Towards colder water

[Donoroto]

This post got me thinking:

I hate it when I give myself an idea, I have an older imersion chiller that I don't use anymore(bought a taller one for the digiboil). Think I'll put it into a cooler with some water, ice and rock salt, then hook it up between the sink and the cooler in the DigiBoil when I do my next brew. Bet I can cut my chill time considerably.

We all know that rock salt lowers the freezing point of water, allowing ice to chill water to a few degrees colder than freezing (32F). But does adding salt actually get 'more cold' out of the mixture?

My thinking is that there's a certain amount of 'cold' in the ice-water mixture, to be removed by the hot wort. I say that adding salt actually decreases the amount of 'cold' available, since the salt is nominally at room temperature. Is this right? Does salt hurt the process?

(Technically, the water does not have 'cold', instead it lacks 'heat'. But thermodynamic nomenclature aside...does salt help or hurt?)

 

[Sunfire96]

Salt (and other solutes) lower the freezing point of water (the solvent), so your water in liquid form can be actually lower than 32F. IIRC the name of the game of chilling with an immersion cooler is your temperature differential (once you're below a certain temp, say 100-110F). Running <32F water through your chiller in 100F wort will get you to pitching temp faster than >32F water through 100F wort.

Salts also raise the boiling point of water, which is part of the advantage of salting your water before using it to cook pasta (the water is hotter than 212F)

 

[Nosybear]

The "more cold" is the salt's heat of solution. So there is technically "more cold" in the ice-salt mixture. Should get down to 7 degrees F.

But since you're not going anywhere near that cold, there's really not a good reason to try using salt.

 

[Craigerrr]

Glycol...

 

[Donoroto]

I see. My thought is that there is only so much cold in all that ice and adding salt, even if it lowers the temperature, does not deliver any more cold to the system.

 

[Sunfire96]

I would recommend doing some research on the websites of immersion chiller manufacturers, like Jaded or CuSS. I remember listening to a podcast featuring the founder of CuSS that discussed the hours of research done about chiller size and shape and when adding ice is beneficial vs too early to give any benefits to chilling. He discussed the importance (and diminishing returns) of the temperature differential between liquids

 

[Craigerrr]

One thing to consider is corrosion from the salt water.
For copper coils it should be fine if you thoroughly rinse immediately after though

 

[HighVoltageMan!]

I’ve experimented with ice baths, salt and “double” immersion chillers. I chilled the wort down to @60-65F or so and then ran the cooling water through a immersion chiller placed in a bucket with 10-15 pounds of ice to cool the well water down. I was able to cool the wort down to 45F, but it took a while. I tried salt in the bucket of iced water, but it didn’t seem to help much.

So I decided to try something new, I still chilled the wort down to @ 60 F with well water, then I put a submersion pump in the bucket of iced water and pumped the ice water through the immersion chiller directly, without the second coil. The wort cools the fastest when the iced water is circulated through the chiller cooling the wort. I return the water back to the bucket.

It cools the wort from 60F to 45F in 15-20 minutes with 10-15 pounds of ice. Craig is right about corrosion, copper forms a green layer from the salt. Salt doesn’t seem to help much, it probably brings more problems than benefits. This technique could be used even if you want to get your wort down to 60F when your chilling water source is too warm. I live in Minnesota, so the water temperature out of my well is @ 50F year round. I only use this technique for lager beers.

 

[Minbari]

one other Thing to consider. Salt may Lower the Temp Slightly,but The amount of "Cold" the Ice Posses is fixed. since you are Looking To Chill a liquid To 70 degrees or so it Doesnt matter if The ice water is 32 or 28. it will be melted when Done. So the work it can do is fixed

 

[Bubba Wade]

@Donoroto Let’s look at this from an engineering perspective. The governing equation is Q=UAdT. Q is the rate of heat transfer, U is the heat transfer coefficient, A is surface area, and dT is the difference in temperature between the two media.

So, will lowering the temperature of the ice water solution speed up the cooling process? Yes. You have a higher dT.

Will this allow you to cool more wort with a single bag of ice? No. The heat of fusion of ice is 333 kJ/kg. A kg of ice will cool 1 kg of wort about 80C with another 0.5 degree drop for every degree below 0C that the ice started out at.

This is probably more than most of you wanted to know, but the 2nd law of thermodynamics is a cruel mistress.

 

[Craigerrr]

I think that @Minbari has a good point. From a physics standpoint, you can neither create, nor destroy energy, you can only cause it to change forms. In this case the thermal energy is in the wort, and must be transferred out of the wort. The capacity of the combination of the ice and water, regardless of the presence of the salt affecting the temperature at which it is liquid or solid, to absorb thermal energy does not change. Unless.... (unless the change in specific gravity due the the presence of salt has a minute affect on the capacity to absorb energy, in which case, I doubt that it would be measurable to any remarkable degree). I can see that the speed at which there is energy transfer might be increased, but that actual volume of thermal energy that can be absorbed cannot possibly be changed, unless the volume of the cold water changes.
My grade 9 shop teacher taught me that you can break a lot of laws, a great many laws in fact. You are not however capable of breaking the laws of physics.

Make sense?

 

[Craigerrr]

To my point, my wife believes that leaving the lid on the pot will cause it to boil faster... while this is true, probably not enough to make any tangible difference. The food in the water however will cook faster... in that the weight of the lid increases the temperature at with the water is boiling, and therefore the food will be cooked sooner.

 

[Donoroto]

@Donoroto Let’s look at this from an engineering perspective. The governing equation is Q=UAdT. Q is the rate of heat transfer, U is the heat transfer coefficient, A is surface area, and dT is the difference in temperature between the two media.

So, will lowering the temperature of the ice water solution speed up the cooling process? Yes. You have a higher dT.

Will this allow you to cool more wort with a single bag of ice? No. The heat of fusion of ice is 333 kJ/kg. A kg of ice will cool 1 kg of wort about 80C with another 0.5 degree drop for every degree below 0C that the ice started out at.

This is probably more than most of you wanted to know, but the 2nd law of thermodynamics is a cruel mistress.

Thank you @Bubba Wade for quantifying what I perceived as being right. Conservation of energy and all that.

@Craigerrr your wife is correct, water does boil faster with the lid on... Evaporation is a major cooling effect, by mostly stopping it you conserve a significant amount of energy.

Simple experimental proof: pot with a quantity of water at a temperature. Heat it on a stove burner at maximum. Twice, once with and once without a cover. Time it to a boil. You might be surprised at the magnitude of the effect. More water amplifies the effect.

 

[Minbari]

@Donoroto Let’s look at this from an engineering perspective. The governing equation is Q=UAdT. Q is the rate of heat transfer, U is the heat transfer coefficient, A is surface area, and dT is the difference in temperature between the two media.

So, will lowering the temperature of the ice water solution speed up the cooling process? Yes. You have a higher dT.

Will this allow you to cool more wort with a single bag of ice? No. The heat of fusion of ice is 333 kJ/kg. A kg of ice will cool 1 kg of wort about 80C with another 0.5 degree drop for every degree below 0C that the ice started out at.

This is probably more than most of you wanted to know, but the 2nd law of thermodynamics is a cruel mistress.

Pretty much what I said with more math and science lol

 

[Hawkbox]

Nerrrrddsss!!! But yes, putting the lid on will cause a more rapid heat increase.

 

[Nosybear]

Nerrrrddsss!!! But yes, putting the lid on will cause a more rapid heat increase.

Yep. Reduces heat loss from the steam.