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SUMMARY:Unsteady flow of yield stress materials - Dr Miguel Moyers-Gonzale
 z\, School of Mathematics &amp\; Statistics\, University of Canterbury\, N
 ew Zealand
DTSTART:20141112T140000Z
DTEND:20141112T150000Z
UID:TALK55098@talks.cam.ac.uk
CONTACT:Vanessa Blake
DESCRIPTION:Viscoplastic materials such as Bingham or Heschel Bulkley flui
 ds have a yield stress which must be exceeded before they flow. Their beha
 viour\nlies somewhere between liquids and solids. In this talk I will pres
 ent experimental and numerical results for two unsteady flow problems invo
 lving a viscoplastic material.\n\nIn the first\, we look at laminar unstea
 dy pipe flow of a Carbopol gel\, which is a model viscoplastic fluid. By l
 ooking in detail at the solid-fluid transition of this material\, we found
  a strong coupling between the irreversible deformation states and the phe
 nomenon of wall slip (where the fluid behaves as if it is sliding along th
 e wall). In addition\, the dependence of the slip velocity on the wall she
 ar stress reveals a Navier-type behaviour only within the fluid regime\, w
 hich provides strong evidence that the wall slip phenomenon is directly co
 upled to the solid-fluid transition.\n\nThe second is the Landau-Levich 'c
 hocolate dipping' problem\, whereby a plate is raised out of bath of visco
 us (in this case viscoplastic) fluid. The fluid drains off the plates as i
 t is raised. The validity of the classical Landau-Levich scaling result is
  investigated via experimental measurement of the width of the coating fil
 m for different values of the yield stress for the slip and no-slip cases.
LOCATION:Lecture Theatre 1\, Department of Chemical Engineering  and Biote
 chnology\, New Museums Site
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