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  #1  
Old 10-18-2008, 12:12 AM
Critical1 Critical1 is offline
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physics of cold, explain this to me

I make most of my own foods and freeze them for use later. I frequently have a nice brick of chili for lunch and to keep it cold until lunch time I usually just wrap it in a nice fleece hoody.

now the question part, after several hours the hoody has ice inside where it has been against the frozen food but the food itself has definitely started to thaw and is usually just cold.

why is there ice on the hoody and cold but not frozen food inside?
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  #2  
Old 10-18-2008, 12:22 AM
DanBlather DanBlather is offline
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A guess: the condensation on the fleece is pure water and has a higher freezing point than the food. The food may be thawed but still less than 32 degrees.
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Old 10-18-2008, 12:29 AM
Santo Rugger Santo Rugger is offline
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A) Chile is way better than chili, you should go that route instead.

B) Dan's SWAG sounds good, the chili has quite a bit of sodium and other ions, lowering the freezing point of the mixture.

C) Just a nitpick, but there's no such thing as cold (only the relative lack of heat). So the cold isn't traveling out through the hoody, the heat is coming in from the outside.
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Old 10-18-2008, 12:39 AM
Deeg Deeg is offline
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Another possibility: fleece, if I recall, is good at wicking away moisture and allowing it to evaporate. The water on the fleece is evaporating quicker than the food, which cools the water around it a bit more than the moisture on the food.
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Old 10-18-2008, 07:46 AM
Napier Napier is offline
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>Just a nitpick, but there's no such thing as cold (only the relative lack of heat).

Just another nitpick - cold and heat are concepts that have had names for millenia, and whether they are "things" depends on your intended use of the word "thing". In the technical definition of "heat", it is thermal energy that is being transferred from one place to another, so there is little heat involved in a Thermos bottle full of hot coffee, at least not until you pour some out. One could argue from that point of view that in the above discussion "cold" is more a thing than "heat" is. While people more often calculate with higher temperatures associated with positive energy values, in all practical situations there is a symmetry between heat and cold as traditionally defined, except that you can't get temperatures below some lower limit (0 K) - and I usually go years between situations where that lower limit matters. As far as I know, and I'm a physicist who's been concentrating on heat transfer and thermal technology for the last several years, you can't say cold is any less a thing than heat is.

Last edited by Napier; 10-18-2008 at 07:47 AM..
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