The wall of drying oven is constructed by sandwiching insulation material of thermal conductivity k = 0.05 w/m°k between thin metal sheets. the oven air is at = 300℃, and the corresponding convection coefficient is ℎ = 30 w/ m2 °k. the inner wall absorbs a radiant flux of ′′= 100 w/ m2 from hotter objects within the oven. the room air at t[infinity],o= 25℃, and overall coefficient for convection and radiation from the outer surface is ℎo = 10 w/ m2 °k. what insulation thickness l is required to maintain the outer wall surface at a safe-to-touch temperature of to = 40 degree c?

86 mm

Explanation:

From the attached thermal circuit diagram, equation for i-nodes will be

Equation 1

Similarly, the equation for outer node “o” will be

Equation 2

The conventive thermal resistance in i-node will be

Equation 3

The conventive hermal resistance per unit area is

Equation 4

The conductive thermal resistance per unit area is

Equation 5

Since  is given as 100,  is 40  is 300  is 25  

Substituting the values in equations 3,4 and 5 into equations 1 and 2 we obtain

 Equation 6

Equation 7

From equation 6 we can substitute wherever there’s with 3000L+40 as seen in equation 7 hence we obtain

The above can be simplified to be

-3000L=1.665-260

Therefore, insulation thickness is 86mm

answer:

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explanation: