Surface wettability effect on nucleate pool boiling heat transfer with titanium oxide (TiO2) coated heating surface

Abstract

Here, we explored the effect of surface wettability on nucleate pool boiling heat transfer performance by employing hydrophilic titanium oxide (TiO2) layer coated on a cylindrical plain aluminum 6061 (Al 6061) as a reference. The comparative heating surfaces are the plain, TiO2 coated and TiO2-water repellent coated surfaces. The water repellent was superimposed on the reference heater before TiO2 coating on it to depress hydrophilicity nature of TiO2. The boiling tests were carried out in steady-state condition and in saturated water under one atmosphere during the entire experiment. The nucleate boiling performance depends on the level of surface wettability. Results showed that TiO2 coated surface contributed to the increasing of nucleate pool boiling performance by 64.1% in comparison to that of the plain surface. The TiO2-water repellent coated surface gave a less enhanced performance than the TiO2 coated surface, and it is underperformed over the plain surface when the wall superheat (ΔT) > 12.3 °C. Boiling visualization demonstrated the augmented heat transfer mechanism by showing more active nucleation sites and more bubble departure frequency on the TiO2 coated surface.