R134a/R23复叠制冷系统级间容量比的优化分析
Optimization of Compressors Displacement Ratio in R134a/R23 Cascade Refrigeration System

为了提高复叠制冷系统的性能以及优化系统设计时各循环压缩机的匹配问题,提出了无量纲参数――级间容量比,即低温循环压缩机进口处的体积流量与高温循环压缩机进口处的体积流量之比。建立了复叠制冷系统的数学模型,分析了级间容量比对中间温度和系统性能系数(COP)的影响,并在蒸发温度为-75～-55℃、冷凝温度为20～50℃及复叠温差为5～13℃的各种工况下,探究了最优级间容量比与工况参数的关系。结果表明:若级间容量比增加,则中间温度增加,COP先增加后缓慢减小,存在使COP最大的最优级间容量比;工况温度对COP的影响大于级间容量比对COP的影响,随冷凝温度上升,最优级间容量增大,蒸发温度上升,最优级间容量比增大;复叠温差增大,最优级间容量比减小;冷凝温度、蒸发温度及复叠温差平均每上升10℃,最优级间容量比变化范围为0.1～0.2。由工况参数和最优级间容量比的计算结果拟合得到了优化关联式,其计算思路和结果分析可为实际设计中各循环压缩机排量的选型匹配提供理论依据。
A dimensionless parameter, the compressor displacement ratio, is proposed to investigate the performance of the R134a/R23 cascade system and optimize the match of compressors of the system. The parameter is defined as the ratio of the compressor inlet volume flow rates between the low temperature cycle and the high temperature cycle. A numerical model is established to analyze the effect of the displacement ratio on the COP and the intermediate temperature. The relationship between the optimal displacement ratio and the operating parameters is discussed under various conditions when the evaporating temperature, condensing temperature and cascade temperature difference are ranged within -75～-55℃, 20～50℃ and 5～13℃, respectively. The results show that the intermediate temperature increases with the displacement ratio, while the COP rises first and then drops slowly. The variation of the operating temperature exerts a stronger impact on the COP than the displacement ratio. The optimal displacement ratio increases with the condensing temperature and the evaporation temperature, and decreases when the cascade temperature difference rises. The correlations of the optimal displacement ratio are obtained by fitting data of the working condition parameters and the optimum compressor displacement ratio