Two concentric spheres of diameter D10.8 m andD21.2 m are

Chapter 13, Problem 13.55

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Two concentric spheres of diameter D1?0.8 m andD2?1.2 m are separated by an air space and havesurface temperatures of T1?400 K and T2?300 K.(a) If the surfaces are black, what is the net rate ofradiation exchange between the spheres?(b) What is the net rate of radiation exchange betweenthe surfaces if they are diffuse and gray with?1?0.5 and ?2?0.05?(c) What is the net rate of radiation exchange if D2isincreased to 20 m, with ?2?0.05, ?1?0.5, andD1?0.8 m? What error would be introduced byassuming blackbody behavior for the outer sur-face (?2?1), with all other conditions remainingthe same?(d) For D2?1.2 m and emissivities of?1?0.1, 0.5,and 1.0, compute and plot the net rate of radiationexchange as a function of ?2for 0.05?21.0