Thermal Stabilization of Variable Loading, Multi-Evaporator Refrigeration Loops via Liquid Recirculation

Refrigeration systems with parallel evaporators are prone to systemic instabilities and thermal excursions, particularly under variable loading conditions. Conventional vapor compression systems require evaporators to discharge at very high vapor qualities to prevent liquid ingress to the compressor. This requires active control algorithms to regulate the flow to individual evaporators. This paper introduces a novel liquid recirculation loop that minimizes the effects of flow maldistribution and prevents dryout using passive components. The loop utilizes a refrigerant phase separator, in conjunction with passive inlet restrictions, to mitigate flow maldistribution and support larger evaporator mass flow rates corresponding to low-to-moderate exit qualities. With greater margin in exit quality before dryout occurs, thermal excursions at the evaporator outlets are readily avoided. Analysis of the flow redistribution for multi-evaporator systems subject to binary (on/off) loading conditions demonstrates the effectiveness of this system for static excursions. Experiments for a two-evaporator system with R134a as the working fluid demonstrate stable heat sink temperatures over a range of loading scenarios.