1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Heat Transfer: Finding temperature at the junction

  1. Mar 12, 2017 #1
    1. The problem statement, all variables and given/known data
    A furnace is constructed with 0.5 m of fire brick, 0.15 m of insulating brick and 0.25 m of ordinary building brick. The inside surface-temperature is 1530K and the outside surface temperature is 525K. The thermal conductivities of the fire, insulating and building bricks are 1.4, 0.21, and 0.7 W/m-K, respectively. Calculate the following per square meter area:
    (a) Total resistance of the wall in K/W
    (b) Rate of heat flow in W
    (c) The temperatures at the junctions of the bricks.

    2. Relevant equations
    Q/T = kAΔT / L

    3. The attempt at a solution
    (a) Total resistance of the wall in K/W: answer 1.43 K/W
    (b) Rate of heat flow in W: answer 703.5 W
    (c) The temperatures at the junctions of the bricks.

    (Temperature drop over firebrick+insulating brick)/(Total temperature drop) = (0.3571+0.7143/1.43)
    Temperature drop over firebrick+insulating brick:
    (1530K-525K) ⋅ (0.3571+0.7143/1.43) = 752.9769 K
    Hence the temperature at the (firebrick & insulating)-ordinary brick interface = (1530K - 752.9769 K) = 777.0231 K

    The correct answer according to the answer sheet is 778 K, there might be a slight difference but I want to make sure that my computation is right?
  2. jcsd
  3. Mar 12, 2017 #2
    Looks OK.
  4. Jul 2, 2017 #3
    why is the solution on letter C like that? i tried equating by (1530 - X) / (0.5 / 1.4) = (X - 525) / (0.25 / 0.7) but its not showing the correct answer...
  5. Jul 2, 2017 #4
    My heat flow rate equations for the three layers are as follows:
    What is the solution to these equations for ##T_1## and ##T_2##?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted