Hydtools,
That is an interesting variant. Never seen partial pressure called ppm, but that's no big deal. I'm sure that the ppm value is really "theoretical partial pressure of moisture at 100% RH" even though it doesn't say so (if not then you would be applying the RH factor twice).
SCF and Sm3 and Nm3 are all MOLAR flow. Yes, when you are talking specifically about air - its also mass flow, but for a given gas (be it methane or hydrogene) a SFC is 1.19804 moles (0.0026412 pound moles - no matter if its air, methane or any other gas.
That is a very interesting point Morten and you are correct. Saying scfm is analogous to mass flow assumes one is referring to one gas. But , I believe that most equations that use scfm also factor in density, and the two together are analogous to mass flow. But, I also haven't given it a whole lot of thought.
For those who haven't seen Morten's magic number before - remember that this applies only if your standard conditions are 60 F and 14.73 psia.
It is like the magic number of 22.41 litres of gas per gram mole that those of us who grew up under the old IUPAC rules of standard conditions being 101.3 kPaa and 0 C came to know and rely on. Unfortunately IUPAC revised their standard pressure to 100 kPaa and the magic number became 22.71 litres per mole.
It true that IUPAC changed _their_ refernce condition - but that why you shold always state your definition somewhere - even when referring to SCF. In Denmark even the Danish Authorities uses 1 atm as the reference pressure for fiscal metering - not 1 bara.
But the most common mistake is to confuse nm3 (at 0 deg C) and Sm3 (at 15 deg C). Here its more than 5%.
