Reconsider Prob. 20–79. Using an appropriate software, plot the rate of natural convection heat transfer as a function of the hot surface temperature of the sphere as the temperature varies from 250 K to 450 K and discuss the results.

Reconsider Prob. 20–79.

Two concentric spheres of diameters 15 cm and 25 cm are separated by air at 1 atm pressure. The surface temperatures of the two spheres enclosing the air are T₁ = 350 K and T₂ = 275 K, respectively. Determine the rate of heat transfer from the inner sphere to the outer sphere by natural convection.