Hi, Danica. Thank you for the feedback.

(1) It's a typo. There is no triangle, it's a 2d rectangle.
(2) There's no heat addition in the system. We expect the vaporization process and backflow will cool down the system. (At the beginning, the bottom half of the rectangle contains the liquid and the upper half of the rectangle contains the mixture (0.02 mass fraction of vapor))
(3) I didn't change any enthalpy. Should I change it?
(4) I think the mesh is fine. Minimum Orthogonal Quality = 1.0 Maximum Aspect Ratio = 1.00245e+01.

By the way, I found out that the residuals of continuity and energy always diverge first. Is there any way to fix it?