Question

Air at ${20}^{o}C$ C and I atm flows over a flat plate at 40 m/s. The plate is 80 cm long and is maintained at ${60}^{o}C$. Properties of air at ${40}^{o}C$ are Pr = 0.7, K = 0.02733 W/mK, $C_p=1.007\frac{kJ}{kgK}\mu =1.906\times {10}^{-5}\frac{kg}{m-s}and\rho =1.128kg/m^3.$
The avergae heat transfer coefficient is ___$Use\overline{Nu}=P{r}^{\frac{1}{3}}(0.036R_e^{0.8}-871)$.

• A. $69W/m^{2}K$
• B. $62W/m^{2}K$
• C. $88W/m^{2}K$
• D. $54W/m^{2}K$

Answer 1

The correct option is C $88W/m^{2}K$

$Pr=0.7,k=0.02733\frac{W}{mK},$

$c_p=1.007\frac{kJ}{kgK},\mu =1.906\times {10}^{-5}\frac{kg}{m-s}$

$\rho =112kg/m^3,U_{\infty }=40m/s,x=0.8m$

$Re=\frac{\rho \times U_{\infty }\times x}{\mu }=\frac{1.128\times 40\times 0.8}{(1.906\times {10}^{-5})}$

Re = 1893809.024

$\overline{Nu}=\left(Pr{)}^{1/3}\right(0.036R{e}^{0.8}-871)$

$\frac{hL}{K}=(0.036R{e}^{0.8}-871)(Pr{)}^{1/3}$

$\Rightarrow h=88.12\frac{W}{m^{2}K}$