This question deals with steady–state radiation heat transfer between a sphere (r₁ = 30 cm) and a circular disk (r₂ = 120 cm), which are separated by a center-to-center distance h = 60 cm. When the normal to the center of disk passes through the center of the sphere, the radiation view factor is given by

Surface temperatures of the sphere and the disk are 600°C and 200°C, 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 emissivities, adjust the distance between them, and provide an (refractory) enclosure. Calculate the net rate of radiation heat exchange between the two bodies if the best values are selected for each of the above modifications.

Transcribed Image Text:

-0.5 F₁₂ = 0,5 {1- [1 +()]*} F12 h