The effect of operating conditions on the performance of a supersonic ejector for refrigeration

A previously developed one-dimensional model, based on a forward marching solution technique of the conservation equations has been used to study ejector operation and performance in a large range of refrigeration working conditions. Several important features of ejector operation characteristics were simulated. Global parameter values, their local distributions along the ejector including the temperature, the pressure and the Mach number were calculated for design and off design conditions. Operation parameters such as the entrainment ratio omega, compression ratios P-exit/P-ev, P-g/P-exit and the geometric ratio (D/D-c)(2) were found to significantly affect performance. The impact of the generator, the evaporator, the condenser and related thermodynamic parameters, which have been assessed in this study, are summarized as: Fluid mixing conditions dictated by the fluid type, the mixing chamber geometry, the inlet and outlet constraints, may lead to off design operation with related stability and performance deterioration Internal superheat generation, due to inefficient mixing and normal shock waves is very important in off design operation Some degree of inlet superheat (around 5 degreesC) is necessary to prevent internal condensation but excess superheat is detrimental to the condenser efficiency at exit Generator pressure conditions and the evaporator temperature significantly affect ejector performance. Crown Copyright (C) 2004 Published by Elsevier Ltd and IIR. All rights reserved.