ACFM & SCFM - Same, Yet Very Different
When discussing a gas flow on a baghouse, I hear CFM quite frequently. Which makes sense as we are discussing the rate a volume of gas is being moved across a point. In this case, it would be cubic feet of gas per minute entering the baghouse.
This is all well and good, but which CFM is being referenced? Actual or Standard?
They both describe the rate a volume of gas is being moved across the point, but the conditions of that gas can be extremely different. Therefore, it is important to understand the conditions of the gas being measured. And when in doubt, ask which is being referenced. You may find out apples and oranges are being discussed.
ACFM – Actual Cubic Feet per Minute
Actual cubic feet of gas per minute, the volume of the gas flowing per minute at the operating temperature, pressure, moisture and elevation.
SCFM – Standard Cubic Feet per Minute
Standard cubic feet per minute. These standards are set by the American Society of Mechanical Engineers (ASME). The volume of gas flow per minute at standard conditions is dry, 70? F and sea level.
If the actual system is at greatly different conditions than to STP (Standard Temperature and Pressure), the system being looked at would be very different to each person in the conversation. Therefore, it is crucial to the discussion—and to correctly identifying root cause and system resolution—that everyone understands what units are being discussed.
Thank you Breanne Malott for the Awesome Graphic!!! (LinkedIn Profile Link)
Senior Process Engineer at Brentwood Industries, Inc.
5 年This is an excellent article.? It is well worth a few minutes time to double-check the basis when given a flow in "cfm" or in "scfm".? As the article points out, an an "acfm" flow is very different from an "scfm", and it is important to understand both terms.? An acfm is an actual volume flow and is used for sizing ductwork, fans, and gas processing equipment.? A scfm is the actual flow corrected to standard conditions, and may be thought of as a psuedo mass flow.? In the world of the Process Engineer, the situation is painfully complex.? The use of the term "scfm" is deeply ingrained and ubiquitous.? The definition of "standard conditions", however, varies by industry.? In the Chemical Industry, standard conditions are based on 32 deg F and 1 atm.? In the Natural Gas and Petroleum Industries, standard conditions are based on 60 deg F and 1 atm.? The Fan Industry uses the ASME definition of 70 deg F and 1 atm.? EPA test methods define standard conditions as 20 deg C and 1 atm.? The old IUPAC basis was 273 deg K (32 deg F) and 1 atm (14.7 psia).? The modern IUPAC basis is 273 deg K and 1 bar (14.5 psia).? It is very, very easy to assume you are on the right page only to later discover you were not.? This can result in mis-sizing process equipment or creating performance problems in the field.? Control systems can be particularly susceptible.? I once had to troubleshoot an air compressor performance problem and found that the annubar had been factory calibrated to read scfm based on 32 deg F while the DCS control algorithm had been written in terms of scfm based on 60 deg F. ?
Applications and Sales. Aplicación y Ventas. Aplica??es & Vendas.
5 年Education and training for designers, maintenance people, projects engineers, etc. related with ventilation systens. Fundamentals is in many ways source of many big mistakes for equipment and systems