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Homework Help: Logarithmic mean temperature difference for heat transfer

  1. May 22, 2016 #1
    1. The problem statement, all variables and given/known data
    [Update: just realized that the LMTD is a temperature difference, so my question was not valid] :P

    Calculate the logarithmic mean temperature difference (LMTD) to heat water flowing through a tube from 21 C (Ti) to 40 C (Te) if the tube has a fixed temperature of 45 C (Ts).
    I should then calculate the length needed, which I can do. I am stuck with calculating the logarithmic mean temperature difference as I get a number that is less than the initial temperature of the water, which I know should be wrong!

    2. Relevant equations
    LMTD = (Ti - Te)/(ln[(Ts-Te)/(Ts-Ti)])

    3. The attempt at a solution
    For the given parameters:
    LMTD = (21-40)/(ln[(45-40)/(45-21)]) = 12.1 C
    Last edited: May 22, 2016
  2. jcsd
  3. May 28, 2016 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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