Surface effects on Sub-cooled pool boiling for smooth and laser-ablated silicon surfaces

Abstract

Smooth and laser-ablated silicon surfaces with wettability ranging from SHI (super-hydrophilic) to SHO (super-hydrophobic) are tested in subcooled pool boiling of water. The experiment focuses on the observation of bubble phenomena using a high-speed camera and the measurement of surface temperature using an infrared camera. The formation and departure of vapor bubbles from the surfaces are found to vary significantly with the surface wettability. Nucleate boiling curves show that both the heat transfer coefficient and the critical heat flux increase with the surface wettability changing from SHO to SHI. For the hydrophilic surfaces (smooth and textured), the heat transfer coefficient increases with the heat flux. For the hydrophobic surfaces (smooth and textured), the heat transfer coefficient decreases with the increasing heat flux. The effect of the surface wettability is quantitatively assessed using the surface-fluid factor. It is found that the factor's value increases with the surface wettability changing from SHI to SHO. The surface effect for the hydrophilic surfaces remains relatively constant over the nucleate boiling range, whereas for the hydrophobic surfaces the effect shows significant dependency on the heat flux. These findings are also revealed from the boiling tests on a biphilic surface consisting of a SHO region and a SHI region.