problem with mass transfer
 

Hi,
I am doing phase-change simulation in vapor chamber with fluent 14.5. The model could be seen in Attachment 34911.
The evaporation should only occur at the evaporation interface. However, the VOF/Mixture simulates the phase-change under the condition that T_cell>T_SAT, which means that the evaporation will happen where the condition meets.
Hence, I have written a UDF to apply the DEFINE_MASS_TRANSFER at the evaporation interface. Attachment 34910
First, I obtained the temperature and pressure at the interface(I am not sure I have written UDF of this part right). Then I wrote the mass transfer UDF, in which I calculated the saturated pressure using the temperature at the interface and then compared it with the local pressure to decide if there is mass transfer happening.
So, I need help to get the interface temperature and then apply the UDF only at the interface not the whole domain.
My email is 815719752@qq.com, I could send you the cas file if you would like.
Thank you.
Regards,
Bill