Question

In the laminar flow of air $(Pr=0.7)$ over a heated plate. If $\delta$ and ${\delta }_T$ denote , respectively, the hydrodynamic and thermal boundary layer thicknesses, then

• A.
  $\delta ={\delta }_T$
• B.
  $\delta >{\delta }_T$
• C.
  $\delta <{\delta }_T$
• D.
  $\delta =0but{\delta }_T\ne 0$

Answer 1

The correct option is C

$\delta <{\delta }_T$
Prandtl number,
$Pr=0.7$
also $Pr={\left(\frac{\delta }{{\delta }_T}\right)}^3$
$\therefore$ $(0.7{)}^{1/3}=\frac{\delta }{{\delta }_T}$
Or $\delta =0.888{\delta }_T$
$\therefore$ $\delta <{\delta }_T$