Kinks in Immersion Chiller: trouble or not?

[JayMac]

Haha, seems like I'm posting everywhere on this forum. That's what I get for starting out with AG brewing and assembling all of my equipment myself!

I was very impatient last night and decided to coil my 50' of copper tubing for my immersion chiller. The coils were fine, but as you all know... bending 1/2" copper in a 90 degree is nearly impossible without a tool... or at least if you don't want any kinks

I tried anyways, and got a few kinks (they could be worse, but luckily I reacted quickly to the kinking). I was wondering if it was worth it to try and bend/shape it out, if I should just cut off from the kink, buy a tool, and do it properly, or just leave it alone.

I'm in my third year of chemical engineering (chill, I'm in Canada so I'm legal!), and as I'm sure quite a few of you are mechanical/chemical engineering, I'm sure some of you know of Bernoulli's equation. Essentially, it would follow from applying this equation to the system, that the kink will have no effect on the flow of water. If we view the system as two points, one being the inlet conditions of the water entering the chiller, and the other being the exit, kinks should have no effect on the flow of water. However, Locally it should affect it, by increasing the water velocity, but immediately after it should slow down again... the conclusion I'm drawing here is essentially... it shouldn't matter, shouldn't it? (Of course the kink would have a higher coefficient than a smooth bend, and would increase the turbulence, but these would contribute to an essentially negligible increase in friction loss).

What do you guys think? Is it really a cause of worry? I could understand in a CFC it would be a problem if the kink was in the wort lines (build up of nasties), but it doesn't seem like a problem to me since this is an IC.

Any input would be much appreciated!

 

[H-ost]

If you feel you will still get a good flow out of it, use it. If it turns out it doesn't have a nice flow then start troubleshooting.

Have you tested it yet? No reason to fix something that isn't broken.

 

[kh54s10]

I'm no engineer but if the water flows through the chiller there should be no problems.

I have small kinks in mine but by the looks of it there is no constriction just a different shape, oval instead of round.

 

[wilserbrewer]

I'm in my third year of chemical engineering (chill, I'm in Canada so I'm legal!), and as I'm sure quite a few of you are mechanical/chemical engineering, I'm sure some of you know of Bernoulli's equation. Essentially, it would follow from applying this equation to the system, that the kink will have no effect on the flow of water. If we view the system as two points, one being the inlet conditions of the water entering the chiller, and the other being the exit, kinks should have no effect on the flow of water.

I went to school a long time ago and guess things have changed since then....back in the old days, a pipe w/ less cross sectional area (kinked)would have less flow than a normal one.

Whether you still have enough flow or not I have no idea, guessing if it is minor damage, it will still work fine but just require more pressure to achieve the same flow rate.

 

[JayMac]

I think I figured it out. It's not due to the pipe having a smaller diameter at the point of restriction, as all this would cause is an increase in velocity in the kinked segment. I believe it's due to the increase in pressure upstream of the kink. Although a hose with a kink will exit at the same pressure (atmospheric) as a non kinked hose, the kinked hose will cause a higher pressure upstream from the restriction. This increased pressure drop over the system is responsible for a decreased flow.

From what I've looked up, it seems studies have been done on fire hose kinks, and it seems that one 90 degree kink exhibits negligible losses, but this is likely a bigger problem with copper. Obviously adding more kinks further complicates the problem, so I may need to cut at least one of the kinks off.

I'll see what I can do about reducing the size of the kink. Then I'll see how fast the hose itself takes to fill up a gallon and I'll do the same with the chiller attached. If they are similar I guess there Is no need to change anything.

 

[buzzkill]

if you can lay kink on hard surface and LIGHTLY tap with hammer you may be able to open it up some.

 

[codycodycody]

I don't understand this kink equation, but I know when my garden hose kinks up, less flow, more pressure.

 

[caseycain]

Hi JayMac,

Let me comment on your worries . First, let me clarify the Bernoulli's equation:

It is an equation meant to generalize, as you say, a local change in diameter for steady-state flow. The keyword being steady-state flow. Total energy is conserved in the localized area, thus volume/sec in = Volume/sec out.

But this doesn't determine what the mass flow rate actually IS. That is determined by, very similar to current flow in conductors, (P_in - P_out)/Resistance, where P is pressure. We care about that total Resistance of your tubing, which is in general made up of 2 factors: lamilar resistance /foot, and the extra resistance that is from the bends/kinks in the system that can affect friction coefficients, etc. In all but the most extreme cases, the resistance introduduced by kinks, dents, even of pretty large size, will be dominated by the lamilar resistance/foot.

The takeaway: Will a pretty good dent/kink affect flow rate? Yes...but it is insignificant. Especially at 50 foot length. Moving the height of the chiller lower (pressure differential due to gravity/Potential energy) would have much more noticeable affect in flow.

In fact, I had a copper tubing coil that I was using as a chiller (20ft 3/8" ID). Recently I decided I would bend it into a shape that looked like the retail versions, without a tube bender (big mistake btw). Even though one bend has a pretty large kink/dent, I can detect no visible decrease in flow rate when hooked up to my pond pump for ice water.

So don't sweat it, you'll be fine!

C. Cain,
PhD student EE

 

[amandabab]

Your an engineer, cut out the kinked 90 degree bend, get a adjustable wrench and throw a brass 90 degree compression fitting on it, brew beer.

 

[beergarcia]

I could not have said it simpler I do not think you need all these equations 50' of 1/2" tubing even at a slowed rate is still going to cool wort. It is not rocket science!

 

[JayMac]

haha thanks guys. It chills my wort in well under 20 mins. I guess reading everything saying "DON'T LET IT KINK" got me a little nervous. Works beautifully