Induction charge on freely levitating particles

Many industrial processes such as electrostatic separation, fluidization and coating rely upon induction charging of fine particles. This paper considers the magnitude of the induction charge on particles levitated in an electric field. The electric force on a particle depends on the electric field strength and the charge on the particle. Three different models to calculate the induced charge based on the particle sizes are presented as well as a model of the levitation process. A high-speed digital imaging system was used to visually measure the particle motion during the experiments to analyze the characteristic particle motion and thus determine the charge on the particle. Three different sizes of semiconductive particles having mass mean diameters (MMD) of 97, 156 and 412 μm were used in the experiments. It is shown that the charging time and charge on a freely levitating particle depends on a number of properties mainly the electric field strength, particle size, and resistivity. It has been found that the charging model, which assumes that the charge is distributed on the whole particle, is most suitable for all particles.