Hello Rob,

My apologies as this is an "old" thread now. I am still quite confused. Perhaps I should add more information. The units of C is mg/L, so while defining the boundary condition for C, I used the value of "specified value" that is in mg/L. So if that's the case, when fluent multiplies the fluid density, the dimension of the unsteady term, for example, will be kgmg/Lsm3. The convective term I suppose will follow, and so in this case I should supply the value of diffusivity in kg/ms right?