12oz can chilling project ideas...

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Hi,

I'm always fond of soda that is ice cold, but often for some reason don't have any in the fridge. I have a small can chiller that works by rotating the can in a tub and you put ice on top which lay on the can. It does a pretty good job in 2 minutes or so, but is noisy and wears out rechargeable batteries pretty quick.

I wonder if some sort of peltier setup could chill a can without the noise and ice? Does anyone have any experience with using peltier's in a project? One issue is the connection between the can and the peltier. Any thoughts?

Thanks,

Alan

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one cheap source of peltiers is the el-cheapo car fridges. I doubt if it would cool your cans quickly though. Calculate the amount of energy needed to cool your can in the given time frame and see if it is feasible. Otherwise get a bottle of liquid CO2 - that should cool it pronto. Failing that, get an old fridge to store your stash of sody-pop.

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Hint - 4.2 kJ/kg/degree C...

So your 12oz (340ml) can requires around 1.5kJ per degree C - room temperature (20C) to icy would be 30kJ.

I have no idea how efficient Peltiers are but that's quite a lot of cooling. To chill it in thirty seconds you'd need to suck heat out at 1kW; in thirty minutes, 15W - either way the same power. That's a lot of D-cells.

Also, you've got the issues of condensation on the chiller plates, and the actual heat transfer to the drink within the can.

The 'turn it round under ice' method works well because the turning stirs the fluid, so it chills evenly, because the motor is only turning the can - the batteries aren't doing the chill, and the fact that the ice is already chilled and needs 2.2MJ/kg/degree to melt.

There's enough energy 'suck' in 1kg of ice at melting point to drop 500kg of water by a degree...

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I'm glad someone can remember highschool thermodynamics - I'd have to reach for the textbook! I hang my head in shame....

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I have one of those car refrigs. that use the Peltiers. It have a noisy fan as well to take the heat away from the heat fins. You can reverse the polarity to heat.

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alwelch wrote:
I have one of those car refrigs. that use the Peltiers. It have a noisy fan as well to take the heat away from the heat fins. You can reverse the polarity to heat.

Well, duh? Surely you can just use *another* peltier to get rid of the heat from the first one? :mrgreen:

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Hats of barnacle for that lesson in thermodynamics, top stuff :)

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barnacle wrote:
Well, duh? Surely you can just use *another* peltier to get rid of the heat from the first one? :mrgreen:

Don't be daft, that wastes energy. Peltiers can work in reverse too, if they have a temperature gradient they will generate a voltage. So you can simply put the peltiers back to back and use the second peltier to power the first one - get cold cans for free! :mrgreen:

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barnacle wrote:
... the fact that the ice is already chilled and needs 2.2MJ/kg/degree to melt.

There's enough energy 'suck' in 1kg of ice at melting point to drop 500kg of water by a degree...

Maybe some of the other Aussies here are old enough to remember a proposal to tow icebergs from Antarctica to Adelaide to solve their water problems. The largest obstacle was finding a zero cost source of energy to melt that big ice cube. Neil's numbers puts that into perspective.

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

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Ooops, Mr Barnacle got the heat of *boiling*, not the heat of *melting* - I should have looked it up.

The correct number to melt 1kg of ice at freezing point is 334kJ, so it cools only seventy-five times its mass one degree as it melts, not five hundred times as I said.

But melting ice in Australia? Easy-peasy and free; cover it with matt black polythene, or something similar. Insolation at ~700W/square meter will melt, what, 0.7/334 ~= 2g per second, eighty-six litres per square meter per day, assuming sun for half the day. (It'll actually be somewhat less than that, since you have to heat the ice to melting point first which takes almost as energy as to melt it, and you'll lose some of the heat in the water, I suspect. And I haven't allowed for non-square angles of sunlight - but I'd take a good bet at fourty litres...