Consider steady heat transfer between two large parallel plates at constant temperatures of T₁ = 290 K and T₂ = 150 K that are L = 2 cm apart. Assuming the surfaces to be black (emissivity ε = 1), determine the rate of heat transfer between the plates per unit surface area assuming the gap between the plates is

(a) Filled with atmospheric air,

(b) Evacuated,

(c) Filled with fiberglass insulation,

(d) Filled with superinsulation having an apparent thermal conductivity of 0.00015 W/m·K.