Experimental investigation of pool boiling heat transfer and critical heat flux of nanostructured surfaces

The present study aims to investigate the effect of pool boiling on nanostructured surfaces. For this purpose, nanocoating was performed on aluminum surface specimens by anodizing and their boiling heat transfer characteristics were compared with those of bare surface of aluminum. Also, the critical heat flux and boiling heat transfer coefficients were evaluated experimentally. Chromic acid and sulfuric acid solutions were utilized as the electrolytes. Prior to anodizing, sandblasting and etching were applied as mechanical and chemical treatments of the surfaces. The coating was performed over three different durations. The maximum critical heat flux was observed to occur in samples which had been weakly etched and anodized for 30 min in the sulfuric acid solution. Critical heat flux increased by 8% compared with that of the untreated aluminum alloy surface. Also, boiling heat transfer coefficient increased by 159% in weakly etched samples. In order to investigate surface characteristics, contact angle and atomic force microscope (AFM) images were used. The surface roughness and real area were measured in six samples. The AFM images indicated that surface roughness increased with anodizing time. The change in roughness was more pronounced in surfaces treated in the chromic acid solution compared with those treated in the sulfuric acid solution.