You only need two phases, air and vapour are both gases. You then have a droplet size, that's set in the solver (generally). I assume gravity is pointing down, common mistake!
What is the bottom inlet? Just wondering how liquid is supposed to leave the domain.
I'd also look to update, R18 is 5-6 years old and there have been significant improvements in both the general code and more interest here to multiphase modelling. We're on 2023R1 now, which I think is equivalent to R24 in old numbering.
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