关键词: 有机朗肯循环, 跨临界循环, 临界温度, 窄点温差, 热力学, 热力学过程, 热力学性质

Abstract: Thermal performance values of 41 working fluids in a trans-critical organic Rankine cycle (ORC) driven by waste heat flue gas of 473.15 K were calculated by means of a theoretical model in which the inlet and outlet temperatures of flue gas were fixed and therefore the thermal efficiency and net work output were unified into one parameter as long as the heat absorbed was given. The influences of pinch point temperature difference (PPTD) in the evaporator and working fluid properties on cycle performance were analyzed. Calculation results showed that for fluids with critical temperature T_c<T_gas,out, and fluids with T_c>0.88T_gas,in, T_c had dominant influence on thermal efficiency. For fluids with T_c between T_gas,out and 0.88T_gas,in, fluid dryness had significant influence on cycle performance, and wet fluids outperformed dry fluids apparently. Wet fluids with T_c between T_gas,out and 0.88T_gas,in exhibited the highest thermal efficiency. For fluids with T_c>0.88T_gas,in, PPTD might lie either inside the evaporator or at the outlet. Thermal performance values of the cycle with PPTD inside the evaporator outperformed that with PPTD at the outlet. Application of such conclusions was confirmed through sensitivity analysis for flue gas inlet and outlet temperatures.

Key words: organic Rankine cycle, trans-critical cycle, critical temperature, pinch point temperature, thermal dynamic, thermal process, thermal property