1 1 Q4) 1 1 1 1 == This question deals with steady-state radiation heat transfer between a sphere (r = 30 cm) and a circular disk (r2 = 120 cm), which are separated by a center-to-center dis- tance h=60 cm. When the normal to the center of the disk passes through the center of the sphere, the radiation view fac- |tor is given by F12=0.51- Surface temperatures of the sphere and the disk are 600C and 200C, respectively; and their emissivities are 0.9 and 0.5, respectively. (a) Calculate the view factors F12 and F21- (b) Calculate the net rate of radiation heat exchange between the sphere and the disk. (c) For the given radii and temperatures of the sphere and the disk, the following four possible modifications could increase the net rate of radiation heat exchange: paint each of the two surfaces to alter their emissivi- ties, adjust the distance between them, and provide an (refractory) enclosure. Calculate the net rate of radia- tion heat exchange between the two bodies if the best values are selected for each of the above modifications.