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Engineering ToolBox > Prandtl Number
The Prandtl Number is a dimensionless number approximating the ratio of momentum diffusivity and thermal diffusivity and can be expressed as
Pr = v / α (1)
where
Pr = Prandtl's number
v = kinematic viscosity (Pa s)
α = thermal diffusivity (W/m K)
The Prandtl number can alternatively be expressed as
Pr = μ cp / k (2)
where
μ = absolute or dynamic viscosity (kg/m s, cP)
cp = specific heat capacity (J/kg K, Btu/(lb oF))
k = thermal conductivity (W/m K, Btu/(h ft2 oF/ft))
The Prandtl Number is often used in heat transfer and free and forced convection calculations.