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I'm looking at building a jockey box with a 70', 5/16" (21.3m, 8mm) stainless steel coil (installed in a drum-style cooler.) Seems to be a good compromise between size, weight and cost.

How quickly can I pull cold beer out of it without it foaming?

My back-of-envelope calculation says a 2133.6cm by 0.8cm coil holds π × 0.42 × 2133.6 = 10723 or just over a litre of beer. The Mythbusters say you can cool a six pack of beer in five minutes with salted ice water, so I'd interpolate that one beer per minute would be achievable.

Can anyone confirm my theory with experimental evidence?

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the updated maths were incorrect - you'd used 0.3125cm - it should have been 0.3125in or ~0.8cm (0.793) for the diameter, and then you only need half that squared for computing the area. –  mdma Aug 10 '12 at 18:30

1 Answer 1

The cooling effectiveness of the coil is a function of several things:

  • Contact surface area
  • Contact time
  • The difference in temperature between the warm beer and cool water.

The MoreBeer Draft Box has 50 feet of 3/8" tubing, providing about 700 square inches of contact surface versus your proposed 69 square inches. So I would say you need to run the beer approximately 10x slower than the MoreBeer model to get similar cooling, which may be prohibitively slow.

Also, Mythbusters is a fun show but I wouldn't trust it for any real measurements or proof of anything. They say that a 6-pack of beer cooled in 5 minutes, but how warm was the beer to start? How much cold water did they use? Was there any circulation? Assuming they had enough water, it probably doesn't matter if you're cooling 1 beer or 6, since all the cans have the same volume and surface area, so I don't think you could cool a single can in only 1 minute.

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Looks like there's a mistake - the surface area of 70 feet x 5/16" is 0.3125 x 3.141 x 70 x 12 = 824 sq inches, so larger than the morebeer. I think you forgot to multiply by the 70 ft by 12. –  mdma Aug 10 '12 at 14:48
    
@mdma: The original poster proposed a 70 inch coil, not 70 feet. Unless that was a typo on Robert's part. –  Henry Jackson Aug 10 '12 at 16:07
    
Ah yes, hehe, or my mistake... I read it as 70 feet, but the OP does write 70 inches, seems very short. –  mdma Aug 10 '12 at 16:15
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You're right, it's 70 feet, not 70 inches. I've adjusted the maths. Join us in the 21st century in order to avoid this confusion in the future won't you please, America? :-P –  Robert Atkins Aug 10 '12 at 17:42
    
Sure - I'm from Europe, I would have happily done it in metric if you wrote all lengths in metric in the original post. PS: It still says 70 inches, I'll edit it. –  mdma Aug 10 '12 at 18:22

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