Test of boiling heat transfer in rectangular channels with offset fins

A boiling heat transfer test system is built to investigate the boiling heat transfer characteristics of two kinds of rectangular channels with offset fins, with R134a as the working medium. The hydraulic diameters of the channels are 1.28 mm and 1.59 mm. The experiments are performed at mass flow rate of refrigerant between 68.5 and 305.5 kg/(m2·s), heat flux between 9 and 42 kW/m2, and saturation pressure between 0.27 and 0.45 MPa, with constant heat flux heating mode. The results show that the channel with smaller hydraulic diameter has stronger heat transfer capability. The influences of heat flux and saturation pressure on boiling heat transfer are related to a value of vapor quality. If the vapor quality is less than this value, the increase of heat flux or saturation pressure would lead to the increase of heat transfer coefficients. If the vapor quality is greater than this value, the boiling heat transfer coefficient will sharply decrease with the increase of vapor quality, and the influences of heat flux and saturation pressure will be much weaker. The value will gradually decrease with the increase of heat flux or saturation pressure. The effect of mass flow rate on boiling heat transfer is related to heat flux. With the increase of heat flux, the influence of mass flow rate tends to the region with greater vapor quality. On the basis of the analysis of these parameters, a new correlation is proposed to predict the boiling heat transfer coefficients of the small sized channels with offset fins under the experimental conditions. © 2017, Press of Chinese Journal of Aeronautics. All right reserved.