Wicking and Spreading of Water Droplets on Nanotubes

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.