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Old 01-11-2012, 12:59 PM   #1
spearko520
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Default Flow Rate For O2

Does anyone have any formulas to determine flow rate for oxygen? I have charts indicating what rates (in liters/min- i can convert that to cfm- i think) are required to reach suggested O2 ratios in ppm. The physical data i would have would be the psi of my gauge on bottle and discharge side, the outlet diameter and length of the discharge tubing, and the atmospheric pressure at point of discharge. There probably should be some sort of co effecient in there for the characteristics of the stone itself, but i figured i'd start with the open end of the hose first, since maybe the stone manufacturer calculated that into the flow rates they suggest on their table. Short of putting a flow meter in line and maybe marking some numbers on my gauges, does anyone know some sort of formula to figure all this out? Thanks in advance!!!

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Old 01-11-2012, 01:40 PM   #2
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The formulas are certainly out there but it isn't sufficient to have the formulas. You must also have good numbers to put into them such as the effective Cv for the stone and I don't know where you would get that. Also, the pressure gauge on the typical regulator isn't that accurate and will be set for such low pressure that it is in the least accurate part of its range. Thus, if you really want to measure flow a flow meter is the only practical way to go. The ones where the flow pushes up on a weight aren't too terribly expensive (unless you buy them from Cole Parmer).

Another approach is to use a sintered stainless "stone" which produces fine bubbles and to set the flow so that the bubbles just break the surface. That method usually works. But in any case all of this is moot unless you know how much O2 you are actually delivering to the wort and to know that you must have a DO meter. Now you are talking serious money.

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Old 01-11-2012, 09:36 PM   #3
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i think i have a curve for the stone. You are right about the psi on my reg- i am at a crack- definitely < 1 psi. I was hoping i can use my manometer and see how many WC" im pushing and plug in some values to some sort of formula and get some cfm. Then I can convert to Liters/minute and use the chart to get a fair idea. right now, i have just been cracking and letting the bubbles break, like you say- for about a minute or so for reg strength, three minutes for high gravity (with another dose in 12 hours)- i haven't been having any problems, but i'm kind of curious. Math is free but meters cost money- i guess i'll have to break it to my accountant that i need another tool. When she asks if it's for beer or work, i will have to once again explain how the two are inextricably linked and can never be divided. Just want to make sure i'm keeping the little guys at their best. Thanks!

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Old 01-11-2012, 09:44 PM   #4
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I just open my reg enough to see the wort churn inline.

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Old 01-12-2012, 02:19 PM   #5
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This data is from measuring with the previous generation version of this Milwaukee meter. 5.5 gallons of wort in a carboy and a .5 micron stone.

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Old 01-12-2012, 11:29 PM   #6
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Thanks - i'm still confused though- how would i determine that i have the flow number (3 l/min)? that's my question. i' wondering if anyone knows the equation for flow - like cfm (l/min)equals something discharge pressure times some coeffiecient for friction loss in tubing x area of discharge over at x atmospheric pressure. The differnece between my reg being cracked a tiny bit and running balls out seems pretty significant - but i am curious to know what that difference is. Thanks for the chart though. Looks like you've got some pretty nice brews in the batter's box...

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Old 01-13-2012, 04:15 AM   #7
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The flow rate is approximately the square root of the pressure drop times a constant. You will have to obtain the constant by calibration. To do this fill a 1 or 2 liter flask with calibration marks on the side with water and the turn it upside down with its mouth beneath the surface of the liquid in a pan. Put the stone into the water in the pan and turn on the gas until you get a reasonable flow rate. Read the pressure on the manometer and then slip the stone into the mouth of the flask at the same time you start a stopwatch. Watch the gas level in the flask and stop the stopwatch when it reaches 1 L or some other convenient number. Divide the number of liters by the number of minutes - that's the flow in LPM. From this find Cv from Cv = P/sqrt(LPM). Then use C in P = Cv*Sqrt(3) to determine the pressure required for 3 LPM (which is quite a big flow IMO). Readjust the manometer for the new pressure and check.

For precise work you would need to correct for temperature and the vapor pressure of water in the head space but precision is not required here.

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Old 01-13-2012, 12:43 PM   #8
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Thanks - you are the man! This will be a fun little science project for my daughter and I.

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