variable geometry ejector, refrigeration
In refrigeration systems ejectors are used to increase the pressure of an entrained or secondary stream using the energy of a high pressure and high temperature primary stream. The lack of flexibility of ejectors contributes to their modest deployment in the refrigeration market and more widely in industry. In general, for gas-gas ejectors, the highest ejector performance is obtained at the critical pressure ratio. For lower pressure ratios the entrainment ratio remains constant, and for higher pressure ratios it drops rapidly to zero. This behavior makes the load control hard to handle. In order to increase the flexibility of ejectors and also the average entrainment ratio, variable geometry solutions exist. Those solutions allow the variation of the primary stream nozzle throat section or the nozzle axial position. With those solutions the secondary mass flow remains limited to a maximum fixed by the mixing chamber diameter. In this paper, a new variable geometry ejector concept is explored that allows increasing the secondary stream flow rate as the discharge pressure decreases. The ejector performance is estimated by computational fluid mechanics. This is compared to a geometry from literature. The case study is an R134a ejector driven refrigeration cycle using waste heat. The interest of the new variable geometry ejector on the seasonal Energy Efficiency Ratio is analyzed.