WO2011064525A1

WO2011064525A1 - Filter medium with a multiplicity of different filter layers and use for testing filter media

Info

Publication number: WO2011064525A1
Application number: PCT/GB2010/002081
Authority: WO
Inventors: Richard Price; Daniel Whittaker
Original assignee: HYDROTECHNIK UK Ltd
Current assignee: HYDROTECHNIK UK Ltd
Priority date: 2009-11-26
Filing date: 2010-11-12
Publication date: 2011-06-03
Anticipated expiration: 2012-05-26
Also published as: GB201013194D0

Abstract

Fluid flows along a fluid path (14) to pass through a filter element (12). The filter element (12) is preceded by an obstacle (24). This creates an eddy region (40) in which fluid flow along the path (14) is reduced, reversed or zero. This is found to improve the performance of the filter elements (12) in removing particulate material from fluid.

Description

FILTER MEDIUM WITH A MULTIPLICITY OF DIFFERENT FILTER LAYERS

AND USE FOR TESTING FILTER MEDIA

The present invention relates to methods and apparatus for fluid filtration.

In one aspect, examples of the present invention provide a fluid filter comprising: a filter element serving, in use, to trap particulate material from a fluid flowing along a fluid flow path which passes through the filter element; and an obstacle member positioned upstream of the filter element in the fluid flow path to create an eddy region in the fluid flow path, in which one or more eddies form in the fluid, during use; the filter element being positioned in the eddy region.

The eddy region may extend downstream of the obstacle member. The filter element may be positioned downstream of the obstacle member. The filter element may abut the obstacle member. There may be a plurality of filter elements positioned in the eddy region. The or each filter element may be planar. The or each filter element may be a sheet of filter material.

There may be a plurality of obstacle members positioned along the flow path, each creating at least one respective eddy region, and each having at least one associated filter element positioned in the respective eddy region. The filter may have a plurality of obstacle members and a plurality of filter elements, the obstacle members and filter elements alternating along the fluid flow path. The filter elements may be in abutment with the preceding and following obstacle members. The or each obstacle member may be a planar member having at least one edge in the flow path to cause the formation of eddies. The, or at least one of the edges may be straight. The, or at least one of the edges, may include a corner at which two straight portions meet to form a discontinuity. The corner may form a right angle between the straight portions. The or each obstacle member may have a plurality of edges in the flow path, to cause the formation of eddies. The or each obstacle member may be a sheet of impervious material.

The or each obstacle member may define at least one aperture having at least one edge in the flow path, to cause the formation of eddies. The or each aperture may be elongate to provide opposed edges which each create an eddy region downstream. The or each aperture may be an elongate slot. The or each obstacle member may define a plurality of slots. The plurality of slots may be oriented to radiate from a common point. The obstacle member may be generally circular, the slots extending radially. The obstacle member may be magnetized.

In another aspect, examples of the present invention provide a method of filtering a fluid, in which: a filter element is provided to trap particulate material from a fluid flowing along a fluid flow path which passes through the filter element; and an obstacle member is positioned upstream of the filter element in the fluid flow path to create an eddy region in the fluid flow path, one or more eddies forming in the fluid within the eddy region, during use; and positioning the filter element in the eddy region.

The eddy region may extend downstream of the obstacle member. The filter element may be positioned downstream of the obstacle member. The filter element may abut the obstacle member. There may be a plurality of filter elements positioned in the eddy region. The or each filter element may be planar. The or each filter element may be a sheet of filter material. There may be a plurality of obstacle members positioned along the flow path, each creating at least one respective eddy region, at least one associated filter element being positioned in each respective eddy region. The filter may have a plurality of obstacle members and a plurality of filter elements, the obstacle members and filter elements alternating along the fluid flow path. The filter elements may be in abutment with the preceding and following obstacle members.

The or each obstacle member may be a planar member having at least one edge in the flow path to cause the formation of eddies. The, or at least one of the edges may be straight. The, or at least one of the edges, may include a corner at which two straight portions meet to form a discontinuity. The corner may form a right angle between the straight portions. The or each obstacle member may have a plurality of edges in the flow path, to cause the formation of eddies. The or each obstacle member may be a sheet of impervious material.

The or each obstacle member may define at least one aperture having at least one edge in the flow path, to cause the formation of eddies. The or each aperture may be elongate to provide opposed edges which each create an eddy region downstream. The or each aperture may be an elongate slot. The or each obstacle member may define a plurality of slots. The plurality of slots may be oriented to radiate from a common point. The obstacle member may be generally circular, the slots extending radially. The obstacle member may be magnetized. Examples of the present invention will now be described in more detail, by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a fluid filter, partially cut away, enlarged for clarity; Fig. 2 is a perspective view of a single filter element of the filter of Fig. 1 ;

Fig. 3 is a perspective view of an obstacle member of the filter of Fig. 1 ;

Fig. 4 illustrates, highly schematically, fluid flow past an edge within the filter of Fig. 1 , enlarged for clarity;

Fig. 5 is an exploded view of an alternative fluid filter;

Fig. 6 is a plan view of an obstacle member of the filter of Fig. 5 and Fig. 6a shows part of Fig. 6 on an enlarged scale; and

Fig. 7 illustrates, highly schematically, fluid flow through slots in the obstacle member of Fig. 6, enlarged for clarity.

Overview

Fig. 1 illustrates one example of a fluid filter 10. The filter 10 comprises a plurality of filter elements 12. In this example, the elements 12 are illustrated as layers of the filter 10, which is constructed in a manner to be described below. A fluid flow path is indicated by an arrow 14. The path 14 passes sequentially through the elements 12 of the filter 10. Each filter element 12 serves, in use, to trap particulate material from fluid flowing along the fluid flow path, which passes through the filter elements 12. The filter 10 also includes several obstacle members 15, among the filter elements 12. As will be described in more detail below, each obstacle member 15 is positioned upstream of a filter element 12 in the fluid flow path 14 to create an eddy region downstream of the obstacle member 15, in which one or more eddies form in the fluid, during use. The filter element 12 is positioned in the eddy region.

In this description, the material to be filtered will be called "fluid" and may be liquid or gas. The material which is removed from the fluid will be called the "filtrand". The clean fluid, after removal of the filtrand, will be called the "filtrate". Structure of a filter element 12

Fig. 2 illustrates one of the filter elements 12. The filter element 12 is in the form of a generally planar disc-like filter structure, having a generally circular periphery

16 and a central aperture 17. In this example, the periphery 16 and the aperture 17 are substantially concentric. The fluid flow path 14 is shown crossing the plane in one direction through the material of the element 12.

Other geometries could be used. The periphery 16 could have another shape. The aperture 17 could have another shape. The aperture 17 could be omitted.

The element 12 may be one or more layers of filter material such as a woven or non-woven filter cloth. The filter material will have a filter characteristic which represents the ability of the material to remove filtrand from fluid. Filter characteristics may be described in various different ways. In one possibility, the filter characteristic is expressed as a micron rating representing the maximum particle size which can pass through the material. For example, a filter material with a 3 micron rating will block particulate material with a particle size of 3 microns or greater. A micron rating may also be called a "pore size", referring to the size of pore in a perforated structure which allows the same particle size to be passed. However, the pore size or micron rating may represent a measurement from an equivalent structure providing the same filter characteristic, rather than an actual measurement of a perforation, because many techniques of filtering particles are available in addition to simple perforated sheets, meshes or the like. Filter materials with many different micron ratings are available. For example, materials with micron ratings as high as 100 microns are available for filtering fluids. Typical filter materials for a wide range of common filter tasks may have a thickness in the region of 1 mm or 2 mm, allowing an element to be constructed with as many as 60 filter elements within a relatively small volume.

Structure of an obstacle member

Fig. 3 illustrates an obstacle member 15 included in the filter 10. Each obstacle member 15 is a planar disc made of an impervious material which is dimensionally stable, such as a synthetic plastics material. Other examples are described below. Apertures 18 are formed in the material of the disc 15. The apertures 18 leave a continuous ring 19 around the outer circumference of the disc 15. A central aperture 20 is surrounded by a continuous inner ring 22. In this example, the rings 19, 22 are connected by spokes 24. The spokes 24 provide straight edges 25a for the apertures 18, extending generally radially, and meeting arcuate inner and outer edges 25b at corners 25c. The edges 25a, b meet at right angles at the corners 25c. In the filter 10, several obstacle member discs 15 are included in the stack of filter elements 12. The outer diameter of the discs 15 is approximately the same as the diameter of the filter elements 12. The diameter of the central aperture 20 is approximately the same as the diameter of the central aperture 17 in the filter elements 12. Accordingly, the discs 15 can be included in the stack of filter elements 12 by placing each disc 15 between two adjacent filter elements 12. In this example, an inner cylinder 26 and an outer cylinder 28 resist fluid leaving the filter 10 unless it has passed through the filter elements 12 by flowing through the filter elements 12 in a direction generally parallel with the cylindrical axis of the filter 0. In this example, the filter elements 12 are not sealed to the cylinders 26, 28. This reduces the risk of damage to the filter elements 12 if they shrink during use, which some filter media may do. Shrinkage of the filter elements 12 would open gaps between the filter elements 12 and one or both of the cylinders 26, 28, potentially leaving open a path through which fluid can bypass the filter elements 12. Gaps between the filter elements 12 and the cylinders 26, 28 could also arise for other reasons, such as production tolerances, inaccurate cutting, sizing or shaping of the material, or the like. However, the obstacle members 15 are dimensionally stable and have dimensions chosen to be a close fit to the cylinders 26, 28. Consequently, even if the filter elements 12 leave gaps, the gaps between the obstacle members 15 and the cylinders 26, 28 will remain small. The path of least resistance for fluid flowing through the filter 10, across an obstacle member 15, will remain the paths through the apertures 18.

This is expected to increase the reliability of the filter 10 by resisting fluid from flowing around the edges of the filter elements 12 even with wider manufacturing tolerances, and may increase the service life of the filter element 10, by continuing to resist this fluid flow even when ageing filter elements 12 begin to shrink.

In addition to this effect of concentrating the fluid flow through the apertures 18, and thus through the filter elements 12, the obstacle members 15 serve as obstacles in the fluid flow path 14 to cause eddies, the formation and significance of which will be described more fully below, after a description of the structure of the filter formed from the filter elements 12 and the obstacle members 15. Structure of the filter

Returning to Fig. 1 , the filter 10 is formed from a stack of planar filter elements 12 arranged at generally parallel planes to form a cylindrical structure, as shown. Obstacle members 15 are also included in the stack. The filter elements 12 and the obstacle members 15 are centred on the cylindrical axis of the structure. This results in a fluid flow path leg 14 which passes sequentially through the filter material of each of the elements 12, in turn, and also through the apertures 18 in the obstacle members 15. The inner and outer cylinders 26, 28 (shown partially cut away in Fig. 1 ) prevent fluid leaking from the filter 10 before passing through all of the filter elements 12 and the obstacle members 15. Upper and lower annular rings 30 define inlet and outlet apertures 32 for the filter 10.

In this example, each of the obstacle members 15 is upstream of a filter element 12 in the fluid flow path 14. The presence of the obstacle member 15, particularly the spokes 24 in this example, presents an obstacle to fluid flowing along the path 14. In particular, the edges 25a, 25b of the apertures 18, particularly the edges 25a of the spokes 24, provide edges which obstruct the fluid flow, and past which the fluid will flow along the path 14. Fig. 4 schematically illustrates the situation, during use. Fluid, indicated generally at 34, is flowing along the flow path 14 from the top of the drawing, as illustrated in Fig. 4, toward the obstacle member 15, of which only the edge 24a of a spoke 24 is visible in Fig. 4. A filter element 12 can be seen, immediately downstream of the spoke 24.

Some of the fluid 34 will flow smoothly past the spoke 24, as illustrated toward the left of Fig. 4. However, closer to the edge 24a, smooth flow of the fluid 34 will be obstructed by the presence of the spoke 24 and the edge 24a. In particular, some fluid must be deflected to avoid the spoke 24, as illustrated toward the right of Fig. 4. A swirling effect is thus caused in the fluid 34, in the vicinity of the edge 24a. That is, one or more eddies 38 form in the fluid flow, in an eddy region 40 around the spoke 24. The filter element 12 is positioned in the eddy region 40. The filtrand leaves the stage at 41.

Within each eddy 38, there will be regions of reduced, reversed or zero flow along the flow path 14. We have found that the presence of the eddies 38, and the positioning of the filter elements 12 in the eddy region 40 results in an improved performance in the filter 10 in removing particulate material from the filtrand 41 . In particular, the reduced, reversed or zero flow allows particles to come out of suspension in the fluid, and to come to rest on the filter element 12, thereby being filtered from the fluid 34. We have observed that because this removal of filtrand arises from the creation of eddies 38, rather than from the normal mechanical filtration action of the filter element 12, particles which are smaller than the nominal pore size of the filter element 12 will nevertheless be captured by the filter element 12. Thus, for example, by creating eddies, as has been described, a filter element 12 with a nominal pore size of 1 micron is found to capture filtrand particulates of a size smaller than 1 micron.

It can be seen from Fig. 4 that the filter element 12 abuts the spoke 24 so that the eddy region 40, downstream of the spoke 24, is filled with filter material.

In the example of Fig. 1 , a large number of filter elements 12 is provided after each obstacle member 15. It is therefore likely that some of the filter elements 12 will be too far downstream of the preceding obstacle member 15 to be within the eddy region 40, and will therefore filter in a conventional manner.

Alternative example

In an alternative example illustrated in Fig. 5, the number of filter elements 12 may be reduced, so that all of the filter elements 12 are positioned in an eddy region 40. In particular, there may be a single filter element 12 between each adjacent obstacle member 15, so that a plurality of filter elements 12 and a plurality of obstacle members 15 alternate along the flow path 14.

The filter illustrated in Fig. 5 has many features in common with the filter described above. Consequently, the same reference numerals are used again in relation to the corresponding features. In the example of Fig. 5, each obstacle member 15 is followed by a single filter element 12 in the form of the disc of filter material of the type described above in relation to Fig. 2. Thus, filter elements 12 and obstacle members 15 alternate along the fluid flow path 14. Each filter element 12 is in abutment with the preceding and following obstacle member 15. Thus, between adjacent obstacle members 15, the eddy regions 40 are full of filter material.

In addition, the obstacle member 15 of the example of Fig. 5 does not have apertures 18 and spokes 24, as illustrated in Fig. 3, but rather has an array of elongate slots 42, illustrated in Fig. 6. Fig. 6a illustrates part of Fig. 6, on an enlarged scale. The slots 42 radiate from a common point 44 (the centre of the circular obstacle member 15). That is, the slots 42 extend radially across the obstacle member 15. The use of slots 42, rather than larger apertures 18, results in the provision of opposed pairs of edges 36 (at opposite sides of the slots 42), which each creates an eddy region 40. In a narrow slot, the whole width of the slot may be in one or other of the eddy regions 40.

The result is indicated schematically in Fig. 7. Fluid, indicated generally at 34, is flowing along the flow path 14 from the top of the drawing, as illustrated in Fig. 7, toward the obstacle members 15, of which only the edges 36 of the slots 42 are visible in Fig. 7. A filter element 12 can be seen, immediately downstream of each obstacle member 15. Some of the fluid 34 may flow smoothly through the centre of the slots 42, as illustrated at 46 in Fig. 7. This will depend on the width of the slot 42. However, closer to the edges 36, smooth flow of the fluid 34 will be obstructed by the presence of the edges 36. In particular, some fluid must be deflected to reach the slots 42. A swirling effect is thus caused in the fluid 34, around each edge 36. That is, one or more eddies 38 form in the fluid flow, in an eddy region 40 which extends downstream of each edge 36. Each filter element 12 is positioned in the eddy regions 40 of the preceding obstacle member 15.

Within each eddy 38, there will be regions of reduced, reversed or zero flow along the flow path 14 as noted above. Accordingly, the reduced, reversed or zero flow again allows particles to come out of suspension in the fluid, and to come to rest on the filter elements 12, thereby being filtered from the fluid 34. Again, particles which are smaller than the nominal pore size of the filter element 12 will nevertheless be captured by the filter element 12. Thus, the filtrand 41 has been filtered to a smaller particle size than would be expected from the nominal pore size of the filter elements 12.

In the example of Fig. 7, a single filter element 12 is provided after each obstacle member 15. All of the filter elements 12 will therefore be within the eddy regions 40. In an alternative example, the number of filter elements 12 between consecutive obstacle members 15 may be increased, and may be increased sufficiently so that not all of the filter elements 12 are positioned in an eddy region 40.

In either example, the obstacle member 15 may be made of a synthetic plastics material, as noted above. Alternatively, other materials which are sufficiently rigid to function as described above could be used, such as card or metal. A metal obstacle member could be magnetized to aid in collecting ferrous particles from the fluid. Many variations and modifications can be made to the apparatus described above, without departing from the scope of the present invention. For example, many different shapes, sizes and relative shapes and sizes can be chosen for the various components illustrated in the drawings. We have observed that the effectiveness of the filter process appears to be enhanced by using straight edges on the obstacle members, to create eddy regions. Forming corners at which two straight edges meet, especially if they meet at right angles, has also been observed to be beneficial. However, many different shapes of edge and of obstacle member are expected to create eddy regions and therefore exhibit benefits as explained above. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A fluid filter comprising: a filter element serving, in use, to trap particulate material from a fluid flowing along a fluid flow path which passes through the filter element; and an obstacle member positioned upstream of the filter element in the fluid flow path to create an eddy region in the fluid flow path, in which one or more eddies form in the fluid, during use; the filter element being positioned in the eddy region.

2. A fluid filter according to claim 1 , wherein the eddy region extends downstream of the obstacle member.

3. A fluid filter according to claim 1 or 2, wherein the filter element is positioned downstream of the obstacle member.

4. A fluid filter according to claim 1 , 2 or 3, wherein the filter element abuts the obstacle member.

5. A fluid filter according to any preceding claim, comprising a plurality of filter elements positioned in the eddy region.

6. A fluid filter according to any preceding claim, wherein the or each filter element is planar.

7. A fluid filter according to any preceding claim, wherein the or each filter element is a sheet of filter material.

8. A fluid filter according to any preceding claim, there being a plurality of obstacle members positioned along the flow path, each creating at least one respective eddy region, and each having at least one associated filter element positioned in the respective eddy region.

9. A fluid filter according to any preceding claim, wherein the filter has a plurality of obstacle members and a plurality of filter elements, the obstacle members and filter elements alternating along the fluid flow path.

10. A fluid filter according to any preceding claim, wherein the filter elements are in abutment with the preceding and following obstacle members.

1 1 . A fluid filter according to any preceding claim, wherein the or each obstacle member is a planar member having at least one edge in the flow path to cause the formation of eddies.

12. A fluid filter according to claim 1 1 , wherein the, or at least one of the edges is straight.

13. A fluid filter according to claim 1 1 or 12, wherein the, or at least one of the edges, includes a corner at which two straight portions meet to form a discontinuity.

14. A fluid filter according to claim 13, wherein the corner forms a right angle between the straight portions.

15. A fluid filter according to any of claims 1 1 to 14, wherein the or each obstacle member has a plurality of edges in the flow path, to cause the formation of eddies.

16. A fluid filter according to any preceding claim, wherein the or each obstacle member is a sheet of impervious material.

17. A fluid filter according to any preceding claim, wherein the or each obstacle member defines at least one aperture having at least one edge in the flow path, to cause the formation of eddies.

18. A fluid filter according to claim 17, wherein the or each aperture is elongate to provide opposed edges which each create an eddy region downstream.

19. A fluid filter according to claim 17 or 18, wherein the or each aperture is an elongate slot.

20. A fluid filter according to claim 17, 18 or 19, wherein the or each obstacle member defines a plurality of slots.

21. A fluid filter according to claim 20, wherein the plurality of slots are oriented to radiate from a common point.

22. A fluid filter according to claim 21 , wherein the obstacle member is generally circular, the slots extending radially.

23. A fluid filter according to any preceding claim, wherein the obstacle member is magnetized.

24. A method of filtering a fluid, in which: a filter element is provided to trap particulate material from a fluid flowing along a fluid flow path which passes through the filter element; and an obstacle member is positioned upstream of the filter element in the fluid flow path to create an eddy region in the fluid flow path, one or more eddies forming in the fluid within the eddy region, during use; and positioning the filter element in the eddy region.

25. A method according to claim 24, in which the eddy region extends downstream of the obstacle member.

26. A method according to claim 24 or 25, in which the filter element is positioned downstream of the obstacle member.

27. A method according to any of claims 24 to 26, in which the filter element abuts the obstacle member.

28. A method according to any of claims 24 to 27, in which a plurality of filter elements are positioned in the eddy region.

29. A method according to any of claims 24 to 28, in which the or each filter element is planar.

30. A method according to any of claims 24 to 29, in which the or each filter element is a sheet of filter material.

31. A method according to any of claims 24 to 30, in which there is a plurality of obstacle members positioned along the flow path, each creating at least one respective eddy region, at least one associated filter element being positioned in each respective eddy region.

32. A method according to any of claims 24 to 31 , in which the filter has a plurality of obstacle members and a plurality of filter elements, the obstacle members and filter elements alternating along the fluid flow path.

33. A method according to claim 32, in which the filter elements are in abutment with the preceding and following obstacle members.

34. A method according to any of claims 24 to 33, wherein the or each obstacle member is a planar member having at least one edge in the flow path to cause the formation of eddies.

35. A method according to claim 34, in which the, or at least one of the edges is straight.

36. A method according to claim 34 or 35, in which the, or at least one of the edges, includes a corner at which two straight portions meet to form a discontinuity.

37. A method according to claim 36, in which the corner forms a right angle between the straight portions.

38. A method according to any of claims 34 to 37, in which the or each obstacle member has a plurality of edges in the flow path, to cause the formation of eddies.

39. A method according to any of claims 24 to 38, in which the or each obstacle member is a sheet of impervious material.

40. A method according to any of claims 24 to 39, in which the or each obstacle member defines at least one aperture having at least one edge in the flow path, to cause the formation of eddies.

41. A method according to claim 40, in which the or each aperture is elongate to provide opposed edges which each create an eddy region downstream.

42. A method according to claim 40 or 41 , in which the or each aperture is an elongate slot.

43. A method according to claim 42, in which the or each obstacle member defines a plurality of slots.

44. A method according to claim 43, in which the plurality of slots are oriented to radiate from a common point.

45. A method according to claim 44, in which the obstacle member is generally circular, the slots extending radially.

46. A method according to any of claims 24 to 45, wherein the obstacle member is magnetized.

47. A fluid filter element substantially as described above, with reference to the accompanying drawings.

48. A method of filtering a fluid, substantially as described above, with reference to the accompanying drawings.

49. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.