Experimental flow boiling heat transfer in a small polyimide channel

New experimental flow boiling heat transfer results averaged along a very low thermal conductivity polyimide channel are presented. The experimental setup consists of a horizontal, 285 mm-long, 2.689 mm inner diameter polyimide tube, heated by a counter-current, external water flow. R245fa is the working fluid, at mass fluxes ranging from 100 to 500 kg m−2 s−1, heat fluxes from 15 to 55 kW m−2, and three saturation temperatures: 35, 41 and 47 °C. Heat transfer coefficient results are presented averaged over the whole polyimide channel for mean vapor qualities ranging from 0.05 to 0.80. High-speed flow visualization was possible downstream of the polyimide tube. Parametric analysis of the results revealed a strong dependence of the heat transfer coefficients on mass flux and vapor quality, and mild influence of the heat flux and the saturation temperature. The experimental database is compared with results obtained for metallic tubes of comparable size in similar experimental facilities. Last, experimental results are contrasted with several heat transfer methods, of which a convective model for annular flow well predicts the heat transfer coefficient values and convective boiling trends.