General questions about particle tracing for fluid flow

Hi all,

I am grateful for your help if you can answer to my questions.

I read in the particle tracing doc that the system should be a dilute or dispersed flow and this means that I should calculate the liquid volume fraction from my results section from my fluid flow model? Is it right?

Q1: what does it mean "the volume fraction of the discrete phase should be much smaller than the volume of continuous phase, generally less than 1%"?

Q2: If I choose formulation: Massless, then there is section "Wall accuracy order: 1 and 2" what is this? I checked the manuals but there was no description.

Q3: In particle properties, what is Charge number Z? what is the affect of this parameter and I read that by default value for Z=-1, but it is 0.

Q4: What is the difference between the "wall" boundary condition and "outlet" boundary condition in massless formulation when wall condition for both of them is Freeze?

Q5: what is the format of txt file for the "Release from Data file" for the initial position? and what is the Index of first column containing position data? Can you provide an example of this section, please?

Q6:What is the function of particle trajectories study in Study step section? When will a user apply this type of study?