Question

Heat radiates from a small sphere suspended in a large room. The surface of the sphere of 1.5 sq. Ft. is at a temperature of 580 °F, and the inside surfaces of the room are at a temperature of 80 °F. Assuming the emissivity of the sphere surface to be 0.30, calculate the radian-heat transfer in BTU/hr.

Answer 1

Rate of radiant heat transfer is given by,

$\frac{Q}{t}=\sigma\epsilon AT^4$

$\epsilon=0.30$

$\sigma=5.67*10^{-8}$

Rate=$5.67*10^{-8}*0.3*1.5*80^4$

=1.0451 BTU/hr