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Re: [Phys-l] sudden Vacuum freezing



Since this thread, I discovered Zap Packs at RAFT *.


"I've been more interested in the question of how one might get a handle on the speed of propagation of the phase change front."

This isn't freezing **, but the apparent behaviour is similar. I've found one may "super cool" to freezer temp. (- 20 C, m.p. 58 C) Then the propagation is more clearly defined and I think more rapid. Because of the definition, it's easily measured using a vid. camera.



* www.raft.net/ideas/Zap%20Packs.pdf


http://www.raft.net/


** It's a hydrate so on heating it's "melting" is the expulsion of the water and it becomes a solution, initially saturated.


http://en.wikipedia.org/wiki/Sodium_acetate


bc thinks finding the function speed(temp.) old make a nice science faire type project.
p.s. as it's rather exothermic a thin layer on Cu sheet may be necessary to suppress the Le Chatelier effect. OTOH, one might compare its propagation w/ the thermal diffusion rate using a thick sample.




John Mallinckrodt wrote:

On May 7, 2007, at 5:03 PM, Michael Edmiston wrote:


John M's movie is great, but I'm having difficulty believing it is solid
ice. As John D. said, some water must remain. In fact, in a typical
freezer in which the temperature is 0F (-18C) I think rough calculation
would indicate only 25% of the water would freeze. So I wonder if what we
see in John M's freezing bottle is the propagation of a slush that is 25%
ice and 75% water.

John (M), have you ever removed the cap and pushed a rod or knife or
something into the bottle to find the consistency of the ice/water/ whatever?


Several of my colleagues have reproduced the experiment, including one who managed to pour the water into a measuring cup and back into the bottle before it froze, but I haven't done so myself. We also considered the latent heat and concluded on that basis that the product couldn't be solid ice. Indeed, the opacity of the product in the video makes it pretty clear that it isn't.

I've been more interested in the question of how one might get a handle on the speed of propagation of the phase change front.

John Mallinckrodt

Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>

and

Lead Guitarist, Out-Laws of Physics
<http://outlawsofphysics.com>

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