Question

Consider a laminar boundary layer over a heated flat plate. The free stream velocity is $U_{\infty }$. At some distance x from the leading edge the velocity boundary layer thickness is ${\delta }_v$ and the thermal boundary layer thickness is ${\delta }_T$. If the Prandtl number is greater than 1, then

• A.
  ${\delta }_V>{\delta }_T$
• B.
  ${\delta }_T>{\delta }_V$
  
• C.
  ${\delta }_v\approx {\delta }_T\sim (U_{\infty }x{)}^{-1/2}$
• D.
  ${\delta }_V\approx {\delta }_T\sim x^{-1/2}$

Answer 1

The correct option is A

${\delta }_V>{\delta }_T$
We know that

$\frac{{\delta }_V}{{\delta }_T}$ $=(Pr{)}^{1/3}$

here Pr >1

$\therefore$ ${\delta }_V>{\delta }_T$