Where m is the solids mass flow rate in lbs/sec and A is the
cross-sectional area of the pipe in ft2. The gas mass flow rate in
lbs/sec is calculated based on the actual cfm of gas and gas
density introduced into the conveying system by the gas mover,
and the internal cross-sectional area of the pipe. Gas can be air
or any other gas. Use air as default if use of a different gas is not
given.