Investigation of the vapor-liquid ejector using eco-friendly working fluid with attentions on pressure lift and internal energy conversion

Abstract

Vapor-liquid ejector is able to lift the discharge pressure higher than the primary flow pressure without consuming any external mechanical energy. In this paper, the actual process and thermodynamically ideal process are established, respectively, to reveal the evolution of the pressure lifting ability degradation. Moreover, the internal energy conversions in each component are explored by splitting exergy into temperature-based exergy, pressure-based exergy and kinetic exergy. Seven eco-friendly working fluids are firstly compared at different operating conditions. It is found that there exists an optimum value for the inlet vapor temperature to maximize the actual pressure lift and a different value for the minimum pressure ratio lift. From the exergy analysis, it is obtained that the highest irreversibility occurs in the mixing chamber for all candidates, followed by the shock, vapor nozzle and diffuser. Meanwhile, the pressure lift destructions inside these components have the same order of magnitude. The exemplary study on cyclohexane which has the highest actual pressure lift and the lowest pressure lift ratio indicates that the major energy conversions in the vapor nozzle and the diffuser are almost constant, while they vary considerably in the mixing chamber and shock. For the vapor-liquid ejector working at the studied conditions, only 5.33% – 21.91% of the temperature-based exergy is usefully converted to pressure-based exergy. This study is helpful to identify the key parameters for improving the performance and facilitating the design of the vapor-liquid ejector.