Pe = VL/D — ratio of convective to diffusive transport. Works for both thermal Pe (D = α, thermal diffusivity) and mass-transfer Pe (D = DAB, mass diffusivity).
Heat & Mass Transfer · Dimensionless NumberPéclet number type:
Solve for:
Definition — two variants:
Physical meaning:
Relationship to other dimensionless numbers:
Typical diffusivity values:
| Fluid / pair | Type | D or α [m²/s] |
|---|---|---|
| Air at 20 °C | α (thermal) | 2.13 × 10⁻⁵ |
| Water at 20 °C | α (thermal) | 1.43 × 10⁻⁷ |
| O₂ in air at 20 °C | DAB (mass) | 1.81 × 10⁻⁵ |
| H₂O vapour in air 20 °C | DAB (mass) | 2.60 × 10⁻⁵ |
| O₂ in water at 25 °C | DAB (mass) | 2.10 × 10⁻⁹ |
| NaCl in water at 25 °C | DAB (mass) | 1.61 × 10⁻⁹ |
Pe in numerical methods — mesh Péclet number:
In computational fluid dynamics, the cell Péclet number Pecell = V Δx / D governs numerical stability. When Pecell > 2, central-difference schemes produce spurious oscillations; upwind schemes or finer meshes are required.