I think you should use unsteady analysis, PRESTO for pressure calculation and Coupled schema.

Hi Dogan, Thank you for your reply. The reference paper simulates steady-state simulations. But I am also trying the transient implicit VOF which resembles the steady-state simulations. I am using PRESTO. Instead of Coupled, I am using SIMPLE. 

Maybe you could obtain the initial results without considering the condense firstly, and then active the condense model. Additionally,  reducing the relax factor could  enhance the stability of the simulation.

My suggestion regarding your problem is to try the Unsteady calculation with the default settings of Fluent when VOF is adopted. Since you are new in the Fluent simulation, so I am recommending you to read the user manual of Fluent carefully,  especially the Chapter which explains about the selection of Solver setting and other associated issues. Hope it will be helpful for your problem.  Additionally, you did not mention that what kind of error message, which you are receiving during the divergence of your calculation. Actually, the error messages are very important to understand the cause of divergence in the most of the calculations with Fluent. Anyway, Good luck! 

Hello, Thank you for your replies. The divergence error message was in vof-1. 

Can anyone please tell me where to put the saturation pressure, is it in specified operating pressure or gauge pressure in inlet and outlet? Also, I dont know the pressure at outlet... Will it still be at saturation pressure? or better use outflow as outlet bc..

Thank you for your help

The vaporization pressure shoulb be set under the fluid properties if you activate a cavitation model. 

You can try to perform your simulation with OpenFOAM using for example the interPhseChangeFOAM solver.

Otherwise at least you can copz all the numerical settings into Fluent.

http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2011/MartinAndersen/Tutorial_interPhaseChangeFoam.pdf

Franco

Hello Franco, Thank you for your reply. I have checked the document. It's another model for condensation based on pressure difference I guess. I am using the Lee model of Fluent. 

There may be more than one solution offered by nature for your problem given your boundary conditions, fluid properties and initial conditions. You may want to read about the Leidenfrost effect, critical heat flux and "boiling crisis". Your simulation, if physically consistent, may not reach a steady state but enter a limit cycle or diverge from on "stable point" in the state space to another "stable point". It would be correct to use "attractor" instead of "stable point", although one doesn't know until the limit cycle develops.