R717/R404A直接接触凝结制冷循环的■分析
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摘要
提出一种R717/R404A直接接触凝结制冷系统,通过热力学计算分析了系统蒸发温度、蒸发-过冷器换热温差、主循环过冷液体过冷度、系统中间温度对系统各部分■损率及系统■效率和性能系数(COP)的影响。当蒸发温度升高,系统COP线性提升,同时系统■效率先增加后减少,在-30℃时达到最大值64.4%;当换热温差增加,系统■效率和COP均下降;当过冷度增加,系统■效率和COP均上升;存在最佳中间温度使得系统■效率和COP均达到最大值。系统中压缩机部分的■损率最大,在12.9%—14.4%之间,其次是节流阀和蒸发-过冷器均在10%左右,说明要提升系统性能,应侧重提高压缩机的效率,减少节流损失,同时优化蒸发-过冷器的设计。
A R717/R404 A direct contact condensation refrigeration cycle is designed and the influences of the evaporating temperature, the evaporation-supercoiled heat exchanger temperature difference, the sub-cooled liquids' sub-cooling degree and the intermediate temperature on the exergy loss rate of each part of supercooler of the system and exergy efficiency and coefficient of performance(COP) of the system are anlyzed through thermodymamic calculation. It is concluded that when the evaporating temperature increases, the COP increases linearly, the exergy efficiency increases firstly and then decreases, and when the evaporating temperature is-30 ℃ the system exergy efficiency reach the maximum value of 64.4%. When the heat exchanger's temperature difference increases, both the exergy efficiency and the COP decrease. And when the sub-cooling degree increases, both the exergy efficiency and the COP increase. There is an optimum intermediate temperature at which both the exergy efficiency and COP get the maximum value. In this system,the exergy loss rate of the compressor is the largest rangin from 12.99% to 14.49%, followed by the throttle valve and the evaporation-supercoiled,both of which are about 10%. Therefore, it should be focused on improving the efficiency of the compressor, reducing the loss of throttling, and optimize the design of the evaporation-supercoiled to improve the performance of the system.
A R717/R404 A direct contact condensation refrigeration cycle is designed and the influences of the evaporating temperature, the evaporation-supercoiled heat exchanger temperature difference, the sub-cooled liquids' sub-cooling degree and the intermediate temperature on the exergy loss rate of each part of supercooler of the system and exergy efficiency and coefficient of performance(COP) of the system are anlyzed through thermodymamic calculation. It is concluded that when the evaporating temperature increases, the COP increases linearly, the exergy efficiency increases firstly and then decreases, and when the evaporating temperature is-30 ℃ the system exergy efficiency reach the maximum value of 64.4%. When the heat exchanger's temperature difference increases, both the exergy efficiency and the COP decrease. And when the sub-cooling degree increases, both the exergy efficiency and the COP increase. There is an optimum intermediate temperature at which both the exergy efficiency and COP get the maximum value. In this system,the exergy loss rate of the compressor is the largest rangin from 12.99% to 14.49%, followed by the throttle valve and the evaporation-supercoiled,both of which are about 10%. Therefore, it should be focused on improving the efficiency of the compressor, reducing the loss of throttling, and optimize the design of the evaporation-supercoiled to improve the performance of the system.
引文
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2 Hameed B Mahood,Alasdair N Campbell,Rex B Thorpe,et al.Heat transfer efficiency and capital cost evaluation of a three-phase direct contact heat exchanger for the utilisation of low-grade energy sources[J].Energy Conversion and Management,2015,106:101-109.
3 宁静红,刘胜春.R744直接接触冷凝制冷循环性能分析[J].化工学报,2018,69(5):2049-2056.Ning Jinghong,Liu Shengchun.Performance analysis on R744 direct contact condensation refrigeration cycle[J].CIESC Journal,2018,69(5):2049-2056.
4 宁静红,诸凯,刘圣春,等.R290直接接触冷凝制冷循环性能分析对比[J].制冷学报,2018,39(6):32-36.Ning Jinghong,Zhu Kai,Liu Shengchun,et al.Analysis and comparison of the refrigeration cycle performance of R290 Direct contact condensation[J].Journal of Refrigeration,2018,39(6):32-36.
5 宁静红,诸凯,刘圣春.R404A直接接触凝结制冷循环的性能分析[J].低温工程,2017(3):38-42.Ning Jinghong,Zhu Kai,Liu Shengchun.Analysis on performance of R404A direct contact condensation refrigeration cycle[J].CRYOGENICS,2017,(3):38-42.
6 宁静红,刘圣春.高温气体与过冷液直接接触凝结制冷循环的性能分析[J].化工学报,2018,69(4):1437-1444.Ning Jinghong,Liu Shengchun.Performance analysis on direct contact condensation refrigeration cycle of high temperature gas with super-cooled liquid[J].CIESC Journal,2018,69(4):1437-1444.
7 司春强,史建斌,肖杨,等.NH3/CO2复叠系统性能分析[J].低温工程,2012(5):37-40.Si Chunqiang,Shi Jianbin,Xiao Yang,et al.Performance analysis of NH3/CO2 cascade system[J].Cryogenics,2012(5):37-40.
8 Yunus A Cengel,Michael A Bolfs.工程热力学[M].北京:机械工业出版社,2009.Yunus A Cengel,Michael A Bolfs.Thermodynamics an Engineering Approach[M].Beijing:China Machine Press,2009.