Instant Cooling to 35deg.F

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snipped-for-privacy@milmac.com (Doug Miller) wrote:

Forgot to add that another effect of the salt is that lowering the melting point causes the phase transition -- which as RJK correctly pointed out is the step that "eats" the most heat -- to occur much sooner.
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Doug Miller (alphageek at milmac dot com)
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I wonder what that means...
Nick
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wrote:

Maybe this will explain it. It is the latent heat of phase change.
http://daphne.palomar.edu/jthorngren/latent.htm
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http://daphne.palomar.edu/jthorngren/latent.htm
Still makes no sense to me.
Nick
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wrote:

Simply that much more energy is absorbed in melting the ice (the phase transition from solid to liquid) than in raising the temperature of the mixture. Google 'latent heat of fusion' or look it up in any high school chemistry text.
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Doug Miller (alphageek at milmac dot com)
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Still makes no sense to me.
Nick
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wrote:

The point is that if your objective is to transfer the heat from the beer to the ice as rapidly as possible, this is best achieved by melting the ice as quickly as possible, with the heat contained in the beer -- which in turn is best achieved by lowering the melting point of the ice by adding salt.
You *do* know that's why you use salt to melt ice, right?
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Doug Miller (alphageek at milmac dot com)
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This makes a little more sense.

Sure. Do you still believe that water is more conductive than ice? :-)
If so, I submit you are unqualified in this discussion.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Not that Doug needs anybody to fend for him, that wasn't the point he made or was intending to make--it was that water is in a practical sense a better heat transfer mechanism than the ice because can achieve a better _overall_ heat transfer rate owing to it being liquid and therefore being in full contact w/ the surface whereas ice isn't...
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snipped-for-privacy@ece.villanova.edu wrote:

Actually, the conductance of the ice is irrelevant. What is important for removing heat is the phase change happening at the surface of the ice. If you could keep the ice in perfect contact all around with the beer can, you would not need the meltwater (and there would be no room for it). As the ice is melting and changing shape, you cannot keep it in contact.
So now the question is: is it better to fill that gap with air or meltwater?
The advantage of water: it is a better conductor of heat than air (although I suspect that the greater effect is due to convention rather than conductance).
A disadvantage of water might occur if you are trying to lower the temperature below 32F using a salt. In that case you would be using some of your cooling power to lower the temperature of earlier meltwater. Also, the meltwater would also better conduct heat from the walls of the vessel holding the mix. Best to just drain the excess meltwater.
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wrote:

I'm not sure I agree...

.. because in order for that phase change to occur, you must first transfer heat from the beer to the ice.

Certainly no disagreement there.

Water, clearly. Air (still air, at least) is an excellent thermal insulator.

Nope, it's due mostly to conduction. Air is a remarkably effective convector. However, before any heat can be removed from the beer can by convection (whether in water or air), it must be transferred from the can to the water or air by conduction. This transfer is far more efficient with water.

No, the meltwater would simply be at the lower temperature from the beginning. I'm guessing you haven't made any more ice cream at home than Richard has. <g>

So insulate the walls of the vessel.

Define "excess". <g> The heat transfer will be most rapid in a bath of icewater. If you don't have enough water to keep both the beer and the ice in a water bath, then you don't have any excess.
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Doug Miller (alphageek at milmac dot com)
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I agree.

Meltwater.
Nick
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Doug Miller writes:

Go ahead an scoff while you speculate about what's best. I get paid as an engineer to analyze, design, and implement flash chilling systems. I know how these things work, in theory and in practice, on a home scale and on a 1000s of liters/hour industrial scale.
At home I flash-chill cans in under a minute, by the process I described, and with the concrete, quantifiable results I have claimed. It's not speculative on my part. I have analyzed and verifed the direct-contact- with-ice principle both ways, that it works, and that the other ways don't work.
Now if you want to erect a conceit that you know better, go do some experiments with your brine notions and report back. Otherwise your hunches and expressions of contempt for wisdom and experience are just idle insults, and a parody of engineering. Which is what Usenet is mostly about.
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Isn't Usenet great, where anybody can pretend to be anything?
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Doug Miller (alphageek at milmac dot com)
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Doug Miller writes:

Except I never pretend. My identity and credentials are plain and easily confirmed.
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Sure, whatever you say. What exactly are your credentials for claiming that gasoline is safe to drink and carbon monoxide is safe to breathe, but common household borax is a deadly poison? What exactly are your credentials for claiming that there is no difference between a parallel circuit and a dead short?
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Doug Miller (alphageek at milmac dot com)
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Doug Miller writes:

You forgot my myth-busting assertion that "adding water to hydrochloric acid is OK".
Your weekly snort of contempt for such has gotten quite old and unoriginal. Proverbs 29:9.
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[snippage restored]
that gasoline is safe to drink and carbon monoxide is safe to breathe, but common household borax is a deadly poison? What exactly are your credentials for claiming that there is no difference between a parallel circuit and a dead short?
[conspicuous failure to respond noted without surprise]

Thanks for the reminder of another example of your peculiar "knowledge" of chemistry and physics. I admit I'd quite forgotten about that one -- of course, it's not quite such a howler as the others, either, so it was easier to forget.

If you don't like having it pointed out that you're posting baloney, the solution is real simple: stop posting baloney.
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Doug Miller (alphageek at milmac dot com)
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I see you are no longer posting about ice and water conductivities :-)
Nick
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wrote:

Tell me, Nick, do you *really* believe ice is a better heat transfer agent than water?
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Doug Miller (alphageek at milmac dot com)
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