An oven wall consists of a 0.635-cm-thick layer of steel ($k_s = 15$ W/m·K) and a layer of brick ($k_b = 0.72$ W/m-K) as shown in the figure below. At steady state, the temperature decreases by 0.7°C across the steel layer. The interface of the steel and brick layers is 300°C.
a) At steady state, how is the heat transfer rate through the steel related to the heat transfer rate through the brick? Justify your answer using ideas from thermodynamics (e.g., systems and energy balances).
b) If the temperature of the outer surface of the brick must be no greater than 40°C to avoid burns if people accidentally touch the hot surface, determine the thickness of brick, in cm, that ensures this safety condition is met.
c) What is the rate of conduction, in kW, per m² of wall surface area?