Solid particles are initially dumped into the lower part of the dryer.  As the dryer spins, the tines push the solid particulate forward.  Collision modeling using the Discrete Element Method accounts for the particle packing behavior against the dryer walls.  The particles are being heated by warm air flowing through the center of the dryer.

The isometric view of the simulation is early on without any heating to the particles. The side view of Rotary Dryer is a few minutes later as the particles are moving down the length and also changing color as they are heated.

The near walls are hidden to view interior in this images.