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

Abstract

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 ( r A), nozzle exit position (NXP) and constant area section length ( L m) – 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 ( p c,crit), showing an optimum at 60 mm from the inlet plane of the ejector mixing section. L m had little influence on λ; however, longer constant area sections resulted in higher p c,crit. For an optimal design, a value of L m = 155 mm was identified.