Floating on Air
Department of Applied Physics,
University of Twente, Enschede, Netherlands
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 and the volume of the entrained droplet. This volume shows a maximum as function of the impact velocity. We physically explain this maximum as a balance between capillary and inertial effects. The experiments are complemented by numerical simulations, based on potential flow for the impacting droplet and a lubrication theory for the gas layer in between the droplet and the surface, and by scaling laws which we derived analytically.
The work is then extended in various directions: For the drop impact on a hot surface heated above the liquid’s 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 also look at the maximum spreading of impacting droplets on such heated surfaces, which is much further than for the impact on non-heated surfaces and shows universal scaling behavior. We also explain under what conditions splashing is achieved and connect it to the vapor and gas flow under the droplet.
In the lecture we will not only show the (beautiful!) phenomena with high-speed visualisations and account for them theoretically, but we will also address various applications of our research in the industrial context.
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. Both 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 AkzoNobel Prize (2012).
Snacks will be provided at 11:30am prior to the Colloquium
RSPE tearoom Oliphant Building 60, ANU campus