Coatings applied to long metallic strips are cured by installing the strips along the walls of a long oven of square cross section. Thermal conditions in the oven are maintained by a long silicon carbide rod (heating element), which is of diameter D = 20 mm and is operated at T₁ = 1700 K. Each of two strips on one side wall has the same orientation relative to the rod (s₁ = 60 mm, s₂ = 20 mm, L = 80 mm) and is operated at T₂ = 600 K. All surfaces are diffuse and gray with ?₁ = 0.9 and ?₂ = 0.4. Assuming the oven to be well insulated at all but the strip surfaces and neglecting convection effects, determine the heater power requirement per unit length (W/m).

Strips. T: Heating element,