Talk:Standard cubic feet per minute

Proposed outline

30 years in turbomachinery aero-thermo development has given me a good feel for how SCFM, ACFM and CFM should be defined and used. However, I'm not quite the expert on how applications and sales misuse these terms. I think all discussions of these definitions need to include the continuity equation.

Where is the discussion of "flow"?

At this moment SCFM has a good start and ACFM is out the window.

I would propose the following outline,

• Fundamentals
  • flow
  • volume flow vs weight flow
  • inlet conditions
• Weight Flow
• CFM, ACFM
• SCFM

Mkoronowski 18:11, 18 March 2007 (UTC)

The discussion of centrifugal fans and the AMCA should be another article

The two sections discussing fans and the ACMA should be deleted and moved to another, new article. This article is about gas flow expressions (SCFM, ACFM, etc.) ... it is not about fans. Unless someone presents a good reason for not doing so, I will delete those sections within a few days. - mbeychok 23:55, 30 March 2007 (UTC)

I have just created a new article entitled Centrifugal fan. Since there have been no reasons posted against my above proposal to remove the fan and ACMA discussions from this article, I am accordingly proceeding to move those sections to the new Centrifugal fan article. - mbeychok 03:49, 5 April 2007 (UTC)

WARNING

Submitted by Mkoronowski 22:49, 13 July 2007 (UTC)

WARNING, this article should be used at your own risk! I think most knowledgeable individuals agree that abbreviations like SCFM and ACFM are seldom used outside academia, manufacturing industries and process industries. Further, professionals using these abbreviations typically prefer that they have academic meaning. As a result, professional organizations in this country, like ASME, ASHRAE, SAE, ASTM, NASA, NIST and API take great pains to define the quantification of flow with the inclusion of any necessary discussion of fluid/gas properties (density included).

Thus, as you have stated, “Standard Conditions” are associated with SCFM. My problem comes with the requisite “Actual Conditions” associated ACFM. This is not common standard practice! My experience is that ACFM is used by the same people that use the term “Free Air”; neither is appropriate.

In contrast, there is a common statement of “Inlet Conditions” that can be associated with ICFM.

I do not believe a discussion of ACFM is relevant unless a majority of the professional societies listed above define and use this term commonly. Until these organizations and their published standards are reference in this article, I warn everyone using this article that I consider it NON-RIGOROUS and QUESTIONABLE.

Submitted by Mkoronowski 22:49, 13 July 2007 (UTC)

Marty, I don't understand what concerns you about the term ACFM. As inferred from your second sentence just above, the term is indeed widely used (and has been for many decades) in the process industries, manufacturing industries and academia. I, myself, spent 40 to 50 years in process designing of oil refineries, natural gas processing and pipelining plants, and petrochemical plants .... and both SCFM and ACFM were very commonly used in designing those facilities. In fact, I might add, I don't understand why you seem to think that engineers working in the process industries and manufacturing industries are somehow unknowledgeable and non-professional. There are thousands of mechanical engineers, chemical engineers and others working in the process industries and manufacturing industries who use ACFM (and its metric system counterpart) on a daily basis to define gas flow rates.

I know that you are a very expert centrifugal compressor aerodynamicist. But, in my opinion, this article was intended to cover the definition of SCFM and ACFM in the much broader general fields of engineering whenever gas flow rates must be defined. It was never intended to focus on the very narrow field of the aerodynamics of centrifugal compressors and fans. If that is why you are concerned, then I would suggest you write a new article devoted to the aerodynamics of centrifugal compressors and fans ... or a new section in this article.

I might also add that there was no reason to be so alarmist in making your comment. Really, there no need for such language as "WARNING, this article should be used at your own risk!!". Regards, - mbeychok 00:00, 14 July 2007 (UTC)

ACFM has a definition, yet ICFM does not?

Submitted by Mkoronowski 19:01, 15 July 2007 (UTC)

This Wiki entry is titled SCFM. Yet, it discusses, SCFM, ACFM and CFM with the specific exclusion of ICFM. My experience has been that use of ICFM is at least as common as ACFM.

Marty, if you feel that the article need a section on ICFM, just go ahead and add one. Regards, - mbeychok 20:14, 15 July 2007 (UTC)

From a different point of view, I’ll wager that many of the problems that occur in processing plants comes from turbo machines either not meeting the flow or pressure rise requirements. Thus the need for standards provided by ASME (like the PTC and Fluid Meters Handbook), ASHRAE (like the Fundamentals Handbook), SAE, and API (like the Code-617). Experience supports that it is important to verify the flow specification with every end user such that the above standards are achieved. Use of ACFM, is often thought of as a less-knowledgeable specification, that almost always leads to a request for any or all of the following; ambient conditions, the inlet static conditions, inlet total/stagnation conditions, flange geometry and a specification of fluid properties. Anything that is necessary to double check the requirements.

My experience in turbo machinery has forced me to clearly understand the specifications from and successfully design equipment for end users that include Linde/Praxair, BOC, Air Products, Liquid Air, Kodak, Shell, Carrier, BP, Exxon, ARAMCO, Trane, Ford, General Motors, Toyota, Big Three, Eastman Chemical and DuPont. I suggest that there have been many difficulties understanding this topic exactly because of the incomplete detail shown in this entry.

Is this wiki entry open to rigorous additions and changes? Until then, the Warning stands.

Submitted by Mkoronowski 19:01, 15 July 2007 (UTC)

Of course, your Warning stands. Removing comments from a Talk page by anyone is frowned upon in Wikipedia. You have misunderstood my comments about the use of ACFM in the process and manufacturing industries because you are focused primarily on compressors. Process plants such as oil refineries or petrochemical plants (for example) have a great deal of equipment other than compressors. They have many, many reactors, absorption towers, distillation towers, flue gas stacks and many hundreds of piping runs, all of which handle gas flows ... and as I said before, it is very common practice to use SCFM and ACFM as appropriate to describe such gas flows. Yes, it it necessary to provide the temperature and pressure defining ACFM. It also necessary to provide the reference temperature and pressure for SCFM because there is no universally accepted set of reference temperature and pressure (see Standard conditions for temperature and pressure ).

The fact that you have encountered some specifications using ACFM without including the relevant temperatures and pressures is no reason to denigrate the use of ACFM. Once again, if you believe this article needs a separate section on ICFM, please write such a section. If you elect to do so, please include how it relates to SCFM. Regards, - mbeychok 20:14, 15 July 2007 (UTC)

Do I understand your comments correctly?

Submitted by Mkoronowski

An addition of ICFM is okay, however:

Additions or changes to SCFM are not allowed.

Additions or changes to ACFM are not allowed.

Additions or changes to CFM are not allowed.

Submitted by Mkoronowski

You are once more mis-interpreting and mis-stating what I said. I never said anything was "not allowed". In fact, I didn't even use the word "allow". It is not up to me to allow or not to allow anything. You may edit or revise anything you want. And subsequent editors will be free to change anything that you or I or anyone else does to the article. That's how Wikpedia works.

I may be wrong but you seem determined to debate and argue rather than have a rational discourse ... so goodbye and good luck. There is no longer any benefit to be gained from continuing this discussion. Regards, - mbeychok 02:22, 16 July 2007 (UTC)

Working Copy for revisions, What do you think?

Submitted by Mkoronowski 19:11, 16 July 2007 (UTC) Submitted by 71.174.227.194 19:08, 16 July 2007 (UTC)
SCFM
(Standard Cubic Feet per Minute) is the volumetric flow rate of a gas corrected to "standardized" conditions of temperature, pressure and relative humidity, thus representing a precise mass flow rate.

$MassFlowRate={\bigg (}Density{\bigg )}{\bigg (}VolumetricFlowRate{\bigg )}$

where

$Density={\bigg (}{\frac {P_{static}}{T_{static}}}{\bigg )}\,{\bigg (}{\frac {1}{R_{GasConstant}}}{\bigg )}$

However great care must be taken, as the "standard" conditions used to determine $P_{static}$, $T_{static}$ and $R_{GasConstant}$ vary between definitions, and should therefore always be checked.

Marty, if you look at the first sentence just above, you will find two links (colored blue), one for volumetric flow rate and one for mass flow rate. By simply clicking on those links, you are automatically taken to the the corresponding Wipedia articles for those subjects. For example, click on mass flow rate and you will find

"Mass flow rate can be calculated from the density of the liquid (or gas), its velocity, and the cross sectional area of flow.

${\dot {m}}$ = ${\rho \cdot V\cdot A}$

where:

${\dot {m}}$ = mass flow rate

${\rho }$ = density

V = velocity

A = flow area

The mass flow rate can also be calculated by multiplying the volume flow rate by the density.

${\dot {m}}$ = ${\rho \cdot Q}$

where:

${\rho }$ = density

Q = volume flow rate"

I don't understand why your two above equations are needed in this article when the reader simply has to click on that link (what I call a Wiki link) to find the essentially the same equations and same information. That is precisely the reason why Wikipedia provides for internal links to existing articles ... so that the same information is not repeated time and time again in other articles.

Also, if one uses the Universal gas law to calculate the density, one obtains:

$Density={\bigg (}{\frac {P}{T}}{\bigg )}\,{\bigg (}{\frac {M}{R}}{\bigg )}$

where M is the molecular weight (molar mass) of the gas whose density is being calculated.

Note that this equation differ from yours in that the molecular weight of the gas is not included in your equation ... and that is because your equation is not using the Universal gas law constant R. Your equation is using the gas specifc constant R_s. The two constants are related by R_s= R/M. I know that many aerodynamicists use R_s without explaining that it is not the Universal gas law constant. But the large majority of the audience for this article will not be aerodynamicists ... they will be engineers, chemists and other technologists who will be confused because they almost always use the Universal gas law constant. It is important to explain which constant is being used.

To summarize:

• I don't believe that your above two equations are needed at all, since readers can easily use the mass flow rate and volumetric flow rate links given in the first sentence of the article to find the same information.
• If is strongly felt by others that the density equation is needed, then it should be the version that uses the Universal gas law constant R because most of the potential audience use the universal constant. See this link to another Wikipedia article: Density.

Regards, - mbeychok 00:20, 17 July 2007 (UTC)

Submitted by Mkoronowski 21:29, 17 July 2007 (UTC)

Thank you for the quick response. You raise valid points. The idea of Wiki is wonderful. I think most of the current audience is either novices interested in the topic or professionals in other areas trying to gain a better understanding. So it is from this perspective that leads me to several of the following thoughts beyond the eventual inclusion of an appropriate ICFM statement.

It is likely that people reviewing this entry include both the process industry and the automotive industry. Obviously, a great portion of the process industry deals with real gases that have pipe velocities limited to 150 ft/s while the turbo/super-charger segment of the automotive industry deals with moist air that have pipe velocities varying to 400 ft/s.

So my concerns are trying to introduce how real gas properties, moist air and compressibility, as they affect conversions from SCFM to ACFM. On a humorous level I am certain that there is an engineering manager out there that will hand calculate some of these parameter values and questions why someone is bring up these other issues in meeting. This is reinforced by a incident where a company’s consultant made a simple error, that allowed a 10% performance bonus to be avoided.

1)What do you think is the best way to address these topics in a general fashion?

2)In your practice, how is the universal gas law corrected for higher velocity real gases?

Submitted by Mkoronowski 21:29, 17 July 2007 (UTC)

Marty, I have been retired for over 7 years and I am 84 years old now and not in very good health. So I am no longer "in practice".

1) As for the best way to address how real gases (rather than ideal gases) affect the relationship between SCFM and ACFM, I suggest you write a sub-section in the ==ACFM== section. Because that is the section where the discussion and equations about relating SCFM and ACFM is currently located. You might entitle it ===Effect of real gas behavior===. Note that subsection title headers have three === at beginning and end whereas full sections have only two == at beginning and end. Also section and subsection headers only capitalize the first letter.

2) During my career, we corrected the Universal gas law to reflect real gases by simply including the compressibility factor Z so that the Universal gas law became PV=ZnRT. See the Wikipedia articles Compressibility factor and Theorem of corresponding states.

3) As for the effect of higher velocity real gases, I am completely ignorant of that subject. In 95+ percent of the time, our process designs were accurate by simply using ideal gas laws and behavior.

4) I am sure that nowadays there are equations of state and simulation programs such as Aspen Plus that can be used when the effect of real gas behavior must be used. And they are probably more accurate than simply using the compressibilty factor.

5) If you use the Universal gas law constant R in any of your edits (including the eventual addition of a new section on ICFM), be sure to use R rather than R_s and to state that it is the Universal gas law constant.

Now just dive in and write your new sub-section and your new section. If you make mistakes in formatting or in subject matter, subsequent editors (myself included) will correct them ... that you can be sure of. I would strongly suggest that you work on them in your personal sandbox and perfect them before you copy and paste them into this article. You can even ask readers (on this Talk page) to review your sandbox and offer comments there before you put them into this article. And keep in mind what I have said before, namely that aerodynamicists will be a very small part ot the potential audience. Engineers, chemists and other technologists will be most of the audience. Regards, - mbeychok 23:53, 17 July 2007 (UTC)

The “standard” conditions are usually defined as "Standard Temperature and Pressure" (STP): or more precisely "Standard Temperature, Pressure and Relative Humidity" (e.g., 1 bar, 0°C, 0%RH).
The definition of Standard Pressure is commonly established at 1 atmosphere of absolute pressure (e.g., 101325 Pascals, 1.01325 bar, or 14.7 psia). In some groups, typically in the United States, variations might occur (e.g., 101,300 Pascals, 100,000 Pascals, 1 bar, or 14.5 psia).

The definition of Standard Temperature in Europe is most often 0°C (32°F). However, in the United States numerous basis are used. Common Standard Temperetures include: 32°F, 60°F (15.5°C), 68°F (20°C), 70°F (21.1°C), 77°F (25°C) and 95°F (25°C).

The definition of Standard Relative Humidity is often 0% or dry for non-air applications. In many air applications definitions of 60% are commonly seen. Only due too the impact upon performance, turbomachinery applications are known to use 100%

Thus, for the same mass flow rate, the value of SCFM using a typical standard from thhe United States can be nearly 10% greater than the European values. For example, a mass flow rate of 1000 kg/hr of air at 1 atmosphere of absolute pressure is 455 SCFM defined at 0°C (32°F) but 489 SCFM defined at 68°F (20°C}, which is the most common basis in the United States.

Current end of proposed revision dated 07/16/07 71.174.227.194 19:08, 16 July 2007 (UTC) Submitted by Mkoronowski 19:11, 16 July 2007 (UTC)

ACFM

Actual Cubic Feet per Minute (ACFM) is the volume of gas flowing anywhere in a system, independent of its temperature and pressure. If the system were moving air at exactly the "standard" condition, then ACFM would equal SCFM. Unfortunately, this usually is not the case as the most important change between these two definitions is the pressure. To move air, a positive pressure or a vacuum must be created. When positive pressure is applied to a standard cubic foot of air, it gets smaller. When a vacuum is applied to a standard cubic foot of air, it expands. The volume of air after it is pressurized or rarefied is referred to as its "actual" volume.

SCF and ACF (for any gas) are related in accordance with the combined gas law:

${\frac {P_{1}V_{1}}{T_{1}}}={\frac {P_{2}V_{2}}{T_{2}}}$

Defining the standard conditions by the subscript 1 and the actual conditions by the subscript 2, then:

$SCF=(ACF)\,{\bigg (}{\frac {P_{actual}}{P_{standard}}}{\bigg )}\,{\bigg (}{\frac {T_{standard}}{T_{actual}}}{\bigg )}$

where $P$ is in absolute pressure units and $T$ is in absolute temperature units (i.e., either kelvins or degrees Rankine).

To be very precise when the gas is air, then the above equation should include correcting for the difference between the relative humidity of the air at the standard and the actual temperature and pressure conditions. In most cases of engineering design, the humidity correction for air is often quite small and hence often ignored.

CFM

CFM is an often confusing term because it has no single definition that applies to all instances. In the most basic sense, CFM means cubic feet per minute. Sounds simple enough right? Unfortunately, air is a compressible gas. To further confuse the issue, a centrifugal fan is a constant CFM device or a constant volume device. This means that, provided the fan speed remains constant, a centrifugal fan will pump a constant volume of air. This is not the same as pumping a constant mass of air. Again, the fan will pump the same volume, though not mass, at any other air density. This means that the air velocity in a system is the same even though mass flow rate through the fan is not.

See also

• Standard conditions for temperature and pressure
• Standard cubic foot
• MMSCFD

External links

• ACFM versus SCFM for ASME AG-1 HEPA Filters
• SCFM (Standard CFM) vs. ACFM (Actual CFM) (Specifically for air flows only)
• "Standard conditions for gases" from the IUPAC Gold Book.
• "Standard pressure" from the IUPAC Gold Book.
• "STP" from the IUPAC Gold Book.
• "Standard state" from the IUPAC Gold Book.
• Gas Density
• Properties of the Atmosphere

References

Submitted by 71.174.227.194 19:08, 16 July 2007 (UTC)

Submitted by Mkoronowski 19:12, 16 July 2007 (UTC)

I have to say I object to the SCFM/ACFM conversion formula because it's misleading and in some cases wrong. From a practical matter most flow meters measure the volumetric flow rate indirectly. For example a rotameter relates Q to the force acting on the float which lines up with a reading but the force scales with the fluid density to the negative one half power. A very different trend is given then the one derived in this article. My objection is the conversion factor is always dependent on the type of flowmeter used and someone looking for information on it takes away an incorrect one size fits all formula from the article instead of the correct "it depends" answer.

BlatantHeroics 05:07, 12 October 2007 (UTC)

BlatantHeroics, with all due respect, I beg to differ with you. The conversion equations in the "ACFM" section are not misleading and are not wrong. They simply provide conversions for gas flows in pipelines, meters and any other process plant equipment ... as derived from the Universal gas law. And that is what the section is about: the conversion of any gas flows from one set of temperature and pressure conditions to another set of temperature and pressure conditions. In some rare cases, the equation may have to incorporate the compressibility factors ... which is quite easily done.

The equations in the "ACFM" section are for not meant for any special conventions or calculations in calibrating volumetric or mass flow meters to a reference set of temperature and pressure conditions. Read reference 1 (in the "ACFM" section) which is from the website of a gas flow meter distributor and provides the same equations as in the "ACFM" section. Also read reference 2 which is from an online tutorial from the U.S. EPA website which again confirms the equations in the "ACFM" section. Or simply talk to any experienced chemical engineer.

Rather than labeling the conversion equations as "misleading or wrong", perhaps what is needed is to create a new article devoted to flow meters. Regards, - mbeychok 08:34, 12 October 2007 (UTC)

I believe my scarcity with words caused my comments to be misinterpreted. What I meant was that I found the section leading to the equation misleading because I feel it does an insufficient job of describing the circumstances of its application such that a user unfamiliar with the jargon will misuse a correct equation in an incorrect circumstance to yield a wrong answer and be oblivious to it. I do agree most of my objection would be best suited for a flow meter article but my concern is that someone will type in SCFM or ACFM before typing in flow meter. What I would like to be able to do is to alert someone in this mindset that this is insufficient and direct them to the proper article without deterring the current article. How to do that I'll need to dedicate some more thought to. BlatantHeroics 03:57, 17 October 2007 (UTC)

22.414 L @STP

As an old neophyte, I was looking for the 1 mole of a gas equals ? volume and only found it in this article - 22.414 L at "STP" with no indication of which STP definition is used. Shouldn't it be included, especially given the warnings in the next paragraph?AMPbd (talk) 01:11, 20 April 2011 (UTC)

Molecular weight of Hydrogen (H2)

Is 2.014 not 1. — Preceding unsigned comment added by 86.2.241.107 (talk) 19:03, 9 June 2011 (UTC)

Compressibility

It would be helpful to include compressibility (Z) terms in the equations both for flowing and reference conditions. The person who showed me this article was trying to use it as an argument for including compressibility and flowing conditions, but to ignore it as reference conditions. My understanding is that using a mixture of compressibilities is always incorrect (although it often makes little difference, since Z is very close to 1 at reference conditions for many gases).

It would be fine to state that as a good approximation it is reasonable to omit both compressibility terms when both flowing and reference conditions are similar (i.e. similar Temp + Press).

Thanks for your consideration,

86.2.241.107 (talk) 19:15, 9 June 2011 (UTC)Andy Walters

Compressibility

It would be helpful to include compressibility (Z) terms in the equations both for flowing and reference conditions. The person who showed me this article was trying to use it as an argument for including compressibility and flowing conditions, but to ignore it as reference conditions. My understanding is that using a mixture of compressibilities is always incorrect (although it often makes little difference, since Z is very close to 1 at reference conditions for many gases).

It would be fine to state that as a good approximation it is reasonable to omit both compressibility terms when both flowing and reference conditions are similar (i.e. similar Temp + Press).

Thanks for your consideration,

86.2.241.107 (talk) 19:15, 9 June 2011 (UTC)Andy Walters

Normal Cubic Meters redirects here

This article has nothing to do with Normal Cubic Meters, the redirect should be altered. — Preceding unsigned comment added by 76.10.151.168 (talk) 18:04, 6 August 2011 (UTC)

That's what I thought, too (and this article here also links to normal cubic metre, so this is a selflink). I'm not an expert at all, though, I was just looking for a matching interwiki link for the articles gathered at Wikidata item d:Q350023 (previously interwikilinked to Standard cubic foot which is obviously not correct, as a foot is not a meter). --YMS (talk) 11:34, 23 September 2013 (UTC)