Dear Mohammed

You should check the quality of the mesh and the CFL.

There is a way to improve the quality of the mesh in Fluent: Mesh... Repair-Improve... Improve (do this many times if needed).

In fact, check the smallest grid size and to calculate the time step size using CFL condition.

Good luck.

Thanks Dr. Mounir for your response. best regards

Dear Mohamed

Check your mesh and your boundary and operating conditions

use body force weight interpolation scheme

Dear Dr.Amina, I think I could not specify the body force weight interpolation scheme if I using the Eulerian multiphase model. Eulerian model will use correction for pressure and velocities via a solution method for coupling between phases. thanks for your response

In my experience a timestep size of 0.04s seems to me way too large for a wall boiling model simulation. On the onset of boiling vapor is produced at the heated wall, which comes along with a sudden increase in the volume being occupied by multiphase mixture (i.e. vapor and liquid). In my observation a smaller timescale was required to get the RPI wall boiling model to convergence. You may want to try to conduct a series of tests, whether the reduction to dt=0.004s or even dt=0.001s would help to improve the convergence behavior of your case. But the behavior might generally depend on the thermal energy being released by the heater and the consequently following boiling regime. You therefore my want to start with smaller values of the applied wall heat flux. If you can obtain a solution with this smaller value of applied heat flux, than you can restart the simulation from this intermediate result and subsequently increase the heat flux up to the desired value.

Regards,

Dr. Th. Frank.