a pipe with inner diameter $30$ mm$,$ thread diameter $35$ mm and length L $($k $=52$

$3\mathrm{.}5$ m$^3$ of water flows through the smat $($W$/$m $\backslash$deg C$).$ whose temperature is $15\backslash$deg C

Air flows over the pipe at a speed of $60$ m$/$s$,$ perpendicular to the body of the pipe.

of water $($p$=0\mathrm{.}98$ g$/$cm$^3,$ Cp$=4\mathrm{.}187$ kJ$/$kg K$.$ k$=0\mathrm{.}659$ W$/$m K$.$

$=0\mathrm{.}433$ x $10^-3)$ since the entrance temperature to the pipe is $80\backslash$deg C$.$ Find the required pipe length for the outlet temperature to be $50\backslash$deg C$.$