Micro/Nano-Engineered Hierarchical Arrays for Enhanced Thin Film Evaporation of Water

This paper focuses on the experimental characterization of enhanced thin film evaporation of water on micro/nano-hierarchical surfaces for lunar ice mining heat pipe. During thermal mining of lunar ice, two approaches can use to re-capture ice on an engineered cold trap: sublimated vapor can be captured near sub-cooled temperature requiring cryogenic heat pipe or superheated vapor can be captured at higher operating temperatures requiring heat pipes with high temperature working fluids. This work aims to investigate the feasibility of conventionally manufactured micro/nano-hierarchical heat pipe with water as the working fluid. One copper micro-pillar surface was manufactured using conventional CNC machining. The square micro-pillar wicks had dimensions of 400 μm width, 500 μm wall-to-wall spacing, and 600 μm height. Micro/nano-hierarchical wick was fabricated by oxidizing the copper micro-pillar surface in a chemical solution to create sharp blade like nanostructures on copper micro-pillar surface. A custom-built water thin-film evaporation test facility was used to run experiments at vacuum pressure, i.e. at saturation pressure (3.2 kPa) for room temperature (25 °C). Deionized water was used as the working fluid. A dry-out heat flux of ~ 79 W/cm2 was achieved for the copper micro-pillar surface, however, the micro/nano-hierarchical wick reached to a heat flux of ~ 151 W/cm2 representing a 90% enhancement from micro-pillar wick.