Investigation on R141b convective condensation in microchannel with low surface energy coating and hierarchical nanostructures surface

Abstract

A facile chemical etching method for fabricating copper surface with hierarchical nanostructures and low surface energy coating was adopted in this study. Experimental investigation on the condensation heat transfer of refrigerant R141b in a rectangular microchannel with hydraulic diameter of 0.67 mm was conducted. The mass flux was of the range from 70 kg/(m2 s) to 850 kg/(m2 s). The effects of surface wettability and wall sub-cooled on the flow and heat transfer characteristics were analyzed. For channels with same nanostructures, the increase of contact angle resulted in the increase of heat transfer coefficient, but it had little effect on the pressure drop during condensation. The experimental results showed that the channel with the contact angle of 21.6° had a 12.81% enhancement in the heat transfer coefficient compared to the original copper channel with the contact angle of 12.8°. Moreover, a composite channel with gradient contact angle had a 16.67% enhancement in the heat transfer coefficient compared to the original one. The hierarchical nanostructures had significant influences on the heat transfer characteristics and pressure drop during convective condensation in microchannel. A higher mass flux resulted in higher heat transfer coefficient and pressure drop, while a higher wall sub-cooled temperature caused a lower heat transfer coefficient during the R141b condensation in a microchannel.