Professor James J Feng's Talk

Nov 30, 2018 - 11:30

Nov 30, 2018 - 12:30

Room 118 Chemical Engg Dept

Seminars

We will describe experiments on two-dimensional bidisperse and polydisperse foams sheared in a Couette device. The bubbles tend to segregate according to their size with larger ones in the middle of the gap and smaller ones closer to the walls. To explain this behavior we first study the migration of a single large bubble in a sea of small monodisperse bubbles. Treating the small bubbles as an effective continuum we find that the Chan-Leal theory for lateral migration of drops can be adapted to predict the bubble migration in our sheared foam.Furthermore the theory can be applied to bidisperse foams where the larger bubbles also interact among themselves. Modeling this interaction as an effective diffusion we are able to predict the observed bubble distributions accurately. We also observed somewhat to our surprise that the size-based segregation always results in a decrease in the apparent shear viscosity for the foam regardless of the initial morphology. Finally we probe the effects of the foam rheology in a wide-gap Couette device. Generally shear-thinning pushes a large bubble inward whereas the first normal stress difference does the opposite. The bubble migration is governed by this competition.Bio-sketch: James J. Feng received his B.S. (1985) and M.S. (1988) from Peking University and his Ph.D. (1995) from the University of Minnesota all in Fluid Mechanics. After a postdoctoral stint at the University of California Santa Barbara he was appointed an associate professor in 1998 at the Levich Institute for Physicochemical Hydrodynamics in New York City. In 2000 he received the NSF Career Award. In 2004 he moved to the University of British Columbia (UBC) in Vancouver Canada as a Canada Research Chair in Complex Fluids and Interfaces with a joint appointment in Chemical and Biological Engineering and Mathematics.He received the CFI (Canada Foundation for Innovation) Leaders Opportunity Award in 2008 and the NSERC (Natural Sci. & Eng. Res. Council of Canada) DiscoveryAccelerator Award in 2009. He was also a UBC Killam Faculty Research Fellow during 2010-2011 and a Visiting Fellow at the Newton Institute Cambridge University in 2013 and 2015. He was elected fellow of the APS (American Physical Society) in 2013 and appointed a Distinguished Scholar in Residence at the Peter Wall Institute for Advanced Studies at UBC for 2014-2015. In 2017 he was an Erskine Fellow at the University of Canterbury in New Zealand and received the CAIMS Research Prize of the Canadian Applied and Industrial Mathematics Society.