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针对低品位余热的利用,将有机朗肯系统与复叠式制冷系统耦合,建立了热力学模型;采用R141b作为朗肯循环系统制冷工质,分别采用R22/R23、R404A/R23、R290/R744、R717/R744四种工质对作为复叠式制冷系统高低温级循环的制冷工质;基于EES软件编写了循环性能计算程序,研究了低温级冷凝温度T_(10)、低温级蒸发温度T_e、蒸发冷凝传热温差ΔT对系统性能COPs以及高低温级质量流量比G的影响,并以COPs与G为评价指标选出最佳工质。结果表明系统的COPs会随着低温级冷凝温度的升高而先增大后减小,并存在一个最佳值;系统COPs随着低温级蒸发温度的升高而增大,随着蒸发冷凝传热温差的增大而减小;高低温级质量流量比随着低温级冷凝温度的增大而减小;R717/R744最适合作为有机朗肯-复叠制冷系统复叠制冷部分工质。
Aiming at the utilization of waste heat with low grade, the organic Rankine system is coupled with the cascade refrigeration system to establish the thermodynamic model. R141b is used as the cooling medium of Rankine cycle system, and R22 / R23, R404A / R23, R290 / R744, R717 / R744 were used as the refrigerating working fluid in high and low temperature cycle of cascade refrigeration system. Based on the EES software, a cycle performance calculation program was prepared and the condensing temperature T 10, cryogenic temperature T_e, The influence of the heat transfer temperature difference ΔT on the system performance COPs and the mass flow rate ratio G at the high and low temperature levels was also studied. The best working conditions were selected with COPs and G as the evaluation indexes. The results show that the COPs of the system first increases and then decreases with the condensation temperature of the low temperature stage, and there exists an optimal value. The COP of the system increases with the evaporation temperature of the low temperature stage. R717 / R744 is most suitable as a refrigerant for cascade refrigeration of organic Rankine-Cascade refrigeration system.