Multifield modeling of particle dynamics in an electrostatic precipitator equipped with pointed-end arista on corona

Journal Pre-proof Multifield modeling of particle dynamics in an electrostatic precipitator equipped with pointed-end arista on corona

Yongqi Tong, Lin Zhang, Shi Bu, Fangyi Chen, Weigang Xu, Ran Wu, Lin Liu, Yushan Xu PII:

S0032-5910(19)31116-7

DOI:

https://doi.org/10.1016/j.powtec.2019.12.016

Reference:

PTEC 15022

To appear in:

Powder Technology

Received date:

24 August 2019

Revised date:

27 November 2019

Accepted date:

8 December 2019

Please cite this article as: Y. Tong, L. Zhang, S. Bu, et al., Multifield modeling of particle dynamics in an electrostatic precipitator equipped with pointed-end arista on corona, Powder Technology(2019), https://doi.org/10.1016/j.powtec.2019.12.016

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© 2019 Published by Elsevier.

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Multifield modeling of particle dynamics in an electrostatic precipitator equipped with pointed-end arista on corona Yongqi Tonga, Lin Zhanga,b,* , Shi Bua,b,c, Fangyi Chena, Weigang Xua,b , Ran Wua, Lin Liua,b , Yushan Xuc School of Mechanical Engineering, Changzhou University, Changzhou 213164, China;

b

Jiangsu Key Laboratory of Green Process Equipment, Changzhou University, Changzhou, China;

c

Kerui Sampling Equipment Co., Ltd, Zhenjiang, China.

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a

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Abstract: Electrostatic precipitator (ESP) is widely applied in dust removal of fine particulates. An

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multi- field coupling model of ESP is summed up, which equipped with pointed-end arista on

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corona. First, a computation work is carried out prior to compare the separation performance of two kinds of electrodes, and the result obviously shows that arista electrode performs better. Then, the

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adopted corona is installed in a honeycomb test section for measurement. Influences of EHD flow,

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supply voltage, gas velocity and particle diameter upon separation efficiency are investigated in

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detail both in computation and measurement. The result implies that separation increase linearly with enhancing supply voltage ranges from 10kV to 50kV and particle diameter ranges from 1μm to 5μm. When particle diameter is larger than 5μm, separation efficiency is up to nearly 100% and barely affected. EHD flow has an significant positive influence on particle motion for particulates smaller than 5μm in low gas velocity. Whereas separation efficiency drops with the rising gas velocity. Keywords: ESP; multi- field; arista electrode; separation efficiency; EHD flow.

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1.

Introduction Atmospheric pollution has always been an issue in the process of industria lization, where fine

particulates need to be addressed very carefully since they are harmful to ecological environment and human health. ESP technique sees a wide application in many areas like chemical engineering, power generation, metallurgy, et al. to remove particle pollutants from exhaust gases. The currently

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used precipitator can separate large particles from gas flow efficiently, however, they lack the

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ability to handle very fine particles which are usually defined to be smaller than 10μm. Therefore, it

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is urgent to make modifications to the present separation devices in order to meet the real needs.

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ESP has long been an area of intense research due to its increasing predominance in separation

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and purification industry. Performance of an ESP is influenced by several factors including electrode configuration, discharge voltage, gas flow velocity and particle concentration, which have

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been the topics of many researchers. Published literatures have shown that several types of

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electrodes have been proposed among which arista is considered to be the best, because the strong

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and uniform electric field produced by arista can accelerate the particles and make them move toward collector more efficiently [1-3]. It has been proved by Miller et al. [4] that field strength can be increased with longer discharge needles or smaller distance between adjacent needles, they have also found that optimal separation efficiency can be obtained if inter-needle spacing is half the distance between plates. Bologa et al. [5] proposed a star-shaped electrode which can create a strong electric field at lower voltage. Kaci et al. [6] measured the electric field between a wedge and a flat plate, they noticed that corona current can be large and stable when distance between plates is much larger than that between electrodes. Kasdi [13] carried out an investigation on the performance of a wires-to-plate precipitator and noticed that discharge effect improves with wider spacing and

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smaller diameter of coronas. Most researchers have paid attention to linear electrode arrays, although some complicated electrodes have been explored, simplifications were consistently employed which ignored field details. In fact, geometry of corona electrode, namely, shape, length and angle affect the field characteristic and separation efficiency of a precipitator. Besides, corona discharging is influenced

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by other parameters including temperature and humidity of air, gas flow velocity, particle

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concentration and pressure. These parameters must be determined carefully in order to obtain a

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desired field strength, current density or charge density distribution, which helps improve separation

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performance [7, 8]. Noll [9] showed that corona current increases with rising temperature and that

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negative corona is more affect by temperature than positive corona. It has to be mentioned that negative corona has more applications than positive corona since it owns a higher discharge

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efficiency [10, 14]. Bian et al. [11] proved that corona inception voltage decreases with increasing

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humidity or lower air pressure. Nouri et al. [12] found that discharge effect gets better at low

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voltage, while it gets worse at high voltage with the increase of humidity. Patiño et al. [14] measured the electric field inside a new type tubular ESP and their observation indicated that decreasing electrode diameter or humidity leads to stronger corona current. Yan et al. [15] studied the influence of charge characteristic upon corona discharging process, they showed that increasing negative electricity makes it easier for gas molecules to absorb free electrons, hence the migration rate of electrons decreases leading to lowered corona current. Octavian et al. [16] used a variable diameter tube ESP to improve particle separation efficiency. Hamouz e t al. [17] analyzed energy loss in a tube ESP, they concluded that radius and spacing of electrodes, gas velocity and charge characteristic can affect the electric field and energy loss in the precipitator. Villot et al. [18]

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investigated electric field and particle separation efficiency under different gas velocity, pressure and composition. Niewulis et al. [19] measured flow field in a small tube ESP with PIV (Particle Image Velocimetry) and examined the effect of gas flow on the separation efficiency. Sa id et al. [20] compared the discharge characteristics of positive and negative electrodes under different gas velocities, they concluded that gas flow field around electrodes has an effect on the separation

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performance.

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The authors have noticed that, previous studies have concentrated on large particles or certain

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kinds of aerosols like water droplets, sulfur oxides and nitrogen oxides. However, there is just a few

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of reports on separation of very fine particles (usually less than 10μm), especially metallic oxides

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which are often seen in industrial exhaust gases. In this work, an experiment was conducted to investigate the separation performance of fine particles ranges from 1 to 10μm, the ingredients of

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particles consist of various metallic oxides. Before measurement, a computational work was carried

Experimental apparatus and methods

2.1. Test facility

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2.

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out to compare the performances of two kinds of arista electrodes in terms of separation efficiency.

The separation experiment was conducted on the electrostatic test facility in Jiangsu Key Laboratory of Green Process Equipment in Changzhou University, presented by Fig. 1. Gas flow is driven by a blower which has a maximum flowrate of 860m3 /h. Particles are supplied by an aerosol generator (Type RGB-1000) which uses a high-speed atomizer to realize a complete mixing. Measurement of particle mass flowrate and concentration can also be done by the generator. The particle diameter spectrometer (Type TSI 3330), applying single particle counting technique achieved by 120° light scattering and filter sampling, has 16 adjustable channels, by which the

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concentration of particles with set diameters can be measured at the same time. The particle properties including materials and size distributions will be discussed in the follow up section. The two-phase flowrate is then measured by a flowmeter to the downstream of the generator, hence the mean velocity at the inlet of the honeycomb tube can be calculated. The flowmeter is impeller type, whose impeller can rotate with the airflow and the rotating speed can be converted into gas velocity.

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The particle collector (Wall of honeycomb tube) is made from stainless steel. The corona also made

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of stainless steel is connected to a DC supplier via an insulating ceramic rod. The arista applied in

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this work is asymmetric arranged pointed end arista with the tip angle of 15°, which is an optimal

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structure obtained by our other work, as shown in Fig.2. The supplier provides a negative voltage

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ranging from 0 to 50kV.

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2.2. Particle properties

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Light hollow microspheres with good fluidity are adopted as working particulates in this

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experiment. The main components of particles are SiO 2 , Al2 O 3 and Fe2 O 3 . Specific chemical compositions are listed in Table 1. The diameter of particulates generated by the aerosol maker ranges from 0.1 to 100μm, yet in this experiment a particle diameter spectrometer (Type TSI 3330) with 16 channels is used which has a measurement range of 0.3 to 10μm. The measured size distribution at the tube’s inlet is displayed in Fig. 3 Separation efficiency of particles in the range of 0.3 to 10μm is of the interest of this research.

2.3. Data processing Separation efficiency of particles of any size can be calculated using the following equation:

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i =(1-

 i,out ) 100%  i,in

(1)

Where ω is the quantitative concentration of particulates, i indicates the ith group of particle diameter, in and out means the inlet and outlet of honeycomb, respectively. The overall separation efficiency η is determined by considering the performance of all kinds of particle sizes within the measured range of 0.3 to 10μm using the following formula: d p ,i 3



3

i , out

i 1 16

i ,in

d p ,i

(2)

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i 1

) 100%

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 =(1-



f

16

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Where dp is particle diameter. Equation (2) implies that the overall separation efficiency account for the mass of the particulates.

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2.4. Uncertainty analysis

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Moff at [21], which is defined as:

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An uncertainty analysis for the measurement is carried out using the method developed by

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e



n i 1

W 2 xi xi

(3)

where e is the measurement uncertainty, W is the estimated parameter, x and Δx are the independent parameter and its associated uncertainty, respectively. The estimated parameter W of this paper is particle separation efficiency. The independent parameters are supply voltage, gas velocity and particle diameter, respectively. In Table 2, the main specification and calculated uncertainty of the measurement instrument is listed. The uncertainty of separation efficiency is thus estimated to be 5.0%.

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3.

Computation

3.1. Multi-field coupling The process of collecting particulates inside the ESP is a process of multi- field coupling, which includes the electric field, airflow field and particle motion field. Fig. 4 shows the coupling relationship of the multi field. The electric field affects the particle motion field via the electric field

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force and ion charge. The ion wind, which also called EHD flow will be discussed in the follow

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sections, generated by the electric field effects the airflow field. The airflow field influences the

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electric field by the ion convection and the particle motion field by the air drag at the same time.

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The particle motion field reacts to the electric field through the space charge, and affects the airflow

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3.2. Geometry and computational mesh

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field through the gas phase and solid phase coupling.

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Since the interaction of multi- field coupling determines the separation of particles inside the

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ESP, in this study, the finite element software COMSOL is employed to analysis the coupling relationship and influences inside the ESP. A honeycomb tube is taken as the study object, the geometry of which is shown in Fig. 5(a), the length and width of each side of the tube are 1500mm and 100mm, respectively. Fig. 5(b) displays the grids of honeycomb tube. The maximum size of grids is 0.018m, and the minimum is 0.0012m. The maximum grid growth rate is 1.5, and the curvature factor is 0.6. The total number of grids is 418,972. The mesh average quality is 0.8946 and the minimum quality is 0.3745.

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3.3. Boundary conditions To obtain credible computational results, reasonable boundary conditions must be imposed to the domain. In this work, since the diameter of regular spherical particles is relatively larger, only electric field charge is considered. The effect of Brownian motion and the disappearance of electric charge causing by collision of charged particles are ignored. The fluid is assumed to be

continuous phase are set to be speed entry boundary and pressure exit boundary ,

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exported

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incompressible, and the distribution of gas flow at the inlet to be uniform. The imported and

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respectively, both of which particle phase are set to escape. That of dust collector and corona is set

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to adhere and reflex, respectively. The physical parameters of air and particulates are listed in Table

Results and discussions

4.1. Effect of EHD flow

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The EHD (electrohydrodynamic) flow, which also called ion wind or secondary wind, is caused by the collision of air flow and lots of ions generated by corona discharge. The internal flow field is in a uniform laminar flow state when there is no voltage applied. With the strengthening supply voltage, the current brought about around corona will yield EHD flow vertical to the air flow as well, which has an influence on the internal flow field. Fig. 6 shows the whole flow streamline under different gas velocities. It can be seen from the figure that when the gas velocity is 0.5m/s, a pair of reverse vortex occur at corona pole. With the growing gas velocity, the vortexes fall off gradually. It is evident that EHD flow has a significant influence on air flow field when the gas velocity is relatively low. With the increase of gas velocity, the effect of EHD flow declines

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gradually till it can be ignored when gas velocity arrives at 2.5m/s. This is because when the air runs at a low speed, EHD flow which is directed from corona to collector can easily disturb air flow, thus vertex formed. When the air runs at a high speed, since the interference ability of EHD flow remains constant for unchanged supply voltage, the enhancing dominant of air flow is less affected. When the air velocity is high enough, the effect of EHD flow can be ignored.

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A computation work is carried out to obtain the effect of EHD flow on separation efficiency

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under different particle diameter, the result of which is shown in Fig. 7 As can been seen from the

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figure that the separation efficiency increases 17.1%, from 63% to 81.9% when particle diameter is

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1μm. With the increasing of particle diameter, the effect of EHD flow falls off till can be ignored at

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the particle diameter of 5μm. This is because particulates around the vortex caused by EHD flow are retarded thus particle residence time extended. Therefore, more particulates migrate to the dust

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collector and separation efficiency increases. When the particle diameter is larger enough which is

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without EHD flow.

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5μm in this case, all particles are captured by dust collector and there is no difference of with or

4.2. Effect of supply voltage

A computation work is carried out first to compare the performance of two kinds of electrode under different supply voltages, named arista electrode and rod electrode, respectively. As can be seen from Fig. 8 that arista electrode perform better than rod electrode obviously, which is because arista electrode has better corona discharge ability. Arista electrode is chosen for further study.

Fig. 9 shows the trajectory diagram of particles under different supply voltages. It can be seen from the figure that more number of particles move to the dust collector and fewer time needed to

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be trapped as supply voltage increasing. This is because higher supply voltage generate stronger electric field strength, under which particles receive stronger electric field force. Thus particulates gain higher drive speed towards the collector.

Fig. 10 shows the separation efficiency under different supply voltages in computation. Separation efficiency of particles of all particle diameter significantly increases with enhancing

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supply voltage, and the increasing rate of separation efficiency slowed down at higher voltage. This

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is because more energy is needed if further improvement in separating performance is demanded.

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To verify the accuracy of computation work, Fig. 11 shows measured particle number concentration under different supply voltages, from which measurement separation efficiency can

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be calculated. The measurement separation efficiency of particles with particle diameter of 1μm and

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gas velocity of 0.5m/s under different supply voltage calculated from Fig. 11 and that of

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computation are put together for a comparison in Fig. 12. As can be seen from the figure that the

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computation and measurement separation efficiency both increase with the enhancing supply voltages, which agrees with the result of Fig. 10 The measured separation efficiency increases from 16.3% to 55.6%. The difference between measurement and computation ranges from 8.6% to 15%. This is because secondary dusting phenomenon causes an decrease in measured separation efficiency. The discrepancy becomes lager as supply voltage enhancing. This is because the number of particulates captured by collector growing with the rising supply voltage will also lead to an increasing number of particulates mixed back to main airflow due to secondary dusting phenomenon.

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4.3. Effect of gas velocity A computation work is carried out first to compare the performance of two kinds of electrode under different gas velocities , named arista electrode and rod electrode, respectively. The maximum gas velocity is limited to 2.5m/s according to industrial application experience value, which is 0.5m/s-2.5m/s. Moreover, higher gas velocity means shorter resistance time for

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particulates, which leads to a reduction in the separation efficiency collection. As can be seen from

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Fig. 13 that arista electrode perform better than rod electrode obviously still. Arista electrode is

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chosen for further study.

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Fig. 14 shows trajectory diagram of particles under different gas velocities. As can be seen

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from the figure that particle resistance time becomes shorter and less particles are captured by the dust collector and as gas velocity increases. This is because under the same supply voltage particles

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receive constant horizontal electric field strength, thus as particle resistance time becomes shorter

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with increasing gas velocity, more particles are taken out of the collector by the airflow and less

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particles which are originally closer to the collector are captured. It is clear that the particle separation drops with rising gas velocity. Fig. 15 shows the curve of particle separation efficiency as a function of gas velocity under different supply voltage and particle diameter. As can be seen from the figure that particle separation efficiency drops as excepted with rising gas velocity under all kinds of supply voltages and particle diameters. Declining trend is more obvious under high supply voltages and less with larger particle diameter. This is because particulates suspended in gas are running with the main airflow, lower gas velocity means longer resistance time inside the tube for particulates, during which more collisions between particles and free electrons occur leading to more fully charge. Due

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to the stronger electric field strength received by particles, the migration of particles is larger and more particles captured by the collector, which means higher separation efficiency. Instead, higher gas velocity leads to higher turbulent energy inside the tube, and the friction received by particles already adhere to the dust collector becomes larger. When the friction increase with rising gas velocity up to stronger than adsorption force, particulates will back mixed into main airflow leading

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to lower separation efficiency, which called secondary dusting.

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To verify the reliability of computation, measurement separation efficiency under different gas

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velocity at 50KV supply voltage and particle diameter of 1μm are obtained via experiment. Fig. 16

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shows the comparison of computation and measurement. As ca n be seen from the figure that the

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trend remains same and agrees with the result in Fig. 15 The error between computation and measurement ranges from 8.5% to 14.3%, which matches well. The measurement separation is

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lower than that of computation. This is because some particulates captured by dust collector are

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blow off again by main airflow and mixed back into gas then taken out of the device. Nevertheless,

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secondary dusting phenomenon is ignored in computation work, which causes computation separation efficiency higher than that of measurement.

4.4. Effect of particle diameter A computation work is carried out first to compare the performance of two kinds of electrode under different particle diameters , named arista electrode and rod electrode, respectively. As can be seen from Fig. 17 that arista electrode perform better than rod electrode obviously still. Arista electrode is chosen for further study. Fig .18 shows the trajectory diagram of particles under different particle diameter when supply

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voltage is 50KV and gas velocity is 0.5m/s. As can be seen from the figure that more particles are captured by collector with larger particle diameter and all particulates are captured when particle diameter is larger than 5μm. In the case of dp =3μm, nearly all particulates arrives at the collector. With the diameter increasing up to 7μm, all particulates are captured, which also shows that larger diameter leads to higher particle separation efficiency. This is because larger particles can charge

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velocity, larger particulates are easier to be captured.

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more thus received stronger electric field force. Therefore, with same supply voltage and gas

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Fig. 19 show the computation separation efficiency under different supply voltages, gas

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velocities and particle diameters. As can be seen from the figure that at all supply voltages and gas

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velocities separation efficiency rising with the increasing particle diameter. The rising trend slow down when particle diameter is larger than 5μm, and achieve 100% when gas velocity is 0.5m/s and

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supply voltage is 50kV. This because when separation is higher than 90%, the effect of particle

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diameter is small. Lager particle charge more and receive stronger electric field strength thus easier

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to be captured leading to higher separation efficiency, which agrees Fig. 18. To verify the reliability of computation work, an experiment is carried out to obtain measurement separation efficiency, which are shown in Fig . 20 for a comparison. As can be seen from the figure that measurement separation efficiency rising with the increasing of particle diameter, which agrees with the result of computation. The error between computation and measurement ranges from 8.7% to 15.2%, which is acceptable, and computation separation efficiency is higher than that of measurement. This is because small release charge after reaching dust collector, then mix back into the main airflow soon and taken out of device eventually, which cause a decrease in separation efficiency. Only adhering of particles is considered and secondary

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dusting phenomenon during the dust removal process is ignored in computation, which leads to a computation separation efficiency higher than that of measurement.

5.

Conclusions A systematic investigation on the separation of fine particulates and multifield modeling of

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particle dynamics in an electrostatic precipitator equipped with pointed-end arista on corona is

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carried out experimentally and numerically. An multifield modeling is summed up. Influence of

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supply voltage, gas velocity and particle diameter on separation efficiency of particle is studied

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through measurement and computation. Besides, effect of EHD flow on separation efficiencies is

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studied. The conclusions are summarized as follows:

1. EHD flow has a significant influence on air flow field when the gas velocity is relatively low.

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With the increase of gas velocity, the effect of EHD flow declines gradua lly till it can be

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ignored. EHD flow mainly has an positive influence on particulates smaller than 5μm.

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2. With enhancing supply voltage, the electric field is strengthened, leading to an improved separation efficiency because of stronger driving force from e lectric. The increasing rate of separation efficiency slowed down at higher voltage, indicating more energy is needed if further improvement in separating performance is demanded. 3. Particle separation efficiency drops with the rising gas velocity because of shorter particle resistance time. Moreover, high gas velocity will cause secondary dusting, which will lower particle separation efficiency. 4. For very fine particulates ranges from 1μm to 10μm in the present study, separation efficiency is within the range of 38% to 75% under the voltage of 30kV and inlet velocity of 0.5m/s. Since

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larger particles are easier to be collected by ESP because of stronger electric driving force, it is suggested to employ coagulation procedures to improve separation performance. Acknowledgment This work is funded by Projects of Jiangsu Provincial Six Talent Peaks (Grant No.GDZB-CXTD-001), Key R&D Project of Changzhou City (Grant No. CE20180322), Key R&D

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Program of Dantu District of Zhenjiang City--Industry Prospect and Common Key Technologies

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(Grant No. GY2018006) and National Natural Science Foundation of China (Grant No. 51606014).

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They are gratefully acknowledged.

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Declaration of interests

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The authors declare that they have no known competing financial interests or personal

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Reference

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relationships that could have appeared to influence the work reported in this paper.

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[4] J. Miller, B. Hoferer, A. J. Schwab. The Impact of Corona Electrode Configuration on electrostatic precipitator Performance. Journal of Electrostatics 44 (1998) 67-75. [5] A. Bologa, H. R. Paur, H. Seifert, T. Wascher, K. Woletz. Novel wet electrostatic precipitator for collection of fine aerosol. Journal of Electrostatics 67 (2009) 150-153. [6] M. Kaci, H. Said. An Investigation on the corona discharge in blade-to-plane electrode

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configuration. Brazilian Journal of Physics 45 (6) (2015) 643-655.

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[7] T. Czech, A. T. Sobczyk, A. Jaworek, A. Krupa. Corona and back discharges in flue- gas

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simulating mixture. Journal of Electrostatics 70 (2012) 269-284.

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[8] K. Yanallah, F. Pontiga, Y. Meslem, A. Castellanos. An analytical approach to wire-to-cylinder

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corona discharge. Journal of Electrostatics 70 (2012) 374-383. [9] C. G. Noll. Temperature dependence of dc corona and charge-carrier entrainment in a gas flow

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channel. Journal of Electrostatics 54 (2002) 245-270.

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[10] J. C. Matthews. The effect of weather on corona ion emission from AC high voltage power

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lines. Atmospheric Research 113 (2012) 68-79. [11] X. M. Bian, X. B. Meng, L. M. Wang, J. M. K. MacAlpine, Z. C. Guan, J. F. Hui. Negative corona inception voltages in rod-plane gaps at various air pressures and humidities. IEEE Transactions on Dielectrics and Electrical Insulation 18 (2011) 613-619. [12] H. Nouri, N. Zouzou, E. Moreau, L. Dascalescu, Y. Zebboudj. Effect of relative humidity on current- voltage characteristics of an electrostatic precipitator. Journal of Electrostatics 70 (2012) 20-24. [13] A. Kasdi. Computation and measurement of corona current density and V-I characteristics in wires-to-plates electrostatic precipitator. Journal of Electrostatics 81 (2016) 1-8.

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[14] D. Patiño, B. Crespo, J. Porteiro, E. Villaravid, E. Granada. Experimental study of a tubular-type electrostatic precipitator for small-scale biomass boilers. Preliminary results in a diesel engine. Powder Technology 288 (2016) 164-175. [15] P. Yan, C. H. Zheng, W. Z. Zhu, X. Xu, X. Gao, Z. Y. Luo, M. J. Ni, K. F. Cen. An experimental study on the effects of temperature and pressure on negative corona discharge in

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high-temperature electrostatic precipitators. Applied Energy 164 (2016) 28-35.

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[16] B. Octavian, N. V. Petru, D. L. Marius. Experimental Study of the Corona Discharge in a

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Modified Coaxial Wire-Cylinder electrostatic precipitator. IEEE Transactions on Industry

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Applications 46 (1) (2010) 3-8.

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[17] Z. Al-Hamouz, A. El-Hamouz, N. Abuzaid. Simulation and experimental studies of corona

22 (2011) 706-714.

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power loss in a dust loaded wire-duct electrostatic precipitator. Advanced Powder Technology

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[18] A. Villot, Y. F. J. Gonthier, E. Gonze, A. Bernis. Numerical Model of Current–Voltage Curve

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for the Wire-Cylinder electrostatic precipitators in Negative Voltage in the Presence of Nonpolar Gases. IEEE Transactions of Plasma Science. 38 (8) (2010) 2031-2040. [19] A. Niewulis, A. Berendt, J. Podlinski, J. Mizeraczyk. Electrohydrodynamic flow patterns a nd collection efficiency in narrow wire-cylinder type electrostatic precipitator. Journal of Electrostatics 71 (2013) 808-814. [20] H. Said, H. Nouri, Y. Zebboudj. Effect of air flow on corona discharge in wire-to-plate electrostatic precipitator. Journal of Electrostatics 73 (2015) 19-25. [21] R.J. Moff at, Describing the uncertainties in experimental results, Exp. Thermal Fluid Sci. 1 (1988) 3–17.

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Duplicates for all tables and figures Table 1. Chemical compositions of working particulates (%) Components SiO2 Al2O 3 Fe2 O3 CaO K2O Na2 O MgO P2 O5 MnO 52.3

31.7

4.9

2.9

2.7

0.8

1.6

0.7

0.1

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Percentage

Table 2. Specifications of measurement uncertainties Instrument (Type)

Particle concentration

particle spectrometer (TSI3330)

Range

Uncertainty

0.3-10μm 5.0%

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Parameter

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Table 3. Physical parameters Air density (kg/m3 )

Air viscosity (kg/m·s)

Ion mobility (m2 /V·s)

600

1.225

1.7894

0.00027

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Particle density (kg/m3 )

Fig. 1 A schematic diagram of the test facility

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Fig. 2 Geometries of coronas equipped with arista

Fig. 3 Size distribution of working particulates

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Fig. 4 Multi- field coupling relationship inside the ESP

(a)

(b)

Fig. 5 Geometry of honeycomb tube (a) and computation mesh (b)

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Fig. 6 Whole flow streamline: A comparison of different gas velocity (U=50kV)

Fig. 7 Effect of EHD flow on separation efficiency under different particle diameter (U=50kV, u=0.5m/s) (computation)

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Fig. 8 Effect of supply voltage on separation efficiency under different electrode shape (u=0.5m/s, dp=1μm) (Computation)

Fig. 9 Trajectory diagram of particles: A comparison of different supply voltages (u=1.5m/s, dp=3μm)

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Fig. 10 Separation efficiency under different supply voltages (u=2.5m/s) (Computation)

Fig. 11 Particle number concentration under different supply voltages (u=0.5m/s) (Measurement)

Fig. 12 Effect of supply voltage on separation efficiency: A comparison of computation and measurement (u=0.5m/s, dp=1μm)

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Fig. 13 Effect of gas velocity on separation efficiency under different electrode shape (U=50kV, dp=1μm ) (Computation)

Fig. 14 Trajectory diagram of particles: A comparison of different gas velocities (U=50kV, dp=3μm)

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Fig. 15 Effect of gas velocity on separation efficiency under different supply voltages and particle diameter (computation)

Fig. 16 Effect of gas velocity on separation efficiency: A comparison of computation and measurement (U=50kV, dp=1μm)

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Fig. 17 Effect of particle diameter on separation efficiency under different electrode shape (U=50kV, u=0.5m/s) (Computation)

Fig. 18 Trajectory diagram of particles: A comparison of different particle diameter (U=50kV, u=0.5m/s)

Fig. 19 Effect of particle diameter on separation efficiency under different supply voltages (Computation)

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Fig. 20 Effect of particle diameter on separation efficiency: A comparison of computation and measurement (U=30kV, u=0.5m/s)

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Graphical abstract

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Highlights:

Particle separation in ESP is studied in measurement and computation.

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Multi-field coupling model is summed up.

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EHD flow improves separation efficiency in low gas velocity for small particles.

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Lower velocity, higher supply voltage serves better particle separation.

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Larger particles are easier to be captured.

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