liquid recirculation, ejector, R410A
Liquid recirculation is a method of improving evaporator performance by supplying the evaporator with more liquid than is evaporated. The excess liquid, which is generally provided by means of an externally driven, mechanical pump, eliminates dryout and increases overall heat transfer coefficient in the evaporator. Liquid recirculation is common in large-scale industrial refrigeration systems, where the additional cost and complexity of the pump is justified by the large size of the system. However, liquid recirculation has yet to gain widespread application in small-scale systems, such as residential or automotive air conditioning. The use of an ejector to provide the recirculation effect rather than a mechanical pump can help liquid recirculation systems gain consideration for small-scale systems. However, the performance of liquid recirculation cycles with and without ejectors for small-scale systems has yet to be thoroughly investigated. This paper presents the results of an experimental and numerical study of the effect of liquid recirculation on the performance of air condition cycles. The refrigerant R410A, commonly considered for residential systems, is used as the working fluid. A numerical model of a liquid recirculation cycle, capable of accounting for heat transfer and pressure drop effects in the evaporator, was developed and used to predict the effect that recirculation ratio (ratio of total evaporator mass flow rate to mass flow rate of vaporized liquid) has on cycle COP. A liquid recirculation cycle with a mechanical pump was constructed and tested at various evaporator mass flow rates for a fixed cooling capacity in order to see experimentally the effect of recirculation ratio on the COP of the cycle. Cycles in which the work recovered by the expansion process in the ejector is used to provide the pumping effect, instead of the mechanical pump, are then presented and analyzed, and the ability of the ejector to act as a viable replacement for the mechanical pump in liquid recirculation systems is discussed.