Abstract
An ejector refrigeration system (ERS) can significantly reduce electricity consumption compared to traditional compressor-based systems. Fabri-choking is an indication of an ejector operating in the idealized condition with a maximum entrainment ratio. Backpressure has a significant influence on ejector performance. Severe degradation in performance is observed when the backpressure increases from the design value. Until now, many works have been performed to design and evaluate the ejector systems. In the majority of these works, it is assumed that the ejector is working with fixed designed backpressure, which gives maximum performance. In almost all of the practical applications of ERS, the backpressure varies, mainly as the cooling load requirement changes. In such practical applications, the flow in the ejector is very interesting, and this paper takes a new look at the transient operation of an ejector with varying backpressure. In the present study, numerical simulations have been used to provide detailed flow physics and, in particular, the occurrence of Fabri-choke in a supersonic ejector. The results obtained reveal compound choking, multiple evolutions of Fabri-choke, and its relation to wave reflections. Results showed that the first and second occurrences of Fabri-choke occurred when the backpressure is reduced by 6.0% and 8.0%, respectively. Methods to ascertain Fabri-choke in numerical simulations and experimental studies were also separately addressed.
