Evaporation UDF
 

I've been looking around here and on the net but haven't found anything good yet.

I've got a hot flow of gas flowing upwards in a pipe, past a small arm where a slow rate of a cold, volatile liquid is being pumped into the large pipe. Geometry is all nicely Hex/Cooper'd. At the conditions of this system, the end state should be the complete evaporation of the liquid into the gas phase, but of course I'd like to know what's happening at a local scale. There's no (effective) interaction between the liquid substance and the hot gas phase beyond mixing, but there is some heat loss due to the latent heat supplied by the hot gas.

I've set up a basic steady-state model using a Mixture multiphase system, with 3 phases: the hot gas, the liquid, and the gas phase of the system. I can do the liquid into the hot gas alone with no problem, but I'm attempting to add the vaporized liquid phase and finding problems with the evaporation model. I know the UDF manual has an example mass transfer (and thus energy transfer) between the two phases, but this seems to assume there's an infinite amount of the liquid phase, AND that there's no upper bound to the saturation of the vapor phase. I've been looking around on the net for something else that I could use, but haven't found anything that seems to meet the needs I have.

I know I could possibly use a DPM, assuming liquid droplets that enter the gas stream, but this would not seem as realistic for the situation based on what I already know.

Has anyone written a general UDF for such a situation or have pointers to information where such a UDF could be generated, or have other suggestions for approaching this problem?