Aug 2, 2007
Mixing and unmixing
I’m on a photography course this week, hence the leaner, meaner Sciencebase posting regime. But, I did find time to chat with technology writer Wayne Smallman on Blah Blah Tech, who pointed out this neat video showing three distinct coloured fluids (dyed corn syrup) being poured into a vessel stirred slowly and then the flow reversed.
You might suspect it is a trick, but it is not. The three coloured liquids end up separated but are not quite as perfectly aligned as they were at the start. Why does this happen? It’s laminar (non-mixing) reverse flow, is tied to the viscous nature of the corn syrup, the smooth flow of the mix and the reverse unmix. I guess the only trick might be that the three fluids are within a thin layer inside the cylinder within which is a second concentric cylinder, the stirrer, oh that and the fact that the “experimenter” cannot actually count! But the essential thing is that corn syrup has a low Reynolds number (this approximates to high viscosity).
Such effects do occur in nature at tidal river confluences where water from different flows barely mix because of differing temperatures and salt concentration. The same phenomena could underlie the seemingly stable patterns we see on Jupiter (it’s lots of viscous layers not mixing).
Anyway, here’s the video
As to what Wayne had to say about it. “Wow, well
effin’
weird, or whatWow, well effin’ weird, or what?!” were his first words. He figured my “science know-how” would do it more justice. Well, personally, I think it’s just effin’ weird too! Seriously, for a more detailed explanation check out this page on the Harvard website. The video has also been discussed on StumbleUpon here.
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David Bradley said,
August 2, 2007 at 10:41 pm
Just in, and kind of related
Animated beer smooth to pour
Researchers from CSIRO and Korea’s ETRI will pour a virtual glass of
beer in San Diego next week at SIGGRAPH 07, the world’s largest computer
graphics conference, to showcase their innovative fluid special effects
software.
CSIRO fluids researcher Dr Mahesh Prakash says the physics of bubble
creation in carbonated drinks like beer is complex.
“As you pour beer into a glass, you see bubbles appearing on what are
called nucleation sites, where the glass isn’t quite smooth,” Dr Prakash
says.
“The bubbles expand to a certain size then rise up in streams to the
surface, where they bump into each other and form a raft of foam that
floats on the top.”
Dr Prakash and his colleagues have captured the maths describing these
processes in software that allows movie makers, film production houses
and others to create super-realistic special effects.