A thermograph is a device responding to the radiant power from the scene, which reaches its radiation detector within the spectral region 9-12?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?m. (b) Calculate the radiant power (W) received by the thermograph in the same range (9-12?m) when viewing, in a normal direction, a small black wall area. 200 mm2, at Ts = 60°C. The solid angle w 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 (200 mm2) and solid angle (0.001 sr) when the wall is a gray, opaque diffuse material at Ts = 60°C with emissivity 0.7 and the surroundings are black at Tsur = 23°C.

352 Wall, T, Surroundings, T Thermograph Furnace interior