Development of New Electrostatic Precipitator for Electric Capture of Airborne Particles

Because airborne viruses such as swine flu, bird flu and foot-and-mouth disease (FMD) spread easily through airborne transmission and the infection is done quickly through the respiratory system, the rapid detection of viral particles is critical. In this work, we designed new electrostatic precipitators to increase the collection efficiency as well as to concentrate the trapped particles on a small area for further tests using CFD-ACE+. The outlets of the precipitator are located at the top next to the inlet instead of the bottom, as is commonly used.

In order to verify the authenticity of the simulations, the electrostatic precipitator previously developed by Dixkens &. Fissan was simulated by the same computer software, and the numerical data were compared with experimental data (Dixkens. The collection efficiency of the new ESP was higher than that of previous ESP developed by Dixkens & Fissan (1999, Aerosol Sci. Technol., pp. .438 -453).

Bioaersol

Liquid impinger

Small bubbles form in the liquid during sampling and can help pick up very small particles by diffusion. The number in the name of the AGI sampler indicates the distance in millimeters between the tip. While the air is accelerated to sonic speed through a single nozzle and moves towards the bottom of the flask in the AGI sampler, the air is accelerated to sonic speed through three tangential sonic nozzles in the BioSampler.

In a study comparing the performance of the commonly used Andersen 6-stage cascade impactor and Reuter's centrifugal samplers (RCS plus) and the flow rate of the Andersen is 28.3 l/min and the flow rate of the RCS plus is 50 l/min and the efficiency of Andersen collection because the airborne mold spore is higher than that of RCS plus [17]. In this study, the collection efficiency of each sampler is higher than others in particular cases [19]. The automatic bioaerosol sampler is inefficient than the liquid sampler such as the AGI 30 in the case of large particles such as fungi [20].

Filter

In addition, a study was conducted comparing the performance of the portable Burkard, SAS Super 90 air samplers, Andersen 2-stage and RCS plus. In addition, a study was conducted comparing the newly designed automatic bioaerosol sampler with the six-stage Andersen sampler, all-glass impinge (AGI 30), Casella slit sampler. Sufficiently large particles are forced downward by gravity and the gravity settling mechanism occurs.

The particle size and the charge of particles and the charge difference with filter determine the electrostatic attraction mechanism. Filters can damage air particles and the drying out can adversely affect culture analysis of air particles. Membrane filter has been used to detect species and concentration of particles in the air and it has been reported that efficiency is similar and the number of detectable particles is almost equivalent to Reyniers air gap sampler [22].

Electrostatic precipitator (ESP)

In another study, physical and biological collection efficiencies were compared for spores of Bacillus subtilis var niger (BG) and Mycobacterium bovis BCG, Pseudomonas fluorescens and two, with efficiencies varying by species, and sensitivity was estimated to vary by different species [29]. Therefore, many people have studied the new design of the electrostatic precipitator to increase the collection efficiency without the discharger. Factors affecting collection efficiency other than particle charge are flow rate, electrode voltage, relative humidity, etc.

In general, collection efficiency increases as RH increases, or flow rate decreases, or voltage increases [32]. In this paper, the effect of flow field and electric field on collection efficiency to capture nanoparticles was investigated and the collection efficiency of newly designed electrostatic precipitator was calculated by using CFD-ACE+. Ny has a higher collection efficiency than a previous solar collector presented by Dixkens & Fissan without the use of a corona discharger, which generates active gases such as ozone and NOx, and these gases attack viral particles and cause structural damage to them.

Figure 1.3 Six different types of bioaerosol samplers. Red lines and arrows indicate the airflow into the sampler

Theory

Details of simulation

A difference of the flow rate between inlet and outlet is less than 0.000008% and the convergence criteria is. In fact, since a velocity profile of fluid can be changed depending on experimental conditions, the velocity profile in experiments is expected to exist between these two velocity profiles. Charge of particles depends on a charging method and the proportion of one negative charge is higher than others in charge equilibrium.

Fully developed velocity profile

Uniform velocity profile

In this paper, to verify the authenticity of simulations, the electrostatic precipitator previously developed by Dixkens & Fissan was simulated using a commercial software CFD-ACE +, after which the results of numerical analysis were compared with experimental data [33] [36] . A diameter of the electrostatic precipitator is 84 mm and a diameter of the electrode is 20 mm and a diameter of the inlet is 6 mm, a height of the electrostatic precipitator is about 187 mm. The collection efficiency of experiments is in the range of results of simulation with two types of velocity conditions (uniform velocity and fully developed velocity).

Figure 2.4 Geometrical structure of collector developed by Dixkens & Fissan

Comparison between numerical data and experimental data

Simulations of newly designed electrostatic precipitators 1 Geometry

Location of outlet
The inner structure
The structure of electrode
The inlet velocity
The intensity of electric field
The collection efficiency as function of the particle size

The impact of the geometric structure on the flow field and electric field must be carefully considered to obtain high collection efficiency, because the geometric structure determines the flow field and electric field. Although the shape and diameter of the electrostatic precipitator and the inlet and the electrode, the location of the inlet and the distance between the inlet and the electrode are the same as a previous model, the height of the electrostatic precipitator, the location of the exhaust, the internal structure of an electrostatic precipitator was modified. The electrode height decreased by reducing the distance (to 15 mm) to remove unnecessary portion.

As a result, a region of zero charge is required between the electrode and ground and the change of location and thickness of zero charge region affects and changes the electric field. In this study, the impact of configuration of no charge region on the collection efficiency was investigated. Therefore, the supporting pole was removed and the area of zero load was modified.

Changing the region of zero charge leads to different electric fields and high collection efficiency. In most of the electrostatic precipitators, low inlet velocity is used to capture particles because the high velocity particles cannot be captured effectively. In this study, when the inlet velocity is 0.172 mm/s (flow rate = 0.31 l/min) and twice (0.344 mm/s), the collection efficiency was calculated to compare with the model designed by Dixkens & Fissan.

When the electric potential applied to the electrode is 25 kV, the collection efficiency was calculated to compare with the model developed by Dixkens & Fissan. In addition, the collection efficiency was calculated as the electric potential is 2kV, 5kV, 10kV, 20kV. The virtual particles used in the simulations are water particles with one negative charge, and the total number of particles is 177, and the electric potential applied to the electrode is 25 kV.

There are two types of inlet velocity conditions: one is constant velocity and the other is fully developed velocity, and the magnitude of inlet velocity is 0.172 mm/s (Q = 0.31 l/min). A decrease in collection efficiency is expected, resulting in the drag force increasing under constant electrical attraction. The collection efficiency of a collector with 2 outputs and 4 outputs is and is higher than that of the previous collector.

Figure 3.1 Flow field of electrostatic precipitator with 2 outlets and 4 outlets simulated by CFD-ACE+

The collection effciency depending on particle size

The collection efficiency depending on the intensity of electric field

When the electric potential applied to the electrode is 2 kV, 5 kV, 10 kV, 20 kV, 25 kV, collection efficiencies were calculated to investigate the relationship between the collection efficiency and the intensity of the electric field. The flow rate at the inlet is the same as in Chapter 4.2, and the particle diameter is 0.1 µm, 0.4 µm, 1 µm, and the other conditions are the same as other simulations.

The collection effciency depending on flow rate (fully developed velocity)

The collection effciency depending on flow rate (uniform velocity)

The collection efficiency when a corona discharger was used

The electrostatic precipitator is more effective at capturing relatively small particles, but it is not effective at capturing relatively large particles. To capture large particles, charging methods are available to increase the amount of particle charge, such as corona dischargers, which is a common method. The electric potential applied to the electrode is 25 kV, and the inlet velocity is identical to previous simulations, and the particle diameter is 0.1 µm, 0.4 µm, 1 µm.

The collection efficiency was in any case measured at 100% and corresponds to the experimental data in the article by Dixkens & Fissan [9].

The collection efficiency with using Corona discharger

It was observed that the collection efficiency increases as the inlet velocity (flow rate) and particle diameter decrease and the electric potential applied to the electrode increases. The collection efficiency of new electrostatic precipitators, calculated by CFD-ACE+, is higher than the collection efficiency of the conventional ones, developed by Dixkens & Fissan, under the same conditions as the inlet velocity, the electric potential, the number of particles, the materials of the particles, etc. .Air blockage by obstacles was reduced by removing the plate support and the location of the no-load area was changed.

In the reference condition, the collection efficiency was estimated as 100% up to the diameter of 0.3 µm and the maximum difference between the previous model and the newly designed models. The collection efficiency was calculated in five electric potential conditions, which are 2 kV, 5 kV, 10 kV, 20 kV, 25 kV. In any case, the collection efficiency of the new ESP was observed to be the same or higher than the previous one.

REFERECES

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20] Pahi, O., 1997, Comparison of commonly used samplers with a new bioaerosol sampler with automatic plate exchange, Journal of Aerosol Science, vol.28, Issue 3, p. Air Sampler and Slit-to-Agar Sampler, Applied and Environmental Microbiology, vol.44, p. 28] Mainelis, G., 2002, Effect of electric charges and fields on damage and viability of airborne bacteria, Biotechnol Bioeng.

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