How the thickness of thermal boundary layer and thickness of hydrodynamic boundary layer related ?

How the thickness of thermal boundary layer and thickness of hydrodynamic boundary layer related ?
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Answer :

Ratio of their thickness = (Prandtl number)-1/3.
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For flow over a flat plate, the ratio of thermal boundary layer thickness, 'xt' and hydrodynamic boundary layer thickness 'x' is equal to (where, NPr = Prandtl number) (A) NPr (B) NPr 1/3 (C) NPr -1 (D) NPr -1/3

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