EXAMPLE 1-11 Heat Transfer between Two Isothermal Plates Consider steady heat transfer between two large parallel plates at constant tem- peratures of T₁ = 300 K and T₂ = 200 K that are L = 1 cm apart, as shown in Fig. 1-44. Assuming the surfaces to be black (emissivity & = 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 urethane insulation, and (d) filled with superinsulation that has an appar- ent thermal conductivity of 0.00002 W/m-K.​