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Homework Help: Need Help with Thermo Energy Transfer problem

  1. Sep 12, 2008 #1
    A 0.2-m-thick plane wall is constructed of concrete. At steady state the energy transfer rate by conduction through a 1-m^2 area of the wall is 0.15 kW. If the temperature distibution is linear through the wall, what is the temperature difference across the wall, in K?

    i dont even know where to start, anything will help...
     
  2. jcsd
  3. Sep 12, 2008 #2
    I have been doing some work on this.. and i have came up with an answer, im pretty sure its not right though..

    Using Fourier's law:

    Qx= -kA[T2-T1/L]

    we know that the Qx is .15kW per 1 m^2, and the thickness of the concrete plane is .2 m

    If .15kW of energy enter 1.0 m^2, then only .03 kW enter the area of .2 m??

    right now i have .03kW= -k(T2-T1/ .2m)

    im stuck..
     
  4. Sep 12, 2008 #3
    Why is this? I don't think you understand the concept of "heat flux" which you represent as Qx. Heat flux is the rate of heat transferred given an area. In math form thats

    q" = [tex]\frac{dQ}{dt}[/tex] = Qx

    So if you have 0.15kw of energy being transferred over 1m^2 of area, what is your heat flux going to be?

    You are also going to need to look up the transfer coefficient (k) for concrete. I imagine this is in your book somewhere.
     
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