What viscosity to use for solid phase in VOF model
 

Hello,

I am modeling a melting problem with a VOF model.
The purpose of the simulation is to get the temperature distribution as well as the flow and shape of the molten metal (Copper).

The initial temperature for the model is room temperature, so the metal is in solid phase and then very high heat flux is added to melt the metal. The metal is supposed to melt in less than 1 sec.

I turned on VOF, gravity, Solidification/melting and energy model in fluent. The model runs and converges. But the problem is that the metal starts to flow even before it melts.

To add the solidus & liquidus temperature and solvent melting heat in the material property, I had to use "FLUID" material type. There properties cannot be specified for Solid material in Fluent (or is there any way?). For the viscosity, I used the viscosity of liquid metal (around 0.004 Pas). But if I use a piecewise linear function to define high viscosity for the initial solid phase, the model diverges after a few iterations and reports that "velocity is diverging and courant number is greater than 250. Use shorter time step". I reduced the time step to 1e-5, and also reduced URF. But the same thing happens. But when I use a constant low viscosity of 0.004 pas, model works. But as I said, in that case the metal starts to flow even before it starts to melt.

Any suggestion?