13.90 A long rod heater of diameter D1 = 10 mm and emissivity ?1 = 1.0 is coaxial with a well-insulated, semi-cylindrical reflector of diameter D2 = 1 m. A long panel of width W = 1 m is aligned with the reflector and is separated from the heater by a distance of H = 1 m. The panel is coated with a special paint (?3 = 0.7), which is cured by maintaining it at 400 K. The panel is well insulated on its back side, and the entire system is located in a large room where the walls and the atmospheric, quiescent air are at 300 K. Heat transfer by convection may be neglected for the reflector surface