imagine that you have three rubber bands, or three strips of stretchy licorice and that you stretch them parallel to each other (even touching), there's no diffusion from one ot the next and you release them the go back to their original state ...
... corn syrup is fairly sticky stuff and with the laminar flow, they are running parallel to each other rather than being intermingled, so it's an impressive demo but I can believe it to be real.
There's some photos around of either two rivers joining or a river flowing into a lake/ocean and because the flows are laminar you can see the silty flow of the river continuing along without merging with the rest of the water around it ...
I could have done without the couple of minutes it took them to announce all the colours of the corn syrup drops they were injecting: if it was a novel you'd say it took ages to get started.
But the laminar flow bit is quite believable: it's all what you're used to. A few years ago people were calling chaos theory "weird", but really we are used to chaotic, or "turbulent" mixing. That video shows what mixing is like when it's not chaotic. You can predict where all the dye particles will go, and you can reverse the mixing to unmix them. In chaotic mixing you can't predict where the dye will go, and you can't unmix it.
And what makes you think the backwards part isn't just reversing the video. The movement both ways looked jerky, as if they'd stirred it smoothly and then edited the footage to make it look jerky in a different pattern forward and backward.
It's the hand movements I was specifically watching. They aren't a reversal of each other as they would be if you played the film backwards. The fingers are curled turning the handle clockwise and much straighter anticlockwise.
That's right, they've used corn syrup to lower the Reynolds number (http://en.wikipedia.org/wiki/Reynolds_number) of the flow down to where it's reliably laminar. If they'd used water they'd probably have had to use a clockwork mechanism to turn the cylinder, instead of their hands, and it would have taken hours. By which time the dye would probably have diffused anyway.
This is the sort of regime insects experience: water behaves to them the way very viscous fluids would behave to us, because their inertial forces are so much smaller in comparison.
The air is drawn in from the room at the back through a filter (to remove environmental particles) and then pushed out. The laminar flow means that any contaminating particles introduced into the hood (i.e on the surface of glassware, on your labcoat) are pushed in a straight line out of the hood. You work from left to right (or right to left) to minimise contamination.
So, for instance, if I was pouring agar plates I would start from the top right hand corner and set out a line of plates, pour those plates, move forward, set out a new line and then pour those plates. You never cross over the "sterile" environment.
As it's shown to us, the three drops could have been in three separate concentric compartments with transparent walls, and so not had the opportunity to mix with one another. Not that I don't believe it, but that seems a bit of a design flaw in a demo like this.
True, but the demonstration of reconstituting the drops by reversing the process would work just as well with drops isolated by walls, or indeed with a single drop.
What the movie needs at the end is a replay from a camera that had been set up to look down from above.
the demonstration of reconstituting the drops by reversing the process would work just as well with drops isolated by walls, or indeed with a single drop
Sure, that's still impressive, but I guess that they used three different colours because non-mixing was part of what they wanted to demonstrate.
Mm, a top-down camera would definitely be a good addition.
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... corn syrup is fairly sticky stuff and with the laminar flow, they are running parallel to each other rather than being intermingled, so it's an impressive demo but I can believe it to be real.
There's some photos around of either two rivers joining or a river flowing into a lake/ocean and because the flows are laminar you can see the silty flow of the river continuing along without merging with the rest of the water around it ...
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But the laminar flow bit is quite believable: it's all what you're used to. A few years ago people were calling chaos theory "weird", but really we are used to chaotic, or "turbulent" mixing. That video shows what mixing is like when it's not chaotic. You can predict where all the dye particles will go, and you can reverse the mixing to unmix them. In chaotic mixing you can't predict where the dye will go, and you can't unmix it.
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Cynic
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This is the sort of regime insects experience: water behaves to them the way very viscous fluids would behave to us, because their inertial forces are so much smaller in comparison.
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So, for instance, if I was pouring agar plates I would start from the top right hand corner and set out a line of plates, pour those plates, move forward, set out a new line and then pour those plates. You never cross over the "sterile" environment.
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(Anonymous) 2007-10-11 07:33 am (UTC)(link)Don't expect to see this in normal life though, conditions had to be set up perfectly for this to happen.
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What the movie needs at the end is a replay from a camera that had been set up to look down from above.
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Sure, that's still impressive, but I guess that they used three different colours because non-mixing was part of what they wanted to demonstrate.
Mm, a top-down camera would definitely be a good addition.