Experimental investigation of the effect of parallel-flow primary nozzle on the performance of the ejector

Geometry of primary nozzle is one of the parameters that affect the performance of a supersonic ejector. In this paper, the effect of using parallel-flow primary nozzle on the performance of a supersonic ejector is experimentally investigated. For this purpose, two primary nozzles, conical and parallel-flow, with the same converging portion and the same ratio of exit surface to throat surface, have been used. The parallel-flow nozzle diverging curve is calculated using the characteristic method. At various positions of the primary nozzle, characteristic curves of the ejectors with conical and parallel-flow nozzles have been compared.The results show that by changing the primary nozzle diverging curve from conical to parallel-flow, at the same position of primary nozzle, the entrainment ratio increases in both critical and subcritical regions. In the critical region, entrainment ratios obtained by the primary nozzle positions 5 mm, 10 mm, and 15 mm are increased by 9.5%, 4.5% and 4.7%, respectively.The optimum position of the primary nozzle changes with changing the primary nozzle diverging curve. At the suitable position of the primary nozzles and without any reduction in critical pressure, the maximum relative increase of entrainment ratio in the critical region is 8%.