A visual mass transfer study in the ejector considering phase change for multi-effect distillation with thermal vapour compression (MED-TVC) desalination system

Abstract

The multi-effect distillation with thermal vapour compression (TVC) seawater desalination system provides an excellent energy-saving scheme by escalating the low-level energy. The internal mass and heat transfer in ejectors is an important element to improve efficiency. In this study, a visual mass transfer simulation model considering real thermodynamic properties is used to observe the inner-mixing process. The assessment is from the perspective of visible mixing layer growth and the effect on entrainment ratio. As shown in the mass percentage distribution graph, there is an inescapable phase change on mixing layer boundary, where the wetness of wet steam can reach to 16.0%. Meanwhile, the mixing layer length predicted by dry model is 25.1% higher than wet model. The condensation weakens the mixing process and leads to shorter length. Under subcritical mode, the cross-sectional area of the entrained flow is deducted and the mixing layer cannot develop completely. The critical pressure range predicted without condensation is 18.5% lower, which causes a misjudgment in entrainment ratio because overvaluing the influence of outlet pressure on entrained flow. Thus, mass transfer during development of the two-phase mixing layer has great impact for MED-TVC system.