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Definition of SCFM

Definition of SCFM

Definition of SCFM

(OP)
Hello,

Does anyone know if there is a widely accepted spec that defines air properties at 'standard' conditions?  I'd like to convert measured CFM to SCFM but I've seen SCFM defined a few ways:
- pressure is usually 1 atmosphere (14.696 psia)
- humidity is usually 0%, or not specified (one source mentioned 60%)
- temperature is sometimes 60F, sometimes 68F, sometimes 25C

Thanks!

ko  (www.ecooling.biz)

RE: Definition of SCFM

You are right that the standard conditions are different and this has been discussed in past threads. The common conclusion among the members is to specify the temperature and pressure conditions based on which the SCFM is calculated to avoid any confusion. However, general notation is 60F, 14.696psia and 0%.

You can visit the following links for various views.
thread798-106556
thread124-95060
thread135-97506
thread378-90884
thread378-97454

Regards,

RE: Definition of SCFM

(OP)
Thanks, quark!  I searched under SCFM but didn't find those threads.

ko  (www.ecooling.biz)

RE: Definition of SCFM

ko99, you just point to each of the listed threads, press your mouse selecting button and voilá.

RE: Definition of SCFM


In Fan Engineering the combinations used for standard air are:

                         U.S.                  SI          
Dry air
Humidity             0%                  0%
Pressure        29.921 in Hg     101.325 kPa
Temperature      70oF               21oC
Density        0.075 lbm/ft3        1.2 kg/m3

Moist air
Humidity            50%                50%
Pressure        29.921 in Hg     101.325 kPa
Temperature     68oF               20oC
Density        0.075 lbm/ft3       1.2 kg/m3    
  

RE: Definition of SCFM

ko99:

There are many definitions of standard conditions that have been used in the USA for a standard cubic foot of gas.  And then there are even more definitions of standard conditions used in the metric world.

It is also true (as already pointed out by others in this thread) that this question has been raised and discussed many, many times in Eng-Tips.

In the USA, the most common definition is the one widely used in the oil and gas industries, namely 60 degrees F and 14.696 psia.  At those conditions, 1 pound-mol of any ideal gas equals 379.48 scf.

But since there are other definitions, one should always state the reference conditions of temperature and pressure when using the term scf.

Milton Beychok
(Contact me at www.air-dispersion.com)
.

RE: Definition of SCFM


Actual pound-molal volumes of real gases after correction for Gas Law deviation show almost negligible differences from the 379.48 scf quoted by mbeychock. These may be significant, however, when measurements involve moneys.

Some molar volumes at the standard conditions stated by mbeychock, are:

Oxygen               379.19
Nitrogen              379.38
Hydrogen            379.72
Methane             378.74
Ethane               376.29
Ethylene             377.08
Propane             372.69
n-Butane            366.66
Carbon dioxide    377.35
Sulfur dioxide     372.12
Ammonia            374.92

RE: Definition of SCFM

25362, that is a very useful list of properties. Could you give a reference for the data please?

Thanks
katmar

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