余热驱动的有机朗肯循环-复叠式制冷系统?分析

Exergy analysis of organic Rankine cycle-cascade refrigeration system powered by waste heat

针对余热的有效利用,建立了有机朗肯循环-复叠式制冷系统的热力学模型,其中:有机朗肯循环系统分别采用R123、R1234ze、R245fa、R600a、RC318、R141b等六种工质;复叠式制冷系统分别采用R22/R23、R404/R23、R290/R744、R717/R744等四种工质对。选择系统?效率作为性能评价指标,运用热力学第二定律研究系统运行参数对系统?效率的影响,分析了系统各部件的?损失,并指出了能量利用的薄弱环节,提出了有效提高系统性能的建议,为系统的优化提供参考。结果表明,对系统?效率而言,R141b和R717/R744是最佳工质。系统主要部件按?损失大小依次为凝汽器、膨胀机、高温级冷凝器、发生器、高温级压缩机、低温级蒸发器、蒸发冷凝器。尽可能提高压缩机的等熵效率,优化设计换热器的结构,减小传热温差,才能减少不可逆损失,提高换热器的?效率。

To utilize waste heat efficiently,the thermodyamic model of compound system combined organic Rankine cycle(ORC)and cascade refrigeration system(CRS)was built,in which R123,R1234ze,R245fa,R600a,RC318 and R141b were selected as working fluids of ORC,and R22/R23,R404/R23,R290/R744 and R717/R744 were chosen as working fluids of CRS.In terms of the second law of thermodynamics,the effects of operating parameters on the system performance were studied,which was evaluated by exergy efficiency.The exergy loss of the system components was analyzed and the bottlenecks of their energy utilization were found out.The advices to the system performance improvement were proposed to provide the guidance of system optimization.The results showed that in terms of exergy efficiency,the optimum working fluids was R141b and R717/R744.The exergy loss of main components was in the descending order as follows:condenser,expander,condenser of high temperature stage(HTS),generator,compressor of HTS,evaporator of low temperature stage and evaporative condenser.The irreversible loss could be reduced by the rising of compressor isentropic efficiency,structure optimization of heat exchanger and temperature difference reduction of heat transfer to improve its exergy efficiency.