Two concentric spheres of diameter D1 = 0.8 m and D2 = 1.2 m are separated by an air space and have surface temperatures of T1 = 400 K and T2 = 300 K.
(a) If the surfaces are black, what is the net rate of radiation exchange between the spheres?
(b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with s1 = 0.5 and s2 = 0.05?
(c) What is the net rate of radiation exchange if D2 is increased to 20 m, with s2 = 0.05, s1 = 0.5, and D1 = 0.8 m? What error would be introduced by assuming blackbody behavior for the outer sur- face (s2 = 1), with all other conditions remaining the same?
(d) For D2 = 1.2 m and emissivities of s1 = 0.1, 0.5, and 1.0, compute and plot the net rate of radiation exchange as a function of s2 for 0.05 s2 1.0.