Charged Collector Research Articles

Fast responding ephedrine detection with miniaturized surface ionization gas sensors

We report on novel kinds of miniaturized gas sensors whose operation is based on the principle of surface ionization (SI). In SI gas sensing adsorbed analyte species are ionized at a heated solid surface and the formed ions are extracted towards an oppositely charged collector electrode positioned a short distance from the emitting surface. Here, we show that SI sensors allow for a fast, sensitive and selective detection of illicit drugs in the presence of large concentrations of solvent water.

Experimental investigations on the multi-jet electrospinning process

Multi-jet electrospinning systems can be designed to increase both productivity and cover area for large-scale nanofibre production. In this work several multi-jet electrospinning setups were tested. A solution of 7 wt% PEO was electrospun varying the number of nozzles between 2 and 16. Tests showed that the divergence angle between jets can be reduced employing a secondary electrode. The standard configuration consisting of a charged solution and a grounded collector plate was used, as was the opposite case of a charged collector and a grounded solution. These configurations were, respectively, tested with positive and negative polarity. Process operating conditions were varied in order to obtain nanofibres without defects. Samples collected were examined with SEM; it was demonstrated that multi-jet electrospinning works with standard and reverse configurations both applying positive and negative polarity. Good quality nanofibres were obtained in both cases.

Simulation of electrical effects with respect to fine particle separation at conditions of pressurized pulverized coal combustion

Realization of the power plant concept with pressurized pulverized coal combustion (PPCC) needs a flue gas nearly free of particulate matter with respect to gas turbine life cycle. Current studies at the pilot plant of the PPCC-development project in Dorsten, Germany, show that the limit for safe turbine operation is now reached with the used multi-stage molten ash separator. The separation principle that leads to the observed improvement of fine particle separation is a subject matter of the current scientific research. Thus computational fluid dynamics (CFD)-modelling carried out at IUTA focuses on the calculation of fine particle dynamics at high temperatures. This includes modelling of particle transport due to inertia and electrophoresis as well as charging kinetics with respect to interaction of electrically charged fine particles and different ceramic collector materials at temperatures up to 1600–1700 K.

Wet Electroscrubbers for State of the Art Gas Cleaning

Current trends observed in air pollution control technology are closely related to the development of new, more efficient hybrid systems, i.e., those, which simultaneously utilize two or more physical mechanisms for dust or gaseous contaminants removal. These systems can operate more economically than conventional devices, especially in the removal of PM2.5 particles. The electrostatic scrubber (electroscrubber), discussed in this paper, is one of such types of devices, which combines advantages of electrostatic precipitators and inertial wet scrubbers, and removes many shortcomings inherent to both of these systems operating independently. The electroscrubber is a device in which Coulomb attraction or repulsion forces between electrically charged scrubbing droplets (collector) and dust particles are utilized for the removal of particles from a gas. Unlike wet electrostatic precipitators in which particles are precipitated only on the collection electrode, in electroscrubbers, the collection of dust particles takes place in the entire precipitator chamber. Compared to inertial scrubbers, the electroscrubbers can operate at lower droplet velocities, but the collection efficiency for a single droplet can be larger than 1. The paper reviews the state-of-the-art of wet electrostatic scrubbing (electroscrubbing) technique used for gas cleaning from dust or smoke particles. Three groups of problems are discussed: (1) The fundamental problems concerning the charged dust particle deposition on a charged collector, usually a drop, with a focus on different models describing the process. (2) The experimental works of fundamental importance to our knowledge referring to the scrubbing process, which can be used for validating the theory. (3) The laboratory demonstrations and industrial tests of different constructions of electroscrubbers designed for effective gas cleaning. The electroscrubber is not designed to replace wet or dry electrostatic precipitators but can be used as a complementary device following the last stage of conventional electrostatic precipitator, which helps to remove submicron particles. It was shown in the paper that a higher collection efficiency of an electroscrubber could be obtained for higher values of Coulomb number (i.e., higher electric charges on the collector and particle), and for a Stokes number lower than5 (i.e., low particle-collector relative velocity).

Collection of submicron particles by an electrostatic precipitator using a dielectric barrier discharge

Although dielectric barrier discharge (DBD) in air has been used to clean hazardous air pollutants (HAPs) because of its high electron density and energy, its potential use as precharging dust aerosol particles is not well known. In this work, we measured the size distributions of bimodal submicron aerosol particles and estimated the collection efficiency of the particles for a hybrid two-stage electrostatic precipitator (ESP) comprised of a DBD charger as the particle charger and an ESP as charged particle collector. Nano-sized particles of NaCl (30–100 nm) and DOS (50–800 nm) were generated by evaporation–condensation and atomization, respectively. Various electrical and flow conditions were applied on the DBD charger: AC applied voltage of 9–11 kV, frequency of 60–120 Hz, and air flow rate of 60 – 180 L min - 1 ( 0.048 – 0.016 s of particle residence time). The particle collection efficiencies increased as the AC applied voltage increased at a fixed frequency–flow rate, whereas the efficiencies decreased as the frequency and flow rate increased at a fixed AC power–flow rate and a fixed AC applied voltage–frequency.

Agglomerate flotation of fine oxide particles

This paper presents experimental data on using both flocculants and surfactants for aggregation and flotation of fines. The work has been performed with water suspensions of two oxides, ZnO and MgO. Conventional flotation collectors (sodium oleate (SOL), sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB)) were used. Commercial high molecular weight polymers (MAGNAFLOC 1440, MAGNAFLOC E-10 and MAGNAFLOC 351) were the flocculants used. Adsorption isotherms of surfactants adsorbing onto the two oxides were determined at natural pH. Adsorption density was the greatest with sodium oleate. Zeta potential measurements indicated that addition of the cationic surfactant caused a positive increase of the zeta potential. The positive zeta potential of MgO decreased with increased anionic surfactant concentration. A decrease in stability indicated that the ZnO suspension pretreated with anionic surfactants caused the formation of larger flocs when the cationic flocculant (MAGNAFLOC 1440) was added. Similar observations were obtained for a MgO suspension pretreated with anionic surfactants and reacted with the nonionic flocculant, MAGNAFLOC 351. The negative charged collector (SDS) appears to be good collector for ZnO floc flotation when hydrophobic flocs are created by the combination of SDS and either cationic or nonionic flocculants.

Adsorption of N-Tallow 1,3-Propanediamine–Dioleate Collector on Albite and Quartz Minerals, and Selective Flotation of Albite from Greek Stefania Feldspar Ore

The adsorption behavior of tallow 1,3-propanediamine–dioleate (Duomeen TDO) collector on albite and quartz minerals is assessed through Hallimond flotation, zeta potential, and diffuse reflectance FTIR investigations, together with the species distribution of the collector. The collector performance on albite separation from a natural feldspar material is evaluated in bench scale flotation tests. The Hallimond flotation responses of the minerals as a function of pH and collector concentration indicate that albite can be selectively floated from quartz at pH 2 where the doubly positively charged collector species adsorb on albite but not on quartz. However, the zeta potential and infrared spectra reveal that the adsorption behavior of the collector is similar on both minerals. The discrepancy in the flotation and adsorption results is attributed to the coarse and fine particle size fractions, and the shorter and longer equilibration periods employed in these studies respectively. The comparable adsorption on fine particles of albite and quartz at pH 2 is explained by the interaction of ammonium ions on silanol groups by hydrogen bonding as well as electrostatic interactions. The changes in zeta potentials are in good agreement with the formation of ionic species and free molecular forms of the collector. The IR spectra show the coexistence of neutral oleic acid together with charged amine species at low pH values in accordance with the species distribution diagram. Selective flotation of albite is accomplished from a natural feldspar material with tallow diamine-dioleate collector at pH 2 using sulfuric acid, only when the feed is deslimed prior to the bench scale flotation tests. An albite recovery exceeding 85% is achieved from a feed material containing about 50% albite.

Effect of Particle Size on the Sticking Probability

In the literature the transport of particles toward an oppositely charged collector in stagnation point flow is described theoretically with the Smoluchowski–Levich solution of the convective-diffusion equation. Using optical reflectometry, the initial adsorption rate in the case of adsorption of negatively charged polystyrene latex particles onto a glass collector covered with positively charged poly(propylene imine) dendrimers was studied at low ionic strength and constant pH. For latex particle sizes varying from 10 to 100 nm, the experimentally obtained values for the initial adsorption rate are systematically lower than the theoretical predictions. The deviations are captured by a sticking probability or collision efficiency that increases linearly from 0.5 to 0.8 within the experimental window. This can be explained by the fact that with particle size the contact area between the incoming particles and the amorphous collector increases and with this the number of sites involved in binding.

Deposition of Biocolloids on a Charged Collector Surface: An Ion-Penetrable Membrane Model

The deposition of biocolloids onto a negatively charged, planar collector surface is modeled theoretically. Here, a biocolloid is mimicked by a rigid core covered by a negatively charged, ion-penet...

Deposition efficiency of dust particles on a single, falling and charged water droplet

A numerical algorithm for simulating dust particle deposition on a charged spherical collector is presented in this paper. Trajectories of the charged dust particles are traced in three-dimensional space by solving the Newton equation, taking into account inertial, air drag, gravitational and electrostatic forces. The collector (charged droplet) falls down freely and its trajectory is also determined. A laminar viscous model is assumed for the airflow in the vicinity of the collector and modeled using the finite-element method in two-dimensional cylindrical coordinates. The deposition efficiency is defined in terms of the volume of space, from which all particles are deposited on the collector. The calculation results for different Stokes, Coulomb, and Reynolds numbers are given.

Air bubble-induced detachment of positively and negatively charged polystyrene particles from collector surfaces in a parallel-plate flow chamber

Electrostatic interactions between colloidal particles and collector surfaces were found to be important in particle detachment as induced by the passage of air bubbles in a parallel-plate flow chamber. Electrostatic interactions between adhering particles and passing air bubbles, however, were found to be less important. Regardless of the charge on the particles, detachment increased linearly with decreasing air bubble velocity and increasing liquid-air interfacial tension. Detachment efficiencies up to 75% could be achieved even for positively charged particles adhering to a negatively charged collector surface, provided that the velocity of the air bubble was low (2.37 mm s-1) and the tension at the liquid-air interface was high (70.08 mJ m-2). The detachment of positively charged particles was most sensitive to the air bubble velocity when adhering to a hydrophobic, negatively charged collector surface and least sensitive when adhering to a positively charged collector surface, but appeared equally sensitive to the liquid-air interfacial tension for all collector surfaces. On the other hand, the detachment of negatively charged particles was most sensitive to both the velocity of the air bubble and the tension at the liquid-air interface when adhering to a positively charged collector surface.

Blocking and ripening of colloids in porous media and their implications for bacterial transport

A model accounting for the dynamics of colloid deposition in porous media was developed and applied to systems containing similarly charged particles and collectors. Colloid breakthrough and intracolumn retention data confirmed that blocking reduced overall colloidal adhesion to soil. The surface coverage at which blocking occurred varied for the type of colloid, as shown by changes in the clean-bed collision efficiency, α 0, and the excluded area parameter, β. Excluded area parameters were relatively high due to unfavorable interactions between particles and collectors, and ranged from 11.5 for one bacterium ( Pseudomonas putida KT2442) to 13.7 and 24.1 for carboxylated latex microspheres with differing degrees of charged groups on their surfaces. Differences in β values for the three colloids were correlated with electrophoretic mobility, with the most negatively charged colloid (carboxylated latex; CL microspheres) having the highest β. No correlation between hydrophobicity and α 0 or β was found. Besides using colloidal particles capable of blocking, the addition of chemical additives to the soil has been suggested as a means for reducing attachment of colloids to porous media. Dextran addition caused an order-of-magnitude reduction in the overall α (for carboxylated-modified latex; CMLs). This reduction was not attributed to blocking, but to the sorption of dextran to the soil which lowered α 0. The filtration-based numerical model used to fit the α 0 and β parameters was used to demonstrate that blocking could result in significantly enhanced bacterial transport in field situations.

Deposition of Polystyrene Particles in a Parallel Plate Flow Chamber under Attractive and Repulsive Electrostatic Conditions

Depositions of negatively charged polystyrene particles in a parallel plate flow chamber to negatively and positively charged collector surfaces are compared at different shear rates and ionic strengths. The observation of adhering particles was done in situ during the deposition process with the aid of an image analyzer and the adsorption and desorption of each particle was monitored individually using a special tracking algorithm. Initial deposition rates j(0)(EXP) were higher to positively charged glass than to negatively charged glass collector surfaces, depending on shear rates and ionic strength. All observed experimental deposition rates were, however, smaller than the Smoluchowski-Levich (SL) approximate solution of the convective-diffusion (CD)equation. Initial deposition rates were also calculated using an exact numerical solution of the CD equation; they were two times higher than the experimentally observed deposition rates for positively charged glass and about equal or lower for negatively charged glass. The desorption rates j(des)(t) Of polystyrene particles on positively charged glass were nearly zero under all conditions, whereas the desorption rates from the negatively charged glass were considerable and finally balanced the adsorption rates j(ads)(t). From the residence time dependent desorption probability beta(t - tau), it could be determined that polystyrene particles on negatively charged collector surfaces have the highest probability of desorption within the first 5-10 min after deposition. Experimental results were subsequently compared with those from a proposed adsorption-desorption model for deposition kinetics, using the parameters derived as an input, and with a Monte Carlo simulation of the deposition process. A high degree of similarity between experimental results, the adsorption-desorption model and the Monte Carlo simulation results was observed, which indicates; the consistency of the applied experimental methods and theoretical models.

Experimental study of a refrigerant charged solar collector

The performance of a heat-pipe solar collector was investigated experimentally using refrigerants R11 as the working fluid. The unit is fabricated locally and its performance is evaluated under Beirut Solar conditions. The heat transfer from the heat pipes to the hot-water storage tank took place through a circular end condenser section of the heat-pipe integrated within the collector frame. Tests of single heat pipes showed that the thermal performance of the heat pipe were dependent on its tilt angle, condenser section length and configuration, and type of internal wick used. A circular condenser end of the heat-pipe performed better than a straight condenser due to increased surface area for heat transfer. The R11-charged solar collector with integrated condenser for secondary cooling of water had an efficiency in early operation hours that reached values higher than 60% for the forced circulation mode. The instantaneous system efficiencies varied from 60 to 20%, which are in the range of conventional water solar collectors. System response was fast and sensitive to the incident solar radiation. The thermosyphonic mode of the system operation generated build up of stored energy in the condenser, resulting in oscillating-type flow thus reducing system efficiency below values obtained with forced circulation. © 1998 John Wiley & Sons, Ltd.

Influence of surface charge on interaction forces in soluble salt flotation systems as determined by atomic force microscopy

The recent nonequilibrium electrophoretic mobility measurements by laser-Doppler electrophoresis coupled with the stability and prevalence of collector colloids in soluble-salt flotation systems suggest that the selective flotation of alkali halides is due to the adsorption of oppositely charged collector colloids by heterocoagulation. Previously reported flotation results confirm this surface charge/collector colloid adsorption model. These results also indicate that the sign of the surface charge has a significant effect on the extent of particle dispersion/aggregation. In this regard, the nature of such particle interaction forces at high ionic strengths are examined to improve our understanding of these systems. Atomic force microscopy (AFM) is now being used to directly measure the interaction forces responsible for the stability of these alkali halide aggregates observed in optical microscopy studies. Results from this study indicate that, while repulsive hydration forces exist between similarly charged hydrophilic particles, attractive forces exist between oppositely charged hydrophilic particles in high ionic strength solutions.

Colloidal Titanium Dioxide Separation from Water by Foam Flotation

ABSTRACT Colloidal titanium dioxide (TiO2) was separated from an aqueous suspension (1000 ppm) by foam flotation using cationic or anionic surfactants. The effects of surfactant dosage, suspension pH value, suspension ionic strength, and gas flow rate on the dispersed-air flotation of colloidal TiO2 were investigated. TiO2 separation was almost complete in optimum conditions. It was found that the coulombic interaction between charged TiO2 particle surfaces and ionic collectors plays a dominant role in this system. Both flotation rate and foamate volume are dependent upon the gas flow rate. Foam flotation may find application in the separation of submicron TiO2 particles in suspend-photocatalyst systems.

Submicron charged dust particle interception by charged drops

This paper presents a numerical algorithm for simulating the trajectories of charged dust particles moving horizontally in the vicinity of a free-falling, oppositely charged liquid droplet. The trajectories are calculated in three-dimensional space relative to the liquid droplet. This approach enables the determination of the envelope of possible trajectories which will result in collection on the droplet. The air drag, electrical, and gravitational forces are taken into account. A number of different models for the air flow around a spherical droplet are compared. The algorithm is used to determine the collection efficiency, according to a newly proposed definition, for a single charged spherical collector.

Interactions between dissimilar surfaces in high ionic strength solutions as determined by atomic force microscopy

The recent non-equilibrium electrophoretic mobility measurements by laser-Doppler electrophoresis coupled with the stability and prevalence of collector colloids in soluble salt flotation systems suggest that the selective flotation of alkali halides is due to the adsorption of oppositely charged collector colloids by heterocoagulation. Previously reported flotation results confirm this surface charge/collector colloid adsorption model. However, the nature of the interparticle forces responsible for heterocoagulation of such oppositely charged particles at high ionic strengths remains to be determined. In this regard, atomic force microscopy was used for interparticle force measurements at high ionic strengths. Model systems such as polystyrene/quartz and silica/sapphire were studied to measure the particle interaction forces prevalent at high ionic strengths. Results from this study indicate that while repulsive hydration forces exist between similarly charged hydrophilic particles, attractive forces exist between oppositely charged particles in high ionic strength solutions. The repulsive forces between similarly charged hydrophilic surfaces at high ionic strengths (2–4 m) are described by a double exponential function with decay lengths of 0.17 and 1.4 nm, depending upon the surfaces involved. On the other hand, attractive forces were observed between oppositely charged hydrophilic surfaces at high ionic strengths (2–4 m) and were described by a single exponential function with decay lengths of up to 9 nm, depending upon the surfaces involved.

Recent contributions to the analysis of soluble salt flotation systems

Abstract The selective separation of alkali halide salts such as KCl from NaCl by flotation in saturated brines (ionic strength ∼ 4 M) is of considerable industrial significance and has been studied by flotation chemists for many decades. Electrokinetic information coupled with the stability and prevalence of certain collector colloids in these soluble salt flotation systems suggest that the selective flotation of alkali halide minerals is due to the adsorption of oppositely charged collector colloids by heterocoagulation. Recent contributions have revealed the nature of the interparticle forces responsible for heterocoagulation of oppositely charged particles at high ionic strengths and the reasons for the deviations of the surface charge of some alkali halides from theory. Because of the progress made in interparticle force measurements at high ionic strengths by atomic force microscopy (AFM), more information is now available and results from recent AFM measurements are reported. Also extension of the simplified lattice ion hydration theory by considering partial hydration of the surface state allows for the prediction of the sign of the surface charge of all alkali halides from first principles. Thus the interactions at high ionic strengths and the deviations of the surface charge of some alkali halides may be explained by structural forces as measured by AFM and the extended lattice ion hydration theory, respectively.

Deposition of aerosol particles on a charged spherical collector

A numerical model for determining the trajectories of a spherical aerosol particle in the vicinity of a spherical collector is presented. The Coulomb, image, Stokes, inertial and gravitational forces acting upon the particle and the collector are taken into consideration in the equations of motion. The system of equations is solved in 3-D space. The flow field in the vicinity of the collector is determined by numerical solution of the Navier-Stokes equations. The examples of aerosol particles' trajectories are presented for a few values of the Coulomb and Reynolds numbers.