Design and performance evaluation of reciprocating refrigeration systems

The characteristic performance curves of vapor-compression refrigeration systems are defined as a plot between the inverse coefficient of performance (1/COP) and inverse cooling capacity (1/Q_evap) of the system. Using the actual data of a simple vapor-compression system, performance curves of the system are obtained. The curves were found to be linear and this linear relation between 1/COP and 1/Q_evap is explained in the light of various losses of the system, resulting from the irreversibilities losses due to finite rate of heat transfer in the heat exchangers and non-isentropic compression and expansion in the compressor and expansion valve of the system, respectively. A finite-time thermodynamic model which simulates the working of an actual vapor-compression system is also developed. The model is used to study the performance of a variable-speed refrigeration system in which the evaporator capacity is varied by changing the mass-flow rate of the refrigerant, while keeping the inlet chilled-water temperature as constant. The model is also used for predicting an optimum distribution of heat-exchanger areas between the evaporator and condenser for a given total heat exchanger area. In addition, the effect of subcooling and super-heating on the system performance is also investigated.