Flooded two-phase flow dynamics and heat transfer with engineered wettability on microstructured surfaces

Flooding caused by excessive droplet feeding on heat dissipation area periodically occurs for droplet-based thermal management, including spray cooling and electro-wetting. The conventional highly wettable texture of surfaces, which is designed for thin film evaporation, has negligible effect on improving thermal performance during flooding. This work examines a combination of micro-pillar structures and engineered wettability that aims to improve the liquid-vapor phase change intensity and heat dissipation rate during flooding. Numerical simulation has been made to investigate the thermal and dynamic impact of the proposed combination structure on boiling and evaporation, with control variables of pillar height and pillar array density. A transient 3-D volume-offluid (VOF) model has been developed to analyze behaviors of bubble growth, coalescence, and departure processes. Parameters including volumetric liquid-vapor mass transfer rate, heat source temperature and heat transfer coefficient are examined. The results indicated the structured surface can reduce bubble sizes and enhance bubble departure rates. The optimized value of pillar height exists. The pillar height has more impact on cooling enhancement than pillar array density when the increased solid-liquid interface area was kept the same.