两相喷射器对压缩-喷射制冷系统性能的影响研究

Influence of Two-phase Ejector on Performance of Compression/Ejection Refrigeration System

采用等面积混合模型,以R134a制冷剂为工质,对两相喷射器建立热力学模型,并用Matlab7.1软件进行编程计算,相关的工质热物性参数,通过调用Refprop7软件获取。分析比较了各混合压力下喷射器内压力变化趋势,喷射器混合压力、系统蒸发温度、冷凝温度以及喷射器等熵效率的变化对两相喷射器性能、制冷系统性能的影响。结果表明:对于所研究的工质和工况,热力学分析方法采用等面积混合模型比较合理;混合压力在理论取值范围内存在一个最优点;随蒸发温度的升高或冷凝温度的降低,喷射器最优混合压力的取值点越靠近引射压力,喷射系数增加,系统COP升高,但是相对于传统压缩制冷循环的性能提高率减小;喷射器及系统性能对喷射器进口段等熵效率的变化较敏感。因而,选取恰当的混合压力值,设计制造等熵效率较高的工作喷嘴对于压缩-喷射制冷系统的性能优化至关重要。

This paper establishes a thermodynamic model of two-phase ejector, having the mixing area in the mixing chamber constant and R134a refrigerant as working medium. Matlab7.1 is used in programming and calculating. Thermo-physical properties of the refrigerant involved are obtained through application of Refprop7. Pressure changes in the ejector at various mixing pressures are analyzed. How changes in mixing pressure, evaporation temperature, condensation temperature and isentropic efficiency can influence the performance of the ejector and the refrigeration system is studied. The results show that under the operational conditions in this study, the constant area model for mixing chamber is appropriate for thermodynamic analysis. Within the theoretical value range, there is an optimum value for mixing pressure. As the evaporation temperature increases or the condensation temperature decreases, the optimum mixing pressure comes closer to the ejection pressure, the entrainment ratio goes up and COP of the system improves. However, compared to traditional compression-refrigeration cycle, the system under study improves on a smaller basis. Besides, COP of the system is more sensitive to changes of the inlet isentropic efficiency. Therefore, appropriate mixing pressure and an operating nozzle with high isentropic efficiency is highly significant to optimizing the performance of the compression-ejection refrigeration system.