Experimental investigation of heat transfer to supercritical R245fa flowing vertically upward in a circular tube

•Supercritical heat transfer characteristics of R245fa was investigated for ORC system.•Effects of mass flux, heat flux, and pressure were discussed.•Heat transfer impairment was found under moderate ratio of heat and mass flux.•Irreproducibility in the heat transfer was observed at certain working condition.•70% of the results were in the range of ± 30% of Yamagata’s correlation. The characteristics of supercritical heat transfer of organic fluid R245fa under heating conditions was investigated experimentally in a vertical tube with an inner diameter of 4 mm and a length of 1.04 m. The heat flux ranges from 15 to 100 kW/m2 and mass flux from 400 to 800 kg/m2 s. The experiments were conducted at pressures of 4.0, 4.5, and 5.0 MPa. The local heat transfer coefficients were determined with respect to the heat flux, mass flux, and pressure. The experimental results show that the heat transfer deteriorates abruptly at moderate heat and mass fluxes, which can be considered as mixed convection, whereas it deteriorates gradually under other working conditions, which can be considered as forced convection. The irreproducibility of the heat transfer is also demonstrated. The experimental data are compared with existing correlations and reveal that 70% of the experimental data can be predicted by Yamagata’s correlation with an accuracy of ± 30%. However, the prediction accuracy under abrupt deterioration conditions needs further improvement.