KNOWN ISSUE: Boundary mass sources can give incorrect answer for heat transfer and additional variables (Class 3 Error)
If boundary mass (Continuity) sources are used together with either (a) volumetric Additional Variables or (b) heat transfer when the MCF/Energy Sink Option is set to 'Specified Mass Fractions and Local Temperature' and the source value is negative, then incorrect answers are obtained.
This is due to the Solver using incorrect variable values in calculating the secondary sources in the additional variable and heat transfer equations.
If possible, use a subdomain source adjacent to the boundary.
ANSYS CFX Release 13.0. A custom executable for ANSYS CFX Release 12.1 is available on request.