TheHygienist
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So I don't want residual sanitizer in my corny keg, I just want to purge the oxygen with CO2 at a low psi. Sure I could use fermentation CO2 to do this, but using my CO2 bottle, these are the calculations. You can use 2 formulas. One is from https://www.gigacalculator.com/calculators/pipe-flow-rate-calculator.php whereas you use a pipe pressure to obtain flow rate. Easy enough.
PSI initial is 5 psi. Final PSI is near zero, say 0.00001 PSI because you will vent gases in the the keg into the atmosphere. I chose a line inside diameter of 4 millimeters. Line (pipe) length of 914 mm, or 3 feet. CO2 has a dynamic viscosity of 0.01502 cP (centiPoise).
Plugging in these parameters, we can see that applying 5 PSI to that line, will flow 0.56 cubic feet CO2 per second, or 33.6 cubic feet per minute, cfm.
So, the ambient air has at the most, 23% oxygen. At 10,000 ppm per 1%, that is 230,000 ppm that needs to be purged. Lets say we want to shoot for diluting that oxygen with CO2 down to 0.1 ppm.
Now we need to use a basic purge equation https://en.wikipedia.org/wiki/Dilution_(equation). We need to solve this equation for time ending, where time intial is of course, zero.
The volume of a 5 gallon corny keg is measured by height 23" and radius 4.25", or 1,305 cubic inches or 0.76 cubic feet. A 3 gallon keg is 0.52 ft3.
We now divide ppm by 1,000,000 to get a decimal for the concentrations. C-initial is 0.23 (230,000 / 1,000,000) and C-final is 0.1 / 1,000,000.
The dilution formula is used to solve for time, t:
Notice that the right side of the equation is negative.
So, solving this for time = 20 seconds (or 11 ft3 CO2).
So, applying 5 PSI of CO2 pressure through a 4 mm line into a 5 gallon corny keg while holding the PRV open to vent, should purge the oxygen down to 0.1 ppm, if you let it flow for 20 seconds. If you want to purge a 3 gallon keg, the time is 13.5 seconds.
You can of course, play with the line internal diameter, pressure, keg volume, and desired final concentration of oxygen to determine the purge time for your specific setup. And I'm just considering the maximum concentration of oxygen as 23% as an enriched atmosphere. You can get away with 21% if you like. For my IPA's, I'll want the final ppm to be lower than 0.1 ppm.
I think this saves a lot of trouble with filling kegs with sanitizer and then trying to get that junk out. Of course if you don't want to use 11 ft3 of CO2 or similar volume, simply purge your kegs with the CO2 blowing off your fermenter. To each his own.
PSI initial is 5 psi. Final PSI is near zero, say 0.00001 PSI because you will vent gases in the the keg into the atmosphere. I chose a line inside diameter of 4 millimeters. Line (pipe) length of 914 mm, or 3 feet. CO2 has a dynamic viscosity of 0.01502 cP (centiPoise).
Plugging in these parameters, we can see that applying 5 PSI to that line, will flow 0.56 cubic feet CO2 per second, or 33.6 cubic feet per minute, cfm.
So, the ambient air has at the most, 23% oxygen. At 10,000 ppm per 1%, that is 230,000 ppm that needs to be purged. Lets say we want to shoot for diluting that oxygen with CO2 down to 0.1 ppm.
Now we need to use a basic purge equation https://en.wikipedia.org/wiki/Dilution_(equation). We need to solve this equation for time ending, where time intial is of course, zero.
The volume of a 5 gallon corny keg is measured by height 23" and radius 4.25", or 1,305 cubic inches or 0.76 cubic feet. A 3 gallon keg is 0.52 ft3.
We now divide ppm by 1,000,000 to get a decimal for the concentrations. C-initial is 0.23 (230,000 / 1,000,000) and C-final is 0.1 / 1,000,000.
The dilution formula is used to solve for time, t:

Notice that the right side of the equation is negative.
So, solving this for time = 20 seconds (or 11 ft3 CO2).
So, applying 5 PSI of CO2 pressure through a 4 mm line into a 5 gallon corny keg while holding the PRV open to vent, should purge the oxygen down to 0.1 ppm, if you let it flow for 20 seconds. If you want to purge a 3 gallon keg, the time is 13.5 seconds.
You can of course, play with the line internal diameter, pressure, keg volume, and desired final concentration of oxygen to determine the purge time for your specific setup. And I'm just considering the maximum concentration of oxygen as 23% as an enriched atmosphere. You can get away with 21% if you like. For my IPA's, I'll want the final ppm to be lower than 0.1 ppm.
I think this saves a lot of trouble with filling kegs with sanitizer and then trying to get that junk out. Of course if you don't want to use 11 ft3 of CO2 or similar volume, simply purge your kegs with the CO2 blowing off your fermenter. To each his own.
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