A cylindrical mixing chamber ejector analysis model to predict the optimal nozzle exit position

Abstract

By introducing the theory of an annular mixing-layer, a new model to predict the optimal nozzle exit position (ONXP) is established and verified for ejectors with a cylindrical mixing chamber. Furthermore, the optimal entrainment ratio, area ratio and dimensionless optimal nozzle exit position (DONXP) of ejectors under different working conditions are analysed by this model. Compared with the experimental data of R141b, R245fa, R134a and R600a ejectors, the entrainment ratio error is within ±10.70%, and the critical backpressure is within ±7%. The introduced theory can accurately predict the ONXP of the R245fa ejectors (within an error of ±15.85%) and the DONXP distribution of the R141b ejectors, and can properly predict the performance of the R134a ejectors under the same dimensions. With an increasing compression ratio, the DONXP decreases, and the rate of decrease is faster when the compression ratio exceeds the value of the inflection point. The compression ratio corresponding to the inflection point is higher for an ejector with a large expansion ratio than that with a small expansion ratio. In addition, the DONXP decreases when the expansion ratio increasing under a small compression ratio while increases when the expansion ratio increasing under a large compression ratio.