Question

Air flows through a 10cm diameter tube at Reynolds number 1700 with thermal conductivity of air as 0.2792 W/mK and constant heat flux condition is maintained with a temperature of pipe is ${50}^{o}C$ above air temp all along the length. The heat transfer transfer per unit length is

• A. 191.6W/m
• B. 106.82 W/m
• C. 12.2 W/m
• D. 24.4 W/m

Answer 1

The correct option is A 191.6W/m

For flow through pipes and with constant heat flux
$Nu=\frac{48}{11}$
$\frac{hD}{k}=\frac{48}{11}$

$h=\frac{48}{11}\times \frac{0.2792}{0.1}=12.18$

$Q=h\pi DL\left(\Delta T\right)$

$\frac{Q}{L}=12.18\times \pi \times 0.1\times 50$

= 191.37 W/m