Answer Happy

A hollow metallic sphere of diameter 0.68 m surrounds aconcentric metallic sphere of diameter 0.36 m. The space betweenthe two spheres is filled with an insulation material with thermalconductivity of 7.8 W/(m·K). The inner and outer spheres aremaintained at 177°C and 129°C respectively. The outer surface ofthe outer sphere is exposed to air at temperature T∞. Meanwhile,the surrounding area can be considered isothermal with temperatureTsur = 116°C. The emissivity of the surface of the outersphere, ε is 0.74, and heat transfer coefficient of air, h is 11W/(m2 ·K). Assume that heat is lost from the outersurface of the outer sphere through convection and radiation.
1) Calculate the heat that passes from the inner sphere to theouter sphere.
2) Determine the temperature of the air, T∞.
3) Identify the thermal resistance resulted from heat transferby convection.