Prandtl Number

The Prandtl Number is a dimensionless number approximating the ratio of momentum diffusivity and thermal diffusivity

The Prandtl Number is a dimensionless number approximating the ratio of momentum diffusivity (kinematic viscosity) and thermal diffusivity and can be expressed as

Pr = v / α         (1)

where

Pr = Prandtl's number

v = momentum diffusivity (m2/s)

α = thermal diffusivity (m2/s)

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. It depends on the fluid properties. 

  • gases - Pr ranges 0.7 - 1.0
  • water - Pr ranges 1 - 10
  • liquid metals - Pr ranges 0.001 - 0.03
  • oils - Pr ranges 50 - 2000

Related Topics

  • Fluid Mechanics - The study of fluids - liquids and gases. Involves various properties of the fluid, such as velocity, pressure, density and temperature, as functions of space and time.

Related Documents

  • Air Properties - SI Units - Ideal gas properties of air at low pressures - in SI units
  • Air Properties - Imperial Units - Thermodynamic properties of air at low pressures - imperial units
  • Carbon Dioxide Properties - Properties of saturated liquid Carbon Dioxide - CO2 - density, specific heat capacity, kinematic viscosity, thermal conductivity and Prandtl number
  • Water - Thermal Properties - Thermal properties of water - density, freezing temperature, boiling temperature, latent heat of melting, latent heat of evaporation, critical temperature and more
  • Dry Air Properties - Dry air properties at temperatures ranging 175 - 1900 K - specific heat capacity, ratio of specific heats, dynamic viscosity, thermal conductivity, Prandtl number, density and kinematic viscosity

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