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23.9.7 Including Mass Transfer Effects

As discussed in Section  23.7, mass transfer effects in the framework of FLUENT's general multiphase models (i.e., Eulerian multiphase, mixture multiphase, or VOF multiphase) can be modeled in one of three ways:

Because of the different procedures and limitations involved, defining mass transfer through cavitation is described separately in Section  23.11.2.

To define mass transfer in a multiphase simulation, either as unidirectional constant or using a UDF, you will need to use the Phase Interaction panel (e.g., Figure  23.9.6).

Define $\rightarrow$ Phases...

1.   In the Phases panel (Figure  23.9.2), click the Interaction... button to open the Phase Interaction panel.

Figure 23.9.6: The Phase Interaction Panel for Mass Transfer
figure

2.   Click the Mass tab in the Phase Interaction panel.

3.   Specify the Number of Mass Transfer Mechanisms. You can include any number of mass transfer mechanisms in your simulation. Note also that the same pair of phases can have multiple mass transfer mechanisms and you have the ability to activate and deactivate the mechanisms of your choice.

4.   For each mechanism, specify the phase of the source material under From Phase.

5.   If species transport is part of the simulation, and the source phase is composed of a mixture material, then specify the species of the source phase mixture material in the corresponding Species drop-down list.

6.   For each mechanism, specify the phase of the destination material phase under To Phase.

7.   If species transport is part of the simulation, and the destination phase is composed of a mixture material, then specify the species of the destination phase mixture material in the corresponding Species drop-down list.

8.   For each mass transfer mechanism, select the desired mass transfer correlation under Mechanism. The following choices are available:

constant-rate   enables a constant, unidirectional mass transfer.

user-defined   allows you to implement a correlation reflecting a model of your choice, through a user-defined function.

FLUENT will automatically include the terms needed to model mass transfer in all relevant conservation equations. Another option to model mass transfer between phases is through the use of user-defined sources and their inclusion in the relevant conservation equations. This approach is a more involved but more powerful, allowing you to split the source terms according to a model of your choice.

figure   

Note that momentum, energy, and turbulence are also transported with the mass that is transferred. FLUENT assumes that the reactants are mixed thoroughly before reacting together, thus the heat and momentum transfer is based on this assumption. This assumption can be deactivated using a text command. For more information, contact your FLUENT support engineer.

When your model involves the transport of multiphase species, you can define a mass transfer mechanism between species from different phases. If a particular phase does not have a species associated with it, then the mass transfer throughout the system will be performed by the bulk fluid material.

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Note that including species transport effects in the mass transport of multiphase simulation requires that Species Transport be turned on in the Species Model panel.

Define $\rightarrow$ Models $\rightarrow$ Species $\rightarrow$ Transport & Reaction...


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