The present invention relates to an air cleaning unit and some parts of the air cleaning unit according to the preamble of the independent claim 1 and according to the preambles of the dependent claims.

Background of the invention

There is a huge need of air cleaning devices for removing the particles, especially particles smaller than 2500 nm in diameter of the indoor air to a level which is healthy to residents. Such needs exists especially in emerging economies, such as China, India and South-East Asia. The Clean Air Delivery Rates (CADR) of such devices need to be substantially high, typically more than several hundred cfm (cubic feet per minute).

Using electrical particle charging for improving air cleaning unit efficiency is a well-known technology. US7 513,933 B2, StrionAir, 17.8.2006, describes a method of operating an air filter assembly including: providing motive force to produce an air flow along a flow pathway, corona precharging particles in the air flow to produce precharged particles, polarizing a fibrous filter to act in symbiosis for enhancement of filtration efficiency by action upon the precharged particles and directing air flow across the fibrous fileter including the precharged particles for enhanced removal thereof, wherein the step of polarizing the fibrous filter includes creating a potential difference between an insulated electrode at an upstream position with respect to a downstream conductive electrode, the downstream conductive electrode being in physical contact with the fibrous filter media in plurality of locations evenly distributed over the entire surface of the filter media. The publication fails to give information in structural details, throw-away distance, CADR or anything similar.

US6364,935B1A, Blueair AB, 6.5.1997, describes a device for cleaning of a gaseous fluid from particles present in said fluid, comprising: a permanently positive or permanently negative high voltage source; a filter spaced apart from said source, said filter comprising a fine filter medium composed of fibers having a fiber diameter of approximately 1 micron or greater, and an average spacing between said fibers of approximately ten times said fiber diameter, said fibers being easily polarized when subjected to an electric charge; means for passing a flow of said fluid past said high voltage source and through said filter; said filter further characterized by an absence of external ehareinp means other than said rjarticles Dassine throueh said filter. The prior art fails to describe the important technical problems of air cleaning units: cleaning only part of the room, having too frequent filter change rate, difficult change and maintenance of corona charger needles and soiling of corona charger earth electrode.

Brief description of the invention The object of the present invention is to provide an apparatus so as to overcome or at least alleviate at least some of the prior art disadvantages. The objects of the present invention are achieved with an apparatus or part of apparatus according to the characterizing portion of claim 1.

The invention comprises an air cleaning unit 11 or parts of such air cleaning unit 11 which overcome the technical problems of the prior art: cleaning only part of the room, having too frequent filter change rate, difficult change and maintenance of corona charger needles and soiling of corona charger earth electrode.

Brief description of the figures

In the following the invention will be described in greater detail, in connection with preferred embodiments, with reference to the attached drawings, in which

Figure 1 is a schematic view of an embodiment of a part of the apparatus where the corona discharge needle is easily disposable;

Figure 2 is a schematic view of another embodiment of a part of the apparatus with non-coiling earth electrode of the corona discharge unit; Figure 3 is a schematic view of an embodiment of an apparatus according to the present invention solving the problem of whole room air cleaning;

Figure 4 is a schematic view of another embodiment of the apparatus where the apparatus comprises a diffusion chamber; and

Figure 5 is a schematic view of another embodiment of a part of the apparatus with a filter with high particle collection capability.

Detailed description of the invention

Figure 3 shows the invented apparatus 1 to overcome the problem of short-circuiting air flow. The air cleaning unit 11 is realized in such a way that the minimum angle 9 between the air outflow 12 and the air intake 13 flow direction 18 is essentially between 80-90o and the maximum angle 9* (=angle 0 + angle 12) is essentially between 135— 150o. This ensures that the outflow air is directed in such a way that the probability of air short-circuit is minimized. Preferably the air outflow can be headed towards free flow. Thus it is not favorable to direct the air towards e.g. the room wall. Preferably air cleaning unit 11 comprises more than one air outflow ways from which the user can select a preferable one. The air cleaning unit 11 also preferably comprises an adjustment member 17 for adjusting the angle between the air outflow 12 and the air intake 13.

In order to achieve the adequate through-out distance of the outflow air (i.e. to reach also the outermost region of the area to be cleaned=, the air out flow area should be such that the outflow air velocity is typically several meters per second (m/s). Thus the air outflow area 14 is maximum Q/5 m2, where Q. is the volumetric flow through the air cleaning unit 11 in m3/s. For the same reason the height distance 13 of air intake and air outflow is at least 3 x Q m, where Q is the volumetric flow through the air cleaning unit 11 in m3/s.

Another problem of the prior art technology is the short replacement time of the filter. This makes the lifetime price of such air cleaning units considerably high. In the current invention the filter size is maximized to ensure rather stable filter capture rate with almost constant air velocity through the filter. Such structure also ensures rather stable Clean Air Delivery Rate (CADR) of the air cleaning unit 11. The large filter area makes it possible to use slow air flow through the filter. With the air cleaning unit of the current invention (see figures 4 and 5), the velocity of the air flow through the filter material (i.e. active filter area) is preferably less than 7 cm/s, more preferably less than 5 cm/s and most preferably less than 3 cm/s. In order to achieve air flow which is low enough (to achieve good collection efficiency and have favorably large filter area) for more than 1300 m3/h air flow, the active filter area 14 of the air cleaning unit 11 should preferably be at least 10 m2. More generally the ratio of the volumetric flow O. through the air cleaning unit, in m3/h, to the active filter area 14, in m2, should be less than 200, preferably less than 150 and most preferably less than 100. One of the distinct features of the current invention is the use of a discharge unit to electrically charge the particles passing through the air cleaning unit 11. While various discharging technologies (such as triboelectric or field charging) can be used, diffusion charging based on the use of a corona discharger is preferred due to its simplicity and the possibility of designing the charger in such a way that the charger soiling can be minimized. Thus, the air cleaning unit 11 of the current invention comprises a unit 10 (see Figure 4) for electrically charging essentially all particles passing through the air cleaning unit 11 by diffusion charging and a filter unit comprising a filter 15, and the air cleaning unit 11 also comprises a diffusion charging chamber 16 between the charging unit 10 and filter 15 with the delay time of the air flowing in the air cleaning unit (11) in the diffusion charging chamber (16) being preferably more than 100 ms, more preferably more than 200 ms and most preferably more than 400 ms.

To achieve a large active filter area 14, the filter material needs to be bended inside the filter 15 (Fig. 5). The bending factor m= (number of filter material passages through the filter width)/(filter width). Typically this number should be five or larger. The active filter area 14 is then m times the filter area A.

A corona needle 1 is an essential part of a corona discharge unit 10. It is essential that the charging unit is especially capable of charging particles between 10 nm and 2500 nm in diameter as the smallest capture efficiency of any air cleaning unit is within this particle size range. It is also essential that the corona discharge needle can be easily cleaned and/or changed, thus overcoming one of the technical problems of the prior art.

In the current invention, the corona discharge needle 1 used in a corona charger 10 for electrically charging airborne particulates in the size range of 10 nm - 2500 nm, comprises a sharp part 2 and a spring-like part 3 which fixes the needle 1 to the support 4 and provides electrical connection between the sharp part 2 and support 4 and also makes the corona discharge needle 1 easily changeable.

In one embodiment of the current invention needle lmcomprises a sharp part 2 having a diameter less than or equal of 0.3 mm and length of less than or equal of 30 mm and a spring-like part 3 which is made from the same material as the sharp part 2 and has the same diameter as the sharp part 2.

In another embodiment of the current invention, the corona discharge needle 1 comprises two sharp parts 2 and a spring-like part 3 comprising four angles 5 having value of 90o +/- 15o.

In another embodiment of the current invention, the corona discharge needle 1 comprises steel, stainless steel, tungsten, platinum, platinum-rhodium or manganese as its material. The corona discharge needle 1 needs to elastic to provide good connection to support 4. Such elasticity can be achieved by material or structural properties of the corona discharge needle 1. It is beneficial for the good behavior of the corona discharge needle 1 that material of the springlike part 3 has Young's modulus between 50-1000 GPa. It is also beneficial that the material of the It is of spring-like part 3 has shear modulus between 20-200 Pa. In order to achieve good electrical charging of particles passing through the air cleaning unit 10, the corona charger comprises of 1-100 individual corona discharge needles, depending on the design and dimensions of the air cleaning unit 10.

In the air cleaning unit 10 of the present invention, the particles are collected in/on the filter 15. It is essential for achieving long maintenance period that the corona discharge unit comprising the corona discharge needle 1 and the counter electrode 6 will be soiled as little as possible. Typically it is the counter electrode 6 which collects the charged particles and gets soiled. Thus it is essential to design the counter electrode 6 in such a way that it minimizes soiling by charged particles.

Without restricting ourselves to any specific theory, it is believed that at least two significant forces affect the particle passing through the air cleaning unit: the force generated by the blower 19 directing particles to direction 18 generated by the volumetric flow Q; and the electrical force dragging the charged particles towards the counter electrode 6. Assuming that the efficiency of the counter electrode collection is maximum 1%, the length of the counter electrode d (see Fig. 2) can be maximum

where d is the counter electrode 6 length, Q. is the volumetric flow through the corona charger (10), m is the mass of the particle in consideration, n is the number of elementary charges on the particle in consideration, lei is the absolute value of the elementary charge e, U is the electrical potential of the corona charger 10 and I is the length 8 of the corona charger 10. If higher collection efficiencies are allowed then the constant 0.01 of Equation (1) is to be changed to a higher value (the constant is -Ιη(Ι-Ξ), where EBis the efficiency).

In one embodiment of the current invention, the maximum length d of the counter electrode 6 is

10 mm.

It is also essential for the present invention that the dimensions of the corona discharge unit are designed for efficient operation of the air cleaning unit 10. Thus in one embodiment of the present invention, the distance between the corona discharge needle 1 tip 20 and the counter electrode 6 is 20-50 mm; and the distance between the corona discharge needle 1 tip 20 and the outermost surface 7 of needle support 4 is less than 20 mm. Preferably the counter electrode 6 of the corona charger 10 is formed from a single piece of metal.

For the electrical operation of the system it is beneficial that the counter electrode 6 is connected to the earth potential of the corona charger 10. It is apparent to a person skilled in the art that as technology advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.