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.
Highlights
Accepted: 1 April 2021Energy-saving topic gains more attention globally
The one-dimensional model is attractive to predict the global performance of an ejector such as predicting the primary and secondary mass flow rates (m p and ms ) and the ejector outlet pressure (P4 )
× 100 m, in percent where m, is the and m, are the secondary mass flow rate obtained from computational fluid dynamics (CFD), and m, secondary mass flow rates obtained from the standard and modified one-dimensional models, respectively
Summary
This pressure threshold is referred to as critical pressure, P Beyond this pressure, the ejector will enter the sub-critical mode operation within which an increase in P will decrease the secondary mass flow rate but has no Outlet pressure, effect on the primary mass flow rate. An secondary ejector isflow usually required to anymore (only the primary flow is choked) This pressure threshold is referred to as critical operate in the critical mode/condition, and it is called the on-design condition. The calculation time is short, in the order of a few minutes or even seconds, compared to that of CFD which can take hours Due to these advantages, the one-dimensional model is attractive to predict the global performance of an ejector such as predicting the primary and secondary mass flow rates (m p and ms ) and the ejector outlet pressure (P4 ). The predicted secondary mass flow rates, ms , obtained using the one-dimensional analytical model were compared before and after incorporating the above-mentioned pressure variation into the model
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