13.45 At the bottom of a large vacuum chamber whose walls are at 300 K, a black panel 0.1 m in diameter is maintained at 77 K. To reduce the heat gain to this panel, a radiation shield of the same diameter D and an emissivity of 0.05 is placed close to the panel. Calculate the net rate of heat gain to the panel. The illustration is of the bottom of a large vacuum chamber is of square shape whose walls are at 300 K, a black panel is maintained at 77 K. A radiation shield of the same diameter D is placed close to the panel.