THERMODYNAMICS OF A VAPOR-COMPRESSION REFRIGERATION CYCLE WITH MECHANICAL SUBCOOLING

Refrigeration and air-conditioning systems, when operating under large temperature differences between the condenser and evaporator, consume significant amounts of energy. A vapor-compression refrigeration cycl e with a mechanical subcooling loop to increase system performance and reduce energy consumption is investigated by using both the first and second laws of thermodynamics. Although the first-law (energy-balance ) approach to system analysis shows improvement in the system coeffici ent of performance (COP) with an increase in the temperature differenc e between the condenser and evaporator, it fails to locate sources of losses. Identifying and quantifying these sources can be a useful desi gn tool, especially in developing or investigating new, more complex r efrigeration cycles. A second-law analysis (in terms of irreversibilit y) has been carried out for both the simple and the vapor-compression refrigeration cycle with a mechanical subcooling loop. It is found tha t the performance of the system can be significantly improved by reduc ing the irreversibilities due to the expansion process. The low-temper ature refrigeration system, when operating at the optimum subcooler sa turation temperature, may have the following features: (i) 85% reducti on in power input; (ii) 65% percent lower irreversibility rate; (iii) 20% reduction in the total refrigerant flow-rate.