Question

A heated spherical ceramic object (diameter = 10 cm) is held in a large enclosure whose walls are maintained at a temperature of 300K. The sphere has an emissivity of 0.7. The rest of the enclosure is filled with stagnant nitrogen at a temperature of 300 K. Properties of the sphere: Density = 4500 kg/m3; heat capacity = 400 J/(kg.K); thermal conductivity = 22 W/(m.K). Assume properties of the sphere do not vary with temperature. a. Determine the rate of heat transfer when its temperature is at 1200K. b. What are the relative contributions of radiation and convection to the rate of heat loss when the sphere is at 1200K. c. What are the relative contributions of radiation and convection to the rate of heat loss when the sphere is at 600K.

explain steps of a) b) and c)

Answer 1