Need help with math problem

[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

[Steve Wiggins]

I guarantee you this will seperate the Dems from the Repubs right quick. We will always have the thinkers vs. the doers.

[Andy Schoen]

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

[Andy Schoen]

Originally posted by glennwith2ns

Originally posted by mattm
You big bunch of math nerds.

Yea , bet they got pocket protectors too>)

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

[condenseddave]

Originally posted by Andy Schoen

Originally posted by glennwith2ns

Originally posted by mattm
You big bunch of math nerds.

Yea , bet they got pocket protectors too>)

And only the best pocket protectors... 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.

[condenseddave]

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?

[condenseddave]

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...