The composite wall of an oven consists of three materials, two of which are of known thermal conductivity, k A = 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. L_B = 0.15 m, but unknown thermal conductivity k_B.

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

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Ts.0 kc 5, 0 kg KA Air LA