massaoverdrachtscoëfficiënten

Mass transfer refers to the movement of mass from regions of higher concentration to regions of lower concentration, often across phase boundaries or within a single phase. It arises from concentration gradients and is influenced by diffusion, convection, and phase change. In engineering and natural systems, mass transfer governs the rates of drying, adsorption, distillation, gas scrubbing, and pollutant transport.

Theoretical descriptions separate diffusion, the gradual spreading of species due to random molecular motion, from convective mass transfer caused by bulk fluid flow. Fick's laws describe diffusion: the diffusive flux J = -D ∇C, with D the diffusion coefficient and C the concentration. When fluid motion matters, the transport is described by the convective-diffusion equation ∂C/∂t + v · ∇C = D ∇^2 C, where v is the velocity field. At interfaces between phases, mass transfer involves interfacial resistance and mass transfer coefficients, linking bulk concentrations to interfacial flux.

Dimensionless analysis uses coefficients such as the Sherwood number Sh = kL/D, the Schmidt number Sc = μ/(ρD), the Reynolds number Re, and the Péclet number Pe = UL/D. These guide correlations for k and diffusion-limited regimes in tubes, packed beds, droplets, or membranes.

Applications span chemical engineering, environmental engineering, food science, and physiology. Experimental methods include tracer tests and concentration profiling; numerical models solve diffusion-convection problems in complex geometries. The topic encompasses multicomponent diffusion, non-ideal mixtures, and temperature-dependent diffusivities, which add complexity beyond simple single-species diffusion. See also diffusion, convection, mass transfer coefficient.