Free ows of loose matter make up the second signicant common class of ows occurring in bulk material handling technology. Primarily, these are ows of dumped materials in various stockpiling systems. Free ows also occur when openbody railway cars are loaded with concentrate or with pellets from feed hoppers. In terms of dynamic interactions between solid matter and air, close approximations can be made by studying ows of material unloaded from rail cars into charging bins of crushers and of other equipment.