Air to Cloth Ratio & The Tale of Two Units
It was the best of units; it was the worst of units… The use of air to cloth ratio hasn’t been around as long as Charles Dickens, I think, but it has been in use for some time. The measurement at its most basic is a Ratio of the Total Volumetric Air Flow through a baghouse in relation to the Total Cloth Area in the baghouse. The ratio is used commonly for design purposes as well as comparing different baghouses, but what about the units of measure that make up the ratio? This is where the ratio becomes “The Tale of Two Units.”
The original units of measure to calculate the Air to Cloth Ratio is a Volumetric Gas Flow Rate divided by Total Cloth Area. Taking the units at face value, a perspective view on Air to Cloth is the number of volumetric units that pass through 1 square of cloth. Using standard imperial units for a baghouse with an Air to Cloth of 4, this would represent 4 ACFM (Actual Cubic Feet per Minute) passing through 1 square foot of Cloth. This is easier to see, in the mind’s eye, with respect to the actions taking place within the baghouse, but can the Units provide a different perspective?
The answer is they can, but they need to be reduced by removing the common units found in the numerator and denominator. This takes a little algebraic gymnastics regarding the volumetric flow rate, which is itself a ratio, divided by an area. Again, with imperial units, this would be ACFM divided by Square Feet. The long and the short is the remaining units are a velocity, and again in imperial units, this would be Feet per Minute. With the same baghouse described above with the Air to Cloth Ratio of 4, the face velocity of the gas at the filter cloth would be 4 Feet per Minute. For some, the mind’s eye has a better view of speed than the number of volumes of a gas passing through one square area of cloth. To each his own.
Thus, “The Tale of Two Units” and how one ratio can be viewed from two different perspectives…
Vice President Of Engineering at CalPortland
5 年In my experience many OEMs and equipment suppliers specify far too high A/C ratios. These result in high maintenance costs and emissions failures. Also when using modern cartridge style filters the A/C needs to be even lower as these cartridges can plug easily if too much dust load is introduced. Another factor of course is the purpose of the dust collector. Is it continuously loaded or periodically loaded?
Regional Sales Manager at Processbarron
5 年Compressed air consumption, air distribution - pressure drop should also be considered.
Principal/Co-Owner at STL Engineering, LLC
5 年Specifying a baghouse on air to cloth alone is not very smart. You have to look at the interstitial velocity as well.