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Chilling with salt?

Northern Brewer General
#1

Instead of my faucet I attach my wort chiller to a pump in a 5-gallon bucket filled with ice and enough tap water to get the get the pump started. I use less than 3 gallons in total after the ice melts, and cool to 60 in about 20 minutes. I know others follow a similar technique.

So here’s the crazy question: has anyone who works this way ever considered adding rock salt to the pump’s bucket? I know from ice cream making, that adding salt to the ice can drop the temperature of the ice water another 20 degrees or more.

It could seriously turbocharge the chiller, or it just make an insignificant improvement. I’d also wonder if pumping salty water could cause corrosion in the pump.

Any opinions? Anyone do this? Is it worth experimenting?

Just a general thanks
#2

I think for sure the salt would have an impact on the workings of the pump. But how about this idea? If you have access to dry ice you can make supercooled alcohol. Get a couple gallons of 90% isopropyl alcohol and a bucket. Put the alcohol in the bucket. Get a couple pounds of dry ice pellets and put them in a smaller bucket that you have punched holes in. Set the small bucket into the larger bucket with the alcohol and the pump. The dry ice will chill the alcohol down to an extremely cold temp but since the alcohol does not freeze it will still flow through the chiller. And the alcohol will not be corrosive to the system.

#3

Salt doesn’t drop the water temp. It only allows the water to remain liquid as the ice chills the water to at or just below 32. Salt would probably mess up the pump.

:cheers:

#4


Try this at home.

  1. Fill a measuring cup with ice, and also fill it with water. (meaning LOTs of ice in the water, not just a couple cubes on top.)

  2. Use your favorite thermometer to prove it’s 32F-ish.

  3. Now pour salt in and stir it real good, (I used my thermometer as a stirrer…)

  4. What happens to the temperature?

I got mine down to 19.5F

#5

Try it with room temperature water, no ice.

#6

Well obviously that wouldn’t do anything to the temperature.
The temperature drop in my scenario happens because the salt depresses the freezing point of water, and forces the state change from solid to liquid. If there’s no ice, there’s no state change. If there’s no state change there’s no magic.

#7

Well obviously that wouldn’t do anything to the temperature.
The temperature drop in my scenario happens because the salt depresses the freezing point of water, and forces the state change from solid to liquid. If there’s no ice, there’s no state change. If there’s no state change there’s no magic.[/quote]

:roll: It lowers the freezing point of the liquid so it remains liquid at 31.9999999 and a few degrees lower. That’s all. No magic in 2014.

:cheers:

#8

Wow. So I may be using wrong terminology! But try what I said above; salt in ice water does lower the temp. Not just a few degrees, I got better than 10 degrees without really trying. It works like magic. Use enough salt that you can’t make any more dissolve.

#9

Saltwater has a much lower freezing point than freshwater does. And the more salt there is in it, the lower the freezing point gets. So in order to know the exact temperature that it’s going to freeze, you have to know just how salty it is. For saltwater that’s as saturated as it can possibly get, the freezing point is -21.1 degrees Celsius or -6 degrees Fahrenheit. This is when the saltwater is 23.3% salt (by weight).
So yes the salt water WILL be colder and therefore increase heat transfer of your exchanger.

From what I remember from school the Fahrenheit scale was based on the temperature that ocean salt water freezes {0 degrees F} and the Celsius scale was based on the temperature that regular water freezes {0 degrees C}.

#10

[quote=“Brew1”]Saltwater has a much lower freezing point than freshwater does. And the more salt there is in it, the lower the freezing point gets. So in order to know the exact temperature that it’s going to freeze, you have to know just how salty it is. For saltwater that’s as saturated as it can possibly get, the freezing point is -21.1 degrees Celsius or -6 degrees Fahrenheit. This is when the saltwater is 23.3% salt (by weight).
So yes the salt water WILL be colder and therefore increase heat transfer of your exchanger.

From what I remember from school the Fahrenheit scale was based on the temperature that ocean salt water freezes {0 degrees F} and the Celsius scale was based on the temperature that regular water freezes {0 degrees C}.[/quote]
Basically this. Just a few nits to pick. Fahrenheit scale is anchored on the freezing point of blood (0F) and normal body temperature (100F). Fahrenheit didn’t get this exactly right, but his tools weren’t the best.

When you add salt to ice, it allows the ice to begin melting at a lower temperature than it would without the salt. So common sense would tell you that if you took ice out of a -10C freezer and added salt, you would end up with an icy brine slurry at -10C. But common sense in this case is wrong; the actual temperature (assuming about a 25% by weight concentration of salt to ice) would be about -20C. The “magic” that makes this happen is called heat of fusion. If a material changes from one state of matter to another (solid → liquid, liquid → gas), it takes additional energy to make the transition. Thus, it pulls energy (heat) out of the surroundings until it gets to a state of equilibrium, which will happen at the transition temperature, or when it runs out of material to phase change (all the ice has melted), or the rate of energy entering the system from the outside equals the rate at which energy is being consumed by the state change. Whichever happens first.

This is the same principle that is at work when you put a wet t-shirt over a carboy (swamp cooler). Energy is being drawn out of the carboy to enable the evaporation of water to vapor, resulting in a lowering of the carboy temperature. The amount of lowering in this case is limited by the rate of energy entering the system from the outside, as well as the ambient humidity, which drives the rate at which water is being evaporated.

Sorry about the long physics lesson, couldn’t resist.

And don’t put a salty brine through your pump unless it is designed for that.

#11

[quote=“rebuiltcellars”]
Sorry about the long physics lesson, couldn’t resist.

And don’t put a salty brine through your pump unless it is designed for that.[/quote]
No really, thanks for the physics. I remembered learning this but couldn’t remember the ‘magic’ words, i.e. “Heat of fusion.” I only did the experiment above because I was doubting my memories.

But back to the practical from theoretical,

If water is 8.3 lbs/gal it would take 1-1.5 pounds of salt per gallon to get concentration in the effective range. With 3-4 gal in the pump bucket that’s 5-ish pounds of salt to make make this work.

While I’m not sure about salt per se, my pump is designed for dirty, gritty, water. So a good flush-out after might limit corrosion.

In summary,
[list=1]

  • Without salt, my chiller only takes ~15-20 min[/*]
  • To get a significant temp drop would require ~5lbs. Or ~$7-10 of salt [/*]
  • The pump would need to be flushed with fresh water after use to limit corrosion potential.[/*] Conclusion: Any time gains in the chilling would likely be negated by pump flush time. That coupled with the salt cost makes this an impractical approach for chilling.

    Thanks for a lively, informative debate.

    • #12

    And while were talking science, one more tid-bit, bar trivia: at STP, 32F is not the freezing point of water. Water freezes at < 32F. At STP, 32F is the “melting” point of ice.

    Cheers

    #13

    Yes, it does. That’s why sea water freezes at 28F.

    #14

    Yes, it does. That’s why sea water freezes at 28F.[/quote]

    No…see >>> [quote=“StormyBrew”]Try it with room temperature water, no ice.[/quote]

    It only lowers the temperature at which liquid water turns to ice. It does not actually lower the temperature of water. In a way, it’s like driving and speed limits. I can paint a new lower limit on the highway speed sign. But, that does not mean my car is going to drive at that lower limit. It just means the limit has changed not the speed of the car.

    If salt dropped the water temperature, it would do so with room temperature water too and it doesn’t. That’s the great thing about science. If it’s false once…it’s always false.

    :cheers:

    #15

    It’s about the ice, not the water.

    Sigh. I give up. You could try it yourself with the ice, it only takes 10 minutes. But I see no one will convince you to rethink your position.

    Have a homebrew, and make some ice cream.
    Life’s too short to worry about stuff like this.

    #16

    Yes, it does. That’s why sea water freezes at 28F.[/quote]

    No…see >>> [quote=“StormyBrew”]Try it with room temperature water, no ice.[/quote]

    It only lowers the temperature at which liquid water turns to ice. It does not actually lower the temperature of water. In a way, it’s like driving and speed limits. I can paint a new lower limit on the highway speed sign. But, that does not mean my car is going to drive at that lower limit. It just means the limit has changed not the speed of the car.

    If salt dropped the water temperature, it would do so with room temperature water too and it doesn’t. That’s the great thing about science. If it’s false once…it’s always false.

    :cheers: [/quote]

    While the salt does lower the temperature at which the ice will freeze it also lowers the temperature of the water as the brine solution is formed. The melting of the ice by the salt is an endothermic reaction which is the mechanism of the temperature change. It won’t happen with room temperature water because there is no endothermic reaction taking place, merely salt dissolving in water.

    The fourth segment in the link below explains in more detail.

    http://www.sci-experiments.com/ice_cream/saltwater.html
    #17

    ^^^ Yes.
    Because the freezing / melting point of the salt water has been lowered below 32F due to the presence of the salt, the ice continues to cool the water and reduce the temperature below the equilibrium point.

    The ice, not the salt, lowers the actual temperature of the water as it melts which is why salt added to room temperature water does not lower the temperature.

    The salt lowers the freezing point or equilibrium point for energy exchange of the water/ice mixture.

    The ice lowers the water temperature.

    :cheers:

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