An electrically heated sample is maintained at a surface

Chapter , Problem 13.34

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An electrically heated sample is maintained at a surface temperature of Ts 500 K. The sample coating is diffuse but spectrally selective, with the spectral emissivity distribution shown schematically. The sample is irradiated by a furnace located coaxially at a distance of Lsf 750 mm. The furnace has isothermal walls with an emissivity of f 0.7 and a uniform temperature of Tf 3000 K. A radiation detector of area Ad 8 105 m2 is positioned at a distance of Lsd 1.0 m from the sample along a direction that is 45 from the sample normal. The detector is sensitive to spectral radiant power only in the spectral region from 3 to 5 m. The sample surface experiences convection with a gas for which T 300 K and h 20 W/m2 K. The surroundings of the sample mount are large and at a uniform temperature of Tsur 300 K. (a) Dete (b) Considering both emission and reflected irradiation from the sample, determine the radiant power that is incident on the detector within the spectral region from 3 to 5 m.