跨临界CO_2蒸气压缩/喷射制冷循环的数值分析

Numerical analysis on transcritical CO_2 vapor compression/ejection refrigeration cycle

为了更合理的描述喷射器扩压室内的压力变化特性,对已有的跨临界CO2蒸气压缩/喷射制冷循环的热力学模型做了改进,并对扩压室新定义了一种压力系数ηd。建立了相应的数学模型并进行数值模拟,考察了该压力系数ηd对制冷循环喷射系数和系统性能系数COP的影响,其结果与常规的扩压效率ηk的影响作用有很好的一致性,说明所改进的热力学模型是可行的;应用该模型分析了压力系数对相关重要参数的影响,结果表明:随压力系数的增大,喷射系数基本不变;COP、压缩机进口温度、喷射器的增压比和喷射器效率增大;压缩机出口温度和压缩比减小;当工作流体压力为9 MPa时,相关参数发生了显著的变化。该压力系数取决于系统喷射器扩压室进出口的压力,方便测量确定。研究方法能够为跨临界CO2蒸气压缩/喷射制冷循环的性能分析提供有益参考。

A thermodynamic model of transcritical CO2 vapor-compression/ejection refrigeration cy-cle was modified to display the pressure variation in diffuser chamber of the ejector. A new pressure coefficient ηd for diffuser chamber was defined. And the corresponding mathematical model was es-tablished for calculated analysis. The effects of the pressure coefficientηd to the ejector entrainment ratio and the coefficient of performance （ COP） of the refrigeration cycle were studied. The results are in good agreement with the effects of common diffuser efficiencyηk . It is shown that the modified thermodynamic model is feasible. The influences of the pressure coefficient on several important pa-rameters were investigated. The results show that the ejector entrainment ratio almost unchanged with the increasing pressure coefficient. And the cycle COP, compressor inlet temperature, ejector pres-sure ratio and ejector efficiency increase with the increasing pressure coefficient. The compressor outlet temperature and the compression ratio decrease slowly with the increasing pressure coefficient. The relevant parameter changes significantly when the pressure of working fluid is 9 MPa. The pres-sure coefficient based on the ejector pressure is easy to measure. This strategy can provide a refer-ence for the study performance on transcritical CO2 vapor-compression/ejection refrigeration cycle.