Hi, I am trying to introduce source terms in the VOF model to simulate evapration. In addition to the source terms for VOF and pressure-correction equations, I want to have a source term for the diffusion equation in the region where the volume fraction of the liquid is between 0 and 1 i.e. at the liquid/gas interface to take into consideration the mass generation of the vapour at the interface. But I don't know how to target the source term for the vapour specie in the gas phase. There is a small note in the urstrm.f file about the same but I can't make out what does it mean. I would appreciate if somebody can help me. Thanks, Raja

To introduce a source term for a species in a phase, add your term in urstrm.f under the area commented for SPECIES - EQ.

You then need to use IPHASE and NUMSPC to determine when your source term values (ATERM,BTERM) are required by Fluent.

Also, note that if you have a net amount of mass being transferred between phases, as you will have in evaporation - you will also need to activate the interphase mass transfer model and modify the usrmst.f subroutine. If you don't do this, no mass will be transferred between the phases and you won't have a mass balance. Also note that usrmst.f requires a volumetric mass rate (kg/m3-s) not a cell rate (kg/s) as other routines (that took a few more weeks to spot since its not documented!)

Good luck!

Greg Perkins