Two large parallel plates are maintained at $T_1=550$ and $T_2=300K,$ respectively. The hot plate has an emissivity of $0\mathrm{.}9$ while that of the cold plate is $0\mathrm{.}7.$

ion shield, $T_3$

Determine the radiation heat flux, in $\frac{W}{m^2},$ without and with a radiation shield formed of a flat sheet of foil placed midway between the two plates. Both sides of the shield have an emissivity of $0\mathrm{.}05.$

$(q_{12}^{\text{'}\text{'}}{)}_{\frac{w}{o}\text{s}\text{h}\text{i}\text{e}\text{l}\text{d}},$

$(q_{12}^{\text{'}\text{'}}{)}_{\text{w}\text{i}\text{t}\text{h}\text{s}\text{h}\text{i}\text{e}\text{l}\text{d}},=\frac{W}{m^2}$