VORTEX FINDER FOR A CYCLONIC SEPARATOR

Abstract

A vortex finder, for a cyclonic separator, includes a plurality of stationary vanes having a round convex front end around which incoming air is guided into the vortex finder, wherein, where air separates from the plurality of stationary vanes inside of the vortex finder, a cross-section of the plurality of stationary vanes has only one sharp edge. Preferably, a mean line of the cross-section of the plurality of stationary vanes does not cross a chord line in an upstream half of the cross-section. Preferably, a side of the plurality of stationary vanes facing the incoming air is provided with a protrusion at a stagnation point. The protrusion may be shaped so as to guide the incoming air into the vortex finder, and may have a concave side following a shape of a neighboring vane, and a rounded top.

Claims

1. A vortex finder for a cyclonic separator, the vortex finder comprising: a plurality of stationary vanes having a round convex front end around which incoming air is guided into the vortex finder, wherein, where the incoming air separates from the plurality of stationary vanes inside of the vortex finder, a cross-section of the plurality of stationary vanes has only one sharp edge.

2. The vortex finder as claimed in claim 1, wherein a mean line of the cross-section of the plurality of stationary vanes does not cross a chord line in an upstream half of the cross-section.

3. The vortex finder as claimed in claim 1, wherein a side of the plurality of stationary vanes facing the incoming air is provided with a protrusion at a stagnation point.

4. The vortex finder as claimed in claim 3, wherein the protrusion is shaped so as to guide the incoming air into the vortex finder.

5. The vortex finder as claimed in claim 3, wherein the protrusion has a concave side following a shape of a neighboring vane.

6. The vortex finder as claimed in claim 3, wherein the protrusion has a rounded top.

7. The vortex finder as claimed in claim 3, wherein the protrusion has a height in a range between 70% and 130% of a gap width between the plurality of stationary vanes.

8. The vortex finder as claimed in claim 3, wherein the protrusion has a height in a range between 85% and 115% of a gap width between the plurality of stationary vanes.

9. The vortex finder as claimed in claim 3, wherein a gap width between adjacent stationary vanes increases from an outside to an inside of the vortex finder.

10. The vortex finder as claimed in claim 1, wherein a vacuum cleaner comprises the cyclonic separator having the vortex finder.

11. The vortex finder as claimed in claim 3, wherein sides of a plurality of protrusions facing into the vortex finder are concave, and sides of a plurality of protrusions facing an outside of the vortex finder are convex.

12. The vortex finder as claimed in claim 1, wherein the vortex finder is shaped in the form of a cylinder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIGS. 1-3 show a cross-section of a first embodiment of a vortex finder in accordance with the present invention;

[0012] FIG. 4 shows the airflow in some more detail; and

[0013] FIGS. 5A-7B illustrate further embodiments of a vortex finder in accordance with the present invention, provided with a protrusion.

DESCRIPTION OF EMBODIMENTS

[0014] FIG. 1 shows a cross-section of a first embodiment of a vortex finder F in accordance with the present invention. The vortex finder F has a plurality of vanes V. An incoming airflow A circulates around the vortex finder F.

[0015] FIG. 2 shows a section of the vanes of FIG. 1 in more detail. In the idealized representation of FIG. 2, air A enters between the vanes into the vortex finder F as a result of suction exercised by a fan (not shown). As a result of inertia, dirt particles D either do not enter the vortex finder A but follow a straight line towards an outer hull of the cyclone, or are bounced off by a subsequent vane V. In this way, dirt D is separated from the air A. At a trailing edge of the vanes V, where air A separates from the vanes V, the vanes have only one sharp edge E. With an airfoil-shaped cross-section of the vanes, a sharp edge means that in a downstream half of the cross-section, upper and lower surfaces of the airfoil intersect at an angle of less than 90°. While in practice, manufacturing restrictions may result in a slight rounding, it still holds that in a downstream half of the cross-section of the vanes, straight lines approximating the upper and lower surfaces of the airfoil in that downstream half, intersect at an angle of less than 90°.

[0016] FIG. 3 shows a mean line M and a chord line C drawn in one of the vanes V. In line with the definitions used in the Wikipedia item on airfoils, the geometry of the airfoil is described with a variety of terms: [0017] The leading edge is the point at the front of the airfoil that has maximum curvature (minimum radius). [0018] The trailing edge is defined similarly as the point of maximum curvature at the rear of the airfoil. [0019] The chord line C is the straight line connecting leading and trailing edges. The chord length, or simply chord, is the length of the chord line. [0020] The mean camber line or mean line M is the locus of points midway between the upper and lower surfaces of the airfoil. Its shape depends on the thickness distribution along the chord.

[0021] In the embodiments shown, the mean line M has a C-shape that does not cross the chord line C. It at least holds that the mean line M does not cross the chord line C in the upstream half of the vane V. In contrast, in the prior art of US2012167336, the mean line has a S-shape and crosses the chord line at least once in the upstream half of the vane. As a result of the prior art concave crescent shape on the upstream surface of the airfoil tip, air is not smoothly entering the vortex finder, resulting in a high pressure loss.

[0022] As a result of the shape of the vanes in accordance with the present invention, air A is smoothly entering the vortex finder F, thereby minimizing pressure loss, so that the suction energy is most efficiently used. This positive effect also results from the feature that at their trailing ends, the vanes only have one sharp edge, so that turbulences resulting from blunt trailing ends are avoided. Such turbulences also contribute to an undesired pressure loss.

[0023] Advantageously, the vortex finder is shaped in the form of a cylinder, which results in that the desired shape of the vanes can be easily manufactured by means of molding.

[0024] FIG. 4 illustrates the air flow in some more detail. While in the idealized representation of FIG. 2 it was suggested that most of the air flow enters into the vortex finder F as a result of suction by the motor-fan aggregate of the vacuum cleaner (not shown), in reality, some of the air flow bumps into the vane V, and another part goes around the vane V. Where the air bumps into the vane V, dirt will be accumulated. The place where the air bumps into the vane V, is called the stagnation point S, which is usually defined (see e.g. Wikipedia) as a point in a flow field where the local velocity of the fluid is zero. Stagnation points exist at the surface of objects in the flow field, where the fluid is brought to rest by the object.

[0025] In accordance with preferred embodiments of the invention, a side of the vanes V facing the incoming air A is provided with a protrusion P at the stagnation point S, to thereby prevent dirt from accumulating on the vanes V at the stagnation points S. By doing so, the pollution can be significantly reduced, without influencing the separation performance or pressure loss.

[0026] It is noted that while the protrusions P are described here in the context of vanes V having only one sharp edge E where air separates from the vane V inside of the vortex finder F, the problem of dirt accumulation at stagnation points where air bumps into the vanes of the vortex finder, and the solution of providing the sides of vanes with protrusions, is not limited to such vanes, and that applicant reserves the right to separately protect (see our application EP20150969.2, reference 2019PF00905) providing different vanes (e.g. those described in US2012167336 or WO2015150435) with protrusions to prevent dirt accumulation from happening.

[0027] It is important that the protrusions P are positioned as close as possible to the stagnation points S. FIG. 12b of WO 2015150435 shows outer trailing end edges 45 resulting from cutting a part out of vanes 41. However, that solution will not help to prevent dirt from accumulating inside the hollow parts at the trailing end faces 42 in which the stagnation points are located. So, in this prior art solution, at the stagnation points, there are no protrusions that prevent dirt from accumulation at the stagnation points, but hollow shapes that collect dirt.

[0028] FIGS. 5A and 5B show a first embodiment of vanes V provided with protrusions P to prevent dirt from accumulating. Here, both sides of the protrusions P are concave.

[0029] FIGS. 6A and 6B show a second embodiment of vanes V provided with protrusions P to prevent dirt from accumulating. Here, the sides of the protrusions P facing into the vortex finder F are concave, and the sides of the protrusions P facing the outside of the vortex finder F are convex.

[0030] The concave shapes of FIGS. 5A-6B serve to ensure that the protrusions P are shaped so as to guide the incoming air A relatively smoothly into the vortex finder F.

[0031] The protrusions P preferably have a rounded top, which is more forgiving as regards manufacturing tolerances than a sharp top. However, a sharp top is possible.

[0032] In a practical embodiment, the vanes are separated by gaps having a gap width of about 1.75 mm; with a different gap width, the size of the other dimensions discussed below needs to be scaled accordingly.

[0033] In the embodiment of FIGS. 5A and 5B, the design goal that the protrusions P are positioned as close as possible to the stagnation points S means that the protrusions P preferably deviate by less than 1 mm from the stagnation points S. The diameter of any rounded tops of the protrusions P is preferably in a range between 0.25 mm and 0.35 mm, such as about 0.3 mm. Compared to the basic shape of the vanes as shown in FIGS. 1-4, the height of the protrusions P is preferably in a range between 0.75 mm and 1.25 mm, such as about 1 mm. The footprint of the protrusions P is preferably in a range between 2.5 mm and 3.5 mm, such as about 3 mm.

[0034] In the embodiment of FIGS. 6A and 6B, the concave sides of the protrusions P are preferably shaped in such a way that a gap width between adjacent vanes V is substantially constant, i.e. these concave sides follow the shape of the neighboring vanes V. Compared to the basic shape of the vanes as shown in FIGS. 1-4, the height of the protrusions P is preferably in a range between 1.25 mm (70% of the gap width of 1.75 mm) and 2.25 mm (130% of 1.75 mm), and more preferably in a range between 1.5 mm (85% of 1.75 mm) and 2.0 mm (115% of 1.75 mm), such as about 1.75 mm, which most nicely results in the protrusions P being located at the stagnation points S. The concave sides of the protrusions P are preferably shaped in such a way that there is a continuous curve from the basic shape of the vane towards the tops of the protrusions P. The diameter of any rounded tops of the protrusions P is preferably in a range between 0.15 mm and 0.25 mm, such as about 0.2 mm.

[0035] In the embodiments of FIGS. 7A and 7B, the protrusions P are shaped such that the gap width between adjacent vanes V increases from the outside towards the inside of the vortex finder F. The gap width increase is preferably gradually and/or continuously. As a result, the gap obtains a diffuser-like shape. Diffusers are known from e.g. I.E. Idel'chik—Handbook of hydraulic resistance (1960). The gap width increase (here between curved shapes of neighboring vanes V) is preferably comparable to a gap width increase between flat plates positioned at an angle of between 5° and 30°, and more preferably about 12°. In one example, the gap has an initial width W.sub.i of 0.9 mm, and, beyond the protrusion P, an end width W.sub.e of 1.75 mm. The protrusion P has a rounded top, a height of 2.3 mm, and a footprint FP of 7 mm.

[0036] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The claimed feature that the vanes V have a protrusion P at a stagnation point S does not mean that the protrusion P must be exactly at the stagnation point S, but merely that the protrusions P are positioned close to the stagnation points S. Measures recited in mutually different dependent claims may advantageously be used in combination.