For a steady-state problem the temperature does not change with time and the first term disappears.

This section is available when a temperature-dependent density defined in a material is used. On the material frame, the density is evaluated onto a reference temperature to ensure mass conservation in the presence of temperature variations. By default the Common model input is used. This corresponds to the variable minput.Tempref, which is set by default to 293.15 K. To edit it, click the Go to Source button (), and in the Default Model Inputs node under Global Definitions, set a value for the Volume reference temperature in the Expression for remaining selection section.

The other options are User defined and all temperature variables from the physics interfaces included in the model.

This section is available when temperature-dependent material properties are used. By default the temperature of the parent interface is used and the section is not editable. To edit the Temperature field, click Make All Model Inputs Editable (). The available options are User defined (default), Common model input (the minput.T variable, set to 293.15 K by default) and all temperature variables from the physics interfaces included in the model. To edit the minput.T variable, click the Go to Source button (), and in the Default Model Inputs node under Global Definitions, set a value for the Temperature in the Expression for remaining selection section.

It is also used if the ideal gas law is applied. See Thermodynamics, Fluid.

The default Absolute pressure pA is taken from Common model input. It corresponds to the minput.pA variable, set to 1 atm by default. To edit it, click the Go to Source button (), and in the Default Model Inputs node under Global Definitions, set a value for the Pressure in the Expression for remaining selection section. When additional physics interfaces are added to the model, the absolute pressure variables defined by these physics interfaces can also be selected from the list. For example, if a Laminar Flow interface is added you can select Absolute pressure (spf) from the list. The last option is User defined.

This section can be edited anytime a material property is concentration dependent; for example, when the Fluid type is set to Moist air with Input quantity set to Concentration.

From the Concentration c (SI unit: mol/m3 or kg/m3) list, select an existing concentration variable from another physics interface, if any concentration variables exist, User defined to enter a value or expression for the concentration, or Common model input which corresponds to the minput.c variable.

Select any component material from the list to define the Fluid material. The default uses the Domain material. It makes it possible to define different material properties for the fluid phase when the domain material corresponds to the solid phase (porous matrix) material.

The default Velocity field u is User defined. For User defined enter values or expressions for the components based on space dimensions. Or select an existing velocity field in the component (for example, Velocity field (spf) from a Laminar Flow interface). The Common model input option corresponds to the minput.u variable. To edit it, click the Go to Source button (), and in the Default Model Inputs node under Global Definitions, set values for the Velocity components in the Expression for remaining selection section.

The thermal conductivity k describes the relationship between the heat flux vector q and the temperature gradient ∇T in q = −k∇T, which is Fourier’s law of heat conduction. Enter this quantity as power per length and temperature.

The default Thermal conductivity k is taken From material. For User defined select Isotropic, Diagonal, Symmetric, or Full based on the characteristics of the thermal conductivity, and enter another value or expression. For Isotropic enter a scalar which will be used to define a diagonal tensor. For the other options, enter values or expressions into the editable fields of the tensor.

The heat capacity at constant pressure Cp describes the amount of heat energy required to produce a unit temperature change in a unit mass.

The ratio of specific heats γ is the ratio of the heat capacity at constant pressure, Cp, to the heat capacity at constant volume, Cv. When using the ideal gas law to describe a fluid, specifying γ is sufficient to evaluate Cp. 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. It is also used if the ideal gas law is applied.

The available Fluid type options are Gas/Liquid (default), Moist air, or Ideal gas. After selecting a Fluid type from the list, further settings display underneath.

This option specifies the Density, the Heat capacity at constant pressure, and the Ratio of specific heats for a general gas or liquid.

If Moist air is selected, the thermodynamics properties are defined as a function of the quantity of vapor in the moist air. The available Input quantity options to define the amount of vapor in the moist air are the following:

If the Standard porous matrix model is selected under Physical Model, select any component material in the Solid material list. The Volume fraction θp for the solid material should be specified. For User defined, enter a value or expression. Or select an existing volume fraction in the component (for example, Volume fraction (dl/dlm1) from a Darcy’s Law interface).

If the Extended porous matrix model is selected under Physical Model (with the Subsurface Flow Module), the Number of solids can be set from 1 to 5. Then for each solid a Solid material list and a Volume fraction field display underneath.

The thermal conductivity kp describes the relationship between the heat flux vector q and the temperature gradient ∇T in q = −kp∇T, which is Fourier’s law of heat conduction. Enter this quantity as power per length and temperature.

The default Thermal conductivity kp is taken From material. For User defined select Isotropic, Diagonal, Symmetric, or Full based on the characteristics of the thermal conductivity, and enter another value or expression. For Isotropic enter a scalar which will be used to define a diagonal tensor. For the other options, enter values or expressions into the editable fields of the tensor.

When the Extended porous matrix model is selected under Physical Model (with the Subsurface Flow Module), and more than one solid is selected in the Immobile Solids section, the thermal conductivities kpi should be specified for each immobile solid. The average property for the porous matrix is given by:

The Density ρp and the Specific heat capacity Cp, p should be specified. For From Material option, see Material Density in Features Defined in the Material Frame if a temperature-dependent density should be set.

When the Extended porous matrix model is selected under Physical Model (with the Subsurface Flow Module), and more than one solid is selected in the Immobile Solids section, the Density and Specific heat capacity should be specified for each immobile solid.

This section sets the averaging model for the computation of the Effective conductivity by accounting for both solid matrix and fluid properties. The following options are available with either the Subsurface Flow Module or the Heat Transfer Module:

When the Extended porous matrix model is selected under Physical Model (with the Subsurface Flow Module), and more than one solid is selected in the Immobile Solids section, these averaging models are modified in the following way:

More locations are available if the Heat transfer in porous media check box is selected under the Physical Model section. For example:

Physics Tab with interface as Heat Transfer in Solids and Fluids, Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media, Heat Transfer in Building Materials or Bioheat Transfer selected: