What's a good way to have particles move around slowly in a constrained space (using newtonian physics)? I've tried to do …

What’s a good way to have particles move around slowly in a constrained space (using newtonian physics)? I’ve tried to do this various ways, say to simulate dust moving around a room in a dream like way, one way I’m currently using, but is a bit unpredictable, is to have a collision object shape outside of the particle emitter, and then a force pushing around the particles. However I find that the particles tend to gather in uniform path pretty quickly, or bounce too wildly off the walls of the collision object.

Any ideas? would be greatly appreciated.