= Effusive molecular energy flux
{title2=$F_E=2k_BT\,n\overline v/4$}
An equilibrium Maxwell-Boltzmann gas has number flux $n\overline v/4$ onto a plane. Molecules crossing the plane are weighted by their positive normal <velocity>, so their mean translational <kinetic energy> is $2k_BT$, rather than the bulk value $3k_BT/2$. The translational <energy> flux is therefore $F_E=n\overline v k_BT/2$. Internal degrees of freedom contribute their mean <energy> per crossing molecule when independent of translational <velocity>.
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