Need help with math problem - Page 2
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  1. #14
    Join Date
    Feb 2004
    Location
    Midwest
    Posts
    9,932
    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



  2. #15
    Join Date
    Nov 2000
    Location
    Waco, Texas, USA
    Posts
    6,153
    I guarantee you this will seperate the Dems from the Repubs right quick. We will always have the thinkers vs. the doers.
    "And remember my sentimental friend......that a heart is not judged by how much you love, but by how much you are loved by others" - Wizard of Oz.

  3. #16
    Join Date
    Apr 2002
    Location
    Ann Arbor, MI
    Posts
    2,985
    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


  4. #17
    Join Date
    Apr 2002
    Location
    Ann Arbor, MI
    Posts
    2,985
    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...

  5. #18
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    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.

  6. #19
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    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?

  7. #20
    Join Date
    Sep 2001
    Location
    East Stroudsburg, PA
    Posts
    13,215
    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...

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