This subnode should be used to specify the properties of a phase change material according to the apparent heat capacity formulation, when modeling heat transfer in solids, fluids, and porous media. This formulation gets its name from the fact that the latent heat is included as an additional term in the heat capacity. Up to five transitions in phase per material are supported. Alternatively, a Stefan condition can be defined on boundaries by using the Phase Change Interface node.

To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box. The Number of phase transitions to model is set in this section. In most cases, only one phase transition is needed to simulate solidification, melting, or evaporation. If you want to model successive melting and evaporation, or any couple of successive phase transformations, choose an alternative value in the Number of phase transitions list. The maximum value is 5.

Depending on the Number of phase transitions, several parts display in the Phase Change section, and several Phase sections display underneath.

This section is only available when the subnode is added under the Solid node. In this particular case, a single density should be defined for all phases to ensure mass conservation on the material frame. Default is taken From material. For User defined, enter a value or expression for ρ. Note that this setting overrides the setting in the Thermodynamics, Solid section of the parent Solid node.

Each transition is assumed to occur smoothly in a temperature interval between Tpc, j → j + 1 − ΔTj → j + 1 ⁄ 2 and Tpc, j → j + 1 + ΔTj → j + 1 ⁄ 2, releasing a total heat per unit volume equal to Lj →j + 1.

The Phase change temperature between phase 1 and phase 2 Tpc, 1 → 2 should be set to define the center of the first transition interval. The default is 273.15 K. Enter any additional phase change temperatures as per the Number of phase transitions.

The Transition interval between phase 1 and phase 2 ΔT1 → 2 should be set to define the width of the first transition interval. The default is 10 K. Enter any additional transition intervals as per the Number of phase transitions.

The value of ΔTj → j + 1 must be strictly positive. A value near 0 K corresponds to a behavior close to a pure substance.

Open the Sketch section for more details on these parameters.

The Latent heat from phase 1 and phase 2 L1 → 2 should be set to define the latent heat per unit mass released during the first phase transition. Enter any additional latent heat values as per the Number of phase transitions.

The value of Lj → j + 1 must be positive. The default is 333 kJ/kg, which corresponds to the latent heat of fusion of water at a pressure of 1 atm.

The different phases are ordered according to the temperatures of fusion. Hence, the material properties of phase 1 are valid when T < Tpc, 1 → 2, while the material properties of phase 2 hold for T > Tpc, 1 → 2.

When more than one transition is modeled, the number of phases exceeds 2, and new variables are created (for example, Tpc, 2 → 3, ΔT2 → 3 or L2 → 3). The phase change temperatures Tpc, j → j + 1 are increasing and satisfy

This defines distinct domains of temperature bounded by Tpc, j − 1 → j and Tpc, j → j + 1 where the material properties of phase j only apply.

In addition, the values of ΔTj → j + 1 are chosen so that the ranges between Tpc, j → j + 1 − ΔTj → j + 1 ⁄ 2 and Tpc, j → j + 1 + ΔTj → j + 1 ⁄ 2 do not overlap. If this condition is not satisfied, unexpected behavior can occur because some phases would never form completely. The values of ΔTj → j + 1 must all be strictly positive.

In each Phase section (based on the Number of phase transitions), the thermal conductivity and thermodynamics properties of each phase must be set. Then, within the transition interval, there is a “mushy zone” with mixed material properties.

Select a Material, phase [1,2,...], which can point to any material in the model. The default uses the Domain material.

When the Phase Change Material subnode is added under a Solid node, the following material properties should be set:

Note that these settings override the settings of the Heat Conduction, Solid and Thermodynamics, Solid sections of the parent Solid node.

When the Phase Change Material subnode is added under a Fluid or Porous Medium node, the following material properties should be set:

Note that these settings override the settings of the Heat Conduction, Fluid and Thermodynamics, Fluid sections of the parent node. In porous media, phase change is considered in the fluid material only.

Physics Tab with Solid, Fluid, or Porous Medium selected in the model tree: