Performance Prediction of Organic Rankine Cycle: Thermodynamic Process Decoupling Based on Fluid Key Properties

The essence of fluids selection and cycle performance promotion and optimization of organic Rankine cycle (ORC) is thermodynamic decoupling revealing of the thermodynamic relationship among cycle configuration, condition and its fluid properties essentially. Different with the traditional numerical calculation method (TNCM), inspiring by the evolution mechanism of thermodynamic cycles, a thermodynamic process cycle decoupling model method (TCSM) of subcritical ORC is tried to be built in this paper, and the deduced efficiency prediction calculation by making efficiencies of Triangle cycle, Carnot cycle and Brayton cycle at the corresponding characteristic temperatures as variables expediently at the same corresponding temperature. Comparing with TNCM, error analysis reveals that TCSM has an acceptable precision for all investigated 21 working fluids at the common state conditions, relative error is about below 1.00% except of near critical or excessive superheated zones. Then, three conclusions are revealed conveniently : If the reduced temperatures of two different pure working fluids are equal, the corresponding ORC efficiencies are equal too; When superheat degree of working fluid increases, cycle ORC efficiency of dry fluid decreases and wet fluid increases, while the variation of efficiency increases linearly with the superheat degree.