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?
Hardly 'hadly 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.

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.

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.

On Sun, 02 Jul 2006 08:31:58 -0400, 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.

This is in error: using old CGS units
heat for fusion of ice is 80 cal/gm specific heat cap near 0degC is
1 cal/gm

Supercool to -40 deg C and its worth roughly another 40% of cooling
power cf. ice at freezing.

Brian Whatcott Altus OK

Brian Whatcott wrote:
On Sun, 02 Jul 2006 08:31:58 -0400, 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.

This is in error: using old CGS units
heat for fusion of ice is 80 cal/gm specific heat cap near 0degC is
1 cal/gm

Supercool to -40 deg C and its worth roughly another 40% of cooling
power cf. ice at freezing.

Brian Whatcott Altus OK

Sorry about the late reply - I've been out sailing.

You're making a common mistake. Although the specific heat of water
is 1 calorie per g-deg C, for ice its only about half that, or .5 cal
per g-deg C, or as I stated .5 BTU/lb-deg F. Thus, super cooling ice
add little cooling capacity.

On Sat, 08 Jul 2006 20:06:58 -0400, Jeff wrote:



This is in error: using old CGS units
heat for fusion of ice is 80 cal/gm specific heat cap near 0degC is
1 cal/gm

Supercool to -40 deg C and its worth roughly another 40% of cooling
power cf. ice at freezing.

Brian Whatcott Altus OK

Sorry about the late reply - I've been out sailing.

You're making a common mistake. Although the specific heat of water
is 1 calorie per g-deg C, for ice its only about half that, or .5 cal
per g-deg C, or as I stated .5 BTU/lb-deg F. Thus, super cooling ice
add little cooling capacity.


This time I checked a little more carefully among the welter of old
American Customary, CGS old scientific and SI units people have been
applying.
First, agree that ice has half the specific heat capacity of water
and agree that fusion of ice takes 80 cal/gm or 80 X 4.2 J/gm or
80 x 4.2 x 1000 J/kg
so -40 degC to melting point provides 20 cal or 20 X 4.2 J/gm or
20 X 4.2 X 1000 J/kg
and
ice to water provides 80 cal/gm or 80 X 4.2 J/gm or 80 X 4.2 X 1000
J/kg

The ratio in question is ( 80 + 20 ) / 80 = 125%
(NOT 140%)

The extra 25% of cooling effect may qualify as "little" or
"appreciable". You choose! :-)

Regards
Brian Whatcott Altus OK

Chris writes:

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?

No, because heat load is proportional to temperature differential.

Now if you put that supercooled ice into watery payload that freezes, then
the supercooling heat sink will convert to new ice in the payload, and a
different process is involved that is more "efficient". However, this is
no better than just freezing your food to start with.

Hardly anybody appreciates that temperature and heat are two different
things.

On Sun, 02 Jul 2006 23:50:59 -0500, Richard J Kinch
wrote:

Chris writes:

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?

No, because heat load is proportional to temperature differential.

Now if you put that supercooled ice into watery payload that freezes, then
the supercooling heat sink will convert to new ice in the payload, and a
different process is involved that is more "efficient". However, this is
no better than just freezing your food to start with.

Hardly anybody appreciates that temperature and heat are two different
things.

This note looks suspect - especially the "what everybody doesn't know"
bit.

Brian Whatcott Altus OK