Question

Air is flowing at a velocity of 3m/s perpendicular to a long pipe as shown in the figure. The outer diameter of the pipe is 6cm and the temperature at the outside surface of the pipe is maintained at ${100}^{o}C$. The temperature of the air far from the tube is ${30}^{o}C$.

Data for air:
Kinematic Viscosity $\left(v\right)=18\times {10}^{-6}{m}^2/s$
Thermal conductivity (k)=0.03 W/mK

$Nu=\frac{hd}{k}=\mathrm{0.024.}R{e}^{0.8}$
The rate of heat loss per unit length (W/m)
from the pipe to the air (up to one decimal)is_____

• A. 2509.5W/m,
• B. 25.095W/m,
• C. 25095W/m,
• D. 250.95W/m,

Answer 1

The correct option is D 250.95W/m,

$Re=\frac{V.d}{v}=\frac{3\times 0.06}{18\times {10}^{-6}}=10000$

$Nu=0.024R{e}^{0.8}$

$\frac{hd}{k}=38.037$

$h=\frac{38.037\times 0.03}{0.06}$

$h=19.00187W/m^{2}K$

$Heattransferrate\left(Q\right)=h.A(T_s-T_{\infty })$

$=19.01187\times \pi \times d\times L(100-30)$

$=19.01187\times \pi \times 0.06\times 1\times 70$

= 250.94W/n