Identification of key affecting parameters of zeotropic working fluid on subcritical organic Rankine cycle according limiting thermodynamic cycle

Highlights: • The equations of limiting performance of zeotropic working fluids for simple ORC and regenerative ORC are expressed. • The limiting performance are calculated using typical zeotropic working fluids. • The zeotropic working fluids properties affecting the limiting performance are analyzed. -- Abstract: Attributing to the research on key parameters analysis and working fluid selection, this paper attempted to propose a quantitative method for the performance of zeotropic working fluids used in subcritical organic Rankine cycle. Based on the graphical analysis method in temperature-entropy diagram, the limiting performances, which could be measured using limiting thermal efficiency and limiting thermodynamics perfection, of 4 typical zeotropic working fluids used in simple and regenerative organic Rankine cycle were proposed and calculated. The key affecting parameters and variation mechanism were analyzed as well. The results show that the limiting thermal efficiency of simple organic Rankine cycle increases with the increasing of latent heat of vaporization in both evaporation and condensation process, slope of working fluid saturated liquid line and the decreasing of temperature glide in both evaporation and condensation process, specific heat capacity of liquid working fluid at constant pressure. In addition to the impact of temperature glide in condensation process on limiting thermal efficiency of regenerative organic Rankine cycle, which should be determined according to specific working fluid, the impact of other parameters on limiting thermal efficiency of regenerative organic Rankine cycle is the same as that of simple organic Rankine cycle. The quantitative description of the limiting performance of zeotropic working fluid is of great significance to the analysis and improvement of cycle performance with an in-depth understanding on mechanism and could guide the selection or design of zeotropic working fluid.