1. The composite wall of an oven consists of three materi- als, two of which are of known thermal conductivity, kA = 20 W/m · K and kC = 50 W/m · K, and known thickness, LA = 0.30 m and LC = 0.15 m. The third material, B, which is sandwiched between materials A and C, is of known thickness, LB = 0.15 m, but unknown thermal conductivity kB.
2. Draw the thermal circuit for the wall and label all temperatures, heat rates, and thermal resistances.
3. What insulation thickness L is required to maintain the outer wall surface at a safe-to-touch tempera- ture of To = 40°C?