Chiller Convection

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Having a look at a lot of the copper coil chillers on this forum, they all seem to be large and extend the whole depth of the pot. I'm wondering if a smaller coil held by wire at the top of a pot would be much more efficient at chilling because it would cause backwards convection. I.e the water surrounding the coil cools, becomes more dense and sinks to the bottom of the pot causing the warmer water to rise to the chiller. Much like having the flame at the bottom of a pot causes a rolling boil.

 

[zebba]

I'm bored, so here's my reasoning...

The important thing seems to me to transfer as much heat from the wort into the water in the immersion coil as possible. Ideally, the water coming out of the coil would be the same temperature as the wort - implying that you have transferred as much heat from the wort into the water as possible. If this was the case (which I doubt, but I'm not experienced in this) then reducing the coil length and exploiting the convection like you've explained seems sound - the water at the top is moderately hotter, so heat exchange would be moderately quicker, and thus moderately more efficient. But if the water coming out of the coil is still cooler than the wort in the kettle, then you're only going to make your system less efficient by reducing the surface area of the coil and as such transferring less of the wort heat into the water.

 

[Finite]

I assume your talking about immersion chillers Paxxy?

The reason for the larger size is to increase the surface area which greatly improves the efficiency of the chiller. In regards to your suggestion, I cant be sure, Ive never tested it. Its an interesting thought but I would guess that the convection from the heat difference wouldn't be nearly enough to remove the boundary layer of cooled wort.

Ive never used an immersion chiller so I cant speculate too much but I suppose some brewers might give the whole job a gentle stir every now and then to keep it working efficiently?

The main factors for efficient heat transfer are:

1. Heat exchange surface area
2. Boundary layer removal via turbulent flow
3. The thermal pressure (logarithmic mean temperature difference)
4. The coefficient of the heat transfer which is dependent alot on 2.

I have recently worked on my plans for a new home brewery and yesterday was looking at the counterflow chiller design. One aspect I wanted to make sure was that the turbulent flow was sufficient to remove the boundary layer. I only have these figures inside a 1/2" tube which is .11m/s so I cant say for sure if that's enough with your method. Sounds like a good excuse for an experiment.

 

[[email protected]]

I'm bored, so here's my reasoning...

The important thing seems to me to transfer as much heat from the wort into the water in the immersion coil as possible. Ideally, the water coming out of the coil would be the same temperature as the wort - implying that you have transferred as much heat from the wort into the water as possible. If this was the case (which I doubt, but I'm not experienced in this) then reducing the coil length and exploiting the convection like you've explained seems sound - the water at the top is moderately hotter, so heat exchange would be moderately quicker, and thus moderately more efficient. But if the water coming out of the coil is still cooler than the wort in the kettle, then you're only going to make your system less efficient by reducing the surface area of the coil and as such transferring less of the wort heat into the water.

I've got a small 3 m coil I'll test out on the weekend, they had them for $15 from bunnings in Randwick, seemed pretty cheap. I figure the best way to cause convection would be to make the coil as flat as possible as to chill the entire top layer.

I'll put it in a spiral and hold it with wire at the top of the pot, see how long it takes to chill 20L to pitching. I'll compare the heat coming out with the heat of the wort as well. I used to use a medium sized chiller (I think it was about 12 m). While the heat transfer was great at the start, the water coming out was close to boiling, as the wort got to around 50C it took a lot longer.

 

[ekul]

You're right that keeping the wort moving over the coils will chill the woret faster however I reckon you'd be better off making something to keep the wort moving, like a slow stirrer or something. I've noticed that when i stir the wort (when whirlpooling) i lose alot of heat quickly. I've never stirred for the whole chilling period so i don't know whether it would work, i've always been too scared to have the kettle open for that amount of time.

People do build/sell whirlpooling chillers, but they need a pump to operate them.

 

[Finite]

You're right that keeping the wort moving over the coils will chill the woret faster however I reckon you'd be better off making something to keep the wort moving, like a slow stirrer or something. I've noticed that when i stir the wort (when whirlpooling) i lose alot of heat quickly.

This is the key. Removing the boundary layer of cooled wort to maximize efficiency. If you want rapid chilling this part if vital. This is why I have chosen a counter-flow chiller but a whirlpool immersion chiller will help improve things alot.

Ive seen a static immersion chiller take 100mins to chill 30L from 100C to 20C
At maximum efficiency you could theoretically do the same batch with the same temperature fluids in 10 minutes.

 

[[email protected]]

So it will basically depend on if it chills fast enough to make the wort roll. My bets on no, but no harm in trying.

 

[Finite]

So it will basically depend on if it chills fast enough to make the wort roll. My bets on no, but no harm in trying.

Thats it, give it a go, report back when you can ill be interested to see how you go.

 

[[email protected]]

Alright, my convection chillers ready to role for a batch of pumpkin ale tomorrow. Also excited to try a new four ring burner and testing out the BIAB method, so a lot of exciting new for tomorrow.

Anyway the convection chiller is 3 m of annealed copper in a spiral. I figure that a rolling convection is more likely to happen if I get as much of the top layer cooling as possible, so that more cooler wort is sinking. This is why i've gone a spiral rather than a coil. Also instead of wiring the coil in position I am going to put some floaties on it so it sits 2-3 cms bellow the surface of the kettle. I figure that if its free to move around it will jiggle a bit and possibly help to break boundary layers.

Anyway I figure most likely option is its going to take over an hour to chill, not cause any convection and use a lot of water in the process. But atleast its going into the bath tub so I can do a load of washing and have a nice warm bath with it afterwards.

Best case I figure is a 25 min chill with the wort turning over it self the whole time.

 

[ekul]

Do you have most of the 3m of copper in the wort?

Whats your plan if it doesn't work? Put it in the bath tub and fill with cold water?

I hope it works for you!

 

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Do you have most of the 3m of copper in the wort?

Whats your plan if it doesn't work? Put it in the bath tub and fill with cold water?

I hope it works for you!

Yep, I bent the ends up for in and out, so there will be a little sticking out. No matter what happens I figure it will work a little bit. 3m of copper coil still has a fair bit of surface area even if there is no convection.

 

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Oh does anyone have any idea of what I should use for flotation devices that won't melt in the boiling wort? Maybe a couple of capped stubbies?

 

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Alright its in to chill right now, there is certainly convection occurring, it has cooled down quite quickly so far, but I would have expected that anyway for the first 50 degrees even with such a short coil. However the heat exchange doesn't feel that great, the water is coming out fairly slowly to get enough heat out of it. I'm predicting it wont fill the tub and will take about 40 mins.

 

[ekul]

So has it cooled down yet?

 

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Alright it took about 45 mins to get down to 35. The problem was at low temperatures the convection stopped. So it got down to about 55 in 15 mins or so but the last 20 degrees took ages. So in the end not that great. It looked fairly promising at the beginning it was rolling around like a light boil.

 

[jyo]

Check out the design on this one. I thought about buying this chiller before I discovered no-chilling.
As you will see, the majority of the coils are at the top of wort to chill the hottest part of the kettle.
A few more lengths of copper coil and this could be on the cards for you, mate.
Cheers, John.

Immersion chiller

 

[ekul]

Thats not that bad paxxy, mine used to get to around 25 in 45mins, and i think my coil is over 3m.

If you have a pump you could get a whirlpool chiller. It pumps the wort in to a whirlpool so that the wort is constantly moving over the coils. Same principle except that the pump is moving the wort, rather than the convection.

 

[[email protected]]

The problem is that last 10 degrees. It would have taken another 45 mins to drop. I gave up on it. I think I'll turn it into a counter chiller using a bucket. It shouldn't be too difficult and a lot more efficient. That's the next project.

 

[ekul]

That last bit is so hard. I'd get mine down to 30 or lower and then chuck in the fridge to bring it down the last little bit. When i started doing double batches it would take forever to get down to temp. I priced an 18m piece of annealed copper, it was $99, so i decided to nochill. So much cheaper. PLus you can brew hard for a few days and get the cubes filled, then ferment at your leisure.

 

[QldKev]

That last bit is so hard. I'd get mine down to 30 or lower and then chuck in the fridge to bring it down the last little bit. When i started doing double batches it would take forever to get down to temp. I priced an 18m piece of annealed copper, it was $99, so i decided to nochill. So much cheaper. PLus you can brew hard for a few days and get the cubes filled, then ferment at your leisure.

Hey Ekul,

If you want to try chillin, feel free to borrow my immersion chiller.

QldKev