Full-operating-condition performance improvement strategy and optimal design of a two-stage ejector with auxiliary secondary flow for MED-TVC systems

Periodic fluctuation of steam-source pressure occurs in the thermal vapor compression multi-effect distillation (MED-TVC) systems. Because ejectors are sensitive to the boundary conditions, as a key component for recovering excess steam in systems, ejectors experience a rapid decline in performance when the steam-source pressure fluctuates and does not satisfy the design condition. This decline negatively impacts the overall system performance and reduces the energy utilization efficiency. Therefore, a two-stage ejector with auxiliary secondary flow (ASF-TSE) and a full-operating-condition performance improvement strategy were developed in this study to enhance the ejector performance under full working conditions and broaden the efficient operation range of ejectors. The flow field characteristics and performance of the ASF-TSE, single ejector (SE), and two-stage ejector (TSE) in the low and design-pressure ranges were compared and investigated. The results showed that within the design-pressure range, the maximum and average increase ratios of the ASF-TSE for entrainment performance compared with the TSE are 17.53 % and 13.43 %. Moreover, the entrainment capacities of the three ejectors were compared and analyzed in the full operating range. Simulation results show that compared with the SE and TSE, the entrainment performance of the ASF-TSE is improved by 87.5 % and 8.0 %, respectively.