Capillary Performance of Nanoporous Aluminum Braided Wicks Prepared by Anodic Oxidation

With the rapid development of two-phase heat exchangers, the further improvement of the capillary performance of their internal wick faces a great challenge. As an important technology in the surface treatment of aluminum alloys, anodic oxidation has been widely used to develop various functional nanostructures. In this study, nanopores with diameters of 30-40 nm were fabricated on the surface of aluminum fibers through anodic oxidation under an oxalic acid system. Results showed that anodizing increased the specific surface area of the aluminum braid by 163 times, and changed its surface wettability from hydrophobic to superhydrophilic. A significant reduction in the effective capillary radius can substantially increase the capillary force of aluminum braids on the basis of capillary theory. Therefore, the nanoporous aluminum braids can be used as a novel wick in the vapor chamber to improve its capillary performance. Capillary rate-of-rise tests with ethanol and acetone were performed to characterize the capillary of this novel wick structure. Infrared thermal imaging was utilized to monitor the capillary rise of aluminum braided wicks. The capillary force of the anodized wicks was greater than that of a normal wick, and the maximum capillary rise height was 81 mm. The nanoporous aluminum braided wicks prepared by anodizing could be applied in heat transfer.