Rob
Ansys Employee

Particles are inert if they don't react/disolve etc. If your bubbles remain as small bubbles (ie no collision) then they're inert. 

DPM particles/bubbles/droplets are injected with a speed and mass flow. Have a look at the options, and pick what makes sense. In your system have a look at a surface injection too. 

Steady tracking will result in a particle track, ie a line showing the flight path of the particle. Transient particles will trigger an injection every particle time step and then show spheres/points of where the particle is. With unsteady particles & steady flow the assumption is that the flow isn't altering with time but you want to see the particle positions. With that you also need to ensure you've run enough particle time steps for everything to settle down and/or reach the state you want to study.