Plug Conveying in a Vertical Tube
  Plug conveying along a vertical tube has been investigated through simulation, using a discrete element simulation approach for the granulate particles and a pressure field approach for the gas. The result is compared with an experiment. The dynamics of a plug are described by porosity, velocity and force profiles. Their dependence on simulation parameters provides an overall picture of plug conveying. 
Martin Strauss, Sean McNamara, Hans J. Herrmann, Gerhard Niederreiter   and Karl Sommer