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Homework Help: Heat transfer through brass and rubber

  1. Apr 29, 2015 #1
    1. The problem statement, all variables and given/known data
    Two identical brass plates, each 0.5 cm thick, are separated by a rubber spacer of thickness 0.1 cm which has the same cross sectional area. If the outer surfaces of the brass plates are kept at 0 °C and 100 °C respectively, calculate the temperature at each side of the rubber spacer given that the thermal conductivity of brass is 500 times bigger than that of rubber.

    2. Relevant equations
    I used dQ/dt= -KA*(change in temperature/distance traveled)
    k is thermal conductivity of material
    3. The attempt at a solution

    I know the rate of heat transfer is the same through the whole thing. K of brass is = to 500K of rubber
    and the heat transfer goes from the 100 side to the 0 side.

    so I made 3 equations

    first one (for 100 degree brass to first side of rubber)

    dQ/dt= -500kA*(T2-100/0.5x10-2)

    Second (for change in temperature over rubber (side one to side two

    dQ/dt= -kA*(T3-T2/0.1x10-2)

    third (second side of rubber to 0 degree brass)

    dQ/dt= -500kA*(0-T3/0.5x10-2)

    I put 2 of the equations equal to eachother but get silly numbers when I solve them (maybe the equations are wrong? or im solving them wrong?)

    thanks for the help
  2. jcsd
  3. Apr 29, 2015 #2
    Solve for the 3 temperature differences in terms of dQ/dt , and then add them up.
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