Experimental study on the off-design operating characteristics of an organic Rankine cycle system using a zeotropic mixture

The temperature slip of a zeotropic mixture in heat exchangers can significantly diminish the exergy loss of the heat exchanger. In a kW-scale organic Rankine cycle (ORC) experimental system, two zeotropic mixtures (R134a/R245fa and R227ea/R245fa) were used to investigate the effects of zeotropic mixtures at varying heat source temperatures (HST) and mass fraction (MF), alongside the effects of pure and zeotropic mixture with the same working fluids filling quantity (WFFQ) on system performance. The experimental results indicated that the system performance parameters exhibit an increasing trend as the HST increases and the MF of R245fa decreases. The maximum net power and exergy efficiency of the system were found to be 1.759 and 25.557%, respectively, achieved by R134a/R245fa (0.5/0.5) at an HST of 100 °C. The maximum thermal efficiency of the system was 6.121%, achieved by R227ea/R245fa (0.5/0.5) at an HST of 120°C. Compared to low boiling point (LBP) working fluids (R134a and R227ea), both zeotropic mixtures can reduce the power consumption of the working fluid pump (up to a maximum of 0.064 kW) and increase the inlet subcooling of the working fluid pump (up to a maximum of 19.333°C). Generator Performance