WO1991005611A1

WO1991005611A1 - Filtration of foreign particles from air

Info

Publication number: WO1991005611A1
Application number: PCT/US1990/005946
Authority: WO
Inventors: Yujiro Yamamoto
Original assignee: Yujiro Yamamoto
Priority date: 1989-10-23
Filing date: 1990-10-16
Publication date: 1991-05-02
Also published as: JPH04506930A; JP2622308B2; AU6885991A

Abstract

Filtering foreign particles from air includes a filter unit (13) having electrodes (16, 17) of different electrical potentials (+,-) sufficiently low to avoid ionization of foreign particles. Flow-through of air of foreign particles under the effect of an electric field cause entrapment of the foreign particles so as to provide fine filtration. Air flow past electrodes (16, 17) are parallel or transverse. The electrodes (16, 17) are symmetrically arranged about a central axis (22). A retaining sheet (28) is placed between electrodes (16, 17).

Description

FILTRATION OF FOREIGN PARTICLES FROM AIR

This application is a continuation-in-part of Serial No. 424,919 filed herein on October 23, 1989, the contents of which are incorporated by reference.

BACKGROUND

This invention relates to filtering air. In particular, the invention relates to removing foreign particles from air so as to produce highly purified air.

Prior air techniques for filtering air are essentially of two kinds. Firstly, there is a mechanical filtering system. In such a system there is no electrical field applied between an air inlet and an air outlet from the filter. There are mechanical obstructions which can be paper, fiber glass or mesh which act as the filtration medium. By passing the air through this filtration medium, purification takes place between the air inlet and air outlet such that foreign particles are entrapped in the filter unit. The effectiveness of these filters is such that only a limited amount of the foreign particles are filtered from the air due to the mechanical filter obstructing the air flow. The finer the mechanical filtration medium the slower the air flow, and this can be disadvantageous.

A different filtering technique is that based on ionization. The ionization process requires a relatively high electric field to be established between oppositely located electrodes. The air passes through the electrical field and the foreign particles are ionized. Capture of the particles is effected by different electrodes downstream from the ionization field, these different electrodes being at higher electric potentials. One drawback of the ionization process is the creation of ozone which is of a nature detrimental to the environment. Moreover, the effective filtering ability of ionization filters is not as fine as desirable. Conventionally ionization filters operate in a range to filter out particles greater than about 0.05 microns in size. Sophisticated and complicated ionization techniques applied to filters could effect filtration by removal of particles greater than about 0.01 microns.

The present invention is directed to a system of enhanced filtration, namely removal of foreign particles which are smaller in size than that obtained by ionization of mechanical filtering.

By the term "air" the applicant intends to include mixtures of gases and a single gas. SUMMARY

According to the invention filtering the foreign particles from air includes subjecting the particles to an electric field formed between at least one pair of electrodes. The electrical potential between electrodes is relatively different, and preferably opposite, and is such that the field essentially avoids effective ionization of the foreign particles in the air. Means is provided for entrapping foreign particles while under the effect of the electric field.

The inlet take of air inflow to the filter unit in which the electrodes are contained is of a nature such that it is higher than the outflow rate from the filter unit air. The flow velocity through the filter unit at the output is preferably less than about 20 feet per minute. The voltage of the electrodes is preferably less than about 20 kv per inch.

In a preferred form of the invention there are multiple cylindrical electrodes arranged about a central point or axis and spaced apart. The air flow passes through the spacing either traversing the electrodes or passing between the electrodes.

The filtering unit of the invention causes the fine particles to act under London/Van Der aals forces as opposed to ionization forces. This has the ability to remove particles greater than about 0.001 microns from the air. With the invented system, particles of smaller size are removed or trapped in the retaining means of a defined pore size, compared to a filter system using the same pore size in the retaining means but operating under ionization or mechanical filtering techniques.

The invention is directed to a filtering apparatus, a cartridge for filtering which is fitted or retrofitted into a housing for a filter unit, and the method of filtering under an electric field which is essentially non-ionizing of the foreign particles.

The invention is now further described with reference to the accompanying drawings.

DRAWINGS

Figures 1, 2, 3 and 4 are views of a first embodiment of the invention illustrating the centralized air inlet and the axial air outlet after radially traversing the electrodes.

Figures 5, 6 and 7 are views of a second embodiment of the invention illustrating the axial air inlet to the filtration unit and axial air outlet over essentially the same cross-section, after axially passing by the electrode.

Figure 8 is a diagrammatic perspective view of a different configuration of the electrodes, the electrodes being formed between spiralling elements. Figures 9 and 10 are views of the electrodes formed in an essentially spherical configuration.

Figure 11 and 12 are views of electrodes of the filter unit, wherein the electrodes constitute means for entrapping foreign particles.

DESCRIPTION

Apparatus for filtering foreign particles from air comprises an inlet 10 for the inflow of air and foreign particles as indicated by arrow 11. The inlet 10 is connected to the casing 12 of a filter unit 13. An outlet

14 is provided from the filter unit 13 so that the air after filtration and removal of the foreign particles can flow outwardly as indicated by arrows 15.

The filter unit 13 includes at least a pair of spaced cylindrical electrodes 16 and 17. In Figure 1 an additional electrode 18 is illustrated. Electrodes 16, 17 and 18 are at relatively different electrical potentials. In this example, the opposite electric potential polarities is indicated by the (+) and (-) charge symbols 19, 20 and 21 respectively. The multiple electrodes 16, 17 and 18 are arranged centrally about an axis 22 for the filter unit 13. The air inlet 10 is also centrally located about the axis 22. The air outflow is also located centrally about the axis 22. The electrodes 16, 17 and 18 are circumferential cylindrical elements of increasing diameter. Inside the central electrode 19 is a space 23, between electrodes 19 and 20 is a space 24, and between electrodes 20 and 21 is a space 25. Beyond the circumference of electrode 18 is a space 26. The space 26 is limited by an outer circumferential element 27 which is at relatively neutral or zero potential. In the spaces 23, 24, 25 and 26 there is located respectively retaining means 28 which act to entrap foreign particles contained in the air from inlet 10 passing in the direction of arrow 11.

The electrodes 16, 17 and 18 and also the outer circumferential element 27 are relatively porous or a plane net or mesh or screen so that air and foreign particles passing through the filter 13 can be directed substantially transversely through the electrodes 16, 17, 18 and element 27 as indicated by arrow 29. The outflow from the filter unit 13 and outer circumferential element 27 is indicated by outlet arrow 30.

Although the flow is illustrated as having only one transverse direction in passing through the electrodes 16, 17 and 18, the air can flow progressively parallel to the axis 22 and transversely relative to the axis 22 as it moves from the inlet 10 towards the outlet 14. In this fashion the airflow can be in parallel and transverse steps relative to the electrodes 16, 17 and 18 or in an essentially transverse radial or diagonal flow between the central narrow inlet 10 and the broader outlet 14.

Flow is preferably transverse to the axis 22, and an optional closure 125 is provided at the downstream end 124 of the circumferential element 27. In this fashion, there is no in-flow from the element 27 in an axial direction. The closure 125 is shown in phantom in Figure 1. The outlet flow velocity per unit area from the outer circumferential element 27 is relatively less than the comparative flow velocity per area at the inlet 16. After exiting from the circumferential element 27, the flow area can be reduced to a size approximately the inlet flow area.

The relative potential of the electrodes 16, 17 and 18 is retained sufficiently low so as effectively to avoid ionization of foreign particles entrained in the air passing through the electrodes 16, 17 and 18. As such, the foreign particles are subjected to London/Van Der Waalε forces and not ionization forces. London/Van Der Waalε forces are related to the spin of the molecules and not ionization characteristics of the particles. The relative different potentials between the electrodes 16, 17 and 18 is in the range of between about 9 kv per inch to 15 kv per inch. An ionization voltage would be about 40 kv per inch. The voltage between electrodes 16, 17 and 18 is retained below 20 kv per inch and effectively below about 15 kv per inch. The configuration between the size of the inlet 10 and the outlet 14 is such that the flow velocity through the filter unit 13 and at the outlet is retained at less than about 20 feet per minute. This permits for the optimized conditions to be applied to the foreign particles so as to achieve a high effective level of filtration.

The retaining substance 28 can be in the form of filtration paper or a mesh network. The retaining means can contain low evaporation liquid substance which increases the capability of the filter for holding sample particles under the electric field such as Exxon FEBIS K-220 (Trademark) . The shape of the retaining means can be selected to maximize entrapment of foreign particles. This may be, for instance, a folded configuration.

With a filter 13 operating under these conditions it has been found that small foreign particles, namely particles greater than 0.001 microns are effectively entrapped in the filter unit 13 between the inlet 10 and outlet 14. The London/Van Der Waals forces are relatively weak forces. The action of this force together with the selected flow rate achieves fine filtration of the air in the filter unit 13. The pores of the mesh are of such a nature that they can be relatively larger than the size of the entrapped particles. The London/Van der Waals forces cause particles which could normally pass through the pores to be trapped instead on or in the pore surfaces.

Comparatively in an ionization or mechanical system, the pore size would determine the minimum size of particles to be filtered. Normally, in a mechanical system, particles that are trapped are larger than the pore size and essentially not much smaller than the pore size. In Figure 4, the pore size is illustrated diagrammatically as 118.

In Figures 5, 6 and 7, an embodiment is illustrated with an air inlet 31 and air outlet 32. The electrodes 33, 34 and 35 are arranged by a central axis 36. Essentially, the air inlet 31 and air outlet 32 are the same diameters. As such the velocity of air flow inlet and the velocity of air flow outlet are essentially the same. The air flow velocity through the filter unit 37 is also essentially the same as the air flow inlet 38 and air flow outlet 39. In this embodiment the air through the filter unit 37 traverses a substantially parallel path between the air indicated by arrow 38 and the outlet air indicated by arrow 39. As such there is essentially no air flow traversal of the electrodes 33, 34 and 35. The electrodes in this embodiment are also cylindrical constructions having a longitudinal depth of a sufficient extent to achieve the requisite filtration of the air. The electrodes 33, 34 and 35 are of different polarities similarly to the electrode configuration in Figure 1. Retaining means 40 is provided between the electrodes 33, 34 and 35.

In the embodiment of Figure 8 a different configuration is illustrated wherein different alternating electrodes 41, 42, 43, 44, 45 and 46 are illustrated. The electrodes are constituted by spiralling elements 47 and 48 respectively. By having the two elements 47 and 48 rolled about the central axis 49 and with suitable spacing 50, 51, 52 and 53 between the elements, an effective filter 54 is obtained. In the embodiment illustrated the retaining substance 55 located in the spaces 50, 51, 52 and 53. Although two elements 47 and 48 are illustrated to constitute the electrodes 41, 42, 43, 44, 45 and 46 respectively, more than two elements 47 and 48 can be provided. The element 48 is fixed to a central cylindrical element 56 which constitutes part of the electrode 42. The air inlet is diagrammatically illustrated by numeral 57 and the air outlet by numeral 58. In the example illustrated there is a narrower air inlet and a broader air outlet. Arrows 157 indicate a transverse outlet flow. In some embodiments there is only outlet flow 157 , as the inlet flow 58 is blocked. In the other cases, there is only outlet flow 58. In the example of Figures 9 and 10 the electrodes are constituted by essentially spherical elements 59, 60 and

61 respectively. The spherical element 59 is the central element and the spherical element 61 is the outer element. Between each of the elements 59, 60 and 61 there is a space

62 and 63 respectively. The space can contain retaining substances 64. The air inlet 65 is diagrammatically illustrated through a inlet tube 66 directed to the central sphere. From there the air radiates in a three dimensional sense from the center 67 as indicated by arrows 68. The air traverses each of the electrodes 59, 60 and 61 over an increasing area and is removed from the casing 69 of the filter 70 through an outlet 71 as indicated by arrow 72. In this embodiment the air outlet 71 is relatively broader than air inlet 66 such that the flow velocity through outlet 71 is less than air inlet 66. The air through the filtration electrodes 59, 60 and 61 passes through at a progressively slower rate due to the increasing surface area of the electrodes about the central point 67.

In the embodiment of Figures 11 and 12 the electrodes are illustrated in a configuration without retaining means. Support bars 73 and 74 respectively are arranged with fingers 75 depending on support by 73 and fingers 76 depending from support by 74. Each of these fingers 75 and 76 relatively overlap so as to provide respectively opposite electric potentials 77 and 78. There is a spacing 79 between each of the fingers 75 and 76. Air flow can be directed axially along arrow 80 relative to the bars 73 or 74 or transversely as indicated by arrow 81 relative to the axis of the bar 73 and 74. A combination of these two directions of air travel would also be operative. From each of the fingers 75 and 76 respectively there are tentacles 82 which act to constitute a network of electrodes of different potentials and members through or past which the air with entrained fine particles moves.

Filtering with the apparatus and method of invention removes foreign particles from the air which are greater than about 0.001 microns in size. This should include viruses, fumes, smoke and larger size molecules. This system accordingly provides for highly purified air outflow for different applications.

In an alternative construction where it is desired to remove particle sizes larger than, for instance, only about 0.5 microns, the filter is constructed to provide a flow rate of about 50 to 100 times greater than a conventional ionization filter. In other words, the construction is one where for the same flow velocity as an ionization filter a higher degree of filtration can be obtained, or alternatively, where a lower degree of filtration is required a higher volume of filtration can be obtained. Where .the filtering retaining medium has essentially the same pore size as for a mechanical filter, by application of the principles of the invention a substantially higher degree of filtration can be obtained. Alternatively, a higher volume of filtration can be obtained. In yet a further arrangement a combination of both higher filtration effect and higher flow velocity can be achieved. The filter unit of the invention is operative with conventional filters and casings for such filters can be retrofitted into existing filters. Additionally, the filter of the invention can be provided as an add-on filter unit or filter cartridge to existing filters. As such that operation of the overall filter is effected sequentially grosser filtering in a conventional mechanical or ionization filter followed by finer filtering with the invented filter unit.

The retaining substances used provide a high surface area thereby to permit for the entrapment or retention of a high volume of foreign matter. The retaining substance can consist of conventional known filtering materials such as fiber mesh, or filter paper.

Applications of the filtering apparatus and method include the intake filter for combustion engines of the internal combustion or diesel configurations. By providing for a higher degree of filtration of incoming air, engines can burn more completely with minimized creation of pollutants such as carbon monoxide. By providing cleaner air for the intake, engine performance is of a higher efficiency and there is less likelihood of wear of moving components. This would increase engine life.

Other applications of the filter include the significant reduction of pollutants generated into the atmosphere from industrial smoke stacks. Additionally, in fabrication or laboratory facilities requiring clean room applications, the purified air can facilitate the manufacture of super high density electronic chip components, high precision mechanisms and optical components.

Moreover, in the health environment different environments can be kept air purified to higher orders than previously possible. The application also has benefit in chemical processing facilities.

Purified air is also important in food processing applications where it is desirable to eliminate potential contaminants. For example, this can improve the quality of vacuum sealed products to prevent deterioration. Additionally, in the home and office environment, enhanced purified air can be provided.

In other situations the electrodes may be surrounded or coated with different substances to protect the electrodes against deterioration effects. Smoothing of deformities on the surface of the electrode can be provided to generate a uniform electrical field within the filter unit.

In the illustrated construction, the air flow inlet is narrower than the air flow outlet the filter unit. In this arrangement the inlet flow velocity to the filter unit is higher than the outlet flow or velocity from the unit. An important feature is that for a given flow rate, the outlet flow velocity from the retaining substance is lower than the inlet flow velocity to the retaining substance. This gives an improved effect. Applications, however, could exist where the reverse is desired or where a common velocity of air flow throughout the filter is desirable.

In an application with automobile engines, for instance, the filter includes the mesh constructed to trap particles of a size of greater than about 5 microns. By application of the filter of the present invention the same mesh can capture foreign particles of a size between about 0.5 microns to about 0.05 microns without impacting the effective flow velocity for the combustion engine. This embodiment operates with a faster outlet flow velocity than inlet flow velocity.

In some embodiments there is an air space between selected electrodes, instead of the retaining^' eans. This could effectively change the air flow velocity to a desired level and can assist in providing different filtering characteristics which are tuned to the specific applications.

Moreover, in different applications it could be desirable to provide a dehumidifier to the air prior to entry into the filter unit. Such a dehumidifier would decrease electrical power consumption between electrodes. Suitable dehumidification to in-flow and/or out-flow of air and flow rate control can be provided for different applications of the filter unit.

Many other examples of the invention exist each differing from the other in matters of detail only. For instance, the retaining means is a planar material which is movable between the two rolls. The one roll can be a storage roll and the other roll is a take-up roll. In this manner, the retaining means between the electrodes is moved progressively so as to provide different and new means for entrapment of particles.

In another form, the inlet surface of the electrode is planar and the outlet surface of the electrode is curvilinear. Between the electrodes there is located retaining means. With this construction the flow velocity between the inlet and outlet decreases, since there is located retaining means. With this construction, the total flow volume between the inlet and outlet remains the same. However, since there is a greater surface area at the outlet relative to the inlet surface area of the retaining means the escaping velocity at the outlet surface is smaller than the inlet velocity at surface. Thus, the particle capturing efficiency is high.

The invention is directed to include an entire filter apparatus, the method of filtering and a cartridge filtering unit for the filter. The scope and content of the invention is to be considered limited only by the appended claims.

Claims

CLAIMS :

1. Apparatus for filtering foreign particles from air comprising an inlet for the inflow of air and foreign particles to a filter unit, an outlet for the outflow of air substantially free of foreign particles from the filter unit, the filter unit including at least a pair of spaced electrodes, the electrodes being at relatively different electric potentials, the air and foreign particles passing through an electric field established by the electrodes and the electric potential of the electrodes being at a level sufficiently low to avoid effective ionization of the foreign particles and means in the filter unit for entrapping the foreign particles under the effect of the electric field.

2. The apparatus as claimed in Claim 1 wherein the effect of the electric field utilizes the London/Van Der Waals force.

3. The apparatus as claimed in Claim 1 wherein at outlet from the filter unit, a flow velocity of the air is less than about 20 feet per minute.

4. The apparatus as claimed in Claim 1 wherein the potential of the electrodes is less than about 20 kv per inch.

5. The apparatus as claimed in Claim 4 wherein the potential of the electrodes is in a range between about

9 kv per inch to about 15 kv per square inch. 6. The apparatus as claimed in Claim 1 including retaining means located between the pair of spaced electrodes, the retaining means being for entrapping the foreign particles.

7. The apparatus as claimed in Claim 1 including multiple spaced electrodes, adjacent electrodes having respectively opposite potentials.

8. The apparatus as claimed in Claim 1 wherein the inlet for air is centrally located relative to an axis about which a first electrode is axially positioned, the first electrode being substantially cylindrical in shape, the air flow in the filter unit being directed radially outwardly through the first electrode and an adjacent spaced cylindrical electrode, and the air outlet having a relatively substantially greater surface area than the air inlet surface area.

9. The apparatus as claimed in Claim 1 wherein the electrodes are spaced cylindrical elements of relatively different diameters, retaining means being located between the cylindrical elements, and an outer cylindrical element being selectively at an electric neutral potential, and wherein the electrodes are porous thereby to permit air flow through the electrodes.

10. The apparatus as claimed in Claim 1 wherein the air inflow is at a flow velocity higher than the flow velocity of the air outflow. 11. The apparatus as claimed in Claim 1 wherein the electrodes are cylindrical spaced elements, each element having a relatively different diameter, the elements being located about a central axis, and means for directing the air between the inlet and the outlet past the elements in a direction substantially parallel to the cylindrical axis.

12. The apparatus as claimed in Claim 1 wherein the electrodes constitute the means for entrapping the foreign particles.

13. The apparatus as claimed in claim 1 wherein the electrodes are constituted by at least two spaced members, the members spiralling outwardly, each of the members having a different potential such that the spirals establish transverse electrodes of different potential.

14. The apparatus as claimed in Claim 1 wherein each electrode is constituted essentially by a sphere, each sphere having a center, and the center of each sphere being substantially in the same location, the inlet to the central sphere and outlet being from the perimeter of the other sphere, and means for spacing the spheres relative to each other and for permitting the inlet to flow respectively through the outer spheres from the inner sphere.

15. The apparatus as claimed in Claim 1 wherein the retaining means includes spaced bars for providing entrapment of foreign particles greater than 0.005 microns. 16. The apparatus as claimed in Claim 1 including retaining means ^"for permitting entrapment of foreign particles greater than about 0.001 microns.

17. The apparatus as claimed in Claim 1 including retaining means, the retaining means including a low evaporative substance.

18. Apparatus for filtering foreign particles from air comprising an inlet for the inflow of air and foreign particles to a filter unit, an outlet for the outflow of air substantially free of foreign particles from the filter unit, the filter unit including multiple spaced electrodes, the electrodes having relatively opposite electric potentials and having a common center, the air and foreign particles passing through an electric field established by the electrodes and.the electric potential of the electrodes being at a level sufficiently low to avoid effective ionization of the foreign particles, and retaining means in the filter unit between the electrodes for entrapping the foreign particles under the effect of the electric field.

19. The apparatus as claimed in Claim 18 wherein at the outlet from the filter unit, a flow velocity of the air is less than about 20 feet per minute, and wherein the potential of the electrodes is less than about 20 kv per inch. 20. A method for filtering foreign particles from air comprising introducing air and foreign particles to a filter unit, removing the air substantially free of foreign particles from the filter unit, establishing an electric field with electrodes at relatively different electric potentials, passing the air and foreign particles through the electric field, the electric potential of the electrodes being at a level sufficiently low to avoid effective ionization of the foreign particles, and entrapping the foreign particles.

21. The method as claimed in Claim 20 wherein a flow velocity of the air at the outlet from the filter is less than about 20 feet per minute.

23. The method as claimed in Claim 22 wherein the potential of the electrodes is less than about 20 kv per inch.

24. The method as claimed in Claim 20 including entrapping the foreign particles in retaining means located between the electrodes.

25. The method as claimed in Claim 20 wherein the air introduced at a flow velocity higher than the flow velocity of the air removed and wherein the air and foreign particle are directed at least in close proximity to the electrodes. 26. The method as claimed in Claim 20 wherein entrapment of foreign particles greater than about 0.005 microns are entrapped.

27. A filter unit including at least a pair of spaced electrodes, the electrodes being for operation at relatively different electric potentials, such that air and foreign particles can be passed through an electric field established by the electrodes, the electric potential of the electrodes being at a level sufficiently low to avoid effective ionization of the foreign particles and means for entrapping the foreign particles under the effect of the electric field.

28. The unit as claimed in Claim 27 wherein the potential of the electrodes is less than about 20 kv per inch.

29. The unit as claimed in Claim 27 including retaining means located between the pair of spaced electrodes, the retaining means being for entrapping the foreign particles.

30. The unit as claimed in Claim 27 including multiple spaced electrodes, adjacent electrodes having respectively opposite potentials.

31. The apparatus as claimed in Claim 1 including means for removing water vapor from the in-flow of air. 32. The method as claimed in claim 20 including reducing the water content of the air.

33. The apparatus of claim 1 wherein the in-flow velocity is greater than the out-flow velocity.

34. The method of claim 20 wherein the in-flow velocity is greater than the out-flow velocity.