Conservation of mass of a species i in an immiscible fluid phase is formulated as

where ϕ is the phase volume fraction, ρi the species density, and u the (mass averaged) velocity of the phase, Di is the diffusion coefficient, and Rm,i is the species mass source. Using the species density definition ρi = cp,iMi, where cp,i is the species phase concentration, and diving by the molar mass Mi, the conservation equation becomes

Choosing to solve for the total concentration ci = ϕcp,i, the equation is

Here DT,i is a turbulent dispersion coefficient accounting for the enhanced transport in turbulent flow. It is added by the Dispersed Two-Phase, Diluted Species coupling feature when the Mixture Model interface is using a turbulence model.

The temperature model input is always available. Select the source of the Temperature. For User defined, enter a value or expression for the temperature in the input field. This input option is always available.

You can also select the temperature solved for by a Heat Transfer interface added to the model component. These physics interfaces are available for selection in the Temperature list.

Specify the phase volume fraction. Select the source of the Volume fraction, continuous phase or the source of the Volume fraction, dispersed phase. When using a Dispersed Two-Phase Flow, Diluted Species coupling feature, the volume fraction is automatically coupled to the one computed by the Mixture Model interface in the same coupling.

If transport by convection is active, the velocity field of the phase in question needs to be specified. Select the source of the Velocity field, continuous phase or the source of the Velocity field, dispersed phase. When using a Dispersed Two-Phase Flow, Diluted Species coupling feature, the velocity is automatically coupled to the one computed by the Mixture Model interface in the same coupling.

Use the Source list to select to pick up diffusion coefficients defined in a material or a Chemistry interface.

Select Material, and a Fluid material to use a diffusion coefficient in a material available in the model. User-defined property groups including a diffusion coefficient output property are available for selection in the Fluid diffusion coefficient list.

Select Chemistry to use a diffusion coefficient from a Chemistry interface added to model component. Diffusion coefficients are automatically defined when Calculate transport properties is selected on the interface level of a Chemistry interface. All defined diffusion coefficients are available for selection in the Fluid diffusion coefficient list.

For User defined, enter a value or expression for the Fluid diffusion coefficient Dc of each species in the corresponding input field. This can be a scalar value for isotropic diffusion or a tensor describing anisotropic diffusion. Select the appropriate tensor type — Isotropic, Diagonal, Symmetric, or Full that describes the diffusion transport, and then enter the values in the corresponding element (one value for each species).