A double-choking theory as an explanation of the evolution laws of ejector performance with various operational and geometrical parameters

Abstract

There are few systematic studies to investigate the inherent reason behind the evolution law of ejector performance, only some simple qualitative or roundabout analysis. In this paper, a double-choking theory is proposed to provide an in-depth explanation of the evolution laws of ejector performance. The systematic investigation and quantitative analysis focus on the influences of various operational and geometrical parameters on the ejector choking flows. Key results revealed that the flow area of the primary jet flow at the choking cross-section Apy almost linearly increases with higher primary flow pressure pp0, while the entrainment choking area Aey declines instead, and thus the entrainment ratio ε decreases. The mixing pressure py significantly increases with entrainment pressure pe0, and Apy partly reduces. Consequently, Aey becomes larger and ε is accordingly with an over-double increase. Apy undergoes a continuous decrease when the area ratio of primary nozzle λt increases, and thus ε rises consistently although Aey1 eventually experiences a slight decrease. However, the choking state of the entrained flow would discontinue as λt exceeds its critical value λtc. Additionally, Aey increases substantially when the area ratio of the constant-area section λ3 enlarges, while Apy and py always remain unchanged. Accordingly, ε follows the same increasing trajectory as Aey. These impactful results could serve as an essential guide for optimizing the ejector design, and also ensure a clearer perspective to understand the fundamental link between the ejector’s entrainment performance and choking flow.