### 7.14.1. Fluid-Specific Sources

Fluid-specific sources are applied directly to fluid as specified and are not multiplied by volume fraction; that is, the sources are assumed to be specified per unit volume of geometry, not per unit volume of the phase. If you have a source expression that is per unit volume of the phase, you must either multiply the source by volume fraction or else use Bulk Sources, which are discussed below.

Fluid-specific sources are not available for equations in homogeneous multiphase flow that span all fluids; Bulk Sources are the only appropriate option for these situations.

Examples of the application of fluid-specific sources:

- Momentum sources:

  Momentum sources must be multiplied by the volume fraction. For details on momentum sources, see Momentum Sources in the CFX-Solver Theory Guide.

- Isotropic and directional loss models:

  The linear resistance coefficient must be multiplied by the corresponding phase volume fraction. The quadratic resistance coefficient should be multiplied by the square of the corresponding phase volume fraction.

- Permeability:

  Resistance coefficients must be multiplied by the corresponding phase volume fraction. The permeability must be divided by the corresponding phase volume fraction.

- Quadratic loss coefficients:

  Quadratic loss coefficients must be multiplied by the square of the corresponding phase volume fraction.

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