|December 6, 2007, 14:12||
Need Help for DIFFUSE FRACTION values
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!
|August 16, 2009, 12:59||
answer for seting up of reflectivity
Join Date: May 2009
Posts: 21Rep Power: 8
diffuse reflectivity = diffuse fraction(1-internal emissivity)
specular reflectivity = 1- diffuse fraction
absorptivity= diffuse fraction* internal emissivity
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