The science of the wort chiller - question

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eviljafar

eviljafar

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I built a wort chiller today from 25' of 3/8 OD copper. Considering I've only got a handful of tools and my kitchen is my "workshop" it all went together pretty easy and there's no leaks so I'm pretty happy. I haven't assemled my burner yet so to test it I boiled up about 23L (6 Gal) of water in pots, poured it into my keggle and cooled it from about 85*C to 22*C (183*F to 66*F) in about 30 mins. That seems OK.

Anyway, after 10 mins or so I'm standing there with a beer in hand, listening to water flow down the drain and watching condesation form on the tubes, and a question pops into my mind.

What volume of water should be flowing through the cooler to cool the wort the fastest?

The reason I ask is because I once heard that if water flows through a car engine cooling system too fast the water doesn't have time to exchange heat and so the engine can overheat. The conclusion of this theory is not to remove the thermostat from *some models* and expect the engine run cooler as the opposite may occur. IE, fast flow doesn't mean maximum cooling. Now I have no idea if this is true or just an old mechanics wives tale.

So I slow the flow down to my chiller and the water exiting the cooler comes out hotter. I guess that means more heat is going down the drain. But when I turn the flow up the copper coil is cooler, so I guess that means the wort is in contact with a colder object. But what is better?

Do I turn the cold water tap on as hard as it will go, do I turn it down until the water exiting the chiller is the hottest, or is there some other "sweet spot", ie not too slow and not too fast that will cool the wort the fastest?
 
I dont know what is 'right' per se, but when I use mine, I go full blast at first, then as I kind of feel it out from there. My understanding is the purpose of the wort chiller is to whisk the heat away, not have the wort in contact with a cool surface, therefore, I think it is more important for the exiting water to be hot than the chiller to be cold. So, as cooling winds down, I will feel the water output and adjust my flow to make this as hot as possible.
 
More flow is better, keeps the delta T as high as possible. Basic thermodynamics.

Some engines, like the 440, the thermostat had a plug that actually blocked part of the flow through the engine, forcing more through the radiator. Taking the stat out meant the water just kept looping through the engine, which over-heated.
 
Another question: which direction do you have the hose water go? Against the wort or with the wort? Does it matter?
 
david_42 said:
More flow is better, keeps the delta T as high as possible. Basic thermodynamics.QUOTE]

yup, what he said.

more flow=faster temp drop but also = more water used. If you don't like wasting water, mess with the temp to get slightly warm water coming out. If it's hot on exit the last few coils really aren't doing anything...

i'm hoping to build a cooling coil that is a double coil system. from sink hookup, to first coil submersed into a bucket with ice water, this will bring the temp of the water darn near 32 before it enters the second coil in the wort.

My hope is that this will waste less water (i can use whats in the bucket for plants etc.) and chill the wort much faster as the initial temp of the water is much cooler :rockin:
Click to expand...
 
Cheesefood said:
Another question: which direction do you have the hose water go? Against the wort or with the wort? Does it matter?
Click to expand...
I go against the flow. I think that is the standard for chillers/condensers.
 
If you want to cool your wort faster, put something colder in it. Think back to your extract days, when you had to chill the wort, and get the proper volume, by adding three gallons of water or so. You kept that water in the fridge for a reason. Thus, if there is something you can do to make your wort chiller colder, like increase the flow rate of water through it, then that is good idea. I am limited by leaks that spring when the flow rate gets too high.

Newton's law of cooling partial explains what's going on with the wort chiller:
Q = hA(To-Ta)
Q = Heat transfer in Watts
h = Heat transfer coefficient
A = Surface area of the heat being transferred
To = Temperature of the object's surface
Ta = Temperature of the surroundings
[http://en.wikipedia.org/wiki/Heat_conduction]​

Ta is the temperature of the wort, and To is the temperature of the chiller. If the difference between these two temps is big, then so is Q. Similarly, if A is big, then you have a chiller with lots of coils and Q is big too. h is a constant. Don't worry about constants. The bigger Q is, the more powerful your chiller is. Who doesn't want a powerful wort chiller? Crank that thing up!

EDIT: There are also other things like convection at play. Won't go into that though.
 
In a counterflow chiller, you want the flows to be opposite. Coldest chill water meets coolest wort. Warm & hot. Not so basic thermo.

For a wort chiller, putting the cooling water in the top reduces stratification. Which matters only if you don't stir at all.
 
I did a couple trials with this when I was using an immersion chiller. I got the same cooling speed with wide-open water as I did with the water running slow enough that it came out warm. So for me it was a wash, but that may be because my tap water is quite cold making the differential quite high to begin with. I was happy though because it meant wasting less water.
 
I dont know much about chillers but I do know a little about engineering. The higher the flow the better because the higher the difference between what is being cooled and what is doing the cooling will make a higher efficiancy. You can sort of think about like each gallon of water that goes through cools the wort a certain amount. Say (these numbers are just for example and not to scale at all) that for each gallon of water that is flowing through at 3 gallons per minute (GPM) cools it 5 degrees. But a gallon of water moving at .5 GPM cools it 15 degrees. This means that in one minute the 3GPM would cool it 15 degrees and the .5GPM would only cool it 7.5 degrees. Like i said these numbers are not even close to being scale but it kind of gives you the idea.
 
I'm in the heating and cooling trade, I built a chiller with 85ft of 1/4'' tubing. I used 2- 3/4'' pipes as manifolds and had 4 loops about 20' long. if you do the rough math a 3/4'' pipe has about .44 sq inches of area, a 1/4'' pipe has about .049 sq inches of area, so a 3/4'' pipe will supply enough water for about up to 9 loops of 1/4'' pipe. I run tap water through the chiller until I'm down to 100-90 degrees and then I have a bucket of ice water that i pump through the chiller, I can chill 6 gallons from boil to 68 degrees in under 7 mins. this is how Trane air conditioner lay out there condensers. instead of having 1 long loop, you have many short loops.

Just an idea,

Nick
 
nicksteck said:
I'm in the heating and cooling trade, I built a chiller with 85ft of 1/4'' tubing. I used 2- 3/4'' pipes as manifolds and had 4 loops about 20' long. if you do the rough math a 3/4'' pipe has about .44 sq inches of area, a 1/4'' pipe has about .049 sq inches of area, so a 3/4'' pipe will supply enough water for about up to 9 loops of 1/4'' pipe. I run tap water through the chiller until I'm down to 100-90 degrees and then I have a bucket of ice water that i pump through the chiller, I can chill 6 gallons from boil to 68 degrees in under 7 mins. this is how Trane air conditioner lay out there condensers. instead of having 1 long loop, you have many short loops.

Just an idea,

Nick
Click to expand...
care to share a pic?
 
nicksteck said:
I'm in the heating and cooling trade, I built a chiller with 85ft of 1/4'' tubing. I used 2- 3/4'' pipes as manifolds and had 4 loops about 20' long. if you do the rough math a 3/4'' pipe has about .44 sq inches of area, a 1/4'' pipe has about .049 sq inches of area, so a 3/4'' pipe will supply enough water for about up to 9 loops of 1/4'' pipe. I run tap water through the chiller until I'm down to 100-90 degrees and then I have a bucket of ice water that i pump through the chiller, I can chill 6 gallons from boil to 68 degrees in under 7 mins. this is how Trane air conditioner lay out there condensers. instead of having 1 long loop, you have many short loops.

Just an idea,

Nick
Click to expand...
+1 :ban: :ban: :ban:
 
nicksteck said:
I'm in the heating and cooling trade, I built a chiller with 85ft of 1/4'' tubing. I used 2- 3/4'' pipes as manifolds and had 4 loops about 20' long. if you do the rough math a 3/4'' pipe has about .44 sq inches of area, a 1/4'' pipe has about .049 sq inches of area, so a 3/4'' pipe will supply enough water for about up to 9 loops of 1/4'' pipe. I run tap water through the chiller until I'm down to 100-90 degrees and then I have a bucket of ice water that i pump through the chiller, I can chill 6 gallons from boil to 68 degrees in under 7 mins. this is how Trane air conditioner lay out there condensers. instead of having 1 long loop, you have many short loops.

Just an idea,

Nick
Click to expand...

Here's the Pic... I'm his Bro-in-law... It's true, boil to 68 in under 7

13248-chillerfmhell1.JPG
 
Seabee John said:
Here's the Pic... I'm his Bro-in-law... It's true, boil to 68 in under 7

13248-chillerfmhell1.JPG
Click to expand...

I build a dual-coil chiller that works great for me... but this is the coolest freakin' chiller ever. I love how you've got the separate input for pumping the ice water, so you don't have to fumble with unhooking the hose. Damn, that's a sweet design.
 
I know there are a lot of people who are interested in saving energy water and time, so how about this for an idea. Why don't you run the chiller so the extra water comes out warm, then reuse the warm water for brewing.

For me the first 5 or 10 gallons come out fairly warm, and would require less energy (propane) and time to reach a boil. The first few gallons may even be the proper temperature to start a mash. If you are not into using the extra water that ran through your chiller to brew with, you can at least use it to clean, stuff is easier to clean with warm star san filled water.

Just a thought, does anyone do this?
 
I definitely save the warm runnings from my chiller! I hate the idea of wasting all that water. I run it into a garbage can and then use it for cleaning up the last of my brewing gear.
 
I made a two 25' ICs from 1/2" Cu. The first coil goes in an ice bath and the other into the wort. My water is from a well and runs a consistent 59deg F, and the water coming out of the ice bath is 39deg F. With both coolers hooked up I can cool 5.5gal from boiling to 68deg in 12 minutes. The last batch I forgot to get ice so I just ran the second coil; went from boil to 68deg in 15 minutes! Apparently not much of a time gain for the cost/work. Haven't tried adjusting flow rates yet, probably ought to dust off my old thermo text and do some of the math...
 
bradsul said:
I definitely save the warm runnings from my chiller! I hate the idea of wasting all that water. I run it into a garbage can and then use it for cleaning up the last of my brewing gear.
Click to expand...
That's a real good idea.:rockin:
 
when i was building the chiller i was worried about it displacing so much wort but it only raised the wort about an 1'' in a 40qt pot. i thought it would have been higher?
 
Just remember to stir (I stir the pot with my IC) - that speeds things up big time. I feel the temp of the output water thru the copper, and when the output side begins to feels less than hot, I swirl it a little and it heats right back up.

This weekend I cooled my 5gal to 68F in 15 minutes.
 
i bought a paint mixer at homedepot and used my drill, the mixer looked like a tiny blower wheel. it really helped chill.

Nick
 

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