Enhanced performance of two-stage ejector based on flow-field coupling effect in MED-TVC systems

Abstract

Steam ejectors serve as prevalent flow devices in multi-effect distillation systems, collecting excess steam and energy to promote sustainable energy utilization. In contrast to traditional ejectors, two-stage ejectors exhibit superior pressurization and vacuum capacities. However, the flow-field coupling effect, which is closely related to the entrainment performance of the two-stage ejector, is rarely explored. In this study, the flow-field coupling effect of the two-stage ejectors is investigated, and two new strategies are proposed to optimize the ejector performance. A concept of two-stage choking and a design principle for a two-stage choking structure is proposed by analyzing the size matching between two stages based on the flow-field coupling effect. Based on the design principle, the optimal structure parameter can be obtained by evaluating the two-stage choking state. Subsequently, a dynamic pressure control criterion based on the flow-field coupling effect is proposed to improve the entrainment performance. The results show that the entrainment performance of the two-stage ejector based on this control criterion is increased by 29.31 % and 4.15 % respectively when the second-stage primary pressure is 300 kPa and 450 kPa. Moreover, simulation results demonstrate that the upper limit of the entrainment performance is determined by the second-stage primary flow pressure.

Keywords

• Flow-field coupling effect
• Two-stage steam ejector
• MED-TVC system
• Computational fluid dynamics