Mathematical Treatment of massless particles, DPM
 

Hi CFD-online forums!!
First time poster, long time lurker, I have been reading this forum for years, but until now I decided to make an account.

After the short Hi... here's my issue.

I already read the whole theory guide regarding DPM, but I can't find how particles that you specify in the injection as "massless" are mathematically dealth with.
I can only assume that their tracking comes from the integration of the velocity field of the fluid in question. Could anybody explain a bit / point me in the right direction to understand this?

What I am trying to do is determine the residence time distribution of water in a pipe / arrange of pipes (I am doing this an an exercise for a more complex design, but I wanted to give it a shot with only pipes), but I can't completely understand what I am mathematically doing.

TL;DR: In the DPM model, how are massless particles mathematically dealth with?

Any help will be highly appreciated!!
Cheers!!!