Applying Physics/Engineering to IC design

I know a lot of you will say that I'm taking this whole thing too far, but we all bring to brewing the skills, knowledge, and curiosity that we apply to the rest of our lives. Plus I really like to ponder questions like this...

All things being equal (water temp, air temp, amount of liquid, square inches of chiller surface), I'm almost certain that there's no noticeable difference in the chill times when comparing one immersion chiller with another. However, just as a quick thought experiment, and I'm hoping to attract some insight from those with a background in engineering/physics, I've got a few questions to raise about chiller design.

1.) Does the amount of spacing between the coils make an impact on chill time?
2.) Should water run into the chiller, spiral down through the wort and then straight back out the top...or should the cold water come straight into the bottom, and spiral upwards?
3.) Would my double spiral design enable more efficient chilling than a single spiral design? (see below)
4.) I've purchased some copper tubing online that has a little bit thicker sidewalls than I've seen at the local hardware shop. The OD is 1/2", but the ID is 13/32"...normally would be 3/8". I know, I know 1/32" isn't really that much...but it's 50' long, so it kinda adds up. Do thicker sidewalls allow for more absorption of heat?
5.) If we grew up on the moon, would we be taller?

Well, my BA says anthropolgy, but I'll take a shot.

Longer tubing will allow more heat transfer, but it should be a diminishing returns thing. Like 20 feet is better than 10 feet, but 30 feet is only a little better...

Besides tubing length, other variables:

flow rate of cold water
delta T, wort v- water in cooling line

That's all I got. I think if your cold water supply is at a high enough pressure it won't matter which way the coil runs in the hot wort.

Poindexter said:

Well, my BA says anthropolgy, but I'll take a shot.

Longer tubing will allow more heat transfer, but it should be a diminishing returns thing. Like 20 feet is better than 10 feet, but 30 feet is only a little better...

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A little hands-on with this particular topic: I replaced 25' of 1/2" copper with 50' of 3/8" copper. Dramatic improvement.
I then added the 1/2" copper coil inside of the 3/8" inch one (with a few feet edited out in the rebuild), and a hose garden y-valve to balance the flow. A bit of improvement maybe, but not dramatic. It did help stiffen up the flimsy 3/8 stuff, though.

Poindexter, regarding diminishing returns, I think what you say is much more true of counterflow chillers than immersion chillers. Because of the way they work, CFC's do generally have a pretty defined point of diminishing returns (if the wort reaches tap water temp 20 feet in, any additional length won't make a difference), but with an IC it's not so clear-cut, and 50 foot 1/2" chillers are not uncommon - I think it's usually more of a question of what you can afford/what is practical to use.

The cooling time of an immersion chiller will benefit more from proper stirring/agitation of the wort during chilling than it will from building a fancier chiller, generally speaking. The first time I tried recirculating the wort with a pump during chilling with my 25'x3/8" IC, I was completely shocked at the improvement.

With that said, I think the design guidelines would be to get as many feet of tubing in there as you can, and to have the tubing evenly spread out throughout the wort. The biggest problem is that you get cool spots in the liquid surrounding the chiller tubing - this is why stirring is so vital. If the coils are all clumped together in a tight spiral, they won't chill as effectively because instead of having a lot of smaller cool areas, it'll just be one large-ish one around the chiller and nowhere else. If you are stirring properly it won't be as big a deal, but I think it will still help to keep the coils more distributed throughout the wort.

1.) Does the amount of spacing between the coils make an impact on chill time?

If you never moved the chiller in the wort, then I suspect that the spacing would have an impact. However, to maximize the efficiency of the chiller, you should move it up and down a bit, and that motion likely negates most of the effects from coil spacing.

2.) Should water run into the chiller, spiral down through the wort and then straight back out the top...or should the cold water come straight into the bottom, and spiral upwards?

To achieve max ΔQ, have the water flow from top to bottom. I doubt it makes much difference in practice.

In a CFC, the coldest chiller water is nearest the coldest wort (i.e., the chilling fluid flows opposite the direction of the wort). This is to maintain a constant chilling effect down the entire coil (minimize the possibility of temperature equilibrium prior to the wort exit point). The same principle does not apply to an IC.

3.) Would my double spiral design enable more efficient chilling than a single spiral design? (see below)

This is probably dependent on your boil kettle geometry. The more evenly you can space cooling coils throughout the kettle, the better the IC will work. For a tall, narrow kettle, a single coil would likely be best. For a short, squat kettle, a double coil could work better.

4.) I've purchased some copper tubing online that has a little bit thicker sidewalls than I've seen at the local hardware shop. The OD is 1/2", but the ID is 13/32"...normally would be 3/8". I know, I know 1/32" isn't really that much...but it's 50' long, so it kinda adds up. Do thicker sidewalls allow for more absorption of heat?

With such a long chiller, I doubt you notice any ill effects from slightly thicker tubing. In theory, thinner walls are better, but copper is a great thermal conductor. I wouldn't sweat this one.

5.) If we grew up on the moon, would we be taller?

If a tree falls in the woods, and no one's around to hear it, does anyone care?

Well I've found a definite answer to #4.
That is, of course, in addition to what Yuri_Rage had posted (which is perfectly accurate, I just wanted to find out exactly what the differences were)

The volumetric heat capacity of water is a staggering 4.184 J, while Copper is 3.45 J. So it seems that while copper is a great conductor of heat, water is the best. I was actually hoping I'd have an advantage with thicker sidewalls, but as it seems, the best I can hope for is a negligible disadvantage.
As a side note, it looks like Iron beats out Copper by a bit at 3.537 J, but who wants to bend up an iron immersion chiller? Also, anyone like rusty beer?

mavol said:

The volumetric heat capacity of water is a staggering 4.184 J, while Copper is 3.45 J. So it seems that while copper is a great conductor of heat, water is the best. I was actually hoping I'd have an advantage with thicker sidewalls, but as it seems, the best I can hope for is a negligible disadvantage.
As a side note, it looks like Iron beats out Copper by a bit at 3.537 J, but who wants to bend up an iron immersion chiller? Also, anyone like rusty beer?

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Well, I'm no mechanical engineer, so take this for what it's worth:
Heat capacity is not the same as thermal conductivity. Copper and water's thermal capacities may be similar, however the thermal conductivity of water is about 0.6, while that of copper is 401 (in W/(m*K)). Someone can correct me if I'm wrong, but this should mean that heat will conduct through the copper so easily it will be essentially negligible as compared to the slow rate at which the water will absorb the heat on the inside, therefore the copper thickness should not make a significant difference.

5) Yes, at the very least the disks in your spinal cord would be thicker.

Funkenjaeger said:

Well, I'm no mechanical engineer, so take this for what it's worth:
Heat capacity is not the same as thermal conductivity. Copper and water's thermal capacities may be similar, however the thermal conductivity of water is about 0.6, while that of copper is 401 (in W/(m*K)). Someone can correct me if I'm wrong, but this should mean that heat will conduct through the copper so easily it will be essentially negligible as compared to the slow rate at which the water will absorb the heat on the inside, therefore the copper thickness should not make a significant difference.

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Good call...I was measuring the wrong thing. Volumetric heat capacity is the amount of heat energy needed to raise the temperature of a given substance by a certain temperature interval. (I love Wikipedia)

Quite right there, Funkenjaeger. Just took a thermo class last semester and you're spot on. If you think about it for a second, it makes a whole lot of sense: clearly water isn't a really good conductor, because if it was, we'd never need to stir the wort to chill it effectively with an IC. It would naturally conduct all of the heat right out .

Having convection forced(stirring) or natural through a temperature gradient will increase the rate of heat transfer.

This is why the chillers have the cold inlet coils towards the top. The rate of heat conduction between the wort and chiller is porportional to the diffrence in temperature between the two.

I wonder how a spiral that just sat at the top would cool.

salzar said:

Having convection forced(stirring) or natural through a temperature gradient will increase the rate of heat transfer.

This is why the chillers have the cold inlet coils towards the top. The rate of heat conduction between the wort and chiller is porportional to the diffrence in temperature between the two.

I wonder how a spiral that just sat at the top would cool.

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I tried this once in a larger batch. I suspended my IC with copper wires from the pot lid & kept it near the top. The top cooled quickly, the bottom much less so. I could run my hand on the outside of my keggle and readily feel the temp difference top to bottom.

All other things being equal, adding forced convection through manual (stirring) or other (whrilpool pump) means is probably going to get you the maximum practical amount of improvement.

Don't ignore the other brewing specific factors though. We want to get the whole wort down throught the critical temp range (minimum DMS production) and we want to avoid as much as possible any methods that would induce HSA.