Heat transfer during dropwise condensation of steam over a mirror polished sol-gel coated aluminum substrate

Abstract

Dropwise condensation (DWC) is a promising heat transfer mechanism in new trends of thermal management and power generation systems to enhance the heat transfer during condensation. Creation of surfaces which can promote dropwise condensation is one of the main issues. For this purpose, a heat transfer surface that can maintain stable dropwise condensation, using hybrid organic-inorganic sol-gel silica coatings functionalized with methyl groups over an aluminum substrate, is developed and tested. This coating displays mildly hydrophilic behavior. Condensation of steam flowing on this surface occurs in dropwise mode with heat transfer coefficient values equal to 150–180 kW m−2 K−1 in the heat flux range between 150 and 510 kW m−2. The importance of the coating thermal resistance is discussed in the paper. The measured heat transfer coefficient is high compared to previous studies of DWC on metallic – and in particular aluminum - substrates. This type of surfaces paves the way to a cheap and green route to promote stable DWC on aluminum substrates without using fluorocarbons or controlled roughness patterns.