Phase change: freezing and convergence problem

Hi,

I'm currently working on a water solution freezing model including the phase change.

I use the COMSOL model : www.comsol.com/model/phase-change-474

Geometry:
I just add a metal part below the water. I impose T_bottom at the base of this metal part.

Definitions:
Then I changed some parameters according to my experiment:

T_trans = -10°C
T_i = -5°C
T_f= -15°C
T_bottom= from T-i to T_f, in 600 seconds

H = from 1 to 0 (volume fraction of water = theta_water)
D becomes < 0 (by definition)


I have one question and one problem:

The question: In Cp_ water and Cp_ice definitions, shall I change the sign before D(T)*lm ? Is it the same for both ? (I noticed a mistake in the tutorial page 12 where they call Rho_ice the density of water)

The problem: I tried different possibilities, unfortunately, it never converges... Even after few days...

Experimentally, I observed an increase of the T°C during the freezing which is coming from the phase change. I would to show it by model.

Does anybody has an idea to adapt the melting model of COMSOL to the freezing one ?

Thanks a lot,

Jb