Performance Analysis of Organic Rankine Cycle With Working Fluid of R245fa/DMF

The effects of pure R245fa and its mixture with DMF on the expander in the organic Rankine cycle (ORC) are compared by constructing a phase equilibrium model for the mixture of organic fluid and DMF. The results show that via changing the liquid-phase molar fraction of R245fa under the condition of limited inlet/outlet pressure ratio of the expander, the phase equilibrium pressure could be reduced with high vapor temperature, while the enthalpy difference of inlet/outlet of the expander could be enlarged with the same pressure ratio. The enthalpy difference of the mixture increased from 19.2 kJ/kg to 22.84 kJ/kg in comparison with the pure R245fa when the liquid-phase molar fraction and the temperature of R245fa are 0.64 and 403 K, respectively. Furthermore, the thermal efficiency of the mixture could be enhanced by 0.6% to 1.3% compared with the pure R245fa at the same pressure ratio.