Effect of an Internal Heat Exchanger on the Performances of a Double Evaporator Ejector Refrigeration Cycle

Abstract

A theoretical investigation is presented about a double evaporator ejector refrigeration cycle (DEERC). Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger (IHX). The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure. Moreover, the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor. To assess accurately the influence of the IHX on the DEERC performance, a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors. The model also accounts for the friction effect in the ejector mixing section. The equations of this model are solved using an Engineering Equation Solver (EES) for different fluids. These are: R134a as baseline fluid and other environment friendly refrigerants used for comparison, namely, R1234yf, R1234ze, R600, R600a, R290, R717 and R1270. The simulation results show that the DEERC with an IHX can achieve COP (the coefficient of performance) improvements from 5.2 until 10%.