As ANSYS staff we're limited in scope to assist: this isn't a simple problem to be able to give a generic answer to.
Your system has two separate fluid zones, and multiphase flow. You also want a chemical reaction in the system, but I'm unsure whether the reaction produces water, or evaporates what is already there.
Can you sketch out the layout, and detail what goes into the system where then it may be possible to give some advice.
In terms of primary & secondary phases, it's dependent on what's going on in the system. I suspect you want all the liquids in one phase and vapour in the other, but hopefully the sketch will clarify.