Question

For thickness of thermal boundary layer to be greater than thickness of hydrodynamic boundary layer, the Prandtle number should be

• A. Greater than 1
• B. Equal to 1
• C. None
• D. Less than 1

Answer 1

The correct option is D Less than 1

We know the relation
$\left(\frac{\delta }{\delta t}\right)=(Pr{)}^{1/3}$

$IfPr>1,\delta >{\delta }_t\Rightarrow HBL>TBL$
$IfPr=1,\delta ={\delta }_t\Rightarrow HBL=TBL$
$IfPr<1,\delta <{\delta }_t\Rightarrow HBL<TBL$