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SUMMARY:(Capillary) Bridge over Troubled Water: establishing the role of s
 urfactants in increasing drag over superhydrophobic surfaces - François J
  Peaudecerf (University of Cambridge)
DTSTART:20170308T130000Z
DTEND:20170308T140000Z
UID:TALK71508@talks.cam.ac.uk
CONTACT:Julius Bier Kirkegaard
DESCRIPTION:Superhydrophobic surfaces (SHS) can potentially achieve drag r
 eduction for both internal and external flow applications. However\, exper
 iments have provided inconsistent results\, with many studies reporting si
 gnificantly decreased performance. While a complete explanation is yet to 
 be found\, it has been proposed that surfactants\, ubiquitous in flow appl
 ications\, could be responsible. However\, testing this hypothesis has bee
 n challenging. Even careful experiments with purified water have shown lar
 ge interfacial stresses\; adding surfactant yields only small drag increas
 es\, potentially revealing a pre-existing contamination of the interface. 
 Other common physical processes\, such as thermal Marangoni stresses and i
 nterface deflection\, could also explain the lower performance.\nWe addres
 s this question with numerical simulations\, including surfactant kinetics
 \, and SHS experiments in a micro-channel\, where we control temperature g
 radients and interface deflections. By imposing a time-dependent pressure 
 gradient\, we are able to drive complex interface dynamics that can only b
 e explained by surfactant gradients. Our results demonstrate the role of s
 urfactants in increasing drag over superhydrophobic surfaces in realistic 
 flow conditions.
LOCATION:MR11\, Centre for Mathematical Sciences\, Wilberforce Road\, Camb
 ridge
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