Numerical analysis of mixing guide vane effects on performance of the supersonic ejector-diffuser system

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.

Supersonic ejector-diffuser system makes use of primary stream with high speed and high pressure to propel the secondary stream through pure shear action. It has many advantages over other fluid machinery such as no moving parts and no direct mechanical energy input. That's why ejector-diffuser system has been used in many engineering industrial applications such as air propulsion and ejector refrigeration. The ejector-diffuser system also can be considered as the most important device of the solar seawater desalination. Generally speaking, the flow field in the ejector-diffuser system is very difficult to be predicted due to the complicated turbulent mixing, compressibility effects and even flow unsteadiness. Many works have been done in the past years to achieve a higher efficiency and improve the performance of the ejector system, but not yet satisfactory, compared with that of other fluid machinery. Considering the complexity and difficulty on the researching, how to enhance the performance of ejector-diffuser system effectively became a significant task. In the present study, several mixing guide vanes were installed at the inlet of the secondary stream of the ejector-diffuser system for the purpose of the performance improvement. The present study aim is to lessen the negative effects on the secondary stream and get a higher level in both pressure recovery and entrainment ratio. A CFD method based on Fluent has been applied to simulate the supersonic flows and shock waves inside the ejector. Numerical analysis results of the mixing guide vane effects were validated with experimental data in the previous work. The comparison of ejector performance with and without the mixing guide vane was obtained and optimal position of mixing guide vane is discussed to increase the performance. The operation characteristics of the ejector system with different numbers of inlet guide vanes are analyzed in detail. The ejector-diffuser system performance is discussed in terms of the entrainment ratio, ejector efficiency, pressure recovery as well as total pressure loss.