Question

Air at 20 C and 1 atm flows over a flat plate at 35 m/s. The plate is 75 cm long and is maintained at 60 с. Assuming unit depth in the x direction, calculate the heat transfer from the plate.

Answer 1

Answer:

Q=3198.744 W/m

Explanation:

Given that

Air temperature=20 C

Velocity V= 35 m/s

Temperature of surface= 60 C

Length of plate= 75 cm

Now first find the properties of air at mean temperature of 20 and 60,it means that  properties of air at  temperature 40 C

$\rho=1.12 \frac{Kg}{m^3}$

$\nu =1.69\times 10^{-5}\frac{m^2}{s}$

$K=0.027\frac{W}{m-K}$

Pr=0.71

Lets find the Reynolds number

$Re=\dfrac{vL}{\nu }$

$Re=\dfrac{35\times0.75}{1.69\times 10^{-5}}$

$Re=15.53\times10^5$

So this is turbulent flow

Nusselt equation of turbulent flow

$Nu=0.037Re^{\frac{4}{5}}Pr^{\frac{1}{3}}$

Now by putting the values

$Nu=0.037\times (15.53\times10^5)^{\frac{4}{5}}\times 0.71^{\frac{1}{3}}$

Nu=2961.68

We know that

$NU=\dfrac{hL}{K_{air}}$

So

$2961.68=\dfrac{h\times 0.75}{0.027}$

$h=106.68\frac{W}{m^2-K}$

So heat transfer

Q=hAΔT

Q=106.68 x 0.75 x 1 x (60-20)

Q=3198.744 W/m