Friction – The friction experience between the solids and the wall of the conveying enclosure along with the inter-particle behaviors and the gas turbulence and solid interaction all lead to an energy loss seen in pneumatic conveying. There have been attempts to describe each of these forces and losses (Molerus, 1996) but little success in quantifying these losses in a most general way as to applicable to all conveyed particles . This all point to a more thorough understanding of the basic
physics of the process. Because pneumatic conveying operations occur in turbulent flow regimes we are even more challenged to probe turbulence and all its nonlinear behaviors in the presence of particles. We have resorted to many correlations for specific materials and tried to generalize with limited success. Trying to isolate the contributions are
being explored and hopefully with new experimental methods and new analyses borrowed from other branches of science and engineering friction will be less of a mystery to us.