Ken-ichiro Tanoue

Tribo-charge and rebound characteristics of particles impact on inclined or rotating metal target

Abstract Tribo-charging of particles has been investigated with particular attention to the effect of impact velocity. The electrical current generated by impact of particles on an inclined or rotating metal target was measured for various impact angles by changing the tangential or normal component of impact velocity. It was found that the tribo-charging current had a maximum value at a certain impact angle. The particle rebound characteristics were also investigated in order to clarify the tribo-charging phenomena of such tendency. Experimentally obtained tangential restitution coefficient had a minimum value at a certain impact angle and increased to unity with the increase in impact angle. On the other hand, normal restitution coefficient had almost constant value up to a certain impact angle. Beyond this angle, the normal restitution coefficient increased sharply and finally exceeded unity. Translational energy loss normalized by initial translational energy had almost constant value as far as the impact angle is smaller than a certain angle. Beyond this critical angle, it decreased linearly to zero. This fact strongly suggests that the contact mode changes from rolling to slipping at this critical angle. Tribo-charging model refined by taking into the rolling and slipping of particle on the metal target agreed well with the experimental results.

Numerical Simulation of Electrostatic Particle Deposition on a Target in Aerosol Flow with and without Effect of Deposited Charged Particles

A two-dimensional simulation of charged aerosol flow has been conducted for electrostatic particle deposition onto targeted areas of a substrate. The distribution of deposited particles changes dramatically according to the kind of substrate. For a substrate made from insulating material, particles deposit uniformly on it except for the edges of the targeted areas, while for a substrate made from conducting material, the effective area for particle deposition becomes narrower than that of the insulator substrate. By adopting a distortion of the electric field due to the charged particle deposition into the simulation code, we have studied the change of both the electric field and the particle deposition with the passage of time. In the course of time, the electric field becomes weak in the targeted areas and particles deposit also in the area outside the targeted area. We have also examined the effects of both initial surface potential and particle concentration on the distribution of deposited particles. The number of particles deposited increases monotonously with an increase in initial potential, and the coefficient of variation for the number of deposited particles in the targeted areas has an almost constant value up to a given initial potential and then decreases. On the other hand, the number of deposited particles has a maximum value at some sufficient concentration of feed particles, and the coefficient of variation has a minimum value at the same concentration.

Numerical simulation of tribo-electrification of particles in a gas–solids two-phase flow

Abstract Numerical simulation of tribo-electrification of particles in a gas–solids two-phase flow has been conducted. Under any injected conditions on the particle, normal component of impact velocity and number of impacts of a particle per unit length have, respectively, a constant value for the calculation beyond the particle stopping distance and impact charge increases linearly with the distance. Although gravity force changes particle motion dramatically, the impact charge increases about 10%. We have also investigated the effects of particle size, air velocity and pipe diameter on the particle motion and the impact charge, which revealed that both the normal component of impact velocity and the number of impacts of a particle decrease exponentially with increasing Stokes number. However, it was found that the effects of air velocity and pipe diameter on the impact charge are qualitatively different from those of the experimental results.

Dependence of charge transfer phenomena during solid–air two-phase flow on particle disperser

An experimental investigation of the tribo-electrification of particles has been conducted during solid-air two-phase turbulent flow. The current induced in a metal plate by the impact of polymethylmethacrylate (PMMA) particles in a high-speed air flow was measured for two different plate materials. The results indicated that the contact potential difference between the particles and a stainless steel plate was positive, while for a nickel plate it was negative. These results agreed with theoretical contact charge transfer even if not only the particle size but also the kind of metal plate was changed. The specific charge of the PMMA particles during solid-air two-phase flow using an ejector, a stainless steel branch pipe, and a stainless steel straight pipe was measured using a Faraday cage. Although the charge was negative in the ejector, the particles had a positive specific charge at the outlet of the branch pipe, and this positive charge increased in the straight pipe. The charge decay along the flow...

Electrostatic control of particle deposition

A two-dimensional simulation has been conducted in an electrostatic powder-coating booth for controlling particle deposition. In the absent of electrostatic forces, most of particles flow along steamlines and cannot deposit on the target. When electrostatic forces (coulombic and image forces) are added in the motion of the particle, the trajectories change significantly near the target. It is found that image force hardly affects the deposited position of the particle. From the calculated force distribution near the aimed region on the target, coulombic force is found to be larger than drag force when the particle is very close to the target. Particles with small Stokes number having small specific charge deposit exactly on the aimed regions. Furthermore the width of the aimed region also affects the accuracy of the particle deposition.