CFD study on the optimal nozzle exit position in a CO_2 two-phase ejector

摘要

The nozzle exit position (NXP) is a significant parameter for an ejector. In this work, a two dimensional (2D)rnhomogeneous CFD model is developed to simulate the two-phase ejector used in transcritical CO_2rnrefrigeration cycle and NXP is focused on. After model validation, the flow fields in ejectors with differentrnNXPs are simulated and an optimal NXP is obtained. According to the numerical results, with the increase ofrnthe NXP, a higher velocity and lower pressure are achieved for the primary fluid in the suction chamberrnwhich enhances the entrainment of the secondary fluid. Oppositely, the flow area of the primary fluid at thernmixer inlet increases with the NXP which reduces the secondary flow rate. A compromise between these twornfactors leads to the optimal NXP with the highest entrainment ratio under the same operating condition. Thernresults are helpful to the optimal design and control of the ejector.