混合工质配比对自复叠制冷循环影响的理论模拟和实验研究

随着制冷行业的快速发展，结构简单、运行可靠、系统效率较高的自复叠制冷系统引起人们的广泛关注。由于自复叠制冷系统性能受混合制冷剂配比影响等问题不利于其在大中型系统中的应用，在理论分析单级自复叠系统性能与工质配比间关系的基础上，对传统的单级自复叠系统进行改造，分别在高低温循环过程安装电子膨胀阀和储液罐、精馏器等部件以更好地调节混合工质的质量流量。采用Matlab软件编程，调用制冷工质物性分析软件NIST Refprop 9.0进行模拟计算，并把三种压比下的模拟计算与实验结果相对照。结果表明：在R23浓度（质量分数）为0.32~0.40时，改进的自复叠系统具有较高的COP，且实验与模拟结果相吻合。实验结果表明系统（火用）效率几乎不受R23浓度变化的影响。进一步表明了自复叠系统性能不受工质配比影响，具有可行性，为自复叠系统在大中型制冷系统中的推广提供了依据。

Theoretical simulation and experimental study on effect of mixture ratio in auto-cascade refrigeration cycle

With the rapid development of refrigeration industry, more attention is being given to the auto-cascade refrigeration system because of its simple structure, reliable operation and higher system efficiency. The performance of auto-cascade refrigeration system is influenced by the ratio of mixed refrigerants, which is not conductive for its application in large and medium scale systems. In the paper, based on the theoretical analysis about the relationship between the auto-cascade system performance and working fluid ratio, the traditional single-stage auto-cascade system is improved. In order to adjust the mass flow of mixed refrigerant the parts including electronic expansion valve, liquid storage tank and rectifier are installed in high and low temperature circulating loop. Programming by Matlab software and invoking Refprop 9.0 are adopted to carry out the simulation. Experimental results are compared with those of theoretical simulation under three compression ratio. The results show that the improved auto-cascade system has the higher COP when R23 mass concentration is between 0.32 and 0.40, and the simulation results agree well with the experiment results. The experimental results show that the system exergy efficiency is almost not affected by the R23 mass concentration. It is further proved that the performance of the auto-cascade system is not affected by the ratio of the working fluids, which provides a basis for the popularization and application of the auto-cascade system in the large and medium-sized refrigeration systems.