Bubble dynamics and heat transfer on a wettability patterned surface

In this paper we studied the enhancement of heat transfer on hydrophilic-hydrophobic patterned surface in a transparent mini chamber. Hydrophobic islands on hydrophilic networks were micro fabricated as patterns on a 1 mm × 1 mm indium-tin-oxide (ITO) glass heater. The hydrophobic islands with size of 100 μm × 100 μm and pitch distance 100 μm are self-assembled monolayers (SAM) of (1H,1H,2H,2H)-Perfluorodecyldimethylchlorosilane (FAS) with contact angle of 100°. The input heat flux for the heater ranges up to 300 W/cm2. It is shown that the critical heat flux (CHF) on the wettability patterned surface was enhanced by 90% in comparison with a hydrophilic surface. The visualization results also show that the mechanism for enhancing heat transfer coefficient (HTC) of a wettability patterned surface is caused by increasing the active nucleation sites, decreasing the bubble departure diameter, remaining residual bubbles, and activating more bubble interactions. Patterns increase the CHF by moderating the Helmholtz instabilities, preventing the formation of an insulating vapor layer.