Spontaneously grown boehmite structures improve pool boiling heat transfer on aluminium surfaces

Abstract

Superhydrophilic nanostructures that function to improve wettability have been proven to enhance boiling heat transfer. Herein, the mechanism for enhancing pool boiling heat transfer on aluminium surfaces by spontaneous growth of boehmite layers in boiling water was comprehensively explored. The morphology and chemical composition of the nanolayers formed on boiling water-treated (BWT) aluminium surfaces were characterized. The surfaces were covered with abundant cross-linked nanosheets and dispersed microclusters after BWT, which were verified to be boehmite. In addition, the effect of BWT time on the thickness and wettability of the boehmite layer was quantitatively studied. The results showed that the aluminium surfaces became superhydrophilic after BWT for 30 minutes, and the thickness and morphology of the boehmite layer achieved near stable after processing beyond 3 hours. Further, BWT samples exhibited excellent thermal performance and reproducibility during pool boiling tests. Compared to the plain copper surface, a 49% higher critical heat flux and a 79.6% higher heat transfer coefficient were demonstrated on BWT aluminium alloy surfaces. The stable and dense boehmite layer was proven to significantly enhance the boiling heat transfer of the substrate by increasing the effective nucleation sites, specific surface area, wettability, and capillary rewetting ability.