Film boiling heat transfer on a completely wettable surface with atmospheric saturated distilled water quenching

The goal of this study is to investigate film boiling heat transfer (FBHT) on a completely wettable surface (CWS) with atmospheric, saturated distilled water (Tsat ∼ 97 °C). The CWS was fabricated using anodic oxidation of a zirconium rod, to achieve a contact angle of θ ∼ 0° with liquid-spreading and this was driven by capillary-wicking into the nano-scale, needle-shaped structures on the surface. To consider independently the effects of the maximum height εmax of the surface roughness, we investigated a roughed zirconium surface (RZS), which was modified by polishing with sandpaper. Quenching experiments were conducted to evaluate the FBHT; the heat transfer coefficient (hfilm) during FBHT, minimum heat flux (q″min) and minimum film boiling temperature (Tmin) were all larger with the CWS than with the bare zirconium surface (BZS) or on the RZS. Through high speed visualization, we observed that intermittent wetting during FBHT resulted in an unstable liquid-vapor interface in case of the CWS. Therefore, the remarkable ability of the CWS to supply liquid when in contact with the heat transfer surface resulted in clear enhancement of the FBHT performance (i.e., increases in hfilm, q″min and Tmin).