Question

A 7 m diameter spherical ball is known to emit radiation at a rate of 340 W when its surface temperature is 880 K. Determine the average emissivity of the ball at this temperature. 𝜎 = 0.1714 x10-8 W/m2K 4 .

Answer 1

$$e=\frac{P}{\sigma AT^4}\\ e=\frac{340}{(0.25\cdot0.1714\cdot10^{-8}) (7)^2(880)^4}=0.027$$