Consider two aligned, parallel, square planes (0.4 m x 0.4 m) spaced 0.8 m apart and maintained at T₁ = 500 K and T₂ = 800 K. Calculate the net radiative heat transfer from surface 1 for the following special conditions:

(a) Both planes are black and the surroundings are at 0 K.

(b) Both planes are black with connecting, reradiating walls.

(c) Both planes are diffuse and gray with (ε₁ = 0.6, ε₂ = 0.8, and the surroundings at 0 K.

(d) Both planes are diffuse and gray (ε₁ = 0.6 and ε₂ = 0.8) with connecting, reradiating walls.

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Shield, D 60 mm Heated tube. D Evacuated 20 mm