Working condition expansion and performance optimization of two-stage ejector based on optimal switching strategy

Ejectors are widely used as steam power cycle components to recover superfluous water vapor. However, in a system for preparing distilled water used for pharmaceutical injection, the ejector periodically deviates from the design condition owing to fluctuations in steam source pressure. In particular, when the pressure is reduced to approximately 75% of the design value, performance is significantly degraded, affecting water production efficiency. To solve this problem, a two-stage ejector with control switching strategy is proposed in this paper. The performance of a series of two-stage ejector structures with different scale ratios was analyzed, and the optimum scale ratio was determined. Furthermore, an optimal switching strategy is devised to ensure that the two-stage ejector maintains stable performance under different primary flow pressures. The numerical results indicate that the entrainment ratio of the two-stage ejector is 79.4% higher than that of the single-stage ejector when the pressure is 60% of that of the designed primary flow. Moreover, the two-stage ejector can maintain satisfactory entrainment performance when the traditional ejector enters reversed mode under 50% of the designed pressure. The experimental results show that the entrainment performance of the proposed two-stage ejector can be improved significantly when power fluid pressure is insufficient.