Influence of geometrical factors on steam ejector performance – A numerical assessment

A number of factors influence the performance of an ejector. In this work, three geometrical factors – the area ratio between the nozzle and constant area section (rA), nozzle exit position (NXP) and constant area section length (Lm) – were considered. The theoretical analysis was carried out by a CFD model of a steam ejector using FLUENT. The results indicated the existence of an optimal area ratio, depending on operating conditions. Therefore, a new feature, a spindle in the primary nozzle is suggested to fine tune the primary flow rate depending on operating conditions. The location of NXP influenced both entrainment ratio (λ) and critical back pressure (pc,crit), showing an optimum at 60 mm from the inlet plane of the ejector mixing section. Lm had little influence on λ; however, longer constant area sections resulted in higher pc,crit. For an optimal design, a value of Lm = 155 mm was identified.