Droplet impact on (superheated) surfaces
Speaker: Detlef Lohse, University of Twente
Series: Baetjer Colloquium
Location: Bowen Hall Room 222
Date/Time: Friday, March 15, 2013, 3:30 p.m. - 4:30 p.m.
A drop impacting on a solid surface deforms before the liquid makes contact with the surface. We directly measure the time evolution of the air layer profile under the droplet using high-speed color interferometry, obtaining the air layer thickness before and during the wetting process. Based on the time evolution of the extracted profiles obtained at multiple times, we measure the velocity of air exiting from the gap between the liquid and the solid, and account for the wetting mechanism and bubble entrapment. The present work offers a tool to accurately measure the air layer profile and quantitatively study the impact dynamics at a short time scale before impact. In case that the liquid droplet impacts on a smooth surface heated above the liquids boiling point, the droplet either immediately boils when it contacts the surface (contact boiling), or without any surface contact forms a Leidenfrost vapor layer towards the hot surface and bounces back (gentle film boiling), or both forms the Leidenfrost layer and ejects tiny droplets upward (spraying film boiling). We experimentally determine conditions under which impact behaviors in each regime can be realized. We show that the dimensionless maximum spreading _ of impacting droplets on the heated surfaces in both gentle and spraying film boiling regimes shows a universal scaling with the Weber number, which is much steeper than for the impact on nonheated (hydrophilic or hydrophobic) surfaces.
Detlef Lohse got his PhD on the theory of turbulence in Marburg/Germany in 1992. As a postdoc in Chicago and later in Marburg and Muenchen he worked on single bubble sonoluminescence. In 1998 he got appointed as Chair of Physics of Fluids at the University of Twente, The Netherlands, where he still is. Lohse's present research subjects are turbulence and multiphase flow, granular matter, and micro- and nanofluidics. Experimental, theoretical, and numerical methods are used in his group. Lohse is Associate Editor of Journal of Fluid Mechanics and several other journals. He is Fellow of the American Physical Society, Division of Fluid Dynamics, and of IoP. He is also elected Member of the German Academy of Science (Leopoldina) and the Royal Dutch Academy of Science (KNAW). He received various prizes such as the Spinoza Prize (2005), the Simon Stevin Prize (2009), the Physica Prize (2011), the George K. Batchelor Prize for Fluid Dynamics (2012), and the Akzo Nobel Prize (2012).