2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

The Effects of Nano Particles on the Leidenfrost Phenomenon

C-K Huang and C-K Lin
National Taipei University of Technology, TW

Keywords:
nano particle, Leidenfrost, droplet boiling

Abstract:
When small amount of liquid mass is deposited on a hot enough solid surface, the liquid may not evaporate rapidly as we expect. Instead, the liquid mass evaporates slowly with a vapor film beneath. This is called the Leidenfrost phenomenon. The Leidenfrost temperature defines the boundary between transition boiling regime with at least partial wetting of the surface, and film boiling regime in which the liquid is separated from the surface by a vapor film. The phase change heat transfer before the Leidenfrost transition is orders of magnitude higher than the value after the Leidenfrost phenomenon starts. Parameters influencing the Leidenfrost transition include size of the liquid mass, deposition velocity, liquid subcooling, solid thermal properties, surface roughness, liquid surface tension and additive. In this study, experiments are intended to simulate Leidenfrost’s original experiment to observe the effects of nano particles on the Leidenfrost phenomenon. Two kinds of nano particles, TiO2 and Al2O3, were dissolved into distilled water (2% mass fraction), and the prepared liquid was deposited on a polished aluminum alloy 6061 heated surface. A precision syringe was used to deposit and control the droplet volume at 20 l. Experimental results are exhibited as evaporation curves. The temperature of rapid raise of curves defines the Leidenfrost temperature. Experimental results show that the nano particles increase the Leidenfrost temperature, and make the low-speed heat transfer of film boiling start to occur at a higher surface temperature. On the other hand, TiO2 particles prolong the evaporation time in the film boiling region, while Al2O3 particles shorten it.

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