SE458163B - Air transport and treatment system - Google Patents

Abstract

An air permeable target electrode (M) is arranged concentrically around a wire-like corona electrode (K). The electrodes are connected to a d.c. voltage source (3) which causes a corona discharge at the corona electrode and an ion wind through the target electrode. The target elecrode is cylindrical, and air flows axially into it through one or both of its open ends. The air exits radially through its air permeable wall. The target electrode may be divided into two separate parts arranged concentrically around the corona electrode (K) in a spaced relationship. In this case, the air flows radially inwards through the interspaces between the different target parts, and the air exits radially through these parts.

Description

F-V ”W 458 163 10 l5 20 25 30 35 2 which are perceived as irritating and can even be häsovåaiiga for humans. It is therefore desirable to have a moderate corona current and a large distance between the corona electrode and the target electrode. Furthermore, as is apparent from the international patent application, the known devices of this kind require a careful shielding of the corona electrode, so that the generated air ions are prevented from traveling in directions other than to the target electrode. Since a device of this kind is not to be used exclusively for air transport, ie. as a clean fan, but also for treating the air, for example cleaning it from air pollutants and / or changing the air temperature, a large air turnover is admittedly desirable, but not a high air flow rate. Rather, a low air flow rate is desired, as this provides a longer residence time for the flowing air at the air treating means and thus a greater efficiency, without the air treating means having to have a large extent in the direction of the air flow. Enclosing the electrode arrangement in an air flow channel, in which the air treating means are arranged together with or downstream of the target electrode, which is the natural and most obvious arrangement, has been found to give rise to significant problems. Thus, it has proved very difficult to achieve an even velocity distribution over the entire cross-sectional area of the air flow duct, which impairs the efficiency of the air treatment means. It is also difficult to avoid that the air-treating means constitute a significant flow resistance, which requires an increase in the potential difference between the corona electrode and the target electrode, which results in an increase in the crown current.

The latter, however, constitutes a serious inconvenience due to the concomitant increased generation of ozone and nitrogen oxides. Furthermore, the electrode arrangement surrounding the walls of the air flow duct has a disturbing effect on the function of the corona electrode, so that the corona discharge and a desired efficient manner. The object of the present invention is therefore that the corona current does not develop to provide an improved air transporting and air treating device of the type indicated in the introduction, which solves most of the problems discussed above.

The characteristics of the device according to the invention appear from the appended claims.

In the following, the basic principle of the invention and possible and advantageous further developments of the invention will be described in more detail in connection with the accompanying drawing, which illustrates by way of example some embodiments of the invention, Figs. 1 and 2 schematically showing an axial section and a radial section, respectively. by a first embodiment of a device according to the invention; Figs. 3, U, 5 and 6 schematically and by way of example illustrate some different possible designs of the measuring electrode and of means for treating the air in a device according to the invention; Figs. 7, 8, 9, 10 and 15 schematically and by way of example illustrate some different possible arrangements at the corona electrode in a device according to the invention for removing harmful gases generated during the corona discharge; Fig. 11 schematically shows an axial section through another embodiment of a device according to the invention; and Fig. 12 schematically shows an axial section through a further embodiment of a device according to the invention; and Figs. 13 and 1u schematically show radial sections through further embodiments of a device according to the invention.

The device according to the invention shown diagrammatically and by way of example comprises a corona electrode K, which consists of a thin wire suspended between only schematically shown, suitably designed holders 1. Furthermore, the device contains a measuring electrode M, which is designed as a corona electrode K coaxially enclosing cylinder. In the exemplary embodiment shown, this measuring electrode M consists of a sparse network of electrically conductive or semiconducting material, which is held in place between two rings 2 of insulating material supported in a suitable manner, not shown in more detail, for example plastic rings. The corona electrode K and the target electrode M are connected 458 163 IU to each of the poles of a direct voltage source 3, this voltage and the distance between the corona electrode and the target electrode, i.e. the diameter of the measuring electrode M, are so adapted that a corona discharge occurs at the corona electrode K. This corona discharge gives rise to ions which, under the influence of the electric field, migrate to the measuring electrode M. As described in more detail in the previously mentioned international patent application, this gives rise to an air flow in the direction of the measuring electrode M. In the present device, therefore, an air flow arises in the manner marked in Fig. 1 by means of arrows 4, i.e. air flows in through the open axial ends of the cylindrical measuring electrode M and flows out in a substantially radial direction through the air-permeable measuring electrode M.

By this arrangement of the measuring electrode M along a corona electrode K concentric surrounding circle several significant advantages are obtained. Thus, the corona discharge occurs symmetrically around the entire corona electrode K, whereby significantly greater total corona current can be achieved with unchanged potential difference and unchanged distance between corona electrode and target electrode than is possible with the arrangements of target electrode described in the previously mentioned international patent application. Alternatively, a smaller potential difference can be used with unchanged corona current. It is further understood that the air flow rate becomes very small in the immediate vicinity of the corona electrode K, which is a significant advantage, as it thereby becomes much easier to neutralize the harmful gases, preferably ozone and nitrogen oxides, which are generated by the corona discharge.

This will be described in more detail below.

A further very significant advantage of an arrangement according to the invention is that the flow areas, for example through the cylindrical measuring electrode M, become very large, which gives correspondingly low flow velocities.

These low flow rates are an excellent advantage, as they allow an efficient treatment of the air, for example purification thereof from aerosol and / or gaseous pollutants or cooling or heating, by means of suitable means for this, which are arranged in the air flow. Path, preferably adjacent to or immediately radially outside the cylindrical measuring electrode M or at the open axial ends of the measuring electrode, where the air flows in, or at both places. Since the flow areas at these places are large, the air treating means also do not give rise to any large flow resistances. Since the corona electrode is essentially completely surrounded by target electrodes, the disturbing effects on the function of the corona electrode K do not occur, which proved to be very troublesome when the electrode arrangement is arranged inside an air flow duct with walls, the inside of which is electrically insulating while the outside is conductive and grounded.

It has been found advantageous that the corona electrode K has such a length that it extends axially beyond the axial ends of the target electrode N. This means, compared with a device where the corona electrode K has the same axial length as the target electrode M, that the potential difference between the corona electrode and the target electrode can be reduced with unchanged corona current and further that the total air circulation through the device increases.

In a device according to the invention, the radial distance between the corona electrode K and the target electrode M is suitably greater than 5 cm 2 and preferably greater than 8 cm. In a device according to Fig. 1, H, the radius of the measuring electrode M, i.e. the distance between the corona electrode K and the measuring electrode M, be approximately equal to the axial height of the measuring electrode M. If the measuring electrode M has a radius of, for example, 1G cm, the corona electrode K can extend, for example, 3-H about outside the axial ends of the measuring electrode M.

As shown in Fig. 1, the corona electrode K and the counter electrode M are advantageously connected to the voltage source 3 via high-impedance resistors 5, which in the event of a short circuit of the corona electrode K and the target electrode M, for example due to an unintentional contact, limit the short circuit current. to a completely harmless value. This makes the device harmless to the touch. In order to further prevent a direct contact of the corona electrode or the target electrode or to eliminate any emergence of electrostatic fields from the device, protective grids can be arranged outside the open axial ends of the M 458 163 10 h. These protective grids can consist of, for example, plastic or, when electrostatic shielding is desired, of semiconducting or conductive material, in which latter case the protective grids are advantageously earthed.

Such protective grids can be placed at a distance of a few centimeters axially from the K ends of the corona electrode and can extend to the outer edges of the plastic rings. An undesired corona current to the protective grids can be prevented by connecting the corona electrode K to a suitable positive or negative potential relative to ground while connecting the target electrode M to a potential of opposite polarity relative to ground, which also significantly reduces the insulation problems of high potentials relative to ground. may cause. To further prevent corona current in the undesired direction from the corona electrode K, annular shield electrodes can be arranged at some axial distance from the ends of the corona electrode K, these shield electrodes being advantageously connected to the same potential as the corona electrode K. In Fig. 1, such annular shield electrodes are schematically shown and denoted by S.

In the embodiment shown in Figures 1 and 2 as an example, the measuring electrode M has been assumed to consist of a sparse network of electrically conductive or semiconducting material. It should be noted in this connection that the currents received by the target electrode are extremely small and that the term "electrically conductive or semiconductor" with respect to the material of the target electrode must be interpreted in this regard. The conductivity of the target electrode material must thus in practice be very low. It will be appreciated that many other designs of the target electrode M are possible. The measuring electrode could thus consist of axially directed rods arranged at a distance from each other along a coronary electrode K concentrically enclosing circle. Instead of such rods, it is also possible in a corresponding manner to arrange disc-shaped or lamella-shaped electrode elements, which extend axially and parallel to the corona electrode K and have their side surfaces radially directed, i.e. parallel to the radially directed air flow through the target electrode. The target electrode may also consist of a plurality of planar, annular electrode elements arranged concentrically around the corona electrode K at axially spaced apart distances from each other. The measuring electrode can also be designed as a helically extending wire or lamella arranged concentrically around the corona electrode. The aforesaid means for treating the air, which means are preferably arranged in connection with or radially outside the measuring electrode M, may be of different types. They can thus, for example, consist of an ordinary mechanical filter for purifying the air from aerosol-shaped pollutants, ie. particles or liquid droplets, or a chemically active filter, for example containing activated carbon, to remove gaseous pollutants from the air. Since the aerosol-shaped contaminants which accompany the air flow out through the measuring electrode M are electrically charged as a result of the ion generation caused by the corona discharge, these electrically charged aerosol-shaped contaminants can advantageously be separated from the air stream by electrostatic means. For this purpose, it is possible, for example, to use an air-permeable structure arranged radially outside the target electrode M, for example in the form of thin lamellae, of electret material. Since the target electrode M has the opposite polarity to the charge of the electrically charged aerosol-shaped contaminants, the contaminants will have a tendency to stick to the target electrode, so this can advantageously also be used as a precipitation surface for the contaminants in an electrostatic filter device, for example of the electrostatic type. capacitor separator. For influencing the temperature of the flowing air, ie. heating or cooling, a suitably designed convector can be arranged radially outside the cylindrical measuring electrode.

Pig. 3-6 show diagrammatically and as examples some different possible designs of the measuring electrode together with some different possible devices for treatment of the flowing air.

In the arrangement illustrated in Fig. 3, the target electrode M is designed in a manner similar to that described above in connection with Figs. 1, 2. Radially outside this target electrode M there is a further cylindrical electrode R, for example consisting of a sparse network of conductive or semiconducting material, which electrode R is grounded and thus has an electric potential which has the same polarity relative to the polarity of the measuring electrode H 458 163 lÛ l5 30 (u Un 8 polarity as the corona electrode K. As mentioned, as a result of the ion generation the pollutants in the air tend to stick to the target electrode M, which has the opposite electrical polarity relative to the polarity of the electrically charged pollutants.Pollutants that do not immediately stick to the target electrode M but pass through it, come under the influence of the electric field between the target electrode H and the further the electrode R is forced to turn back towards the target electrode M, so that they securely attach to it. the consequence of this is that the force exerted on the charged pollutants of the electric field between the two electrodes M and R is able to overcome the radially outwardly directed air flow through the electrodes M and R. Due to the low air flow rate, this is easy to achieve. The electrode R can thus be considered as a reflector electrode for the charged pollutants, which provides a very efficient separation of the ssa from the air stream.

Pig. 4 shows a similar arrangement with a grounded reflector electrode R arranged radially outside the target electrode M, which in this case consists of a plurality of annular, flat electrode elements arranged concentrically around the corona electrode and at an axially spaced distance from each other. Also in this case, the electrode element of the measuring electrode M will serve as electrostatic precipitation surfaces for aerosol-shaped pollutants in the air stream, the purification effect being increased by the precipitation surfaces of the measuring electrode having a significant extent in the direction of air flow, so that the charged pollutants the precipitation surfaces and thus a greater opportunity to walk to these- Pig. Fig. 5 shows an arrangement in which the measuring electrode M in a similar manner as in Fig. 4 consists of a number of planar annular electrode elements arranged concentrically around the corona electrode and at axial distance from each other, and the electrode elements belonging to the measuring electrode M are arranged between them. similar, flat ring-shaped electrode elements 6, which are connected to earth and which thus together with the electrode element of the target electrode M form an electrostatic capacitor separator of known type. Under the influence of the electric field between the electrode element of the measuring electrode M and the electrode elements 6, the electrically charged aerosol-shaped contaminants present in the air migrate to the target electrode M and adhere to its electrode element. Due to the low air flow rate, the residence time of the contaminants between the electrode elements M and 6 becomes relatively long, which provides an efficient purification.

Pig. Fig. 6 shows an arrangement similar to that of Fig. 3 with a measuring electrode M and a reflector electrode R arranged radially outside it, which together with the measuring electrode forms an electrostatic separator for aerosol-shaped pollutants in the air stream, in the manner described in connection with Fig. 3.

Furthermore, the device according to Fig. 6 comprises a convector 7 of suitable design, which is designed as a cylinder arranged radially outside and enclosing the reflector electrode R. By means of this convector 7, the temperature of the air flow can be influenced, i.e. the air can be heated or cooled. Due to its large flow area and the low air flow rate, the convector 7 has a very high efficiency and can be designed in a suitably known manner so that it does not constitute a large flow resistance for the air flow. Due to the efficient separation of aerosol-shaped contaminants at the target electrode M, the convector 7 remains clean and does not need to be cleaned or replaced. On the other hand, of course, the measuring electrode M must be cleaned or replaced at regular intervals. The convector 7 itself can also form reflector electrodes by electrically connecting it to earth. In such a case, the reflector electrode R is superfluous.

Another interesting embodiment of a device according to the invention is shown schematically and in axial section in Fig. 12. This embodiment differs from the embodiment shown in Fig. 1 and 2 in that one axial end of the target electrode is closed by means of a flat, tight disc 15, which thus replaces the plastic ring 2. This disc was suitably made of an insulating material within its central part and was used for attaching one end of the corona electrode K. At a greater radial distance, it is suitable for the disc 1b to consist of or be provided with a coating of an electrically conductive or semiconductive material, which is preferably electrically grounded. In the embodiment shown in Fig. 12, the measuring electrode M is designed in a manner similar to that shown in Fig. 5, and there is also an annular, electrically grounded electrode element 6 in a manner similar to Fig. 5. In a device according to Fig. 12, thus the air flow it marked by the arrows 4. In a device with this embodiment, the measuring electrode M should have an axial height which is approximately half as large as in a device designed according to Figs. 1, 2.

As mentioned above, the air flow rate in the vicinity of the corona electrode K becomes very low in a device according to the invention, which makes it easy to effectively remove and neutralize the harmful or dangerous gases, especially ozone and nitrogen oxides, the corona discharge. This can be done, for example, by means of an arrangement according to Fig. 7, which shows a wire-shaped corona electrode K supported in a suitable manner, not shown in more detail along the center axis of the cylindrical measuring electrode not shown in Fig. 7. At the ends of this corona electrode K, small sleeve or tubular elements 8 are arranged, which consist of or contain a chemically active, for example activated carbon, capable of absorbing or catalytically decomposing said harmful gases nitrogen oxides. substance,, such as ozone and Due to the very insignificant air flow in the immediate vicinity of the corona electrode K, this can happen very efficiently. As shown in Fig. 7, these chemically active absorber elements 8 may be electrically connected to a slightly lower potential than the corona electrode K, whereby they will act as excitation electrodes or excitation elements, which make it possible to maintain a corona discharge at the corona electrode K with a reduced potential difference between the corona electrode and the target electrode. ïig. 15 schematically illustrates another, similar arrangement for neutralizing the harmful gases generated by the corona discharge at the corona electrode. In this arrangement, the corona electrode K is concentrically surrounded by a plurality of axially spaced annular disks 21 which consist of or contain or are coated with a chemically active substance capable of absorbing or catalytically decomposing the harmful gases generated by the corona discharge. Since the air flow in the vicinity of the corona electrode K is very small, the discs 21 can effectively neutralize said gases, which have no appreciable tendency to be carried away by an air flow. The air ions generated in the corona discharge can migrate unhindered to the surrounding measuring electrode, not shown in Fig. 15, between the annular disks 21. In order that the disks 21 should not act as a shield relative to the corona electrode K and thereby disturb the corona discharge, the disks 21 are advantageously connected to earth via a very large resistor 22, so that the charges which the disks 21 may receive are conducted away. The boards 21 may consist of conductive, semiconducting or insulating material. It will be appreciated that other structures consisting of or containing chemically active substances capable of absorbing or catalytically decomposing the harmful gases may also be arranged around the corona electrode K, provided that the structures have such a geometric design that they transmit the ions and are connected to such an electrical potential that they do not shield the corona electrode.

Pig. 8 schematically shows another arrangement for removing the harmful or dangerous gases generated during the corona discharge from the vicinity of the corona electrode K. This arrangement consists of a tube 9, which is connected to an air extraction device, not shown in more detail, for example a fan or air pump, and which has its inlet end 9a axially directed towards one end of the corona electrode K, so that it is closest around the corona electrode 10. The existing air layer, which contains said harmful gases, is continuously sucked away through the tube 9. Since the air flow around the corona electrode K is very small, only a small amount of air needs to be sucked away through the tube 9.

The extracted air with the accompanying harmful gases can be led to a device for purifying the air from said gases or be discharged at some place where the gases in question can not cause any inconvenience. As shown in Fig. 8, at the opposite end of the corona electrode K, a pipe 10 connected to a source of compressed air (not shown) may be arranged so that it directs an air flow along the corona electrode K in the direction of and into the exhaust pipe 9. On this In this way, an even more efficient removal of the harmful gases generated during the corona discharge can be achieved. The tubes 9 and 10 can also serve as excitation electrodes, in that they are electrically conductive at least at their ends and connected to a potential which is slightly lower than the potential of the corona electrode.

Pig. Fig. 9 schematically shows a further arrangement for the same purpose, which arrangement comprises an air suction device arranged along the center axis of the cylindrical measuring electrode, not shown in more detail, in a similar manner to the tube 9, tube 11, which is connected to a suitable Fig. 8. However, the end of the tube 11 is closed, so that air is sucked in only through the perforation in the wall of the tube. The corona electrode in this case consists of a plurality of wire-shaped electrode elements K, which are arranged parallel to and around the tube 11, so that corona current can be emitted in all directions to the surrounding target electrode (not shown in Fig. 9). To reduce the required potential difference between the corona electrode and the target electrode, the tube ll can also serve as an excitation electrode for the corona electrode K in the manner previously described, in that the tube ll is formed of an electrically conductive or semiconducting material and connected to a potential which is somewhat lower than the K potential of the corona electrode. The opposite arrangement is also possible for the removal of ozone and nitrogen oxides from the immediate vicinity of the corona electrode, as schematically illustrated in Fig. 10. In this arrangement a number of perforated tubes are sol, for example three or 30 four, arranged parallel to and around the corona electrode K, the tubes 16 being connected to an air extraction device, so that the air present in the immediate vicinity of the corona electrode K is sucked in through the perforated wall of the tubes 16. These tubes 16 can also advantageously serve as excitation electrodes for the corona electrode K, in that they consist of electrically conductive or semiconducting material and are connected to a potential which is slightly lower than the potential of the corona electrode K.

As appears from the theoretical account in the previously mentioned international patent application, the distance between the corona electrode and the target electrode, ie. the diameter of the measuring electrode M in a device according to Figs. 1, 2, depending on the potential difference between the corona electrode and the measuring electrode and on the desired size of the corona current. It is thus not possible without further ado to increase the total air turnover by means of a device of the embodiment shown in Fig. 1, 2 only by increasing its dimensions and thus also the diameter of the measuring electrode. An increased air circulation instead requires a greater axial length of the device. In this case, however, the inlet areas at the axial open ends of the cylindrical measuring electrode are reduced relative to the outlet area through the mantle surface of the measuring electrode, which entails an increased flow resistance and can further lead to an unevenly distributed air flow through the measuring electrode. Instead, an arrangement of the type schematically shown in Fig. 11 should be suitable. In this arrangement, a plurality of devices 12 of, for example, the embodiment shown in Figs. 1, 2 and described above are arranged axially one after the other at a mutual axial distance, so that there are spaces between the devices 12 into which the air can flow in. to the devices l2 in the manner marked by arrows.

In such an arrangement, an air treating means, for example a cylindrical convector and / or chemical absorbent 13, may be arranged around both the air driving units 12 and the spaces between them, so that both the inflowing air and the outflowing air pass through the convector 13 or through some other air handling unit arranged in a similar manner.

J CJ 25 458 165 II An alternative embodiment of a device according to the invention with a large axial extent for increased total air circulation is shown as an example and schematically in radial section in fig. In this embodiment, the measuring electrode is divided into a number, in the example shown two, arcuate electrode elements M1 and M2, which are arranged at a circumferential distance from each other along a corona electrode K coaxially enclosing cylinder surface, so that between them target electrode elements M1, M2 there are gaps lß. In this case, an air flow arises through the device of the kind shown by arrows, ie. the air flows in substantially radially through the gaps 14 between the target electrode elements M1, M2 and flows out substantially radially through them. Conveniently, the flow area of the interstices should be substantially equal to the flow area through the measuring electrode elements M1, M2.

In an embodiment according to fig. 13 with two or more arcuate measuring electrodes arranged concentrically around the central corona electrode, it is advantageous if the arcuate measuring electrodes have a radius of curvature which is less than the radial distance to the corona electrode, i.e. so that the ends of the arcuate measuring electrodes are at a shorter distance from the corona electrode than the middle portions of the measuring electrodes.

This is schematically illustrated in fig. ln. It has been found that this gives a more even distribution of the air flow through the entire area of the measuring electrodes.

Pig. ln also illustrates two different, possible designs of such arcuate measuring electrodes. The left measuring electrode M1 in the figure here consists of a number of disc- or lamellar-shaped electrode elements arranged parallel to each other and perpendicular to the direction of the corona electrode K in basically the same manner as illustrated in Fig. H. Between these measuring electrode elements there may be further grounded electrode elements corresponding to electrode elements 6 in fig. 5. The one on the right in fig. lu consists of a number of disk- or lamellar-shaped electrode elements extending axially between insulating endplates 17, only one of which is visible in the drawing, and which are substantially radially oriented relative to the corona electrode K.-Between them Measuring electrode elements M2 there are disc- or lamellar-shaped electrode elements 18, which are arranged in a manner similar to the measuring electrode elements M2 but which are connected to ground. These electrode elements 18 have the same purpose as the electrode elements 6 shown in Fig. 5 and described above, and thus together with the target electrode elements M2 form a capacitor separator. Advantageously, these further electrode elements 18 are arranged at a slightly greater distance from the corona electrode K than the measuring electrode elements M2, so that no substantial part of the corona current goes to the electrode elements 18.

In an embodiment according to Figs. 13 and 14, ozone and nitrogen oxides can be removed very efficiently from the immediate vicinity of the corona electrode K, by blowing the corona electrode K from one side by means of a slit-shaped conduit 19 connected to a source of compressed air, while sucking air away from the other corona electrode K. side through a similarly slit-shaped conduit 20 connected to an air extraction device 20. The conduits 19 and 20 thus have towards the corona electrode K the orifices 19a and 20a, respectively, which are long narrow or slit-shaped and extend over substantially the entire length of the corona electrode K in the direction perpendicular to the drawing plane. These wires 19, 20 will not appreciably interfere with the corona discharge at the corona electrode K and therefore will not appreciably change the required potential difference between the corona electrode and the target electrodes. The wires 19 and 20 can also serve as excitation electrodes for the corona electrode K in the manner previously described, in that at least the parts of these wires 19, 20 located closest to the corona electrode K are electrically conductive or semiconductive and connected to a potential which is somewhat lower than the K potential of the corona electrode.

With an embodiment of the type shown in Figs. 13 and 14, substantially the same advantages are achieved as with an embodiment according to Figs. 1, 2 or Fig. 12.

It will be appreciated that the number of arcuate target electrodes may be greater than two, for example three or four. It is also understood that the target electrodes may otherwise be designed in different ways and combined with means for treating the flowing air, as described above. At the device 458 163 lb according to fig. 13, measuring electrodes M1, M2 are thus combined with reflector electrode elements R1 and R2, respectively, as described in connection with Fig. 3. It will also be appreciated that means for treating the air can also be placed in or at the spaces lu serving as inflow openings. In a device formed on it in fig. 13 or 14, it is convenient to close the axial ends of the device so that air cannot flow in through these ends.

Claims (3)

A device for treating air, comprising a corona electrode (K) and at least one air permeable measuring electrode (M) arranged at a distance from the corona electrode and a DC voltage source (3) whose two poles are connected to the corona electrode the respective measuring electrode, the shape and potential difference of the corona electrode and the distance between the corona electrode and the measuring electrode being such that an air ion generating corona discharge occurs at the corona electrode, characterized in that the measuring electrode (M) is arranged substantially symmetrically electrode symmetrically. (K) on a corona electrode concentric surrounding circle. Device according to claim 1, characterized in that the measuring electrode (M) extends along the circumference of the entire said circle. Device according to claim 2, characterized in that the target electrode (M) has a substantially cylindrical extent. R. Device according to claim 1, characterized in that the measuring electrode comprises a plurality of spaced apart parts (M1, M2) with the same electrical potential arranged at a mutual peripheral distance from each other along said circle. 5. A device according to claim 2, characterized in that said parts of the measuring electrode (M1, M2) are arcuate and have a circumferential extent substantially corresponding to the peripheral extent of the gaps (1b) between adjacent parts of said measuring electrode along said electrode. Device according to claim 5, characterized in that said parts of the measuring electrode (M1, M2) have a substantially sub-cylindrical extent. Device according to any one of claims U - 6, characterized in that said parts (M1, M2) of the measuring electrode have a radius of curvature which is less than the radial distance to the corona electrode (K). 'rf 458 163 18 8. A device according to any one of claims 1 - 7, characterized in that the corona electrode (K) is wire-shaped and arranged to substantially coincide with the center axis of said circle. Device according to claim 8, characterized in that the wire-shaped corona electrode (K) has a length exceeding the axial extent of the target electrode (M). l0. Device according to one of Claims 1 to 9, characterized by elements (8, 21) arranged near the corona electrode (K) and containing a chemically active substance capable of absorbing or catalytically decomposing harmful gaseous substances generated by the corona discharge. ll. Device according to one of Claims 1 to 9, characterized in that means for separately removing air from the immediate vicinity of the corona electrode (K) and thus harmful gaseous substances generated during the corona discharge and for disposing of the air thus removed and the consequent harmful gaseous substances. Device according to claims 8 and 10, characterized in that said means comprise a tube (9) connected to an air extraction device, the end of which is arranged axially directed towards one end of the wire-shaped corona electrode (K). Device according to claim 12, characterized in that a pipe (10) connected to a source of compressed air has its end directed axially towards the other end of the corona electrode (K) to direct an air flow along the corona electrode. lU. Device according to claim 11, characterized in that said means comprises a tube (11) connected to an air extraction device, which extends coaxially along the center axis of said circle and whose wall is perforated, and the corona electrode comprises a plurality of wire-shaped electrode elements (K ) arranged parallel to and around said tube (ll). Device according to claim 11, characterized in that said means comprise a number of tubes (16) with a perforated wall connected to an air extraction device, which are arranged parallel to and around the corona electrode (K). Device according to claim 11, characterized in that said means comprise means (19) for blowing the corona electrode (K) perpendicular to its longitudinal direction and from one side thereof and means (20) for sucking air from the corona electrode (K). ) opposite side and in a direction substantially perpendicular to the longitudinal direction of the corona electrode. l7. Device according to any one of claims 1 - 16, characterized by means arranged at or radially outside the measuring electrode (M) for treating the air flow flowing out through the measuring electrode in a substantially radial direction. Device according to claim 3, characterized by means arranged at the open axial ends of the cylindrical measuring electrode (M) for treating the air flow flowing through these open ends in a substantially axial direction. l9. Device according to claim 5, characterized by means arranged in said spaces (lä) between the different parts of the measuring electrode (M1, M2) for treating the air stream flowing in through these spaces in a substantially radial direction. Device according to claim 3, characterized in that it comprises a plurality of cylindrical measuring electrodes (12) with associated corona electrode and arranged around a common axis at mutually axially spaced apart from each other, so that there are annular spaces between closely spaced measuring electrodes. , and means (13) are provided at said annular spaces for treating the air flow inflowing through these spaces in a substantially radial direction. 21. Device according to any one of claims 17 - 20, characterized in that said air treating means are designed for mechanical purification, electrostatic purification, chemical purification and / or temperature influence of the air flow. Device according to one of Claims 1 to 21, characterized in that the radial distance between the corona electrode (K) and the measuring electrode (M) amounts to at least 5 cm and preferably at least 8 cm. Device according to claim 3, characterized in that both axial ends of the cylindrical measuring electrode (M) are open and that the axial length of the measuring electrode substantially corresponds to the radial distance between the corona electrode (K) and the measuring electrode (M). Device according to claim 3, characterized in that one axial end of the cylindrical measuring electrode (M) is airtight and that the axial length of the measuring electrode substantially corresponds to half the radial distance between the corona electrode (K) and the measuring electrode (M). M).