Phase Change Material
This node should be used to solve the heat equation after specifying the properties of a phase change material according to the apparent heat capacity formulation. 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.
Number of Transitions
To display this section, click the Show button () and select Advanced Physics Options. 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 2 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.
Phase Change
The parameters for the definition of the transition temperature intervals are set in this section.
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.
The Latent heat from phase 1 and phase 2 L1 → 2 should be set to define the total heat per unit volume released during the first 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.
About the Phases
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.
Phase
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.
The following material properties should be set:
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Thermal conductivity kphase[1,2,...]. The default uses the material values for phase i. For User defined select Isotropic, Diagonal, Symmetric, or Anisotropic based on the characteristics of the thermal conductivity, and enter another value or expression. The default is 1 W/(m·K).
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Density ρphase[1,2,...]. The default is 1000 kg/m3.
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Heat capacity at constant pressure Cp, phase[1,2,...]. The default is 4200 J/(kg·K).
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Ratio of specific heats γ phase[1,2,...]. The default is 1.1
Theory for Heat Transfer with Phase Change
It is useful to choose three or more phase transitions to handle extra changes of material properties such as in mixtures of compounds, metal alloys, composite materials, or allotropic varieties of a substance. For example, α, γ, and δ-iron are allotropes of solid iron that can be considered as phases with distinct phase change temperatures.
When Surface-to-surface radiation is activated, the Opacity subnode is automatically added to the entire selection, with Transparent option selected. The domain selection can’t be edited. To set some part of the domain as opaque, add a new Opacity subnode from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
To satisfy energy and mass conservation in phase change models, particular attention should be paid to the density in time simulations. When the material density is not constant over time — for example, dependent on the temperature — volume change is expected. The transport velocity field and the density must be defined so that mass is conserved locally. A Moving Mesh Interface (described in the COMSOL Multiphysics Reference Manual) can be used to account for model deformation.
Phase Change: Application Library path Heat_Transfer_Module/Phase_Change/phase_change
Continuous Casting: Application Library path Heat_Transfer_Module/Thermal_Processing/continuous_casting
Cooling and Solidification of Metal: Application Library path Heat_Transfer_Module/Thermal_Processing/cooling_solidification_metal
Location in User Interface
Context menus
Heat Transfer>Phase Change Material
Heat Transfer in Solids>Phase Change Material
Heat Transfer in Fluids>Phase Change Material
Heat Transfer in Porous Media>Phase Change Material
Heat Transfer in Building Materials>Phase Change Material
Bioheat Transfer>Phase Change Material
Heat Transfer with Surface-to-Surface Radiation>Phase Change Material
Heat Transfer with Radiation in Participating Media>Phase Change Material
Ribbon
Physics Tab with interface as Heat Transfer, Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media, Heat Transfer in Building Materials, Bioheat Transfer, Heat Transfer with Surface-to-Surface Radiation or Heat Transfer with Radiation in Participating Media selected:
Domains>interface>Phase Change Material