Question

The top of an insulated cylinder container is covered by a disc having emissivity $0.6$ and conductivity $0.167$ $W{K}^{-1}{m}^{-1}$ and thickness 1 cm. The temperature is maintained by circulating oil as shown in figure. Find the radiation loss to the surrounding in $J{m}^{-2}{s}^{-1}$ if temperature of the upper surface of the disc is ${127}^{\circ }$ and temperature of the surrounding is ${27}^{\circ }$

• A. $595J{m}^{-2}{s}^{-1}$
• B. $545J{m}^{-2}{s}^{-1}$
• C. $495J{m}^{-2}{s}^{-1}$
• D. None of these

Answer 1

The correct option is A $595J{m}^{-2}{s}^{-1}$

The rate of heat loss per unit area due to radiation
$=ϵ\sigma (T^4-T_0^4)$
$=0.6\times 5.67\times {10}^{-8}\left[\right(273+127{)}^4-(273+27{)}^4]=595.4J{m}^{-2}{s}^{-1}$