Analysis of the thermodynamic performance of the organic Rankine cycle (ORC) based on the characteristic parameters of the working fluid and criterion for working fluid selection

The objective of this paper is to establish a method for directly correlating the thermal properties of working fluid with the thermodynamic performance of ORC (organic Rankine cycle) to explore the effect of the thermal properties of working fluid on the thermodynamic performance of the cycle. On the basis of thermodynamic theory, the thermal properties of the working fluid in the ORC are abstracted into characteristic parameters, T-smax, limiting temperature difference, B and C. Based on the characteristic parameters, x (feature function of the heat addition process), (T) over bar (1)(average temperature of heat addition), (T) over bar (2) (average temperature of heat rejection) and the exergy efficiency of 16 working fluids in the ORC are investigated. The results indicate that the change rules forT(smax) and critical temperature T-cr for different working fluids are generally the same. With the increase in T-g,T-out (temperature of the heat source medium at the evaporator outlet), although the increased evaporation temperature T-1 increases (T) over bar (1), decreased x values weaken the increase in the amplitude of (T) over bar (1). The change rules for x and (T) over bar (1) for different working fluids are opposite at low T-g,T-out while the same at high T-g,T-out. The transition temperature T-z, limiting temperature difference and T-cr are the main indicators for evaluating T-1 of different working fluids. The change rules for7 and B for the different working fluids are generally opposite, and B can be used as the criterion for working fluids with low (T) over bar (2). The effects of (T) over bar (1) on exergy efficiency is stronger than that of (T) over bar (2), while the effect of (T) over bar (2) cannot be ignored at high T-g(,out). The characteristic parameters of the working fluid explain the limitation of using T-cr as the criterion for working fluid selection, and establish the criterion for appropriate working fluid.