About System, Cells and Regions

This section or topic is specific to Console Mode.

For Graphical Mode, see Diffusion Module Terminology in Graphical Mode.

A system normally consists of one cell. This cell contains one or several regions in which the diffusion problem is to be solved. A system of diffusion equations is solved for each region. The size of the system is the sum of sizes of all the regions in all the system’s cells.

The interface between two regions typically moves as the result of a simulation, that is, the regions grow or shrink. Such an interface is called an inner interface. The boundary of a cell is called an outer interface and the condition of this type of interface may be affected by the choice of boundary conditions.

For some simulations it is useful to have several cells in a system. Matter can move between cells. However, it is assumed that there is diffusional equilibrium between all cells (this means that there are no differences in diffusion potentials between cells). In other words, the size of a cell is fixed during the simulation.

By default this is a closed system, which means that matter cannot move across its boundaries. However, you can change this setting for both the lower boundary (left side/centre) and the upper boundary (right side/surface) of the system. You can also set these boundary conditions to vary as a function of time, temperature and/or pressure.