Melting and Solidification

Melting is the process which changes the state of matter from solid to liquid. It takes place when a solid substance is heated to the melting temperature. The opposite process is called solidification.

For pure substances, for example water, the melting and solidification usually take place at one temperature, that is, the liquidus and the solidus are at the same temperature. The melting-solidification model that is implemented in Simcenter STAR-CCM+ does not track the liquid-solid interface explicitly. Instead, the model uses an enthalpy formulation to determine the distribution of the solidified portion of the liquid-solid phase.

For melting-solidification, the enthalpy of the liquid-solid phase $h_{\text{ls}}\text{*}$ includes the latent heat of fusion $h_{\text{fusion}}$ :

where $h_{\text{ls}}$ is the sensible enthalpy.

The relative solid volume fraction ${\alpha \text{*}}_s$ is defined as the portion of the volume of the liquid-solid phase that is in the solid state. In the enthalpy model, the relative solid volume fraction ${\alpha \text{*}}_s$ is a function of temperature:

where $T\text{*}$ is the normalized temperature that is defined as:

The function $f\left(T\text{*}\right)$ is called the fraction solid curve. For a linear dependence between ${\alpha \text{*}}_s$ and $T\text{*}$ , the solidification path is defined as:

The solidification path can also be specified as a table, in which case linear dependencies are assumed between the points in the table. The values of temperature in the table have to increase monotonically as the values of the relative solid fraction decrease monotonically.

If melting and solidification take place at one temperature (that is, $T_{\text{solidus}}=T_{\text{liquidus}}$ ), a linear solidification path is assumed and a small temperature interval of 0.002 K is introduced automatically. The physical properties of the liquid-solid phase can be constant, or can be a function of temperature and the relative solid volume fraction.