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SUMMARY:Sailing On Diffusion - Tom Peacock (MIT)
DTSTART:20091022T130500Z
DTEND:20091022T141500Z
UID:TALK20622@talks.cam.ac.uk
CONTACT:Doris Allen
DESCRIPTION:When a density-stratified fluid encounters a sloping boundary\
 , diffusion alters the fluid density adjacent to the boundary\, producing 
 spontaneous along-slope flow. Since stratified fluids are ubiquitous in na
 ture\, this phenomenon plays a vital role in environmental transport proce
 sses\, including salt transport in rock fissures and ocean-boundary mixing
 .  Here we show that diffusion-driven flow can be harnessed as a remarkabl
 e means of propulsion\, acting as a diffusion-engine that extracts energy 
 from microscale diffusive processes to propel macroscale objects. Like a s
 ailboat tacking into the wind\, forward motion results from fluid flow aro
 und an object\, creating a region of low pressure at the front relative to
  the rear. In this case\, however\, the flow is driven by molecular diffus
 ion and the pressure variations arise due to the resulting small changes i
 n the fluid density. This mechanism has implications for a number of impor
 tant systems\, including environmental and biological transport processes 
 at locations of strong stratification\, such as pycnoclines in oceans and 
 lakes. There is also a strong connection with other prevalent buoyancy-dri
 ven flows\, such as valley and glacier winds\, significantly broadening th
 e scope of these results and opening up a new avenue for propulsion resear
 ch.
LOCATION:MR13\, CMS
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