Design and performance evaluation of refrigeration systems using thermodynamic models

Finite time thermodynamic models which simulate the working of actual vapor compression refrigeration systems are developed. The characteristic performance curves of the refrigeration systems that include simple vapor compression system, mechanical subcooling and two-stage systems are presented in terms of the coefficient of performance (COP) and cooling capacity of the system (Q˙evap). Using the data obtained from the thermodynamic models, performance curves of the systems are obtained. The resulting relationship between the COP and Q&dotbelow;˙ evap is explained in light of various irreversible losses of the system. These losses are due to finite rate of heat transfer in the heat exchangers and the non-isentropic compression and expansion in the compressor(s) and expansion valve(s) of the systems, respectively. The thermodynaic models are also used for predicting an optimum distribution of the total heat exchanger area between the individual heat exchangers of the systems. The results obtained from the thermodynamic models are also compared with an actual performance of a simple vapor-compression system. It is found that the performance characteristics predicted by the thermodynamic model is very close (within +/-2%) than that shown by actual experimental results.