Recently, there has been intensive research on the use of nanotechnology to improve the wettability of solid surfaces. It is well-known that nanostructures can improve the wettability of a surface, and this is a very important safety consideration in regard to the occurrence of boiling crises during two-phase heat transfer, especially in the operation of nuclear power plant systems. Accordingly, there is considerable interest in wetting phenomena on nanostructures in the field of nuclear heat transfer. Much of the latest research on liquid absorption on a surface with nanostructures indicates that liquid spreading is generated by capillary wicking. However, there has been comparatively little research on how capillary forces affect liquid spreading on a surface with nanotubes. In this paper, we present a visualization of liquid spreading on a zircaloy surface with nanotubes, and establish a simple quantitative method for measuring the amount of water absorbed by the nanotubes. We successfully describe liquid spreading on a two-dimensional surface via one-dimensional analysis. As a result, we are able to postulate a relationship between liquid spreading and capillary wicking in the nanotubes.
Self-assembled foam-like graphene (SFG) structures were formed using a simple nucleate boiling method, which is governed by the dynamics of bubble generation and departure in the graphene colloid solution. The conductivity and sheet resistance of the calcined (400°C) SFG film were 11.8 S·cm–1 and 91.2 Ω□−1, respectively, and were comparable to those of graphene obtained by chemical vapor deposition (CVD) (~10 S·cm–1). The SFG structures can be directly formed on any substrate, including transparent conductive oxide (TCO) glasses, metals, bare glasses, and flexible polymers. As a potential application, SFG formed on fluorine-doped tin oxide (FTO) exhibited a slightly better overall efficiency (3.6%) than a conventional gold electrode (3.4%) as a cathode of quantum dot sensitized solar cells (QDSSCs).
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