Determination of system that provide optimum operating conditions in cooling cycles working under low temperature-high pressure

In refrigeration cycles, but single-stage vapor systems have good performance at -20oC. Coefficient of performance and second law efficiency of system decreases rapidly at low evaporation temperature and highest condenser temprature. Especially between -30 and -60oC evaporation tempratures. Single-stage vapor compression systems will be unsufficient. So for such that low evaporation temperature it will be necessary to use multi stage refrigeration systems. As it is known the compressor exit temperature above 100oC is undesirable situation. If the compressor exit temperature is too high; lubricating of oil burning and to increase the thermal stress in mechanical components of the compressor, it also causes the spoiled of the fluid properties. Therefore, using of a multi stage refrigeration cycles operating stability of the system, the pressure ratios, the volumetric efficiency, the exit temperatures of the compressor become suitable for operating conditions. In this study some refrigerants are discussed in terms of compressor exit temperature, volumetric efficiency, coefficient of cooling performance, second law efficiency and environmental impact. Based on the design conditions and within the refrigerant, first and second law of thermodynamics has been applied to the system. Then coefficient of performans, the second law efficiency, the compressor exit temperature, volumetric efficiency, second law efficiency and power consumption has been identified. Required comparison made between single-stage and multi stage refrigeration cycles. Also suitable alternative fluids, have been determined by comparing their performances with each other. Key Words: First law analysis, Second law analysis, Second law efficiency, Irreversibility, Multi stage refrigeration.