View Full Version : 250cfm to lbs of air
02-13-2006, 02:13 PM
I need help can anyone help me convert 250cfm to lbs of ait assuming the temp is 70 deg.F
02-14-2006, 10:55 PM
I have the data for dry air at 20º C, which is 1.225 kg/m³. This is only about 68º F, but it is as close as I could find, and should provide a fairly accurate estimate.
1 ft³ = 0.0764741882572885 pounds
250 * 0.0764741882572885 = 19.118547064322125
250 CFM is about 19.11 pounds/minute
05-15-2006, 09:13 PM
i had originally had a much larger explanation with calculations but my computer turned off right as i finished.
any ways, use the percent composition of the different gasses in "air" to find what one mole of "air" weighs. which turns out to be 28.9701 g/mol.
use the equation V= [nRT]/P (where V=volume, n= # of moles, R= 0.08206, T=temp in kelvin and P=pressure in atm(which i assumed to be 1)) to find the volume of one mole of gas at 70 degrees (294.261 kelvin) which is equal to 24.1471 L
250cfm = 7079.21 L/min
divide that by 24.1471 to get moles per minute = 293.1703 mol/minute
multiply that by 28.9701 g/mol to get grams per minute = 8493.1718
divide this by 28.35 to get ounces per minute
and divide again by 16 to get pounds per minute
in the end you get 18.7239 pounds per minute
07-02-2007, 10:36 AM
Please check your calculation since I believe that 70 Centigrade is actually 343.15 degres Kelvin.
Otherwise, the calculations are in order. This would result in a lower value.
The headers do not align but you see the values.
Temp in K Temp in C Air Volume- Liters Flow rate -mol/min Flow rate -grams/min Flow rate -ounces/min Flow rate -lbs./min
298 25 24.9529 283.7024554 8218.888503 214.3126076 13.39453798
309 36 25.8740 273.6030152 7926.306712 206.6833562 12.91770976
313 40 26.2090 270.1064911 7825.012057 204.0420354 12.75262721
343 70 28.7210 246.4820166 7140.60867 186.1957932 11.63723708
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