Definition of SCFM 1

[ko99]

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 (

http://www.ecooling.biz)

 

[quark]

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,

 

[ko99]

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

ko (

http://www.ecooling.biz)

 

[25362]

ko99, you just point to each of the listed threads, press your mouse selecting button and voil[á].

 

[25362]

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 70^oF 21^oC
Density 0.075 lbm/ft³ 1.2 kg/m³

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

 

[mbeychok]

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)
.

 

[25362]

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

 

[katmar]

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

Thanks
katmar

 

[25362]

The data can be obtained from

http://webbook.nist.gov/chemistry/

by looking at fluid properties.