Consider two concentric spheres of diameter D1 (m) and Da (m) as shown in Figure Q4(b). These two spheres are separated

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Consider two concentric spheres of diameter D1 (m) and Da (m) as
shown in Figure Q4(b). These two spheres are separated by an air
space and have surface temperature of T1 (°C) and Ta (°C).
Evaluate the net rate of radiation exchange between the spheres if
both surfaces of the spheres are considered as black.
Evaluate the net rate of radiation exchange between the surfaces if
the surfaces are considered as diffuse and gray with E1 = 0.5 and Ez
= 0.05. Explain the meaning of high and low emissivity, & value.
ill. Evaluate the net rate of radiation exchange if Dz is changed to X
(m), with E2 = 0.05, E1= 0.5 and same initial given Di (m). Then,
evaluate the net rate of radiation exchange assuming blackbody
behaviour for the outer surface with all other conditions remaining
the same.
iv. Consider answer obtained from (i) and (li), which one is higher?
Explain your answer.
# Refer Table Q4(b) for value of D1, D2, T1, T2 and X