Configuration dependence and optimization of the entrainment performance for gas-gas and gas-liquid ejectors

This paper describes a numerical study of entrainment behavior and its configuration dependence for gas-gas and gas-liquid ejectors. A computational fluid dynamics (CFD) model is developed and experimental validation is undertaken over a wide range of operation conditions for ejector with different configurations. The predicted values by CFD simulation prove to be in good agreement with the experimental data. The investigation results indicate that pseudo-shock length has a dominant effect on entrainment performance and geometry optimization. Significant difference is noted in pseudo-shock length for gas-gas and gas-liquid ejectors, and this is mainly because the viscosity similarity markedly differs within the range of 0.01-1.0, depending on the primary and secondary fluids of usage. Therefore the optimum mixing tube length to diameter ratio is about 1-2 for general gas liquid ejectors while 5-7 for gas gas ejectors. As an exception to the general gas liquid ejectors, the optimum LID ratio in He-LH2 ejector is about 4, lying between that of the gas-gas ejector and gas-liquid ejector but still consistent with the pseudo-shock length. If the maximum allowable length of ejector mixing tube is less than the optimum value, placing the primary nozzle exit upstream of the mixing tube can greatly improve the entrainment performance. (c) 2011 Elsevier Ltd. All rights reserved.