CST2013: Material Parameters: default - Thermal

Modeling: MaterialsNew/EditNew MaterialThermal

Edit Object Properties (navigation tree: Materials:material1PropertiesThermal)

This is a dialog page of the Material Parameters dialog box.

This dialog offers the possibility to define thermal properties of a material.

Thermal properties are independent of the chosen problem type. Their values will be the same for all defined material sets.

Type

Three different types of thermal materials are available:

Material density info

This field is for information purpose only, since it is important for transient thermal calculations.

General

In this frame, general thermal material properties are defined.

Thermal conductivity

Enter the thermal conductivity of a material here. If a zero conductivity is specified the material is not taken into account for a thermal simulation.

Heat capacity

This field allows to enter the specific heat capacity in [kJ / (K kg)]. This setting is relevant only for transient thermal simulations.

Nonlinear:

Shows up the Nonlinear Thermal Material Properties dialog. In this dialog, the dependencies of thermal conductivity as well as specific heat capacity on temperature can be defined. The default values of corresponding thermal properties must be non-zero, otherwise an error message will be shown.

Thermal diffusivity

The thermal diffusivity value is shown for information purpose only. It is calculated from the conductivity, the heat capacity and the density of a material.

a = k / (rho * cp * 1000)

With:

a: Diffusivity [m2 / s]

k: Thermal conductivity [W / K  /m]

rho: Density [kg / m3]

cp: Specific heat capacity [kJ / K / kg

Materials with high thermal diffusivity react rapidly to the temperature to of their surroundings, because they conduct heat quickly in comparison to their volumetric heat capacity. If materials with very high diffusivities are used for the transient thermal simulation, the computation time might rise, because the a high diffusivity value lowers the time step of the simulation scheme.

Bioheat properties

Bloodflow coefficient

The Bloodflow coefficient is a parameter of the bioheat equation. It determines the influence of blood at a certain temperature inside the tissue volume V. The reference temperature for the bloodflow (usually: 37 C) can be defined in the thermal solver specials dialog boxes of the stationary- and the transient solver.

Basal metabolic rate

The Basal metabolic is a parameter of the bioheat equation. It describes the amount of heat  which is produced by tissue per volume V.

Convection transfer coefficient

This parameter allows to consider convection processes on voxel models. Typically this parameter is used with a material describing skin. For coarse voxel models it is advisable to use fat in addition. Only voxel-surfaces which are between the voxel material and the background material are taken into account.

This picture shows which voxel-surfaces are used for the convection model. The red lines mark the surfaces on skin-voxels, while the blue line marks a surface on a fat-voxel.