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Homework Help: Blackbody Rooftop

  1. Apr 30, 2014 #1


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    1. The problem statement, all variables and given/known data
    The black roof of a building has an emissivity of 0.9 and an absorbtivity of 0.8 for solar radiation. The sun beats down at midday with an intensity of 300 BTU / hr ft2.

    a) If the temperature of the air and the surroundings is 68 °F, if the wind velocity is negligible, and if no heat penetrates the roof, what is the equilibrium temperature of the roof ? For the rate of conduction / convection use q/A = 0.38 (T) 1.25, where T is the temperature drop between the roof and air in degrees F.

    b) What fraction of the heat from the roof is lost to radiation.

    2. Relevant equations

    3. The attempt at a solution
    For this problem, assume the effective sky temperature on that day is -10F. also, the "rate of conduction / convection" just means the overall rate of conduction + convection away from the roof.

    I am wondering if I approached this correctly. I used wolframalpha to solve the equation.

    Attached Files:

  2. jcsd
  3. Apr 30, 2014 #2


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