Diffusive Flux Links to/from Cells

In addition to transporting mass out of or into Cells via advective mass flux links, mass can also be transported via diffusive mass flux links.

Diffusive mass flux links are used to transport mass through a fluid via the process of molecular diffusion. Diffusive mass transport is driven by a concentration gradient, with mass diffusing from high concentration to low concentration. The constant of proportionality is referred to as the diffusive conductance:

Diffusive Mass Flux = (Diffusive Conductance) * (Concentration Difference)

The diffusive conductance is a function of the properties of the species and fluids involved, and the geometry of the diffusive process. This is discussed in detail in Appendix B of the Contaminant Transport User’s Guide.

Diffusive mass flux links between Cells are bi-directional (mass can be transported in either direction). The pathway from which the link was created is referred to as the Outflux pathway, and the other pathway in the link is referred to as the Influx pathway. Diffusive fluxes away from the Outflux pathway are, by convention, positive.

Note: If the volume of the Fluid associated with a diffusive flux link goes to zero, a fatal error will occur. That is, you cannot simulate diffusion through a system in which the volume of the fluid through which the mass is diffusing goes to zero.