Numerical and One-Dimensional Studies of Supersonic Ejectors for Refrigeration Application: The Significance of Wall Pressure Variation in the Converging Mixing Section

Abstract

This paper studies the pressure variation that exists on the converging mixing section wall of a supersonic ejector for refrigeration application. The objective is to show that the ejector one-dimensional model can be improved by considering this wall’s pressure variation which is typically assumed constant. Computational Fluid Dynamics (CFD) simulations were used to obtain the pressure variation on the aforementioned wall. Four different ejectors were simulated. An ejector was obtained from a published experimental work and used to validate the CFD simulations. The other three ejectors were a modification of the first ejector and used for the parametric study. The secondary mass flow rate, m˙s, was the main parameter to compare. The CFD validation results indicate that the transition SST turbulence model is better than the k-omega SST model in predicting the m˙s. The results of the ejector one-dimensional model were compared before and after incorporating the wall pressure variation. The comparison shows that the effect of the pressure variation is significant at certain operating conditions. Even around 2% change in the average pressure can give around 32% difference in the prediction of m˙s. For the least sensitive case, around 2% change in the average pressure can give around 7% difference in the prediction.

Keywords

• ejector refrigeration
• one-dimensional model
• computational fluid dynamics (CFD)
• transition SST turbulence model
• converging mixing section
• wall pressure variation