Coated metallic disks are cured by placing them at the top of a cylindrical furnace whose bottom surface is electrically heated and whose sidewall may be approximated as a reradiating surface. Curing is accomplished by maintaining a disk at T₂ = 400 K for an extended period. The electrically heated surface is maintained at T₁ = 800 K and is mounted on a ceramic base material of thermal conductivity k = 20 W/m ? K. The bottom of the base material, as well as the ambient air and large surroundings above the disk, are maintained at a temperature of 300 K. Emissivities of the heater and the disk inner and outer surfaces are ?₁ = 0.9, ?_{2, i} = 0.5, and ?_2,o = 0.9, respectively. Assuming steady-state operation and neglecting convection within the cylindrical cavity, determine the electric power that must be supplied to the heater and the convection coefficient h that must be maintained at the outer surface of the disk in order to satisfy the prescribed conditions.

Transcribed Image Text:

300 K - T 4- 200 mm . 25 mm k- 20 W/m-K -T,= 300 K +120 mm