Changes in Boiling Heat Transfer Performance by Controlling the Oxidation State of Copper Nanoparticles

The wettability of the copper nanoparticle layer formed on the boiling heat transfer surface was controlled by combining it with an appropriate heat treatment, and the copper nanoparticle layer was applied to a saturated pool boiling experiment using pure water. Specifically, a copper nanoparticle layer was formed by applying copper nanoink to the end surface of a copper cylinder, which serves as the heat transfer surface, and a hydrophobic Cu₂O particle layer was obtained by heat treatment under reduced pressure. Next, a pattern of CuO regions exhibiting hydrophilicity was formed on the Cu₂O particle layer by irradiating it with a carbon dioxide laser. When the entire boiling heat transfer surface was made into a hydrophilic surface (CuO), the critical heat flux (CHF) value was about three times higher than that of a smooth copper surface. In addition, by finely refining the pattern of the CuO region, the CHF value could be increased to 95% of that of a completely hydrophilic surface while keeping the area of the hydrophilic region constant (75%).

Dropwise Condensation using Composite Coating of Copper Nanoparticles and Particulate Polymers

Dropwise condensation has a better heat transfer rate than film condensation, but surface treatment methods that can maintain dropwise condensation for a long time are still in the development stage. In this study, we propose a method to spray a composite of copper oxide nanoparticles with polytetrafluoroethylene and polyimide as binders onto the heat transfer surface.