Saltwater Ice

[pimpsqueak]

If dropping temperature is your goal then freeze pure water and add salt to it after you have placed it around your fermenter. You will drop the temperature more but you will have to make more frequent trips to your shed and back with ice.

Well now, that is certainly not what I'm after. Basically, there's a bunch of terms and principles that are being thrown around here that I don't understand and truthfully, I have no wish to fully understand. At the end of the day, if the temp drops even slightly, I win. If I replace the ice less often to maintain the same temp, I win. If there is no change at all to the temp of longevity of the ice, then the status quo is maintained and all I lose is some salt that has been sitting in the bag so long that the rubber band sealing it shut had corroded.
The best thing is that no matter the result, it will be a lesson learned for me and might help others searching for answers on the same subject.

Shall we start a pool on the outcome? Who's in?

 

[unrealeous]

Its all a question of how much energy can the ice/water solution absorb- where he is obviously trying to maximise it to keep his brew colder for longer.

Total energy = energy for (heating ice + melting + heating water)

Assuming it takes the same energy to melt brine as it does water - we can remove the melting part. Its about 334 kJ/kg-K

Starting temp = -14.6
Ending temp = ambient = 20? degrees

For pure water the amount of energy to heat water is 4.187 kJ/kg-K and 2.108 kJ/kg-K for ice
For salt water the constants are ~3.8 kg/kg-K for water and ~2 kg/Kg-k for ice (from Sammus post_.

Q(pure) = 2.108(14.6) + 4.187(20) = 114.5
Q(Brine) = 2(0.6) + 3.8(34) = 130.4

So with the above numbers the brine wins... but of course - assumptions are the mother of all fcukups.

[Edit] However, if we then add the melting part (334) to both - there is only a 4% difference in the total amount of energy absorbed... Basically - you are wasting your time with Salt Find a better way to insulate the system.

 

[DanRayner]

try checking the phase digram for sodium chloride and water

http://www.chemguide.co.uk/physical/phaseeqia/saltsoln.html

Yep. And that same phase diagram states that you only get ice and solid salt at temperatures below -21C and we're talking about temperatures around -14C at which the salt stays in solution even when frozen

 

[[email protected]]

I'm betting on loss. Feshwater ice and saltwater ice will both be equal temp if put in the same freezer, just as would anti freeze or a stone. But the melting point will be lower. This means the salt ice will not last as long because if the ambient temp around the ice block gets to -10 or whatever it will start to melt, which will be well before the freshwater ice starts melting. For keeping something at a temperature well above 0 then youre better off with the slower melting ice. It will cool an item down quicker because the melted saltwater will cause a greater surface area and transfer more cold, but it will not last as long.

If you start using salt water ice you also have to worry about any leakage causing major corosion to anything it gets on.

I can see where your coming from though. If you goto the fish markets and somethings covered in saltwater ice, it can be frozen. This is because the heat transfer is better as described above and the freezer used to freeze saltwater ice is also colder. The main reason that salt water ice is ever used though is because it keeps the fish looking better when it melts, the freshwater can damage the product.

 

[Strange Brew]

Its all a question of how much energy can the ice/water solution absorb- where he is obviously trying to maximise it to keep his brew colder for longer.

Total energy = energy for (heating ice + melting + heating water)

Assuming it takes the same energy to melt brine as it does water - we can remove the melting part.

Starting temp = -14.6
Ending temp = ambient = 20? degrees

For pure water the amount of energy to heat water is 4.187 kJ/kg-K and 2.108 kJ/kg-K for ice
For salt water the constants are ~3.8 kg/kg-K for water and ~2 kg/Kg-k for ice (from Sammus post_.

Q(pure) = 2.108(14.6) + 4.187(20) = 114.5
Q(Brine) = 2(0.6) + 3.8(34) = 130.4

So with the above numbers the brine wins... but of course - assumptions are the mother of all fcukups.

AAAAARRRRRRGGGG!!!!!!!

Salt segregates from water when frozen!!!!
Salt segreagates from water when frozen!!!!!!!!!
Salt segregates from water when frozen!!!!!!!!!!!!!!!!!!!!!!!!!

I'm sorry, I said it once before but people still don't seem to believe me.

Just check the phase diagram link I posted above.

There is no such thing as frozen salt water. Water will freeze and you will be left with pure ice and salt solution until you get to -21degC. So you are losing all the enthalpy of fusion of the water that doesn't freeze at -14.6degC because it is now a highly concentrates salt solution which WONT FREEZE. You will never freeze all the liquid above 21degC no matter how much salt you have in there because....

SALT SEGREGATES FROM WATER WHEN FROZEN!!!!!
:icon_vomit:

 

[unrealeous]

AAAAARRRRRRGGGG!!!!!!!

Salt segregates from water when frozen!!!!
Salt segreagates from water when frozen!!!!!!!!!
Salt segregates from water when frozen!!!!!!!!!!!!!!!!!!!!!!!!!

I'm sorry, I said it once before but people still don't seem to believe me.

Just check the phase diagram link I posted above.

There is no such thing as frozen salt water. Water will freeze and you will be left with pure ice and salt solution until you get to -21degC. So you are losing all the enthalpy of fusion of the water that doesn't freeze at -14.6degC because it is now a highly concentrates salt solution which WONT FREEZE. You will never freeze all the liquid above 21degC no matter how much salt you have in there because....

SALT SEGREGATES FROM WATER WHEN FROZEN!!!!!
:icon_vomit:

You failed science, didn't you.

 

[Strange Brew]

Yep. And that same phase diagram states that you only get ice and solid salt at temperatures below -21C and we're talking about temperatures around -14C at which the salt stays in solution even when frozen

NOOOOOOOOO. There is pure solid ice and then there is salt in solution which is unfrozen. Which means NO enthalpy of fusion for that portion.

 

[Strange Brew]

You failed science, didn't you.

You failed reading phase diagrams 101. It is right there. For any salt concentration you cannot get 100% ice above -21degC. You will get ice and salt solution. This happens because....

SALT SEGREGATES FROM WATER WHEN FROZEN!!!

 

[unrealeous]

You failed reading phase diagrams 101. It is right there. For any salt concentration you cannot get 100% ice above -21degC. You will get ice and salt solution. This happens because....

SALT SEGREGATES FROM WATER WHEN FROZEN!!!

The OP has said his freezer only goes to -14.6 degrees and 18% salt solution



You failed science didn't you

 

[Dave70]

So whats the matter with my glycol idea? I thought it was a ripper.

Or do you blokes just want have a argument about salt or something?

 

[Strange Brew]

The OP has said his freezer only goes to -14.6 degrees and 18% salt solution

View attachment 44452

You failed science didn't you

Which, according to the lever rule on the phase diagram would give him about 5% ice, and 95% salt solution (unfrozen).

 

[Leigh]

The OP has said his freezer only goes to -14.6 degrees and 18% salt solution

Which puts you in the little triangle that says "ice + salt solution". The word "ice" means the solid form of water.

I'm waiting for QB, being the resident physicist, to log on. Then this thread will get interesting!

 

[DanRayner]

NOOOOOOOOO. There is pure solid ice and then there is salt in solution which is unfrozen. Which means NO enthalpy of fusion for that portion.

Wow dude, you gotta get some of that ice and salt solution and cool down

I just read that solid-liquid article and Strange Brew is right, I was wrong. It's strange but it's like when you partially freeze beer or coke. You get little crystals of ice (H2O only) and a higher concentration of everything else until everything else freezes and, in this case, you get frozen water and salt (which is also a solid) - separate. Both are frozen but both are separate.

Does it then make any difference to the overall chilling effects of the pimpsqueak's experiement?

 

[Strange Brew]

Wow dude, you gotta get some of that ice and salt solution and cool down

I just read that solid-liquid article and Strange Brew is right, I was wrong. It's strange but it's like when you partially freeze beer or coke. You get little crystals of ice (H2O only) and a higher concentration of everything else until everything else freezes and you get frozen water and salt - separate.

Does it then make any difference to the overall chilling effects of the pimpsqueak's experiement?

Yeah probably. This post has made me want to try partially freezing beer though and then decanting the liquid to make a higher alcohole content brew.

 

[DanRayner]

Which puts you in the little triangle that says "ice + salt solution". The word "ice" means the solid form of water.

Meaning you get solid H2O crystals and solid salt crystals - unmixed.

 

[Strange Brew]

Wow dude, you gotta get some of that ice and salt solution and cool down

I just read that solid-liquid article and Strange Brew is right, I was wrong. It's strange but it's like when you partially freeze beer or coke. You get little crystals of ice (H2O only) and a higher concentration of everything else until everything else freezes and, in this case, you get frozen water and salt (which is also a solid) - separate. Both are frozen but both are separate.

Does it then make any difference to the overall chilling effects of the pimpsqueak's experiement?

The 'yeah probably' in my previous post reffered to yeah I should probably get some ice and salt water solution and cool down.

The difference it will make to pimpsqeaks experiments is that he will be using pure ice a lot more quickly.

 

[DanRayner]

Yeah probably. This post has made me want to try partially freezing beer though and then decanting the liquid to make a higher alcohole content brew.

That would be an eisbock

 

[Strange Brew]

Meaning you get solid H2O crystals and solid salt crystals - unmixed.

While solution can refer to either solid, liquid or gas it is clear from the layout of the phase diagram that in this context solution is meant to mean liquid (salt mixed with water). So that triangle is for solid pure ice and liquid salt solution. The solid solubility of salt in water is zero.

 

[Strange Brew]

That would be an eisbock

Eisbock it is then, without the salt

 

[schooey]

Heh... I love the way a thread grows legs at this place.

Pimp, SB is right, you'll get no benefit from doing this, in fact, it will be less efficient than just freezing water. Think about ice on a road. It lays there frozen until along comes ranger Bob and chucks some salt on it. The ice melts and the traffic flows again even though the ambient temp hasn't changed. Why? Because the salt has decreased the melting point of the ice. It's kinda the reverse of what you're after.