Would you mind doing the math for
10 lbs of -70 C ice,
10 lbs of 0 C Ice, and
10 lbs of 0 C water?
I don't have the temp dependent specific heat curves.

Thanks,

Chris

Jeff wrote:
Chris wrote:
For water, the heat of fusion is about 80 times specific heat...
So -70 C ice would have almost twice the cooling effect
as the same amount of barely frozen ice, right?

Wrong. You should look up the Heat Capacity of cold ice. Its only
0.5 BTU/lb-degree at freezing, but it goes down so that by -50 F its
only 0.4.

Since the Heat of Fusion is 144 BTU/lb, sub-cooling even 100 degrees
only adds a small amount of cooling capacity.

Hardly 'hadly effective'.

No, its hardly effective.


And yes, twice as much ice also works, but we knew that.
That's why I recommended to carry an extra cooler w/ ice,
not a lab freezer. But I am sure a liquid nitgrogen cooler
would be practical fo use on a boat, too.


Richard J Kinch wrote:
Chris writes:

IF you want to go high tech and do have access to lab freezers (where
else would you get dry ice..., you can also 'supercool' your normal
ice before the trip. Ice at -70 C will last a lot longer than at -3 C,
with no extra weight.
For water, the heat of fusion is about 80 times specific heat, so
supercooling ice is hardly effective. You're much better off just using a
little more ice.

Dry ice is no good for refrigeration because it is too cold and difficult
to regulate to a higher temperature. By the time you build a contraption
to regulate the chill, you've lost any weight advantage over ice, assuming
you don't need sub-freezing temperatures.

I remember as a child seeing another child severely injured at my dad's
company picnic. Someone brought popsicles in dry ice, the kid got into
them, and took a lick.

Liquid nitrogen is a more practical wasting refrigerant since the liquid is
easy to throttle. That's what some reefer trucks use.