Superwetting copper hydroxyl nitrate wicks for the sweating-boosted air cooling on finned tubes

Abstract Air cooling system (ACS) gains more attention because of the global water crisis, however its applications are limited by the inherent low heat transfer coefficient of air. Evaporative heat transfer is promising to address the challenge in ACS. By mimicking the primary mechanism of mammals to effectively dissipate heat during physical exercise, a sweating-boosted air cooling (SBAC) strategy is proposed and experimentally demonstrated on plain walls in our previous study. We have shown that the copper oxide (CuO) wicks played a critical role in the thermal performance of SBAC. In this research, we develop superwetting copper hydroxyl nitrate (Cu-HDS/NO 3 ) wicks to further enhance SBAC on finned copper tubes. Cu-HDS/NO 3 crystals are directly synthesized on copper substrates via a three-step wet chemical oxidization process. The time-dependent surface morphology and crystal structures of Cu-HDS/NO 3 are characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The newly developed wicks are superior in spreading water and thermally stable for SBAC under a wide range of working conditions. The performance of SBAC on a finned copper tube coated with Cu-HDS/NO 3 wicks has been experimentally evaluated. The SBAC on as-developed wicks enhances the effective heat transfer coefficient (HTC) by 379.9% and reduces the total thermal resistance by 76.1%. The effects of wall temperature and air velocity on the thermal performance of SBAC are systematically characterized. We have shown that the super wicking capacity well complements the SBAC at low air velocity, hence makes the super wicking Cu-HDS/NO 3 more attractive in the practical applications of SBAC. The developed Cu-HDS/NO 3 wicks are promising in implementing SBAC strategy over current ACS.