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Homework Help: Energy emitted by radiation from a pipe

  1. Sep 4, 2010 #1
    1. The problem statement, all variables and given/known data
    A vertical steam pipe of diameter 8 cm and emissivity e=0.8 has it's surface at 950C. The surrounding air and the temperature of the room and things in it are at 270C.
    What is the heat emission rate H from the pipe, for meter length, by radiation?

    2. Relevant equations
    Stefan's law: [itex]R=e\sigma T^4[/itex]
    [tex]\sigma=5.672\times 10^{-8}\left[Watt/m^2\right][/tex]

    3. The attempt at a solution
    [tex]R=0.8\cdot 5.672\times10^{-8}\left(373^4-300^4\right)=511\left[Watt/m^2\right][/tex]
    [tex]H=511\cdot \pi \cdot 0.08\cdot 1=128\left[Watt/m\right][/tex]
    [tex]128\left[Watt\right]\div 4.186=30.6\left[Calorie/Sec/m\right][/tex]
    The answer, according to the book, is [itex]29\left[Calorie/Sec/m\right][/itex]
  2. jcsd
  3. Sep 4, 2010 #2
    95C is ~368K not 373K, though using 368K I get only 28 cal/s/m
  4. Sep 4, 2010 #3
    The book uses Kelvin as Celsius+273
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