Thermodynamic Principle Of Organic Rankine Cycle With Variable Properties Of Working Fluids

The properties of working fluids including saturated line shape and critical temperature are limited by specific fluid,general principle of the influence of working fluid's properties on cycle performance cannot be investigated through organic Rankine cycle?ORC?.Based on the trapezoidal cycle?TPC?and its model,the mathematical model of cycle performance?net output power,thermal efficiency?and working fluid's properties?the slope of saturated lines,critical temperature?is presented,consequently,properties of working fluids can be regarded as independent variable,it will be available to study the influence of working fluids'properties on cycle performance.Working fluid with linear saturated line is proposed to simulate the optimized conditions of actual working fluids,and study the influence of heat source temperature and working fluids'properties on cycle performance.The empirical formulas of shift-temperature of heat source(T_h,shift)both in ORC and TPC are presented,respectively,their deviations are listed compared with numerical calculations.Based on working fluid with linear saturated line,general principle of optimized condition under T_h,shift is researched.The paper obtains general principle of the influence of working fluid's properties on cycle performance.Optimized conditions?optimized evaporation temperature,the maximum net output power?are mainly depended on heat source temperature,properties of working fluids have little effect on it,and the character will be more obvious when the heat source temperature is lower.Results show that:the average deviation of optimized conditions of 14 actual working fluids and corresponding working fluids with linear saturated line is less than 0.9%.The deviations of empirical formulas of T_h,shift both in ORC and TPC compared with their actual values are less than 1.97%and 0.68%,respectively.