I asked this question last night and got an answer. The answer is totally appreciated, but my gut feel is there is something mathematically wrong here... I was expecting the wind speed to be upwards of 40km/hr, not .7km/hr. Would someone be able to review the math used in the answer? Thank you kindly.
The Original Question...
Convert CFM to KMPH?
ok... I have a fan with a 36" diam capable of moving 10,354cfm. The fan is mounted in a round tube that tapers down to a 2'X2' square tube. Through the 2' x 2' section of tube, approximately what sort of wind speed can I expect? Also, can you provide a formula that can help me calculate this for different CFM values.
The Answer I got...
2' x 2' = 4 square foot cross section
10354 ft3/min / 4 ft2 = 2588.5 ft/min
2588.5 ft/min * 0.000305 km/ft = 0.7894925 km/hr
This, of course, asuumes 100% efficiency. I hope this helps you.
2007-11-17 16:33:44 · 4 answers · asked by seanb_111 1 in Science & Mathematics ➔ Engineering
Hmmmm.... I see what he did... Okay it's simple... take the answer provided above and multiply by 60 to get your answer. See, all they did was take a Kil. per hour and broke it down to Kil. per minute and forgot to convert it back.... basically, a cubic foot is equal to .02 k/hr. Now divide .02 by 60 so both factors are now per minute not min vs. hr. Get it? so he's representing KPM not KPH. Other than that, I don't know, I've never tried to figure anything like this out before. see if it's right.... = .7894925KPM * 60 Min. = 47.36955 KPH..... Hope i've helped. have a goodnight.
2007-11-17 17:54:18 · answer #1 · answered by alan s 1 · 0⤊ 0⤋
When doing this type of problem there is a very easy way to set this up in excel ..right now i cant tell you where to get that data but just keep looking...any way you calculate the velocity of the 10354cfm in the 36" area...by finding the area of the 36" circle =7.065sq ft then divide that into the 10354which equals 1465.53ft/min
now you neck this down to a 2x2 square which has 4 sq ft...so you take the same 10354cfm divide it by the 4 sq ft and you get 2588.5 ft/min which is good
now convert feet to km .000348km/ft x 2544.5=.885486 km/min then times 60 for the hours 53.13 km/hr...
This looks right to me but check it...i think you just may have left off the hour part in your question ....from the E
2007-11-18 01:06:34 · answer #2 · answered by Edesigner 6 · 0⤊ 0⤋
Actually your friend gave an answer of 0.7895 km/hr. This is not correct. He changed his unit without converting. What his answer really is, is 0.7895 km/min and not 0.7895 km/hr. One more conversion is needed.
0.7895 km/min*60min/1hr=47.34km/hr.
2007-11-18 02:27:17 · answer #3 · answered by Scott S 4 · 0⤊ 0⤋
I'm no math whiz, so I can't check everything but I believe the answer forgot to convert minutes to hours.
If I'm correct your answer should be multiplied by 60
.7895X60= 47.37 KPH
2007-11-18 00:44:41 · answer #4 · answered by don_sv_az 7 · 1⤊ 0⤋