Under forced convection and atmospheric pressure conditions, heat transfer characteristics were studied using an annulus channel of a heater rod with highly-wettable surface. Improvement of phase change heat transfer under boiling and condensation process requires that either liquid heated or vapor cooled can contact a heat transfer surface effectively, but either a vapor layer or a liquid film can be formed repeatedly on the surface during boiling and condensation processes. As oxide

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... tor materials are known to be highly wettable, TiO 2 was coated on a heater rod surface. The Leidenfrost temperature for the TiO 2 coated surface was higher than that for the uncoated surface. Under mass flux conditions from 600 to 1 700 kg/m 2 s, the heater rod surface temperature at variable power conditions was measured. A higher heat flux at the point where the forced convection vaporization started and a larger critical heat flux were observed for the TiO 2 coated surface than that for the uncoated surface.