A horizontal structure consists of an 10-mm-thick layer of copper and an 10-mm-thick layer of aluminum. The bottom surface of the composite structure receives a heat flux of 100 kW/m^2, while the top surface is exposed to convective conditions characterized by h= 40 W/m^2·K, T[infinity] =25°C. The initial temperature of both materials is Ti, A = Ti, B=25°C, and a contact resistance of 200 × 10^−6 m^2·K/W exists at the interface between the two materials. Required:
a. Determine the times, both in seconds, at which the copper and aluminum each reach a temperature of 90°C. The copper layer is on the bottom.
b. Repeat part (a) with the copper layer on the top.