On 9/6/2011 1:04 AM, Invisible wrote:
> On 06/09/2011 06:25 AM, Jim Henderson wrote:
>> On Mon, 05 Sep 2011 21:12:15 -0400, Alain wrote:
>>
>>> You can have water that stay liquid down to -10°C and possibly even
>>> less. You need a container with very smooth surface and no particles in
>>> suspention. In this state, a vibration can be just enough to cause
>>> almost instant crystalisation.
>>
>> Which is actually quite cool
>
> I see what you did there.
>
> I've got a box of hand warmers at home. They contain a super-saturated
> solution (of what I don't know). Once you provide a nucleation point,
> the whole lot crystallises within a few seconds. It also gets quite warm
> in the process. (This is what makes it good for warming your hands.)
Seen those. There is also some expensive shirt that was made for 
joggers, which uses a similar principle, though, in that case, I get the 
impression they formulated the material so it crystalized faster than 
normal in cold temperatures, releasing heat, but softening faster than 
normal too, absorbing it, thus keeping you cooler, or warmer, depending 
on conditions.

Always wondered, in the case of the whole "heat pack" thing though if 
you couldn't make one that did the reverse, and was "recoolable", or 
whatever. The principle being, of course, than it is rechargable, so 
long as the solution doesn't change (often the plastic is 
semi-permiable, so loses moister over time, and stops working), so when 
you let it cool slowly, it "holds" the excess energy. When you apply 
kinetic energy to it, it instantly starts losing all of what it 
retained, and crystallizes. You would basically need to do the reverse, 
somehow, for a "cold pack", crystallizing it, so as to "lose" more heat 
than it needs in a stable state, then.. there comes the rub. Other than 
that it would liquify as it absorbed the heat, instead of crystallizing, 
like the supersaturation, I am not clear how you would manage to make it 
so it could recharge effectively.

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