One dimensional model of an ejector with special attention to Fanno flow within the mixing chamber

Abstract

Ejector refrigeration systems are less power intensive when compared to conventional refrigeration cycles, mainly due to their ability to use low-grade heat sources to reduce electrical power requirements. The efficiency of these systems is largely dominated by the performance of the ejector. Therefore, it is essential that the performance characteristics of the ejector are predicted using a mathematical model to aid design analysis. Though numerous mathematical models of ejectors exist, this paper improves upon the one-dimensional mathematical model of the ejector and validates its accuracy by comparing it with experimental data available in the literature for the R141b refrigerant. The novelty of this improved model is that Fanno flow concept has been applied to capture frictional compressible flow that is occurring in the mixing chamber of the ejector. In addition, rather than assuming a constant heat capacity ratio γ, the proposed model further enhances the accuracy of the model by averaging the γ between each segment of the flow within the ejector. Validations have revealed that the entrainment ratio was predicted within 4% absolute error, while the condenser operating pressure predictions have an average absolute error of 5% with respect to experimental measurements.