The diameter and surface emissivity of an electrically heated plate are D = 300 mm and ε = 0.80, respectively. (a) Estimate the power needed to maintain a surface temperature of 200°C in a room for which the air and the walls are at 25°C. The coefficient characterizing heat transfer by natural convection depends on the surface temperature and, in units of W/m2.K, may be approximated by an expression of the form h=0.80(Ts - Too)1/3. (
b) Assess the effect of surface temperature on the power requirement, as well as on the relative contributions of convection and radiation to heat transfer from the surface.