Enhanced pool boiling heat transfer on grooved surfaces by wettability modification with nanoparticle coatings

This work investigates the enhancement of pool boiling heat transfer upon grooved surfaces through wettability modification, which is achieved by domain-selectively coating of highly hydrophilic or hydrophobic nanoparticles. Three wetting configurations are selected, including complete hydrophilicity, hydrophobicity, and 3D heterogeneous wettability. The heterogeneous configuration consists of hydrophilic grooves and hydrophobic fin tops. Compared with the grooved surface without coating, the heterogeneous configuration generates a 114% of increase in the maximum heat transfer coefficient at groove width of 1000 mu m, which is 82 and 19 percentages higher than that for complete hydrophilicity and hydrophobicity, respectively. With adjusting the groove width, the heat transfer coefficient exceeds 100 kW/(m(2) K) at wall superheat of 8 degrees C. High-speed visualization of bubble dynamics demonstrates that the configuration of 3D heterogeneous wettability possesses the advantages of the other two wetting configurations. The hydrophobic fin tops ensure the surface with a high nucleation activity. The hydrophilic coating in grooves promotes bubble departure by driving the bubble to move towards the fin tops, which is also proven by simulation. The combination of groove structure and 3D heterogeneous wettability effectively prevents the massive bubble coalescence at a higher heat flux, which the configuration of complete hydrophilicity can't solve.