Please do $3\mathrm{.}12($NOT $3\mathrm{.}11)$

$3\mathrm{.}11$ In a crossflow heat exchanger, hot air at atmospheric pressure with an average

free$-$stream velocity of $3\frac{m}{s}$ flows across a bank of tubes in an in$-$line arrange$-$

ment with $x_l=x_t=5cm($see Figure $3\mathrm{.}2).$ The tube diameter is $2\mathrm{.}5$ cm $.$ The array

has $20$ rows in the direction of flow. The tube wall temperature is $30C,$ and the

average air temperature in the bundle is assumed to be $300C.$ Calculate the aver$-$

age heat transfer coefficient and repeat the calculation if the array has six rows in

the flow direction.

$3\mathrm{.}12$ Repeat Problem $3\mathrm{.}11$ for a heat exchanger that employs a bank of staggered bare

tubes with a longitudinal pitch of $4$ cm and transverse pitch of $5$ cm $.$