Experiment on flow boiling heat transfer of R134a in mini-channel of flat tube

An experimental study about R134a refrigerant flow boiling in a horizontal multiport flat tube mini-channel with the hydraulic diameter of 0.63mm and 0.72mm was carried out. The refrigerant was heated in uniform heat flux. The experiments were performed at the mass flux in range of 82-621kg/(m2·s), heat flux in range of 9.7-64kW/m2, saturation pressure in range of 0.22-0.63MPa and vapor quality in range of 0-1. Results showed that when the vapor quality in range of 0-0.6, the local heat transfer coefficients of mini-channel were higher than those of conventional channel, nucleate boiling was the main contributing factor, the local heat transfer coefficients increased with increasing heat flux and saturation pressure, but had little dependence with mass flux. When the vapor quality was bigger than 0.6, the local transfer coefficients decreased sharply; the influences of heat flux and saturation pressure on local heat transfer coefficient were small, but closely related to mass flux. Gungor-Winterton correlation was modified based on the experimental R134a flow boiling heat transfer coefficient from present study and published literatures, with -1.71% of the mean relation deviation and 19.24% of the mean absolute relation deviation respectively, showing an obvious improvement.