Hot engine oil is being transported in a horizontal pipe $(k=15\frac{W}{m}*K,D_i=5(cm))$ with a wall thickness of $5$ mm $.$ The pipe is covered with a $5-$mm$-$thick layer of

insulation $(k=0\mathrm{.}15\frac{W}{m}*K).$ A length of $2$ m of the outer surface is exposed to cool air at $10C.$ If the pipe inner surface temperature is at $90C,$ determine the outer

surface temperature in $C.$ Begin the calculations by using a film temperature of $50C.$

Given: The properties of air at $T_f=50C.$

$k=0\mathrm{.}02514\frac{W}{m}*K,$

$v=1\mathrm{.}516{10}^{-5}\frac{m^2}{s},$

$Pr=0\mathrm{.}7309$