Chapter 12, Problem 12.80P

A thermograph is a device responding to the radiant power from the scene, which reaches its radiation detector within the spectral region $9-12\mu m$ . The thermograph provides an image of the scene, such as the side of a furnace, from which the surface temperature can be determined.

(a) For a black surface at 60?C, determine the emissive power for the spectral region $9-12\mu m$

(b) Calculate the radiant power (W) received by the thermograph in the same range ( $9-12\mu m$ ) when viewing, in a normal direction, a small black wall area, $200m{m}^{2,}at{\text{ T}}_s={60}^{\circ }C$ .The solid angle $\omega$ subtended by the aperture of the thermograph when viewed from the target is 0.001 sr.

(c) Determine the radiant power (W) received by the thermograph for the same wall area ( $200m{m}^{2,}$ ) and solid angle (0.001 sr) when the wall is a gray, opaque, diffuse material at ${\text{T}}_s={60}^{\circ }C$ with emissivity 0.7 and the surroundings are black at ${\text{T}}_{sur}={23}^{\circ }C$ .