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Homework Help: Rate of Heat Transfer of a Composite Pipe

  1. Jul 11, 2017 #1
    1. The problem statement, all variables and given/known data
    A composite pipe made of steel pipe ( ks = 16 W/m.K) of inner and outer radius of 0.5 and 1.0 cm and a plastic pipe (kp = 0.092 W/m.K) of inner and outer radius of 1 and 1.25 cm, respectively. If the inner surface of the steel is maintained at 900 °C and outer surface of plastic is maintained at 300 °C. The rate of heat transfer per unit length is close to?

    2. Relevant equation
    Outside area of pipe: Ao=π*do
    Inside area of pipe: Ai=π*di

    3. The attempt at a solution
    Sigma is boltzmann's constant (6.6667E-8 W/m^2.K^4) I do not know if these equations are the right ones to use because i cannot find an equation for the emissivity. What equation am i missing to solve?
  2. jcsd
  3. Jul 11, 2017 #2


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    The mechanism for heat transfer in this problem is conduction ?
  4. Jul 11, 2017 #3
    Okay... With that being said i need to use these equations:
    qk=(ΔT)/(Rk steel + Rk plastic)
    Rk steel= (ln |ro steel/ri steel|) / (2πkl)
    Rk plastic= (ln |ro plastic/ri plastic|) / (2πkl)

    and use 1 m for the length of the pipe?
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