Electrostatic precipitators are devices that remove charged particles from an air stream. We present the design and characterization of an electrostatic precipitator that is intended to be incorporated into aerosol sampling equipment. Hardware and software components of the design are open, all components can be directly purchased from vendors, and the device can be assembled with standard tools. Generic components are used to allow the repurposing of parts for other uses. The computer-controlled high-voltage power supply box associated with the project can be used for other common high-voltage applications in Aerosol Science and Technology, such as data acquisition and control systems for scanning mobility particle sizers. Computational fluid dynamics simulations are used to quantify the 3D flow field. The transfer function associated with the partial transmission is characterized through modeling and experiments. The observed transfer function is unique but deviates from the ideal transfer function due to the distortion of the flow near the inlet and the outlet of the device. Singly charged particles up to 624 nm and 253 nm can be completely removed for 0.5 L min-1 and 1 L min-1, respectively. We anticipate that our device will increase the accessibility of the technique to a broader audience.
Electrostatic precipitators are devices that remove charged particles from an air stream. We present the design and characterization of an electrostatic precipitator that is intended to be incorporated into aerosol sampling equipment. Hardware and software components of the design are open, all components can be directly purchased from vendors, and the device can be assembled with standard tools. Generic components are used to allow the repurposing of parts for other uses. The computer-controlled high-voltage power supply box associated with the project can be used for other common high-voltage applications in Aerosol Science and Technology, such as data acquisition and control systems for scanning mobility particle sizers. Computational fluid dynamics simulations are used to quantify the 3D flow field. The transfer function associated with the partial transmission is characterized through modeling and experiments. The observed transfer function is unique but deviates from the ideal transfer function due to the distortion of the flow near the inlet and the outlet of the device. Singly charged particles up to 624 nm and 253 nm can be completely removed for 0.5 L min-1 and 1 L min-1, respectively. We anticipate that our device will increase the accessibility of the technique to a broader audience.
Engineering and materials scienceEducational tools and open source alternatives to existing infrastructureMeasuring physical properties and in-lab sensorsField measurements and sensorsAerosol sampling equipmenthttps://doi.org/10.5281/zenodo.5295817https://doi.org/10.5281/zenodo.5295711https://doi.org/10.5281/zenodo.5295725
Hardware in context
Electrostatic precipitators (EP) have been in use since the early 1900 s. In EPs, charged particles are passed between two electrodes that create an electrostatic field. The electrostatic field deflects the particle either toward or away from the electrode and deposits it on the surface. The transmission efficiency of the EP depends on the particle size, the number of elementary charges on the particles, the electric field strength, and the residence time of the particle within the field [1]. Electrostatic precipitators are commonly used to purify gases in industrial processes [2], to control indoor air pollution [3], to collect particles onto substrates for further analysis [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], to control particle size evolution [14], and to remove charged particles from an air stream as part of a chain of aerosol instruments [15], [16], [17]. Commercial versions for removal of particles as part of aerosol instrumentation are available. For example, the Electrostatic Precipitator from Cambustion Ltd. (Cambridge, United Kingdom) that is used as an accessory with the centrifugal particle mass analyzer [17].
Hardware description
This work details the design and characterization of an EP that has the purpose to remove charged particles from an air stream. The EP was developed in-house as part of the dual tandem differential mobility analyzer (DMA) [16], [18], which is used to create dimer particles for viscosity measurement (e.g. refs. [19], [20], [21], [22]). A simple DMA possesses an annulus gap between inner and outer cylinder columns where the applied electric potential drags the charged particles depending on their mobility with the sheath flow [23].Fig. 1 shows a technical drawing of the precipitator. Since the items were ordered from vendors in the United States (U.S.), the U.S. customary measurement system units are used throughout to maintain readability. Conversions from the U.S. to metric units are 1′ (one foot) = 30.48 cm and 1″ (one inch) = 2.54 cm. The design is that of a cylindrical capacitor. Sample is introduced at a 90°angle through a T-shaped tube fitting. The sample, consisting of charged particles and carrier gas, flows through the annulus gap. The outer tube is electrically grounded. The inner tube is held at a constant potential. Charged particles are deflected either toward or away from the center rod. All particles with electrical mobility exceeding a threshold value will be filtered by the device. Particles without electric charge or particles with low electrical mobility exit with air flow.
Fig. 1
Technical drawing of the electrostatic precipitator.
Technical drawing of the electrostatic precipitator.Photographs of the assembled instrument are provided in Fig. 2. The charge-carrying electrode consists of a 29″ long, 1/4″ diameter, 316L stainless steel rod. The outer conductor is a 12″ long, smooth-bore, seamless 316 stainless steel tubing with 3/4″ outer diameter and 0.065″ wall thickness. Ultra high molecular weight polyethylene tubing, 3″ long, 3/4″ outer diameter, and 1/4″ inner diameter are used to mount the inner electrode and to electrically isolate the electrode and outer wall on both sides of the device. Compression fittings (Swagelok, Solon, Ohio, U.S.A.) are used to seal the device. Stainless steel reducing union tee fittings, (3/4″ x 3/4″ x 3/8″) tube outer diameter connect the (3/4″) polyethylene tube and stainless steel tubes and provide a (3/8″) inlet and outlet mounted at a 90-degree angle relative to the streamwise flow. The outer wall is grounded. The inner electrode is connected to a high-voltage DC power supply. The inner electrode and compression fittings are unsafe to touch and are electrically isolated using enclosures made from acrylonitrile butadiene styrene (ABS) plastic. The entire device is placed in a secondary enclosure for stability and ease of transport. The (3/8″) inlet/outlet is connected to a (3/8″ to 1/4″) reducing union that passes the flow through to the outside of the secondary enclosure. Assembly of the device requires standard tools, including a power drill, a saw, and wrenches. The cost of the hardware is less than $700 (All costs are in USD).
Fig. 2
Assembled electrostatic precipitator. The numbering of the parts is given in the following instruction.
Assembled electrostatic precipitator. The numbering of the parts is given in the following instruction.The device is controlled via a custom-made high-voltage power supply box that consists of a single board computer (Raspberry Pi-4), a multifunction data acquisition board, and a variable output high-voltage DC power supply. Fig. 3 shows a schematic of the power supply box. A photograph is provided in Fig. 4. The system consists of two boxes, one for the electrostatic precipitator (Fig. 2) and a second one for the power supply box (Fig. 4). The female high voltage cable wire (HV, see in Fig. 4, Power Box Top View) in the power supply box is connected to the male high-voltage cable (middle bottom in Fig. 4) in the precipitator. The traces are given in red lines in Fig. 4. The design guidelines of the box were to minimize cost, build upon a 100% freely licensed software stack, and be versatile to allow for a re-purposing of the box for different use cases. The enclosure (14.6″ x 10.6″ x 5.9″) holds a variable 0–10 kV DC high-voltage power supply (model 10A12-P4-F-M−AT20, UltraVolt, Inc., Ronkonkoma, New York, U.S.A.), a 12 V DC power supply (Mean Well RS-15–12 Series) to power the high voltage power supply, a Raspberry Pi single-board computer (Raspberry Pi 4 Model B, Raspberry Pi Foundation, Cambridge, United Kingdom), and a DAQC2 Pi-Plate which is a multifunction data acquisition and control card (Wallyware Inc., Duluth, Georgia, U.S.A).
Fig. 3
Schematic of the high-voltage power supply box.
Fig. 4
Assembled materials to operate the electronic box. The numbering is discussed in the build instructions.
Schematic of the high-voltage power supply box.Assembled materials to operate the electronic box. The numbering is discussed in the build instructions.The DAQC2 plate provides 0 to 4.095 V 12-bit resolution digital-to-analog output, which is used to control the high voltage output from the UltraVolt power supply between 0 and 8825 V. The high voltage power supply output voltage and output current are monitored using 16-bit resolution analog-to-digital inputs. The wiring diagram of the DAQC2 plate is provided in Fig. 5. The selected Raspberry Pi operating system image is the 64-bit version of Raspberry Pi OS (derived from Debian Linux), running on a 64 GB microSDXC UHS-I memory card. Software written in the Julia language provides a graphical user interface that is used to set the voltage, displays a time series of voltage and current readings, and saves the data to disk. The graphical user interface can be accessed remotely from any computer via a secure shell connection and a locally installed X-server.
Fig. 5
Wire diagram of the Raspberry Pi, DAQC2, and power supplies.
The novelty of this work is that the design is fully open (See Table 1). Only widely available off-the-shelf products are used. Assembly requires only standard tools. One design criterion was to reduce the cost of the device. In literature, lowering the cost of a device (e.g. sensor) would provide the detection of the source contribution of the aerosols [24], and would fill the gaps between the economical deficiency and science [25]. Opportunities for additional cost savings are discussed at the end of this work.
Table 1
Design file list including technical drawing of the EP, assembled parts of EP and electronic box, connectors, software screenshot, wire diagram, and software source code.
Design file name
File type
Open source license
Location of the file
EP_1technical_drawing
pptx
CC BY-NC-SA 4.0 International
https://doi.org/10.5281/zenodo.5295817
EP_2assembled
pptx
CC BY-NC-SA 4.0 International
https://doi.org/10.5281/zenodo.5295817
EP_3schematic_high_voltage_power_supply_box
pptx
CC BY-NC-SA 4.0 International
https://doi.org/10.5281/zenodo.5295817
EP_4assembled_high_voltage_power_supply_box
pptx
CC BY-NC-SA 4.0 International
https://doi.org/10.5281/zenodo.5295817
EP_5wire_diagram
pptx
CC BY-NC-SA 4.0 International
https://doi.org/10.5281/zenodo.5295817
zapperDAQ
multiple
GPL-3.0 License
https://doi.org/10.5281/zenodo.5295725
DAQC2Plate
multiple
GPL-3.0 License
https://doi.org/10.5281/zenodo.5295711
openHardwareDesignPrecipitator2021
multiple
GPL-3.0 License
https://doi.org/10.5281/zenodo.5295817
EP_1technical_drawing.pptx corresponds to Fig. 1.
EP_2assembled.pptx corresponds to Fig. 2.
EP_3schematic_high_voltage_power_supply_box.pptx corresponds to Fig. 3.
EP_4assembled_high_voltage_power_supply_box.pptx corresponds to Fig. 4
EP_5wire_diagram: EP_5wire_diagram.pptx corresponds to Fig. 5.
zapperDAQ: The data acquisition and control software repository.
DAQC2Plate: Julia wrapper of the data acquisition plate device driver.
openHardwareDesignPrecipitator2021: Repository includes data files and processing scripts.
Another design consideration was to keep the components modular and re-usable so that the materials can be repurposed for other uses after the project is completed. The device is simple enough that a graduate student without an engineering background can build it as part of a research project.Open designs such as the one presented here ensure that the science is accessible and that the instrumentation is affordable to a wider audience. It also provides an opportunity for the design to be improved upon [26], [27].The cost associated with building this device is less than that of the commercially available analog.Wire diagram of the Raspberry Pi, DAQC2, and power supplies.
Design files summary
Design file list including technical drawing of the EP, assembled parts of EP and electronic box, connectors, software screenshot, wire diagram, and software source code.EP_1technical_drawing.pptx corresponds to Fig. 1.EP_2assembled.pptx corresponds to Fig. 2.EP_3schematic_high_voltage_power_supply_box.pptx corresponds to Fig. 3.EP_4assembled_high_voltage_power_supply_box.pptx corresponds to Fig. 4EP_5wire_diagram: EP_5wire_diagram.pptx corresponds to Fig. 5.zapperDAQ: The data acquisition and control software repository.DAQC2Plate: Julia wrapper of the data acquisition plate device driver.openHardwareDesignPrecipitator2021: Repository includes data files and processing scripts.
Bill of materials summary
Bill of materials to construct the EP, including the electronic box, and cabling connections are provided in Table 2, Table 3, and Table 4, respectively. The items used in the bill of materials are not unique and substitutions for already available parts or from different vendors are possible. Small changes in dimensions will not affect the basic performance of the device.
Ground wire, Southwire E51583 F 90deg Cwire AWG 14
1
60
60
Southwire
Multiple
Table 4
Bill of materials to construct the connecting cabling.
Designator
Component
Number
Cost per unit - currency(USD)
Total cost – currency (USD)
Source of materials
Material type
-
Ethernet cable
-
-
-
-
Other
Molex 10112133
CONN HOUSING 13POS .100 HI PRESS
1
1
1
Digikey
Multiple
Molex 10112023
Headers & Wire Housings HOUSING 2 POS
1
1
1
Mouser
Plastic
Molex 08-55-0124
Headers, SOCKET 22-30AWG REEL Reel of 5000
100-pack
1
1
Allied electronics
Multiple
-
Screws
-
-
-
-
Steel
-
Screw/washer
-
-
-
-
-
Panduit DNF18-250FI-M
Terminals FREC-DSC 22-18 250X032 NYL RED
1-pack
5
5
Digikey
Multiple
Raspberry Pi Foundation KSA-15E-051300HU Black
Raspberry Pi 15.3W USB-C Power Supply
1
8
8
Digikey
Multiple
BNTECHGO FBA_SW20G10008F05C7
Cable wires, 20 AWG
1-pack
10
10
BNTECHGO
Multiple
LevitonR51-515PV-0OR
Ground plug, 15 Amp 125-Volt 3-Wire Plug, Orange
1
3
3
Leviton
Multiple
Southwire E51583 - AWG 14
Ground wire, Southwire E51583 F 90deg Cwire AWG 14
1
60
60
Southwire
Multiple
Bill of materials to construct the EP.Bill of materials to construct the power supply.Bill of materials to construct the connecting cabling.
Build instructions
Fig. 2 shows a photograph of the fully assembled EP. The numbers indicated in instructions correspond to the numbers in Fig. 2. Required tools include wrenches covering the sizes 1/4″, 9/16″, and 3/4″ or two adjustable wrenches, a drill, a metal tube cutter, and screwdrivers. Personal protective equipment should be worn when working with power tools, including goggles and gloves.Cut the polyethylene tube (#3) in half to get two polyethylene tubes 3″ long.Cut the stainless steel rod (#2) with a metal tube cutter to the desired length. We used 29″. Avoid creating any deformation on the rod during the cutting process.Place the stainless steel rod (#2) into the outer 3/4″ tube (#1) to create two concentric cylinders.Insert the concentric cylinders (#1 and #2) into one side of the 3/4″ x 3/4″ x 3/8″ union tee fitting (#5) having placed back and front nylon ferrules of 3/4″ size (#7 and #8).Tighten the nut with wrenches 1/8 turn past finger tight. Insert the polyethylene tube (#3) into the other side of the 3/4″ x 3/4″ x 3/8″ union tee fitting (#5) until the front ferrule seats against the body of the 3/4″ nuts.Tighten the nut with wrenches 1/8 turn past finger tight.Drill a hole into the plastic enclosure (#4).Pass the polyethylene tube through the drilled hole and insert polyethylene tube with 3/4″ back and front nylon ferrules (#7 and #8) until the front ferrule seats against the body of the 3/4″ nuts of the reducing union of 3/4″ x 1/4″ (#6). This step should be inside of the plastic enclosure (#4).Repeat the previous step for the other side of the cylinders too.Pass the 1/4″ back and front nylon ferrules (#9) through the rod between the 1/4″ nut (#16) and reducing union (#6). Make sure to tighten all the connections.Drill two holes into the metal enclosure box (#13) for both inlet and exit of the flows.Place the reducing port connector (#15) between the 3/8″ nuts and 1/4″ nuts.Connect the 1/4″ union (#10) to the 1/4″ nut (#16) with a bulkhead union (#11) which should pass through the drilled hole.Tighten all the connections 1/8 turn past finger tight using wrenches.Use washers (#14) for the drilled holes for both sides of the bulkhead union (#11) then tighten the union connections.Place a 1/4″ nut for the inlet of the EP by using a port connector (#12).Repeat the steps for the outlet side of the flow.Fig. 4 shows a photograph of the fully assembled power supply box. The numbers indicated in instructions correspond to the numbers in Fig. 4. A screwdriver, drill, wire terminal and crimper, and wire stripper are necessary tools for assembly. A voltmeter is needed for testing. To start the assembly. Instructions for MOLEX connections are given below;The connection between the power supply (#3) and Raspberry Pi is done using MOLEX connectors which include rectangular connectors (housings) (#10 and #11), headers (#12), and colored wires (#17).For the MOLEX connectors, the user needs to have a MOLEX-type wire cutter and a MOLEX-type hand crimper (for 10-22AWG according to the wire selection).First, match the wire gauge with a labeled hole on the wire cutter then strip the wire with a wire cutter by placing the wire into the proper hole. Cut the insulation of the wire. Slide the naked wire into the header (#12).Use the compression tool side of the crimper to slide the wire with the connector until they sit and compress the crimper to lock the header to the wire.Put slightly the locked wire connection into the housing (#10 or #11).Then repeat the previous steps for all colored wires (#17) to complete the power supply (#3) connection.Drill a hole into the ABS plastic enclosure box (#9) for the power switch button (#6) and outlet of the electrical socket for the EP (see further discussion below). Female nylon fully insulated connectors should be used for the wiring connection of the power switch button (#6). (The power switch needs to be ordered and wired to match the country's power grid).Then, make proper holes into the mounting plate (a part of #9), for the DIN rails (#5), and power supplies (#3 and #4).All wire connections are recommended to be completed outside the box before the last installation.Connect ground wire (#19) to the ground pin on the electrical plug (the biggest pin of the orange plug, see #18 in Fig. 4), and make sure to connect the ground pin to the ground wire of the plug.Use zip ties to connect the ground wire to the outside of the EP.Use a zip tie to connect a high-voltage cable (see further below, (HV) in Fig. 4 HV) to the inner rod. Attach the DIN rails (#5), Raspberry Pi (#2), DAQC2plate (#1), and power supplies (#3 and #4) to the bottom of the box.Connect the signal wires according to the wiring diagram given in Fig. 5.The wire installation step can be completed after placing the mounting plate into the box.After the last installation, it is crucial to test the continuity of the system to ensure that it is grounded and not shorted before powering up the device.The Ultravolt power supply is delivered with a custom connector specified in the order. We recommend selecting the desired connector and cable length when ordering the power supply. The “AT20” in the Ultravolt 10A12-P4-F-M-AT20 refers to the connector on the power supply output, which mates to the CA-15KV-1000. These options are shown in Fig. A1. The power supply was originally ordered to interface with a different instrument. However, for maximum safety, it is more desirable to have the CA-15KV-1000 connector facing outward from the box (14 in Fig. 4). We, therefore, cut the UV connector and spliced the high-voltage output from the power supply with the CA-15KV-1000 assembly. The splice-point is insulated with regular electrical tape and several layers of Kapton tape (Polyimide). A second high voltage cable connects the EP to the box. We had obtained a number of these cables from a surplus sale and thus had the cable on hand. The connector corresponds to the Amphenol-Alden A400QX“L” series. The connector/cable assembly can be ordered directly from Amphenol-Alden, independently of the power supply. Although the cable assembly is relatively inexpensive (∼$40), the company requires a minimum order of $750 for custom cables. We, therefore, recommend either request all extra cables when ordering the power supply or discuss other options with the company's sales representative.
Fig. A1
Connectors used in our system.
Operation instructions
After the installation, the safety issue is important for the operation of EP. Before plugging in (Fig. 4 #18) and switching on EP (Fig. 4 #6), make sure to pursue the following steps of 1) software installation and 2) high-voltage safety.
Software
The data acquisition and control software is stored on GitHub https://github.com/mdpetters/zapperDAQ. The README.md file includes detailed installation instructions. Fig. 6 shows a screenshot of the user interface. The user interface allows the user to toggle the power using an on/off switch and set the voltage. The on/off switch sends a voltage to the “ENABLE” pin (Fig. 5) and provides a software means to power down the device. The setpoint voltage sends the appropriately scaled voltage to the “REMOTE ADJUST” (Fig. 5). The system reads the reported high voltage and current from the respective pins. The time series displays the measured current and voltage. Note that the read voltage by the DAQC2Plate is biased. The reasons are not fully clear, but might be related to an impedance mismatch. Calibration is used in the software to correct for the bias. We recommend performing your own calibration between the setpoint voltage and the readout. We have observed no bias when reading the HVmon pin with a standard voltmeter or with a different multifunction DAQ device, such as the LabJack U3 or LabJackU6. Performing a precise voltage calibration is critical when generating low voltages (<200 V) and when voltage accuracy is important for the application (e.g when using the system to power a scanning mobility particle sizer). The calibration is less critical when the objective is limited to removing all particles. The primary purpose for displaying the readout voltage is to provide user feedback on the instrument state. Arcing will result in unstable readout voltage. Corona effects will show an unsteady readout current.
Fig. 6
Screenshot of the graphical user interface.
Screenshot of the graphical user interface.The current monitor is directly read by the analog-to-digital converter. Per specification of the power supply model, the current monitor includes a leakage current from the internal resistors. We do not subtract the leakage current in the software and thus the displayed current scales with the applied voltage. In the case of corona formation, the current visibly increases and the time series becomes noisy. For applications that require precise characterization of the current, users can subtract the leakage current in software, build an analog summing circuit, or invest in the “-I5 interface option” which provides improved monitoring capabilities.
High-Voltage safety
The safety advice here is provided for information. Users are responsible for conducting their own risk assessment. Users operate the device at their own risk. It is the sole responsibility of the user to follow all federal, state, local, and institutional safety protocols. We strongly recommend a safety audit by appropriately trained personnel before powering up the device for the first time.Electrical hazards may cause several damages to the human body. Electrical hazards include all power connections from the AC outlet and the high voltage applied to the electrostatic precipitator. Follow the standard safety protocols when working with 110 V/220 V AC power.The electrostatic precipitator's highest normal operating voltage is 3 kV DC, which refers to a high voltage platform during handling. However, the power supply may produce up to 10 kV output. For this reason, all calculations are carried to 10 kV. To reduce the electric shock of the system the high voltage supplies, the electrical cables, and Raspberry Pi are enclosed in an acrylonitrile butadiene styrene (ABS) plastic box. Parts with exposed high voltage are placed inside a secondary ABS enclosure. ABS plastic has a dielectric strength between 16.7 kV/mm [28]. The ABS plastic boxes have a thickness of at least>1 mm and are expected to insulate the user from electrical hazards even in the case of catastrophic failure (e.g. a detached wire).According to the most current international standard for Safety requirements for electrical equipment for measurement, control, and laboratory use BS EN 61010–1:2010 + A1:2019 [29], the DC voltages present in dry locations exceeding 70 Volts up to 15 kV is considered hazardous only if the current exceeds 2 mA DC or if the stored charge exceeds 45 μC[29]. In our high-voltage supply (#3 in Fig. 4), the highest voltage is 10 kV, and the current is 0.4 mA (for the Entire Output Voltage Range specified in the online datasheet). For additional safety requirements, a similar limiting consideration is applied to the EP where the stored charge on the rod is also calculated for the highest voltage value of 10 kV similar to the study of McGinness et al. (2019)[30]. The stored charge (Q in Coulombs) of the inside rod of the EP is Q = CxV where V is the voltage (in Volt) and C is the capacitance (in Farad). The capacitance is C = where ∈ is the permittivity of air 8.85x10−12F/m between the inner and outer rode, L = 0.3048 m (12″, the length of the cylinder), b = 0.007874 m (outer electrode radius), and a = 0.003175 m (rod radius). So the capacitance of the rod is 18.7 pF and the stored charge on the rod for 10 kV would be 18.7 pF × 10000 V = 0.187 μC. Thus, the calculated stored charge of the rod of EP with a high-voltage supply for 10 kV is also well below the standard values.Please note that the user should frequently inspect all cable connections. Always switch off all the power supplies and detach the main power cable before servicing the instrument. Even if the current is low, never touch cables, connectors, or power supplies during operation. Disconnect the plug or switch off the green button in case of emergency (see Fig. 4, #6). To avoid any injuries, it is important to always keep the cables and high voltage supplies dry.The EP box is grounded together with the outer rod. The polyethylene tube isolates the device on both sides. The edge points of the rods are also secured with ABS plastic boxes to provide further safety. Never open the secondary enclosures or touch the inner rod while in operation. At an operating voltage > 3 kV the system may arc. The excess current is deposited through the ground. To avoid unwanted accidental arcs, we strongly recommend testing the control voltage sent by the software with a voltmeter to ensure that the signal lines are working correctly.
Validation and characterization
Theory of the EP
Electrical mobility (z) can be simply defined by the movement of an electrically charged particle in an electric field [31]. In other words, electrical mobility is the ratio of the terminal velocity of the particle (the velocity calculated by the balance between the drag force and the electrostatic force) and the electrical field [31].The relationship between mobility and mobility diameter is:where z is the electrical mobility, k is the number of charges on the particle, e is the elementary charge, Cc is the Cunningham slip flow correction factor, η is the fluid viscosity, χ is the dynamic shape factor which is used due to increases drag forces for non-spherical cases, and D is the mobility diameter. Dve is the volume equivalent diameter and for non-spherical particles it is considered as a diameter that particle would have if it were melted to form a droplet including the voids in its shape [32]. For spherical particles χ = 1 and the mobility diameter and particle diameter are identical. Non-spherical particles have well-defined mobility diameter, and χ > 1 [23]. Typical values for χ are1.08 for cubical particles and up to 1.88 for agglomerates (e.g talc) [31].The DMA is used to size select particles based on their electrical mobility. As a first approximation, the tube can be modeled as a rudimentary version of a cylindrical DMA. For the cylindrical DMA and balanced flows, where the inlet and outlet flows have an equal flow rate throughout the instrument, the particle mobility selected by a DMA is given by [33]:where zs (m2/Vs) is the selected mobility, qsh is the flow rate, L is the column length, r1 and r2 are the radii of the inner and outer section of the annulus, and V is the potential applied between the two electrodes. Under given physical dimensions (constant L and r), particle electrical mobility becomes a function of qsh and V. Larger zs corresponds to a smaller mobility diameter. The precipitator does not have a sample flow or separate exit slit. As will be shown later using numerical simulation, Equation (2) predicts the critical mobility for the EP. Particles with electrical mobility larger than zs will all be removed. Some fraction of particles with electrical mobility less than zs will transmit. The largest completely removed mobility diameter is computed by applying zs to Equation (1). We define the transfer function such that the function defines the probability of a charged particle to leave the instrument along the stream at applied voltage [33]. For the electrostatic precipitator, we expect the transfer function to scale with the ratio z/zs.
Trajectory model
The particle trajectory through a cylindrical capacitor is given by a set of coupled differential equations [34], [35].where the radial electric field at position r, and ux(r) is the streamwise velocity at position r. The velocity profile ux(r) in the annulus is parabolic. The analytical steady-state solution for an incompressible, laminar flow of a Newtonian fluid in an infinitely long pipe annulus is given in the supplement of ref. [35]. Equations (3), (4) can be integrated numerically to find the particle trajectory through an idealized precipitator, assuming steady-state flow and neglecting entrance effects.We modeled the trajectory of particles through the EP precipitator with dimensions r1 = 1/8″ (inner electrode radius), r2 = 3/8″ (outer electrode radius), and L = 12″ (nominal electrode length). Particles of two different mobilities (colors) are released at three different starting locations. The assumed flow rate and voltage are 1 L min−1 and 346 V, respectively. The mobility of blue trajectories corresponds to zs and is computed using Eq. (1). The mobility of the yellow trajectory is 1/2 the value of the blue trajectory.The mobility parameter accounts for the electrical field strength, sheath flow, and physical dimensions of the precipitator for the ideal case. Thus, a particle’s radial position at the entrance of the precipitator will be the determining factor on whether it is removed from the flow. Unlike a DMA, the EP has no particle-free sheath flow and no exit slit. Without the sheath flow, particles are present at all radial coordinates, presumably at a uniform distribution. Fig. 7 shows example simulations for particles released at the three radial positions at the inlet of the instrument. Particles released closer to the center electrode are all captured by the wall of the inner electrode. The particles having mobility zs starting the furthest from the center electrode impact on wall of the inner electrode just before the exit of the column. Particles having mobility z < zs starting the furthest from the center electrode do not reach the wall of the electrode and will transmit. However, particles with the same mobility released closer to the center rod will be captured. Hence a fraction of particles having z < zs will transmit. Repeating the calculation for 200 trajectories released between r1 < r < r2 and evaluating the weighted fraction of trajectories not reaching the wall of the electrode is a measure of the expected transmission efficiency. The weight accounts for the fraction of fluid passing through the pipe for a given streamline.
Fig. 7
Modeled trajectory of particles through the EP precipitator with dimensions r1 = 1/8″ (inner electrode radius), r2 = 3/8″ (outer electrode radius), and L = 12″ (nominal electrode length). Particles of two different mobilities (colors) are released at three different starting locations. The assumed flow rate and voltage is 1 L min−1 and 346 V, respectively. The mobility of blue trajectories corresponds to zs and is computed using Eq. (1). The mobility of the yellow trajectory is 1/2 the value of the blue trajectory. The corresponding particle sizes for blue and yellow lines are 100 nm and 150 nm, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Modeled trajectory of particles through the EP precipitator with dimensions r1 = 1/8″ (inner electrode radius), r2 = 3/8″ (outer electrode radius), and L = 12″ (nominal electrode length). Particles of two different mobilities (colors) are released at three different starting locations. The assumed flow rate and voltage is 1 L min−1 and 346 V, respectively. The mobility of blue trajectories corresponds to zs and is computed using Eq. (1). The mobility of the yellow trajectory is 1/2 the value of the blue trajectory. The corresponding particle sizes for blue and yellow lines are 100 nm and 150 nm, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)The ideal transfer function of the cylindrical EP Fig. 8 shows the transfer function for the ideal cylindrical EP. Zero transmission is observed for z > zs. Transmission linearly increases with decreasing z/zs. In Fig. 7, particles are attracted to the inner rod. Reversing the polarity will deposit the same particles on the outer cylinder. The modeled ideal transfer function shown in Fig. 7 is independent of the direction of the electrical drift velocity, i.e. of the polarity of the power supply. As will be shown later, the ideal transfer function is not observed. Computational fluid dynamics (CFD) simulations are used to assess differences between the ideal precipitator and design used here.
Fig. 8
Ideal transfer function of the cylindrical EP.
Ideal transfer function of the cylindrical EP.
Computational fluid dynamics (CFD) simulations
Significant entrance and exit distortions of the transfer profile are expected due to the placement of the inlet perpendicular to the streamwise flow. Simulations of the 3D flow profile were carried out using the OpenFOAM v8 free-software toolbox. The annulus gap was discretized into an algorithmically created structured cylindrical grid with 151,334 hexahedral cells. Flow velocity at the inlet was set such that the average volumetric flow rate through the gap was 1 L min−1. The outlet pressure is fixed. Flow velocity at the walls was set to zero. Initial flow velocity inside the domain volume was set to zero. Simulations were carried out using the icoFoam solver, which applies the PISO algorithm [36] to solve for the evolution of the incompressible flow through the domain. Simulations were carried out for 4 s. Fluid trajectories were computed using the Runge-Kutta method. The simulation case files (mesh generation and solver settings) are easily adaptable to simulate altered geometries and are made available with the data repository.Fig. 9 shows the model domain for the CFD simulations. The inlet (left) and outlet (right) are modeled to represent the Swagelok T-fitting. At the entrance to the tube, the flow decelerates. Streamlines wrap around the inner cylinder to make up the flow along the tube on the side opposite the inlet. At ∼ 3 cm past the inlet, the 3D flow profile is fully equilibrated. Similarly, ∼3 cm before the outlet the flow accelerates and the streamlines curve toward the outlet of the device. Some of the streamlines flow into the dead volume to the left of the inlet and to the right of the outlet.
Fig. 9
Fluid dynamic simulation domain and fluid streamlines for a precipitator with dimensions r1 = 2/16″ (inner electrode radius), r2 = 3/8″ (outer electrode radius), L = 12″ (nominal electrode length), ri = 3/16″ (inlet radius). X, Y, and Z axes are shown in [m].
Fluid dynamic simulation domain and fluid streamlines for a precipitator with dimensions r1 = 2/16″ (inner electrode radius), r2 = 3/8″ (outer electrode radius), L = 12″ (nominal electrode length), ri = 3/16″ (inlet radius). X, Y, and Z axes are shown in [m].Fig. 10 shows the radial velocity distribution at three x-coordinates within the domain: close to the entrance and exit of the system and in the center where the flow is laminar. Near the entrance and exit, the fluid velocity is maximized at the side facing the inlet/outlet (see yellow dashed lines in Fig. 9 for reference). Flow velocity at the backside of the precipitator is reduced. In the center section of the domain, the modeled velocity distribution is within 1% of the analytical solution for the incompressible, laminar flow of a Newtonian fluid in an infinitely long pipe annulus.
Fig. 10
Streamwise velocity as a function of the radial coordinate near the inlet (0.015 m), the middle (0.194 m), and near the outlet (0.29 m) of the domain as predicted by the CFD simulation. The color scale for the inlet/outlet panels corresponds to the angular coordinate in a cylindrical coordinate system with (x,r,θ), where × is as in Fig. 7, r is the radial distance from the centerline, and θ is the angle. θ = 0° aligns with the z-axis in Fig. 7 and corresponds to the inlet side of the precipitator. θ = -180° aligns with the backside of the precipitator. Color in the middle panel corresponds to the analytical solution for the incompressible, laminar flow of a Newtonian fluid in an infinitely long pipe annulus (black) and the velocity at cell interfaces (red points). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Streamwise velocity as a function of the radial coordinate near the inlet (0.015 m), the middle (0.194 m), and near the outlet (0.29 m) of the domain as predicted by the CFD simulation. The color scale for the inlet/outlet panels corresponds to the angular coordinate in a cylindrical coordinate system with (x,r,θ), where × is as in Fig. 7, r is the radial distance from the centerline, and θ is the angle. θ = 0° aligns with the z-axis in Fig. 7 and corresponds to the inlet side of the precipitator. θ = -180° aligns with the backside of the precipitator. Color in the middle panel corresponds to the analytical solution for the incompressible, laminar flow of a Newtonian fluid in an infinitely long pipe annulus (black) and the velocity at cell interfaces (red points). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)The CFD simulations highlight several important points. Flow distortion near the entrance and exit is significant. Residence time and the electric field strength depend on the fluid trajectory. Since the inner electrode carries charge all the way through, and since the electric field near the inlet is distorted, the effective length of the precipitator will depend on the inlet geometry and to some extent on the flow rate. The dependence on flow rate is because the entrance length depends on the Reynolds number, which is set by the inlet diameter and flow rate. Some particles will be trapped in the volume to the left of the inlet and to the right of the outlet. Since the electric field remains active there, particles with long residence times in those areas will be lost. From the CFD simulation, it is expected that the true transmission efficiency is less than the ideal transmission efficiency shown in Fig. 8.
Experimental method
The transmission efficiency was characterized using experiments. Fig. 11 shows the schematic of the setup. To determine the transfer function of the precipitator, monodispersed aerosol was size selected by the DMA and fed through the system while varying the EP voltage. Fraction transmitted was monitored via particle counters on the inlet and outlet. Observations were made at multiple flow rates and different particle mobility diameters selected by DMA. Ambient particle concentration drawn from the lab air was found to be stable enough for the time scales of the experiment. Aerosols (range between 50 nm and 150 nm) are routed through the neutralizer (210Po) prior to entering a high-flow DMA [37] that is set up with a recirculating sheath flow loop of 9 L min−1. The DMA is operated at a constant voltage (negative polarity, Spellmann SLN10, Hauppauge, NY, USA) to classify particles by mobility (zDMA). The monodisperse flow is split between a condensation particle counter (CPC, TSI Model 3771) operated at 1 L min−1 and the EP. Note that the EP was operated with a power supply of opposite polarity than the DMA, resulting in a collection of the particles on the outer wall of the EP. The choice of positive polarity power supply was dictated by the ability to control low voltages. The choice of positive polarity power supply was dictated by the ability to control low voltages. The control logic of the Ultravolt units is 0–5 V for lowest-to highest voltage for positive polarity power supplies and 5–0 V for lowest-to-highest voltage. Since the DAC system is limited to a maximum 4.095 V signal, the negative polarity power supply cannot be as easily controlled to generate low voltages needed for the transmission experiments.
Fig. 11
Schematic view of the transmission experiments.
Schematic view of the transmission experiments.The outlet of the EP is connected to a second CPC also operated at 1 L min−1 flow rate. Optionally, particle-free dilution air (Teledyne Model 701, Teledyne Inc., Thousand Oaks, California, U.S.A.) is added between the outlet of the EP and CPC 2. Adding dilution air reduces the flow rate through the EP and alters the sheath-to-sample flow rate of the DMA. The ratio of CPC 2 (corrected for dilution) and CPC 1 concentration provides a measure of the transmission efficiency. Measurements with the unpowered EP were used to correct for the offset between the CPCs, which was < 10% and consistent with the manufacturer's specified accuracy of the instruments. Transmission efficiency was characterized by setting a combination of voltages to the DMA and EP followed by integrating counts for 4 min. The zero transmission for zDMA/zs corresponds to the voltage value where the transmission becomes near zero (see Fig. A2 in the Appendix).
Fig. A2
The voltage range for the experiment until the fraction transmitted becomes near zero.
The mean ratio of the two CPCs was computed for a 4 min time segment. Error propagation was used to estimate the 95% confidence interval of the mean for each ratio. Experiments were performed for flow rates of 1, 0.8, 0.6, and 0.5 L min−1 flow rate through the EP. The critical zs were computed according to Equation (1). However, the length was adjusted to an effective length, where the effective length was adjusted such that transmission for zDMA = zs was zero.
Results and discussion
The derived effective lengths are 0.13 m, 0.15 m, 0.208 m, and 0.215 m and increase with decreasing flow rate. The notion of an effective length is qualitatively supported by the CFD simulations, which show significant entrance and exit distortions. The increasing effective length with decreasing flow rate is expected because the entrance length scales with the inlet Reynolds number. Higher flow rates result in longer entrance length and thus shorter effective length. The entrance length for laminar flow in a pipe scales linearly with the Reynolds number [38]. The figures for Reynolds number versus flow rate and Reynolds number versus effective lengths (12′- derived effective lengths) are given in the appendix as a Fig. A4 and Fig. A5.
Fig. A4
Reynolds number versus flow rate within the EP.
Fig. A5
Reynolds number versus effective length(m) for the EP.
Fig. 12 summarizes the transmission efficiency experiments (see Fig. A3 for the transmission of particles in the EP according to the CPCs), which comprise a range of flow rates and mobility diameters. Error bars are omitted from the figure for clarity. The average 95% confidence interval of the derived ratio was ± 0.061. After adjustment for the effective length, the data collapse onto a single transfer function that is described by the empirical formula . The observations show that the transmission efficiency is significantly smaller than the predicted value for the ideal EP (Fig. 8), even after adjustment for the effective length. The exact reason for the deviation is not known, but particles trapped in the dead volumes to the left of the inlet and to the right of the outlet are a plausible explanation. Despite these non-idealities, the transfer function is reproducible. However, the transfer function should be verified experimentally for each instrument and flow rate rather than relying on the empirical model. In most cases, the purpose of the EP is to remove all charged particles of certain mobility. For this application, the precise transfer function is not relevant and only the value of zs is important.
Fig. 12
Observed transmission efficiency of different particle mobility diameters (shapes) and flow rates (color). The solid blue line corresponds to the model . (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. A3
Time series for CPC1 and CPC2 data for 4 min scan of an applied voltage of 20 V. The data correspond to 140 nm particles of 0.6 L min−1. Black lines represent concentration as count entering the EP and blue lines show the concentrations as count exiting the EP after an applied voltage for 4 min. The time series of the ratio value of each CPC is given in a green line and the mean value is shown with a red line. The time-series data example for the 2 CPCs is given in Fig. A3 for 140 nm particles of 0.6 L min−1. The CPC counts for an applied voltage are given in blue and black lines. The average of the CPCs ratio values is given in green lines with a mean value (red line). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Observed transmission efficiency of different particle mobility diameters (shapes) and flow rates (color). The solid blue line corresponds to the model . (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)The largest recommended voltage applied to the EP for the selected configuration is 3 kV. For larger voltages arcing may occur. Fig. 13 summarizes the voltage required to remove 50% or 100% of singly charged particles as a function of mobility diameter, calculated using zs based on the observed effective length. Values are tabulated in Table A1. At 0.5 L min−1 and 1 L min−1 flow rate, for this geometry of EP, the largest diameters of singly-charged spherical particles that can be removed with 100% efficiency are 624 nm and 253 nm, respectively. The expression T = (1- zDMA/zs)3 can be used to estimate the transmission for particles larger than the cutoff. For example, a 1 μm particle and a 0.5 L min−1 flow rate the calculated transmission is 0.0765, based on a critical mobility of 1.8 × 109 m2 V−1s−1 and zDMA of 1.1 × 109 m2 V−1s−1.
Fig. 13
Relationship between voltage and diameter in the EP. Solid lines represent the size where particles are removed to 100%. Dashed lines correspond to a 50% removal efficiency. Calculations are based on Eq. (1), , and the effective length associated with the flow rate.
Table A1
Digitized version of Fig 13 in main manuscript. The voltages, diameters, and % 50 particle diameters for 2 flow rates of 0.5 and 1 L min−1 are given for spherical particles in the EP.
1 L min−1
0.5 L min−1
V (Volt)
D (nm)
50%D (nm)
D (nm)
50%D (nm)
10
10.86476
24.34499
19.99626
45.52782
40.20202
22.10593
50.52408
41.22762
97.73265
70.40404
29.54059
68.45689
55.60197
135.6928
100.6061
35.5952
83.4524
67.51588
168.8782
130.8081
40.87097
96.81874
78.05513
199.5739
161.0101
45.62977
109.1228
87.69123
228.7472
191.2121
50.01371
120.6705
96.67929
256.9058
221.4141
54.11008
131.6488
105.1756
284.3496
251.6162
57.97705
142.1817
113.2838
311.2698
281.8182
61.65567
152.3559
121.077
337.7949
312.0202
65.17618
162.2351
128.6089
364.0145
342.2222
68.56164
171.8674
135.92
389.9928
372.4242
71.83005
181.2902
143.0422
415.7773
402.6263
74.99583
190.5332
150.0007
441.4032
432.8283
78.07073
199.6203
156.8159
466.8976
463.0303
81.06446
208.5711
163.5048
492.2814
493.2323
83.98515
217.402
170.0815
517.5708
523.4343
86.83971
226.1267
176.5579
542.7786
553.6364
89.63405
234.7568
182.944
567.9154
583.8384
92.37327
243.3023
189.2487
592.9894
614.0404
95.06183
251.7716
195.4794
618.0076
644.2424
97.70363
260.1723
201.6429
642.9756
674.4444
100.3021
268.5108
207.7447
667.8981
704.6465
102.8604
276.7928
213.7902
692.7794
734.8485
105.3811
285.0232
219.7837
717.6227
765.0505
107.8667
293.2066
225.7294
742.4312
795.2525
110.3195
301.3468
231.6308
767.2073
825.4545
112.7414
309.4473
237.4913
791.9534
855.6566
115.1343
317.5113
243.3137
816.6715
885.8586
117.4998
325.5416
249.1006
841.3635
916.0606
119.8394
333.5408
254.8546
866.031
946.2626
122.1545
341.511
260.5778
890.6754
976.4646
124.4464
349.4545
266.2722
915.2981
1006.667
126.7162
357.373
271.9396
939.9003
1036.869
128.9651
365.2683
277.5817
964.4833
1067.071
131.194
373.1418
283.2
989.048
1097.273
133.4039
380.9951
288.7959
1013.595
1127.475
135.5956
388.8294
294.3708
1038.126
1157.677
137.77
396.6459
299.9259
1062.642
1187.879
139.9278
404.4456
305.4622
1087.143
1218.081
142.0698
412.2297
310.9809
1111.629
1248.283
144.1965
419.9989
316.4828
1136.103
1278.485
146.3086
427.7541
321.9688
1160.563
1308.687
148.4067
435.4961
327.4399
1185.012
1338.889
150.4913
443.2256
332.8967
1209.449
1369.091
152.563
450.9433
338.3399
1233.875
1399.293
154.6222
458.6498
343.7704
1258.291
1429.495
156.6694
466.3457
349.1885
1282.697
1459.697
158.7051
474.0314
354.5951
1307.093
1489.899
160.7296
481.7074
359.9905
1331.48
1520.101
162.7434
489.3744
365.3754
1355.859
1550.303
164.7468
497.0325
370.7502
1380.229
1580.505
166.7402
504.6823
376.1154
1404.591
1610.707
168.7239
512.3241
381.4713
1428.946
1640.909
170.6982
519.9582
386.8185
1453.293
1671.111
172.6634
527.585
392.1572
1477.634
1701.313
174.6199
535.2048
397.4878
1501.967
1731.515
176.5679
542.8178
402.8107
1526.295
1761.717
178.5076
550.4243
408.1262
1550.616
1791.919
180.4394
558.0246
413.4346
1574.931
1822.121
182.3634
565.6189
418.7361
1599.241
1852.323
184.2799
573.2074
424.0311
1623.545
1882.525
186.1892
580.7903
429.3197
1647.844
1912.727
188.0913
588.3679
434.6023
1672.138
1942.929
189.9866
595.9402
439.879
1696.427
1973.131
191.8752
603.5075
445.1501
1720.711
2003.333
193.7573
611.0699
450.4158
1744.991
2033.535
195.6332
618.6276
455.6762
1769.267
2063.737
197.5028
626.1808
460.9315
1793.538
2093.939
199.3666
633.7295
466.182
1817.806
2124.141
201.2245
641.2739
471.4278
1842.069
2154.343
203.0767
648.8142
476.6689
1866.329
2184.545
204.9235
656.3504
481.9057
1890.586
2214.747
206.7648
663.8826
487.1382
1914.839
2244.949
208.601
671.4111
492.3666
1939.088
2275.152
210.4321
678.9358
497.591
1963.335
2305.354
212.2582
686.4568
502.8115
1987.578
2335.556
214.0794
693.9744
508.0282
2011.818
2365.758
215.8959
701.4885
513.2413
2036.055
2395.96
217.7079
708.9992
518.4508
2060.29
2426.162
219.5153
716.5066
523.6569
2084.522
2456.364
221.3184
724.0109
528.8597
2108.751
2486.566
223.1171
731.512
534.0592
2132.977
2516.768
224.9117
739.0101
539.2555
2157.201
2546.97
226.7022
746.5052
544.4488
2181.423
2577.172
228.4887
753.9973
549.6391
2205.643
2607.374
230.2713
761.4867
554.8264
2229.86
2637.576
232.0501
768.9732
560.0109
2254.075
2667.778
233.8252
776.457
565.1927
2278.287
2697.98
235.5966
783.9382
570.3717
2302.498
2728.182
237.3645
791.4167
575.5481
2326.707
2758.384
239.1289
798.8927
580.7219
2350.914
2788.586
240.8899
806.3661
585.8933
2375.119
2818.788
242.6475
813.8371
591.0621
2399.322
2848.99
244.4019
821.3057
596.2286
2423.523
2879.192
246.1531
828.772
601.3928
2447.723
2909.394
247.9012
836.2359
606.5546
2471.921
2939.596
249.6462
843.6975
611.7142
2496.117
2969.798
251.3882
851.157
616.8717
2520.312
3000
253.1273
858.6142
622.0269
2544.505
Relationship between voltage and diameter in the EP. Solid lines represent the size where particles are removed to 100%. Dashed lines correspond to a 50% removal efficiency. Calculations are based on Eq. (1), , and the effective length associated with the flow rate.The primary use for the EP described here is to remove charged particles in the dual tandem DMA [16], [19], [22], [39]. Traditionally, EPs have been used for estimating the neutral fraction after passage through a bipolar neutralizer. A typical setup generates particles, size-classifies particles in a DMA, passes the particles through a bipolar charger [40], [41], [42], [43] followed by passage through the EP [44], [45], [46], [47]. The EP here is suitable for this type of experiment for particles with D < ∼600 nm. Another potential application is the purification of air in an indoor environment. However, since the EP only removes charged particles, an aerosol charging device must be used upstream. Unipolar aerosol chargers generally charge 100% of particles with one or multiple charges for D > ∼20 nm [48]. Unipolar charging can impart > 10 charges for particle D > 100 nm. Thus, the EP here could be used for removal of all particles > 20 nm at a higher flow rate than characterized here. The exact flow rate is unclear due to the effects of turbulence and entrance length in the EP, and flow rate limitations of a hypothetical unipolar aerosol charger. Assuming a flow rate of 2 L min−1, it would require 500 s to effectively filter 1 m−3 of air. High performance filters are likely a more efficient and more cost-effective method to purify indoor air.In this study, we describe and characterize a low-cost design of an electrostatic precipitator. The largest diameters for 100% removal efficiency of singly charged particles are 253 nm and 624 nm for 1 and 0.5 L min−1 flow rates, respectively for the given geometry of the EP. The upper size cut can be changed by changing the length of the tube. The total accommodated flow can be changed by scaling the tube dimensions.The transfer function for the transmitted particles differs from the ideal precipitator. Even though the transfer function is non-ideal, it is unique for a range of flow conditions. We suspect that the largest source of deviation from the model is due to the variable effective length of the precipitator, and deviation from the theoretically expected transmission efficiency at z < zs. Non-idealities are attributed to the distortion of the flow at the entrance and exit points of the device. The observed non-idealities are qualitatively consistent with computational fluid dynamics simulations of the flow profile.The main focus of this study was to design an open-hardware electrostatic precipitator to completely remove charged particles from a stream. The design is versatile, with components such as the fittings and the power‐supply box of the electrostatic precipitator able to be reused in other projects. The power supply box can be used in other common aerosol science applications, including unipolar corona charging [49] or electrospray aerosol generation [50].The high-voltage power supply described here was used because we use the same units to power many of our scanning mobility particle sizer (SMPS) systems [51]. Indeed, the power supply box can be used for SMPS data acquisition and control if a USB-to-serial adapter is added to read the concentration from the condensation particle counter. Without the high-voltage power supply (the estimated cost is less than $300), the setup can function as a generic low-cost data acquisition system with GUI (graphical user interface) control.Additional cost savings are possible if the objective is limited to removing charged particles from the stream, without the need to adjust the voltage. For such a system a mechanical on/off switch and lower-cost high voltage power supply are sufficient. For example, we estimate that an on/off power box with a fixed 1 to 3 kV supply line to the EP can be built for ∼$300 using the Q-series modules from XP-power (Allen, Texas, USA). Such a solution would provide a ∼$400 cost savings over the approach and also obviate the need for a single-board computer and software control. Hardware costs can also be reduced further by using cheaper brass fittings or lower quality compression fittings.Keeping the cost low and the components generic and reusable may provide a gateway to use the design in a classroom setting to teach students about instrument design and development. Since no machining is needed, assembly of the EP is simple enough that non-engineering graduate students can build the device as part of a research project. Thus, this work may help broaden participation in aerosol science and technology.
Potential design improvements
Several design choices were made ad-hoc or were based on existing equipment.For example, the high-voltage connector assembly could be more elegant. We used a NEMA metal box (see Fig. 2, #13) for the EP enclosure. Drilling through the box is difficult and the overall weight is larger than necessary. A corresponding lighter plastic enclosure might be cheaper and easier to work with.The power supply box (see Fig. 4, #9) was not tall enough for DIN rail mounting of the Raspberry Pi computer as intended. If the users prefer to assemble our configuration, they might select a smaller box. If they wish to mount the computer vertically, they would need to select a taller box to accommodate the space for the Raspberry Pi power supply. The use of cable zip ties for ground and electrical connectors is not elegant but works and allows for flexibility in the design. Affixing formal connectors would improve the design.
CRediT authorship contribution statement
Sabin Kasparoglu: Formal analysis, Data curation, Validation, Writing – original draft, Visualization. Timothy P. Wright: Conceptualization, Methodology, Writing – review & editing, Software. Markus D. Petters: Supervision, Methodology, Resources, Data curation, Conceptualization, Methodology, Software, Funding acquisition, Project administration, Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Specifications table
Hardware name
Electrostatic Aerosol Precipitator
Subject area
Engineering and materials science
Educational tools and open source alternatives to existing infrastructure
Hardware type
Measuring physical properties and in-lab sensors
Field measurements and sensors
Aerosol sampling equipment
Closest commercial analog
Cambustion Aerosol Electrostatic Precipitator
Open source license
All software is distributed under the GPL-v3 license. The design is licensed under the Attribution-NonCommercial-ShareAlike 4.0 International Public License (CC BY-NC-SA 4.0 International)
Authors: J M Roux; R Sarda-Estève; G Delapierre; M H Nadal; C Bossuet; L Olmedo Journal: Environ Sci Pollut Res Int Date: 2015-10-10 Impact factor: 4.223
Authors: Aleksandra Marsh; Sarah Suda Petters; Nicholas Ernest Rothfuss; Grazia Rovelli; Young Chul Song; Jonathan Philip Reid; Markus Dirk Petters Journal: Phys Chem Chem Phys Date: 2018-06-06 Impact factor: 3.676
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