Exery Analysis of Vapour Compression Refrigeration System

Thermodynamic processes in refrigeration systems release large amount of heat to the environment. Heat transfer between the system and the surroundings environment takes place at a finite temperature difference, which is a major source of irreversibility for the cycle. Irreversibility causes the system performance to degrade. The Losses in the cycle need to evaluate considering individual thermodynamic process that make up the cycle. First law analysis is still the most commonly used method in the analysis of thermal systems. The first law is only concerned with the conservation of energy, and it gives no information on how, where, and how much the system performance is degraded. Exergy analysis is powerful tool in design, optimization and performance evaluation of energy systems. The principle and methodologies of exergy analysis are well established. An exergy analysis is usually aimed to determine the maximum performance of the system and identify the sites of energy destruction. Exergy analysis of complex systems can be performed by analyzing the components of the systems separately. Identifying the main sites of exergy destruction shows the direction for potential improvements.

In the present work, a computational model based on the exergy analysis is presented for the investigation of exergy losses, the second law efficiency and the second law efficiency and the coefficient of performance (COP) of a vapour compression refrigeration cycle. It is found that the evaporating and condensing temperatures having strong effects on the exergy losses in the evaporator and condenser, on the second law efficiency and COP of the cycle but little effects on the exergy losses in the compressor and the expansion valve.It is also found that degree of sub cooling and Degree of super heating have strong effects on exergy losses, second law efficiency and COP of the cycle.