According to PM2.5, the average annual concentration is 10mcg/m3 and the average daily concentration is 25mcg/m3; exceeding the average annual PM10 of 20 µg/m3 and the average daily 50 µg/m3) increases the risk of respiratory diseases, diseases of the cardiovascular system and some oncological diseases, pollution has already been classified as a group 1 carcinogen. Highly toxic particles (containing lead, cadmium, arsenic, beryllium, tellurium, etc., as well as radioactive compounds) are dangerous even at low concentrations.
The easiest step to reduce negative impact dust on the body - installation effective cleaner air in the bedroom, where a person spends about a third of the time.
Dust sources
Large natural sources of dust are volcanic eruptions, the ocean (spray evaporation), natural fires, soil erosion (for example, dust storms: Zabol, Iraq), earthquakes and various soil collapses, plant pollen, fungal spores, biomass decomposition processes, etc.Anthropogenic sources include fossil fuel combustion processes (energy and industry), transportation of fragile/bulk materials and loading operations(see Vostochny port, Nakhodka, Vanino port, Khabarovsk Territory), crushing of materials (mining, production of building materials, agricultural industry), mechanical processing, chemical processes, thermal operations (welding, smelting), exploitation Vehicle(exhaust of internal combustion engines, abrasion of tires and road surface).
The presence of dust particles in the premises is due to the intake of polluted outdoor air, as well as the presence of internal sources: the destruction of materials (clothes, linen, carpets, furniture, building materials, books), cooking, human life (epidermis particles, hair), moldy fungi, house mites dust, etc.
Available Air Purifiers
To reduce the concentration of dust particles (including the most dangerous - less than 10 microns in size), household appliances are available that work on the following principles:- mechanical filtration;
- air ionization;
- electrostatic precipitation (electrostatic precipitators).
- high hydraulic resistance of the filter element;
- the need for frequent replacement of an expensive filter element.
During operation, the air ionizer electrically charges dust particles suspended in the air of the room, due to which the latter, under the action of electrical forces, are deposited on the floor, walls, ceiling or objects in the room. The particles remain in the room and may return to suspension, so the solution does not look satisfactory. In addition, the device significantly changes the ionic composition of the air, while the impact of such air on people has not been studied enough at the moment.
The operation of an electrostatic cleaner is based on the same principle: the particles entering the device are first electrically charged, then attracted by electric forces to special plates charged with the opposite charge (all this happens inside the device). When a layer of dust accumulates on the plates, cleaning is performed. These purifiers have a high efficiency (over 80%) of particle trapping different sizes, low hydraulic resistance, and do not require periodic replacement of consumables. There are also disadvantages: the production of a certain amount of toxic gases (ozone, nitrogen oxides), a complex design (electrode assemblies, high-voltage power supply), the need for periodic cleaning of the precipitation plates.
air purifier requirements
When using a recirculating air purifier (such a purifier sucks air from the room, filters it, and then returns it to the room), the characteristics of the device (single-pass efficiency, volumetric efficiency) and the volume of the target room must be taken into account, otherwise the device may be useless. For this purpose, the American organization AHAM developed the CADR indicator, which takes into account the single-pass cleaning efficiency and the volumetric performance of the cleaner, as well as a method for calculating the required CADR for a given room. There is already a good description of this indicator here. AHAM recommends using a purifier with a CADR value greater than or equal to five room volume changes per hour. For example, for a 20m2 room with a ceiling height of 2.5m, the CADR should be 20 * 2.5 * 5 = 250m3/h (or 147CFM) or more.Also, the cleaner during operation should not create any harmful factors: exceeding the permissible values of the noise level, exceeding the permissible concentrations of harmful gases (in the case of using an electrostatic precipitator).
Uniform electric field
From the course of physics, we remember that near a body with an electric charge, a electric field.The force characteristic of the field is the intensity E [Volt/m or kV/cm]. tension electric field is a vector quantity (has a direction). It is customary to represent the tension graphically by force lines (the tangents to the points of the force curves coincide with the direction of the tension vector at these points), the magnitude of the tension is characterized by the density of these lines (the more densely the lines are located, the greater the value of the tension in this area).
Consider the simplest system of electrodes, which consists of two parallel metal plates located at a distance L from each other, a potential difference of voltage U from a high voltage source is applied to the plates:
L= 11mm = 1.1cm;
U = 11kV (kilovolt; 1kilovolt = 1000volt);
The figure shows an approximate location lines of force. It can be seen from the line density that in most of the space of the interelectrode gap (with the exception of the region near the edges of the plates), the intensity has same value. Such a uniform electric field is called homogeneous . The value of tension in the space between the plates for this electrode system can be calculated from a simple equation:
This means that at a voltage of 11 kV, the intensity will be 10 kV / cm. Under these conditions, atmospheric air filling the space between the plates is an electrical insulator (dielectric), that is, it does not conduct electricity, so no current will flow in the electrode system. Let's check it out in practice.
In fact, air conducts electricity very little.
Atmospheric air always contains a small amount of free charge carriers - electrons and ions formed as a result of exposure to natural external factors– for example, background radiation and UV radiation. The concentration of these charges is very low, so the current density is very small values, my equipment is unable to register such values.
Equipment for experiments
A high voltage source (HPV), a test electrode system and a "measuring stand" will be used for small practical experiments.
The electrode system can be assembled into one of three options: "two parallel plates", "wire-plate" or "teeth-plate": 
The interelectrode distance for all variants is the same and is 11 mm.
The stand consists of measuring instruments:
- voltmeter 50kV (microammeter Pa3 50µA with additional resistance R1 1GΩ; 1µA reading corresponds to 1kV);
- microammeter Pa2 at 50 μA;
- milliammeter Pa1 at 1mA.
At high voltages, some non-conductive materials suddenly start to conduct current (such as furniture), so everything is mounted on a sheet of Plexiglas. This mess looks like this: 
Of course, the accuracy of measurements with such equipment leaves much to be desired, but for observing general patterns it should be enough (better than nothing!). With the introductions over, let's get down to business.
Experiment #1
Two parallel plates, uniform electric field;L=11mm=1.1cm;
U = 11…22kV.
According to the readings of the microammeter, it is clear that there is no electric current. Nothing has changed at 22kV, and even at 25kV (the maximum for my high voltage source).
| U, kV | E, kV/cm | I, µA |
|---|---|---|
| 0 | 0 | 0 |
| 11 | 10 | 0 |
| 22 | 20 | 0 |
| 25 | 22.72 | 0 |
Electrical breakdown of the air gap
A strong electric field can turn an air gap into an electrical conductor - for this it is necessary that its strength in the gap exceeds a certain critical (breakdown) value. When this happens, ionization processes begin to take place in the air with high intensity: basically impact ionization And photoionization, which leads to an avalanche-like increase in the number of free charge carriers - ions and electrons. At some point in time, a conducting channel (filled with charge carriers) is formed, covering the interelectrode gap, through which the current begins to flow (the phenomenon is called electrical breakdown or discharge). In the zone of ionization processes, there are chemical reactions(including the dissociation of molecules that make up the air), which leads to the production of a certain amount of toxic gases (ozone, nitrogen oxides).Ionization processes
Impact ionization
Free electrons and ions of various signs, always present in atmospheric air in a small amount, under the influence of an electric field will rush in the direction of the electrode of opposite polarity (electrons and negative ions - to positive, positive ions - to negative). Some of them will collide with atoms and molecules of air along the way. If kinetic energy moving electrons / ions is sufficient (and it is the higher, the higher the field strength), then during collisions electrons are knocked out of neutral atoms, resulting in the formation of new free electrons and positive ions. In turn, new electrons and ions will also be accelerated by the electric field and some of them will be able to ionize other atoms and molecules in this way. So the number of ions and electrons in the interelectrode space begins to increase like an avalanche.
Photoionization
Atoms or molecules that have received an insufficient amount of energy for ionization during a collision emit it in the form of photons (the atom / molecule tends to return to its previous stable energy state). Photons can be absorbed by any atom or molecule, which can also lead to ionization (if the photon's energy is sufficient to detach an electron).
For parallel plates in atmospheric air, the critical value of the electric field strength can be calculated from the equation:
For the electrode system under consideration, the critical strength (under normal atmospheric conditions) is about 30.6 kV/cm, and the breakdown voltage is 33.6 kV. Unfortunately, my high voltage source cannot deliver more than 25kV, so to observe the electrical breakdown of air, I had to reduce the interelectrode distance to 0.7cm (critical strength 32.1kV/cm; breakdown voltage 22.5kV).
Experiment #2
Observation of electrical breakdown of the air gap. We will increase the potential difference applied to the electrodes until an electrical breakdown occurs.L=7mm=0.7cm;
U = 14…25kV.
Gap breakdown in the form of a spark discharge was observed at a voltage of 21.5 kV. The discharge emitted light and sound (click), the arrows of the current meters deviated (meaning that the electric current flowed). At the same time, the smell of ozone was felt in the air (the same smell, for example, occurs during the operation of UV lamps during the quartzization of rooms in hospitals).
Volt-ampere characteristics:
| U, kV | E, kV/cm | I, µA |
|---|---|---|
| 0 | 0 | 0 |
| 14 | 20 | 0 |
| 21 | 30 | 0 |
| 21.5 | 30.71 | breakdown |
Non-uniform electric field
Let's replace the positive plate electrode in the system of electrodes with a thin wire electrode with a diameter of 0.1mm (ie R1=0.05mm), also located parallel to the negative plate electrode. In this case, in the space of the interelectrode gap, in the presence of a potential difference, heterogeneous electric field: the closer the point of space to the wire electrode, the higher the value of the electric field strength. The figure below shows an approximate distribution pattern:
For clarity, it is possible to build a more accurate picture of the intensity distribution - it is easier to do this for an equivalent electrode system, where the plate electrode is replaced by a tubular electrode located coaxially to the corona electrode:
For this electrode system, the strength values at the points of the interelectrode space can be determined from a simple equation:
The figure below shows the calculated picture for the values:
R1=0.05mm=0.005cm;
R2=11mm=1.1cm;
U = 5kV;
The lines characterize the value of tension at a given distance; the values of adjacent lines differ by 1 kV/cm.
From the distribution pattern, it can be seen that in most of the interelectrode space, the intensity changes insignificantly, and near the wire electrode, as it approaches it, it increases sharply.
corona discharge
In the electrode system wire-plane (or similar, in which the radius of curvature of one electrode is significantly less than the interelectrode distance), as we saw from the picture of the distribution of tension, the existence of an electric field with the following features is possible:- in a small area close to the wire electrode, the electric field strength can reach high values (significantly exceeding 30 kV / cm), sufficient for the occurrence of intense ionization processes in the air;
- at the same time, in most of the interelectrode space, the electric field strength will take on low values - less than 10 kV/cm.
In the interelectrode gap with a corona discharge, two zones are distinguished: ionization zone (or discharge case) And drift zone:
In the ionization zone, as you might guess from the name, ionization processes take place - impact ionization and photoionization, and ions of different signs and electrons are formed. The electric field present in the interelectrode space affects electrons and ions, due to which electrons and negative ions (if any) rush to the corona electrode, and positive ions are forced out of the ionization zone and enter the drift zone.
In the drift zone, which accounts for the main part of the interelectrode gap (the entire space of the gap except for the ionization zone), ionization processes do not occur. Here, a lot of positive ions drifting under the action of an electric field (mainly in the direction of the plate electrode) are distributed.
Due to the directed movement of charges (positive ions close the current to the plate electrode, and electrons and negative ions to the corona electrode), an electric current flows in the gap, corona current .
In atmospheric air, depending on the conditions, a positive corona discharge can take one of the following forms: avalanche or streamer. The avalanche form is observed in the form of a uniform thin luminous layer covering a smooth electrode (for example, a wire), there was a photo above. The streamer form is observed in the form of thin luminous filamentous channels (streamers) directed from the electrode and more often occurs on electrodes with sharp irregularities (teeth, spikes, needles), photo below:
As in the case of a spark discharge, side effect The occurrence of any form of corona discharge in the air (due to the presence of ionization processes) is the production of harmful gases - ozone and nitrogen oxides.
Experiment #3
Observation of a positive avalanche corona discharge. Corona electrode - wire, positive power;L=11mm=1.1cm;
R1=0.05mm=0.005cm
Discharge Glow:
The corona process (an electric current appeared) began at U = 6.5 kV, while the surface of the wire electrode began to be uniformly covered with a thin, weakly luminous layer and the smell of ozone appeared. It is in this luminous region (the corona discharge sheath) that the ionization processes are concentrated. With an increase in voltage, an increase in the intensity of the glow and a nonlinear increase in the current were observed, and when U = 17.1 kV was reached, the interelectrode gap overlapped (the corona discharge turned into a spark discharge).
Volt-ampere characteristics:
| U, kV | I, µA |
|---|---|
| 0 | 0 |
| 6,5 | 1 |
| 7 | 2 |
| 8 | 20 |
| 9 | 40 |
| 10 | 60 |
| 11 | 110 |
| 12 | 180 |
| 13 | 220 |
| 14 | 300 |
| 15 | 350 |
| 16 | 420 |
| 17 | 520 |
| 17.1 | overlap |
Experiment #4
Observation of a negative corona discharge. Let's swap the power supply wires of the electrode system (negative wire to the wire electrode, positive wire to the plate electrode). Corona electrode - wire, negative power;L = 11 mm;
R1 = 0.05 mm = 0.005 cm.
Glow:
Coronation began at U = 7.5 kV. The nature of the glow of the negative corona differed significantly from the glow of the positive corona: now separate pulsating luminous points equidistant from each other appeared on the corona electrode. With an increase in the applied voltage, the discharge current increased, as well as the number of luminous points and the intensity of their glow. The smell of ozone was stronger than with a positive corona. The spark breakdown of the gap occurred at U = 18.5 kV.
Volt-ampere characteristics:
| U, kV | I, µA |
|---|---|
| 0 | 0 |
| 7.5 | 1 |
| 8 | 4 |
| 9 | 20 |
| 10 | 40 |
| 11 | 100 |
| 12 | 150 |
| 13 | 200 |
| 14 | 300 |
| 15 | 380 |
| 16 | 480 |
| 17 | 590 |
| 18 | 700 |
| 18.4 | 800 |
| 18.5 | overlap |
Experiment #5
Observation of a positive streamer corona discharge. Let's replace the wire electrode in the electrode system with a sawtooth electrode and return the polarity of the power supply to its original state. Corona electrode - toothed, positive power;L=11mm=1.1cm;
Glow:
The corona process began at U = 5.5 kV, and thin luminous channels (streamers) appeared on the tips of the corona electrode directed towards the plate electrode. As the voltage increased, the size and intensity of the glow of these channels, as well as the corona current, increased. The smell of ozone was similar to that of a positive avalanche corona. The transition of a corona discharge to a spark discharge occurred at U = 13 kV.
Volt-ampere characteristics:
| U, kV | I, µA |
|---|---|
| 0 | 0 |
| 5.5 | 1 |
| 6 | 3 |
| 7 | 10 |
| 8 | 20 |
| 9 | 35 |
| 10 | 60 |
| 11 | 150 |
| 12 | 300 |
| 12.9 | 410 |
| 13 | overlap |
As was seen from the experiments, the geometric parameters of the corona electrode, as well as the polarity of the supply, significantly affect the pattern of current variation with voltage, the value of the discharge ignition voltage, and the value of the gap breakdown voltage. These are not all the factors affecting the corona discharge mode, here is a more complete list:
- geometric parameters of the interelectrode space:
- geometric parameters of the corona electrode;
- interelectrode distance;
- the polarity of the power supply supplied to the corona electrode;
- parameters of the air mixture filling the interelectrode space:
- chemical composition;
- humidity;
- temperature;
- pressure;
- impurities (aerosol particles, for example: dust, smoke, fog)
- in some cases, the material (value of the electron work function) of the negative electrode, since electrons can be detached from the surface of the metal electrode during bombardment with ions and during irradiation with photons.
Electric air purification: working principle
The principle of electrical cleaning is as follows: air with suspended particles of pollution (particles of dust and / or smoke and / or fog) is passed at a speed of Vv.p. through the interelectrode gap in which the corona discharge is maintained (positive in our case).
Dust particles are first electrically charged in the corona discharge field (positively), and then attracted to the negatively charged plate electrodes due to the action of electrical forces.
Particle charging
Drifting positive ions, which are present in large quantities in the interelectrode corona gap, collide with dust particles, due to which the particles acquire a positive electric charge. The charging process is carried out mainly by two mechanisms − shock charging ions drifting in an electric field and diffusion charging ions involved in the thermal motion of molecules. Both mechanisms operate simultaneously, but the first is more significant for charging large particles (more than a micrometer in size), and the second for smaller particles. It is important to note that with an intense corona discharge, the rate of diffusion charging is much lower than the shock one.Charging processes
The shock charging process proceeds in a stream of ions moving from the corona electrode under the action of an electric field. Ions that are too close to the particle are captured by the latter due to molecular attractive forces acting at short distances (including the mirror image force due to the interaction of the ion charge and the opposite charge induced by electrostatic induction on the surface of the particle).
The mechanism of diffusion charging is carried out by ions involved in the thermal motion of molecules. An ion that is close enough to the surface of the particle is captured by the latter due to molecular forces of attraction (including the mirror image force), therefore, an empty region is formed near the surface of the particle, where there are no ions:
Due to the resulting concentration difference, diffusion of ions to the surface of the particle occurs (the ions tend to occupy the empty region), and as a result, these ions are trapped.
With any mechanism, as the particle accumulates a charge, a repulsive electric force begins to act on the ions located near the particle (the charge of the particle and ions of the same sign), so the charging rate will decrease over time and at some point stop completely. This explains the existence of a particle charge limit.
The amount of charge acquired by a particle in the corona gap depends on the following factors:
- the ability of the particle to charge (the charging rate and the limiting charge, more than which the particle cannot be charged);
- the time allotted for the charging process;
- electrical parameters of the area in which the particle is located (electric field strength, concentration and mobility of ions)
Drift and particle settling
There is an electric field in the interelectrode space of the corona electrode system, therefore, the Coulomb force Fк immediately begins to act on the particle that has received any charge, due to which the particle begins to shift in the direction of the collecting electrode - a drift velocity W arises:
The value of the Coulomb force is proportional to the charge of the particle and the electric field strength at its location:
Due to the movement of a particle in the medium, a resistance force Fс arises, depending on the size and shape of the particle, the speed of its movement, as well as the viscosity of the medium, therefore, the increase in the drift velocity is limited. It is known that the drift velocity of a large particle in the field of a corona discharge is proportional to the electric field strength and the square of its radius, while that of a small particle is proportional to the field strength.
After some time, the particle reaches the surface of the collecting electrode, where it is held by the following forces:
- electrostatic attractive forces due to the presence of a charge on the particle;
- molecular forces;
- forces due to capillary effects (in the case of the presence of a sufficient amount of liquid and the ability of the particle and the electrode to wetting).
These forces oppose the air flow, which tends to rip off the particle. The particle is removed from the air stream.
As you can see, the corona gap of the electrode system performs the following functions necessary for electrical cleaning:
- production of positive ions to charge particles;
- providing an electric field for directional drift of ions (necessary for particle charging) and for directional drift of charged particles towards the collecting electrode (necessary for particle deposition).
Several factors can have a significant impact on the electrical cleaning process:
- high quantitative concentration of pollution particles; leads to a deficiency of ions (most of them are deposited on particles), as a result of which the intensity of corona decreases, up to termination (the phenomenon is called corona locking), deterioration of the parameters of the electric field in the gap; this leads to a drop in the efficiency of the charging process;
- accumulation of a layer of dust on the collecting electrode:
- if the layer has a high electrical resistance, then it accumulates an electric charge of the same sign as the charge of the drifting particles (and the polarity of the corona electrode), as a result of which:
- the intensity of the corona discharge decreases (due to the deformation of the electric field in the gap), which negatively affects the process of charging particles and the process of particle drift to the collecting electrode;
- the charged layer has a repulsive effect on the deposited particle, which has a charge of the same sign, which negatively affects the deposition process;
- if the layer has a high electrical resistance, then it accumulates an electric charge of the same sign as the charge of the drifting particles (and the polarity of the corona electrode), as a result of which:
- electric wind (the appearance of an air flow in the direction from the corona electrode towards the collecting electrode) in some cases can have a noticeable effect on the trajectory of particles, especially small ones.
Electrode electric filter systems
As you move away from the corona electrode in the direction along the plates, the value of the field strength decreases. Let us conditionally single out an active region in the interelectrode gap, within which the field strength takes on significant values; outside this area, the processes required for electrical cleaning are inefficient due to insufficient tension.
The scenario of the movement of a pollution particle in practice may differ from that described earlier: for example, the particle will not reach the collecting electrode (a), or the deposited particle may for some reason break away (b) from the collecting electrode, followed by entrainment by the air flow:
It is obvious that in order to achieve high cleaning quality indicators, it is necessary that the following conditions are met:
- each particle of contamination must reach the surface of the collecting electrode;
- each particle that has reached the collecting electrode must be securely held on its surface until it is removed during cleaning.
- increase in drift velocity W;
- decrease in air flow velocity Vv.p.;
- increasing the length S of the collecting electrodes in the direction of air movement;
- a decrease in the interelectrode distance L, which will lead to a decrease in the distance A (which the particle must overcome in order to reach the collecting electrode).
Of greatest interest, of course, is the possibility of increasing the drift velocity. As noted earlier, it is mainly determined by the magnitude of the electric field strength and the charge of the particle, therefore, to ensure its maximum values, it is necessary to maintain an intense corona discharge, and also to ensure sufficient residence time (at least 0.1 s) of the particle in the active region of the gap (so that the particle managed to get a significant charge).
The value of the air flow velocity (at a constant size of the active region) determines the residence time of the particle in the active region of the gap, and, consequently, the time allotted for the charging process and the time allotted for the drift process. In addition, an excessive increase in speed leads to the occurrence of the phenomenon of re-entrainment - to pulling out the precipitated particles from the collecting electrode. The choice of flow rate is a compromise, since a decrease in speed leads to a drop in the volumetric productivity of the device, and a significant increase in a sharp deterioration in the quality of cleaning. Usually the speed in electrostatic precipitators is about 1 m/s (may be in the range of 0.5…2.5 m/s).
An increase in the length S of the collecting electrode will not be able to have a significant positive effect, since in the elongated part of the interelectrode gap outside the conditional active region (large distance from the discharge electrode), the electric field strength and, therefore, the drift velocity of the particle will be small:
Installing an additional discharge electrode in the extended part will greatly improve the situation, but for a domestic appliance this solution may cause problems with the production of toxic gases (due to the increase in the total length of the discharge electrode):
Devices with such an arrangement of electrodes are known as multi-field electrostatic precipitators (in this case, a two-field electrostatic precipitator) and are used in industry to purify large volumes of gases.
Reducing the interelectrode distance (L → *L) will lead to a decrease in the path (*A< A), который необходимо преодолеть частице, чтобы достигнуть осадительного электрода:
Due to the reduction of the interelectrode distance, the potential difference U will be reduced, due to which the size of the active region of the interelectrode gap will also decrease. This will lead to a reduction in the time allowed for the charging process and the particle drift process, which in turn can lead to a decrease in the quality of cleaning (especially for small particles with low charging ability). In addition, reducing the distance will result in a reduction in the cross-sectional area of the core. The problem of area reduction can be solved by parallel installation of the same electrode system:
Devices with such an arrangement of electrodes are known as multi-section electrostatic precipitators (in this case, two-section) and are used in industrial installations. This design has an increased length of the corona electrode, which can cause problems with the production of toxic gases.
A hypothetical high efficiency electrical filter would probably contain a number of electrical fields and cleaning sections:
Each particle entering this multi-section multi-field electrostatic precipitator would have time to receive the maximum possible charge, since the device provides an active charging area of great length. Each charged particle would reach the surface of the collecting electrode, since the device provides a long active deposition area and reduces the distance that a particle needs to overcome in order to settle on the electrode. The device could easily cope with the high dust content of the air. But such an arrangement of electrodes, due to the large total length of the corona electrodes, will produce an unacceptably large amount of toxic gases. Therefore, such a design is completely unsuitable for use in a device designed to purify the air that will be used by people for breathing.
At the beginning of the article, an electrode system consisting of two parallel plates was considered. She has a very useful properties in the case of its use in a household electrostatic precipitator:
- the electric discharge in the electrode system does not flow (there are no ionization processes), therefore, toxic gases are not produced;
- a uniform electric field is formed in the interelectrode space; therefore, the breakdown strength of the interelectrode gap is higher than that of the equivalent gap with a corona electrode.
Let us replace the second corona wire electrode in the two-field electrode system with a plate electrode:
The air purification process in the modified electrode system is slightly different - now it proceeds in 2 stages: first, the particle passes through a corona gap with an inhomogeneous field (active region 1), where it receives an electric charge, then enters a gap with a uniform electrostatic field (active region 2), which ensures the drift of the charged particle to the collecting electrode. Thus, two zones can be distinguished: the charging zone (ionizer) and the precipitation zone (precipitator), which is why this solution has received the name - two-zone electrostatic precipitator. The breakdown strength of the interelectrode gap of the precipitation zone is higher than the breakdown strength of the gap of the charging zone; therefore, a greater value of the potential difference U2 is applied to it, which provides a greater value of the electric field strength in this zone (active region 2). Example: consider two gaps with the same interelectrode distance L=30mm: with a corona electrode and with a plate electrode; the breakdown value of the average strength for a gap with an inhomogeneous field does not exceed 10 kV/cm; the breakdown strength of the gap with a uniform field is about 28 kV/cm, (more than 2 times higher).
An increase in the field strength will improve the quality of cleaning, since the force that ensures the drift of charged dust particles is proportional to its value. Remarkably, the electrode system of the deposition zone consumes almost no electricity. In addition, since the field is uniform, along the entire length of the zone (in the direction of air movement), the intensity will take on the same value. Due to this property, it is possible to increase the length of the electrodes of the precipitation zone:
As a result, the length of the active deposition region (active region 2) will increase, which will provide an increase in the time allotted for the drift process. This will improve the quality of cleaning (especially for small particles with a low drift velocity).
One more improvement can be made to the electrode system: to increase the number of electrodes in the settling zone:
This will lead to a decrease in the interelectrode distance of the precipitation zone, resulting in:
- the distance that a charged particle needs to overcome in order to reach the collecting electrode will decrease;
- the breakdown strength of the interelectrode gap will increase (it can be seen from the equation of the critical tension of the air gap), due to which it will be possible to provide even higher values of the electric field strength in the deposition zone.
The length of the active region 2 in the direction of air movement in this case, which is important, will not decrease. Therefore, an increase in the number of electrodes in the precipitator will also improve the quality of cleaning.
Conclusion
Ultimately, we came up with a two-zone electrode system that has a high quality of removal of suspended particles, even small ones, which are most difficult to capture (low chargeability and, therefore, low drift rate) at a low level of toxic gases produced (assuming use of a positive avalanche corona). The design also has disadvantages: at a high quantitative concentration of dust, the corona locking phenomenon will occur, which can lead to a significant decrease in cleaning efficiency. As a rule, residential air does not contain this amount of pollution, so this problem should not arise. Due to a good combination of characteristics, the devices with similar electrode systems are successfully used for fine air purification in rooms.If possible, the next part will contain materials on the design and assembly at home of a full-fledged two-zone electrostatic air purifier.
Many thanks to Yana Zhirova for the provided camera: without it, the quality of photo and video materials would be much worse, and there would be no photos of the corona discharge at all.
Nazarov Mikhail.
Sources
- Electrophysical fundamentals of technology high voltage. I.P. Vereshchagin, Yu.N. Vereshchagin. - M.: Energoatomizdat, 1993;
- Purification of industrial gases by electrostatic precipitators. V.N. Uzhov. - M .: Publishing house "Chemistry", 1967;
- Technique of dust collection and purification of industrial gases. G.M.-A. Aliev. - M .: Metallurgy, 1986;
- Industrial gas cleaning: Per. from English. - M., Chemistry, 1981.
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Unfortunately, the air in our homes cannot be called perfect. Moreover, on the street it is much cleaner, because it is cleaned by the sun and natural ionization, blown by the wind, moistened by rain. Can we create such conditions in our home to purify the air? Airing and vacuuming alone will not be enough: they are not able to destroy dust and decay products: carbon monoxide, nitrogen oxides, ammonia and much more. Of course, there is a way out - to buy such an air purifier device. If we talk about how the air purifier works, then everything is simple. The air in the room passes through the device, and dust, allergens, fluff, tobacco smoke, chemicals settle on its filters. Now manufacturers offer various devices: with a carbon or HEPA filter, plasma, ionizing, photocatalytic and air washing.
Let's just say that the cost of such a device is not low. And besides, deciding which is the best is not so easy. Therefore, if you have skillful hands, we suggest that you create a device with your own hands.
How to do
The proposed air purifier is an air washer, where water acts as a filter, which purifies the air from allergens, dust, and dirt. As a result, the air is not only purified, but also humidified. In addition, water is the cheapest filter.
The air in modern homes can hardly be called clean: it contains a large amount of dust, as well as a variety of toxins emitted by furnishings.
To combat this, air purifiers are designed, different models of which are offered by modern market household appliances. In addition to a ready-made expensive device, you can also make an air purifier with your own hands, saving a significant amount on this.
What kind of cleaners can be made?
Before you start developing a homemade air purifier, you need to determine what level of moisture is contained in the air of the apartment. This indicator should not fall below 30% and at the same time exceed 75%. You can determine the level of this parameter using a conventional psychrometer. If the moisture content in the air mixture of the room does not meet this standard, it is necessary to make not just an air purification device, but a device that, in addition to its main function, will also humidify or dry the air.
Depending on the humidity level of the air mixture, one of two types of cleaners can be made:
- for air mixture with high moisture content;
- for dry air.
Device for dry environment
To make an air purifier with a low moisture content, you need to prepare the following materials:
- a plastic container with a tight-fitting lid;
- a low-power fan, which is a good computer cooler;
- water, best distilled;
- power source for the cooler - it can be ordinary batteries.
First of all, holes are made in the lid of the container to secure the fan. It should be noted that such a design must be fixed as securely as possible, otherwise the fan may fall into the water, which will lead to a short circuit.
To ensure economical energy consumption, such a home-made device can be equipped with a relay that will turn off and start the cleaner at certain, predetermined intervals. When assembling electrical circuit in this case, care must be taken to ensure that the fan is not supplied with a voltage exceeding its nominal value.
Installing the cover homemade device in place, a do-it-yourself indoor air purification device is ready. By turning it on, the air from the room will enter the container, where it will mix with water particles, thus moistening. All harmful microorganisms and dust contained in it absorb water particles. As a result of all this, the air will become not only cleaner, but also humid.
Additionally, the device can also be equipped with a carbon filter by installing it on the fan. In this case, it will be possible to provide even more reliable air purification in the house.
In addition, to heighten the effect, some masters advise putting some kind of silver product on the bottom of the container, which will ensure the purification of water inside the container.
Humid Air Device
The second option is a do-it-yourself air purifier for a too humid environment, when this figure is more than 60%. In this case, additional humidification of the air mixture is not required.
To make such a device, you need to prepare:
- plastic container and lid to it;
- low power fan;
- common salt;
- any porous material - gauze, foam rubber, cotton wool or something similar.
Two holes are made in the container on opposite sides at different levels - one for installing the cooler, the other for passing the air mixture. The next step in creating a homemade cleaner is to install a fan on the first hole, and the selected cleaning material on the second. Salt is poured inside the container, which should be slightly lower than the cooler and at the same time completely cover the filter.
The principle of operation of the made device is that the air entering it passes through the salt, on the surface of which harmful substances and excess moisture from the air will settle. At the same time, the pure air mixture will be saturated with salt particles - chloride ions with sodium. Passing through a porous filter, such a mixture will contribute to the destruction of microbes living in the home, thus providing double air purification.
It should be noted that when making such a device, it is recommended to choose a low-power fan. Otherwise, salt crystals will constantly drum on the walls of the plastic container, thus creating unnecessary noise.
Thus, we considered two main options homemade devices, which provide good air purification in the home. Of course, such simple instrument designs that can be easily made with your own hands, even without special skills, literally from improvised means, do not differ. high level efficiency compared to serious factory models.
But if you take into account the difference in the price of the finished device and the total cost of the materials used for a homemade cleaner, any complaints are simply inappropriate.
Content:
The current ecological situation in many cases is far from favorable. Environment is predominantly contaminated. Dust and other small particles enter the premises of residential buildings and other objects where people are located. It is possible to solve the problem with the help of air cleaners. They are especially indispensable for home use. The principle of operation of the air cleaner may be different in each model, so this factor must be taken into account when buying a device.
Purpose of the air cleaner
Almost all people breathe house dust every day. She only seems safe, gradually building up various problems with health. Dust itself quite often leads to complications and malfunctions of the respiratory system. In addition, exposure to dust can cause inflammation in the mucous membranes and lead to various skin diseases. The likelihood of diseases due to dust is significantly increased with a weakened immune system incapable of protecting the body.
Even more harm is caused not by the dust itself, but by all kinds of bacteria and other microorganisms contained in it. Many of them are disease-causing and pose a serious health hazard.
The task of providing clean and fresh air is successfully solved by using air purifiers. All types of air purifiers contribute to the guaranteed and high-quality purification of the air space of the premises.
The principle of operation of air purifiers
The principle of operation of air cleaners is quite simple. The scheme of operation is the drawing of air through the inlet, its further passage through different kinds cleaning and subsequent release into the room in a clean state.
However, no type of air purifier is capable of a full replacement for wet cleaning or a vacuum cleaner. These devices are capable of passing through themselves dust in small quantities and only that which is in suspension. Dust that has settled on surfaces remains in place and is not affected by the air purifier. Great importance For normal operation The air cleaner has additional air filtration. It is recommended to use the minimum power of the device, in order to avoid strong air currents, due to which dust may appear.
The principle of operation of the air cleaner is reflected in the designs of various devices. In the operation of humidifiers, air is cleaned using wet filters, where dust settles. Devices - air filters are equipped with several filter stages, through which polluted air circulates and returns to the room already cleaned. For additional cleaning, the filters are treated with special substances - photocatalysts that destroy bacteria and other harmful elements.
Ionizers use special anions that can attract dust particles. Combined purifier designs simultaneously use filtration, humidification and other functions. The main component of all cleaning devices are filters. It is they who are entrusted with the main task of cleaning. The simplest and cheapest are mechanical filters made in the form of a coarse mesh that performs preliminary air purification. As a rule, they are used in combination with other types of filters. Water filters are also designed for coarse cleaning. Wet plates are used to collect dust, and then it accumulates in containers with water.
Fine cleaning takes place with the help of carbon filters used in combination with coarse cleaning devices. Photocatalytic filters use ultraviolet radiation to oxidize and decompose all kinds of harmful impurities. Under its influence, any toxic substances are neutralized.
How to choose an air purifier
The efficiency of air purification largely depends on right choice air cleaner. Experts recommend, first of all, to take into account the size of the room. The larger the volume and area, the greater the power of the device should be.
It should be remembered that the principle of operation of the air cleaner used in a particular model directly affects the quality of cleaning. The higher the quality indicators, the more powerful and expensive the device should be. For example, the effect of a photocatalytic filter far exceeds the capabilities of a mechanical device that filters only large particles.
Useful additional functions are ionization and humidification, which significantly improve the quality of cleaning. It is of great importance, therefore, the power of the air cleaner must be selected in accordance with the mode and schedule of its use. It is desirable that the device works quietly, especially if there are small children in the family.
Not so long ago, the topic was raised how to clean an apartment or a separate workplace from tobacco smoke. But it turns out that for other conditions, you can assemble a simple air purifier with your own hands. True, we make a reservation, knowledge of the rules for installing electrical devices and safety requirements are required.
When the need arises for purifiers with additional features
Humidity is considered normal from 30 to 75 percent, while for different types premises are subject to different standards.
You can check this indicator using conventional psychrometers (the simplest is two conventional thermometers, the working capsule of one of which is placed in a humid environment, while the humidity is determined by the difference in instrument readings). More convenient are modern electronic devices that are highly accurate.
If the humidity in the room does not meet the standards, you should think about how to make an air purifier that will not only trap dust, but also humidify or dehumidify the air as an additional option.
As a basis for all the proposed devices, we will take the already described design of a plastic container and a conventional computer fan (cooler). When assembling, the following main points must be considered:
- The depth of the plastic container should be at least 50-70 mm (the larger this indicator, the less often you will have to change the water in the device).
- The role of an additional filter and aerator is played by water poured onto the bottom of the container. For safety reasons, its level should not reach the fan by at least 30 mm, otherwise moisture may enter the electrical parts of the structure.
- Considering that the operation of even a small fan causes a certain vibration, it is necessary to securely fasten the cooler using standard bolts. If reinforcement is needed, a cut-to-size sheet metal plate can be used.
- When air passes through the structure, dust partially settles in air droplets that are in suspension. This also increases the humidity in the room.
By the way, especially lazy people use a washing vacuum cleaner to humidify the air, which works on a similar principle.
Recommended for rooms with high humidity levels homemade cleaner air, capable of removing excess moisture from the room atmosphere.
In principle, the design of such a cleaner practically does not differ from the device described above. Only instead of water, salt is used as a filtering agent, covered with a layer of porous material. Ordinary table salt has a significant moisture absorption, pay attention to its condition in a damp room.
When the air flow passes through the salt filter layer, there is a significant absorption of water vapor, while the porous material ensures the retention of dust particles.
It is worth noting that for such home-made devices, a fan with a low impeller speed should be used.
Otherwise, a powerful air flow can bring salt crystals into suspension, as a result of which the level of noise generated during operation will increase significantly (salt will beat against the walls of the vessel and the fan impeller).
Silica gel can also be recommended as a high-tech desiccant, packages of which can be found in packages of branded shoes and other wardrobe items. But it should be borne in mind that this reagent quickly absorbs moisture, so the effectiveness and long-term operation of the cleaner can only be achieved with a significant layer of the substance. Therefore, the depth of the container used as the body of the cleaner must be increased.
If there is a need to clean the air in rooms with a large area, it is recommended to purchase factory-made units. At the moment, you can choose a purifier with a wide variety of filters that provide both humidification and dehumidification in automatic mode.
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