Saltwater Ice

[pimpsqueak]

Temperature control is (wait for it...) a hot topic on here and while I have my own ebay temp controller, I don't have a fridge to use it on . Yet.
I live on the 3rd floor and while my fermenting is done in the shed, the brewing happens 3 floors up, in my kitchen. In my shed I have no power or water, only light, but as a bonus it's pretty well insulated from the sun on all sides except for the door.
I'm using ice to chill a large ice box for fermenting and another one for conditioning and I'm sure there must be others doing the same.
Anyway, I did a bit of googling for info on saltwater ice today and while I understand the theory, I really wanted a list of saltwater concentrations and their freezing points.
My freezer only runs down to -14.6 degrees, so I can't freeze a 100% saturated saltwater solution, as it has a freezing point of -21 degrees. I really need to know what saltwater concentration freezes at -14 degrees, so I can make the coldest ice possible.
Until some kind soul provides this info for me, I am getting my science on.
Currently I have 3 bottles in the freezer with 30g/l, 60g/l and 90g/l concentrations of salt. I shall see which one/s freeze and narrow it down from there. I will post my findings in here, just in case others are curious.

 

[Bribie G]

That would be good information, please post results.
I tried doing salt ice a couple of years ago, but my freezer just wasn't up to it and I ended up with 5L jerrycans of just very cold brine.
At the time I was fermenting under a doonah with ice bottles, during a hot spell, and of course the idea of ice is the latent heat of melting, which just didn't happen with the brine.

I didn't actually lose the two brews involved but they were a bit funky, having been at 25 degrees for their primary.

 

[Dave70]

Why not get yourself some ethylene glycol (anti freeze for your car) and add it at different concentrations?

Here's a table from wiki -

http://en.wikipedia.org/wiki/Ethylene_glycol

- 48 cold enough for ya?

Ethylene glycol freezing point vs. concentration in water

 

[schooey]

Using this calculator at 101.3 kPa (atmospheric) you need about 187 PSU (Practical Salinity Units) to make the water freee at -14C

187 PSU, as far as I can tell with a quick google, equates to 187000 ppm of salt.

 

[unrealeous]

187 PSU, as far as I can tell with a quick google, equates to 187000 ppm of salt.

Or about .44 quintals of salt per hogshead of water.

 

[pimpsqueak]

Using this calculator at 101.3 kPa (atmospheric) you need about 187 PSU (Practical Salinity Units) to make the water freee at -14C

187 PSU, as far as I can tell with a quick google, equates to 187000 ppm of salt.

And that dear sir, is exactly what I couldn't find yesterday. (Thankyou) 187g/l it is, though I expect it will take a few days to freeze solid. The 30 and 60g/l froze overnight but the 90g/l is still in a thick slushy consistency.

- 48 cold enough for ya?

I wish.
Perhaps if I could tuck a few bottles up Mr Freeze's clacker to get it down that far.

 

[DanRayner]

I went another way.

Saturation point of salt in water is around 35g of salt per 100mL of water.

Salt saturated water freezes at -21C.

Water with no salt freezes at 0C.

You want to know how much salt can be dissolved in water and still freeze at -14C? Is it not just a fraction of the distance between 0C and -21C?

14/21 = 0.66666

0.66666 x 35 = 23.33g/100mL water or 233g/L

This only works if the relationship for dissolution of salt in water and that solution's subsequent freezing temperature is a linear one.

Anyone see any problems with these assumptions of simple equations?

cheers,

D

 

[unrealeous]

This only works if the relationship for dissolution of salt in water and that solution's subsequent freezing temperature is a linear one.

Anyone see any problems with these assumptions of simple equations?

The relationship is not linear. http://wapedia.mobi/thumb/9ac5499/en/max/4...ezing_point.jpg

But would be a good starting point without any other info

 

[DanRayner]

The relationship is not linear. http://wapedia.mobi/thumb/9ac5499/en/max/4...ezing_point.jpg

But would be a good starting point without any other info

Ah. I see, good point.

But it is kinda/sorta/almost linear for the temps/solutions we are talking about and I was close - so it looks like it's 200g/L?

 

[pimpsqueak]

Ah. I see, good point.

But it is kinda/sorta/almost linear for the temps/solutions we are talking about and I was close - so it looks like it's 200g/L?

According to the calculator, at Sydneys atmospheric pressure it should be 185 g/l. I did initially consider doing the math but I pretty much assumed it wasn't going to be a linear scale.(Besides, experimenting is fun) The extra 15 g/l of salt will push me past the freezing capabilities of my freezer, so I'm happy I held off long enough for peoples helpful contributions to come in.

 

[Strange Brew]

Temperature control is (wait for it...) a hot topic on here and while I have my own ebay temp controller, I don't have a fridge to use it on . Yet.
I live on the 3rd floor and while my fermenting is done in the shed, the brewing happens 3 floors up, in my kitchen. In my shed I have no power or water, only light, but as a bonus it's pretty well insulated from the sun on all sides except for the door.
I'm using ice to chill a large ice box for fermenting and another one for conditioning and I'm sure there must be others doing the same.
Anyway, I did a bit of googling for info on saltwater ice today and while I understand the theory, I really wanted a list of saltwater concentrations and their freezing points.
My freezer only runs down to -14.6 degrees, so I can't freeze a 100% saturated saltwater solution, as it has a freezing point of -21 degrees. I really need to know what saltwater concentration freezes at -14 degrees, so I can make the coldest ice possible.
Until some kind soul provides this info for me, I am getting my science on.
Currently I have 3 bottles in the freezer with 30g/l, 60g/l and 90g/l concentrations of salt. I shall see which one/s freeze and narrow it down from there. I will post my findings in here, just in case others are curious.

I'm not quite sure what you're trying to do here. If your freezer is -14.6 degrees then both a salt solution and pure water will come out of the freezer at -14.6 degrees. Adding salt will just reduce the heat capcity and enthalpy of fusion which will reduce the cooling capacity of your ice. Salt can be added to ice after freezing to drop the temeprature because it fasilitates melting which allows the latent heat to be converted into a lower sensible heat (temperature). This gives you an short term lower temperature but does not actually increase the overall heat energy that can be absorbed.

What you are trying to do seems to be long term cooling for which temperature is not as important as specific heat and enthalpy of fusion. As far as these go water is as good as you can get (Ammonia is better but that won't really work for your setup).

Honestly mate I think your wasting your time. Buy some store brought ice from the shop and chuck that in there.

 

[unrealeous]

I'm not quite sure what you're trying to do here. If your freezer is -14.6 degrees then both a salt solution and pure water will come out of the freezer at -14.6 degrees. Adding salt will just reduce the heat capcity and enthalpy of fusion which will reduce the cooling capacity of your ice. Salt can be added to ice after freezing to drop the temeprature because it fasilitates melting which allows the latent heat to be converted into a lower sensible heat (temperature). This gives you an short term lower temperature but does not actually increase the overall heat energy that can be absorbed.

What you are trying to do seems to be long term cooling for which temperature is not as important as specific heat and enthalpy of fusion. As far as these go water is as good as you can get (Ammonia is better but that won't really work for your setup).

Honestly mate I think your wasting your time. Buy some store brought ice from the shop and chuck that in there.

Specific heat © for water is 4.187 kJ/kg-K and 2.108 kJ/kg-K for ice

Or in other words - it takes less energy to heat ice up than it does water - so having -14 degree water is advantageous.

The latent heat for melting ice is 334 kJ/kg - but that's the same in both cases (ie -14 degree ice or 0 degree ice)

 

[pimpsqueak]

I'm not quite sure what you're trying to do here. If your freezer is -14.6 degrees then both a salt solution and pure water will come out of the freezer at -14.6 degrees. Adding salt will just reduce the heat capcity and enthalpy of fusion which will reduce the cooling capacity of your ice. Salt can be added to ice after freezing to drop the temeprature because it fasilitates melting which allows the latent heat to be converted into a lower sensible heat (temperature). This gives you an short term lower temperature but does not actually increase the overall heat energy that can be absorbed.

What you are trying to do seems to be long term cooling for which temperature is not as important as specific heat and enthalpy of fusion. As far as these go water is as good as you can get (Ammonia is better but that won't really work for your setup).

Honestly mate I think your wasting your time. Buy some store brought ice from the shop and chuck that in there.

Why on earth would I pay for store brought ice? I may as well skip the middle man and buy a case of VB while I'm at it.

We will see if saltwater ice makes a difference tonight when I get home. Using normal ice I have been able to maintain a constant temp of 18.9 while the ambient temp in the shed fluctuates from 23 to 25. I am hoping to see a drop in temp from using colder ice. If I can get a drop in temp, I will be able to figure out what concentration drops the temp in the ice box to a desired figure (I'm hoping to hit 16 deg)
Any drop in temp is a win, so if that's the case, I won't have wasted any of my time. *crosses fingers*

 

[Sammus]

Specific heat for water is 4.187 kJ/kg-K and 2.108 kJ/kg-K for ice

Or in other words - it takes less energy to heat ice up than it does water - so having -14 degree water is advantageous.

The latent heat for melting ice is 334 kJ/kg - but that's the same in both cases (ie -14 degree ice or 0 degree ice)

That maybe so, but Strange Brew made the same point I was thinking while reading this thread. The frozen water and frozen saline will be at the exact same temperature. The OPs impression is equivalent to thinking that no matter the ambient temperature, water will stay at 100C until outside temperature raises above that and it boils.

salt water's specific heat capacity is marginally lower than fresh water (3.9ish), and I suspect it would be a bit lower for the ice. Salt is good for a cheap antifreeze, it won't make stuff freeze colder though, that depends on your freezer. Using salt water, your bits will freeze slightly more quickly, but theyll warm up more quickly too.

 

[Strange Brew]

Specific heat for water is 4.187 kJ/kg-K and 2.108 kJ/kg-K for ice

Or in other words - it takes less energy to heat ice up than it does water - so having -14 degree water is advantageous.

The latent heat for melting ice is 334 kJ/kg - but that's the same in both cases (ie -14 degree ice or 0 degree ice)

Salt segregates from water upon freezing. You get ice and salt, so you end up with -14.6degC pure ice anyway with the same heat capacity. Of course now when you take it out of the freezer it will start absorbing a spontaneous burst of energy as the ice begins to melt and disolves the salt again so by the time you have it down at the shed you have already lost a good portion of the cooling capacity. You can avoid this by keeping it as a liquid but then you lose the latent heat which is the biggest contribution.

Cheers,
Alex

 

[Strange Brew]

Why on earth would I pay for store brought ice? I may as well skip the middle man and buy a case of VB while I'm at it.

We will see if saltwater ice makes a difference tonight when I get home. Using normal ice I have been able to maintain a constant temp of 18.9 while the ambient temp in the shed fluctuates from 23 to 25. I am hoping to see a drop in temp from using colder ice. If I can get a drop in temp, I will be able to figure out what concentration drops the temp in the ice box to a desired figure (I'm hoping to hit 16 deg)
Any drop in temp is a win, so if that's the case, I won't have wasted any of my time. *crosses fingers*

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.

 

[unrealeous]

Salt segregates from water upon freezing. You get ice and salt, so you end up with -14.6degC pure ice anyway with the same heat capacity. Of course now when you take it out of the freezer it will start absorbing a spontaneous burst of energy as the ice begins to melt and disolves the salt again so by the time you have it down at the shed you have already lost a good portion of the cooling capacity. You can avoid this by keeping it as a liquid but then you lose the latent heat which is the biggest contribution.

With respect - I think you are talking out your arrrrse.

Can you back it up with a link to a respected site detailing your (wild h34r: ) claims

 

[DanRayner]

I'm not quite sure what you're trying to do here. If your freezer is -14.6 degrees then both a salt solution and pure water will come out of the freezer at -14.6 degrees. Adding salt will just reduce the heat capcity and enthalpy of fusion which will reduce the cooling capacity of your ice. Salt can be added to ice after freezing to drop the temeprature because it fasilitates melting which allows the latent heat to be converted into a lower sensible heat (temperature). This gives you an short term lower temperature but does not actually increase the overall heat energy that can be absorbed.

What you are trying to do seems to be long term cooling for which temperature is not as important as specific heat and enthalpy of fusion. As far as these go water is as good as you can get (Ammonia is better but that won't really work for your setup).

Honestly mate I think your wasting your time. Buy some store brought ice from the shop and chuck that in there.

I would guess he's doing it to lower the melting point of the ice that he's creating.

A change of state from solid to liquid requires more energy input and for the time that there is still ice floating around in the liquid then that liquid stays at the melting point.

So if you have a (normal) glass of ice water then the temperature of the liquid in the glass (assuming there is enough convection currents to mix it all up) will stay at 0C until all the ice has melted.

If he's doing that at -14C with this concentration of brine does that mean the liquid surrounding the brine-ice will be colder or colder for longer than if he puts -14C normal ice into normal water?

 

[Strange Brew]

I would guess he's doing it to lower the melting point of the ice that he's creating.

A change of state from solid to liquid requires more energy input and for the time that there is still ice floating around in the liquid then that liquid stays at the melting point.

So if you have a (normal) glass of ice water then the temperature of the liquid in the glass (assuming there is enough convection currents to mix it all up) will stay at 0C until all the ice has melted.

If he's doing that at -14C with this concentration of brine does that mean the liquid surrounding the brine-ice will be colder or colder for longer than if he puts -14C normal ice into normal water?

Maybe if he was trying to cool his fermenter to -14degC then that would help but otherwise temperature is irrelevant. The ice will be up to melting at no time. Look at the difference between specific heat and enthalpy of fusion.

 

[Strange Brew]

With respect - I think you are talking out your arrrrse.

Can you back it up with a link to a respected site detailing your (wild h34r: ) claims

try checking the phase digram for sodium chloride and water

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