Heat transfer under spray cooling of laser-textured superhydrophilic titanium surface

The relevance of the work is due to the need to improve the efficiency and uniformity of spray cooling of large surfaces in heat-loaded systems. An experimental study of heat transfer during spray cooling with water of unmodified and laser-textured titanium surfaces measuring 70 × 70 mm² was carried out under heating conditions below the saturation temperature. Laser treatment led to the formation of a developed micro- and sub-microrelief and a significant increase in surface hydrophilicity: the water contact angle decreased from 60° for unmodified titanium to 4.8° for the modified surface. It has been shown that under the same heating and spray cooling conditions, the laser-textured surface provides a lower average temperature and more uniform wetting of the working area, including peripheral regions. At a heat flux density of 14.3 W/cm 2 , the average temperature of the modified surface was 1.4–1.6 °C lower than that of the unmodified surface. The maximum achieved heat flux density increased from 16 W/cm 2 for the original surface to 20 W/cm 2 for the laser-modified surface. It was found that under identical spray cooling and heating conditions, the heat transfer coefficient of the modified surface exceeded that of the unmodified surface by 14–42%, with the relative increase growing as the coolant flow rate increased. The obtained results indicate that increased hydrophilicity promotes more uniform liquid distribution, efficient liquid film renewal, and intensification of single-phase convective heat transfer. The practical significance of this work lies in substantiating the use of laser texturing of titanium surfaces as a method to enhance the intensity and spatial uniformity of spray cooling over large surfaces.