5.5. Thermal Properties

Thermal material properties are defined via the TB,THERM command. These include thermal conductivity (TBOPT = COND), enthalpy (TBOPT = ENTH), and specific heat (TBOPT = SPHT). For porous media, the fluid specific heat can also be defined (TBOPT = FLSPHT).

5.5.1. Thermal Conductivity (`TBOPT` = COND)

The thermal conductivity can be isotopic, orthotropic, or anisotropic. The full 3 x 3 thermal conductivity matrix is:

Define up to nine constants:

Isotropic thermal conductivity matrix -- Define

only. (The

and

values are assumed to be

Orthotropic thermal conductivity matrix -- Enter three constants:

, and

. The program assigns values of zero to the off-diagonal conductivity constants (

Anisotropic thermal conductivity matrix -- If you define the first six constants (

), the program makes the conductivity matrix symmetric (that is,

General nonsymmetric anisotropic thermal conductivity matrix -- Define all nine constants.

Constant	Meaning
C1
C2
C3
C4
C5
C6
C7
C8
C9

All defined constants are based on the element coordinate system. By default, the element coordinate system is the global coordinate system.

For thermal elements, only the first three constants (C1, C2, and C3) can be used to define isotropic or orthotropic thermal conductivity.

For coupled pore-pressure-thermal elements, all nine constants (C1 to C9) can be defined.

Define temperature- or field-dependent data for the data table via the TBTEMP or TBFIELD commands, respectively.

5.5.2. Enthalpy (`TBOPT` = ENTH)

Enthalpy can be defined as a function of temperature using the TB command. The variation in enthalpy, , as a function of temperature, , for a material with specific heat capacity, , and density, ,is calculated from the equation . A typical plot of enthalpy as a function of temperature is shown below for a material that undergoes freezing or melting phase change.

Figure 5.1: Enthalpy vs. Temperature

Define enthalpy via TB,THERM,,,,ENTH followed by commands to specify the data points that characterize the temperature-enthalpy curve. It is important to note that enthalpy must be defined only as a function of temperature by issuing command pairs to specify temperature (via TBTEMP or TBFIELD) and corresponding enthalpy data points (TBDATA or TBPT) along the curve. If TBFIELD is used, it must be issued with Type = TEMP; any other Field variable types will produce erroneous results.

5.5.3. Specific Heat (`TBOPT` = SPHT)

Define specific heat via TB,THERM,,,,SPHT. Input the specific-heat value as C1 on the TBDATA command.

For porous media, this is considered to be the solid-skeleton specific heat.

5.5.4. Fluid Specific Heat (`TBOPT` = FLSPHT)

For porous media, you can define fluid specific heat via TB,THERM,,,,FLSPHT. Input the fluid specific-heat value as C1 on the TBDATA command.