Determine the net heat transfer by radiation between two surfaces A and B. expressed as watts per square meter of area B, if the temperatures of A and B are 500 and 200°C, respectively, and the emissivities of A and B are 0.90 and 0.25, respectively. Both surfaces are gray. 

(a) Surfaces A and B are infinite parallel planes 3 m apart. 

(b) Surface A is a spherical shell 3 m in diameter, and surface B is a similar shell concentric with A and 0.3 m in diameter. 

(c) Surfaces A and B are flat parallel squares 2 by 2 m. one exactly above the other, 2 m apart. 

(d) Surfaces A and B are concentric cylindrical tubes with diameters of 300 and 275 mm, respectively. 

(e) Surface A is an infinite plane, and surface B is an infinite row of 100-mm-OD tubes set on 200-mm centers. 

(f) Same as part (e) except that 200 mm above the centerlines of the tubes is another infinite plane having an emissivity of 0.90, which does not transmit any of the energy incident upon it. 

(g) Same as part (f) except that surface B is a double row of 100-mm-OD tubes set on equilateral 200-mm centers. For part (e) F= 0.66; for (ƒ), F = 0.88; for (g), F= 0.98.