In this paper the mechanism of contact- or tribo-electrostatic charging of powder was briefly reviewed.Although it is often referred that ‘electrostatics is mysterious’, but the fact should be noted that the entire system of the electromagnetism, such as Coulomb’s law, is ultimately well established. After this, there are parts of knowledge on electrostatics as well understood, miss-understood sometimes, and questions leftover, and these should be separated carefully. The central question to be answered is how much amount of charge is held by each particle. On this topic, two mechanisms of charge generation and of charge fixation were reviewed and discussed in general.

View full abstract

This paper reviews the tribo-electrification of particles in solid-air two-phase turbulent flow with a particle feeder, an ejector, a stainless-steel branch pipe and a stainless-steel straight pipe. An unexpected charge transfer occurred between the ejector and the branch pipe, which could not be explained solely by the contact potential difference. In the ejector, an electrical current in air might be produced by the self discharge of particles with an excess charge between a nickel diffuser in the ejector and a stainless steel nozzle or the stainless steel pipe due to a reversal in the contact potential difference between particles and the stainless steel. When dual coaxial glass pipes were used as a particle disperser, the specific charge of the Polymethylmethacrylate particles became more positive along the particle flow direction due to the contact potential difference between a material of the particle and the stainless steel.

View full abstract

Process tomography system was developed by detecting a displacement current induced by an electrically charged particle. The intensity of displacement current was confirmed by comparing the experimental signals with those calculated from a numerical solution of electrical field generated by an electrically charged particle. Without any adjustment factor, the estimated signals showed a good agreement with the experimental data in both time domain and signal intensity, suggesting that the induced signal is predictable by the numerical analysis and the sensor can be designed and optimized solely by numerical analyses. Fourier transform was applied to extend the single electrically charged particle model to multiple particle system. The Fourier spectra of displacement currents from multiple particles were conserved to those from superimposed many displacement currents. From the retrieved individual displacement current, it was possible to obtain the particle velocity and the amount of electrical charge carried by the particle. Furthermore, the detection system of charged particle’s position with an array of sensors was developed based on the concept of ‘circle of Appolonius’.

View full abstract

Relation among transfer efficiency of paint particles, characteristics of coated film and operation condition of electrostatic powder coating with corona spray gun was investigated by both experiment and computer simulation.The computer simulation of electrostatic powder coating process was developed by hybridization of distinct element method (DEM) and large eddy simulation (LES). DEM calculates the trajectories of paint particles having both particle size distribution and particle charge distribution based on the equation of motion of each paint particle and LES is the simulation method for three dimensional turbulent flow. Electric field between the coating spray gun and coating plate is estimated by solving Poisson’s equation under given boundary conditions. The numerical results, such as the velocity profiles of jet stream from the spray gun, the particle size distribution of coated paint particles on the target plate, were in good agreement with experimental data. We found that there is an appropriate particle size distribution for given coating condition because smaller particles have lower transfer efficiency of paint particles. A higher applied voltage to the coating gun led to a flatter surface of coated plate a higher transfer efficiency. Fundamental understanding on electrostatic powder spray coating condition can be deepened by the developed computer simulation.

View full abstract

In this study an experimental setup was developed that enabled us to investigate effects of pressures on generation and growth of sulfuric acid aerosol by photo-oxidation of gaseous SO₂. Changes in particle size distributions of generated aerosol at reduced and standard atmospheric pressures were measured. Particle size distributions of generated sulfuric acid aerosols were measured at the initial SO₂ concentration of 1 and 5 ppm and mean residence time of 2.31, 4.62 and 9.25 s, and the effects of pressure on the growth of sulfuric acid aerosols were investigated. The growth of sulfuric acid aerosol by coagulation as well as condensation was enhanced at reduced pressure due to the increase in particle diffusion coefficient in both transition and continuous regimes.

View full abstract

We observed high sulfate ion concentrations in Fukuoka and Osaka city using an aerosol mass spectrometer and an ion chromatograph method in the end of July, 2012. The mass concentration of sulfate ion reached ca. 35 μg m^-3 on 25 July in Fukuoka. The mass concentration of PM_2.5 exceeded 50 μg m^-3 and that of sulfate ion was between 10and 20 μg m^-3 for several hours on 29 July in Osaka. The simulation using Spectral Radiation- Transport Model for Aerosol Species (SPRINTARS) showed that the air mass with a high sulfate ion concentration first covered the Korean peninsula in July 2012 and then spread over the northern part of Kyushu and the Honshu regions of Japan. This indicates that the observed high sulfate ion events were possibly due to the trans-boundary air pollution. Since air pollution with a high sulfate ion concentration potentially causes adverse health effect, the monitoring of trans-boundary air pollution is necessary even in summer.

View full abstract

From January 2013, severe air pollution in Chinese cities including Beijing was reported and Japanese people were afraid of PM_2.5 as a new toxic substance. JAAST provided the information about PM_2.5 using the official homepage. People are very much concerned whether the commonly used masks are effective against PM_2.5. This article introduces health effect of aerosol inhalation, structures of surgical masks and dust respirators, performance of fibrous filters against aerosol particles, and fitness between masks and wears. In terms of effectiveness of masks, the fitness of masks is more important than the filter performance against aerosol particle inhalation.

View full abstract