Pool boiling enhancement via biphilic surface comprising superhydrophilic TiO₂ and superhydrophobic Teflon arrays

The ever-increasing power density overloads the heat removal capability of miniaturized power electronic devices and thus an efficient liquid cooling method needs to be strategized. Herein, we introduce a biphilic surface consisting of both superhydrophilic TiO₂ and superhydrophobic Teflon. The purpose of this unique combination is to decrease the superheat (T_sat) by efficiently releasing vapor bubbles via the superhydrophobic surface and to increase the critical heat flux (CHF) using efficient wetting supplied by the superhydrophilic surface. The superhydrophilic TiO₂ layer was deposited by the room temperature aerosol deposition method, whereas the superhydrophobic Teflon dots were deposited by the atmospheric supersonic cold spraying method. Each Teflon dot was 1 mm in diameter and the dots were patterned in the form of n×n arrays, where n varied from 1 to 5. The optimal CHF (187 kW·m⁻²), superheat, and effective heat transfer coefficient (4.6 kW·m⁻²·k⁻¹) were observed for the 4 × 4 sample, beyond which the cooling effect deteriorated because of the excessive area covered by the Teflon dots. While the Teflon dots facilitated efficient bubble release, securing sufficient flow passage with the aid of a hydrophilic wetting area was also critical; thus the combination of the superhydrophobic and superhydrophilic surfaces was optimally balanced.