Boundary-layer thickness equality: condition on the Prandtl number (Pr). When do the thermal and hydrodynamic boundary-layer thicknesses become approximately equal over a surface in external flow? Choose the correct value of Pr that ensures δᵗ ≈ δ.
Mechanical Engineering
Heat Transfer, Refrigeration and Air Conditioning
Difficulty: Easy
Choose an option
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Aequal to one
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Bgreater than one
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Cless than one
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Dequal to Nusselt number
Answer
Correct Answer: equal to one
Explanation
ConceptThe Prandtl number Pr = ν/α compares momentum and thermal diffusivities. When Pr ≈ 1, momentum and heat diffuse at similar rates, so the thermal (δᵗ) and velocity (δ) boundary layers have comparable thicknesses.
Final Answerequal to one.