Question

Gas at atmospheric pressure and ${40}^{o}C$ flows with a velocity is 5m/s over a 2m long flat plate whose surface is kept at a uniform temperature of ${120}^{o}C$. The average heat transfer coefficient $\left(inW/m^{2o}C\right)$ over the 2m length of the plate if the properties of gas at mean film temperature are
Kinematic viscosity = $2.107\times {10}^{-5}{m}^2/s,$
Thermal conductivity = 0.03025 W/mK,
Prandtl number = 0.6965.
Average Nussult number = Nu = $0.664R{e}^{0.5}$.
$P{r}^{0.3}....ForLaminarflow$
Average Nussult number = Nu = 0.0375
$R{e}^{0.8}.P{r}^{0.3}....$For turbulent flow

• A. 410
• B. 3.1
• C. 17.68
• D. 6.2

Answer 1

The correct option is D 6.2

$R_e=\frac{VL}{v}=\frac{5\times 2}{2.107\times {10}^{-5}}$

$=4.746\times {10}^5<5\times {10}^5\left(laminarflow\right)$

For laminar flow,

$\overline{Nu}=\frac{\overline{h}L}{K}=0.664R{e}^{0.5}P{r}^{0.3}$

$\frac{\overline{h}\times 2}{0.03025}=0.664(4.746\times {10}^5{)}^{0.5}(0.6965{)}^{0.3}$

$\overline{h}=6.2W/m^{2}K$