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| {{Merge from|Actual cubic feet per minute|discuss=Talk:Standard cubic feet per minute#Merger proposal|date=August 2011}}
| | Myrtle Benny is how I'm known as and I really feel comfy when people use the complete title. California is exactly where I've always been residing and I love every day residing here. My day job is a meter reader. Doing ceramics is what my family members and I enjoy.<br><br>my web-site ... [http://www.lankaclipstv.com/blog/165665 www.lankaclipstv.com] |
| '''Standard cubic feet per minute''' (SCFM) is the [[volumetric flow rate]] of a gas corrected to "standardized" conditions of [[temperature]] and [[pressure]], making it the equivalent of the [[mass flow rate]] of the gas. However, great care must be taken, as the "standard" conditions vary between definitions and should therefore always be checked. Worldwide, the "standard" condition for pressure is variously defined as an absolute pressure of 101,325 [[pascal (unit)|pascals]], 1.0 bar (i.e., 100,000 pascals), 14.73 psia, or 14.696 [[psia]] and the "standard" temperature is variously defined as 68 °F, 60 °F, 0 °C, 15 °C, 20 °C, or 25 °C. The relative humidity (e.g., 36% or 0%) is also included in some definitions of standard conditions. There is, in fact, no universally accepted set of standard conditions. (See [[Standard conditions for temperature and pressure]]).
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| The temperature variation has the largest effect. In [[Europe]], the standard temperature is most commonly defined as 0 °C, but not always. In the [[United States]], the standard temperature is most commonly defined as 60 °F or 70 °F, but again, not always. A variation in standard temperature can result in a significant volumetric variation for the same mass flow rate. For example, a mass flow rate of 1,000 kg/h of air at 1 atmosphere of absolute pressure is 455 SCFM when defined at {{convert|32|°F|°C|abbr=on}} but 481 SCFM when defined at {{convert|60|°F|°C|abbr=on}}.
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| In countries using the SI metric system of units, the term "[[normal cubic metre]]" (Nm<sup>3</sup>) is very often used to denote gas volumes at some normalized or standard condition. Again, as noted above, there is no universally accepted set of normalized or standard conditions.
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| ==Actual cubic feet per minute==
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| {{main|Actual cubic foot per minute}}
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| [[Actual cubic foot per minute]] (ACFM) is the volume of gas flowing anywhere in a system, independent of its temperature and pressure. If the system were moving a gas 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 a gas, a positive pressure or a [[vacuum]] must be created. When positive pressure is applied to a standard cubic foot of gas, it is compressed. When a vacuum is applied to a standard cubic foot of gas, it expands. The volume of gas after it is pressurized or rarefied is referred to as its "actual" volume.
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| SCF and ACF for any gas are related in accordance with the [[combined gas law]]:<ref name=Warehouse>[http://www.controlswarehouse.com/select.htm Controls Warehouse website] (scroll down to "Gas Flow Measurement"</ref><ref name=EPA>[http://www.epa.gov/eogapti1/module2/rate/rate.htm U.S. EPA website] (scroll down to "Conversion between Actual and Standard Gas Flow Rates"</ref><ref>{{cite book|author=Mark Ladd|title=Introduction to Physical Chemistry|edition=3rd Edition|publisher=Cambridge University Press|year=1998|isbn=0-521-57881-7}} (Equation 5.2, page 200)</ref>
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| :<math>\frac {P_1V_1} {T_1} = \frac {P_2V_2} {T_2}</math>
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| Defining standard conditions by the subscript 1 and actual conditions by the subscript 2, then:<ref name=Warehouse/><ref name=EPA/><ref>{{cite book|author=Robert J. Heinsohn and John M. Cimbala|title=Indoor Air Quality Engineering: Environmental Health and Control of Indoor Pollutants|edition= |publisher=CRC Press|year=2003|isbn=0-8247-4061-0}} (page 33)</ref>
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| :<math>{\rm SCF} = {\rm ACF}\,\cdot\,\left(\frac{P_{\rm actual}}{P_{\rm standard}}\right)\,\left(\frac{T_{\rm standard}}{T_{\rm actual}}\right)</math>
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| where <math>P</math> is in absolute pressure units and <math>T</math> is in absolute temperature units (i.e., either [[kelvin]]s or degrees [[Rankine scale|Rankine]]).
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| 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.<ref>[http://www.engineeringtoolbox.com/scfm-acfm-icfm-d_1012.html SCFM versus ACFM] (Specifically for air)</ref> In most cases of engineering design, the humidity correction for air is often quite small and hence often ignored.
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| ==Cubic feet per minute==
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| [[Cubic feet per minute]] (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. Unfortunately, gases are [[compressibility|compressible]], which means that a figure in cubic feet per minute cannot be compared with another figure when it comes the mass of the 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.
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| ==See also==
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| *[[Gas laws]]
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| *[[Standard conditions for temperature and pressure]]
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| *[[Standard cubic foot]] (SCF)
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| *[[Million standard cubic feet per day]] (MMSCFD)
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| ==References==
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| {{reflist}}
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| ==External links==
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| *[http://www.xchanger.com/tools_gfc.htm Xchanger Inc, webpage] Calculator for SCFM, NM3/hr, lb/hr, kg/hr, ACFM & M3/hr gas flows.
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| *[http://www.gerardgarcia.com/ACFM-versus-SCFM.html ACFM versus SCFM for ASME AG-1 HEPA Filters]
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| *[http://www.pdblowers.com/scfm_v_acfm.htm SCFM (Standard CFM) vs. ACFM (Actual CFM)] (Specifically for air flows only)
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| * [http://goldbook.iupac.org/S05910.html "Standard conditions for gases"] from the [[IUPAC]] ''Gold Book''.
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| * [http://goldbook.iupac.org/S05921.html "Standard pressure"] from the [[IUPAC]] ''Gold Book''.
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| * [http://goldbook.iupac.org/S06036.html "STP"] from the [[IUPAC]] ''Gold Book''.
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| * [http://goldbook.iupac.org/S05925.html "Standard state"] from the [[IUPAC]] ''Gold Book''.
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| *[http://www.grc.nasa.gov/WWW/K-12/airplane/fluden.html Gas Density]
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| *[http://www.aeromech.usyd.edu.au/aero/atmos/atmos.html Properties of the Atmosphere]
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| *[http://www.airisagas.com/media/ACFM_to_SCFM_vs_ICFM.pdf ACFM vs. SCFM vs. ICFM]
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| [[Category:Fluid dynamics]]
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| [[Category:Gases]]
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| [[Category:Chemical engineering]]
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Myrtle Benny is how I'm known as and I really feel comfy when people use the complete title. California is exactly where I've always been residing and I love every day residing here. My day job is a meter reader. Doing ceramics is what my family members and I enjoy.
my web-site ... www.lankaclipstv.com