The composite wall of an oven consists of three materials, two of which are of known thermal conductivity, kA = 20 W/m?K and kC = 50 W/m?K, and known thickness, LA = 0

The composite wall of an oven consists of three materials, 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 = 0.15m but the thermal conductivity kB is unknown.

Under steady-state operating conditions, measurements reveal an outer surface temperature of Ts,o = 20 °C, an inner surface temperature of Ts,i = 600 °C, and an oven air temperature of T&= 800 °C. The convection coefficient h inside the oven is known to be 25 W/m2?K. What is the value of kB?