Light-induced enhancement of critical heat flux on TiO₂ coatings with specific surface topology

Although many studies have been carried out to explore boiling heat transfer enhancement via thin-film coating, few studies have concentrated on the precise control of the microstructure, and hence the surface properties, of the coatings and the relationship of the surface properties with the resultant heat transfer performance. Herein, we employed two methods, atomic layer deposition (ALD) and magnetron sputtering (MS), to prepare TiO₂ thin layers on copper substrates. The optical properties and surface topographies of the coatings made by the two methods were investigated with ultraviolet–visible spectra, scanning electron microscopy, and atomic force microscopy. It was found that the microstructure and hence the surface wettability of the coating could be precisely controlled using UV light irradiation. The hydrophilicity over the surfaces obtained by different methods increased in the order of non-coated < MS < ALD. Both the coating thickness and surface topology played an important role in the boiling heat transfer process. Significantly, the sample with the thinnest TiO₂ coating of 40 atomic layers deposited via the ALD method showed the best heat transfer performance, with a critical heat flux (CHF) 68% higher than that of the pure copper surface. We believe this work provides valuable guidance for improving surface modification methods for enhanced boiling heat transfer.