考虑实际压缩效率的NH_(3)/CO_(2)复叠制冷系统热力学分析

Thermodynamic Analysis of NH_(3)/CO_(2) Cascade Refrigeration System Considering Actual Compression Efficiency

为优化复叠制冷系统的运行参数,本文对NH_(3)/CO_(2)复叠制冷系统进行了热力学分析,搭建了NH_(3)/CO_(2)复叠制冷系统实验台,获得了部分工况点的实验数据,并与采用不同压缩机等熵效率经验公式的热力学分析结果进行对比及误差分析,最终采用与实验数据相吻合的压缩机等熵效率经验公式,对系统的最大性能系数、最佳中间温度及最优级间容量比随系统蒸发温度、冷凝温度、复叠传热温差、高低温回路过冷度及过热度的变化进行了多工况下的理论分析。结果表明:蒸发温度对最大性能系数及最佳中间温度的影响最大,蒸发温度每增加5℃,系统最大性能系数提高约18.5%,最佳中间温度升高约2.23℃;冷凝温度对最优级间容量比的影响最大,冷凝温度每提高5℃,最优级间容量比增大约6.34%,而低温回路过热度对最优级间容量比的影响最小。建立了性能参数与工况的关联拟合公式,可为复叠制冷系统的优化运行提供依据。

A thermodynamic analysis was conducted on an NH_(3)/CO_(2) cascade refrigeration system to optimize the operating parameters.An NH_(3)/CO_(2) cascade refrigeration system test platform was built,and the experimental data at some working points were obtained.Comparative and error analyses were performed using the thermodynamic analysis results of empirical formulas for different compressor isentropic efficiency.The formula that is consistent with the experimental data was used to analyze the maximum coefficient of performance(COP_(max)),the optimal intermediate temperature(T_(LC,opt)),and the optimal inter-stage capacity ratio(n_(V,opt))of the system under variable temperature conditions.The temperature conditions included the evaporating temperature(T_(e)),condensing temperature(T_(e)),cascade heat exchange temperature difference,and subcooling and superheating in the high-and low-temperature loops.The results show that T_(e) has the greatest influence on COP_(max) and T_(LC,opt).When T_(e) increased by 5℃,the COP_(max) of the system increased by approximately 18.5%,and the T_(LC,opt) increased by approximately 2.23℃.T_(e) had the greatest influence on n_(V,opt),and the low-temperature loop superheat had the least influence on n_(V,opt).For every 5℃increase in T_(e),the n_(V,opt) increased by approximately 6.34%.A correlation fitting formula between the performance parameters and working conditions is proposed,which can provide a reference for the optimization of operations in a cascade refrigeration system.