>Jim,
>
>As a Computer Engineer I cannot argue with your explanation of the use of
>hot water in Zambonis, in fact it sounds quite logical.  But I was wondering
>if you could offer a similar explanation for why (and if) hot water truly
>freezes faster than cold.
>
>If you put hot water and cold water in two separate containers, and place
>them in a freezer, it has been argued that the hot water will freeze first.
> I haven't actually tried it, but I can't get myself to believe it.  The hot
>water has a lot more calories to get rid of before it can become a solid,
>and I can't believe the explanation that evaporation makes up for this.  I
>can believe that the hot water cools faster initially due to the greater
>temperature differential to the surrounding air, but does enough water
>evaporate to make it a significantly smaller amout of water?  or is there
>another reason?
>
>Help me understand this if you have time.  I would appreciate it.
>
> - Eric
>-------------------------------------------------------------------------------
 
I did a scientific experiment yesterday to see if hot water does indeed
freeze faster than cold in a "bulk" setting.  We all agree that hot water,
in a thin layer on top of ice, does freeze faster than if the water was
cold.  But, does a glass of hot water freeze faster than a glass of cold
water.  Here is the experiment:
        300 mls of tap water, as hot as the tap could make it (about 145 F.)
        300 mls of tap water, as cold as the tap could make it (about 50 F.)
        Both waters were placed into 400 ml beakers which were also
equilibrated
                to the temp of the water that they would contain.
        The beakers of water were placed side by side in a freezer on a wire
                rack.
 
I watched the beakers for several hours and can say that the beaker
containing cold water froze first.  It began freezing in about 1.5 hours
and the beaker containing hot water began freezing after about 2 hours.
As far as evaporation goes, I melted the ice and measured how much water
was left in each beaker.  There was not a measurable amount of difference
between either beaker.  This suggests that evaporation may have occured but
not to a markeable degree.
As far as varibles are concerned:
        The beakers themselves were either warmed or cooled by running lots of
        either hot or cold water through them so that the beaker could not act
        as a heat sink.
        The beakers were placed onto a wire rack in the freezer so that almost
        all heat transfer was beaker to air or water to air.  Air does not
        accept heat this way very well and if the beakers would have been placed
        onto a solid shelf, the majority of heat transfer would be out the
        bottom of the beaker.
If someone does this experiment using a freezer with a solid shelf, then I
would guess that the results may be different because the warm beaker would
"melt" into the frost on the shelf and heat transfer through the bottom of
the beaker would be much more effecient than with the cold beaker which
would not "melt" inot the frost, therefore the hot beaker may freeze
faster.
The one unequivicable result of this experiment and this report is that I
have way to much time on my hands.
Flame away.
 
Jim Lawrence