89. For a cylinder of height h , the surface area is A c = 2 π rh , and the area of a sphere is A o = 4 π R 2 . The net radiative heat transfer is given by Eq. 18-40. (a) We estimate the surface area A of the body as that of a cylinder of height 1.8 m and radius r = 0.15 m plus that of a sphere of radius R = 0.10 m. Thus, we have A ≈ A c + A o = 1.8 m 2 . The emissivity ε = 0.80 is given in the problem, and the Stefan-Boltzmann constant is found in §18-11: σ = 5.67 × 10 –8 W/m 2 ·K 4 . The “environment” temperature is T env = 303 K, and the skin temperature is T = 5 9
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