Mass flow rate (URGENT)

Good morning,

I’m hoping for a response to this question as well.
I have LIGGGHTS vtk dataset, struggling with the workflow on how to measure particle flow rate through a surface or volume.
Visualisation of particles works fine, Can see velocity, animate the simulation. Managed to get temporal particle streaming to work.
Visualisation of stress and wear on meshes is all good.
I have experimented with slices, surface flow and integration but struggle to get results.