Many research works have generally divided the back pressure range of steam ejectors into critical, subcritical and malfunction modes based on the change of the entrainment ratio. In this study, we innovatively define and compare the abnormal and normal modes of the over-expanded, fully expanded and under-expanded states for a steam ejector using the CFD method and find that the steam ejector can maintain almost the same the secondary fluid mass flow rate under the normal mode of different expanded states. A comparison of different nozzle expansion states is also carried out. The results demonstrate that huge flow separation zones occur in the mixing chamber and diffuser in the under-expanded state, causing a drop in the secondary fluid mass flow rate compared with other expanded states. In addition, the irreversibility analysis illustrates that the steam ejector could minimize entropy production under the over-expansion state to obtain the optimal entrainment rate. More importantly, this paper provides a theoretical reference for maximizing the entrainment ratio or the secondary fluid mass flow rate from the perspective of the nozzle expansion state.

许多研究工作一般根据夹带比的变化将蒸汽喷射器的背压范围分为临界、亚临界和故障模式。在这项研究中，我们创新地定义和比较了蒸汽喷射器的过膨胀、完全膨胀和欠膨胀状态的异常和正常模式，使用 CFD 方法，发现蒸汽喷射器可以保持几乎相同的二次流体质量正常模式下不同膨胀状态下的流量。还进行了不同喷嘴膨胀状态的比较。结果表明，在膨胀不足的状态下，混合室和扩散器中存在巨大的流动分离区，与其他膨胀状态相比，导致二次流体质量流量下降。此外，不可逆性分析表明蒸汽喷射器可以最大限度地减少过度膨胀状态下的熵产生以获得最佳夹带率。更重要的是，本文从喷嘴膨胀状态的角度为最大化夹带比或二次流体质量流量提供了理论参考。