An Improved Preliminary Design Method for Ejectors Available to Purchase

A preliminary design method is presented for evaluating ejector geometries and predicting variations in aerodynamic performance due to changes in configurations and flow conditions. The method is based on steady, quasi-one dimensional conservation equations for mass, momentum, and energy with corrections to account for losses due to the primary nozzle exit, inlet to the mixing tube, frictional shear forces on the mixing tube walls, and outlet non-uniformity in the velocity profile from the mixing tube. The entrainment ratio, which is defined as the induced secondary flow (cold) rate divided by the primary (hot) flow rate, is first compared to ideal performance, which is obtained without losses. Next the results of the model are compared to experimental data, obtained from several ejector configurations and flow conditions, and agreement within three percent is shown. The usefulness of this method for preliminary design trade-off studies is demonstrated by comparison with a one-fifth scale cold-flow facility. Finally, the factors that contribute to performance degradation are identified and quantified. It is shown that the primary factor limiting performance is the nonuniformity in the exit momentum flux.