Need help with math problem

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• 01-19-2005, 09:02 PM
midhvac
Thanks again Andy. I got it now. The reason for my questions was that I was trying to figure out how the different ductulator formulas work so I could use my scientific calculator to do them, or plug them into an Excel spreadsheet application. Somebody else here was asking about the formulas a while back, but nobody knew them. I found a formula that calculates the pressure drop per 100' when the cfm and duct diameter are known:

pd = (.109136 x CFM^1.9)/dia^5.02

But I wanted to know how to find the diameter when CFM and pd are known. With your help, I've got it now. My \$8.99 Casio scientific calculator won't allow me to use a decimal point in a fractional exponent, so I couldn't do ^1/5.02. So I just changed it from a fraction to a decimal equivalent of .1992

dia = (.109136 x CFM^1.9/pd)^.1992

• 01-19-2005, 09:34 PM
Steve Wiggins
I guarantee you this will seperate the Dems from the Repubs right quick. We will always have the thinkers vs. the doers.
• 01-19-2005, 10:55 PM
Andy Schoen
Quote:

Originally posted by midhvac
But I wanted to know how to find the diameter when CFM and pd are known. With your help, I've got it now. My \$8.99 Casio scientific calculator won't allow me to use a decimal point in a fractional exponent, so I couldn't do ^1/5.02. So I just changed it from a fraction to a decimal equivalent of .1992

dia = (.109136 x CFM^1.9/pd)^.1992

You've got the idea. :)

If I'm reading your equation correctly (I really should look it up), you can get precise answers doing the following on your Casio:

calculate A:

A = CFM^1.9

next B:

B = .109136 x A /pd

next C:

C = LN(B) this is the natural log of B (I'm assuming the Casio has log functions)

next D:

D = C / 5.02

finally E:

E = exp(D) this is the e^x function which is inverse to the natural log

• 01-19-2005, 11:01 PM
Andy Schoen
Quote:

Originally posted by glennwith2ns
Quote:

Originally posted by mattm
You big bunch of math nerds. :D :D
Yea , bet they got pocket protectors too>)

And only the best pocket protectors... :D We're still trying to figure out where to put that Parker name on them... :)
• 01-20-2005, 12:34 AM
condenseddave
Quote:

Originally posted by Andy Schoen
Quote:

Originally posted by glennwith2ns
Quote:

Originally posted by mattm
You big bunch of math nerds. :D :D
Yea , bet they got pocket protectors too>)

And only the best pocket protectors... :D We're still trying to figure out where to put that Parker name on them... :)

Do me a favor-------------DON'T put it on there.:D
• 01-20-2005, 12:35 AM
condenseddave
Quote:

Originally posted by Steve Wiggins
I guarantee you this will seperate the Dems from the Repubs right quick. We will always have the thinkers vs. the doers.
Are you lost again, buttcheek?
• 01-20-2005, 12:37 AM
condenseddave
Quote:

Originally posted by ac rookie
I think I am going into another field. I will never figure this stuff out!!!
It's not hard. Actually, to accomplish what Mid wants to accomplish, you spend fifty bucks on a ductulator that does this FOR you...:D
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