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5.113 A flue passing hot exhaust gases has a square cross section, 300 mm to a side. The walls are constructed of refractory brick 150 mm thick with a thermal conductivity of 0.85 W/m-K and thermal diffusivity of a=5.5 x 10-7 m-/s. Initially with no flue gases flowing the walls are at , a uniform temperature of 25°C. The interior surface is suddenly exposed to hot gases at 350°C with a convection coefficient of 100 W/m²-K, while the exterior surface experiences convection with air at 25°C and a convection coefficient of 5 W/m²-K. Using the implicit, finite-difference method with a grid spacing of 50 mm and a time increment of 1 h, plot the temperature distribution in the wall at 5, 10, 50, and 100 h as a function of time after introduction of the flue gases using MATLAB. a