$r_{o}+t=0.04+0.02=0.06m$
Solution:
$h=\frac{Nu_{D}k}{D}=\frac{10 \times 0.025}{0.004}=62.5W/m^{2}K$ $r_{o}+t=0
$\dot{Q}=h \pi D L(T_{s}-T_{\infty})$