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Homework Help: Thermal resistances adding formula

  1. Mar 25, 2013 #1
    1. The problem statement, all variables and given/known data
    Prove a rule for adding of Thermal resistances
    for: A)R1 and R2 in Series
    B)R1 and R2 in Parallel

    2. Relevant equations

    3. The attempt at a solution
    According to the book the result should be :
    A) R = R1 + R2
    B) 1/R = 1/R1 + 1/R2

    So i thought we can get some ideas from the theory of Electrical resistance because these formulas are similar for example here: http://www.grc.nasa.gov/WWW/k-12/airplane/ohmrser.html .
    However, I dont know how to start (in Thermodynamics there is no Electric current etc., so we can hardly use Ohm´s formula like in previous case).
    Thanks for help
    Last edited: Mar 25, 2013
  2. jcsd
  3. Mar 25, 2013 #2
    The thermodynamic analog of current is the Heat Current defined as the rate of flow of heat through the material and the analog of voltage is temperature difference
  4. Mar 25, 2013 #3
    OK, thank you.
  5. Mar 25, 2013 #4
    I get it
  6. Mar 25, 2013 #5


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    Science Advisor
    Homework Helper
    Gold Member

    Not exactly but...

    heat flow = ΔT/Thermal Resistance

    which is similar to

    Current = ΔV/Electrical Resistance

    I'll let you work out the units.
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