Numerical study for the influences of primary nozzle on steam ejector performance

Abstract The influences of primary nozzle on the performance of steam ejectors were investigated numerically, and the effects of the primary nozzle outlet diameter as well as the divergent section length under different entrained stream pressures on the steam ejector were analyzed and discussed. The results revealed that the entrainment ratio of steam ejector initially increases sharply with the primary nozzle outlet diameter and then decreases after the outlet diameter exceeds a certain value. Therefore, there is an optimum range for the primary nozzle outlet diameter at which the ejector obtains its best performance. It was also disclosed that the divergent section length has only a comparatively weak effect on the ejector performance. The entrainment ratio increases slowly first with the divergent section length to its maximum and then decreases gradually due to the increase of flow frictional drag. Hence there also exists an optimum value for the divergent section length at which the steam ejector performs best. However, it should be stressed that this largest entrainment ratio corresponding this optimum divergent section length differs little from the non-optimum value which means we can design the divergent section with a wider range of the length.