This subnode is used to specify the properties of a phase change material when modeling heat transfer in solids, fluids, and porous media. It uses the apparent heat capacity method which describes the phase transition within a temperature interval where latent heat is included as an additional term in the heat capacity – hence, the name of the method. 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.

In this section, the characteristics of the phase transitions from phase j to phase j+1 are defined. This means that the phase transition function α j → j + 1 is specified, which at the same time corresponds to the volume fraction of phase j+1.

The Phase transition function describes how the transition from phase j to phase j+1 occurs. Heaviside (the default) describes a transition as a smooth step function with continuous derivatives up to second order and Linear a transition as a linear function. Each transition is assumed to occur in a temperature interval ΔTj → j + 1 around the phase change temperature Tpc, j → j + 1. During phase change between the temperatures Tpc, j → j + 1 − ΔTj → j + 1 ⁄2 and Tpc, j → j + 1 + ΔTj → j + 1 ⁄2, a total heat per unit volume equal to Lj →j + 1 is released.

With User defined, an arbitrary function for α j → j + 1 can be defined. The default expression is flc2hs(T-273.15[K],5[K]), which corresponds to the default Heaviside phase transition function.

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 and at a temperature of 273.15 K.

When choosing a user define phase transition function, define the Phase transition between phase 1 and phase 2 directly. Enter an expression for the phase transition function α 1 → 2 that explicitly describes the volume fraction of phase 2. Enter any additional functions as per the Number of phase transitions. The values of α 1 → 2 should lie in the interval from 0 to 1. The default expression is flc2hs(T-273.15[K],5[K]) which corresponds to the default Heaviside phase transition function. See the Phase Transition Function section in the Theory for Heat Transfer with Phase Change chapter for more details about the definition of α 1 → 2.

When using Heaviside or linear for the phase transition function, the phases are ordered according to the temperatures of fusion. Hence, the material properties of phase 1 are used when T < Tpc, 1 → 2, while the material properties of phase 2 hold for T > Tpc, 1 → 2. Within the phase transition interval the properties are mixed ac

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:

Physics tab with Porous Medium>Fluid selected in the model tree: