Instant Cooling to 35deg.F

[never]

Go to Ireland sometime and order a Guiness. You'll find that you've never actually had one before. The stuff they ship out is very different from what they serve on the home field.

[clot]

Loved it. Cans and bottles do not go with beer!

[Richard J Kinch]

Nope. The heat of fusion, not the specific heat, is what flash chills. As I said, the phase change is crucial.

[terry]

On Aug 30, 9:22 am, [e-mail] (Doug Miller) often writes.: .

Doug: That reference to the Boston Tea party, which in turn led to American Independence, always amuses! . But even more amusing was an occasion (in the eraly 1960s) when myself, an ex Brit. had to explain to a good friend and neighbour at that time, an American serviceman (Tech. Sgt.) of Mexican extraction, the significance to American history of the Boston Tea Party! . His wife though was from Massachusetts or Maine (somewhere in New England) and one would have thought she would have explained it!

Regards. Terry

[Doug Miller]

It doesn't seem that you've ever made ice cream at home.

Quite right that the phase change is crucial. However, you're utterly mistaken when you think that the cooling will be most rapid if the melt water is drained away. The objective is to remove heat from the can of beer as rapidly as possible, and that will happen when the beer is immersed in a bath of icewater. Not when it's immersed in a pile of ice.

And the reason for that is that water is a better conductor of heat than ice, and thus heat transfers from the beer can to water faster than it transfers from the beer can to ice. On top of that, water transfers heat away from the beer can by convection as well as conduction, and obviously ice won't.

In short, rapid heat transfer is the name of the game, and you get that with icewater, not with ice.

[nicksanspam]

I tend to agree.

Water has a 0.596 W/mC conductance, vs 2.26 for ice. But it's hard to keep the can completely in contact with ice, and that way, the heat transfer from the ice is limited to the can surface. If the can is in a large well-stirred bath of ice and water, the ice will have lots of heat transfer area to water, and the can surface will be very close to the temp it would be if the entire can surface were in contact with ice.

Nick

[Doug Miller]

Well, maybe... that depends at least in part on the relative masses of the ice, and the can of beer. Figure a can of beer at somewhere around 350 grams. Pop a room-temperature beer into, say, 20 or 30 kg of ice at -20 deg C in a well-insulated container, and the beer will eventually assume pretty near the same temperature as the ice, long before any significant melting of the ice can occur.

OTOH, put the same beer, and the same 20 or 30 kg of ice at -20 C into a water bath, and the beer will *never* get colder than 0 C.

Which, of course, is why you add salt when you're making homemade ice cream: so that the ice will melt at a lower temperature, giving you a water bath that's much colder than 0 C.

[dpb]

...

That "well-insulated" would have to be adiabatic, but in that case the end result would be about right if the mass of the ice were large wrt the beer.

The prize! _Finally_, somebody made a cogent explanation...

[M Q]

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.

[Doug Miller]

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.

[Doug Miller]

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.

So insulate the walls of the vessel.

Define "excess". 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.

[nicksanspam]

I wonder what that means...

Nick

[nicksanspam]

I agree.

Meltwater.

Nick

[Ralph Mowery]

Maybe this will explain it. It is the latent heat of phase change.

[Doug Miller]

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.

[nicksanspam]

Still makes no sense to me.

Nick

[Nick Pine]

Still makes no sense to me.

Nick

[Doug Miller]

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?

[nicksanspam]

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

[dpb]

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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