Conical-cylindrical mixer ejector design model for predicting optimal nozzle exit position

Abstract

Precisely predicting the optimal nozzle exit position (ONXP) of a vapor ejector is highly desirable for optimizing the performance of an ejector refrigeration system. Based on the theory of the shear mixing-layer and the adiabatic frictional flow equations in a conical-cylindrical mixer, a new design model to predict the ONXP for a conical-cylindrical mixer ejector (CCME) is proposed and verified. Furthermore, the evolution laws of the dimensionless optimal nozzle exit position (DONXP) and critical entrainment ratio (Ercri) for different design conditions (i.e., the expansion ratio E and critical compression ratio Ccri) are investigated. Based on a comparison of the experimental values and the predicted data, the relative deviations of the DONXP, Ercri, and Ccri are within ±14.81%, ±16.99%, and ±10.76%, respectively. The critical entrainment ratio decreases as the critical compression ratio increases but increases as the expansion ratio increases, and both with an increasingly slower rate of change. The variations in the DONXP with the varying critical compression ratio and expansion ratio are similar to that in Ercri. Results further indicate that a well-constructed CCME allows the critical entrainment ratio to attain the design values by adjusting its nozzle exit position to the ONXP when the expansion ratio is changed.