Too cheap for a stout faucet

[mordantly]

co25 or whatever mix in a standard co2 bottle? did they change the valve?

[Brandon]

co25 or whatever mix in a standard co2 bottle? did they change the valve?

Great timing on this post. I happen to get a 70/30 mix just today. My guy has some adapters he uses.

[ajdelange]

[quote="Mylo" The law of partial pressures means that your 30 PSI of beergas will only result on 10 PSI of CO2 on your beer ....
Mylo[/quote]

Partial pressure calculations have to be done on absolute pressure (PSIA). Thus the statement above is correct as written if PSI means PSIA. OTOH if 30 PSI means 30 PSIG which is usually what we mean when we refer to gas pressure it corresponds to 44.7 PSIA and the absolute pressure of CO2 in a 30% mix is 0.3*44.7 = 13.41 PSIA which is less than one atmosphere. The corresponding gauge pressure is 13.41 - 14.7 = -1.29 PSIG.

[mordantly]

where does this -1psi come into play? thats a vaccum, no?

[ajdelange]

No, that's just the partial pressure of CO2 specified relative to 1 atmosphere (which is what ordinary gauges read). Thus, in this example, the partial pressure of CO2 is less than one atmosphere though the total pressure (sum of the partial pressures of nitrogen and CO2) is appreciably greater. If you had a container filled with this mix and somehow extracted all the nitrogen (react it with something, pass it through a molecular sieve that won't pass CO2...) and measured the pressure in the cylinder after the nitrogen was gone you would measure a partial vacuum.

Consider a bottle with pure nitrogen in it (no CO2 or anything else). The partial pressure of CO2 in such a bottle is -14.7 PSIG which is 0 psia.

[wunderbier]

The law of partial pressures means that your 30 PSI of beergas will only result on 10 PSI of CO2 on your beer ....
Mylo

Partial pressure calculations have to be done on absolute pressure (PSIA). Thus the statement above is correct as written if PSI means PSIA. OTOH if 30 PSI means 30 PSIG which is usually what we mean when we refer to gas pressure it corresponds to 44.7 PSIA and the absolute pressure of CO2 in a 30% mix is 0.3*44.7 = 13.41 PSIA which is less than one atmosphere. The corresponding gauge pressure is 13.41 - 14.7 = -1.29 PSIG.

I'm totally handicapped when it comes to this stuff, but is this how you'd figure out how many volumes that would be?

13.41 PSIA => 13.41PSI / 14.7 PSI = 0.912 atm

n/V = Vol. x (density/MW)
n/V = Vol. (L of CO2 / 1 L of beer) x (1.96 g of CO2 / L of CO2)/(44 g of CO2 / mol of CO2)
Vol. = 22.45(n/V) = 22.45(P/RT)
(*taken from Fix's PoBS)

Vol. = 22.45 x 0.912 atm / (0.0821 x 283 K) = 0.881 Volumes of CO2.

(Or, even more basically, that at standard temperature the 0.912 atm would mean 0.912 Volumes of CO2?)

[mordantly]

hmm. 14.7 psi only applies at sea level. but i get the jist of it.