Thank you very much Rob. So S2S is not applicable to our problem but MC seems an interesting option. What I am note sure is how the MC model in ANSYS Fluent deals with the absorption coefficient of the solids particles and their scattering in the eulerian phase (submodel used of the effective absorption and scattering of the solids phase in the Eulerian model). For example: Is the MC model doing an average of the solids absortivity (and the same for the scattering) weighted with their volumetric fraction? Where can I find such information?