[NatureNS] speed at which ice melts

Date: Sun, 18 Feb 2007 14:34:07 -0400
From: David & Alison Webster <dwebster@glinx.com>
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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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