Mechanism on traveling wave transport of particles

Numerical and experimental investigation were carried out on transport of particles in an electrostatic traveling field. A three-dimensional hard sphere model of the Distinct Element Method was developed to simulate dynamics of particles. Forces applied to particles in the model were the Coulomb force, the electrostatic force due to polarization of particles in the non-uniform field, the gravity, and the viscous drag. Friction and repulsion between particle-particle and particle-conveyer were included in the model to replace initial conditions after mechanical contact. Two kinds of experiments were performed to confirm the model. One was the measurement of charge of particles that is indispensable to determine the Coulomb force. Charge distribution was measured from locus of free-fallen particles in a parallel electrostatic field. Averaged charges of bulk particles were confirmed by the measurement with a Faraday cage. The other experiment was measurements of bulk and differential dynamics of particles on a conveyer consisting of parallel electrodes to which four-phase traveling electrostatic wave was applied. The calculated results agreed with those measured and the following were clarified : (1) Coulomb force is the most predominant to drive particles. (2) The direction of particle transport did not always coincide with that of the traveling wave but partially changed depending on the frequency of the traveling wave, the particle diameter, and the electric field. (3) Although some particles overtook the traveling wave at the very low frequency, the motion of particles was almost synchronized with the wave at the low frequency. (4) The transport of some particles delayed to the wave at medium frequency and almost all particles were transported backward at high frequency.