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

• Published in: Case studies in thermal engineering 2024-08, Vol.60, p.104757, Article 104757
• Main Authors: Han, Qingyang, Sun, Wenxu, Yao, Ailing, Zhang, Hailun, Yang, Zhenfa, Jia, Lei, Xue, Haoyuan
• Format: Article
• Language: English
• Subjects: Computational fluid dynamics; Flow-field coupling effect; MED-TVC system; Two-stage steam ejector
• ISSN: 2214-157X; 2214-157X
• DOI: 10.1016/j.csite.2024.104757

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.