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Hi Andy & All, Feb 18, 2007
My guess would be that there was a wind that night or very good air
flow of cool air, from upslope, around the bucket. A cold wind would
sweep heat from the bucket as rapidly as heat reached the side and thus
create a steep cooling gradient within the bucket. In a word (two
actually); wind chill.
Even if there is active air circulation in a house there may be dead
spots that are out of the flow and a cold bucket would be sitting in a
pool of cold air. The floor, other things being equal, is the coldest
part of a room so there would be no convection of warm air around the
bucket to warm the cold sides. The only mechanism for heat flow to the
bucket, apart from a bit by conduction through the bottom and by
conduction from slightly warmer air through the sides (air is a good
insulator) would be radiation.
If the bucket were in calm air and in a heated room and took 48
hours to thaw on the floor, then my guess would be that it would thaw in
about 24 hours if hung at eye level and about 12 hours if hung near the
ceiling.
Yours truly, Dave Webster Kentville
Andy Moir/Chris Callaghan wrote:
> Here's a question. The other night we left a bucket of water out for
> the horse and donkey. The overnight temperature dropped to about
> -12c. It was a squarish plastic bucket, probably about 12 inches by
> 12 inches by about 14 inches high. (I apologize for being metrically
> challenged on some measurements). The water was frozen into a solid
> block by morning. In all, the bucket was probably outside for 12
> hours. We brought the bucket in the house, where the temperature was
> about 17C. After 48 hours of being inside, there was still ice
> floating in the bucket. My question is, why does it take so much
> longer for the water to thaw than to freeze. To my mind, if it took
> 12 hours (or less) to freeze at -12C temperature, shouldn't it take
> less time to thaw at a temperature in excess of +12C?
>
> Andy in Freeport
>
>
>
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