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Standard cubic feet per minute (SCFM) is the volumetric flow rate of a gas corrected to "standardized" conditions of temperature and pressure. It is related to the mass flow rate of the gas by a multiplicative constant which depends only on the molecular weight of the gas. There are different standard conditions for temperature and pressure, so care is taken when choosing a particular standard value. Worldwide, the "standard" condition for pressure is variously defined as an absolute pressure of 101,325 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. 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 but 481 SCFM when defined at . In countries using the SI metric system of units, the term "normal cubic metre" (Nm3) 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. ==Actual cubic feet per minute== (詳細は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. SCF and ACF for any gas are related in accordance with the combined gas law:〔(Controls Warehouse website ) (scroll down to "Gas Flow Measurement"〕〔(U.S. EPA website ) (scroll down to "Conversion between Actual and Standard Gas Flow Rates"〕〔 (Equation 5.2, page 200)〕 : Defining standard conditions by the subscript 1 and actual conditions by the subscript 2, then:〔〔〔 (page 33)〕 : where is in absolute pressure units and 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.〔(SCFM versus ACFM ) (Specifically for air)〕 In most cases of engineering design, the humidity correction for air is often quite small and hence often ignored. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Standard cubic feet per minute」の詳細全文を読む スポンサード リンク
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