Charge relaxation process dominates contact charging of a particle in I atmospheric conditions (original) (raw)
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Control of electrostatic charge on particles by impact charging
Advanced Powder Technology, 2007
The control of electrostatic charge on particles in gas-solids pipe flow has been studied experimentally and theoretically. Alumina particles of 3.3 µm in count median diameter were dispersed in airflow and pneumatically transported in the dilute phase. Five different materials were used for the transport pipes, and the relationships between the particle charge and the pipe length were obtained. The polarity and the amount of particle charge were found to depend on the pipe material and the length. In order to control the particle charge, a system combining two different pipe materials was proposed depending on the particle-charging characteristics. The charge controlled by this method was in good agreement with the theoretical calculation. Furthermore, it was found that the distribution of particle charge as well as the average can be controlled.
Particle charge in the bulk of gas discharges
Physical Review E, 2005
An experimental determination of particle charge in a bulk dc discharge plasma covering a wide range of neutral gas pressures, was recently reported ͓S. Ratynskaia et al., Phys. Rev. Lett. 93, 085001 ͑2004͔͒. The charges obtained were several times smaller than the predictions of collisionless orbital motion limited theory. This discrepancy was attributed to the effect of ion-neutral collisions. In the present paper a more detailed description of this experiment is provided and additional experimental results obtained with particles of different sizes are reported. The measurements are compared with molecular dynamics simulations of particle charging for conditions similar to those of the experiment, with other available experimental data on particle charge in the bulk of gas discharges, and with a simple analytical model accounting for ion-neutral collisions. All the considered evidence indicates that ion-neutral collisions represent a very important factor, which significantly affects ͑reduces͒ the particle charge under typical discharge conditions.
The effect of the generation and handling in the acquired electrostatic charge in airborne particles
Powder Technology, 2009
The measurement of the charge distribution in laboratory generated aerosols particles was carried out. Four cases of electrostatic charge acquisition by aerosol particles were evaluated. In two of these cases, the charges acquired by the particles were naturally derived from the aerosol generation procedure itself, without using any additional charging method. In the other two cases, a corona charger and an impact charger were utilized as supplementary methods for charge generation. Two types of aerosol generators were used in the dispersion of particles in the gas stream: the vibrating orifice generator TSI model 3450 and the rotating plate generator TSI model 3433. In the vibrating orifice generator, a solution of methylene blue was used and the generated particles were mono-dispersed. Different mono-aerosols were generated with particle diameters varying from 6.0 × 10 − 6 m to 1.4 × 10 − 5 m. In the rotating plate generator, a poly-dispersed phosphate rock concentrate with Stokes mean diameter of 1.30 × 10 − 6 m and size range between 1.5 × 10 − 7 m and 8.0 × 10 − 6 m was utilized as powder material in all tests. In the tests performed with the mono-dispersed particles, the median charges of the particles varied between − 3.0 × 10 − 16 C and −5.0 × 10 − 18°C and a weak dependence between particle size and charge was observed. The particles were predominantly negatively charged. In the tests with the poly-dispersed particles the median charges varied fairly linearly with the particle diameter and were negative. The order of magnitude of the results obtained is in accordance with data reported in the literature. The charge distribution, in this case, was wider, so that an appreciable amount of particles were positively charged. The relative spread of the distribution varied with the charging method. It was also noticed that the corona charger acted very effectively in charging the particles.
Unipolar charging of small aerosol particles
J Colloid Interface Sci, 1975
Calculations are presented of the unipolar charging rate of small aerosol particles in the transition and free molecule regimes of Knudsen number. Numerical results for the charging rate in the transition regime are obtained from a constant collision frequency model of the Boltzmann equation. These results confirm experimental observations that the unipolar charging rates for larger particle charges are only weakly pressure dependent even when the Knudsen number is relatively small. Also, the modification of the near free molecular unipolar charging rate by ion-neutral molecule collisions, is found to depend importantly and in a complex manner on particle size and total particle charge when the image force is included in the ion-particle interaction.
Calculations of bipolar charging of aerosols
Journal of Colloid and Interface Science, 1975
The acquisition of electric charge by the particles of an aerosol is a subject which heretofore has received only incomplete treatment, much of it based upon intuitive considerations. In this paper we present a rigorous treatment of the subject based upon the difference equations for charging of monodisperse and polydisperse aerosols in the presence of ions of both signs but unequal mobilities. The stochastic equations are written and the conditions of their solution are described for positive and negative small ions of mobilities 1.4 cm2/V-sec and 1.9 cm2/V-sec, respectively. Numerical calculations are presented of the time-dependent charge distributions and small ion number densities. Their relation to small-ion production, aerosol particle number concentration, and polydispersity is discussed. These results are compared where possible with calculated and experimental results of other workers. These calculations demonstrate for the first time that for bipolar charging a significant difference arises in polarity between the larger and smaller particle components of a polydisperse aerosol owing to unequal charging rates. CALCULATIONS OF BIPOLAR CHARGING OF AEROSOLS The particles of most aerosols may carry positive or negative electric charge as a result of their formation processes or their exposure to the charge-carrying constituents of the suspending medium. If an aerosol is initially charged, it is frequently of interest to know the conditions and time necessary to bring it to a state of minimum charge (1). In the normal atmosphere, the aerosol charge distribution and its evolution toward a steady state, bipolar distribution, are of interest in assessing the environmental effects of aerosol charge, a matter discussed elsewhere (2). Information on the time dependence of the number densities of the small ions, which are the source of the acquired aerosol charge, is a useful by-product
Journal of Aerosol Science, 2012
Electrical charging of non-radioactive aerosols was studied. The mean charge acquired by the poly-dispersed and mono-dispersed aerosols is determined for the two cases, viz. with and without the presence of additional ion pairs generated by gamma radiation. The results are separated accordingly by determining average charge acquired by the aerosols in three generation route (atomization, combustion and vaporization & condensation) and compared with the charge acquired in the presence of gamma radiation field. Using theoretical formulation developed by Clement and Harrison, the mean charge acquired by the aerosols (mono-dispersed) for a given concentration of both aerosols and ion pairs were calculated and compared with that of experimental results. The study is extended to determine the mean charge obtained for the distribution of DOP aerosols (poly-dispersed), by varying number concentration of aerosols and number concentration of ionpairs. It is found that the mean charge acquired by the aerosols increases with increase of ion pair concentration for a given concentration of aerosols.
Experimental Determination of Dust-Particle Charge in a Discharge Plasma at Elevated Pressures
Physical Review Letters, 2004
The charge of dust particles is determined experimentally in a bulk dc discharge plasma in the pressure range 20 -100 Pa. The charge is obtained by two independent methods: one based on an analysis of the particle motion in a stable particle flow and another on an analysis of the transition of the flow to an unstable regime. Molecular-dynamics simulations of the particle charging for conditions similar to those of the experiment are also performed. The results of both experimental methods and the simulations demonstrate good agreement. The charge obtained is several times smaller than predicted by the collisionless orbital motion theory, and thus the results serve as an experimental indication that ion-neutral collisions significantly affect particle charging.
Contact charging of oxidized metal powders
Zeitschrift f�r Physik B Condensed Matter, 1991
Samples of oxidized metal powders (Ag, A1, Cr, La, Nb, Ni, Ti) were repeatedly contacted with a gold plate under high vacuum conditions. The charge transfer was measured on both the samples and the gold plate. We observed charge saturation after one contact in most cases. Positive and negative polarities were detected. The charge densities were calculated and correlated with work functions of oxidized metals. Contact electrification of aluminum shows exceptional behavior with repeated contacts.
Electrification of fine particles by impact on a polymer film target
Advanced Powder Technology, 2003
Impact charging between ne particles and polymer lm has been investigated both theoretically and experimentally. A powder, y-ash of 12 ¹m mass median diameter, was dispersed and accelerated in air ow, and then the particles were impacted on a target whose frontal surface was covered with a polymer lm and the rear side was a metal plate. The lms used were in the range of 25-250 ¹m thick. The rear metal plate was grounded and the electric currents caused by impact charging were measured with an electrometer. Two types of currents were detected, i.e. induction current and conduction current. The induction current was due to the charge accumulating on the lm, whereas the conduction current was due to the dielectric breakdown arising from the particle impact. Using a lm with small arti cial holes, the conduction current was detected. This fact shows that insulating material can be utilized as an effective charging wall as long as the charge accumulation on the material is well suppressed.