Experimental Study on Flow Boiling Heat Transfer and Pressure Drop Characteristics of R245fa in a Dimpled Flat Tube

In this study, the flow boiling heat transfer and pressure drop of R245fa in a dimpled flat tube were experimentally measured. The effects of vapor quality and heat flux were analyzed accordingly. The experimental results showed that with an increase in vapor quality, the surface coefficient of heat transfer first increased and then decreased, and the corresponding vapor quality at the maximum surface coefficient of heat transfer was affected by the heat flux. When the heat fluxes were 2 kW/m², 5 kW/m², and 10 kW/m², the surface coefficient of heat transfer reached its maximum value at vapor qualities of 0.35, 0.40, and 0.45, respectively, and then gradually decreased. Increasing the heat flux had little effect on the frictional pressure gradient, but it was beneficial for improving the surface coefficient of heat transfer. The decrease in the surface coefficient of heat transfer with an increase in vapor quality was due to the suppression of nucleate boiling. A comparison of the experimental results for R245fa and R134a indicated that vapor quality and heat flux have different effects on the surface coefficient of heat transfer. Under the same conditions, the ratio of the surface coefficient of heat transfer between R245fa and R134a ranged from 0.64 to 1.31.