1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thermal Conductivity - Estimate Temperature

  1. Apr 29, 2014 #1
    1. The problem statement, all variables and given/known data

    2mxl49.png

    Given an insulating case outer surface at 25C, radiates heat to surroundings at 20C. Find temperature inner surface.

    2. Relevant equations



    3. The attempt at a solution

    The heat is conducted through a thickness of 2.5mm, with a temperature difference of 5oC. Thus ##\frac{\partial T}{\partial z} = 2000##. Using ##k = 0.02##:

    We have a value for the flux:

    [tex]J = k\frac{\partial T}{\partial z} = 40[/tex]

    Using Stefan's Law:

    [tex]J = \sigma T^4[/tex]

    We get ##T = 163K##, and boy that is one cold case!(-110oC)
     
  2. jcsd
  3. May 1, 2014 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You seem to think the 5oC difference is between the iPod and the outside of the case.
    Looks to me as if that temperature difference is to be calculated from the flux.
    Stefan's law works two ways: 25 to 20 should be something like [tex]J = \sigma \left ( T_{\rm case}^4 - T_{\rm environment}^4 \right )[/tex]
     
  4. May 2, 2014 #3
    That's right, because ##J## is the net flux (caused by a temperature gradient). The answer turns out to be ##26.8^o##, which looks right.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Thermal Conductivity - Estimate Temperature
  1. Thermal Conductivity (Replies: 2)

  2. Thermal conductivity (Replies: 0)

Loading...