Device for cleaning of indoor air

Abstract

A device for cleaning of indoor air comprising capacitor precipitators, each consisting of two electrode elements or two groups of electrode elements connected to the respective pole of a high voltage source, air transported fans, at least one corona electrode and at least one counter electrode. The corona electrode and the counter electrode are each connected to the respective pole of a high voltage source. The device includes two air flow ducts for the air to be cleaned, which air flow ducts are placed along an axial reference line (AA) at a distance (d) from each other in the direction of the axial reference line (AA). Each air flow duct is associated with a capacitor precipitator and an air moving fan. At least one corona electrode is provided in the space between the air flow ducts. At least one counter electrode is located adjacent to the air flow ducts circumference. The air flow direction through the one air flow duct is diametrically opposite the air flow direction through the second air flow duct, and the air to be cleaned is passed into the space between the air flow ducts.

Claims

1. A device for cleaning of indoor air, comprising two capacitor precipitators, each including at least one corona electrode and at least one counter electrode, wherein said at least one corona electrode and said at least one counter electrode are each connected to a respective pole of a high voltage source, wherein the device comprises two cylindrical air flow ducts, the two cylindrical air flow ducts being coaxially located along an axial reference line and spaced apart from each other, and wherein: each of the two cylindrical air flow ducts is associated with a respective one of the capacitor precipitators and includes a respective air transporting fan, the at least one corona electrode of each capacitor precipitator is provided in the space between the air flow ducts, and the at least one counter electrode of each capacitor precipitator is disposed at a periphery of a respective one of the two cylindrical air flow ducts, thereby generating an electrostatic field between the at least one corona electrode and the counter at least one electrode of each capacitor precipitator, and the air respective transporting fan of each of the air flow ducts is arranged to operate such that air flows through a first one of the two cylindrical air flow ducts in a direction which is diametrically opposite to the direction of air flowing through of a second one of the air flow ducts, and the air to be cleaned is passed into the space between the two air flow ducts and through the electrostatic field.

2. The device according to claim 1, wherein the at least one counter electrode comprises two counter electrodes, each have a respective flat annular surface, wherein the annular surfaces define an opening of a diameter larger than an impeller of the respective air transporting fan, and wherein the annular surfaces extend substantially perpendicular to air flow through the respective cylindrical air flow ducts.

3. The device according to claim 1, wherein a tube-like counter electrode extends between the adjacent ends of the two cylindrical air flow ducts.

4. The device according to claim 1, wherein the at least one corona electrode is designed as a carbon brush extending axially and being secured in a holder.

5. The device according to claim 1, wherein the at least one corona electrode consists of two carbon brushes, which extend axially and face each other.

6. The device according to claim 1, wherein the at least one corona electrode is a thin wire extending axially between holders.

7. The device according to claim 1, wherein the at least one corona electrode is designed as a ring that is mounted axially in a space between the two cylindrical air flow ducts, and wherein a periphery of the ring is provided with corona elements comprising carbon fiber bristles or small tips.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention is in the following explained with reference to the accompanying drawings, wherein:

(2) FIG. 1 schematically shows a cross section through an air cleaning apparatus in accordance with the invention.

(3) FIG. 2 schematically shows a modified air cleaning device.

(4) FIG. 3 schematically shows a modified solution of the corona.

(5) FIG. 4 schematically shows the connection of the corona electrode and the counter electrode to respective poles of a high voltage source.

DETAILED DESCRIPTION OF THE INVENTION

(6) The air cleaning device shown in FIG. 1 comprises two tube-shaped air flow passages L1, L2 arranged axially to each other and spaced with an axial distance d to each other wherein the two circular capacitor precipitators 12a and 12b, respectively, are arranged (seen from the air flow direction through the device) one at the outlet of the air flow duct L1 and one at the outlet of the air flow duct L2. The corresponding capacitor precipitator is accompanied by an air moving fan 13a and 13b, respectively, and by a holder 14a and 14b, respectively, the latter being designed as annular plates of electrically insulating material. A carbon brush (corona) K1, K2 is disposed in the center of the respective holders 14a, 14b.

(7) The air flow duct L1, L2 is larger than the respective diameter of the impeller of the fan 13a and 13b with an angular surface (counter electrode) 16a and 16b, respectively, extending from each fan impeller and the respective tubular casing of the air flow ducts L1, L2.

(8) The capacitor precipitators are designed according to SE-A 9602211-6 i.e. comprising two band-like electrode elements connected to the respective pole+, of a high voltage source 20, as shown in FIG. 4. The corona electrodes K1, K2 are electrically connected to the appropriate terminal of the high voltage source (shown as the + terminal in FIG. 4), whereby an electrostatic field formed between corona electrodes K1, K2 and counter electrodes 16a and 16b, which are made from or lined with conductive or semi-conductive material and electrically grounded. Thereby a ionization chamber 18 is formed extending from the corona electrodes K1, K2 to the counter electrodes 16a, 16b.

(9) FIG. 2 shows a modified embodiment of the apparatus wherein the inlet 19 of the ionization chamber 18 is provided with an air permeable cylindrical surface (counter electrode 16c), which is electrically connected to the same voltage pole as the counter electrodes 16a, 16b. Thereby the electrostatic field is slightly changed from the corona electrodes to the counter electrodes. In practice a greater air volume (larger ionization chamber) is achieved for charging of the particles in the incoming air flow.

(10) As is shown in FIG. 1, the respective corona electrode K1, K2 face each other and are quite close together. The fact that they are electrically connected to the same pole of a high voltage source forces the ion clouds formed by the respective corona K1, K2 to spread radially and in the direction towards the counter electrodes 16a, 16b, 16c corresponding to the opposite direction to the incoming air flow.

(11) The influx of air to be cleaned is such that all air entering the device must pass through the electrostatic field formed between the corona electrode or electrodes K1, K2 and the counter electrodes 16a, 16b, 16c. In the case shown in FIG. 1 where two annular counter electrodes 16a, 16b are provided, the air inlet 19 is disposed axially between these, so that the incoming air stream is divided into partial air streams. The first partial air stream passes through the electrostatic field formed between a first corona electrode K1 and a first annular counter electrode 16b and further (to the right in the figure) by a first fan 13b and through a first capacitor precipitator 12b, in which charged particles are trapped. The first partial air stream thus passes to the left in the figure through the electrostatic field formed between a second corona electrode K2 and a second annular counter electrode 16a and further past a second fan 13a and through a second capacitor precipitator 12a, arranged to collect charged particles. The air transport direction through the device is shown by the arrows in FIG. 1.

(12) Laboratory tests show that even so-called quiet fans, such as brand Ebmpapst in combination with capacitor precipitator according to SE-A 9692211-6 i.e. a capacitor precipitator with extremely low air resistance cannot provide greater airflow than 1 m/s to and maintain quiet operation. Actually, the range of 0.5-0.75 m/s, more suitable to achieve silent or quiet operation which is the primary purpose of this invention. It is also vital to provide efficient charging of particles, which as previously described in SE 940010-4, requires relatively large source chamber (long dwell time) if the demand for low ozone development must be fulfilled.

(13) The surprise of the present invention is that even at relatively small distance d, sufficient charging of particles is achieved and thereby also the requirements for large capacity air cleaning (CADR) in combination with low noise and negligible ozone generation are achieved.

(14) Laboratory tests show that the minimum distance d should not be less than 30% of the air flow scan lens L1, L2 radius and preferably not less than radius.

(15) In order not to disturb the electrostatic field formed between corona electrodes K1, K2 and counter electrodes 16a, 16b and 16c the impeller blades should be made of electrically insulating material, e.g. plastic. There are also requirements on the design of the holder 14a, 14b so that those cover the motors of the fan, which are generally made of metal and grounded, by overlap.

(16) A practical example of the device of the present invention comprises two capacitor precipitators with 400 mm diameter and 50 mm wide electrode element, an ionization chamber with distance d equal to 120 mm and two fans with 300 mm diameter. With an air flow rate of about 0.7 m/s about 600 m3/h CADR is achieved, which is very much for this type of device at quiet operation.

(17) In the embodiment shown in FIG. 2, the counter electrode 16c is formed of a perforated cylindrical surface. The counter electrode 16c may also be formed of e.g. fins or other suitable means forming a perforated cylindrical shape. The influx of air to be cleaned is thus effected through the perforated cylindrical surface so that all the air entering the device is forced to pass through the electrostatic field formed between the corona electrode or electrodes K1, K2 and the perforated cylindrical surface of the counter electrode 16c.

(18) The use of such a counter electrode 16c defines the extension of the ionization chamber from corona electrode/electrodes to the perforated cylindrical surface of the counter electrode 16c. A counter electrode 16c with a perforated cylindrical surface can be combined with ring-shaped counter electrodes 16a, 16b. In some cases, where the air velocity through the capacitor precipitators is lower than 0.7 m/s, however, the counter electrode 16c alone define the ionization chamber. The surfaces 16a, 16b may be formed of an insulating material.

(19) The diameter of the counter electrode 16c can be greater than the air flow duct diameter. As for the counter electrodes 16a and 16b, respectively, these can be seen from the circular opening around the fan impeller transform to square or rectangular surfaces.

(20) Regarding the corona electrodes K1, K2, laboratory tests have shown that it is not necessary to provide two corona electrodes. A corona electrode in the form of a carbon fiber brush alone can provide charging of the particles.

(21) A suitable design of the corona electrode is also shown in FIG. 3 which electrode consists of a ring 17a disposed axially in the air gap between the flow passages L1 and L2, respectively, wherein the ring's periphery consists of corona elements 17b of the type comprising carbon fiber blades, or small laces.

(22) It is of course not necessary that the corona electrode is formed as a carbon fiber brush. Other prior art corona elements can be used. It is essential that these are designed substantially axially symmetrical with respect to the counter electrodes. Further, it is important that all the air drawn into the device is forced to go through the electrostatically charged field between the corona electrode and the counter electrode, so that substantially all particles are charged.

(23) Even an elongated corona electrode in the form of a thin wire disposed axially eligible.

(24) The present invention is not limited to any specific polarity of the accession of the electrode elements of the capacitor precipitators or the polarity of the corona.

(25) Hence, the corona can also be connected, e.g., to the grounded pole of a high voltage source, wherein the counter electrode may be connected to another pole of high voltage source negative or positive.

(26) In an alternative embodiment, the air moving fans 13a, 13b are interchanged with the corresponding capacitor precipitator 12a, 12b.