Development of a Theoretical Model for Predicting Performance of a Gas Ejector in Different Boundary Conditions and Working Fluids

Abstract

Ejectors are devices designed to suck fluid, steam or gas (primary fluid) from a closed space using a powerful jet of steam (secondary fluid), usually operated under specified boundary conditions using specific working fluids. If ejectors are to be used under new boundary conditions, predicting their performance requires either numerical or experimental studies. This paper presents a simple theoretical model capable of accurately predicting the performance of an ejector, given its geometry and boundary conditions, under different operating conditions. The model can predict the entrainment ratio, critical back pressure, and break-up back pressure using a given simple performance curve. The accuracy of the model is validated using computational fluid dynamics (CFD) simulations. Two ejectors with different geometries, dimensions, and boundary conditions are studied using ANSYS Fluent 19.2, and the results are compared with those from two other studies. The model successfully predicts the performance of all four ejectors across a wide range of operating conditions. Finally, the model is extended to any working fluid and temperature and validated numerically using air as the working fluid instead of water vapor. The results show that the model has an entrainment ratio error of less than 2%. It’s worth noting that this model’s applicability is contingent upon simultaneous changes to both the primary and suction streams by the same factor. Under these conditions, the model aligns closely with CFD-simulations.