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  • -Music-

  • When we were working with Desten and his high-speed camera

  • We tried one of our favourite experiments, Neil's burning cauldron

  • Now, the demonstration consists of two parts

  • The first one is taking a metal vessel, and pouring in liquid oxygen

  • When you watch it normally, it's just pouring stuff out of a thermal flask

  • What's interesting in high-speed, is that as it goes in, the oxygen actually breaks up

  • -Music-

  • There's been a lot of research by different people about how liquids fall

  • And, it's quite complicated, because it's a combination of surface tension, viscosity

  • But here, you have the added complication that the liquid is very cold, compared to the air

  • So it's actually boiling

  • When it goes in, there's a sort of cloudiness

  • But that's just the water vapour in the air

  • You end up with a rather foggy looking liquid

  • -Music-

  • The second part of the experiment is dropping in a piece of hot charcoal

  • The first thing that quite surprises me is that as this piece of charcoal comes down

  • and hits the surface, it actually bounces up again

  • -Music-

  • But, because it bounces up again, and presumably the hot charcoal has vaporised

  • a bit more oxygen

  • It actually starts burning, when it's in the air

  • And as it comes down again, it burns quite brightly

  • -Music-

  • I think about it for a moment, you've got a very hot piece of charcoal

  • on top a very cold liquid

  • So the liquid immediately under the charcoal will be boiling

  • and will be generating gas

  • Which probably, causes the charcoal almost to float above the surface of the liquid

  • -Music-

  • And if you look carefully, you can see that the charcoal keeps on burning brightly

  • And then, it goes dimmer again

  • And then bright, and dim, it's sort of pulsing

  • And I think, and again, I haven't done any control experiments

  • but it seems quite likely, that what happens is that, when it's sitting on oxygen gas

  • It burns rather more brightly, it uses up that gas

  • And then sinks down onto the surface of the liquid

  • The hot charcoal vaporises some more, and it starts burning again

  • lifted up on the oxygen cloud, so it goes up and down

  • But, the key point

  • is that, I as a chemist, see that something that I thought was fairly straight forward

  • is actually more interesting, and more complicated than I thought

  • Not to, inflame things or try and make too much of the chemistry, physics rivalry

  • But it seems like in some of those thoughts we had, it's like the chemistry is well understood

  • But it's the physics that's really interesting, and add in this extra dimension when we see it in high-speed

  • I think that's a very sensible point

  • Because, very often, in the short term, in the short time scale, it is the physics

  • the mixing of the reactions, or the viscosity, or whatever

  • that determines what happens

  • And you could uh- you that it's chemical engineering rather than physics

  • But, it is this combination of the chemical process, and the physical one, that is very interesting

  • It is important because many of the phenomenon we observe, even when we look at it slowly

  • Is the result of these two effects, but we don't always realise they're going on



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液態氧 (慢動作) - 視頻週期表 (Liquid Oxygen (slow motion) - Periodic Table of Videos)

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    林宜悉 發佈於 2021 年 01 月 14 日