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SUMMARY:Bubble instabilities in rigid and flexible vessels - Anne Juel (Un
 iversity of Manchester)
DTSTART:20101105T160000Z
DTEND:20101105T170000Z
UID:TALK27007@talks.cam.ac.uk
CONTACT:Dr C. P.  Caulfield
DESCRIPTION:The displacement of a liquid by an air finger is a generic two
 -phase flow that underpins applications as diverse as microfluidics\, thin
 -film coating\, enhanced oil recovery\, and biomechanics of the lungs. I w
 ill present two intriguing examples of such flows where\, firstly\, multip
 le states of bubble propagation are generated by a simple change in tube g
 eometry\, and secondly\, flexible vessel boundaries suppress viscous finge
 ring instability.\n\n1) Microscale process engineering requires precise co
 ntrol of bubbles and droplets. We investigate geometry-induced control and
  find that a centred constriction in the cross section of rectangular tube
 s can lead to new families of steadily propagating bubbles\, which localiz
 e in the least-constricted regions of the cross section. Tuning the constr
 iction geometry can cause a switchlike transition from centered to localiz
 ed bubbles at a critical value of the flow rate: a mechanism for flow-rate
 -driven bubble control. The accompanying large change in bubble volume cou
 ld be significant for liquid recovery applications.\n\n2) We investigate t
 he radial displacement of a viscous liquid by an air\nbubble in an elastic
  Hele-Shaw cell\, i.e. an elastic membrane separated from a glass plate by
  a thin liquid film. We find that the presence of the elastic membrane sup
 presses the viscous fingering instability that always arises in the rigid 
 configuration. The interface now becomes unstable beyond a critical flow r
 ate that decreases as K^{-1/4} (K is the bending stiffness of the membrane
 )\, and we propose a physical mechanism for damping that agrees with our e
 xperimental findings.
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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