Enable Radiation

If you want to enable surface-to-surface radiation in conjugate heat transfer analysis, you can enable the Radiation option.

Procedure

In the Wizard or General Settings on the Analysis Type tab, select the Radiation check box.
Select an appropriate Radiation model:
- Discrete Transfer. This model is recommended for cases with high-temperature gradients or with compact radiation sources (i.e. with high power heat sources such as incandescent lamps, furnaces or other heat sources of temperatures greater then 1000 K) and geometric-optical effects of the shadows, focusing and etc.
- Discrete Ordinates. This method allows the solution of radiation in absorptive (semi-transparent) media and to model spectral dependencies. The accuracy of the solution depends on the number of discrete directions used. This model is recommended for most cases with low-temperature variations or without compact radiation sources (for example, for electronics cooling, the greenhouse effect, and cabin comfort analysis).
Also, in the Calculation Control Options dialog, you can specify the radiation model parameters on which the calculation time and accuracy depends (see “Radiation Settings” for details).
Select an appropriate type of radiation:
- Specify the Environment temperature to enable the environment radiation from the ambient space. You can specify the Environment temperature for both external and internal analyses. It denotes that the computational domain’s far-field boundaries radiates heat (Q) into the computational domain according to the following formula: Q = ε·σ·T 4, where ε is the emissivity coefficient (ε = 1 for blackbody), σ is the Stefan-Boltzmann constant and T is the specified Environment temperature.
- Select the Solar radiation check box to enable directional radiation from the ambient space (see “Solar Radiation” for details).
Select the Absorption in solids check box if you want to consider absorption of radiation in solid bodies in your project.
Restriction:
This option is available for the Discrete Ordinates model only.

Tip
You do not need to select this option if you want to consider solids fully transparent to any type of radiation (thermal, solar or both).

The Absorption coefficient is specified in the solid material definition in the Engineering Database as a constant or depending on wavelength (see “Transparency and Absorption in Solids” for details).
Select the Spectral characteristics check box to consider the radiation spectrum in your project.
Restriction:
This option is available for the Discrete Ordinates model only.

To define the radiation spectrum, specify the following Spectral characteristics:
- Number of bands.
  
  If Discrete Ordinates model is selected, specify the number of spectrum bands.
  
  You can specify at least 2 and up to 10 spectrum bands.
  
  Tip
  In case of the Discrete Ordinates model, the calculation time, CPU time and memory resources depends linearly on Number of bands. So it is recommended to use the values less than 5.
- Band edge.
  
  If Discrete Ordinates model is selected, specify the wavelength values defining the boundaries between bands.
  
  For example, if you define a two-bands spectrum, you have to specify the edge between two bands; if you define three bands, you have to specify two edges: between the first and second band, and between the second and third band.
- Environment radiation. Select the spectrum of the ambient environment Radiation Source from the list of pre-defined and user-defined spectrum definitions available in the Engineering Database.