Fig 23 - uploaded by Svetlana Kojevnikova
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A plot of the minimum number of rows required for complete interception of 10 m aerosol trajectories, and their subsequent collection by 200 m drops (a) as a function of !Qq; (b) as a function of B/D . 151;151 array, z "0.61 m.
Source publication
The collection mechanism of charged aerosols by a two-dimensional array of oppositely charged drops is conisdered. Trajectories of aerosols are computed, using a new simulation program, under conditions of gravity sedimentation of the collecting drops and aerosols. Electric forces, given in spherical coordinate system of each drop, are projected on...
Citations
... The analysis of particle trajectories and the demonstrated improvement in the effectiveness of spherical charged collectors as collection devices have been extensively validated, both theoretically [15][16][17][18][19][20][21][22][23][24][25][26][27] and experimentally [9,[28][29][30][31][32][33][34][35][36][37][38][39][40]. Given the comprehensive literature mentioned above, it is crucial to conduct a thorough review and exploration of the most relevant literature that has made significant contributions to this field. ...
... However, in contrast to their previous work [17], the flow field in the vicinity of the collector is determined by numerically solving the Navier-Stokes equations rather than using a creeping flow approximation. Simultaneously, Kojevnikova and Zimmels [19] conducted an analysis on the trajectory of charged aerosols captured by a two-dimensional array of sedimenting charged spherical droplets. The study utilized an in-house developed code and approximated the air flow using a creeping flow model. ...
This study investigates particle dynamics impacting a charged spherical collector through experiments and simulations, revealing the influence of the collector’s non-uniform potential field. Electrostatic and drag forces govern trajectories, while gravity and dielectrophoretic forces play a minor role. Positive electrostatic and negative drag work are comparable, offering critical insights into particle energy budgets. Closer proximity to the collector center leads to a greater energy budget, causing uneven particle collection. Analysis of fractional energy loss indicates a critical point where electrostatic work dominates over viscous dissipation. This analysis is crucial for analyzing particle deposition behavior in non-uniform electric fields.
... The analysis of particle trajectories and the demonstrated improvement in the effectiveness of spherical charged collectors as collection devices have been extensively validated, both theoretically [15][16][17][18][19][20][21][22][23][24][25][26][27] and experimentally [9,[28][29][30][31][32][33][34][35][36][37][38][39][40]. Given the comprehensive literature mentioned above, it is crucial to conduct a thorough review and exploration of the most relevant literature that has made significant contributions to this field. ...
... However, in contrast to their previous work [17], the flow field in the vicinity of the collector is determined by numerically solving the Navier-Stokes equations rather than using a creeping flow approximation. Simultaneously, Kojevnikova and Zimmels [19] conducted an analysis on the trajectory of charged aerosols captured by a two-dimensional array of sedimenting charged spherical droplets. The study utilized an in-house developed code and approximated the air flow using a creeping flow model. ...
... For opposite-polarity, charged-droplets and charged-particles WES, particles deposit onto the droplet due to electrostatic attraction forces. Many studies, including numerical simulations (Pilat et al. 1974;Wang et al. 1986;Jaworek et al. 1997Jaworek et al. , 2002Kojevnikova and Zimmels 2000;Yang et al. 2003;Zhao and Zheng 2008;Carotenuto et al. 2010) and experimental tests (Kraemer and Johnstone 1955;Balachandran et al. 2003;Jaworek et al 2006b;Krupa et al. 2013), suggest that droplet-target deposition of the particles is more effective. One important reason is that the distances of deposition from particles to droplets are much closer than to chamber walls, closer distance in turn strengthens the electrostatic attractions. ...
Particles deposited on a free-fall charged droplet were experimentally studied. A droplet, charged under 40% Rayleigh limit, fell through the particle chamber to capture particles by electrostatic attractions. The velocity of the droplet was smaller than 2.1 m/s. The particle-laden droplet eventually spread on a glass slide, which was further analyzed using optical microscope. It was found that the equivalent number of particles captured by the charged droplet were larger than that of uncharged ones by one order of magnitude at least. Remarkably, particles on the charged droplet agglomerated into a large cluster, which indicates that the agglomerated cluster can be actively precipitated due to the gravity force if the droplet completely evaporates. The front side of the charged droplet was the predominant region to capture the particles. However, the actual area of capture was smaller than hemispheric surface.
Copyright © 2017 American Association for Aerosol Research
... and was close to about 185 nm. The obtained value of h resulted from the particles deposition due only to hydrodynamic and image-charge forces among charged droplets and non-charged particles [19,27,[34][35][36][37]. However, since the hydrodynamic mechanisms were the same as for uncharged spray, they did not appear to have a significant role in the particle capture when electrostatic forces operate, and the removal efficiency obtained with the CDES configuration should be only related to electrostatically driven particle capture mechanisms. ...
This paper presents experimental results obtained with a prototype of wet electrostatic scrubber suitably designed to remove fine and ultrafine particles from exhaust gases. Experiments were carried out on a model combustion gas containing particles with diameters from 10 to 450 nm, which can be negatively charged in a specially designed corona charging unit. A full-cone spray nozzle with induction electrode was used to generate positively-charged water droplets (5% of the Rayleigh limit) with a mean diameter of about 290 μm. The particles removal efficiency was determined for different magnitudes of electric charges on particles and droplets and for two values of liquid-to-gas ratio, equal to 0.88 and 1.15. The experiments revealed that when both particles and droplets were left uncharged, the removal efficiency was very small. When only droplets were charged, the efficiency was of about 35% in number. The highest efficiency, overcoming 91%, was achieved when both particles and droplets were oppositely charged.
... In order to optimize the electroscrubbing process, the process is considered as a two-body system of a single droplet and a spherical particle, and the electrostatic interaction between the particle and droplet is included to the equations of motion of the particle, which is solved by the assumption that the particle is much smaller than the droplet and other charged particles and droplets are sufficiently far to exert any force on these both. In another approach, the collective effects of interaction between charged particles and charged droplets have been considered by Kojevnikova and Zimmels [2000], while statistical approach has been proposed by Carotenuto et al. [2009Carotenuto et al. [ , 2010. ...
... Jung and Lee [33] adopted this model for the determination of collection efficiency of multiple spheres, but without consideration of the electrostatic effects. Complex numerical model has been developed by Kojevnikova and Zimmels [37,38,90]. The collection for a single particle was determined in a regular two-or three-dimensional set of stationary collectors. ...
New regulations regarding the PM1 emission by power plants and transport vehicles require novel technical solutions for the abatement of particulate matter emission in submicron size range. Particles of this size are difficult to remove by conventional methods, and therefore various variants of wet electrostatic scrubbers have been developed. In such devices, the electrostatic forces between charged particles and collectors (water droplets) are used to permanently remove them from the gas. The paper focuses on the state-of-the-art of wet electrostatic scrubbing technique used for the removal of submicron particulate matter from exhaust gases with particular emphasis upon marine Diesel engines.
... Meanwhile, another complication is that an array of spray nozzles is often required to control fugitive dust emission instead of a single nozzle. Kojevnikova and Zimmels have provided a comprehensive simulation of aerosol collection by an array of oppositely charged drops in two-and three-dimensional space [11,12]. They suggested that the collection efficiency of high-inertia aerosols would correspond to the number of rows of water arrays while the collection efficiency of low-inertia aerosols would be proportional to the collection radius and distance between the aerosols and the droplets. ...
... For the system consisting of a nozzle which could generate water droplet with a size range of 80-100 m, a maximum removal efficiency of about 17% could be realized. As also confirmed by the experimental results, Type 1 nozzle which could generate smaller droplets could provide a higher removal efficiency, Á total when compared with Type 2 nozzle [11]. Anyway, it should be noted that Á total is significantly lower than Á c0j . ...
A deterministic model to predict the inertia-interceptional dust removal efficiency of open-space water spraying is developed based on momentum and mass balances of water droplets and dust particles. The effect of polydisperse dust particles and water droplets generated by different nozzles on the total removal efficiency (ηtotal) is examined. The small water droplets with narrower distribution could provide the acceptable removal of dust particles while the relatively large dust particles also provide the large ηtotal value. The ηtotal predicted by the developed model is in the range of 19.6–23.8% with a relative error of 2% when compared with the measuring data. The ηtotal with the use of polydispersity of water droplets and dust particles is more accurate than that with the use of average size of water droplets and dust particles.Graphical abstractDependence of total dust removal efficiency upon water droplet and dust particle size within the simulated boundary.Research highlights▶ We developed a deterministic model to predict the inertia-interceptional dust removal efficiency of open-space water spraying. ▶ The effect of polydisperse dust particles and water droplets generated by different nozzles on the total removal efficiency is examined. ▶ The total removal efficiency predicted by the developed model is in the range of 19.6 to 23.8% with a relative error of 2% when compared with the measuring data.
... Theoretical results [17][18][19][20][21][22][23][24] and proofs-of-concept [25][26][27][28][29][30][31][32][33][34] of the potentialities of the wet electrostatic scrubbing can be found in literature mainly for the case of micrometric size particles. ...
Water electrostatic scrubber (WES) represents an alternative technology for the abatement of that submicronic fraction of particulate – belonging to the so-called Greenfield gap – usually hardly captured with other cleaning techniques. The promising potentialities of WES are recognized by the scientific and industrial communities, but the design of this kind of reactor is far from being optimized.This work reports a mathematical model to evaluate the particle removal efficiency in wet electrostatic scrubbers. The model is used to find out optimal working condition of WES units, through the maximization of the particle collection efficiency in function of different process parameters: contact time, specific water consumption, water/gas relative velocity, size and charge of sprayed droplets. The model has been validated by comparison with different experimental data available in literature, both for charged and uncharged scrubbers. Then it is applied to a reference case study to obtain generalizable results.The model shows that the process optimization for micronic and submicronic size particles follows different criteria. For micronic particles, the collection efficiency increases for higher water/gas relative velocity, with a small effect of droplet diameter and a moderate increase with the droplet charge. On the contrary, in the Greenfield gap, the water/gas velocity plays a secondary role in the capture mechanisms, while a substantial increase of collection efficiency by improving the droplet charge level and reducing the droplet size has been observed.With reference to the actual performances of water spraying and charging devices, the model predicts that a collection efficiency as high as 99.5% can be reliably obtained in few seconds with a water consumption of 100ml/m3 by adopting droplet diameters around 100μm and charge to mass ratio from 1 to 3mC/kg, corresponding to droplet charge equal to 10–30% of Rayleigh limit.
... However, these models are limited to a set up such as a few spherical or cylindrical collectors, arranged in line. Recently, the collection of aerosols by arrays of larger drops was studied by simulation of their trajectories [13,14]. Intricate trajectories and unexpected collection patterns were found and the meaning of collection efficiency was revised accordingly. ...
... The numerical solutions were obtained by the Runge-Kutta routine which was also used elsewhere to solve intricate aerosol trajectories in arrays of charged collecting drops [13,14]. The time step, set initially at dt = 2 × 10 −5 s, was adjusted in order to match changes in velocity along the trajectory, and thus expedite calculations at the same level of accuracy. ...
Self-expansion patterns of unconstrained assemblies of charged particulates are simulated by solution of their individual trajectories. The general behaviour of these systems is considered regarding their expansion shape and structure. As the particulates cannot be described, in general, in terms of massless charged entities, the complete equation of motion, inclusive of the inertial and other size effects, must be applied to each and every member of the assembly. It is shown that irrespective of the initial position of the particulates and the time dependent shape of the assembly, when expanding in free space or else the particulates are identical in size, shape and mass, they self-expand asymptotically into a circular or spherical shape with an inner structure that tends to uniformity. This behaviour persists irrespective of the size and charge level of the particulates, or whether they form a single or multiple separate groups in one, two and three dimensions. In this context, ionic gaseous assemblies that fit into the realm of continua, are included. Two- and three-dimensional examples of simulation outputs for different particulate assemblies, illustrate typical self-expansion patterns. Internal structures that evolve in two-dimensional self-expanding arrays are shown to be different compared to those obtained in three dimensions. These simulations show that models of particle capture by random self-expanding arrays of charged particulates, may lack physical grounds, as they contradict the asymptotic mode of uniform and ordered self-expansion that is expected from the array.
... on charged particles. Charging of suspended particles by ions up to controlled mobilities in APED is used for size measurement [5-7, 136-138, 141,142], for self-repulsion to preserve high interfacial areas [12,284,296], as well as for coulombian agglomeration of bipolar aerosols for filtration [297][298][299][300][301][302], powder production [303] and particle coating [245]. Indeed, the coagulation of charged aerosols has been shown to be suitable for the production of composite and coated particles [10,118,131,287]. ...
This review addresses the production of nano-particles and the processing of particles injected in atmospheric pressure electrical discharges (APED). The mechanisms of formation and the evolution of particles suspended in gases are first presented, with numerical and experimental facilities. Different APED and related properties are then introduced for dc corona, streamer and spark filamentary discharges (FD), as well as for ac filamentary and homogeneous dielectric barrier discharges (DBD). Two mechanisms of particle production are depicted in APED: when FD interact with the surface of electrodes or dielectrics and when filamentary and homogeneous DBD induce reactions with gaseous precursors in volume. In both cases, condensable gaseous species are produced, leading to nano-sized particles by physical and chemical routes of nucleation. The evolution of the so-formed nano-particles, i.e. the growth by coagulation/condensation, the charging and the collection are detailed for each APED, with respect to fine powders production and thin films deposition. Finally, when particles are injected in APED, they undergo interfacial processes. Non-thermal plasmas charge particles for electro-collection and trigger heterogeneous chemical reactions for organic and inorganic films deposition. Heat exchanges in thermal plasmas enable powder purification, shaping, melting for hard coatings and fine powders production by reactive evaporation.
