how to model two particles of different sizes

Hi,

Am new to the Particle Tracing Module, so I have a few basic questions

I need to represent two particles of sizes 5 micron and 10 micron and study their velocity profile

Next, I have designed micro-pillar structures inside my micro channel to do particle sorting. My channel depth (z axis) is 30 micron, while my micro-pillar is 25 micron. Hence I expected only 5 micron particles can pass through. But the simulation using 10 micron particle, also shows their movement past these micro structures.

Please help me on how to simulate these particle - sorting mechanism

thanks for the help, in advance