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Old 02-01-2013, 12:48 PM   #1
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Default Saltwater or Tap to Chill IC

So, I made a fool of myself in another thread by not thinking through something that I had just taken for granted. That frozen water never got below 32 degrees. (Something about igloos and sled dogs burying themselves in snow, but that turns out to be an insulation and wind chill thing.) I did a little experiment and, given enough time, the salt water and tap water did indeed both get well below freezing.

But it brought up another question that I can't find the answer to. The frozen tap water got warmer quicker than the salts water. The water in that container pretty quickly went to 32 degrees, where the salt water stayed well below freezing for a long time. Were their outside factors that caused this or is that the way it will always happen?

My thinking is that the cold had to go somewhere. This would mean that swapping frozen tap water bottles in a chiller bucket would be better than using salt water in them because more cold is being transferred to the chilling. If the salt water retains it's chill longer it's better at keeping the food in your ice chest from spoiling, but not what we're looking for when trying to drop our wort temperature as quickly as possible.


Salt on left / Tap on right:
(If left in freezer long enough they would both end at the zero degree setting of the freezer.)

saltwater2.jpg  
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Old 02-01-2013, 12:51 PM   #2
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I would think the benefit of using salt water for a slightly quicker chill would be negated by the cost and trouble of adding salt to the water?

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Old 02-01-2013, 12:59 PM   #3
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I should clarify that the salt water would be in frozen water bottles in a bucket, not directly in the water being pumped through the IC. They could be reused indefinitely. The question is if it is of any benefit or actually could be a detriment to use salt water in the bottles?

edit:
Just thinking that if the salt water holds its chill longer it might be a better for the bottles swapped out in a swamp chiller?

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Old 02-01-2013, 01:13 PM   #4
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Salt lets water stay liquid at lower temps... it melts sooner, so just like calibration on a thermometer, as long as you have a mixture of ice and water, the water will be right at the melt temp(32f for fresh, 26f or whatever depending on salinity)

Also, there is a specific gravity difference, so there is a difference in mass, but I suspect that the differential is too all to measure a thermal mass difference with kitchen equipment, though that's only a guess.

Also, in your test you have different size containers... that's an important variable.

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Old 02-01-2013, 01:21 PM   #5
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You're talking about this pretty common phenomenon, right?

Quote:

Why Does Adding Salt to Water Make it Colder?
By Christine Lehman, eHow Contributor
Salt is often used in ice cream makers to make the water surrounding the inside container cold enough to freeze the cream. In fact, within half an hour or so, the super cold water can freeze sweetened cream enough to turn it into ice cream. How does salt make water so cold?


Water Physics
To understand this phenomenon better requires an understanding of the relationship between temperature and the physical states of water. The movement of water molecules is dependent on the temperature of the water. Warm temperatures mean fast movement. If the movement gets fast enough, steam is produced. Cold temperatures mean less movement until the temperature reaches a point low enough to stop molecular movement altogether in a process we call freezing.


Freezing Point
So how does salt (sodium chloride) make water colder? In essence, it does not. Salt works to depress the freezing point of water so the water can become colder than 32 degrees Fahrenheit (zero degrees Celsius) before it turns to ice. In fact, water containing salt can reach temperatures of nearly minus 6 degrees F.

When ice cream is made, cream is placed into a canister and rotated within an ice bath. If no salt is added to the ice bath, the lowest temperature it can reach is 32 degrees F. While the cream can freeze at this temperature, it can do so more quickly at a lower temperature. When salt is added to the ice bath (usually rock salt in ice cream making), it comes into contact with the thin layer of water on the surface of the melting ice. The salt dissolves and the water becomes salty. This salt water has a lower freezing point, so the temperature of the ice bath can get even colder, thus freezing the ice cream more quickly.

Uses of Salt to Melt Ice

The principle of salt lowering the freezing point of water is used frequently to keep roads safe in winter. During snow and ice events, trucks spread a thin layer of salt on roadways. This causes snow and ice to melt on impact rather than freeze and makes the roads wet rather than icy and dangerous. However, there is a limit to how cold water can become before freezing; in extremely frigid temperatures, applying sand to the roads to increase friction is more useful than applying salt. Types of salt other than sodium chloride can be used in colder temperatures. Calcium chloride and magnesium chloride, for example, can melt ice at low temperatures. However, some of these compounds can be detrimental to the environment and are used only occasionally.



Effects of Crushing Ice
Using crushed ice with salt will provide a greater surface area on which salt can be dissolved, resulting in faster melting. Using more pieces of crushed ice in your ice cream maker, for example, will be more effective than using fewer large cubes.

Boiling Salt Water
While salt will lower the freezing point of water, it does not lower the boiling point. In fact, salty water will boil at a higher temperature than non-salty water. Again, adding salt to water does not lower the temperature.
Anyone who's ever made icecream or chilled beer fast with this method has experienced this. In fact that's why before I got my wort chiller and was just doing stovetop brewing I always added rock salt to the icebath in my sink.

This mildly annoying video illustrates this.

https://www.youtube.com/watch?v=96CIKxkiBKY
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Old 02-02-2013, 12:28 PM   #6
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Quote:
Originally Posted by rayfound View Post
Also, there is a specific gravity difference, so there is a difference in mass, but I suspect that the differential is too small to measure a thermal mass difference with kitchen equipment, though that's only a guess.
It follows that the gel filled freezer packs have no chilling advantage over something filled with water or is that something different?


Quote:
Originally Posted by Revvy View Post
You're talking about this pretty common phenomenon, right?
Not entirely. It's more about any advantage of using water bottles with either saltwater or plain tap water to swap out in a IC chiller bucket w/ pump or swamp chiller. Salt in the water itself would be a chilling advantage, but be a disposal and waste problem. Saltwater bottles could be reused, but it turns out, are no better.
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Old 02-02-2013, 03:12 PM   #7
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Quote:
Originally Posted by AnOldUR View Post
It follows that the gel filled freezer packs have no chilling advantage over something filled with water or is that something different?
Not sure... neither that or frozen bottles is as good as ice thrown in loose, allowing the fresh meltwater to intermix with the water being pumped.
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