Effects of operating conditions and cooling loads on two-stage ejector performances

This paper presents a two-stage ejector-based multi-evaporator refrigeration system using R134a as the refrigerant and the effects of variable operating conditions such as back pressure and evaporating temperature and cooling loads on each stage are investigated by using CFD simulations. The simulation results indicate that: (1) three operational modes: critical mode, subcritical mode and back flow mode are available for each stage when two stages combine with each other, but the range of pressure lifting ratio generating subcritical and back flow modes is not the same with each other; (2) the entrainment ratio of the first-stage is mainly influenced by the variation of the evaporating temperature of refrigerating and freezing chambers, while the entrainment ratio of the second-stage of is more influenced by the change of the evaporating temperature of the air-conditioning chamber; (3) the effect of the mass flow rate of the first-stage primary flow on the entrainment ratio of the first stage is more significant, while the effect of the mass flow rate of the second-stage primary flow on the entrainment ratio of the second-stage is more evident.