massotransporten

Massotransporten (mass transport) refers to the movement of mass within and between systems, driven by gradients or forces. It encompasses diffusion, bulk convection, and migration under electric or other fields. The concept is central to chemical engineering, environmental science, biology, and materials science, where predicting how substances spread or are distributed is essential.

Diffusion is the net movement of species from regions of higher to lower concentration due to random molecular motion. Fick's first law states that the diffusive flux J equals minus the diffusion coefficient D times the concentration gradient, J = -D∇c. Fick's second law describes how concentration changes in time, ∂c/∂t = D∇²c. Convection, or bulk transport, occurs when the carrier fluid moves and carries dissolved substances with it, contributing a convective flux Jconv = c u, where u is the local velocity. The total mass flux is the sum of diffusion and convection, and many problems are described by the advection–diffusion equation.

Migration refers to transport driven by external forces, notably electric fields in electrolytes, where ions move through electromigration. Osmotic transport describes solvent flow across membranes driven by chemical potential differences and osmotic pressure.

Applications of mass transport span reactor design, separations and drying processes in chemical engineering; pollutant dispersion and groundwater transport in environmental science; nutrient and signal transport in biology; and ion transport and electrode processes in energy storage and electronics. Key concepts include mass transfer coefficients and dimensionless numbers such as the Peclet number, which compares the relative strength of advection to diffusion, and the Sherwood number, used to quantify mass transfer at boundaries.

In summary, mass transport explains how and why material moves, integrating diffusion, convection, and migration to describe transport phenomena across disciplines.