Its the same boundary condition as they have in the paper. Its so that I can set the contact angle at the wall to 0°, as setting it as symmetry implies the contact angle at the wall is 90°. As a result, it will create dropwise flow and cause the results to deviate away from the Nusselts' model as the theorectical model assumes no surface tension effects.

The convergence is fine. The continuity is always less than one. I've set a globel courant number to be equal to 0.4 to ensure no divergence. The paper does include a solid region for their further investigations. However, just for the validation section, they consider the outer surface as a thin wall. So its' the same as what I show in my model.

As for the mass transfer rate, I've used their proposed mass transfer rate for condensation. Here is the equation:

I've incorperated this equation as a UDF for the DEFINE_MASS_TRANSFER macro and everything seems fine. I get a steady rate of condensation with no divergence issues.

Also here is what I have for the multiphase model options:

Additionally, I've set the viscous model to be laminar. All fluid properties are constant at saturation conditions. I just dont know where my problem lies as everything so far looks good. Its just that the film thickness is bigger than it should be in comparison to the papers' result.