Question

For a fluid with a Prandtl Number of 1000.0, the hydrodynamic layer is thinner than the thermal boundary layers. a) True b) False

Answer 1

Answer:

(b)False

Explanation:

Given:

 Prandtl number(Pr) =1000.

We know that   $Pr=\dfrac{\nu }{\alpha }$

  Where $\nu$ is the molecular diffusivity of momentum

             $\alpha$ is the molecular diffusivity of heat.

 Prandtl number(Pr) can also be defined as

    $Pr=\left (\dfrac{\delta }{\delta _t}\right )^3$

Where $\delta$ is the hydrodynamic boundary layer thickness and $\delta_t$ is the thermal boundary layer thickness.

So if Pr>1 then hydrodynamic boundary layer thickness will be greater than thermal boundary layer thickness.

In given question Pr>1 so  hydrodynamic boundary layer thickness will be greater than thermal boundary layer thickness.

So hydrodynamic layer will be thicker than the thermal boundary layer.