Hi Rob, 
Many thanks for the response. 
Can I ask if you can explain on your response a bit more please, I still dont have the clarity on the parcel and particle concepts, and especially with fractional number of particles.  
Also, can you please explain,
  1. If the particles are tracked, how are the equations solved for number of particles which is less than unity?
  2. You mentioned the terms were mis-used from the early days of Fluent's DPM model. Does this inconsistent in terminology still continue? 

Thanks in advance.