Performance Predictions of Dry and Wet Vapors Ejectors Over Entire Operational Range

Abstract

Abstract:If a traditional ideal-gas ejector model is used to evaluate the performance of a wet vapor ejector, large deviations from the experimental results will be unavoidable. Moreover, the model usually fails to assess the ejector performance at subcritical mode. In this paper, we proposed a novel model to evaluate the performance of both dry and wet vapors ejectors over the entire operational range at critical or subcritical modes. The model was obtained by integrating the linear characteristic equations of ejector with critical and breakdown points models, which were developed based on the assumptions of constant-pressure mixing and constant-pressure disturbing. In the models, the equations of the two-phase speed of sound and the property of real gas were introduced and ejector component efficiencies were optimized to improve the accuracy of evaluation. It was validated that the proposed model for the entire operational range can achieve a better performance than those existing for R134a, R141b and R245fa. The critical and breakdown points models were further used to investigate the effect of operational parameters on the performance of an ejector refrigeration system (ERS). The theoretical results indicated that decreasing the saturated generating temperature when the actual condensing temperature decreases, and/or increasing the saturated evaporating temperature can improve the performance of ERS significantly. Moreover, superheating the primary flow before it enters the ejector can further improve the performance of an ERS using R134a as a working fluid.

Performance analysis and optimization of an ejector refrigeration system using alternative working fluids under critical and subcritical operation modes

“…These coefficients were mostly taken as constant in earlier studies such as Huang et al [5], Chen et al [18] and Chen et al [40] giving significant errors. In line with recent studies [21,22], correlations of ejector coefficients have been developed as functions of the generator and evaporator pressure ratio and the ejector area ratio. For R141b, results in Huang et al [5] have been used to derive the correlations using regression analysis.…”

“…With Eqns. (1) - (22), the performance of the ejector system operating under the critical mode is obtained. The resulting pressure in Eqn.…”

“…The resulting pressure in Eqn. (22) represents the critical condensing pressure and the corresponding saturation temperature is the critical condensing temperature. The entrainment ratio, μ is a critical parameter in characterizing ejector performance.…”

“…4, the considered refrigerants are either dry or isentropic working fluids. Dry and isentropic working fluids were considered in this study: firstly, to ensure that the Huang et al [5] model can be applied with reasonable accuracy, and secondly because it has been shown that dry refrigerants give higher values of the entrainment ratio compared to wet refrigerants [22]. Moreover, with dry working fluids, the possibility of having liquid droplets during expansion in the nozzle is eliminated and thus there is no need to superheat the fluid entering the ejector.…”

Energetic Optimization and Exergetic Performance Investigation of an Ejector System Using HCFO-1233zd(E) as a Refrigerant

“…R1233zd(E) is a dry working fluid and has a shape on the T-s diagram similar to that of R141b and R245fa (Mwesigye and Dworkin, 2018). Dry refrigerants are beneficial since they give higher values of the entrainment ratio compared to wet refrigerants (Li et al, 2017a). In addition, using dry working fluids ensures that there are no liquid droplets during expansion in the nozzle, eliminating the need for superheating the fluid entering the ejector.…”