A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are kA and kB and the specific heat capacities are CPA and CPB for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when_________________?

Correct answer: C. kA < 0.5 kB

  • A. CPA > CPB
  • B. CPA < CPB
  • C. kA < 0.5 kB
  • D. kA >2 kB

Explanation

At steady state the same heat flux passes through both plates, so the temperature drop is proportional to thickness divided by conductivity. Since plate B is twice as thick, plate A has the larger drop when kA is less than kB/2.

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