owing to its zero ODP and negligible GWP. Furthermore, carbon dioxide also has desirable thermodynamic properties, such as large specific heat, low viscosity, and large heat conductivity. Carbon dioxide CO₂ has low critical pressure and temperature which are 7.36 MPa and 31.1°C, respectively. The low critical temperature causes the heat rejection process to occur above the critical point and heat absorption process to happen below the critical point. However, due to the high throttling loss, the energy efficiency of the basic transcritical CO₂ cycle is lower than that of the conventional low pressure refrigeration cycle.

In the present study three different kinds of transcritical carbon dioxide cycles that are the transcritical cycle with expansion valve (called also the conventional transcritical cycle), the transcritical cycle with expander and the transcritical cycle with ejector are analyzed. The effect of operating parameters on the maximum performance and exergy efficiency of the three cycles is investigated. Results reveal that replacing the expansion valve by an expander or an ejector does not only improve the maximum COP and the exregy efficiency but also reduces the optimal heat rejection pressure.

Anahtar Kelimeler

• Transcritical,CO2 Refrigeration Cycle,Expansion,COP

Kaynakça

1. [1] Bolaji, B.O., Huan, Z., “Ozone depletion and global warming: Case for the use of natural refrigerant – a review”, Renewable and Sustainable Energy Reviews, 2013, 18; 49-54.[2] Lorentzen, G., “The use of natural refrigerant: a complete solution to the CFC/HCFC predicament”, International Journal of Refrigeration, 1994, 18; 190-197.[3] Kim, M.H., Pettersen, J., Bullard, C.W., “Fundamental process and system design issues in CO2 vapor compression systems”, Progress in Energy and Combustion Science, 2004, Vol. 30, No.2, pp. 119-174.[4] Austin, B.T., Sumathy, K., “Transcritical carbon dioxide heat pump systems: A review”, Renewable and Sustainable Energy Reviews, 2011, 15; 4013-4029.[5] Bansal, P. , “A review Status of CO2 as a low temperature refrigerant: Fundamen tals and R&D opportunities”, Applied Thermal Engineering, 2012, 41; 18-29.[6] Ma, Y., Liu, Z., Tian, H.A., “Review of transcritical carbon dioxide heat pump and refrigeration cycles”, Energy, 2013, 55; 156-172.[7] Zhang, J.F., Qin, Y., Wang, C.C, “Review on CO2 heat pump water heater for residential use in Japan”, Renewable and Sustainable Energy Reviews, 2015, 50; 1383-1391.[8] Yang, J.L., Ma, Y.T., Li, M.X, Guan, h. Q. ,“Exergy analysis of transcritical carbon dioxide refrigeration cycle with an expander”, Energy, 2005, 30; 1162-1175.[9] Zhang, Z., Ma, Y. , Li, M. , Li, Z., “Recent advances of energy recovery expanders in the transcritical CO2 refrigeration cycle”, HVAC&R Research, 2013, 19; 376-84.[10] Shariatzadeh, O. J., Abolhassani, S., Rahmani, M., Nejad, M. Z.,“Comparison of transcritical CO2 refrigeration cycle with expander and throttling valve including/excluding internal heat exchanger: Exergy and energy points of view”, Applied Thermal Engineering, 2016, 93; 779–787. [11] Li, D., Groll, E. A., “Transcritical CO2 refrigeration cycle with ejector-expansion device”, International Journal of Refrigeration, 2005, 28; 766–773. [12] Deng, J. Q., Jiang, P.Q., Lu, T,. Lu, W.,“Particular characteristics of transcritical CO2 refrigeration cycle with an ejector”, Applied Thermal Engineering, 2007, 27; 381-388.[13] Elbel, S.,“Historical and present developments of ejector refrigeration systems with emphasis on transcritical carbon dioxide air-conditioning applications”, International Journal of Refrigeration, 2001, 34; 1545-1561.[14] Sumeru, K., Nasution, H., Ani, F. N., “A review on two-phase ejector as an expansion device in vapor compression refrigeration cycle”, Renewable and Sustainable Energy Reviews, 2012, 16; 4927-4937.[15] Sarkar, J., “Ejector enhanced vapor compression refrigeration and heat pump systems-A review”, Renewable and Sustainable Energy Reviews, 2012, 16; 6647-6659.[16] Xiangjie, X., Omer, S., Worall, M , Riffat, S., “Recent developments in ejector refrigeration technologies”, Renewable and Sustainable Energy Reviews, 2013, 19; 629-651.[17] Besagni, G., Mereu, R., Inzoli, F.,“Ejector refrigeration: A comprehensive review”, Renewable and Sustainable Energy Reviews, 2016, 53; 373-40. [18] Robinson, D. M., Groll E. A., “Efficiencies of transcritical CO2 cycles with and without an expansion turbine”, International Journal of Refrigeration, 1998, 21; 577-589.