Frozen Conduits

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GoldDigger

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But the problem is... the water is already frozen. If you add enough anti-freeze that's above 32?F, yeah, you're adding enough thermal mass to thaw the ice. You could do the same with just about any liquid.... including plain tap water.

In order to physically thaw the water (ie, convert it from a solid to a liquid), you need to increase it's temperature.

If you have a lump of ice that is inside a sealed container with no chemical interaction possible, then you need to add heat to thaw the ice (or else change the pressure by a very large amount!).

But if a surface of the ice is exposed to a salt brine (or pure salt) or to antifreeze, some of the water molecules at the interface will leave the ice surface and then not refreeze because they are mixed with the salt or antifreeze.
Eventually the entire ice block can dissolve this way, ending up as a lower temperature liquid with no addition of heat energy from the outside.

The heat necessary to melt the ice comes from the heat that is withdrawn to lower the temperature of the liquid around the ice to below 32F.
 

ggunn

PE (Electrical), NABCEP certified
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Electrical Engineer - Photovoltaic Systems
But the problem is... the water is already frozen. If you add enough anti-freeze that's above 32?F, yeah, you're adding enough thermal mass to thaw the ice. You could do the same with just about any liquid.... including plain tap water.

In order to physically thaw the water (ie, convert it from a solid to a liquid), you need to increase it's temperature.

This discussion is causing me to have negative flashbacks from a Physical Chemistry course I was compelled to endure many years ago...

When you pour antifreeze or alcohol or salt water onto ice, even if the liquid is at 32 degrees, there is some diffusion of the water from the ice into the other stuff and vice versa. The water thus removed from the ice does not refreeze because it then part of a solution with a lower freezing point. Depending on the surface area of the ice which is involved this can be a fast or slow process which will eventually thaw the ice.

That said, however, many people erroneously think that a piece of ice is always at 32 degrees. 32 degrees is the equilibrium temperature of an ice and pure water mixture, and because of the delta heat of melting involved with the change of state of water between a solid and a liquid, a well mixed combination of ice and water will stay at 32 degrees until all the ice is melted. But ice itself can be much colder than 32 degrees, the same as a solid piece of iron is not always at 2800 degrees F (its melting point). The ice could conceivably be cold enough to freeze the alcohol or whatever you hit it with.

My brain hurts.
 
My theory (disclaimer: I had horrible chemistry teachers in HS and college, but I think I am good are scientifically reasoning my way through)

I dont think I believe the video, or am misunderstanding what exactly they are doing. Take two trays of ice that are at 0 degrees (all temps will be F). Add 0 degree salt to one. The salt will "melt" some of the ice by the mechanism posted previously by myself and others, which just to reiterate, isnt actually melting, its dissolving into water that naturally is melting and making a solution that has a lower melting point thus it doesnt refreeze. I think the temperature remains the same - one tray is 0 degree ice, the other is 0 degree ice with some 0 degree saline solution. The goal and result of the home made ice cream trick is just to make liquid that is the same temperature as the ice - there is no lowering of temperature. It just freezes the ice cream faster than the ice alone would because now you have a liquid and it makes perfect contiguous contact with drum so there is much better energy transfer than irregular chunks of ice.

There are some reactions that release energy when the combination is made, i.e the two component parts of spray foam, curing concrete, or oxygen and hydrogen . There are others that absorb energy, i.e a cold pack which I think is just water and ammonium nitrate. But note these are chemical reactions making compounds where water and salt is just a mixture. I dont think mixtures ever give off or absorb energy.
 

sparkyrick

Senior Member
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Appleton, Wi
All I know is, my method worked
smiley-with-glasses12.gif
 

GoldDigger

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My theory (disclaimer: I had horrible chemistry teachers in HS and college, but I think I am good are scientifically reasoning my way through)

I dont think I believe the video, or am misunderstanding what exactly they are doing. Take two trays of ice that are at 0 degrees (all temps will be F). Add 0 degree salt to one. The salt will "melt" some of the ice by the mechanism posted previously by myself and others, which just to reiterate, isnt actually melting, its dissolving into water that naturally is melting and making a solution that has a lower melting point thus it doesnt refreeze. I think the temperature remains the same - one tray is 0 degree ice, the other is 0 degree ice with some 0 degree saline solution. The goal and result of the home made ice cream trick is just to make liquid that is the same temperature as the ice - there is no lowering of temperature. It just freezes the ice cream faster than the ice alone would because now you have a liquid and it makes perfect contiguous contact with drum so there is much better energy transfer than irregular chunks of ice.
...

OK, looking at your example of the two trays, note that in the second tray you end up with some solid ice and some salt brine. Since it requires heat energy (NOT the same as a rise in temperature!!!) to convert the ice into liquid water in the brine, the overall temperature of that tray must have decreased to below 32F while the first tray will remain at 32F.

To understand the ice cream maker you have to know that at 32F the milk and sugar solution will NOT freeze at all. So the ice and salt brine mixture in the outer shell must get to a temperature below 32F for the ice cream maker to work. The better heat transfer from the liquid to the inner container than you would get from just chips of ice is an added bonus. An ice and water mixture would also transfer the heat quite well, but would not produce a low enough temperature.
 

electricalist

Senior Member
Location
dallas tx
This discussion is causing me to have negative flashbacks from a Physical Chemistry course I was compelled to endure many years ago...

When you pour antifreeze or alcohol or salt water onto ice, even if the liquid is at 32 degrees, there is some diffusion of the water from the ice into the other stuff and vice versa. The water thus removed from the ice does not refreeze because it then part of a solution with a lower freezing point. Depending on the surface area of the ice which is involved this can be a fast or slow process which will eventually thaw the ice.

That said, however, many people erroneously think that a piece of ice is always at 32 degrees. 32 degrees is the equilibrium temperature of an ice and pure water mixture, and because of the delta heat of melting involved with the change of state of water between a solid and a liquid, a well mixed combination of ice and water will stay at 32 degrees until all the ice is melted. But ice itself can be much colder than 32 degrees, the same as a solid piece of iron is not always at 2800 degrees F (its melting point). The ice could conceivably be cold enough to freeze the alcohol or whatever you hit it with.

My brain hurts.
Yes. Methanol and water mix well. Alcohols don't freeze. Pour alcohol on frozen water and it dissolves into the alcohol. No heat no rhyme no reason
 

GoldDigger

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Yes. Methanol and water mix well. Alcohols don't freeze. Pour alcohol on frozen water and it dissolves into the alcohol. No heat no rhyme no reason
Please believe me that alcohols will also freeze if you get the temperature low enough!

As far as using alcohol as an antifreeze additive, just as with the glycols you will get a lower freezing point for the properly proportioned (eutectic) mixture than you will get for water alone or alcohol alone. (Specify which alcohol, of course, since the actual temperatures will differ.)
 

electricalist

Senior Member
Location
dallas tx
I think anti freeze for a radiator and anti freeze for things like gas are different. Glycol ethylene and water are polar opposites so emulsifiers are added to bond them so the radiator liquid doesn't freeze. In fuel alcohols ..yes can be froze if need be. Are to absorbent water into the alcohol and allow the fuel to burn. A more diluted alcohol that works the same is window washing fluid.
To thaw a conduit rubbing alcohol works as well as anything
 
OK, looking at your example of the two trays, note that in the second tray you end up with some solid ice and some salt brine. Since it requires heat energy (NOT the same as a rise in temperature!!!) to convert the ice into liquid water in the brine, the overall temperature of that tray must have decreased to below 32F while the first tray will remain at 32F.

To understand the ice cream maker you have to know that at 32F the milk and sugar solution will NOT freeze at all. So the ice and salt brine mixture in the outer shell must get to a temperature below 32F for the ice cream maker to work. The better heat transfer from the liquid to the inner container than you would get from just chips of ice is an added bonus. An ice and water mixture would also transfer the heat quite well, but would not produce a low enough temperature.

Ok right, its all about the latent heat of fusion. Forgot about that. Ice must absorb energy to change to a liquid. The energy is drawn from the molecule's surrounds. Because the brine doesnt refreeze, this energy is not given back out, so it gets colder and colder. I always have to think about this for a minute because it seems counterintuitive at first: its temping to think, "well the ice is absorbing energy so its getting hotter" but no, its absorbing the energy from the surrounds making the surrounds colder. The energy isnt heating up the molecule that is absorbing the energy because it is latent energy so its not resulting in a increase in temperature. Just like boiling water: you are clearly adding energy, but the temperature isnt increasing.
 

kwired

Electron manager
Location
NE Nebraska
But the problem is... the water is already frozen. If you add enough anti-freeze that's above 32?F, yeah, you're adding enough thermal mass to thaw the ice. You could do the same with just about any liquid.... including plain tap water.

In order to physically thaw the water (ie, convert it from a solid to a liquid), you need to increase it's temperature.
You don't need to increase temperature, you only need to lower freezing point. Put salt on ice and it starts to liquify even if still below 32F, that is why we have "ice melt" which is just a salt compound in the northern regions of the country. Liquid materials that lower freezing point of water just happen to interact with the water molecules faster then the solid salt does. Once you get a little brine started though you begin to have more liquid that can flow to other still frozen water molecules. Of course you need enough "antifreeze" component to allow continued lowering of freezing point or else it only will melt a certain amount of ice and may still freeze again if temp is low enough, but the part that is mixed will thaw first and at a lower temp when warmed then the purer portion of ice will.
 

kwired

Electron manager
Location
NE Nebraska
Doesnt sodium create heat when mixed with water? The purer the sodium the more heat transfer.

That mixture results in a chemical reaction though where when done you have sodium hydroxide and hydrogen gas. Any water left is just because there was not enough sodium to react with all of the water, but what water was involved is no longer water, and what sodium was involved is no longer sodium.

With salt compounds in water you just end up with a mixture of dissolved salt in the water.
 

electricalist

Senior Member
Location
dallas tx
I did some work for a Dr. and he said they would make pure sodium and drop it down the least used drain in class and leave,,,he said wanna see what it does,,,,nope.
 

kwired

Electron manager
Location
NE Nebraska
I did some work for a Dr. and he said they would make pure sodium and drop it down the least used drain in class and leave,,,he said wanna see what it does,,,,nope.

Potassium is similar in nature, has similar characteristics as it is in same column of periodic table of elements and has same number of free electrons, but AFAIK is more violent when it reacts. Lithium should have some similar reaction as well.
 
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