Question

If air flowrate at STP is 4 cubic feet per minute, what is the mass flow rate?

Answer 1

The relation between mass flow and volumetric flow of gases is

Q = mRTZ/144P

where,

Q = Actual Cubic feet per minute = 4 cubic feet per min
m = mass flow in lb/min = ?
P = Pressure in psia = 14.7 psia
R = Universal gas flow constant =R/MW_air = 1545 (ftlbf/lb mol ^oR) / 28.873 lb/lb mol
T = Gas temperature in ^oR = (68 ^o F + 460) = 528 ^o R
Z = compressibility = 1.0 for pressures below 50 psig


m = Q*144P / RTZ = (4 * 144* 14.7 )/ [1545/28.873]*528*1.0 = 0.299 lb/min

mass flowrate of air = 0.299 lb/min