### 1.6.2. Diffusive Transport Equations for Additional Variables

The general form of the diffusive transport equation for an Additional Variable (non-reacting scalar) is:

| (1–174)

where:

- is the mixture density, mass per unit volume.

- is the conserved quantity per unit volume, or concentration.

- is the conserved quantity per unit mass.

- is a volumetric source term, with units of conserved quantity per unit volume per unit time

- is the kinematic diffusivity for the scalar.

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