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Old 07-30-2010, 11:08 PM   #1
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Default Thermal Dynamics of a IC

After some discussion in another thread (http://www.homebrewtalk.com/f51/dual...hiller-101156/), I came across a question that requires someone with a bigger brain than me. With an imersion chilleris there a point where the distance the water has traveld through the copper tube no longer produces any added cooling effect? I'm just wondering because I'm about to build an IC and whats the point of getting one thats 50ft of copper when it won't cool any more efficently than one that is 20ft of copper. If it makes any different I boil in a coverted sanke, typically 10 to 12 gallons.

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Old 07-30-2010, 11:22 PM   #2
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I think you would see a difference between 20 and 50 feet of coil. The amount of difference will depend on the temperature of the cooling water.

Not sure if that helps...

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Old 07-30-2010, 11:43 PM   #3
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No doubt the water temp plays a large role, but I've still seen the cold ground water of the Pacific NW come out nice and hot from a 50ft coil. I suppose you would have to consider that as the wort cools the cold water will reach further into the coild befor reaching the same temp as the wort.

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Old 07-30-2010, 11:59 PM   #4
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It's not so much length as surface area, and longer is the easiest way to get more surface area. Flowrate is also important, so if you have low water pressure, and a lot of pressure drop (long coil of small diameter tubing), your cooling ability would actually diminish. It's hard to express the differences scientifically because of all the variables, but 50 ft of larger diameter copper will significantly increase your cooling time over 20-25 ft. I also have pretty cool water here in OR (probably very similar to yours), and I can chill 11 gallons from boil to pitching temp in 10-15 minutes with my 50' 1/2" ID chiller year round.

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Old 07-31-2010, 12:14 AM   #5
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The cooling water temp plays a big part for the reason seen with a rapid temp drop that dramatically slows as everyone tries to get down the last 20 or so degrees. All of the various scientific formulas related to heat transfer show that the temp differential is a prime factor in heat transfer - not the actual temp of either the hot or cold substance. The heat transfer rate from wort to chiller tube at the start of the coil is much greater than the heat transfer rate at the end of the coil because the temp differential between wort and chiller tube is decreasing along the length of the tube. It would take elaborate scientific tests to determine the most efficient length. Suffice to follow anecdotal evidence. But, the question remains - would two 25' coils with independent cooling flows be more efficient than one 50' coil?

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Old 07-31-2010, 12:56 AM   #6
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That’s true I didn't even consider flow rate, and yes it does appear that there are too many variables. I suppose one could find out the best (most efficient) length if they could keep water pressure as a constant, but I'm not interested in building several chillers of different lengths to fit my particular set up.

I would have to think that the two coil set up would have to work better if you fed them for independent sources, that way the temp differential would be greater at two points in the kettle. So could the best solution be to save the inner coils to be fed off a bucket of ice water after the outer coil is providing diminishing returns?

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Old 07-31-2010, 01:01 AM   #7
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Here is what I wrote on the other related thread -

My plan is to use a $18 garden pump from Harbor Freight. Sit it in a bucket and connect to my not-yet-built dual chiller (that will have two parallel water circuits). Use a garden hose to keep the bucket full and start the pump. When the wort temp drop slows down significantly, start dumping ice into the bucket. When the chiller discharge gets down to garden hose temp, divert the discharge into the bucket and turn off the garden hose. Continue dumping ice until wort temp is where I want it.

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Old 07-31-2010, 01:10 AM   #8
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Efficiency is hard to figure, but you might be able to figure out other factors.

Like cost might be a factor, also wort displacement might be an issue. If you are maxing out your boil kettle and you try to shove 50' 1/2" of copper in the kettle for the last 15 minutes of boil (to sanitize) you could may have some spillage.

(I've always wanted to use the word spillage ). My IC is only 12' of 1/2" and it works great... I don't get 10-15 minute speeds though. To improve the performance I wait until the cooling water cools down and I catch it in a tub... I put my kettle in the tub so I get IC cooling and a cold bath cooling (inside and outside the kettle) at once.

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Old 07-31-2010, 01:14 AM   #9
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That makes sense. At any rate, it better than my old method of throwing my kettle in to bathtub

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Old 07-31-2010, 01:31 AM   #10
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Quote:
Originally Posted by spriolo View Post
Efficiency is hard to figure, but you might be able to figure out other factors.

Like cost might be a factor, also wort displacement might be an issue. If you are maxing out your boil kettle and you try to shove 50' 1/2" of copper in the kettle for the last 15 minutes of boil (to sanitize) you could may have some spillage.
Agree. The science is interesting, but definitely over my head. I figure to build a chiller based on a flexible combination of my limited knowledge, reasonable sounding anecdotal evidence cited by others, within my budget, good money value, job size-matched with expansion capability, and doable within my limited skills. From all indications, what I plan will work and I am sure I can modify in different ways and it will still work.
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