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John R. Grace - One of the best experts on this subject based on the ideXlab platform.
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Comparison of theory with experiment for single bubbles in Charged fluidized Particles
Powder Technology, 2016Co-Authors: Farzaneh Jalalinejad, John R. GraceAbstract:Abstract Previous numerical studies, focused on single bubbles, predicted that electrostatics can cause bubble elongation in gas-fluidized beds. However, there was a lack of experimental evidence to test the numerical predictions. This study compares experimental bubble size and shape in beds with two levels of charging. The results indicate that single bubbles are smaller and more elongated in a bed with higher Charge density. Instability of bubble roofs for Particles of high electrostatic Charge density was also observed. The experimental results are in agreement with the previous simulation results, with uniform Particle Charge density in the lower part of the bed and differences in the upper part. New simulations allowing for spatial variation of Charge density show that bubble shape and stability are functions of the Particle Charge density distribution. Differences between simulation and experimental results are likely due to non-uniform distribution of Charge on Particles.
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simultaneous measurements of Particle Charge density and bubble properties in gas solid fluidized beds by dual tip electrostatic probes
Chemical Engineering Science, 2015Co-Authors: Chuan He, Xiaotao Bi, John R. GraceAbstract:Abstract The aim of this work was to develop a new dual-tip electrostatic probe for in-situ measurements of Particle Charge density and bubble properties in bubbling fluidized beds. Probes containing two retractable, vertically-aligned tips were tested in a lab-scale two-dimensional fluidized bed operated in both single bubble injection and freely bubbling modes, with glass beads and polyethylene Particles of narrow size distributions as bed materials. Different decoupling methods were proposed and employed to analyze the electrostatic signals from the probes. The estimated Particle Charge density and bubble rise velocity were found to follow the same trends as those measured by a Faraday cup sampling system and obtained from video images respectively, with relative errors depending on the decoupling methods and probe configurations, especially for polyethylene Particles.
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Monitoring Electrostatics and Hydrodynamics in Gas–Solid Bubbling Fluidized Beds Using Novel Electrostatic Probes
2015Co-Authors: John R. GraceAbstract:The ability of recently developed novel electrostatic probes to monitor Particle Charge density and hydrodynamics in freely bubbling two- and three-dimensional fluidized beds of glass beads and polyethylene Particles is demonstrated. Particle Charge density and bubble properties in the beds were altered by abruptly changing superficial gas velocity or by impulsively adding antistatic agent to the bed. The probes were then utilized to quantitatively monitor the Particle Charge density and bubble rise velocity. The current signals from the probes responded quickly and significantly to abrupt changes in the superficial gas velocity. By analyzing time-series signals from the probes, the Particle Charge density and the bubble rise velocity deduced from the probes were found to be of similar order of magnitudes and changed consistently with those obtained from Faraday cup and video measurements. Charge densities from the Faraday cup decreased when an antistatic agent was added, as registered by the probe
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A novel dual-material probe for in situ measurement of Particle Charge densities in gas-solid fluidized beds
Particuology, 2015Co-Authors: John R. GraceAbstract:Abstract Particle Charge density is vitally important for monitoring electrostatic Charges and understanding Particle charging behavior in fluidized beds. In this paper, a dual-material probe was tested in a gas–solid fluidized bed for measuring the Charge density of fluidized Particles. The experiments were conducted in a two-dimensional fluidized bed with both single bubble injection and freely bubbling, at various Particle Charge densities and superficial gas velocities. Uniformly sized glass beads were used to eliminate complicating factors at this early stage of probe development. Peak currents, extracted from dynamic signals, were decoupled to determine Charge densities of bed Particles, which were found to be qualitatively and quantitatively consistent with Charge densities directly measured by Faraday cup from the freely bubbling fluidized bed. The current signals were also decoupled to estimate bubble rise velocities, which were found to be in reasonable agreement with those obtained directly by analyzing video images.
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Measurement of Particle Charge-to-mass ratios in a gas–solids fluidized bed by a collision probe
Powder Technology, 2003Co-Authors: Aihua Chen, John R. GraceAbstract:Specific Particle Charges, defined as the Particle Charge-to-mass ratio or the net Charge per unit mass, in fluidized beds have been deduced from signals registered by a miniature ball probe when a single gas bubble passed the probe in a fluidized bed based on a recently developed Charge induction and transfer model. The results indicate that the specific Charge is insensitive to the size of single bubbles passing the probe. The increase of relative humidity at RH
Vladimir E. Fortov - One of the best experts on this subject based on the ideXlab platform.
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effect of trapped ions and nonequilibrium electron energy distribution function on dust Particle charging in gas disCharges
Physical Review E, 2009Co-Authors: G. I. Sukhinin, S N Antipov, O F Petrov, A. V. Fedoseev, Vladimir E. FortovAbstract:: Dust-Particles charging in a low-pressure glow disCharge was investigated theoretically. The dust-Particle Charge was found on the basis of a developed self-consistent model taking into account the nonequilibrium character of electron distribution function and the formation of an ionic coat composed of bound or trapped ions around the dust Particle. The dust-Particle Charge, the radial distributions of electron density, free and trapped ions densities, and the distribution of electrostatic potential were found. It was shown that the non-Maxwellian electron distribution function and collisional flux of trapped ions both reduce the dust-Particle Charge in comparison with that received with the help of the conventional orbital motion limited (OML) model. However, in rare collisional regimes in plasma when the collisional flux is negligible, the formation of ionic coat around a Particle leads to a shielding of the proper Charge of a dust Particle. In low-pressure experiments, it is only possible to detect the effective Charge of a dust Particle that is equal to the difference between the proper Charge of the Particle and the Charge of trapped ions. The calculated effective dust Particle Charge is in fairly good agreement with the experimental measurements of dust-Particle Charge dependence on gas pressure.
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The Influence of Trapped Ions and Non-equilibrium EDF on Dust Particle Charging
AIP Conference Proceedings, 2008Co-Authors: G. I. Sukhinin, S N Antipov, O F Petrov, A. V. Fedoseev, Vladimir E. FortovAbstract:Dust Particles charging in a low‐pressure glow disCharge was investigated theoretically with the help of model for trapped and free ions coupled with the self‐consistent solution of Poisson equation for electric potential. Non‐equilibrium (non‐Maxwellian) character of electron energy distribution function depending on gas pressure and electric field was also taken into account on the basis of the solution of kinetic Boltzmann equation. The results were compared with the experimental measurements of dust Particle Charge depending on gas pressure. It was shown that the calculated effective Charge, i.e. the difference of the dust Particle Charge and trapped ion Charge, is in a fairly good agreement with the experimental data.
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micron sized Particle Charge measurements in an inductive rf gas disCharge plasma using gravity driven probe grains
Physical Review E, 2004Co-Authors: Vladimir E. Fortov, O F Petrov, A D Usachev, A V ZobniAbstract:A method for measuring the interactions of Charged dust Particles within a three-dimensional dust cloud in a plasma is presented. The measurements have been performed with the help of gravity-driven heavy Charged probe Particles, which moved through a dust cloud levitating at the diffuse edge of an inductively coupled rf disCharge plasma. Assuming a screened Coulomb potential surrounding each Particle, both the Particle Charge and the effective screening length were calculated from an analysis of the elastic Particle interactions for 20, 30, and 50 Pa of neon pressure. The basic parameters of the bulk disCharge plasma have been diagnosed with a Langmuir probe to compare the experimental data with those deriving from different theoretical approaches. The observed discrepancies are discussed.
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Experimental determination of dust Particle Charge at elevated pressures
The 31st IEEE International Conference on Plasma Science 2004. ICOPS 2004. IEEE Conference Record - Abstracts., 2004Co-Authors: S. Ratynskaia, S. Khrapak, M.h. Thoma, Markus Kretschmer, R.a. Quinn, A. Zobnin, A. Usachev, O Petrov, Gregor Eugen Morfill, Vladimir E. FortovAbstract:Summary form only given. Experiments with dust Particle flow in a horizontal DC disCharge tube (experimental facility PK-4) are conducted for Particles with radius of 0.6 micron. For relatively high pressures the flow is stable and the Charge is calculated from the force balance. Decreasing pressure, a sharp threshold for onset of dust wave instability is observed. We use a linear dispersion relation to find a value of Charge for which the transition from stable to unstable regime occurs at experimentally found threshold pressure. The threshold depends strongly on the dust number density and varying the dust density we are able to determine Particle Charge in the pressure range 30-60 Pa. Molecular dynamic simulations taking into account ion-neutral collisions were also carried out-for the parameters similar to those of the experiments. Results of both experimental methods and simulations show reasonable agreement (within experimental error). The Charge obtained is a few times smaller than the OML theory predicts, the result which we associate with the effect of ion-neutral collisions for the neutral pressure range used in experiments.
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dependence of the dust Particle Charge on its size in a glow disCharge plasma
Physical Review Letters, 2001Co-Authors: Vladimir E. Fortov, Anatoly P Nefedov, Vladimir I. Molotkov, M Y Poustylnik, V M TorchinskyAbstract:Measurements of the Charge of dust grains have been performed in a quasineutral plasma over a wide range of grain sizes. A new method was established for measuring the Charge on grains levitating in the striations of a dc glow disCharge. A single dust Particle is moved out of a dust cloud with the help of a focused laser beam. When it leaves the beam it returns back to the cloud, and the Charge on the grain is derived from the analysis of the returning trajectory. The obtained dependence of the dust-grain Charge on its size was found to be strongly nonlinear in the experimental conditions. The problem of the charging of dust Particles in a plasma is one of the main tasks to be studied. In a plasma dust Particles acquire a Charge (typically it is negative), interact with each other, and their presence may lead to a significant change of the plasma properties. Since the electrostatic energy of interacting Particles strongly exceeds their thermal energy, the Particles can form an ordered lattice. The so-called plasma crystals have been widely studied with respect to lattice formation [1,2], phase transitions [3], and waves and instabilities [4]. The determination of the grain’s Charge is very important in all of these experiments in order to reveal whether the dust system is strongly or weakly coupled [5]. The Charge of the dust grains is of great interest to understand the behavior of particulates in processing plasmas used for thin-film production, in processes of growing Particles in the gas phase by nucleation and aggregation [6] as well as for the study of space plasmas, e.g., interstellar clouds and planetary rings [7]. There is a requirement to obtain reliable experimental data on the value of the dust-Particle Charge over a wide range of grain sizes and plasma parameters. However, no methods for measuring the Charge on the dust Particles were proposed for the direct current (dc) disCharge dusty plasma. For rf disCharge plasmas several methods have been developed. In the first method, initiated by [8,9] the Charge is derived from a response of a simple ordered system (chain, monolayer, etc.) of dust Particles on a periodical disturbance. In the second method [10], the Charge was determined from the trajectories of the Particles in binary collisions. In the third method [11], Mach cones were excited in a 2D crystal by the fast dust Particles, and the Charge was derived from the analysis of these waves. However, the crucial condition for the application of these methods is low neutral gas pressure (of the order of 10 22 10 21 torr). In this Letter, we present the results of the measurements of the Charge on dust grains in the striations of a dc disCharge obtained with a new method. The experiments were carried out in a glass disCharge tube [12] of 36 mm diameter and 40 cm interelectrode distance. The glow disCharge with cold electrodes was produced in neon in the range of pressures 0.5 1.5 torr. The disCharge current varied from 0.4 to 3 mA. In this range of parameters, regimes with standing striations existed. Dust Particles were stored in a container with a grid at the bottom, positioned above the anode. Through the shaking of the container, the Particles were dispersed into the plasma region then levitated in the striations where they formed ordered structures. Melamine-formaldehyde Particles of 1.87, 4.82, and 13.57 mm diameter were used. A 50 mW diode laser was used for the illumination of the Particles. The scattered light was observed by a CCD video camera. The specificity of the striations of a dc glow disCharge is such that a stable levitation of dust Particles occurs at relatively high pressures (0.5 2 torr). At lower pressures self-excited waves are developing in the dusty plasma structures [4], making the measurement of the Charge with the techniques, cited above, impossible.
Shuji Matsusaka - One of the best experts on this subject based on the ideXlab platform.
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Control of Particle Charge by atmospheric pressure plasma jet (APPJ): A review
Advanced Powder Technology, 2019Co-Authors: Shuji MatsusakaAbstract:Abstract Atmospheric pressure plasma jets (APPJs) have more advantages regarding flexibility of operation than low pressure plasmas. Because the ions and/or electrons in the APPJ can be arbitrarily extracted to a gas-phase space by changing the DC bias voltage and efficiently deposited onto Particle surfaces in an external electric field, this operating technique can be applied towards controlling Particle Charge. Several methods to control the Particle Charge using an APPJ system have already been reported. This article summarizes the specifications and operations of these systems, their mechanisms of Charge transfer, and methods for Particle charging, based on previously reported work. The methods are categorized into three groups, i.e., direct charging of Particles, direct charging of a powder bed, and indirect charging of Particles, and the corresponding experimental setups, procedures, results, and discussions are presented.
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prediction of Particle charging in a dilute pneumatic conveying system
Aiche Journal, 2013Co-Authors: Poom Bunchatheeravate, Jennifer S Curtis, Yusuke Fujii, Shuji MatsusakaAbstract:When Particles are transported in pipelines, they acquire electrostatic Charges as they come into contact with the pipe wall. Charged Particles can cause problems such as Particle agglomeration, blockage, and explosion. Understanding the Particle Charge can help to prevent these issues. This study investigates a technique for predicting the Particle Charge in a straight pipe of any given length, as well as the pipe length at which electrostatic equilibrium occurs, through experimentation in a short 1-m pipe section. Experimentation with five different types of Particles and four pipe wall materials at longer pipe lengths were used to validate the technique. This predictive technique is applicable to a range of Particle shapes and sizes under the restriction that Charge transfer is due to impact charging. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2308–2316, 2013
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Electrostatics of the Granular Flow in a Vertical Pneumatic Conveying System
2004Co-Authors: Yan Zhang, Shuji Matsusaka, Chi-hwa Wang, Hiroaki MasudaAbstract:The phenomenon of electrostatic Charge generation in a pneumatic conveying system was studied. The main parameters used for quantitative characterization of the phenomenon included induced current, Particle Charge density and equivalent current of the Charged granular flow. These were measured using a Digital Electrometer, Faraday Cage and Modular Parametric Current Transformer (MPCT) respectively. Three different flow patterns corresponding to the different electrostatic effects within the pneumatic conveying system were observed and these were classified as the disperse flow, half-ring flow and ring flow patterns. It was found that the induced current, Particle Charge density and equivalent current increased with decreasing flow rates. Electrostatic effects generally become stronger with time and this may lead to clustering behavior occurring even in the disperse flow regime.
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simultaneous phenomenon of Particle deposition and reentrainment in Charged aerosol flow effects of Particle Charge and external electric field on the deposition layer
Advanced Powder Technology, 2000Co-Authors: Indra Adhiwidjaja, Shuji Matsusaka, Susumu Yabe, Hiroaki MasudaAbstract:Abstract Formation of a Particle deposition layer has been investigated as a simultaneous phenomenon of Particle deposition and reentrainment in a turbulent aerosol flow. Aerosol Particles passed through a corona Charger were pneumatically transported into a glass tube equipped with a ring-type electrode. The deposition layers formed on the tube wall under various conditions were then quantitatively analyzed with particular attention to the effects of Particle Charge and external electric field on the deposition layer. The Charged Particles formed a filmy deposition layer around the electrode independent of the polarity of the Particle Charge and applied voltage. The mass of the deposition layer increased with elapsed time and became constant after an equilibrium state of Particle deposition and reentrainment had been achieved. The time dependence was represented by an exponential equation; the time constant decreased with increasing Particle Charge and/or applied voltage, and the equilibrium mass of the deposition layer increased with Particle Charge. Furthermore, it was found that an appropriate arrangement of electrodes to control external electric field eliminates the filmy deposition layer.
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Simultaneous phenomenon of Particle deposition and reentrainment in Charged aerosol flow — effects of Particle Charge and external electric field on the deposition layer
Advanced Powder Technology, 2000Co-Authors: Indra Adhiwidjaja, Shuji Matsusaka, Susumu Yabe, Hiroaki MasudaAbstract:Abstract Formation of a Particle deposition layer has been investigated as a simultaneous phenomenon of Particle deposition and reentrainment in a turbulent aerosol flow. Aerosol Particles passed through a corona Charger were pneumatically transported into a glass tube equipped with a ring-type electrode. The deposition layers formed on the tube wall under various conditions were then quantitatively analyzed with particular attention to the effects of Particle Charge and external electric field on the deposition layer. The Charged Particles formed a filmy deposition layer around the electrode independent of the polarity of the Particle Charge and applied voltage. The mass of the deposition layer increased with elapsed time and became constant after an equilibrium state of Particle deposition and reentrainment had been achieved. The time dependence was represented by an exponential equation; the time constant decreased with increasing Particle Charge and/or applied voltage, and the equilibrium mass of the deposition layer increased with Particle Charge. Furthermore, it was found that an appropriate arrangement of electrodes to control external electric field eliminates the filmy deposition layer.
Hiroyuki Ohshima - One of the best experts on this subject based on the ideXlab platform.
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Potential distribution around a Charged spherical colloidal Particle in a medium containing its counterions and a small amount of added salts
Colloid and Polymer Science, 2004Co-Authors: Hiroyuki OhshimaAbstract:A theory is developed for the potential distribution around a Charged spherical colloidal Particle carrying ionized groups on the Particle surface in a medium containing its counterions (i.e., counterions produced from dissociation of the Particle surface groups) and a small amount of added salts on the basis of the theory of Imai and Oosawa. Numerical solutions to the Poisson–Boltzmann equation for the potential distribution are obtained for the case of dilute (but not infinitely dilute) Particle suspensions of volume fraction φ ≪1 for κa ≪1 (where κ is the Debye–Hückel parameter and a is the Particle radius). Here we have taken into account the effects of (i) counterions from the Particle surface groups, and (ii) the finite Particle volume fraction. These effects, which are usually neglected in the conventional Poisson–Boltzmann equation, are found to be important. It is found that, as in the case of completely salt-free media, there is a certain critical value of the Particle Charge (which is the same as that for the completely salt-free case). When the Particle Charge is lower than the critical value, the potential is given by a Coulomb potential. If the Particle Charge is higher than the critical value, then counterions are accumulated in the vicinity of the Particle surface (counterion condensation) and the potential becomes less dependent on the Particle Charge. The above behaviors can be observed even for the case where the electrolyte concentration is higher than the concentration of counterions from the Particle surface groups, if the conditions φ ≪1 and κa ≪1are both satisfied.
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electrophoretic mobility of a soft Particle in a salt free medium
Joint International Conference on Information Sciences, 2004Co-Authors: Hiroyuki OhshimaAbstract:Abstract A theory is presented for the electrophoretic mobility μ of dilute spherical soft Particles (i.e., polyelectrolyte-coated Particles) in salt-free media containing only counterions. As in the case of other types of Particles (rigid Particles and liquid drops) in salt-free media, there is a certain critical value of the Particle Charge separating two cases, the low-surface-Charge case and the high-surface-Charge case. For the low-Charge case, the mobility is proportional to the Particle Charge and coincides with that of a soft Particle in an electrolyte solution in the limit of very low electrolyte concentrations κ →0 (Huckel's limit), where κ is the Debye–Huckel parameter. For the high-Charge case, however, μ becomes essentially constant, independent of the Particle Charge, due to the counterion condensation effect.
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potential distribution around a polyelectrolyte coated spherical Particle in a salt free medium
Journal of Colloid and Interface Science, 2003Co-Authors: Hiroyuki OhshimaAbstract:Simple analytic approximate expressions for the solution to the Poisson-Boltzmann equation around a spherical Particle coated with an ion-penetrable polyelectrolyte layer in a salt-free medium containing counterions only are derived. The results of the calculation of the potential distribution using the approximate solution are found to be in good agreement with exact numerical results. It is shown that as in the case of a Charged rigid Particle, there is a certain critical value of the Particle Charge, separating two cases, that is, the low-Particle-Charge case and the high-Particle-Charge case. In the low-Charge case the potential is essentially the same as if counterions were absent and thus the potential is proportional to the Particle Charge. In the high-Charge case counterion condensation occurs in the polyelectrolyte layer region, so that the dependence of the potential on the Particle Charge is considerably suppressed.
Yongrong Yang - One of the best experts on this subject based on the ideXlab platform.
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Online measurement of Particle Charge density in a gas-solid bubbling fluidized bed through electrostatic and pressure sensing
Powder Technology, 2017Co-Authors: Jingyuan Sun, Yang Yao, Zhang Qing, Zhengliang Huang, Jingdai Wang, Zuwei Liao, Yongrong YangAbstract:Abstract Electrostatic phenomena widely exist in various olefin polymerization fluidized bed reactors, due to the continuous collision and friction of dielectric Particles and the low-humidity reaction environment. The measurement of Particle Charge density is essential for monitoring and controlling the electrostatic level as well as probing the hydrodynamic characteristics in a fluidized bed. In this work, a non-intrusive online measurement system, employing ring-shaped sensing electrodes and a pressure transducer, is designed and implemented on a fluidized bed test rig. A modified model considering the influence of spatial sensitivity of the electrodes is proposed to predict the Particle Charge density in the fluidized bed, based on the measured induced electrostatic current and pressure drop signals. Experimental results have demonstrated that the induced electrostatic current and pressure drop signals show remarkable similarity, with the two PSDs both mainly distributed within 0.5–5 Hz, which indicates close relationship between the two signals. The predicted Particle Charge density increases with the superficial gas velocity and decreases with the injection content of liquid anti-static agent (LAA), showing the same variation tendencies as that measured through a Faraday cup. When the electrode width is 20 mm, the mean absolute relative errors for the direct method, area method and envelope method are 12.7%, 14.7% and 13.5%, respectively, indicating that the direct method is the most reliable signal processing approach proposed in this work.