Need help regarding phase change models in ansys fluent
 

Hello! I am trying to model a plate heat exchanger (PHE) in which the working fluid undergoes a phase change. Details regarding the PHE can be found here.
Anyways, to put it as briefly as possible, pure liquid ammonia enters one channel and hot liquid water enters the other channel. The ammonia vaporizes due to the conjugate heat transfer between the two channels and the plate. The water temperature decreases a little but doesn't undergo any phase change. At the exit, ammonia vapor has a volume fraction of around 70% and liquid ammonia 30%. I want to model this entire process in Fluent.
I have tried looking up literature but nothing good pops up. Infact, there is still no clarity about the heat transfer mechanism in phase change in PHEs. I would really appreciate it if someone could suggest which model in Fluent will be a good starting point. As of now, I am tinkering around with the VOF model but I don't know if what I am doing is even right. I am sorry if I have missed something glaringly obvious; I am just a student using Fluent for the first time. Thanks!