Flux

The Flux node can be used to specify the total mass flux across a boundary. The total inward flux is defined in the manner of:

–n iu + ji = N0 i

(3-1)

In Equation 3-1, N0,i (SI unit: Pa·s/m) is an arbitrary flux expression for species i and can be a function of i, temperature, pressure, or even electric potential. Set the mass flux of all species except the one computed from the mass constraint, which ensures that the sum of the mass fractions is equal to one (see Species).

The Flux feature can, for example, be used to describe a heterogeneous

reaction or a separation process occurring at the boundary.

Tip

B O U N D A R Y S E L E C T I O N

From the Selection list, choose the boundaries to apply a flux boundary condition.

I N W A R D F L U X

Specify the Inward mass flux for each species individually. Select the check box for the species to prescribe a flux and enter a value or expression for the flux in the corresponding field. To use another boundary condition for a specific species, click to clear the check box for that species’ flux.

Use a positive value for an inward flux.

Note

Inflow

The Inflow node adds a boundary condition for an inflow boundary, where a condition for all species is specified. The condition can be specified using these quantities:

•The mass fraction: 0

•The mole fraction: x x0

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