Synergistic Effects of Hydrophilic-Hydrophobic Porous Structures for Enhancing Nucleate Pool Boiling Heat Transfer

Abstract

Boiling is an efficient mode of heat transfer and has important applications that use high heat flux systems. However, a single wettable boiling surface is not appropriate for the dual requirements of low superheat for nucleation and high critical heat flux. Here, we present a hydrophilic composite and a functional hydrophilic-hydrophobic partitioned porous structure that significantly improves boiling heat transfer performance via a double-sintering process. The superheat requirement for the onset of nucleate boiling decreased from 2°C on the single hydrophilic porous structure to 1°C on the hydrophilic-hydrophobic porous structure, the critical heat flux was reduced by 3.3% in the early stages of boiling (below 250 kW/m²), the heat transfer efficiency increased by 20%, and the heat transfer was comparable to that of the hydrophilic porous structure. Bubble dynamics were observed using a high-speed camera. The results demonstrate that the bubble nucleation sites mainly occur in the hydrophobic region and this is attributed to a decrease in the energy barrier for nucleation. The bubble dynamic statistics revealed that the product of the diameter of the bubble and the bubble escape frequency are similar for composite surfaces and hydrophilic porous surfaces, which is consistent with Zuber’s conclusion. The synergistic effect of the hydrophilic-hydrophobic partitioned porous structure can promote nucleation in the hydrophobic region and retain capillary suction for liquid reflux in the hydrophilic region to enhance boiling heat transfer. This work enables the large-scale deployment of heat exchanger surface processing technology because of its low cost, availability, and reliability.