| Based on the theory of irreversible thermodynamics and trapezoidal cycle,this paper presents an irreversible thermodynamics analysis of the cyclic heat transfer process of the organic Rankine cycle(Organic Rankine Cycle,ORC),and an thermodynamic irreversible parameter that characterizes the heat transfer process in the thermodynamic cycle,which named irreversible degree of heat transfer of external cycle.The theoretical model and the mathematical formulas between the irreversible degree of heat transfer of evaporator,condenser and the whole cycle and cycle performance(net power output,thermal efficiency and exergy efficiency)are built,and the relationship are studied.The influence of different parameters,such as heat source inlet temperature,evaporation temperature,condensation temperature,pinch point temperature difference and Jacob number of working fluid on the irreversible degree of heat transfer are analyzed.Between the irreversible degree of heat transfer of the whole cycle and the evaporator have the same change rule,there is shift-temperature of heat source is similar to the net work,when the heat source temperature is lower than the shift-temperature of the working fluid,irreversible degree has the minimum value;otherwise,the irreversible degree will decrease monotonously with the evaporation temperature without the minimum value.However,there is no relation between the irreversible degree of heat transfer of the condenser and the working fluid properties or evaporation temperature,and the irreversible degree decreases monotonously with condensation temperature increase.The results show that the relative deviation between the theoretical calculation and numerical simulation of organic Rankine cycle is less than 5%.Jacob number is the important factor on the irreversible degree.The influence of heat source temperature on the irreversible degree is obvious,followed by the pinch point temperature difference.Study on the relationship and change rule between the irreversible degree and cycle performance,the results showed the irreversible degree of external cycle and net power output,thermal efficiency and exergy efficiency have nearly linear decreased relationship when the inlet and outlet of heat source temperature have a fixed value;when the heat source temperature is lower than shift-temperature of heat source,it is proven the optimal or maximum value of net power output,thermal efficiency and exergy efficiency does not exist a certain relationship with the minimum value of irreversible degree. |
