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Old   December 6, 2007, 14:12
Default Need Help for DIFFUSE FRACTION values
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I have to find values for the "Diffuse Fraction" that are needed in my CFX-Radiation simulation. Diffuse fraction is defined as: ratio of the diffuse reflectivity to the sum of the diffuse and specular reflectivity.

DF = rho_d / (rho_s + rho_d) <= 1.0

with rho_s + rho_d = 1

The materials are: - polished steel - plexiglas - ZnSe - 3M black velvet paint (blackbody)

I made an estimation considering the surface roughness and the emitted radiation wavelength @ 380 K. When the roughness is much smaller than the wavelength, specular reflection is dominant, otherwise diffuse reflection.

BUT what is the order of magnitude???

My assumptions are:

DF_steel = 0.1 --> rho_s / rho_d = 9

DF_plexi = 0.05 --> rho_s / rho_d = 19

DF_ZnSe = 0.05

DF_blackpaint = 1 --> rho_d = 1, rho_s = 0

Are these values somehow plausible?

What are the values you use for your radiation simulation???

A keyword for this could be "Bidirectional Reflectance Distribution Function" (BRDF)

Can someone help please?!

Thanks in advance!


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Old   August 16, 2009, 12:59
Default answer for seting up of reflectivity
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diffuse reflectivity = diffuse fraction(1-internal emissivity)
specular reflectivity = 1- diffuse fraction
absorptivity= diffuse fraction* internal emissivity
zhang.limin is offline   Reply With Quote


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