Midterm Grading Comments

Midterm Grading Comments - Midterm Comments General...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
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 lb-mol. 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 lb-mol/379 SCF = 0.031 lb-mol 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 (lb-f) 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 lb-f, go straight to SI units. There is never any confusion there. A kg is a unit of mass, and a Newton (kg-m/s 2 ) is a unit of force.
Background image of page 1
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.

Ask a homework question - tutors are online