Effect of surface wettability on boiling and evaporation

Titanium dioxide, TiO2, is one of the photocatalysts that has a very unique characteristic. The surface coated with TiO2 exhibits extremely high affinity for water by exposing the surface to UV light and the contact angle decreases nearly to zero. On the contrary, the contact angle increases when the surface is shielded from UV light. We applied this superhydrophilic nature to enhancement of boiling and evaporation heat transfer. Experiments of pool boiling and evaporation of single water droplet have been performed to manifest the effect of high wettability on heat transfer characteristics. Both of TiO2-coated and non-coated surfaces were used for comparison in each experiment. It is found that (1) the critical heat flux (CHF) of TiO2-coated surface is about two times larger than that of non-coated one, and (2) Leidenfrost temperature increases as the contact angle decreases. The superhydrophilic surface can be an ideal heat transfer surface.