Question

Consider a gray and opaque surface at 0°C in an environment at 25°C. The surface has an emissivity of 0.8. If the radiation incident on the surface is $240W/m^2,\text{the radiosity of the surface}\left(inW/m^2\right)is$ ___________

• A. $399.95W/m^2$
• B. $2999.5W/m^2$
• C. $29.995W/m^2$
• D. $299.95W/m^2$

Answer 1

The correct option is D $299.95W/m^2$




$Given,ϵ=0.8$

$T_a=0^{\circ }C=273K$

$\text{For opaque body}.,\tau =0$

$\alpha +\rho =1$

$ϵ=\alpha \left(Kirchof{f}^{\prime }sLaw\right)$

$\rho =(1-ϵ)$

Radiosity = leaving energy from the surface

$=\rho \times 240+ϵ\sigma T_s^4$

$=(1-ϵ)\times 240+0.8\times 5.67\times {10}^{-8}\left({273}^4\right)$

$=(1-0.8)\times 240+0.8\times 5.67\times {10}^{-8}\left({273}^4\right)$

$=299.95W/m^2$