Peclet number, or officially known as Péclet number, is a dimensionless number that represents the ratio of advection and diffusion caused by heat transfer.

It can be expressed in the following equation:

where;
Pe : Péclet number
U : Characteristic speed [m/s]
L : Characteristic length [m]
α : Thermal diffusivity [m2/s]

The greater Péclet number becomes, the more convection effects act on thermal transfer.
Péclet number can also be expressed in the equation below using Reynolds number (Re) and Prandtl number (Pr).

Péclet number is named after the French physicist Jean Claude Eugène Péclet.