problem

Water flows in a $9$ m duct having $0\mathrm{.}20\mathrm{.}4m^2$ cross$-$section at a rate of $0\mathrm{.}2\frac{m^3}{s}$ with the inlet temperature of $80C.$ If the duct wall temperature is constant at $60C,$ calculate the heat Transfer rate per unit length and also the exit temperature.

What will be the heat transfor rate and exit demp. if we use a $9-$m circular pipe that provides the same surface area as of

duct surface area.