advekdiffúziós

Advekdiffúziós is a term referring to processes governed by both advection and diffusion, the combined transport of a scalar quantity (such as mass, heat, or a contaminant) by bulk flow and by molecular or turbulent mixing. The behavior is commonly described by the advection–diffusion equation: ∂c/∂t + v · ∇c = ∇ · (D ∇c) + S, where c is concentration, v the velocity field, D the diffusion (or dispersion) tensor, and S source or sink terms.

The relative importance of advection and diffusion is often characterized by the Péclet number, Pe = UL/D, with U a characteristic velocity, L a length scale and D a diffusion coefficient. High Pe indicates advection-dominated transport with sharp fronts; low Pe indicates diffusion-dominated, smooth spreading. Heterogeneous media and anisotropic diffusion alter transport patterns and can produce preferential pathways or retardation.

Analytical solutions exist for simple geometries and source types (for example Gaussian plume solutions for steady point sources in uniform flow), while more complex or realistic problems require numerical methods: finite difference, finite volume, finite element, and particle-tracking schemes. Numerical modeling often needs stabilization techniques in advection-dominated regimes to avoid spurious oscillations.

Advekdiffúziós phenomena are central in environmental engineering (groundwater and air pollutant transport), chemical reactor design, heat transfer, and biological transport. Extensions include reactive advection–diffusion with chemical or biological reactions, and coupled multiphase transport in porous media. Limitations of models arise from assumptions about scale separation, homogeneity, and the representation of turbulence or subgrid mixing.