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Homework Help: Transposition Help

  1. Mar 29, 2012 #1
    Just need a bit of help with this.

    A = ( ( 2 X pi X k X L ) / (Ln(1.041) ) X (D - E)

    I know everything except D. How do i find it?
  2. jcsd
  3. Mar 29, 2012 #2


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    The expression needs clarification.

    Are all the variables scalars? (I presume so)

    In that case: step 1 - move everything except (D-E) to the left side and get:

    D-E = A Ln(1.041)/( 2 X pi X k X L ) (I switched left and right)
    Now add E to both sides.
  4. Mar 29, 2012 #3


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    Hi Tweaked9107! :smile:
    (please write a small x, or *, for "times" :wink:)

    That's of the form A = B/C(D - E) …

    multiply both sides by (D - E), then expand that bracket, then shove the E stuff over to the RHS :wink:
  5. Mar 29, 2012 #4
    In it's actual form it's:

    Heat Transfer = ((2 * pi * heat coefficient * length) / Ln(Outside Diameter - Inside Diameter)) X (Inside Temperature - Outside Temperature)

    That gives you heat transfer. My problem is i know all the figures for one end of the pipe to give me an answer. But i'm now trying to calculate what the inside temperature is further along the pipe. Whether than takes away any vagueness im not sure?
  6. Mar 29, 2012 #5


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    Is the D- E in the numerator or denominator of your original fraction? mathman is assuming it is in the numerator, tiny-tim is assuming it is in the denominator.
  7. Mar 29, 2012 #6
    I'll be perfectly honest. I have no idea what you mean.
  8. Mar 29, 2012 #7


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    Your equation is ambiguous in the last term. Is it multiplying the numerator or denominator?

    Can you use more parenthesis to remove this ambiguity?
  9. Mar 30, 2012 #8


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    he means, is it on the top or the bottom (of the fraction)? :smile:

    (and parentheses are brackets :wink:)
  10. Mar 30, 2012 #9

    Ray Vickson

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    He means: is it [tex] A = \frac{2 \pi k L}{\ln(1.041)} (D-E)= \frac{2 \pi k L (D-E)}{\ln(1.041)} [/tex] or is it
    [tex] A = \frac{2 \pi k L}{\ln(1.041) (D-E)}?[/tex]

    If you mean the first form you should write it as 2 pi k L (D-E)/ln(1.041), but if you mean the second form you should write 2 pi k L/[ln(1.041) (D-E)]. Use brackets.

  11. Mar 30, 2012 #10
    The first one was correct yes. So the first reply by mathman was correct. Thanks for your help guys, and sorry for posting in the wrong section.
    Last edited: Mar 30, 2012
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