# Péclet Number

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## Peclet number

[pə′klā ‚nəm·bər]## Péclet Number

a dimensionless number that is a similarity criterion for processes of convective heat exchange; named after the French physicist J. C. Péclet (1793–1857). The Péclet number *Pe* = *vl*/*a* = *C _{p}ρvl*/γ, where

*l*is the characteristic linear dimension of the surface of heat exchange,

*v*is the fluid velocity relative to the heat exchange surface,

*a*is the thermal diffusivity,

*C*is the specific heat at constant pressure, ρ is the density, and λ is the thermal conductivity of the fluid. The number

_{p}*Pe*characterizes the relationship between the convective and molecular processes of heat exchange in the flowing fluid. The process of molecular conduction predominates at low

*Pe*values, and the process of heat exchange by convection of the fluid predominates at high

*Pe*values. The relation between the Péclet number, the Reynolds number

*Re*, and the Prandtl number

*Pr*is given by the equation

*Pe*=

*Re*×

*Pr*.