Enhancement of critical heat flux (CHF) in pool boiling with anodized copper surfaces

Abstract

Present work reports the creation of Cu(OH)2 nanoneedles on a copper surface using an anodization process for extending critical heat flux (CHF) limit in pool boiling applications. Three anodized samples have been prepared by applying three different current densities. Surface morphology and wetting characteristics of the anodized surfaces are presented. The characteristics of nanoneedles depend upon the applied current density. The formation of Cu(OH)2 nanoneedles during the anodization process is confirmed by phase analysis using XRD confirms. The formation of Cu(OH)2 nanoneedles increases the wettability and wickability of the anodized surfaces compared to the plain surface. At high current density, the anodized surfaces show nearly super hydrophilic behaviour. Due to enhanced wettability, the wall superheat required for nucleation is more, and nucleation site density is less for anodized copper surfaces. Bubble departure size is also more for anodized surfaces compared to the plain copper surface. The anodized surfaces show a higher CHF value compared to the plain copper surface. Rewetting of the boiling surface occurs by capillary wicking in the anodized surfaces, which delays the dryout phenomena resulting in CHF enhancement. A maximum enhancement of 39.74% in CHF is observed for the C-9 anodized surface compared to the plain copper surface.