2017 Volume 43 Issue 5 Pages 319-326
Applying an external electric field enables electrostatically charged particles to move without any external mechanical forces. As a result, electrostatic-based techniques have attracted considerable attention in the field of particle handling. In this experiment, a plate electrode and a mesh electrode were used for lower and upper electrodes, respectively. Dielectric particles (glass beads with particle diameters of 100 µm) were piled on the lower electrode. A voltage of +5 kV was applied to the lower electrode, and the upper electrode was grounded, producing an electric field directed upwards. Owing to induction charging, the electric charge polarity of the particle layer is identical to that of the lower electrode, leading to particles in the upper layer being levitated by the Coulomb forces. The observation of both the particle behavior and the levitation process using a high-speed microscope camera showed that agglomerates as well as individual particles were levitated. The dielectric particles were polarized in the electric field, the electrostatic interaction between which leads to the formation of chain agglomerates. When the specific charge of the particles was small, the resulting Coulomb force was small, and the agglomerate did not levitate. However, when the magnitude of the total Coulomb force of the primary particles consisting the agglomerate exceeded the interparticle and gravitational forces, the agglomerate levitated. Estimating particle charge based on both electric field analysis and particle trajectory analysis showed that the specific charge of the agglomerate decreases and the interparticle force increases with an increase in the number of primary particles in the agglomerate.
