Exergy analysis of a two-stage refrigeration cycle using two natural substitutes of HCFC22 Ahmed Ouadha*, Mohammed En-nacer, Lahouari Adjlout and Omar Imine Department of Marine Engineering, Faculty of Mechanic, University of Science and Technology at Oran, P.O. Box 1505 Oran El-M'naouar, 31000 Oran, Algeria E-mail: ouadha@univ-usto.dz E-mail: Mohammed.Ennacer@pwc.ca E-mail: adjlout@univ-usto.dz E-mail: imineo@univ-usto.dz *Corresponding author Abstract: The aim of the present paper is to carry out a detailed exergy analysis of a two-stage vapour compression cycle by calculating its components exergetic losses. The exergy equations have been developed using refrigerant thermodynamic properties computed by means of a simple model of local equations of states. The results of the exergy analysis of a two-stage refrigeration system operating between a constant evaporating temperature of 30  C and condensation temperatures of 30, 40, 50 and 60  C with two natural substitutes of HCFC22, namely, propane (R290) and ammonia (R717) as working fluids, are presented. It is found that the most significant losses occur in the compressors, expansion valves and condenser. Furthermore, it is shown that the optimum inter-stage pressure for a two-stage refrigeration system is very close to the saturation pressure corresponding to the arithmetical mean of the refrigerant condensation and evaporation temperatures. Keywords: ammonia; equations of state; exergy analysis; inter-stage pressure; natural refrigerants; propane; two-stage refrigerating cycle. Reference to this paper should be made as follows: Ouadha, A., En-nacer, M., Adjlout, L. and Imine, O. (2005) `Exergy analysis of a two-stage refrigeration cycle using two natural substitutes of HCFC22', Int. J. Exergy, Vol. 2, No. 1, pp.14±30. Biographical notes: Ahmed Ouadha is Senior Lecturer at the Department of Marine Engineering, in Oran, Algeria. He graduated from the University of Science and Technology, in Oran, Algeria in 1995 with a BEng degree and in 1999 with a Master degree. Currently, he is Vice Head of the Department of Marine Engineering. Mohammed En-nacer is currently working at Pratt & Whitney Canada, in Longueil, Quebec. He graduated from the University of Science and Technology in Oran, Algeria in 1986 with a BEng degree and from the Odessa Institute of Marine Engineering, in Odessa, Ukraine in 1991 with a PhD degree. Lahouari Adjlout is a Professor at the Department of Marine Engineering, in Oran, Algeria. In 1990 he graduated from Liverpool University UK, with a PhD degree. He has refereed many journal and conference papers. Int. J. Exergy, Vol. 2, No. 1, 2005 14 Copyright # 2005 Inderscience Enterprises Ltd.