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32.3.5 Define/Models/Radiation...

The Define/Models/Radiation... menu item opens the Radiation Model panel.



Radiation Model Panel


The Radiation Model panel allows you to select a model for radiation heat transfer and set the associated parameters. See Sections  13.3.10- 13.3.13 for details about the items below.

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Controls

Model   indicates which model, if any, is used to calculate radiation heat transfer. See Section  13.3 for details about modeling radiation heat transfer.

Off   disables the calculation of radiation heat transfer.

Rosseland   enables the Rosseland radiation model.

P1   enables the P-1 radiation model.

Discrete Transfer (DTRM)   enables the discrete transfer radiation model (DTRM).

Surface to Surface (S2S)   enables the surface-to-surface (S2S) radiation model.

Discrete Ordinates (DO)   enables the discrete ordinates (DO) radiation model.

Iteration Parameters   contains parameters related to the DTRM, S2S and the DO models. This portion of the panel will appear only if Discrete Transfer (DTRM), Surface to Surface (S2S), or Discrete Ordinates (DO) is selected as the Model.

Flow Iterations per Radiation Iteration   controls the frequency with which the radiation terms are updated as the continuous phase solution proceeds. The Flow Iterations Per Radiation Iteration parameter is set to 10 by default. This implies that the radiation calculation is performed once every 10 iterations of the solution process. Increasing the number can speed the calculation process, but may slow overall convergence.

Number of DTRM Sweeps   controls the maximum number of sweeps of the radiation calculation during each global iteration. The default setting of 1 sweep implies that the radiant intensity will be updated just once. If you increase this number, the radiant intensity at the surfaces will be updated multiple times, until the tolerance criterion is met or the number of radiation sweeps is exceeded.

This item appears only when Discrete Transfer is selected as the Model.

Number of S2S Sweeps   controls the maximum number of sweeps of the radiation calculation during each global iteration. The default setting of 5 sweeps implies that the radiosity will be updated multiple times, until the tolerance criterion is met or the number of radiation sweeps is exceeded.

This item appears only when Surface to Surface is selected as the Model.

Tolerance   determines when the radiation intensity update is converged. It is defined as the maximum normalized change in the surface intensity from one DTRM sweep to the next (see Equation  13.3-91).

This item appears only when Discrete Transfer or Surface to Surface is selected as the Model.

View Factors   contains parameters related to the S2S model. This portion of the panel will appear only if Surface to Surface is selected as the Model. See Section  13.3.12 for more information about the use of these parameters.

Methods   contains controls for computing view factors or reading in previously-computed view factors.

Compute/Write...   opens the Select File dialog box, in which you can specify a name for the file where FLUENT should save the view factors after computing them.

Read...   opens the Select File dialog box, in which you can specify the file from which FLUENT should read view factors.

Parameters   contains controls for setting view factor parameters.

Set...   opens the View Factor and Cluster Parameters panel, in which you can set parameters related to surface clusters and view factors.

Partial Enclosure   allows you to specify the Temperature of the partial enclosure for the S2S model.

Angular Discretization   contains parameters for angular discretization and pixelation for the DO model. This portion of the panel will appear only if Discrete Ordinates is selected as the Model. See Section  13.3.13 for more information about the use of these parameters.

Theta Divisions, Phi Divisions   define the number of control angles used to discretize each octant of the angular space (see Figure  13.3.3).

Theta Pixels, Phi Pixels   are used to control the pixelation that accounts for any control volume overhang (see Figure  13.3.7 and the figures and discussion preceding it).

Non-Gray Model   contains parameters related to the non-gray DO model. This portion of the panel will appear only if Discrete Ordinates is selected as the Model. See Section  13.3.13 for more information about the use of these parameters.

Number of Bands   specifies the number of bands for the non-gray radiation.

Wavelength Intervals (n=1)   contains inputs that define each wavelength band. (It appears only when the Number of Bands is non-zero.) For each band, you can specify a Name, as well as the Start and End wavelength of the band in $\mu$m. Note that the wavelength bands are specified for vacuum ( $n=1$). FLUENT will automatically account for the refractive index in setting band limits for media with $n$ different from unity.

Solar Load   contains parameters related to solar load model that can be used to calculate radiation effects from the sun's rays that enter a computational domain. It is available only for 3D version of FLUENT. See Section  13.3.18 for more information about the use of these parameters.

Model   indicates which model is used to calculate radiation effects.
Off   disables the calculation of solar radiations.

Solar Ray Tracing   enables the solar ray tracing algorithm

DO Irradiation   enables the DO irradiation option. Select Discrete Ordinates under Model before selecting this option.

Sun Direction Vector   contains the components of sun direction vector.
X, Y, Z   are the components of the sun direction vector.

Use Direction Computed from Solar Calculator   enables the use of direction vector computed from the solar calculator.

Illumination Parameters   contains illumination options.
Direct Solar Irradiation   is the amount of energy per unit area due to direct solar irradiation.

Diffuse Solar Irradiation   is the amount of energy per unit area due to diffuse solar irradiation.

Spectral Fraction   is the fraction of incident solar radiation in the visible part of the solar radiation spectrum. The spectral fraction is not used for DO irradiation since the DO implementation is intended only for a single band. This parameter is available only for Solar Ray Tracing.

Update Parameters   contains update parameters for transient simulations.
Time Steps per Solar Load Update   specifies the number of time steps that will direct the FLUENT solver to update the solar load data for the specified flow-time intervals in the unsteady solution process .



Solar Calculator Panel


The Solar Calculator panel allows you to set parameters related to the calculation of solar load models. See Section  13.3.18 for details. This panel opens when you click on the Solar Calculator... button in the Radiation Model panel.

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Controls

Global Position   contains the parameters to define the position of solar radiation.

Longitude   specifies the longitude of the desired location in degrees. Values may range from $-180$ to $180$, where negative values indicate the Western hemisphere and positive values indicate the Eastern hemisphere.

Latitude   specifies the latitude of the desired location in degrees. Values may range from $-90$ (South pole) to $90$ (North pole) with $0$ defined as the equator.

Timezone   specifies the local time zone of the desired location in hours relative to Greenwich Mean Time (+-GMT). This integer value can range from $12$ to $-12$.

Starting Date and Time   contains parameters to specify date and time.
Day of Year   contains parameters to specify day and month.

Time of Day   contains parameters to specify hour and minutes.

Grid Orientation   specifies the orientation as the vectors for North and East in the CFD grid system of coordinates.

Solar Irradiation Method   contains parameters to choose the solar irradiation method.
Theoretical Maximum   enables theoretically maximum solar irradiation method.

Fair Weather Conditions   enables fair weather condition solar irradiation method.

Sunshine Factor   is a linear reduction factor for the computed incident load that allows for cloud cover to be accounted for, if appropriate.


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