Optimum ratio of hydrophobic to hydrophilic areas of biphilic surfaces in thermal fluid systems involving boiling

Pool boiling has a high heat removal capability and is considered as one of the most effective cooling methods due to utilization of latent heat of vaporization. Surface wettability plays a key role in boiling heat transfer since it controls the contact line between liquid, gas, and solid phases. Here, surfaces with mixed wettability (biphilic) were fabricated for assessing the effect of biphilic surfaces on bubble dynamics and boiling heat transfer as well as for the determination of an optimum hydrophobic area to the total surface area (A* = A_Hydrophobic/A_total) to achieve the best heat transfer performance. Pool boiling experiments were conducted on biphilic surfaces with A* ranging from 0.19% to 95%. It was shown that biphilic surfaces directly affected both the critical heat flux (CHF) and boiling heat transfer. According to the experimental results, the surface with A* of 38.46% delivered the highest CHF enhancement (197 W/cm², and maximum boiling heat transfer enhancement of 103%) among the tested biphilic surfaces. To represent a better understanding of related heat transfer mechanisms, bubble dynamics was obtained using a high-speed camera system. Visualization results revealed that bubble formation took place sooner on biphilic surfaces with A* of higher than 38.46%, thereby triggering the generation of vapor blanket on the surfaces and CHF occurrence at lower heat fluxes.