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Homework Help: Transfer of heat question

  1. Apr 20, 2010 #1
    1. The problem statement, all variables and given/known data

    The amount of heat per second conducted from the blood capillaries beneath the skin to the
    surface is 240 J. The energy is transferred a distance of 2.0×10−3mthrough a body whose surface area is 1.6 m2. Assuming that the thermal conductivity is that of body fat 0.2 J /(s ⋅m⋅o C) , determine the temperature difference between the capillaries and the surface of the skin.

    So k = .2
    A = 1.6 m^2
    L = 2.0 x 10^-3m

    I'm not sure what the 240 J goes as? Is that Q?


    2. Relevant equations

    This is basically where I'm stuck... I'm not sure what equation to use.

    I was thinking possibly Q = k * A * change in T * time all divided by L .... but there's no mention of time?


    3. The attempt at a solution
     
  2. jcsd
  3. Apr 21, 2010 #2
    You wrote down the right equation. Notice that give you a rate of heat transfer so you can divide time over to the left side of the equation.

    Then it's just a substitution of information problem.
     
  4. Apr 21, 2010 #3
    So...

    Q/t = k * A * change in T / L

    240 = .2 * 1.6 * change in T / 2 X 10^-3

    So the answer would be 1.5 degrees?

    I think that's right... thanks
     
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