Fluid mechanics/heat transfer fundamentals: define the Reynolds number. Using symbols: ρ = density, V = characteristic velocity, l = characteristic length, μ = dynamic viscosity, ν = kinematic viscosity. Select the correct expression for the Reynolds number (Re).
Mechanical Engineering
Heat Transfer, Refrigeration and Air Conditioning
Difficulty: Easy
Choose an option
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ARe = (ρ V l)/μ
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BRe = (μ V l)/ρ
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CRe = (k l)/h
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DRe = (ρ cᵖ V)/k
Answer
Correct Answer: Re = (ρ V l)/μ
Explanation
DefinitionThe Reynolds number quantifies the ratio of inertial to viscous forces: Re = (ρ V l)/μ = V l/ν.
Why A is correctDimensions: [ρ]·[V]·[l]/[μ] → (kg·m⁻³)(m·s⁻¹)(m)/(kg·m⁻¹·s⁻¹) = 1 (dimensionless), as required.
Final AnswerRe = (ρ V l)/μ.