Energy-Efficient Rate-Based Particle Separation

The effective separation of particles is key to numerous processes and industries handling solid materials. Despite this fact, particle separations techniques remain typically quite ``low tech'' and often are energy-intensive (e.g., sieving) or environmentally unfriendly (e.g., froth floatation) or both. Rate-based separation processes, on the other hand, represent a unique approach to particle separation that has the potential to be more flexible, more efficient, and more environmentally friendly than existing ``low tech'' techniques. In the present paper, we highlight passive granular ratchets, where particles of differing properties flow through a device often called a Galton board. In this type of device, the gravity-driven flow of particles down an inclined plane causes collisions between the particles and the evenly distributed pegs along the board. Dissipative collisions between particles as well as between paticles and pegs results in a diffusion-like motion of particles perpendicular to the flow. The extent of separation (i.e., how far one type of particle is removed from another) depends on the different distances traversed by the two types of particles and, ultimately, on the collision rate and energy dissipation for particle-peg events. A simple theory, will be set.