压缩机容量比固定的双级压缩热泵系统变工况性能分析

Performance Analysis of Two-stage Vapor Compression Systems with Fixed Compressor Cylinder Volume Ratio under off-design Conditions

针对压缩机容量比固定的双级压缩系统,基于能量平衡法和分析法对2种级间喷射冷却的双级压缩循环的制热性能及效率进行了对比分析。结果显示:级间喷射过程改善了高压级压缩机的运行工况,减小了冷凝和节流过程的损失,并使喷射循环的制热量、制热COP和效率高于无喷射循环,但其性能的改善随蒸发温度升高和冷凝温度降低而逐渐减小。同时,喷射循环在变工况运行过程中存在压比最小运行工况,在压缩机容量比为2.81,冷凝温度为40℃时,系统最小运行压力比为3.67。

Heating performances and exergy efficiencies are analyzed for two types of two-stage vapor compression systems with refrigerant injection and fixed compressor cylinder volume ratio,based on both the first and second law of thermodynamics.Results show that,the injection process improves the performance of the system by decreasing the exergy losses during the condensing and throttling process,resulting in higher heating capacity,coefficient of performance and exergy efficiency than systems without refrigerant injection.However,the performance improvements decline with an increase in the evaporating temperature or with a decrease in the condensing temperature.Furthermore,there exist minimum operation pressure ratios for systems with refrigerant injection under off-design conditions.The minimum operation pressure ratio is 3.67 for refrigerant injection systems with the compressor cylinder volume ratio of 2.81 at the condensing temperature of 40 ℃.