For the fluid flowing over a flat plate with Prandtl number great

For the fluid flowing over a flat plate with Prandtl number great
| For the fluid flowing over a flat plate with Prandtl number greater than unity, the thermal boundary layer for laminar forced convection

A. is thinner than the hydrodynamic boundary layer

B. has thickness equal to zero 

C. is of same thickness as hydrodynamic boundary layer

D. is thicker than the hydrodynamic boundary layer

Please scroll down to see the correct answer and solution guide.

Right Answer is: A

SOLUTION

δ = the thickness of the hydrodynamic boundary layer; the region of flow where the velocity is less than 99% of the far-field velocity.

δT = the thickness of the thermal boundary layer; the region of flow where the local temperature nearly reaches the value (99%) of the bulk flow temperature

\(\begin{array}{l} \frac{δ }{{{δ _T}}} = {\left( {{\rm{Pr}}} \right)^{\frac{1}{3}}}\; \end{array}\)

Given: Pr > 1 ⇒ δ > δT

Hence the thermal boundary layer is thinner than the hydrodynamic boundary layer.

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