A disk $8-$mm in diameter is positioned at the center of an isothermal, hemispherical enclosure. The disk is diffuse and gray with an emissivity of $0\mathrm{.}8$ and is maintained at $1000$ K $.$ The hemispherical enclosure, maintained at $300$ K $,$ has a radius of $100$ mm and an emissivity of $0\mathrm{.}85.$

Calculate the radiant power, in $W,$ leaving an aperture of diameter $2\mathrm{.}5$ mm located on the enclosure as shown.

$q_{ap}=W$