Nonisothermal Mixture Model
Use the Mixture Model () multiphysics coupling to simulate heat transfers in fluids containing one or more dispersed phases.
The Phase Transport and the Heat Transfer in Fluids interfaces, which are coupled by the Nonsiothermal Mixture Model multiphysics coupling, solve together for conservation of mass of the dispersed phases and heat transfer in the mixture.
The Nonisothermal Mixture Model multiphysics coupling provides the mixture thermal conductivity, heat capacity at constant pressure, and ratio of specific heats to the heat transfer interface.
In the Phase Transport interface, it sets the Temperature in the Model Input section. When the Nonisothermal Mixture Model multiphysics coupling is used together with a Mixture Model multiphysics coupling that couples the Phase Transport interface with a single-phase flow interface (laminar or turbulent), it also sets the Temperature in the Model Input section of the Mixture Model coupling.
Settings
The Label is the default multiphysics coupling feature name.
The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is nitmm1.
Domain Selection
When nodes are added from the context menu, you can select Manual (the default) from the Selection list to choose specific domains to define the mixture model, or select All domains as needed.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The Phase transport and Heat Transfer lists include all applicable physics interfaces.
The default values depend on how this coupling node is created.
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If it is added from the Physics ribbon (Windows users), Physics contextual toolbar (Mac and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.
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If it is added automatically when a multiphysics interface is chosen in the Model Wizard or Add Physics window, then the two participating physics interfaces are selected.
You can also select None from either list to uncouple the node from a physics interface. If the physics interface is removed from the Model Builder, for example Phase Transport is deleted, then the Phase transport list defaults to None as there is nothing to couple to.
Model Inputs
The thermal conductivity, heat capacity at constant pressure, and ratio of specific heats of each phase can be defined through user inputs, variables, or by selecting a material. For the latter option, additional inputs, for example temperature or pressure, may be required to define these properties.
Temperature
This input appears when a material requires the temperature as a model input. By default, the Temperature model input is set from the Heat Transfer interface.
Absolute Pressure
This input appears when a material requires the absolute pressure as a model input. The absolute pressure is used to evaluate material properties, but it also relates to the value of the calculated pressure field. The Absolute Pressure model input is per default computed from the Heat Transfer interface. If the Heat Transfer interface is coupled to a single-phase flow (laminar or turbulent) interface using the Nonisothermal Flow multiphysics coupling, the absolute pressure will be taken from the single-phase flow interface.
The Absolute pressure field can be edited by clicking Make All Model Inputs Editable () and entering the desired value in the input field.
Model Inputs and Multiphysics Couplings in the COMSOL Multiphysics Reference Manual
Continuous Phase Properties
Select the fluid materials to use for the material properties of the continuous phase. The default material used for the Continuous phase is the Domain material.
Heat conduction
The default Thermal conductivity kc (SI unit: W/(m·K)) uses values From material (as selected in the Materials section for the Continuous Phase Properties). For User defined select Isotropic, Diagonal, Symmetric, or Full based on the characteristics of the thermal conductivity, and enter values or expressions f or the thermal conductivity or its components. For Isotropic enter a scalar which will be used to define a diagonal tensor. In this case the default is 0 W/(m·K). For the other options, enter values or expressions into the editable fields of the tensor.
Fluid Material
Both the heat capacity at constant pressure Cp,c and ratio of specific heats γc of the continuous phase can be defined.
The default Heat capacity at constant pressure Cp,c (SI unit: J/(kg·K)), uses values From material. It describes the amount of heat energy required to produce a unit temperature change in a unit mass. For User defined enter another value or expression. In this case, the default is 0 J/(kg·K).
The default Ratio of specific heat γc (SI unit: 1), uses values From material. It is the ratio of the heat capacity at constant pressure of the phase, Cp,c, to the heat capacity at constant volume, Cv,c. For User defined enter another value or expression. In this case, the default is 1. For common diatomic gases such as air, γ = 1.4 is the standard value. Most liquids have γ = 1.1 while water has γ = 1.0. γ is used in the streamline stabilization and in the variables for heat fluxes and total energy fluxes.
Dispersed Phase Properties
The number of Dispersed Phase Properties sections depends on the number of phases defined in the coupled Phase Transport interface: the number of sections is equal to the number of dispersed phases, which is in turn equal to the number of phases defined in the coupled Phase Transport interface minus one.
Select the fluid materials to use for the material properties of the phase. The default material used for the Phase is the Domain material.
Heat conduction
The default Thermal conductivity kd (SI unit: W/(m·K)) uses values From material (as selected in the Materials section for the Dispersed Phase Properties). For User defined select Isotropic, Diagonal, Symmetric, or Full based on the characteristics of the thermal conductivity, and enter values or expressions for the thermal conductivity or its components. For Isotropic enter a scalar which will be used to define a diagonal tensor. In this case the default is 0 W/(m·K). For the other options, enter values or expressions into the editable fields of the tensor.
Fluid Material
Both the heat capacity at constant pressure Cp,d and ratio of specific heats γd of the phase can be defined.
The default Heat capacity at constant pressure Cp,d (SI unit: J/(kg·K)), uses values From material. It describes the amount of heat energy required to produce a unit temperature change in a unit mass. For User defined enter another value or expression. In this case, the default is 0 J/(kg·K).
The default Ratio of specific heat γd (SI unit: 1), uses values From material. It is the ratio of the heat capacity at constant pressure of the phase, Cp,d, to the heat capacity at constant volume, Cv,d. For User defined enter another value or expression. In this case, the default is 1. For common diatomic gases such as air, γ = 1.4 is the standard value. Most liquids have γ = 1.1 while water has γ = 1.0. γ is used in the streamline stabilization and in the variables for heat fluxes and total energy fluxes.
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See Theory for the Nonisothermal Mixture Model Interfaces
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See Theory for the Phase Transport Mixture Model Interfaces
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See Theory for the Nonisothermal Flow and Conjugate Heat Transfer Interfaces
If a physics interface is deleted and then added to the model again, then in order to reestablish the coupling, you need to choose the physics interface again from the Phase transport or Fluid flow lists. This is applicable to all multiphysics coupling nodes that would normally default to the once present interface. See Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.