FLUENT 6 - Identifying cells on the free surface interface to define inter-phase mass transfer.

While modeling heterogeneous mass and heat transfer using the VOF model, it is often required to define a mass transfer coefficient only in cells that contain the interface.
For a simple two phase model, it is easy to locate cells on the interface by looking at the phase fraction value. The phase fraction will be either zero or one inside the individual phases but will have intermediate values in cells on interface

Hence, the DEFINE_MASS_TRANSFER udf macro can use a test like the following to locate cells that contain the interface:

vof_cutoff = 0.05;
if ( (C_VOF(c,t) > vof_cutoff ) && (C_VOF(c,t) < (1 - vof_cutoff) )
{ < cell is on the interface> }
{ < cell is inside a phase> }

The DEFINE_MASS_TRANSFER macro is described in the UDF Manual:
<a target=_blank href="http://www.fluentusers.com/fluent/doc/ori/html/udf/node57.htm">http://www.fluentusers.com/fluent/doc/ori/html/udf/node57.htm</a>http://www.fluentusers.com/fluent/doc/ori/html/udf/node57.htm

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