Question

A fluid flowing over a flat plate has the following properties : dynamic viscosity $=25\times {10}^{-6}$ kg/ms, specific heat =2.0 kJ/kgK, thermal conductivity 0.05 W/mK. The hydrodynamic boundary layer thickness is measured to be 0.5 mm. The thickness of the thermal boundary layer would be

• A.
  0.1 mm
• B.
  0.5 mm
• C.
  1.0 mm
• D.
  None of these

Answer 1

The correct option is B

0.5 mm
$Pr=\frac{\mu C_p}{k_f}=\frac{25\times {10}^{-6}\times 2\times {10}^3}{0.05}$ = 1

$\Rightarrow \frac{\delta }{{\delta }_t}=1$

Now $\delta =0.5mm$
Therefore $\delta ={\delta }_t=0.5mm$