Learning Forum

[vidyadhar.kpm]

Hello,

I am simulating heat transfer from an array of fins. I am considering conduction in the fins, natural convection in the surrounding fluid and radiation exchange among fins. I am using S2S radiation model in ANSYS Fluent to model radiation exchange among the fins.

I have this doubt :

How the calculated radiosity values will be applied? Are they applied as source terms in the energy equation of fluid? Or are they applied in an energy balance condition at the fin-fluid interface as a boundary condition. 

I request anyone to clarify on this.

Thanking you,

vidyadhar

[Nikhil N]

Hello, 

Have a look at this section of the theory guide: 5.3.7. Surface-to-Surface (S2S) Radiation Model Theory (ansys.com)

If you are not able to access the link, please refer to this forum discussion: Ansys Learning Forum

 

Nikhil

[vidyadhar.kpm]

Hello Nikhil,

Thank you for the reply. I have already read the section.

In that section, it is mentioned that Radiosity values are calculated at all the mesh faces/clusters. Then they are used to calculate wall temperatures.

1. It is mentioned that radiation source terms are highly non-linear. What are these source terms? Do they mean radiosity values?

2. It is also mentioned about distribution of flux and source terms appropriately. What is the description of flux and source term here?

3. There is a source term Sh in the heat tranfer energy equation 5.2-1. In that section 5.2, it is mentioned that when one of the radiation models are used, Sh includes radiation source terms. Please clarify, if S2S model is used, what is Sh and how it is computed.

4. Will Sh be used in Energy equation 5.2-1 when S2S model is used? Or the computed radiosity values are used as a boundary condition at the surfaces to determine temperatures?

I request you to kindly let me know about these.

Thanks in advance!

Vidyadhar

[vidyadhar.kpm]

Hello Nikhil,

May I reframe my question to make it simple:

How the radiation values (calculated using radiosity matrix equation) are coupled to the fluid's energy equation? Is it through a source term or through a boundary condition at the surface.

Request anyone to kindly clarify this.

[SVV]

Hi,

The radiosity matrix is coupled with the temperature of the cell as shown in the document shared by Nikhil. This value of radiation flux is then considered as the heat input to the system along with the other sources of heat.

[vidyadhar.kpm]

Hello swathi,

1. I request you to kindly elaborate how the calculated radiation flux values are given as heat input to the system? Is it through a boundary condition at the participating wall (convection heat flux = conduction heat flux + Net radiation heat flux).

2. Or is it also through any volumetric heat source? I guess while using S2S model, the heat input to the system (radiosity values) is not done through any volumetric source terms. 

3. I have this confusion. In all other radiation models, where there is a participating fluid, then there is a meaning of volumetric heat source due to radiation. ( This is true even when there are heat sources in fluid or solid domain.) But when S2S model is used, I dont think there is any contribution from the radiosity values on the volumetric heat sorce due to radiation? Please correct me if I am not understanding S2S model in this regard.

Regards,

Vidyadhar

[vidyadhar.kpm]

Hello Swathi,

Thanks for the reply. 

I understand that from the radiosity matrix equation: KJ=E, radiosity values are dependent on temperature of the participating surfaces. The Radiosity values are calculated from this equation.

After that, how these values are used to modify the temperature of the participating surfaces?

[Rob]

The radiation source is added into the energy equation,  https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v221/en/flu_th/flu_th_sec_hxfer_theory.html

[vidyadhar.kpm]

Hello Rob,

Thanks for the reply.

In the energy equation, we can add volumetric source terms (W/m^3). In S2S radiation model, I have not mentioned any source term value. 

If the model itself estimates the source term and adds in the energy equation, then will it add in the energy equation of fluid or solid?

If it is added as a source term, can you please describe how it is calculated per unit volume? And is it added in the neighbouring one layer of cells next to the boundaries participating in radiation exchange or where is it added?

I request you to kindly clarify these doubts.

Thanks and Regards,

Vidyadhar

[Rob]

I can only refer you to the documentation, I'm not permitted to expand on that. However, given the model refers to cluster temperatures I suspect it's a surface addition.