| Popis: |
In this study, feasibility of nanoparticles-assembled bi-porous structure on a heating surface is focused on in order to develop a new cooling device of on-vehicle inverters. In order to coat nanoparticles as a porous layer, boiling adhesion method (BAM) is originally introduced, in which water or water-ethanol solution with mono-dispersed nanoparticles is dropped or sprayed onto a high temperature surface, and then the nano-particles deposit onto the heat transfer surface during the boiling. In addition, it is expected that boiling bubbles initially produce micro to mini scale of pores at the same time. This unique foam-like porous layer has both a micro to mini-pore structure with high permeability for discharging vapor and nano scale pore structure with a much stronger capillary effect as well as high wettability. For these reasons, it is expected to increase the boiling heat transfer performance, including critical heat flux, due to highly enhanced active liquid-vapor exchange. From fundamental experiments, it is confirmed that the boiling adhesion method can produce bi-porous structures composed of nano-scale pores and micro-scale pores and that a water droplet intensely boils and evaporates on a high temperature wall with the nanoparticles bi-porous layer even under Leidenfrost conditions. In addition, the life time of the droplet drastically decreases both in a high temperature and low temperature regimes, which proves that the nanoparticles-assembled bi-porous layer has quite a high potential to enhance the boiling heat transfer under high heat flux conditions. |
