Numerical investigation of the nozzle expansion state and its effect on the performance of the steam ejector based on ideal gas model

• Published in: Applied thermal engineering Vol. 199; p. 117509
• Main Authors: Li, He, Wang, Xiaodong, Ning, Jiuxin, Zhang, Pengfei, Huang, Hailong, Tu, Jiyuan
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 25.11.2021; Elsevier BV
• Subjects: CFD model; Diffusers; Ejectors; Entrainment; Entropy generation; Flow separation; Fluid dynamics; Heat transfer; Ideal gas; Mass flow rate; Nozzle expansion state; Nozzles; Optimization; Steam ejector; Steam power; CFD model; Nozzle expansion state; Steam ejector; Flow separation; Entropy generation
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2021.117509

[Display omitted] •Nozzle over-expanded, full-expanded and under-expanded states were investigated.•The normal operating condition range for the steam ejector was determined.•The shear stress inside the working fluid of the steam ejector is solved.•The flow separation phenomenon is found in the mixing chamber and diffuser.•The entropy generation under different nozzle expansion states is studied. 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.