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I'd not expect that to make much difference as sub 10micro (ish - very ish) particles tend to follow the carrier fluid fairly closely. Read up on relaxation time and settling velocity for more background. In the model with the larger size, how does the size distribution look? 

Where are you trying to apply the turbulent values? If they're boundary conditions then I'd favour Turbulent Intensity and Hydraulic Diameter for internal flows. Unlike the flow & thermal bc's the turbulent values need to be close to reality as the solver will rectify errors over the first few domain length scales (pipe diameter for internal flow) hence always allowing sufficient space upstream of the area of interest. You don't put the experimental probes right next to the pump so why constrain the CFD model?