Learning Forum

[gopalakrishna.gangisetty]

I used Discrete Ordinates (DO) Model since it is the only model with 'semi-transparent' and 'non-gray' mode.

I want to give material A (semi-transparent) transmissivity or emissivity like this:

Thickness of the material is 0.005 m,

Absorption coefficients

Band 1 = 57.5

Band 2 = 57.5

Band 3 = 57.5

Band 4 = 1842

As I understood I cannot set internal emissivities (e) and transmissivities (t)directly to semitransparent material, may be diffuse fraction need to be set ?

 t=0.75 in 0 to 4 µm, or e = 0.25, Rho = 0

t= 0.75 in 4 ~8 µm, or e = 0.25, Rho = 0

t=0.75 in 8~14 µm, or e = 0.25, Rho = 0.

t = 0.0001 in 14 – 1000 µm, or e = 0.9999, Rho =0

But when I change BC type of  a material A from opaque to semi-transparent in boundary condition - radiation tab,
I made four bands, 0 – 4, 4 – 8, 8-14, 14-1000 µm in Model - Radiation - Number of Bands = 4

but I could only change Direct / Diffuse Irradiation and Diffuse Fraction of each band, not transmissivity or emissivity of each band.

Please, someone can guide me, it would be a great help,

Is it possible to give each band different emissivities or diffuse fraction?

Or my assumption would be : diffuse fraction should be 1 , since reflection is zero ?

 

[Essence]

Hello,

For semi-transparent walls, Fluent automatically calculates the reflectivity and transmissivity from the refractive index of the material. You can input refractive index of the material on a per-band basis (choose refractive-band method) in the Material Create/Edit dialog box. Consequently the reflectivity and transmissivity are band-dependent.

For opaque walls, you can input band-dependent emissivity on the "Radiation" tab of the wall boundary condition dialog box.

[gopalakrishna.gangisetty]

 

Hello Mr. Essence, 

Thank you very much for the response. I am using semi – transparent material and its emissivity is 0.25 for Long wave radiation, Refractive index is 2.2. I followed the instructions given by you. In the radiation tab, There is an option called beam direction where the default is X = 0, Y = 0 and Z = 1. I have an acceleration due to gravity set in Y direction = -9.81 m/s2. Then What is beam direction. Should it be X = 0, Y = 1 and Z =0 or X = 0, Y = -1 and z = 0 given the Y = acceleration due to gravity = 9.81 and this application for natural convection ?

Please kindly help me. 

 

[gopalakrishna.gangisetty]

Thank you very much for the response. I am using semi - transparent material and its emissivity is 0.25 for Long wave radiation, Refractive index is 2.2. I followed the instructions given by you. In the radiation tab, There is an option called beam direction where the default is X = 0, Y = 0 and Z = 1. I have an acceleration due to gravity set in Y direction = -9.81 m/s2. Then What is my direction. Should it be X = 0, Y = 1 and Z =0 or X = 0, Y = -1 and z = 0 given the Y = acceleration due to gravity = 9.81 and this application for natural convection ?

Please kindly help me. 

[Essence]

Can you share the screenshot(s) of the panel you are referring to?

[gopalakrishna.gangisetty]

Hello Sir, Thank you for the reply and please find the screenshots below : 

Given that the acceleration due to gravity is set in the Y-direction (g=−9.81 m/s2), indicating that gravity acts downwards, the positive Y-direction should be oriented upwards. Therefore, for natural convection modeling in this scenario, the direction of the beam for semi-transparent material should be $X=0$,$Y=1$, and Z=0 or X=0,Y= -1, and Z=0? 

[Essence]

 

Just a question. What is the range of temperature of your domain?

 

[gopalakrishna.gangisetty]

Hello Sir, 

At room temperature (298 K), the surrounding environment registers a temperature of 278 K. In our radiative heat transfer analysis, the objective is to dissipate heat from the building space to the surroundings, and subsequently to the cooler sky at 268 K. The skylight contains air and other greenhouse gases, and we aim to measure the transmitted radiative heat flux specifically within the wavelength range of 8 to 13 micrometers.

[Essence]

Thanks for the response. Please refer the Ansys guide link (section 5.3.6.7.5) for more information on beam direction and related topics.

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v241/en/flu_th/flu_th_sec_mod_disco.html?q=beam%20direction