Optimization of liquid jet ejector geometry and its impact on flow fields

Abstract

Liquid jet liquid (LJL) ejectors have wide industrial application and the improvement in their efficiency is sought to increase the viability of their use. This study performs the optimization of the entire geometry of an LJL ejector with multiple parameters to maximize energy efficiency. The approach with multiple parameters allows to identify key geometrical features and interdependent parameters, like nozzle position and mixing chamber length, with respect to performance. Computational fluid dynamics (CFD) and optimization simulations were performed to optimize the parameters of Bézier curves that characterize the device's geometry. The optimization results showed that the ejector efficiency curve is sensitive to the nozzle and the suction chamber geometries. Simulations that consider the nozzle diameter and the nozzle position along ejector axis (NXP) as parameters of the optimization process resulted in higher efficiency values than those that kept these parameters fixed. The optimization of the diffuser curve, including the diameter of the diffuser and the length of the mixing chamber, also contributed to increase the efficiency of the device. It was observed that the increase in the length of the mixing chamber and the spacing of the nozzle imply similar effects in the efficiency and in the pressure, velocity and energy dissipation rate profiles confirming some correlation of these parameters on the performance. One may observe the effect of geometry modification through optimization on the flow profiles in key sections of the ejector: the flow profiles in the optimized geometry tend to be more homogenous, hence less dissipative, and it is also confirmed by local energy dissipation rate.