The front door of an oven is made up of walls made up of materials A, B and C, juxtaposed. The walls that make up the door have thermal conductivities, kA= 20 W/(m.K), kB= 0.027 W/(m.K) and kC= 50 W/(m.K) and known thicknesses LA=0.30 m and LC=0.15 m. At steady state operation, measurements indicate that the air temperatures inside the oven and its inner walls are equal to 600 oC (the temperature of the inner surface of the door is not known). The convective coefficient of air (inside and outside the oven) is 25 W/(m2.K) and the radiation coefficient is hr=25 W/m2K. outside the air is at 25oC. Based on this information: (a) schematic the thermal circuit for the system; (b) estimate the minimum thickness of wall B to ensure that the temperature of the outer surface of the door (exposed to ambient air) is ≤40oC in order to ensure the safety of operators; (c) estimate the temperature of the surface of the oven's inner wall Answer: (b) 40 mm; (c) 592.5oC
The front door of an oven is made up of walls made up of materials A, B and C, juxtaposed. The walls that make up the door have thermal conductivities, kA= 20 W/(m.K), kB= 0.027 W/(m.K) and kC= 50 W/(m.K) and known thicknesses LA=0.30 m and LC=0.15 m. At steady state operation, measurements indicate that the air temperatures inside the oven and its inner walls are equal to 600 oC (the temperature of the inner surface of the door is not known). The convective coefficient of air (inside and outside the oven) is 25 W/(m2.K) and the radiation coefficient is hr=25 W/m2K. outside the air is at 25oC. Based on this information:
(a) schematic the thermal circuit for the system;
(b) estimate the minimum thickness of wall B to ensure that the
temperature of the outer surface of the door (exposed to ambient air)
is ≤40oC in order to ensure the safety of operators;
(c) estimate the temperature of the surface of the oven's inner wall
Answer: (b) 40 mm; (c) 592.5oC
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