Dust Removal Mechanism of the Vibrating String Filter with Charged Water Mist

The traditional dust removal technology is difficult to meet the strict requirements of environmental protection, so it is of practical significance and research value to study how to purify fine dust in workshop. Fine dust can be suspended in the atmosphere, while reducing the air quality. Excessive inhalation of dust may result in disease. So it should be paid close attention to dust control. The water mist charging process has experienced three stages: induction charge, corona charge transition, and corona charge. When the discharge distance is 80mm, the charge-mass ratio of droplet and the current of water mist are most affected by corona voltage. The significant impact analysis of orthogonal experiment is studied. The result of the orthogonal experiment is analyzed by the variance method. It is noted that the inlet wind speed has the highest influence, and the discharge distance has a least influence on the dust removal efficiency. The discharge distance is 80mm, and the voltage working band is suitable for the normal voltage regulation of the electrostatic precipitator. The condensation efficiency of charged droplets on dust is beneficial to reduce the negative effect of excessive wind speed on wet vibrating string grid and to improve the effective handling volume of dust collector. The charge-mass ratio of water mist is improved effectively, and the dust removal efficiency is increased in the vibrating string filter with charged water mist. Theoretical analysis and experimental studies showed that the vibrating string filter with charged water mist is as a new composite efficient dust removal technology that can effectively deal with the purification of fine dust particles in the gas stream, especially in respiratory dust removal.


Introduction
The research of wet string gate filter dust removal technology started in the wet layer. The wet string gate filter precipitator was introduced in 1988 [1]. Metal string grid dust removal technology was novel, unique structure, reliable work, and it was large-scale application in China in the world [2]. The advantages of wet string gate filter precipitator included large span of treated dust concentration, low energy consumption, small space, and large air volume per unit treatment [3,4]. However, it had certain limitations in anticorrosion performance, which reduced the length of working life of the dust collector when it was encountered corrosive gas [5]. The wet string gate filter precipitator was only used for underground mining, especially had been popularized in coal mining dust removal, and was less used in the field of industrial dust control [6,7].
Scholars began to turn to joint action of traditional electrostatic dust removal technology and wet string grid filter dust removal technology. In 1992, Jingliang and Rongce proposed the study of charged water mist and wet filter dust removal [8]. Ying and Kun et al. conducted a computer simulation on the dust removal process of water mist electrostatic grid and simulated the water mist charged dust capture process and theoretical analysis [9,10]. In 2014, Yang et al. studied the defogging performance of bipolar corona chord grids by directly applying high pressure on the chord grids to form an electric field between the grids to achieve the purpose of dust removal [11]. However, the current research on water fog charge technology was limited to the atomization characteristics and charge characteristics of water fog, and there were no many research on the improvement of water fog charge electric device structure to improve the charge to mass ratio of water fog [12]. The research on the filter and dust removal technology of charge water vibration grid filter was relatively shallow.
The significance of the factors affecting the efficiency of dust removal is analyzed and compared in the dust removal device, through the orthogonal experiment. The charge characteristics of water mist charge of voltage current characteristic, charge-mass ratio of water mist, and cloud current of water mist are studied. Not only the corona voltage of working band is measured at different discharge distances but also the charge-mass ratio of water mist is measured in the steady voltage working band by using a self-made instrument for measuring the charge-mass ratio of water mist. The experimental study on the collection of respiratory dust in charged and uncharged water mist is analyzed to determine the collection capacity of the dust remover for particles with different particle sizes. The dust removal technology by the vibrating string filter with charged water mist has the advantages of wide application range, high purification efficiency, and simple structure in the process of further improving the treatment of fine dust. The research result shows that as a new type of compound and high efficiency dust removal technology, the vibrating string filter with charged water mist can efficiently purify the fine dust particles in the handling air flow, and the efficiency of the removal of respiratory dust is considerable. According to cited literature and current situation of the field application of the electrostatic precipitators [13][14][15], the main problems are as follows: (1) Ionization duty ratio is very low. At present, the calculated ionization duty ratio is about 1:8 × 10 −5 by direct high voltage corona discharge (total volume of corona ionization discharge channel/total volume of electric dust field). The ionization duty ratio can be increased to 2 × 10 −2 by using a high electric field ionization discharge method. It can be seen that the ionization duty ratio of electrostatic precipitators can be improved by the order of magnitude. (2) Charged particles have low momentum. The ionic momentum of electrostatic precipitator is 5 × 10 −23 g•m/s, and its transport term is about 10 7 /cm 3 . When the ionic momentum increases to 100 × 10 −23 g•m/s, the ion transport term reaches about 10 10 /cm 3 . It can be seen that for each order of magnitude increase in ionic momentum, the corresponding ion concentration and its transport term will increase by about two orders of magnitude. But how to improve the charge to mass ratio of the mist at the same time to achieve effective purification efficiency of fine dust and dust removal mechanism, it remains to be further study. The vibrating string filter with vibrating water mist can solve the problem of low ion transport term in electrostatic precipitator by improving the momentum of charged particles. The vibrating string filter with vibrating water mist can improve the collecting ability of submicron and micron dust. The vibrating string filter with vibrating water mist can significantly reduce the volume, weight, and energy consumption of electrostatic precipitator space.

Experimental System of Vibrating String
Filter with Charged Water Mist Set-up 2.1. Experimental Model of Vibrating String Filter with Charged Water Mist. The vibrating string filter with charged water mist, which is a new type of electrostatic precipitator, is applied to collect dust, and the nozzle is the HYD type of low pressure fine solid cone of spray nozzle, on which water mist is electrically charged under negative high voltage in form of prickly electrode corona. The experimental device system of vibrating string filter with charged water mist, which is shown in Figure 1, is mainly constituted of six parts of sending dust, ventilation system, water supply system, power supply system, spray charging system, and dust collector system in the vibrating fiber filter [4,12]. The experimental dust is 270 mesh limestone powder treated by drying, and the dust emission rate is changed by adjusting inclination angle of dust guiding tube in the dust generator. This process is repeated continuously to produce a large number  2 International Journal of Rotating Machinery of free electrons and positive and negative ions in the corona area, which is called corona charge. In this experiment, corona charging is adopted, and annular electrode corona is shown in Figure 1 [16]. The dust laden air flow enters the dust collector through the air inlet pipe and passes through trapping by electrically charged mist; then, the dust is intercepted and is removed by the water mist of vibrating wire grid, and finally, the clean air current discharges through air exportation of fan.    International Journal of Rotating Machinery MATLAB software. The slope of the fitting line is supposed as k 1 and k 2 , respectively, and the included angle of the fitting line, namely, the atomization angle, can be obtained by input command alph = atand ðabsððk 1 − k 2 Þ/1 + k 1 * k 2 ÞÞ, as shown in Figure 2. The atomization angle is very important to spray range size effect, the atomization angle is larger and the dispersion is lower, and the atomization characteristic is more stable.

Determination of Spray Quantity.
Spray flow rate is one of the key factors affecting the quality of atomized droplets. The volume method is used to determine spray quantity in this experiment. When the spray pressure is adjusted to 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, and 0.5 MPa, the water mist is collected with a measure cup of known mass and timed with a stopwatch timer. The collected water mist is measured and recorded by an electronic analytical balance with a precision of 0.1 mg. According to droplet mass and collection time, the flow parameters of the nozzle under different pressures are obtained. In theory, the relationship between the flow rate of the single-line pressure atomizing nozzle, the nozzle aperture, and atomizing pressure is as follows: where q v : Volume flow, m 3 /s,  The ratio of charge-mass is an index to reflect the charged situation of water droplets [17,18]. The net target method is used to measure the charge-mass ratio of water mist in the experiment, in order to compare the law of charge-mass ratio of water mist, and the device structure is used to test the ratio of charge-mass of water mist, as shown in Figure 3. The water mist is sprayed into the metal receiver with multilayer metal mesh after it is charged by the stinger corona. The water flows downstream to the measuring cylinder, which is suspended by an insulated rope. Because the negative corona is used to charge the water mist in this experiment, the negative electrode of the precision micro ammeter is used to connect the cylinder to measure the spray body current of water mist, the other end is grounded, while the corresponding measuring time is recorded by a stopwatch. Meanwhile, the mass of fog drops is measured by an electronic balance. The accuracy of electrostatic charge is millicoulomb (mC). The accuracy of current intensity is microampere (μA). The accuracy of droplet mass is gram (g).  The calculation formula of charge-mass ratio is as follows: where β: Charge-mass ratio, mC·Kg -1 , q: Electrostatic charge, mC, I: Current intensity, μA, t: Measuring time, s, m: Droplet mass, kg.

Measurements of Orthogonal Experiment of Influence Factors of Dust Removal Efficiency
The significant influencing factors are obtained by variance analysis, based on the results of orthogonal experiment, and the influence factors of orthogonal experiment are analyzed according to intuitive analysis method [19][20][21]. The principle behind the selection of discharge distances of 40, 60, and 80 mm is related to the size of the vibrating string grid, the size of the schematic diagram, and the corona voltage [22].
where η i : Dust reduction efficiency(i = 1, 2, ⋯, 9), K: Sum of factors efficiency, T: Arithmetic mean of sum of squares of efficiency of each factor, U j : Square sum of dust removal efficiency of factor j, Q j : Sum of square deviation. The specific analysis results are shown in Tables 1 and 2. 3.2. Method of Intuitive Analysis. According to the influence factors, such as inlet wind speed, discharge distance, and electric field intensity in orthogonal experimental variance analysis on the efficiency of dust reduction, the influence factors of orthogonal experiment are analyzed, as shown in Figure 4. Through orthogonal experiment, the results of orthogonal experiment are analyzed by the method of variance analysis. Given that F 0:25 ð2, 2Þ = 3, F 0:10 ð2, 2Þ = 9, F 0:05 ð2, 2Þ = 19 , and F 0:01 ð2, 2Þ = 99, a higher value of F indicates a significant influence of this factor, which is the main factor; otherwise, it is a secondary factor. As the value of F value is zero or very small, it is an irrelevant factor. According to the significance analysis of the influencing factors in Table 2, it is concluded that the effect of inlet wind speed on the dust reduction efficiency of the vibrating string filter with charged water mist is highly significant, and the effect of the average electric field intensity on the dust reduction efficiency is significant, the discharge distance has a certain influence on the dust reduction efficiency, but it is not significant. The influence of various factors on the dust removal efficiency is arranged as follows: inlet wind speed > average electric field intensity > discharge distance.
The influence degree of inlet wind speed, discharge distance, and average electric field intensity on dust removal efficiency is intuitively expressed as Figure 4. The dust removal efficiency changes with the change of the inlet wind speed. The inlet wind speed is greater, the dust removal efficiency is lower, and the change rate of dust removal efficiency increases from small to large with the increase of inlet wind speed based on Figure 4(a). This is because the size of the inlet wind speed determines the length of the particle residence time, which is the length of the condensation time between the particle and the charged droplet. When the inlet wind speed is less than 10 m/s, with the increase of inlet wind speed, the period film-forming is longer in the wet vibrating grid, and the filtering effect is gradually increased, which slows down the change of dust reduction efficiency caused by the increase of inlet wind speed. When the inlet wind speed is greater than 10 m/s, the disturbance frequency around the flow becomes larger in the vibrating string grid, and the period of the wet vibrating string fiber grating film is shorter, which makes the liquid film more easily broken, so the change rate of dust removal efficiency increases.
The electric field strength has a great influence on the filtering and dust removal efficiency of the vibrating string filter with charged water mist, and the dust removal efficiency increases with the increase of the average field strength, according to the orthogonal experimental results, as shown in Figure 4(c). When the working voltage is changed, the working current, the electric field intensity, and the watermist charge-mass ratio all change, and when the average electric field intensity is at the peak before the air is broken down, the water-mist charge-mass ratio is the largest and the dust remover operates best. Therefore, the electric field strength not only affects the enhancement of the watermist charge-mass ratio but also affects the dust capture.
The relationship curve between dust removal efficiency and discharge distance is shown in Figure 4(b). As the discharge distance increases, the dust removal efficiency increases gradually. When the discharge distance is 80 mm, the dust removal efficiency is the highest. In a certain range of discharge distance, with the increase of discharge distance, the induced charge of water mist becomes smaller and smaller, and the charge of corona plays the main role. But the effect of induced charge and corona charge is just the opposite, so the effect of induced charge is smaller. The corona charge is larger, and the charge-mass ratio of water mist is higher, which leads to the increase of dust reduction efficiency. The discharge distance has a certain effect on the dust removal efficiency of the dust collector, but it is not obvious.
In summary, when the inlet wind speed is appropriate, the discharge spacing is 80 mm, and the electric field is high, and the dust removal efficiency is high in the vibrating string filter with charged water mist.

Results and Elaboration of Single Factor
Test of Affecting Dust Removal Efficiency     International Journal of Rotating Machinery the range of stable voltage band when the electrostatic precipitator works normally. In order to obtain a wide stable corona voltage band, and the corona current is measured by a precision micro ammeter in the discharge distance of 40 mm, 60 mm, and 80 mm corona voltage, as shown in Figure 5 and Table 3. At the same corona voltage, the current generated by the water mist is much larger than that generated by the air corona, which is almost 3 times the current of the air corona. With the increasing of discharge distance, the corona current produced by water mist charge decreases gradually. Compared with the air corona, the initial corona voltage of water mist charge decreases to 10 kv and the breakdown voltage remains the same when the discharge distance is 40 mm, and the initial corona voltage decreases to 15 kv and the breakdown voltage decreases to 40 kv when the discharge distance is 60 mm. As the discharge distance is 80 mm, the initial corona voltage of water mist charge decreases to 15 kv, and the breakdown voltage decreases to 45 kv. Under the same corona voltage, the corona current of water mist becomes larger, so it is beneficial to improve the charge-mass ratio of water mist.

Charge-Mass
Ratio of Water Mist. The charge-mass ratio of water mist is an important index of the performance of water mist dust collector. The research shows that the ability of collecting fine dust after charged droplet is greatly improved. Under different voltages, the mode of water mist charging is different, which is divided into three stages: inductive charge region, corona charge transition region, and corona charge region. With the increase of the charge voltage, the water mist charging mode changes gradually from inductive to corona, as shown in Figure 6. When the working voltage is small, due to the negative high voltage of the spurs electrode, the positive charge is produced in the surface induction of the nozzle, and the contact charge occurs when the water mist flows through the nozzle, which makes the droplet carry the corresponding positive charge.
With the gradual increase of the working voltage, the negative ions which are generated by the corona in the air of the thorn electrode gradually increase. After the neutralization of the contact between the fog drops with inductive positive charge and the negative ions in the air, the fog drops begin to be negatively charged, and with the passage of contact time, the negative charge of the fog drops increases continuously and finally reaches saturation. The charge of corona charged by water mist is much larger than that of inductive charge. The influence of corona voltage with discharge distance is 40 mm, 60 mm, 80 mm, and 100 mm, respectively, in the water-mist charge-mass ratio, as shown in Figure 7. It experiences three stages: induced charge, corona charge transition, and corona charge. At the same discharge distance, the water mist charge-mass ratio first decreases and then increases, changing from positive charge to negative charge,    The ratio of charge-mass of water mist increases in parabola, which is best when the discharge distance is 80 mm.
The different discharge distance influences the ratio of charge-mass of water mist as shown in Figure 8. The ratio of charge-mass of water mist increases first and then decreases, with the increase of distance. When the discharge distance is 80 mm, the optimal atomization charge state is achieved. When the discharge distance is small, the space between the nozzle and the thorn electrode is small, the work voltage band is short, and breakdown is easy to occur.
With the increase of the discharge distance, the space between the nozzle and the thorn electrode becomes larger, the work voltage band is wider, and the negative ion concentration is higher under the high voltage. However, when the discharge distance is too large, the concentration of negative ions produced by corona reaches saturation. And the ionization space is the larger, and the concentration of ions is the more diluted, which is not conducive to increasing the ratio of charge-mass of water mist.
The current and voltage of water mist cloud is measured by the network method, and the relation curve between corona voltage and current of water mist cloud is drawn as Figure 9. With the increase of negative high voltage, the current of water mist cloud decreases first and then increases, and the direction of current changes. Similar to the variation of charge-mass ratio of water mist, the generation of current of water mist cloud is mainly divided into three stages: the formation of primary current, the disappearance of current, and the formation of secondary current. Firstly, the water mist is positively charged by flowing through the positively charged nozzle, and the directional movement of the charge creates a current. Secondly, when the positively charged water mist cloud enters the corona anion region, the positive and negative charges, which makes the current gradually reduce or even disappear, are neutralized. Finally, the water mist cloud after neutralization continues to contact with the negative ions in the air, thus forming a water mist cloud with negative charge. The moving direction of the water mist cloud remains unchanged, so the direction of the secondary current changes. When the corona voltage remains unchanged, the secondary current of water mist cloud increases first and then decreases with the increase of discharge distance, and the best discharge distance is l = 80 mm.
The corona voltage effects on the power of injected water mist cloud as shown in Figure 10. With the increase of corona voltage, the effective power of injected water mist cloud increases as parabola until it breaks through the air to form spark discharge. When the discharge distance is   In summary, the corona voltage influence on the chargemass ratio of water mist, current of water mist cloud, and power of injected water mist cloud is analyzed, respectively. It is concluded that the best discharge distance of water mist charged is 80 mm.

Inlet Wind Speed Influence on Dust Removal Efficiency.
According to the results of orthogonal experiment, when the discharge distance is determined to be 80 mm and the average electric field intensity is 3.6 kv/cm and 4.2 kv/cm, the comparative experiment is carried out under the conditions of different inlet wind speeds. The different inlet wind speeds' influence on the dust removal efficiency is measured by the experiment, as shown in Figure 11. As the average electric field intensity is higher in the vibrating string filter with charged water mist, the dust removal efficiency is higher. When the average electric field intensity is the same, the dust removal efficiency decreases with the increase of inlet wind speed, and the decreasing amplitude firstly increases and then decreases. When the inlet wind speed is small, the electric field intensity influence on dust removal efficiency is great. As the inlet wind speed increases, the electric field intensity influence on dust removal efficiency decreases continuously.
The mechanism of water mist charge, inertial capture, and electric dust removal plays a very important role in the process of the vibrating string filter with charged water mist. The mechanism of water mist charge capture is mainly through the condensation, settlement, and electrostatic dust removal between the droplets of the charged water mist and the dust. As the strength of electric field increases, the quantity of charged water mist increases. And dust particles is collided and coagulated obviously, dust is collected under the action of inertial capture and electric dust removal. When the filtration wind speed reaches a certain value in the vibrating string fiber grid with charged water mist, the purification efficiency of the vibrating string fiber grid gradually decreases with the further increase of the wind speed. The main reason is that when the filtration wind speed is too high, the condensing efficiency of charged droplets and dust decreases, and the vibration amplitude of the fiber grating increases, so that the droplet and dust particles can easily cross the gap of the fiber grille. Thus, the probability of formation of purifying liquid membrane on the fiber grating is reduced, and the efficiency of dust capture by inertial collision is reduced.
The condensation and efficiency of the charge droplet on the dust is beneficial to slow down the negative effect of excessive wind speed on the vibrating string filter with charged mist, which can improve the purification treatment air volume of the dust collector more effectively. The optimum treatment inlet wind speed of the electrostatic precipitator is 5.45 m/s.

Burr Number Effect on Dust Removal Efficiency.
In the experiment, the discharge spacing is selected 80 mm, and the inlet wind speed is 5.45 m/s. Under different corona volt-ages, the effects of 0, 4 and 6 burrs on the dust removal efficiency are studied, respectively, as shown in Figure 12.
According Figure 12, when the corona voltage is less than 33 kv and the number of burrs is the same, the dust removal efficiency increases with the increase of corona voltage. When the corona voltage is greater than 33 kv, the dust removal efficiency begins to stabilize. Under the same corona voltage, the dust removal efficiency increases gradually with the number of burrs. According to the superposition principle of point charge space field strength, the electric field intensity can be achieved by changing the voltage between different poles or the number of prickle tip points separately.
The water mist droplets are small enough to stay at the tip, and short circuit is not easy to be formed by using burr tip discharge. When the concentration of dust in the air flow is too high, the ion wind by the corona of the tip of the burr tip produced and water mist are washed continuously, so that the dust in the air flow can be not detained near the corona pole, and the prickly corona pole is kept in a clean state. It overcomes the problem that some anisotropic charged dust accumulates in the discharge pole and weakens the electric field intensity and avoids the corona block. By observing the reading of the galvanometer and the no-load corona voltage in the high concentration dust experiment, it is found that the corona current in the air is less than the corona current when the water mist is charged. But when the normal corona voltage is working, the corona current increases slightly with the increase of the dust concentration in the air flow, and with the further increase of the dust concentration, the positive charged particles near the corona pole are close to the negative corona electrode and deposited. The corona discharge effect is greatly reduced by dust concentration, the corona pole is enlarged, and corona current is decreased. Therefore, the vibrating string filter with charged water mist, which can adapt to the change of different dust concentration in operation, can prevent the "corona occlusion" caused by high concentration of dust, and its operation state is relatively stable.

Electric Field Intensity Influence on Dust Removal
Efficiency. According to the variance analysis of orthogonal experiment, the electric field intensity has a significant influence on the dust removal efficiency in the vibrating string fil-ter with charged water mist. The experiment is conducted by changing the average electric field intensity in order to obtain the average electric field intensity influence on the dust removal efficiency, as shown in Figure 13.
Before the air breakdown, when the electric field strength is less than 4.2 kv/cm, the dust removal efficiency increases with the rise of the average electric field intensity in the vibrating string filter with charged water mist. When the electric field strength is more than 4.2 kv/cm, the dust fall efficiency is not obvious with the increase of the average electric field strength. Because the electric field intensity is greater, the area of equipotential surface with high potential is larger, which causes to enter this region the droplet electronics corona electrically charged probability to increase. This increases the corona charge probability of fog droplets entering the region and effectively increases the chargemass ratio of water mist. Charged droplets are condensed and collected as a result of inertial collisions between droplets and dust particles through turbulence and electric field forces. When the electric field intensity reaches a certain degree, the corona charge of the droplet reaches the Rayleigh limit. The electric field intensity is continuously increased, and the electric fog drops are broken due to the electrostatic repulsion force which is larger than the surface tension, so that the particle size of the fog drops is too small, and the dust particles are not easily collected, and the dust removal efficiency is improved slowly.

Water Mist Charge-Mass Ratio Effect on Dust Reduction
Efficiency. The water mist charge is the main part in the vibrating string filter with charged water mist, and the size of the charge-mass ratio of water mist is the important factor that affects dust removal efficiency. When the inlet wind speed is 5.45 m/s and the discharge spacing is 80 mm, the different water mist charge-mass ratio influence on dust removal efficiency is obtained as shown in Figure 14. The dust removal efficiency is almost the same as that of the wet vibrating string fiber grid when the water mist chargemass ratio is 0. As the charge-mass ratio of water mist is   10 International Journal of Rotating Machinery between 0 and 4.5 mc/kg, the dust removal efficiency increases with the increase of charge-mass ratio of water mist. When the water mist charge-mass ratio increases to a certain extent, the rise of dust removal efficiency tends to be stable and remains unchanged.

Analysis on the Efficiency of Graded Dust Removal
In the process of industrial production, respiratory dust is the real "culprit" that endangers human health, so it is necessary to analyze the efficiency of classifying dust removal. The efficiency of fractional dust removal is calculated by using mass analysis method. According to the results of the orthogonal test, the experimental conditions are the atomization pressure of 0.5 MPa, the discharge distance is 80 mm, the inlet wind speed is selected to be 5.45 m/s, 10.33 m/s, and 14.41 m/s, respectively, and the graded dust removal efficiency is obtained as shown in Figure 15. According to Figure 15, under the condition of the same inlet wind speed, the efficiency of fractional dust removal increases with the increase of dust particle size and finally tends to 100% at a certain particle size. With the increase of inlet wind velocity, the dust removal efficiency of the same particle size decreases gradually. Under the experimental conditions of inlet wind speed of 5.45 m/s, the collection and purification efficiency of respiratory dust with particle size below 5 m can reach 90.68%. The reason is that the inlet wind speed is smaller, the dust pellet, the electrically charged droplet and the airflow relative motion free space is bigger. Under the attraction of electric field and the action of water film, the collision and condensation process of dust and charged droplets was easier to occur. Therefore, the fractional dust removal effect of small inlet wind speed is considerable.

Comparative Analysis on the Efficiency of Charged Water Mist Dust Removal and Water Mist Dust Removal
The vibrating string filter with charged water mist is a new type of composite electrostatic precipitator. The dust removal efficiency of wet vibrating string filter is compared with that of vibrating string filter with charged water mist, in order to further determine that this dust collector has superior purification effect on fine dust.  Table 4. According to Table 4, compared with the dust removal technology of wet vibration string fiber grating, the dust removal technology of the vibrating string filter with charged water mist has been greatly improved in the dust removal efficiency of the total dust and the dust removal efficiency of the respiratory dust. The total dust removal efficiency of the vibrating string filter with charged water mist is 4.46% higher than that of wet vibrating string fiber grid, and the purification efficiency of respiratory dust is 9.54% higher than that of wet vibrating string fiber grid. According to the results, the effect of water mist charge on the improvement of respiratory dust removal is more obvious. In order to further understand the purification rules of charged water mist on respiratory dust, the columnar chart of the dust removal efficiency comparison between charged and uncharged water mist was drawn, as shown in Figure 16. With the increase of inlet wind speed, the effect of water mist charge on dust removal efficiency of respiratory dust is slightly larger, and both of them decrease with the increase of inlet wind speed.

Conclusions
(1) The result of the orthogonal experiment is analyzed by the variance method. It is noted that the inlet wind speed has the highest influence, and the discharge distance has a least influence on the dust removal efficiency. The influence of various factors on the dust removal efficiency is arranged as follows: inlet wind speed > average electric field intensity > discharge distance (2) The water mist charging process has experienced three stages: induction charge, corona charge transition, and corona charge. As the discharge distance is 80 mm, the corona voltage has the greatest influence on the water-mist charge-mass ratio, water-mist cloud current, and the power injected into the water-mist cloud (3) The dust reduction efficiency decreases with the increase of inlet wind speed. When the inlet wind speed is small, the electric field intensity has a great effect on the dust removal efficiency, and with the increase of the inlet wind speed, the electric field intensity influence on the dust removal efficiency decreases continuously. The condensation efficiency 11 International Journal of Rotating Machinery of charged droplets on dust is beneficial to reduce the negative effect of excessive wind speed on wet vibrating string fiber grid and to improve the effective handling volume of dust collector (4) Before the breakdown of air, when the electric field intensity is less than 4.2 kv/cm, with the increase of the average electric field intensity, the isobaric area of the high potential is also larger, resulting in an increase in the probability of the corona charge of the fog droplets entering the region. The chargemass ratio of water mist is improved effectively, and the dust removal efficiency is increased in the vibrating fiber grid dust remover with charged water mist (5) The purification effect of water mist charge on respiratory dust is a very obvious improvement, and the efficiency of dust removal respiration dust is increased by 9.54%, which achieves the goal of high efficiency dust removal and treatment of respiratory dust in airflow

Data Availability
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Conflicts of Interest
The authors declare that there is no conflict of interest regarding the publication of this paper.