Thermal Analysis Degree C / W and W / (m * K)

Discussion in 'General Electronics Chat' started by Johnb3_1, Apr 16, 2011.

  1. Johnb3_1

    Thread Starter New Member

    Apr 15, 2011
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    I am new to Heat Sink selection and calculations.

    I have run into two different representations for units of measure.

    For instance, I found some Thermal Joint Compound information that states that the thermal resistance is:

    0.05 Deg C / W.

    A table below that says that the Thermal Conductivity is:

    0.735 W / (m * K)

    Can someone walk me through the steps? I would like to understand mathematical relationship between these two values.


    Can you point me to where I can read it or write out the math form the conversion?

    Thanks

    John
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  3. someonesdad

    Senior Member

    Jul 7, 2009
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    Any basic heat transfer or physics book will give a decent introduction. I'd suggest going to your library, but it appears most folks don't use libraries anymore. If you're interested in an online summary, the basic phenomenon usually goes under the name of Fourier's law of heat conduction; see http://en.wikipedia.org/wiki/Conduction_(heat) for more info. You'll also see where the thermal resistance is defined as the reciprocal of thermal conductance. It's a useful concept where a bunch of layers are stacked because the resistances add to give the total thermal resistance. You've probably heard the term "R-value" in the context of home insulation and it's really referring to a thermal resistance.

    Note the Fourier Law is really for a steady-state type situation. When you start changing things with things like step changes in temperature and heat distributions, throughout a region of space, you really need to solve problems with the heat equation -- and then you're into second order parabolic partial differential equations for fun and profit.
     
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