Richard,

I DO understand what CFM and SCFM mean. I worked with compressor
specification and air system analysis ,around the worl, for 25 years.
Please explain upon what authority you base your contention about CFM.
For one thing your definition of "Standard Conditions", which is what
the S stands for, does not match anything I have ever seen anywhere in
the world and believe me I have seen about every definition of SCFM
there is. A CFM is just what it says it is. One Cubic Foot per
Minute at any temperature, pressure or humidity. It can be used to
define VOLUME flow for any gas, but does not necessarily have any
relation to MASS flow (except in an accidental context). Common
compressor terms include ACFM, ICFM, SCFM, etc,etc.. ACFM is "actual
cfm which refers to whatever the compressor produces at discharge
conditions(say 125 psi , 300 deg F and 100% rh for instance). ICFM
is "inlet cfm" which is flow at whatever conditions happen to be at
inlet (say 12.7 psi , 20 deg F and 14% rh) , SCFM is the MASS flow at
standard conditions which, in the USA are generally 14.696 psig, 60
deg F and 0% relative humidity. In Europe it is standardized as 1 bar
pressure 0 deg C and 0% relative humidity or alternately 1 bar,25 deg
C and 0% rh, the primary requirement being to use the same convention
at all times. Incidentally in the USA, 379 STANDARD cubic feet of
air weigh 28.79 lbm and contain one mole of air. SCFM seldom has any
relationship to conditions at the inlet of the compressor since 0% rh
is virtually unobtainable in nature. Inlet pressure, temperature and
rh have very large effects on system performance and can result in
changes of several hundred horsepower on medium to large compressors.
Gary Hallenbeck
Senior Technical Specialist (Ret.)
Western Region
Ingersoll-Rand Air Compressors

On Wed, 24 Dec 2003 19:32:33 -0600, Richard J Kinch
wrote:

Grant Erwin writes:

CFM does not equal mass flow

No, this is wrong again. CFM *does* equal mass flow.

I think you don't understand what "CFM" and "SCFM" mean.

One CFM means a cubic foot of air at 1 atm pressure ("free" air), flowing
per minute. Or the equivalent mass of air at any other pressure. It does
NOT mean one cubic foot of air at any other pressure.

The "S" prefixed simply specifies the input free air is understood to be at
68 deg F and 36 percent relative humidity, to simplify the variations of
system performance (usually, but not always, slight) due to those
variables.