A 0.5 m diameter disc heater is horizontally placed and enclosed concentrically in a hemispherical shaped surface. The surface of the enclosure having an emissivity of 0.7 is maintained at 500 K. The disc heater, having emissivity of 0.8 is maintained at 1200 K. This diameter of the hemisphere is 2 m and the remaining base area enclosed is open to surroundings at 300 K and may be considered as black with reference to radiation exchange. Sketch the schematic and thermal radiation network. Using thermal network method, calculate the heat exchange between heater and hemispherical enclosure and that between heater and surroundings. Neglect convection heat transfer. Assume heater and hemispherical surface are opaque, diffuse and gray.