Specify Wall Conditions

Double-click a Value cell to edit the cell contents or select the appropriate parameter type.

If you want to specify a coordinate-dependent or time-dependent value, click Dependency  in the corresponding Value box (see “Dependency”).

The following types of wall conditions are available depending on the analysis type and physical features specified on the Analysis Type tab:

• Default outer wall thermal condition (if the Internal analysis type is selected and the Conduction option is enabled on the Analysis Type tab).

  In case of Internal analysis with Conjugate Heat Transfer, you must specify a thermal condition applied by default to all the outer model walls. This condition allows you to define the heat exchange between the external flow and the outer model walls for internal analysis.

  The following thermal conditions can be set on the outer model walls:

  • Adiabatic wall. This is a heat-insulated wall.

  • Heat transfer coefficient. The heat flow (Q) through the outer walls is denoted by the user-defined Heat transfer coefficient (h), Temperature of external fluid (Tf), the calculated temperature of the outer wall (Tw) and the wall area (A): Q = h(Tf – Tw)A.

  • Heat transfer rate (total heat transfer rate). Positive values indicate heat flow from the solid to the outer media; negative values indicate heat flow from the outer media to the solid.

  • Heat flux (heat transfer rate per unit area). Positive values indicate heat flow from the solid to the outer media; negative values indicate heat flow from the outer media to the solid.

  • Wall temperature. Specifies the outer wall temperature.

  Click Dependency if you want to specify coordinate-dependent, time-dependent values or apply the results from another calculation as wall boundary conditions for the current project (see “Dependency” for details).

  You can redefine the default heat condition for a specific outer wall:

  • to specify the Heat generation rate or Surface heat generation rate conditions, use a Surface Source (see “Create a Surface Source”);

  • to specify the Heat transfer coefficient use an Outer Wall boundary condition (see “Create an Opening Condition”).

• Default wall thermal condition (if the Fluid Flow option is enabled and the Conduction option is disabled on the Analysis Type tab).

  If you do not intend to solve a Conjugate Heat Transfer problem, you must specify one of the following heat wall conditions applied by default to all of the model walls contacting with the fluid:

  • Adiabatic wall. This is a heat-insulated wall. By default all walls are skin friction surfaces.

    Tip

    If you want the wall to be adiabatic and frictionless, you must create an Ideal Wall boundary condition on the appropriate faces (see “Create an Opening Condition”).

  • Heat transfer rate (total heat transfer rate). Positive values indicate heat flow from the wall to the fluid; negative values indicate heat flow from the fluid to the wall.

  • Heat flux (heat transfer rate per unit area). Positive values indicate heat flow from the wall to the fluid; negative values indicate heat flow from the fluid to the wall.

  • Wall temperature.

  As applicable, simply type the value in the box which name corresponds to the selected condition.

  Click Dependency if you want to specify coordinate-dependent or time-dependent values (see “Dependency” for details).

  You can define a different heat condition for a specific wall:

  • to set Temperature and Heat transfer coefficient conditions, use a Real Wall boundary condition (see “Create an Opening Condition”).

  • to set Heat flux and Heat transfer rate use a Surface Source (see “Create a Surface Source”).

• Default wall radiative surface and Default outer wall radiative surface (if the Radiation option is enabled on the Analysis Type tab).

  If the surface-to-surface radiation is considered, you must specify the surface emissivity properties for all walls within the model.

  To apply surface emissivity properties, click  and select the desired radiative surface currently available in the Engineering Database.

  • The Default wall radiative surface denotes the surface emissivity properties applied by default to all walls within the model except for the outer model walls within an internal analysis.

    Note:

    In the standard version you can only specify the Default wall radiative surface of the following types: Wall to ambient (blackbody or with a custom-defined emissivity coefficient) or Non-radiating.

• Roughness (if the Fluid Flow option is enabled on the Analysis Type tab).

  You can specify the default wall Roughness value applied on all model walls.

  The roughness is defined by the shape of dents randomly distributed over a surface.

  Figure 1. The roughness definition.
  

  

  
  

  Numerically, the value of specified roughness is defined by the Rz parameter:

  	(1)

  You can set the roughness in micrometers, microinches or custom units.

  If there are particular walls in your model with different Roughness value, you can specify it later using the Real Wall boundary condition (see “Create an Opening Condition”).

• Slip conditions (if the Fluid Flow option is enabled on the Analysis Type tab and the Non-Newtonian liquids are selected as the project’s Default fluid type on the Fluids tab).

  In case of an analysis involving Non-Newtonian Liquids, you can specify slip conditions, which are applied to all model walls. Slip conditions can be specified separately for each of the non-Newtonian liquids in the project (see “Slip Conditions (Default Wall Conditions)” for details).

• In the Wizard dialog, click Next or click a link on the Navigator pane to switch to the corresponding tab of the Wizard.

• In the General Settings dialog, click Apply to update and proceed with settings.

  - or -

  Click OK to apply the changes and exit the dialog.