Pécletnummer

The Péclet number, denoted as Pe, is a dimensionless quantity used in fluid dynamics and heat/mass transfer to describe the ratio of advective transport to diffusive transport. It is named after the French physicist Jean Claude Eugène Péclet. The Péclet number helps to determine whether convection or diffusion dominates a particular process. A high Péclet number indicates that advection is much more significant than diffusion, meaning that the substance or heat is primarily carried along by the bulk flow of the fluid. Conversely, a low Péclet number suggests that diffusion is the dominant mechanism, and the substance or heat spreads out relatively quickly due to random molecular motion, independent of the bulk flow.

The Péclet number is typically defined as the product of the Reynolds number (Re) and the Prandtl number (Pr) for heat transfer, or the Schmidt number (Sc) for mass transfer. For heat transfer, Pe = Re * Pr = (v * L / ν) * (ν / α) = v * L / α, where v is the characteristic velocity, L is the characteristic length, ν is the kinematic viscosity, and α is the thermal diffusivity. For mass transfer, Pe = Re * Sc = (v * L / ν) * (ν / D) = v * L / D, where D is the mass diffusivity.

In practical applications, the Péclet number is crucial for understanding phenomena such as heat exchangers, chemical reactors, and transport in porous media. For example, in heat exchangers, a high Péclet number implies efficient heat transfer due to strong convection, while a low Péclet number might indicate limitations due to slow diffusion. Similarly, in reaction engineering, it helps in assessing how quickly reactants are transported to the reaction site compared to how quickly they react.