How do cyclonic dust separators work? I have a background in engineering so I am somewhat embarrassed to say that I don't understand how a seemingly simple cyclonic dust separator works.  Here is a link to video of such a device in operation.
It is just that the particles are denser than the air and are forced out by a lack of centripetal force?  Does the device need to be cone shaped to get this effect or is the cone chosen for dust removal purposes?  Any papers / talks at an advanced undergraduate level would be appreciated.  
 A: Cyclonic separators work through airflow management and centrifugal force. In the video, you see the air enter tangentially at the top of the separator, which makes the air spin around the axis of the separator. In addition, the suction at the top center makes a secondary air flow up the axis and down the walls of the separator. Since dust is heavier than air, the centrifugal force pushes the dust towards the walls and the downward flow zone, leaving the central upward flow zone dust-free. The dust exits the bottom and the clean air exits the top. Voila: separation.
A: These have been in use for a long time in commercial woodworking, and agricultural tractor engine air cleaner pre-filters. John Deer released a video thirty years ago with excellent images of their operation. The same principle is used in automotive fuel tank swirl chambers surrounding fuel pumps and pump inlets. In my VERY SIMPLYFIED LAYPERSON'S UNDERSTANDING everything likes to travel in a straight line and the bigger the thing the harder it tries to go straight.  A washing machine uses the same principle, with liquid exit holes at the top of the drum. When I was very young washing machines did not have safety interlocks so we could watch this action during the spin cycle.  The external cone shape on an industrial sawdust separator is to funnel the unwanted particles to a collection point. Most of these require an additional bag or paper filter to catch the smallest particles. Check out all the latest household vacuum cleaners to discover how many use cone shapes and to see into the clear collection chambers and observe this action.
