Fluent User defined Scalars and UDF
 

Hi, I am trying to solve 2 user defined scalar mass transport equations in a system where there is air bubble rising from a submerged orifice in aqueous solution of surfactant SDS. Im using VOF model in fluent. My 1st equn is scalar C (bulk concentration) to be solved only in water domain (ie volume fraction = 0) and 2nd scalar equation is for f (surface concentration) to be solved only in the region of interface ( 0 < volume fraction < 1).
Is it possible to limit the solution domain of above scalar equations using a UDF?
and if yes, is there a way to put boundary condition on the interface region for the same?
Thanks,
Anirudh