Answer Happy

A hollow metallic sphere of diameter 0.68 m surrounds a concentric metallic sphere of diameter 0.36 m. The space between the two spheres is filled with an insulation material with thermal conductivity of 7.8 W/(m⋅K). The inner and outer spheres are maintained at 177∘C and 129∘C respectively. The outer surface of the outer sphere is exposed to air at temperature T∞​. Meanwhile, the surrounding area can be considered isothermal with temperature Tsur ​=116∘C. The emissivity of the surface of the outer sphere, ε is 0.74 and heat transfer coefficient of air, h is 11 W/(m2⋅K). Assume that heat is lost from the outer surface of the outer sphere through convection and radiation. a) Calculate the heat passes from the inner sphere to the outer sphere. 1 b) Determine the temperature of air, T∞​. c) Identify the thermal resistance resulted from heat transfer by convection.