Ice to keep something from freezing?

[deckofficer]

Just a thought type of question.

If I wanted to prolong something from freezing in below 0*F ambient temperatures, wouldn't it be better to place in an insulated ice box with a large block of ice than without any ice?

[S/V Illusion]

It's a matter of temp gradient. A warm insulated box will stay warmer without ice. A cold box (below freezing temp) will warm in the presence of ice. The practical answer to your question is - it depends on variables like volume, temp gradient, efficacy of the insulator of the box, leakage, etc...

[Ziggy]

Originally Posted by S/V Illusion

A cold box (below freezing temp) will warm in the presence of ice.

It depends on the temperature of the ice. If the ice is colder than ambient the box will get colder when you put the ice inside. If the ice is warmer than ambient, the box will warm up. But the ice box temperature will not rise above freezing as long as there is any ice in it.

If you want the box to stay above freezing, put some liquid water in it.

[Wanderlust]

You would do better if you put water in there. Most foods freeze at a lower temperature than water, in which case the water will freeze first. The additional mass also shares the heat loss, so the time will be longer.

But the bigger benefit of water is the fact that it takes about 80 times the energy to freeze as it does to drop it 1 degree Celcius. So while the internal temperature may drop steadily to 0 degrees, it will not get colder until the water has frozen.

However. while the above may be true theoretically, there will be a slight difference in practical usage. The inside temperature will drop slightly below zero, as there needs to be a temperature differential for the freezing to occur.

Seawater freezes a couple of degrees lower than fresh water. So if what you don't want frozen has a still lower freezing point, then choose seawater.

[Wotname]

Originally Posted by deckofficer

Just a thought type of question.

If I wanted to prolong something from freezing in below 0*F ambient temperatures, wouldn't it be better to place in an insulated ice box with a large block of ice than without any ice?

Surely it would depend on the substance involved. For instance, if the something is say nitrogen or even petrol, then it really doesn't matter.

I would be using the ice to mix in my drink or keep the beer warm.

[chris_gee]

Putting ice in lowers the temperature of the ice box to 0 c. If the ambient temperature is the same in the boat, and ice box, ie enough to freeze stuff ie below 0 c that will warm the box. If that is not the case then it will cool it.
Presumably the box starts warmer than the ambient. Eventually they would reach the same. For shorter times, the ice would cool the box bringing it closer to freezing. Heat transfer slows as the temperature difference declines, but that would happen anyway so that doesn't make a difference. All that happens is the ice cools the box closer to ambient lessening the time to freezing.

[David M]

Is this a test Bob? I know you are also a marine engineer who knows this stuff.

[deckofficer]

Originally Posted by David M

Is this a test Bob? I know you are also a marine engineer who knows this stuff.

David,

BTW, I'm just a dumb deckie.

Everything you have taken the time to post is always spot on. I was reflecting back to a physics class at CMA, had Jim Wheeler, who still teaches there, and my recollection was there is always a large energy jump when changing states, i.e., a liquid to a solid or gas. So, I think if you were in very cold ambient temperature (well below freezing), then a volume of water in the insulted ice chest would give the longest time before other items in the cooler would freeze. When the water froze, then as ice, would continue to keep other items from freezing until evaporating (a gas), then you no longer have any mass that can give off heat and the outside temperature will equalize with the inside and your stored items would freeze.

So, you see David, I'm not sure and was bouncing this off of others. Now that you found this thread, I will know for sure, so step me through it.

[Cavalier]

Originally Posted by deckofficer

Just a thought type of question.

If I wanted to prolong something from freezing in below 0*F ambient temperatures, wouldn't it be better to place in an insulated ice box with a large block of ice than without any ice?

Think in terms of energy and specific heat capacity and the whole problem gets easier.

The 'heat capacity' (sometimes known as thermal capacity) of a substance is the amount of heat required to alter the substance's temperature by a given amount. Specific heat capacity (SHC) of a substance is similar but also takes into account the amount of heat required per unit mass of the substance. The SI units for SHC are J per gram kelvin - J/(g.K)

Water at -10degC (water ice) has a SHC of 2.11 J/(g.K)
Water at 25degC (pure water) has a SHC of 4.181 J/(g.K)
SeaWater at 25degC (1.03SG saltwater) has a SHC of 3.985 J/(g.K)

Note that water-ice requires much less heat per unit mass to alter its temperature than pure water at roughly room temperature. The same is true in reverse and in that sense ice would lose, to a colder environment, its thermal energy at a higher rate than liquid water.

Looking at the numbers above, putting the food in a sealed container in water at room temperature in an insulated container would take much more time to freeze than the same situation but with an equal mass of ice inside: The liquid water simply has more initial thermal energy to be lost than the ice (which is already cold).

Obviously, this seems like a no-brainer, as in food it is the water content which freezes (in a freezer) and not the more solid food matter. The fats will stiffen etc, but not much is happening to your flour for a while... the water in the cells of the organic foods (such as an apple) will freeze and expand and rupture the cell-walls, so when it's defrosted it looks like a sad watery mess and tends to discolor and ruins quicker.

What you may be thinking of when you hark back to physics lessons is the vapor-pressure of gases above a liquid as a medium/transport for energy loss.

As school kids we used to run inside and fill up a cup with hot water to throw on the ground outside (to make a skid-pan) instead of cold water as the steam coming off the hot water initially would act as a much more efficient transport drawing thermal energy away from the mass of water. Cold water on the otherhand would more readily form a layer of ice on the surface but in the process would create an insulative barrier reducing the rate at which the thermal energy in the remaining liquid water could be lost to the cold air above. The hot water would generally freeze solid quicker than the cold water!

Ice is a better insulator than liquid water, but liquid water starts off with more energy initially - so for the same mass will take longer to freeze.

Hope this made sense

[Cavalier]

Originally Posted by deckofficer

BTW, I'm just a dumb deckie.

No such thing as a dumb deckie!

[Wotname]

Originally Posted by Cavalier

Think in terms of energy and specific heat capacity and the whole problem gets easier.

The 'heat capacity' (sometimes known as thermal capacity) of a substance is the amount of heat required to alter the substance's temperature by a given amount. Specific heat capacity (SHC) of a substance is similar but also takes into account the amount of heat required per unit mass of the substance. The SI units for SHC are J per gram kelvin - J/(g.K)

Water at -10degC (water ice) has a SHC of 2.11 J/(g.K)
Water at 25degC (pure water) has a SHC of 4.181 J/(g.K)
SeaWater at 25degC (1.03SG saltwater) has a SHC of 3.985 J/(g.K)

Note that water-ice requires much less heat per unit mass to alter its temperature than pure water at roughly room temperature. The same is true in reverse and in that sense ice would lose, to a colder environment, its thermal energy at a higher rate than liquid water..................................
Hope this made sense

Cavalier, is the emphasised part above a typo? If not, can you explain a little more as I don't understand how (pure) water could be at -10degC.

[Cavalier]

Originally Posted by Wotname

Cavalier, is the emphasised part above a typo? If not, can you explain a little more as I don't understand how (pure) water could be at -10degC.

Hi,

It's not a typo.. more of a terminology oddity.. i put "water ice" to differentiate it from "Nitrogen ice" (as some people call it).. but it's still good old H2O, just in solid form. The point was to show that the SHC of ice is actually much lower than water. When you start trying to introduce heat into ice the near-crystalline structures start to dissociate quite quickly into clumps approaching liquid form -this happens locally to the heat source at first (i.e. outside in), and ice - being solid, is not capable of convecting like liquid water - the transmission of heat through ice is a somewhat different mechanism than liquid water.

On another note, you can get liquid water down below 10degC, and not in ice form if you're willing to add other components such as salt (NaCl) or Glycol (anti-freeze) compounds.

Phil

[deckofficer]

Phil,

You bring up another mind puzzler. We all know water will boil at lower than 212F / 100 C, if in a container that is brought into a vacuum. We do that all the time to make potable water using discarded heat from the engine. Can the freeze point of water be altered by a pressure other than atmospheric? I.e., a vacuum or pressure vessel?

[Wotname]

Originally Posted by Cavalier

Hi,

It's not a typo.. more of a terminology oddity.. i put "water ice" to differentiate it from "Nitrogen ice" (as some people call it).. but it's still good old H2O, just in solid form. The point was to show that the SHC of ice is actually much lower than water. When you start trying to introduce heat into ice the near-crystalline structures start to dissociate quite quickly into clumps approaching liquid form -this happens locally to the heat source at first (i.e. outside in), and ice - being solid, is not capable of convecting like liquid water - the transmission of heat through ice is a somewhat different mechanism than liquid water.

On another note, you can get liquid water down below 10degC, and not in ice form if you're willing to add other components such as salt (NaCl) or Glycol (anti-freeze) compounds.

Phil

Well I learn something new every day - Nitrogen ice - never heard the term before! I would have guessed it was a bad way of expressing "solid nitrogen"!

For me, water is liquid H2O, ice is solid H2O, "water ice" is a mixture of liquid H2O and solid H2O both at 0 degC and cant exist at any other temperature. I am using H2O to denote pure water as you rightly pointed out that when pure water is compounded by other substances, the numbers change.

[David M]

Originally Posted by deckofficer

David,

BTW, I'm just a dumb deckie.

Everything you have taken the time to post is always spot on. I was reflecting back to a physics class at CMA, had Jim Wheeler, who still teaches there, and my recollection was there is always a large energy jump when changing states, i.e., a liquid to a solid or gas. So, I think if you were in very cold ambient temperature (well below freezing), then a volume of water in the insulted ice chest would give the longest time before other items in the cooler would freeze. When the water froze, then as ice, would continue to keep other items from freezing until evaporating (a gas), then you no longer have any mass that can give off heat and the outside temperature will equalize with the inside and your stored items would freeze.

So, you see David, I'm not sure and was bouncing this off of others. Now that you found this thread, I will know for sure, so step me through it.

Wheeler is still there?...wow. Lloyd Kitazono is still there also. Once in a while I take one of his oceanography classes out on the research boat and show them how the professionals do it.....LOL. He is a great guy. We have all kinds of sampling gear and electronics to impress them...

Yeah, I remember the additional energy it takes to jump from a solid to a liquid state for water and the giving up of energy in the opposite direction. I'm not sure how much it would work in the scenario you described. Maybe give Jim a call

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