# Set Up Species Transport Modeling

Species transport modeling gives you the capability to simulate and track multiple species in a fluid flow by using the scalar transport equations for each of them individually.
1. From the Flow ribbon, click the Physics tool.
2. Under the Physics models settings, enter a value for Number of passive species.
You can define up to nine species.
Once species transport is defined in the Physics Setup dialog:
• The diffusivity of each species can be defined in material library.
• All material properties can be set as a functions of species concentration. This models a ‘miscible’ property relative to mixing of multiple fluids.
• You can define the concentration of each species at all inlet boundaries using the species tab.
• You can define species concentration or fluxes on wall boundary conditions.
• In addition, you can specify species source per unit volume or per unit mass for a species transport equation. The definition can be constant or varying.
• You can define the initial concentrations of species.