I want to do a simulation of an air flow.
how can I make a Particlesys to follow a path for example. Thats all I want to know.
Check My file, thats the closest I can get 
Attachments
particletest.blend (417 KB)
If you just want the particles to follow the curve you need to remove the follow path constraint on the sphere, remove the plane and then make the curve a CurveGuide (Fields tab of the physics buttons). Put the sphere at the beginning of the curve and the particles should follow the curve. You can add a time IPO to the sphere to control the speed of the particles.