Size segregation under different gravity levels by using polyhedral particles

Particle mixtures of different sizes can segregate upon external excitation, which is called the Brazil nut effect (BNE). Since the BNE is a possible reason for large boulders depositing at the small body surface, the conditions and mechanisms regarding BNE have aroused broad concern in planetary science. Different from previous works, this paper further investigates this effect by using nonspherical polyhedral particles at different gravity levels. Numerical results of size segregation are presented to validate that a nonspherical polyhedral BNE is scalable if van der Waals cohesive interactions are not involved. Additionally, the attitude adjustment of the intruder would bring uncertainties to BNE, but it is eliminated upon the intense external vibration. The influence of the van der Waals force on BNE is also investigated. The van der Waals force strongly increases the stability of the particle system under a microgravity environment;therefore, the van der Waals force suppresses the BNE, and the scaling law is not applicable. However, when the particle system is under the Earth's gravitational environment with intense vibration, the van der Waals force benefits the BNE. The reason is that the cohesion force will increase the convective effect of the loosely structured particle system. Different shapes of intruders are also created. The intruder's oblateness influence on the BNE is further studied. It is difficult for the intruder to reorient the posture vertically as its increasing oblateness decreases the contact area, thus weakening the BNE.