Bubble dynamics and heat transfer performance on micro-pillars structured surfaces with various pillars heights

摘要

Micro-pillars structured surfaces have been found to enhance nucleate boiling significantly, as compared with smooth surfaces. In this study, a VOF-based (volume of fluid) numerical model is developed to investigate the single-bubble dynamics on micro-pillars structured surfaces in nucleate boiling, aiming to understand the effect of pillar height (h) on boiling enhancement. The model is solving by the commercial CFD (computational fluid dynamics) solver Fluent. The results show that increasing h modifies remarkably the bubble morphology. An interesting phenomenon is observed for larger h that the bubble bottom undergoes expansion, shrinkage, and re-expansion in gaps between micro-pillars in the growth stage, so that a mushroom-like bubble is generated, with a small root and a large head. The modified bubble morphology promotes the bubble departure, leading to a shorter departure time. Moreover, increasing h also enhances both evaporation rate in the microlayer and evaporation rate on the liquid-vapor interface, and thereby increasing bubble departure diameter. Thus, the shorter departure time and larger departure diameter are responsible for the enhanced boiling heat transfer on micro-pillar structured surfaces with larger h.