Question

Air flows over a heated plate at a velocity of 50 m/s. The local skin friction coefficient at a point on a plate is 0.004. The following properties for air are, $density=0.88kg/m^3,viscosity=2.286\times {10}^{-5}kg-m/s,specificheat=1.001kJ/kgK,$ thermal conductivity of air = 0.035 W/mK and use St.$P{r}^{1/3}=C_{fx}/2.$

The average heat transfer per unit area if the temperature differences is ${60}^{o}C$ and the flow is assumed to be laminar

• A. $7014W/m^3$
• B. $14028W/m^2$
• C. $701.4W/m^2$
• D. $1402.8W/m^3$

Answer 1

The correct option is B $14028W/m^2$

Total heat transfer (average heat transfer)

$=\overline{h}.A.\Delta T$

$\overline{h}=2h_x$ (For laminar flow)

$Q=2h_x.A\Delta T$

$Q=2\times 116.89\times 1\times 60$

$Q=14027.56W/m^2$