Prandtl number

related topics
{math, energy, light}
{acid, form, water}
{area, part, region}
{ship, engine, design}

The Prandtl number Pr is a dimensionless number approximating the ratio of momentum diffusivity (kinematic viscosity) and thermal diffusivity. It is named after the German physicist Ludwig Prandtl.

It is defined as:

where:

Note that whereas the Reynolds number and Grashof number are subscripted with a length scale variable, Prandtl number contains no such length scale in its definition and is dependent only on the fluid and the fluid state. As such, Prandtl number is often found in property tables alongside other properties such as viscosity and thermal conductivity.

Typical values for Pr are:

For mercury, heat conduction is very effective compared to convection: thermal diffusivity is dominant. For engine oil, convection is very effective in transferring energy from an area, compared to pure conduction: momentum diffusivity is dominant.

In heat transfer problems, the Prandtl number controls the relative thickness of the momentum and thermal boundary layers. When Pr is small, it means that the heat diffuses very quickly compared to the velocity (momentum). This means that for liquid metals the thickness of the thermal boundary layer is much bigger than the velocity boundary layer.

The mass transfer analog of the Prandtl number is the Schmidt number.

See also

References

  • Viscous Fluid Flow, F. M. White, McGraw-Hill, 3rd. Ed, 2006

Archimedes · Atwood · Bagnold · Bejan · Biot · Bond · Brinkman · Capillary · Cauchy · Damköhler · Dean · Deborah · Eckert · Ekman · Eötvös · Euler · Froude · Galilei · Graetz · Grashof · ‎Görtler · Hagen · Keulegan–Carpenter · Knudsen · Laplace · Lewis · Mach · Marangoni · Morton · Nusselt · Ohnesorge · Péclet · Prandtl (magnetic · turbulent· Rayleigh · Reynolds (magnetic· Richardson · Roshko · Rossby · Rouse · Ruark · Schmidt · Sherwood · Stanton · Stokes · Strouhal · Suratman · Taylor · Ursell · Weber · Weissenberg · Womersley

Full article ▸

related documents
Triangulum
Hour angle
Directive gain
Quintessence (physics)
Guided ray
Alpha Arietis
Atom probe
Galactic coordinate system
Édouard Roche
Brightness temperature
Spica
Equuleus
Umbra
Icosidodecahedron
Rayleigh number
Kirkwood gap
Thermosphere
Solid-state physics
Microphotonics
Groups of minor planets
Canes Venatici
Altair
Gauss (unit)
Equatorial coordinate system
Jerk
Coulomb
C-symmetry
Angle excess
Zenith
Nereid (moon)