Effect of surfactant on boiling heat transfer of structured surfaces

Boiling is a promising cooling strategy for systems with high thermal loads, and enhancing its performance is essential to ensure reliable thermal management to improve the performances of high-heat-flux systems. The use of surfactant additives as a passive enhancement method offers high fidelity because of its competitive cost, simplicity, and convenience in reducing the surface tension of the fluid to facilitate bubble detachment. While surfactant-enhanced boiling has been widely studied, its interaction with engineered surfaces possessing varying levels of cavity activation superheat remains insufficiently explored. In this study, we investigate the boiling characteristics of micropillar structures in surfactant solutions using a non-ionic surfactant, by employing surfaces with different nucleation sites density. Specifically, we compare a Si micropillar surface and a micropillar surface coated with reduced graphene oxide (rGO), which introduces a lower cavity activation superheat. Our results reveal that the combination of surfactants and surface engineering leads to significant improvements in boiling heat transfer, primarily due to modified bubble dynamics such as suppressed coalescence and enhanced nucleation activity. For the uncoated micropillar surface, the addition of surfactants increased the heat transfer coefficient and critical heat flux by up to 154 % and 41 %, respectively. Furthermore, we investigate the boiling-inversion effect of surfactant solutions on micropillar surfaces coated with a wide cavity size distribution. rGO-coated micropillar surface exhibited even greater enhancement, with maximum improvements of 493 % in heat transfer coefficient and 196 % in critical heat flux compared to the plain surface under DI water conditions, which highlight the synergistic effects of surfactant solutions and surface design.