Three-Dimensional Biphilic Structures Elevating Pool Boiling Heat Transfer

Abstract

Ideal combination of micro/nanostructure and wettability enables dense bubble nucleation, rapid bubble departure and lateral liquid replenishing. Creating such combination is crucial for enhanced boiling heat transfer; yet it still remains challenging. Herein, to improve the boiling heat transfer performance, a configuration consisting of micropillars with hydrophobic tops and the in-between superhydrophilic microchannels was created using a one-step laser milling approach. By visualizing the bubble dynamics, we elucidated that the hydrophobic tops of the micropillars allowed efficient bubble nucleation and evolution while the superhydrophilic microchannels isolated the aggregation of bubbles for rapid departure. Moreover, the lateral liquid replenishing was as well ensured by the inherent strong capillary of the microchannels due to the additional Laplace pressure gradient. The exquisite coordination between the 17.1% area fraction of hydrophobic tops of the micropillars and the 0.3 mm-depth superhydrophilic microchannels contributed to a critical heat flux of 2098 kW/m2 and heat transfer coefficient of 80 kW/m2·K. The obtained critical heat flux was 98.5% higher than the plain copper and showed maximum 221.8% improvements compared to previous research. Our work presented new examples of configuring the combination of structure and wettability. These configurations can be tailored to achieve various functionalities for different applications.

Keywords: Bubble dynamics, biphilic surfaces, superhydrophilic, laser milling, pool boiling