Enhancement of a heat transfer performance on the Al6061 surface using microstructures and fluorine-doped diamond-like carbon (F-DLC) coating

Abstract

Dropwise condensation (DWC) is one of the most important phenomena to improve the heat transfer performance of steam condensation system. To promote DWC on hydrophilic metals, non-metallic hydrophobic promoters are coated on the surface. Non-metallic coatings are relatively easy to be degraded due to lack of mechanical and chemical properties. In this study, fluorine-doped diamond-like carbon (F-DLC) was used to obtain DWC on Al6061. Prior to F-DLC coating, microtextures were fabricated on Al6061 for the structural wettability control. DWC was successfully obtained with a small size of condensates after the microblasting and nanostructured F-DLC coating on Al6061. The synergic effects of microtextures with Cassie-state contact angle and hydrophobicity of nanostructured F-DLC led the superhydrophobic transformation of the surface. The contact angle increased about 115% from 66° to 142° after the microblasting and nanostructured F-DLC coating. The resulting DWC improved heat transfer performance of Al6061 significantly, 205%, as the dropwise condensates were rapidly eliminated from the surface. The variations on contact angle hysteresis before and after the steam condensation analysis revealed that the superhydrophobicity and DWC mode can be stably maintained under the steam condensing conditions.