Forum Moderator
If you have a multiphase system the second phase (carbon) cannot diffuse within the carrier fluid. If the carbon is modelled as a species then it's a molecular mixture so there is no diameter.nLooking at the effect of temperature. In reality that will cause buoyancy driven flow in the carrier fluid. If you've not switched to a temperature dependent density and don't have a temperature gradient nothing will happen.nHave a very careful read through the Fluent manual covering species (non reacting flow) and multiphase modelling. The courses listed at the very top of the page may also be of use. Then you'll understand what is being assumed in the models to repose the question and simulation settings.n