Interfacial area concentration is defined as the interfacial area between two phases per unit mixture volume. This is an important parameter for predicting mass, momentum and energy transfers through the interface between the phases. When using the Eulerian multiphase model with non-granular secondary phases, you can have Ansys Fluent compute the interfacial area in one of two ways:
use a transport equation for interfacial area concentration as described in Interfacial Area Concentration. This allows for a distribution of bubble diameters and coalescence/breakage effects.
use an algebraic relationship between a specified bubble diameter and the interfacial area density.
The algebraic interfacial area concentration models are derived from the surface area to
volume ratio, 
, for a spherical bubble or droplet:
 | (14–206) |
where 
is the bubble or droplet diameter. The algebraic
models available when using the Eulerian multiphase model are:
Particle model (default)
For a dispersed phase,
, with volume fraction, 
, the particle model estimates the interfacial area density, 
as 
(14–207)
Symmetric model
The symmetric model treats both phases
and 
symmetrically. Phases 
and 
can be continuous or dispersed. The interphase area density is calculated as: 
(14–208)
where
and 
are the volume fraction of the phase 
and phase 
, respectively, and 
is the characteristic length scale computed as follows: Ishii model (boiling flows only)
The Ishii model, which is only available when the boiling model is activated, also modifies the particle model and results in a piecewise linear function of
that approaches 0 as 
approaches 1. 
(14–211)
In Fluent,
is chosen as 0.25.Gradient model
For the description of the Gradient model, refer to Algebraic Models.
User-Defined (boiling flows only)
See
DEFINE_EXCHANGE_PROPERTYin the Fluent Customization Manual.
