Unaffectedness of improved wettability on critical heat flux enhancement with TiO2 sputtered surface

Abstract

The improvement of surface wettability has been considered as a key factor of nanofluid critical heat flux (CHF) enhancement. However, the authors found that improved wettability did not influence on CHF at all. In this paper, the independent effect of surface wettability on CHF was experimentally investigated. The wettability of surface was controlled by DC plasma sputtering of TiO2 without any formation of porous structure. By controlling sputtering time of TiO2 from 12 s to 600 s, various contact angles were obtained from 62° to 11°. Compared to 82° of the bare surface, wettability was improved for all sputtered surface, but CHF was not changed meaningfully. The CHF data had no meaningful relationship at all with the variation of contact angle, so we concluded that wettability cannot be a main parameter of CHF and its enhancement.