Geometrical Optimization of a Steam Jet-Ejector Using the Computational Fluid Dynamics

Abstract

The vacuum systems play crucial role in various industries including, but not limited to, power generation, refrigeration, desalination, and aerospace engineering. There are different types of vacuum systems. Among them, the ejector or vacuum pump is highly utilized due to its low capital cost and easy maintenance. Generally, the better operation of a vacuum system can dramatically affect the performance of its upper-hand systems, e.g., the general efficiency of a thermal power plant cycle. This can be achieved if such vacuum systems are correctly designed, implemented, and operated. The focus of this work is on an existing steam jet-ejector, whose primary flow is a high pressure superheated steam and the suction flow is a mixture of steam and air. The main goal of this work is to optimize the geometry of the ejector including the nozzle exit position (NXP), the primary nozzle diverging angle, and the secondary throat length, etc. From the computational fluid dynamics perspective, there are some major challenges to simulate this ejector. It requires predicting the correct turbulent fluid flow and heat transfer phenomena with great complexities in treating the mixed subsonic and supersonic flow regimes, very high and very low pressure regions adjacent to each other, and complex mixing two phase flow jets. Indeed, the latter one has been almost neglected in literature. The main concern of this study is to reduce the consumption of motive steam, i.e., to increase the entrainment ratio via modifying the ejector geometry and investigating its performance under different operating conditions that helps to save the water consumption.

A novel 1D model approach to optimize the entrainment ratio of a steam ejector and introducing novel definitions of ejector efficiency

“…Numerous attempts have been made to enhance the ejector efficiency through geometrical optimization. The impact of nozzle exit position (NXP) on the ejector performance has been explored by various researchers [21]- [27]. In addition, certain studies have concentrated on variable area ejectors [3], [5], [28]- [31].…”