Chemical Engineering Interview Question:

What is the difference between CFM (cubic feet per minute) and SCFM (standard cubic feet per minute)?

Submitted by: Administrator

CFM and SCFM are both measures of flow rate. CFM might refer to either the flow rate of a gas or a liquid, whereas SCFM refers only to the flow rate of a gas. The same mass flow rate of a gas (i.e., lbs/minute) is equivalent to various volumetric flow rates (i.e., CFM) depending upon the gas pressure and temperature. Thus, when gas flow rates are specified, it is very important to specify at what pressure and temperature the gas was measured. When the gas flow rate is specified as SCFM, it means that the flow rate was measured at a set of standard pressure and temperature conditions.

In the USA, the most common set of standard conditions used in industry is 60 degrees Fahrenheit and one atmosphere of pressure. Note that we have stressed most common, because there are other standard conditions that may be used. It is always best to spell out what standard conditions are being used (i.e., 1200 SCFM at 60 degrees F and 1 atmosphere pressure). When gas flows are expressed simply as CFM, the reader is can only speculate as to what gas temperature and pressure apply to that flow rate ... and, because of that, the CFM flow rate cannot be converted to a mass flow rate
Submitted by: Administrator