Learning Forum

[a.arshad]

I am modeling the radiation heat transfer by selecting the DO model for PCM filled double glazzing window. Please see the picture below. I am not sure about the values for Free stream temperature and external radiation temperature, as the initial temperature is 288.7K. Do I need a UDF for both? If, yes, please share the UDF if someone has already done this or knows how to write the UDF and import it into FLUENT. Also, do what will be the values for theta and Phi for Beam Width? Angle between window and ground is 90 degree. 

Thanks. 

 

[SRP]

Hi

The free stream temperature typically refers to the temperature of the fluid outside the window, which in your case might be the ambient air temperature. You can set this temperature based on the environmental conditions of your simulation. If you're uncertain, you can choose a value close to the ambient temperature where the window is placed.

The external radiation temperature is the temperature of the surroundings external to your system that emit radiation. Again, this can be approximated based on the environmental conditions. It's often close to the free stream temperature but can be different if there are other heat sources nearby

If you need to use a UDF for setting these temperatures, you can write a define_profile  to specify the temperature distribution at the boundary. However, as mentioned earlier, this might not be necessary for setting free stream and external radiation temperatures.

By default, the number of Theta Divisions and the number of Phi Divisions are both set to 2. For most practical problems, these settings are acceptable, however, a setting of 2 is considered to be a coarse estimate

For more details, Please refer to fluent user's guide: 14.3.5. Setting Up the DO Model (ansys.com)

Thank you.

[a.arshad]

Hi, 

Thank you for replying. The angle between window is 90 deg. So, I put the theta = 90 and phi = 0 in Beam width. Did I put the correct values? Also, I clicked the "Apply Direct Irradiation Parallel to the Beam". So does it depend on the beam width values? 

In below Ansys guide, It is mentioned "The default beam width in ANSYS FLUENT is  degrees which is suitable for collimated beam radiation". I could not understand the logic of 1e-6.

https://www.afs.enea.it/project/neptunius/docs/fluent/html/th/node115.htm

In below picture, It is showing both theta and phi are divided by 2. So if I gave 90 then should I give 90/2=45? Please guide 

 

Thank you.