Design and investigation of a two-stage vacuum ejector for MED-TVC system

Abstract

Few studies have been conducted on vacuum ejectors used in the multi-effect distillation with thermal vapor compression systems to maintain the vacuum environment and draw out non-condensable gases. In this study, a two-stage vacuum ejector was proposed and investigated systematically to improve the desalination system performance. Seven different ejector models were presented for comparison, and the most optimized structure was selected using computational fluid dynamics simulation (CFD). A structure with a scale ratio of 0.45:1 between the first and second stage ejectors was proposed to satisfy the matching constraints and obtain optimal performance in the ejector design. Furthermore, a CFD investigation was conducted and the inner flow phenomenon inside the ejector was presented. Under the condition of a primary pressure of 600 kPa and back pressure of 100 kPa, the two-stage ejector could provide superior suction pressure of approximately 5.3 kPa with a more compact structure. In such a vacuum environment, the evaporating temperature can be reduced to approximately 35 °C, and hence, a reduction of both the system energy consumption and scaling phenomenon inside the evaporator can be achieved. An experimental investigation was performed for verification, and the experimental data were in acceptable agreement to the simulation results. It is expected that the conclusion of this study can contribute to two-stage ejector design and optimization.