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  • Oxygenation ppm Lpm calculation

    Having trouble trying to decide what flow rate to use for in-line oxygenation. We still do not have a DO meter, but we do have an oxygen regulator with a flow meter on it now. We used to just eyeball it with the sight glass and a regular psi regulator. I've seen a few forumlas for roughly calculating oxygen ppm, and based on what I've plugged into those, they say I should be running my oxygen somewhere between 3.5 and 5.5 LPM during the transfer (which agrees with other people's calulcations i've seen on the board).

    With the old sightglass eyeball method, we would turn the oxygen on just enough so you could barely see bubbles in the sightglass with a flashlight and run it for the entire knock out. Now with the flow meter, 3.5 LPM seems like A LOT more than we were using before. I have to turn the flowmeter down to almost nothing, probably less than 0.5 LPM to get a similar flow to what we did before...

    We transfer at about 23 to 24 gallons per minute through about 47 feet of 1.5 inch hose, usually around 68F. Knock out takes about 30 minutes normally.

    So have we been under-oxygenating, or am I just way off here?

  • #2
    3.5 and 5.5 LPM during the transfer (which agrees with other people's calulcations i've seen on the board).

    With the old sightglass eyeball method, we would turn the oxygen on just enough so you could barely see bubbles in the sightglass with a flashlight and run it for the entire knock out. Now with the flow meter, 3.5 LPM seems like A LOT more than we were using before. I have to turn the flowmeter down to almost nothing, probably less than 0.5 LPM to get a similar flow to what we did before...
    Which calculations have you seen for 3.5-5.5 LPM? Most I've seen are more in the 0.5 to 1 LPM range. We run ours at 0.5 LPM (20 BBL knocked out in ~30-40 min) and have been pleased w/ the results so far. Obviously won't know for sure until we get a DO meter, but sometimes you have to work w/ what you have!

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    • #3
      Hmm, well now I can't find the old thread on here I was looking at... but it seems like .5 to 1 lpm is more appropriate. I guess I need a more accurate flowmeter, the one we have goes to 15lpm, and the low side is not that accurate...

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      • #4
        According to my calculations, if your oxygen pressure is at 1 bar / atmosphere, then assuming you are looking for 10 ppm, you want 0.61 litres / minute. So yes, it sounds as though you need a much smaller range flowmeter to get the accuracy.
        dick

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        • #5
          Thank you, that sounds about right. I guess we were not that far off before, but it will be nice to be consistent instead of guessing every time.

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          • #6
            By "flow meter" I assume you have a rotameter? Is this rotameter calibrated specifically for oxygen? Or what other gas? At what temperature? And what pressure? Do you have a fine aeration stone? Or are there large bubbles of oxygen that would not be completely dissolved, but instead be swept out of the fermenter with the onset of fermentation? In other words, will ALL of the oxygen added actually be dissolved? If we know these, then the calculation is quite straightforward. Let me know.
            Phillip Kelm--Palau Brewing Company Manager--

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            • #7
              This is the meter I have now. It is meant for oxygen. I don't know the specifics of it, got it used. http://i.imgur.com/m4SZ7Rg.jpg

              It is hooked up to a regulator supplying 1 bar pressure to it. I believe our stone is a 2 micron. O2 bubbles appear to be pretty fine and seem to be mostly absorbed, wort coming through the sight glass is clear, however a sample pulled from the fermenter is cloudy.

              Running this meter at .5 LPM still seems like more than what we were doing before, so maybe we have been under-oxygenating a little bit...

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              • #8
                They all look pretty much the same. The dimensions of the float and the rate of change of internal diameter of the tube change slightly from gas to gas depending on the density of the gas, but the differences are too subtle to be seen by eye. However if this meter is designed to be used with air, not pure oxygen for instance, then the differences will be so minor that it is not really worth worrying about. But the key with any gas injection is to obtain consistency of flow rate. Once you have consistency, then you can adjust the flow up or down according to the yeast / fermentation performance. Just because you are aiming for say 10 ppm, and consistently achieving that, doesn't mean that this is actually the optimal amount to add for your specific yeast, wort and other fermentation conditions. You have a rotameter to allow you to get repeatable gas injection - that is the first step only in getting optimal fermentation performance.
                dick

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                • #9
                  Calculation...

                  Dick does due diligence once again. Flow rate, stopwatch, taste, and measurements are the key. There are adjustment factors that you can look up for different gases, temperatures, and pressures than your meter is designed/calibrated for. That's a different exercise, and not really useful. More useful is cell counts and taste. TFA1337, Your meter is at least calibrated for the right gas. So let's make this easy and assume that your flow meter is also calibrated for 1 bar gauge pressure at 20C; the exact conditions that you are using it--at least for my assumption. And then I'll use some other assumptions about your specific conditions; like SG of 1.050 and an initial O2 concentration of 14ppm. At 23.5 gallons wort/minute=89 liters wort/minute, your calculation is as follows:
                  89 liters wort*1.050kg wort/liters wort=93.45kg wort
                  93.45kg wort*14kgO2/1,000,000kg wort=0.00131kgO2
                  0.00131kgO2*1000gO2/kgO2=1.31gO2
                  1.31gO2/32gO2/molO2=0.0409molO2
                  0.0409molO2*22.4 liters O2(@STP)/mol=0.916liters O2(@STP)
                  Somebody please check my math.
                  That is just less than 1 liter/min @STP. You are measuring at one atmosphere above STP, so this rate would actually be cut in half. Hence you would be looking at about half a liter per minute pure O2 IF you are getting 100% saturation. So CharlosCarlies and the rest are just about spot on for an academic review. How's the beer? Yeast growth? Cell counts? I think you're doing it about right with the new technique.

                  And by the way Warren, could you show us the calculation using Luddite measurements? ;^}
                  Last edited by gitchegumee; 08-12-2014, 06:43 AM.
                  Phillip Kelm--Palau Brewing Company Manager--

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                  • #10
                    I haven't used the calculator, but the logic is spot on. It is more or less what I use in my spreadsheet calc, except that I have not used wt / wt, but wt /volume - which of course introduces a difference to your calculation. But wt / vol has worked well when I have commissioned aeration & oxygenation units to get in the right ballpark before tweaking according to fermentation / yeast growth & vitality / beer flavour results. I used this particular calc because generally, dissolved oxygen is expressed as mg / litre (refer to Haffmans and Hac Lange optical oxygen sensors publicity blurb for examples).
                    dick

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                    • #11
                      Ok, I'm trying to turn gitchegumee's reply into a general purpose spreadsheet, and I have two questions.

                      Q1: Am I correct that, since we assume things like perfect 100% dissolving & similar, that it's ok to bump the flow rate by some buffer (50%? 2x?) to account for that.

                      (Further assume: O2 is relatively cheaper than a bad batch and I'm not particularly worried about over-oxygenation.)

                      Q2: Does it appear that I've correctly captured the math bits, here?

                      Click image for larger version

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                      NOTE: This is MacOS's Numbers.app, but I'd be happy to export it & share with anyone who asks.


                      Thanks!

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