Change the reflectivity of a material

[Emily.I]

Hi,

I want to change the reflectivity of a material? At the moment all I can change is the emissivity which isn't the same...

Any help?

Thank you,

Emily

[Joey.X]

Hi, Emily, 

In general, the interplay of energy exchange by thermal radiation is characterized by the following equation, and has relation as below,

Absorptivity + Reflectivity + Transmissibility=1                ----------------   (1)

For opaque surface (ASIM/MP thermal radiation has this assumption),   Transmissibility=0

so   Absorptivity + Reflectivity =1                              ----------------   (2) 

Using Kirchhoff's law states that in thermal equilibrium,

Emissivity = Absorptivity                                         ----------------   (3)  

Combing (2) and (3), gets

Emissivity  + Reflectivity =1                                

So here you can see the dependency between surface Emissivity and Reflectivity.  

Two extrame examples:

- Black body (  perfect black body, Emissivity=1,  Reflectivity=0)

- White body ( Snow is close white body,  Reflectivity=0.90  at visible light,  Emissivity is small)

Hope the this helps.

[Emily.I]

Well, what I really want to change is the albedo...

[Joey.X]

Albedo could be converted to Reflectivity depending on what kind of Albedo and what the material properties. 

Beware the cases of water, glass or snow on the surface, the transmissibility is not trivial, that violates the ASIM/MP's assumption of opaque surface.

[John_Holtz]

Hi Emily,

Perhaps you can explain what you want to do, and someone can suggest a way to do it. Other than mentioning emissivity, which implies radiation which implies heat transfer, we do not know anything about your simulation.

P.S. What's the difference between albedo and reflectivity? In my circle of friends (astronomy), albedo is the amount of reflected light. If you exaggerate light to mean all forms of radiation, then wouldn't albedo and reflectivity be the same?