Ambient air pressure influence on the dynamic Leidenfrost temperature of impacting droplets

Veldhoven, A. van and Capelleveen, B.F. van (2014) Ambient air pressure influence on the dynamic Leidenfrost temperature of impacting droplets.

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Abstract:Water droplets impacting a superheated silicon surface either exhibit boiling via contact (contact boiling), where they make direct contact with the surface, or boiling via a vapour film which separates the droplet from the surface (film boiling, Leidenfrost boiling). The transition from contact to film boiling depends, ceteris paribus, on the surface temperature and the kinetic energy of the droplet. In this study this relationship is investigated for the ambient air pressure. The conditions under which each regime is observed are determined experimentally. After verifying previous results at atmospheric pressure, we show that the transition region occurs at significantly lower temperatures at a set kinetic energy when pressure is decreased. We propose a qualitative relation for this change and present physical arguments as to why the ambient pressure influences this boiling behaviour. We also show that the maximum deformation ß = Dmax/D0 of impacting droplets in the film boiling regime scales with the Weber number, We, as ß~ We 0:35, regardless of surfacetemperature or ambient pressure. This scaling is, within error margins, in line with the theory, which predicts a scaling of ß~We 3/10 .
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Subject:33 physics
Programme:Applied Physics BSc (56962)
Link to this item:http://purl.utwente.nl/essays/65829
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