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The aim of this paper is to develop a thermodynamic model for a water-to-water heat pump using propane as refrigerant. This model is based on the thermodynamic principals and heat transfer fundamental laws. The performances of the heat pump have been looked at as function of the water temperatures at the entry of the evaporator and the condenser. The results show that the cooling and heating COP of the system increase slightly when increasing the evaporator water inlet temperature and decrease when increasing the condenser inlet water temperature. However, in cooling mode, the exergy efficiency decreases when increasing the inlet water temperatures to evaporator and condenser, while, in heating mode, it increases. Furthermore, it is shown that the exergy efficiency in the cooling mode does not produce the same behaviour as that of the COP.

Free convection in an inclined square cavity with partial partitions has been investigated, by numerically solving the partial differential balance equations of mass, momentum, and energy. The analysed configuration has three undulations and three partitions. Investigations have been performed for different inclination angles, partition lengths and Rayleigh numbers, while keeping the Prandtl number constant. The results show that the hot wall geometry with partitions affects the heat transfer rate in the cavity. It has been found in the present numerical study that the mean Nusselt number decreases notably compared with the heat transfer in the square undulated cavity without partitions.

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.