The wall of a drying oven is constructed by sandwiching an

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QUESTION:

The wall of a drying oven is constructed by sandwiching an insulation material of thermal conductivity k 0.05 W/mK between thin metal sheets. The oven air is at T,i 300 C, and the corresponding convection coeffi- cient is hi 30 W/m2 K. The inner wall surface absorbs a radiant flux of qrad 100 W/m2 from hotter objects within the oven. The room air is at T,o 25 C, and the overall coefficient for convection and radiation from the outer surface is ho 10 W/m2 K. (a) Draw the thermal circuit for the wall and label all temperatures, heat rates, and thermal resistances. (b) What insulation thickness L is required to maintain the outer wall surface at a safe-to-touch temperature of To 40 C?

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QUESTION:

The wall of a drying oven is constructed by sandwiching an insulation material of thermal conductivity k 0.05 W/mK between thin metal sheets. The oven air is at T,i 300 C, and the corresponding convection coeffi- cient is hi 30 W/m2 K. The inner wall surface absorbs a radiant flux of qrad 100 W/m2 from hotter objects within the oven. The room air is at T,o 25 C, and the overall coefficient for convection and radiation from the outer surface is ho 10 W/m2 K. (a) Draw the thermal circuit for the wall and label all temperatures, heat rates, and thermal resistances. (b) What insulation thickness L is required to maintain the outer wall surface at a safe-to-touch temperature of To 40 C?

ANSWER:


(a)

Temperature of inside wall surface, Ti = 300°C
Temperature of outside wall surface, To = 40°C
Convection coefficient of inner wall surface, hi = 30 W/m^2 K
Radiant flux absorbed by inner wall surface, qrad = 100 W/m^2
Convection coefficient of outer w

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