Author Topic: Measuring resistance and carbonation?  (Read 1083 times)

Offline darkmorford

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Measuring resistance and carbonation?
« on: July 13, 2011, 12:43:49 AM »
(Two questions in one topic, but they're both involving test/measurement techniques)

Is there an inexpensive way to measure the volumes of CO2 in a particular beverage? One of the things I use my CO2 tank for is recharging sodas that have gone flat, and I'd like to bring the drinks back to their original carbonation level. I've turned up several places online citing 3.7 volumes for most sodas, but there have been a few claiming that the average is 5+! It also wouldn't hurt if I try to replicate a particular beer.

Secondly, I'm wondering how I could measure the flow resistance in my particular setup. Certainly the charts in sources like the Draft Beer Manual give good ballpark figures, but with so many variables involved there's something to be said for testing and getting the actual numbers. Whether it's beer or soda, getting the balance right is important.

Examples or ideas for DIY solutions are fine, too; I'm no engineer, but I'm plenty comfortable at the hardware store.

Offline Will's Swill

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Re: Measuring resistance and carbonation?
« Reply #1 on: July 14, 2011, 01:44:21 AM »
I got nuthin' for ya on the CO2 volume.  At least nothing practical.  I suppose you could put a CO2 saturated liquid in a new container with air in the headspace and a pressure gauge and derive the volume of CO2 originally in solution from the pressure at which the new container stabilizes.  But I'd think it woudl be easier just to experiment.

Flow resistance is easier.  I assume that you're talking about flow resistance from a keg through your beer lines?  If so, given the pressure in the keg and the change in height from the liquid surface in your keg to your tap, you can measure the flow rate from your tap and use Bernoulli's equation to figure out the head loss in your system due to flow resistance.
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Offline a10t2

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Re: Measuring resistance and carbonation?
« Reply #2 on: July 14, 2011, 01:57:42 AM »
Is there an inexpensive way to measure the volumes of CO2 in a particular beverage?

I guess you'd need to define "inexpensive", but they're pretty cheap by the standards of brewing equipment. This is the one I have: http://www.beveragefactory.com/draftbeer/regulators/detectors/2701-BCT_Beer_Carb_Tester.shtml

I'm sure you could rig up something similar and save some money.
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Offline darkmorford

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Re: Measuring resistance and carbonation?
« Reply #3 on: July 14, 2011, 06:40:29 PM »
I guess you'd need to define "inexpensive", but they're pretty cheap by the standards of brewing equipment. This is the one I have: http://www.beveragefactory.com/draftbeer/regulators/detectors/2701-BCT_Beer_Carb_Tester.shtml

I'm sure you could rig up something similar and save some money.
Quote from: Will's Swill
I got nuthin' for ya on the CO2 volume.  At least nothing practical.  I suppose you could put a CO2 saturated liquid in a new container with air in the headspace and a pressure gauge and derive the volume of CO2 originally in solution from the pressure at which the new container stabilizes.  But I'd think it woudl be easier just to experiment.
Amusingly, it looks like that's exactly what that gadget does! And it seems like it'd be pretty easy to rig up something similar; pour the liquid into a 2-liter bottle, seal it with a carbonator cap, then attach a pressure gauge to a gas disconnect and stick it on there. The trick then is calculating the CO2 volume from that pressure and temperature. I'm not entirely sure I know the math involved in deriving that, and the same goes for the flow rate. Like I said, not an engineer. Anyone want to give me a crash course? :P
« Last Edit: July 14, 2011, 07:42:39 PM by darkmorford »

Offline Will's Swill

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Re: Measuring resistance and carbonation?
« Reply #4 on: July 17, 2011, 12:58:54 AM »
Here's a good description of the process for determining volumes of CO2 in solution:

http://www.meheen-mfg.com/tankcarb.html

I think an assumption here is that the headspace in the sample container is small.

The equation for flow resistance expressed as head loss, and a calculator are here:

http://www.ajdesigner.com/phpbernoulli/bernoulli_theorem_equation_head_loss.php

If the variables with the subscript 1 refer to the surface of the beer in the keg, and the variables with subscript 2 refer to the beer exiting the tap, then you can set Z1 = 0, Z2 = the height difference of the tap from the surface of the beer, P1 = the pressure in the keg, P2 = 0, V1 = 0 (an approximation to keep things easy, or you can calculate V1 from V2), V2 = the volume/unit time from the tap divided by the cross-sectional area of the tap outlet.
Is that a counter-pressure bottle filler in your pocket, or are you just happy to see me?