When is it useful?
Péclet number compares transport by flow with transport by diffusion. This calculator asks for thermal diffusivity α, so it computes a heat-transfer Péclet number. A mass-transfer Péclet number would instead use the species diffusivity.
Formula and inputs
Enter characteristic speed v in m/s, length L in m, and thermal diffusivity α in m²/s. The units of vL and α are both m²/s. Define the speed and length for the actual process being compared.
Open this calculatorWorked example
For v = 0.01 m/s, L = 0.1 m, and α = 1×10⁻⁷ m²/s, Pe = 0.01 × 0.1 ÷ 1×10⁻⁷ = 10,000.
Interpreting the result
The large value in this example indicates strong flow transport relative to thermal diffusion on the chosen length scale. Around Pe = 1, both effects can matter; no single cutoff applies universally.
Limits and cautions
Boundary conditions and geometry still shape the actual temperature field. In turbulent flow, an effective diffusivity may be defined differently, so a molecular-only Pe does not equal total heat transfer.
Formula and concept reference: Penn State — Dimensionless numbers in transport. We created the sample inputs and calculations for this guide.