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Is it possible to give each band different emissivity in Fluent Radiation?

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Old   January 30, 2020, 20:40
Default Is it possible to give each band different emissivity in Fluent Radiation?
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Hi, I'm trying to model radiation with box (1 bottom + 4 side is aluminum, upper case is material A)'

Geometry is simple : Cube with 6 side (1 bottom / 4 side / 1 top)





1. When you use radiation model - Discrete radiation and Solar Ray Tracing in Solar Load, you can change spectral fraction (V/V+IR)

What is difference between visible and infrared in Fluent radiation?

I know that visible is nearly 300nm~700nm and infrared is 700nm~, but does ANSYS Fluent separate visible and infrared region with wavelength range as I mentioned above? Or do they just separate them by energy percetage regardless of wavelength?

ex) Direct Solar Irradiation = 1000W/m^2

Spectral Fraction = 0.5

-> Visible 50% (=500W/m^2) + Infrared 50% (=500W/m^2)



2. How can I give different transmissivity with more than 3 wavelength region?

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 like this:

ex) t=0.9 in 300~700nm

t= 0.1 in 700~8000nm (0.7 ~ 8 micro-meter)

t=0.9 in 8000nm~13000nm (8 ~ 13 micro-meter)

(t is transmissivity)



But when I change BC type of upper case (material A) from opaque to semi-transparent in boundary condition - radiation tab, there is only transmissivity (and absorptivity on left side) of Direct Visible and Direct IR.

I made three band (300~700 / 700~8000 / 8000~13000) in Model - Radiation - Number of Bands, but I could only change Direct / Diffuse Irradiation and Diffuse Fraction of each band, not transmissivity or emissivity of each band.



Is it possible to give each band different emissivity?



I'll be glad if someone could give me some advice.
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Old   January 31, 2020, 05:13
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Fluent expects three values, one for IR, one for visible and other for shading. So, you have 0.9 for first value, 0.1 for second, and 0.9 for rest.
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Old   September 22, 2021, 02:27
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Quote:
Originally Posted by jswony11 View Post
Hi, I'm trying to model radiation with box (1 bottom + 4 side is aluminum, upper case is material A)'

I made three band (300~700 / 700~8000 / 8000~13000) in Model - Radiation - Number of Bands, but I could only change Direct / Diffuse Irradiation and Diffuse Fraction of each band, not transmissivity or emissivity of each band.



Is it possible to give each band different emissivity?



I'll be glad if someone could give me some advice.
It can be done by set just in material mixture, or air of you don't use species.
Dear swony11 send me polinomial or other expression for scattering and rest term for the bands1-3 0.3-0.7microm 0.7-8 and 8-13 as you wrote early. It's very need to me.
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Old   July 25, 2023, 06:03
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hello, I think you first need to choose the 3 bands in the radiation section (DO method), then you choose gray-band for the absorption coefficient in the materials section and finally semi-transparent in the boundary conditions for each wall. You will find the variation in absorption and transmission for each band (below in the boundary conditions in the radiation section). I hope this solves your problem
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