A black sphere 2 in. in diameter is placed in an oven as illustrated in Fig. 9.2. The walls of the oven are maintained at 800°F and we can assume that the air in the oven is also at 800°F. Estimate the percentage of the total heat flux to the sphere which results from radiation when the surface temperature of the sphere is 200°F, 400°F, and 600°F. Use the results of Sec. 7.9 to estimate the free-convection film heat transfer coefficient.
