Generate an appropriate mesh for your internal radiation simulation, being sure to address the following considerations:

Launch Ansys Polydata and create a task for the mesh created in the previous step.

Define a nonisothermal sub-task to model the flow and/or heat conduction in your problem.

Create a separate sub-task to calculate internal radiation, by clicking Create a sub-task in the task menu.

  Create a sub-task

The Create a sub-task menu will open.

1. Click Internal radiation for the sub-task type.

     Internal radiation

2. When prompted, enter a name for the sub-task and click OK. The internal radiation sub-task menu will open.

Define the domain where the internal radiation sub-task applies (that is, the domain for Equation 13–12), by clicking Domain of the sub-task in the sub-task menu.

  Domain of the sub-task

The Domain of the sub-task menu will open.

1. Select subdomains from the upper list and click Remove until it displays a group of subdomains that all share a common set of internal radiation parameters.

2. Click Upper level menu to return to the internal radiation sub-task menu.

Specify the material data parameters for the internal radiation sub-task, by clicking Material data in the sub-task menu.

  Material data

The Material Data menu will open.

1. Click Data for Internal Radiation Model to open the menus that allow you to define the units and parameters.

     Data for Internal Radiation Model

2. A panel will open to warn you if no system of units is known. Click OK to open the Current System of Units menu, where you can use the menu items and related panels to define the unit system for simulation. Your inputs allow Ansys Polydata to automatically convert the Stefan-Boltzmann constant into the appropriate units.

   After you have completed your inputs, click Upper level menu to open the Material data for internal radiation menu.

3. Define the parameters for angular discretization and the properties of the medium (see Equation 13–12, Equation 13–13, and Equation 13–15), by performing the following steps in the Material data for internal radiation menu:

   1. Define the number of discrete radiative directions (that is, , the number of solid or planar angles into which the domain is discretized). The model will be more accurate if you specify higher values, but the calculation will be more expensive in terms of memory and CPU.

        Modify Nd

      Enter an even integer for New value in the panel that opens. For 2D simulations, you must enter an even integer between 4–30. For 3D simulations, enter one of the following integers: 6, 8, 12, 14, 20, or 30. Then click OK.

   2. Define the absorption coefficient of the medium.

        Modify a

      Enter a New value in the panel that opens and click OK.

   3. Define the refractive index of the medium.

        Modify n

      Enter a New value in the panel that opens and click OK.

   4. Define the scattering coefficient ().

        Modify sigma_s

      Enter a New value in the panel that opens and click OK.

   5. If you do not want to use an absolute system for temperature, define the value for absolute zero in the current system for temperature.

        Modify T0

      Enter a New value in the panel that opens; for example, if you want to use the Celsius temperature scale instead of Kelvin, enter -273.15. Then click OK.

   6. Define the forward-scattering factor for the Delta-Eddington phase function.

        Modify f

      Enter a New value in the panel that opens and click OK.

   7. Define the asymmetry factor for the Delta-Eddington phase function.

        Modify C

      Enter a New value in the panel that opens and click OK.

4. Click Upper menu level repeatedly to return to the internal radiation sub-task menu.

Define the radiation boundary conditions on the boundary sets (or along intersections of subdomains) that form the boundary of the domain of the internal radiation sub-task, by clicking Radiation boundary conditions in the sub-task menu.

  Radiation boundary conditions

The Radiation boundary conditions menu will open and allow you to perform the following steps:

1. Select a boundary from the list for which you want to modify the default radiation boundary condition.

2. Click Modify to open the Radiation boundary condition along boundary <ID> menu.

   1. Select the boundary condition type you want to impose from the following options:

      • To guarantee continuity of the irradiance field across the boundary, click Interface.

          Interface

        Note that this option is only available for boundaries that border the domain of another sub-task. You must make sure that the sub-tasks on either side of the boundary define it as an Interface and have the same number of radiative directions (defined using the Modify Nd menu item in step 6.(c)i.).

      • To specify that the boundary behaves like an insulated wall (which is equivalent to a radiative symmetry condition), click Insulated boundary / symmetry. This is the default selection for the axis of symmetry in axisymmetric tasks, and corresponds to a Diffuse gray wall condition where the values for emissivity and transmittance are set to 0, such that all incident radiative energy is diffusely reflected.

          Insulated boundary / symmetry

      • To specify a condition where a fraction of incident radiative energy is absorbed by the boundary and converted to heat, another fraction is lost through the boundary, and the rest is reflected, click Diffuse gray wall. This is the default selection, except as noted in the previous description.

          Diffuse gray wall

        The Diffuse gray wall along boundary <ID> menu will open. Click Modify emissivity.

          Modify emissivity

        A panel will open in which you can revise the New value, which defines the local value of the emissivity. The emissivity represents the fraction of radiative energy that is absorbed by the boundary. A value of 0 means that the incident energy that has not passed through the boundary due to the transmittance (as described in the description that follows) is entirely reflected in all directions, whereas a value of 1 means that it is all converted into heat. Click OK to return to the Diffuse gray wall along boundary <ID> menu.

        Click Modify transmittance.

          Modify transmittance

        A panel will open in which you can revise the New value, which defines the local value of the transmittance. The transmittance represents the fraction of incident radiative energy that passes through the boundary and escapes from the domain of the internal radiation sub-task. Note that no radiative energy coming from outside the domain can enter through the diffuse gray wall boundary. A value of 1 for transmittance means that all of the incident energy is lost from the domain through transmittance, whereas a value of 0 means that it is all eligible for reflection and absorption. Click OK to return to the Diffuse gray wall along boundary <ID> menu.

   2. Click Upper level menu to return to the Radiation boundary conditions menu.

3. Repeat steps 7.(a)–7.(b)ii. for each additional boundary you want to modify.

4. Click Upper level menu repeatedly to return to the task menu.

Repeat steps 4.–7.(d) to create any additional internal radiation sub-tasks with unique sets of material data parameters.

If you want to set conditions on internal boundaries within the domain of an internal radiation sub-task, perform the steps that follow. Internal boundaries allow you to specify that a fraction of the incident radiative energy is absorbed by the boundary and converted to heat, another fraction passes through the boundary, and the rest is reflected.

1. Click Define sub-models in the task menu to open the Define sub-models menu.

     Define sub-models

2. Click Create a new sub-model to open the Create a sub-model menu.

     Create a new sub-model

3. Click Diffuse gray wall imposed.

     Diffuse gray wall imposed

   Specify a name for the sub-model by revising New value in the panel that opens, and click OK. The sub-model menu will open.

4. Specify the PMeshes (created in step 1.) that define the domain of the sub-model by clicking Domain of the sub-model.

     Domain of the sub-model

   The Domain of the sub-model menu will open.

   1. Select PMeshes from the lower list and click Add until the upper list displays all of the internal boundaries that share a common set of diffuse gray wall parameters.

   2. Click Upper level menu to return to the sub-model menu.

5. Specify the parameters of the sub-model by clicking Diffuse gray wall parameters.

     Diffuse gray wall parameters

   The Diffuse gray wall parameters menu will open.

   1. Click Modify emissivity (along darts direction).

        Modify emissivity (along darts direction)

      A panel will open in which you can revise the New value, which defines value of the emissivity applied to the faces of the internal boundary that have a positive normal (as indicated by the direction darts in the Graphics Display window). The emissivity represents the fraction of radiative energy that is absorbed by the boundary. A value of 0 means that the incident energy that has not passed through the boundary due to the transmittance (as described in the description that follows) is entirely reflected in all directions, whereas a value of 1 means that it is all converted into heat. Click OK to return to the Diffuse gray wall parameters menu.

   2. Click Modify emissivity (opposite to darts direction).

        Modify emissivity (opposite to darts direction)

      A panel will open in which you can revise the New value, which sets the value of the emissivity (as defined in the previous description) applied to the faces of the internal boundary that oppose the positive normal. The opposing faces are those that do not display direction darts in the Graphics Display window. Click OK to return to the Diffuse gray wall parameters menu.

   3. Click Modify refractive index (along darts direction).

        Modify refractive index (along darts direction)

      A panel will open in which you can revise the New value, which defines value of the refractive index applied to the faces of the internal boundary that have a positive normal (as indicated by the direction darts in the Graphics Display window). The refractive index represents the ratio of the velocity of radiation in a vacuum to the velocity of radiation in the medium adjacent to these faces of the boundary. A higher value increases the amount of radiation that is emitted by the boundary due to absorption. Click OK to return to the Diffuse gray wall parameters menu.

   4. Click Modify refractive index (opposite to darts dir).

        Modify refractive index (opposite to darts dir)

      A panel will open in which you can revise the New value, which sets the value of the refractive index (as defined in the previous description) applied to the faces of the internal boundary that oppose the positive normal. The opposing faces are those that do not display direction darts in the Graphics Display window. Click OK to return to the Diffuse gray wall parameters menu.

   5. Click Modify transmittance.

        Modify transmittance

      A panel will open in which you can revise the New value, which defines the local value of the transmittance. The transmittance represents the fraction of incident radiative energy that passes through the internal boundary to the other side. A value of 1 for transmittance means that all of the incident energy passes through, whereas a value of 0 means that all the incident energy is eligible for reflection and absorption. Click OK to return to the Diffuse gray wall parameters menu.

6. Click Upper level menu repeatedly to return to the Define sub-models menu.

7. Repeat steps 9.(b)–9.(e)iii. to create any additional sub-models with unique sets of diffuse gray wall parameters.

Click Upper level menu repeatedly to return to the task menu, and continue defining the task as necessary.