Defining Radiation In ANSYS® Thermal Analyses

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Radiation is one of the most important elements of heat transfer and thermal problems in engineering. When you are doing thermal analyses in ANSYS®, you can define the required radiation as a boundary condition to surfaces or bodies.

Here, we explain how to define radiation in ANSYS® thermal analyses and how to make required adjustments correctly.

How To Define Radiation In ANSYS® Mechanical? 

Select the ‘Radiation’ option.

To define radiation in ANSYS® thermal analyses, right-click on thermal analysis as shown in the screenshot above. Hover your mouse on ‘Insert’ then click on ‘Radiation’. 

Select the geometric features for radiation.

After that, select the geometric features that you want to define radiation on them. Then click on the ‘Apply’ button to complete the selection. 

Select the radiation type.

There are two options available to apply radiation; To Ambient and Surface to Surface.

  • To Ambient option; If this option is selected, the radiation exchange is taking place between ambient temperature and the selected geometric feature. You need to define ‘Emissivity’ and ‘Ambient Temperature’. 
  • Surface to Surface option; In this case, the radiation exchange is between the defined surfaces in the thermal analysis. You need to define ‘Enclosure’, ‘Emissivity’, and ‘Ambient Temperature’. 

What Is Emissivity And How To Define It In ANSYS®?


Emissivity is the rate of radiation of the selected surface or body compared with the black body at the same temperature. It takes a value between 0 and 1.

Defining emissivity as tabular.

You can define emissivity as tabular data in which you can enter the values for changing temperature shown above. Click on the little pop-up menu and select ‘Tabular(Temperature)’.

Enter the required values in the table.

Define from the ‘Tabular Data’ as shown above. Define temperatures and corresponding emissivities for each temperature from tabular data.

Defining emissivity as a time function.

Also, you can define emissivity as a time function. What you need to do is, select the ‘Function’ option as shown above. Then enter the function in which the variable is ‘time’ as shown above again. You can change the ‘Number Of Segments’ that divides the time interval in entered value.

Definition Of Ambient Temperature

We defined the importance of ambient temperature for radiation definition in ANSYS®. All the definition options valid for emissivity are also valid for ambient temperature definition. 


Enter the enclosure number same with the radiating surfaces in the analysis. You can select the ‘Enclosure Type’ as ‘Open’ or ‘Perfect’. For the ‘Perfect’ option, radiation takes place only between selected faces. And the ambient temperature is not important. For the ‘Open’ option, ambient effects are included for radiation. 


The definition of radiation is very simple as you understand in ANSYS® mechanical thermal analysis. 

Do not forget to leave your comments and questions below about the definition of radiation in ANSYS® Mechanical.

NOTE: All the screenshots and images are used for educational and informative purposes. Images used courtesy of ANSYS, Inc.

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