This preview shows page 1. Sign up to view the full content.
Midterm Comments
General comments:
1)
A standard cubic foot (SCF) is NOT a measure of volume.
It is a measure of
mass.
379 SCF is equal to one lbmol.
It is NEVER correct to convert the volume of gas
in some control volume at an arbitrary temperature and pressure into moles using the 379
SCF/lbmol conversion.
Example: An annulus of 11.76 ft
3
contains methane at 135 F and 100 psia. What
is the mass of methane?
WRONG ANSWER: 11.76 ft
3
× 1 lbmol/379 SCF = 0.031 lbmol
RIGHT ANSWER:
11.76 ft
3
/
.
One could
evaluate the molar volume from the ideal gas law:
2) A pound mass (lb or lbm) is a unit of mass. A pound force (lbf) is a unit of force. It is
NEVER correct to write 1 psi/day = 1 lb of gas per day per in
2
of annulus.
HINT: if you have trouble remembering the conversion between lb and lbf, go
straight to SI units.
There is never any confusion there.
A kg is a unit of mass, and a
Newton (kgm/s
2
) is a unit of force.
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 02/13/2012 for the course PGE 421K taught by Professor Bryant during the Spring '11 term at University of Texas.
 Spring '11
 BRYANT

Click to edit the document details