Absorptivity, emissivity and reflectivity of a surface
 

Hello All..

i am trying to simulate a reflector and an absorber using CFX, for the radiation i am using monte carlo model....
the setup is like this.....
the geometry is trapezoidal with top wider and bottom narrower. the top, bottom and the sides each form a seperate domain and the interior is fluid domain with properties of air.
the sides are aluminium and reflective but i want to give them absorptivity =of 0.05 reflectivity =0.95 and emissivity= 0.08
the bottom is silicon having absorptivity= 0.8 nad emissivity =0.35..

but the solid fluid domain interface only allows you to specify diffuse fraction and emissivity.....
the source radiation enters from the top and should get reflected by the reflectors and fall on silicon which will get heated up...

so my question is how can i simulate a reflective and absorptive surface