Thermodynamic Analysis of a Modified Ejector-Expansion Refrigeration Cycle with Hot Vapor Bypass

Abstract

In this study, a modified ejector-expansion refrigeration cycle (MERC) is proposed for applications in small refrigeration units. A vapor bypass circuit is introduced into the standard ejector expansion refrigeration cycle (ERC) for increasing the ejector pressure lift ratio, thereby lowering the compressor pressure ratio in the MERC. A mathematical model has been established to evaluate the performances of MERC. Analysis results indicate that since a two phase vapor-liquid stream is used to drive the ejector in the MERC, a larger ejector pressure lift ratio can be achieved. Thus, the compressor pressure ratio decreases by 21.1% and the discharge temperature reduces from 93.6°C to 82.1°C at the evaporating temperature of -55°C when the vapor quality of two phase vapor-liquid stream increases from 0 to 0.2. In addition, the results show that the higher ejector component efficiencies are effective to reduce the compressor pressure ratio and the discharge temperature. Actually, the discharge temperature reduces from 91.4°C to 82.1°C with the ejector component efficiencies increasing from 0.75 to 0.85 at the two phase stream vapor quality of 0.2. Overall, the proposed cycle is found to be feasible in lower evaporating temperature cases.