AU727153B2 - Static fluid flow mixing apparatus - Google Patents

Description

S&F Ref: 404899D1

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

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Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Labatt Brewing Company Limited 150 Simcoe Street Post Office Box 5050 London Ontario N6A 4M3 Canada Jeffrey Cooke, Glen Austin and Michael Jerome McGarrity Spruson Ferguson St Martins Tower 31 Market Street Sydney NSW 2000 Static Fluid Flow Mixing Apparatus The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c Description [0001] The invention relates to a static mixer comprising a longitudinally elongated conduit having tabs that are arranged with respective first edges adjacent the conduit wall, and respective opposed second edges that are spaced radially inwardly from the conduit wall, said mixer further comprising a central body extending generally coaxially along at least a portion of the longitudinal extent of said conduit and defining between said central bodies surface and said conduit wall, an annular space.

[0002] Furthermore, the invention relates to the use of such static mixer.

[0003] More generally, the invention relates to static mixers and especially to static mixers having both radial and longitudinal flow in an elongated fluid-mixing conduit.

[0004] As a generalization, typical static mixers include fluid redirecting tabs, vanes, baffles, or the like, that are arranged in a fluid conduit and which are typically operable to divide, subdivide, separate adjacent subdivided flows, and then recombine the subdivided flows into a "shuffled" whole, as the fluid passes through that conduit.

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[0005] In a departure from that more typical approach, U.S. A-4,929,088 discloses a tab "'"arrangement in a fluid conduit that has lower fluid back pressures than are associated with -the more typical approach to more typical static mixer designs. In particular, this known •25 tab arrangement operates by creating radial vortex flow patterns that are generally transverse to the longitudinal flow through the fluid conduit in which these tabs are mounted. This results in a plurality of cross-stream mixing flows that are transverse to the longitudinal flow of the fluid along the length of the conduit. This approach is disclosed as an enhancement over the kind of mixing that would be expected to naturally 30 occur in a conduit under turbulent fluid flow conditions.

[0006] Furthermore, a static mixer of the type mentioned in the beginning is disclosed in DE-A-539 423, in which however the fluid redirecting means do not have the form of I pads and are thus not operable as fluid foils.

(H:]OO987.doc:SaF [0007] Finally, GB-A-1212633 discloses an irradiation apparatus comprising mixing means in the form of pads, which pads however, in contrast to the present invention, are arranged in the irradiation apparatus.

[0008] In accordance with the present invention, there is provided an improved static mixer of the type mentioned in the beginning, which is characterized in that said tabs are operable as fluid foils which, with fluid flowing through said mixer conduit, have greater fluid pressures manifest against their upstream faces and reduced fluid pressures against their downstream faces, and wherein a resultant pressure difference in the fluid adjacent, respectively, the mutually opposed faces of each of the tabs causes a longitudinal flow of fluid through said conduit over and past each said tab, to be redirected, thereby resulting in the addition of a. radial cross-flow component to the longitudinal flow of fluid through the conduit.

[0009] Thus, a central elongated body is deployed within the static mixer conduit, in a central region of reduced mixing. Such a region, for example, tends to exist between diametrically-opposed, radially-convergent, cross-stream mixing flows within that conduit. In any case, this centrally-located body occupies a zone in which there would otherwise be a reduced cross-flow. The presence of this central body results in the fluid flowing past it tending to be more efficiently mixed--in that there is less of a tendency for an unmixed "channel" of longitudinal fluid flow to establish itself within the center of the conduit.

o 25 [0010] Furthermore, tabs are each arranged with respective (preferably leading, upstream) edges adjacent the conduit wall and respective (preferably trailing, downstream) opposed edges that are spaced radially inwardly from the conduit wall.

These tabs are operable as fluid foils which, with fluid flowing through the mixer, have greater fluid pressures manifest against their upstream faces and reduced fluid pressures 30 against their downstream faces. This pressure difference in the fluid adjacent.

respectively, the mutually opposed faces of each of the tabs then causes the longitudinal flow over and past each tab to be redirected, thereby resulting in the addition of a radial cross-flow component to the longitudinal flow of fluid through the conduit.

[I1:]00987.doc:SaF [0011] The present invention further includes the use of the static mixer according to the present invention for mixing a fluid flowing through said conduit, wherein radial crossstream mixing results from said flow redirecting tabs redirecting a longitudinal fluid flow from the conduit wall across an intervening space of annular cross-section towards the surface of the inner body. Thus, the static mixing is performed over a longitudinal extent of a mixing volume having an annular cross-section. More specifically, thile method of the present invention relates to cross-stream mixing in a fluid flow, in which tabs mentioned herein redirect a longitudinal fluid flow from an outer, fluid containment boundary surface, across an intervening space having an annular cross-section towards an inner boundary surface. Preferably, the tabs are ramped and arranged in the fluid flow between the respective boundary surfaces, to cause the fluid to flow over the edges of each such tab to deflect the generally longitudinal fluid flow inwardly from the fluid containment boundary surface, across the intervening space (having he aforesaid annular crosssection), towards an inner boundary surface. The inner boundary surface defines a volume, which, but for the presence of that surface, would permit passage of a central longitudinal flow of non-uniform fluid mixing.

[0012] In a particularly preferred form, the fluid flow over the edges of each tab results in the flow being deflected inward and up the inclined surface of the tab to generate a pair !of tip vortices in the fluid flow past each tab. The vortices of each such pair have mutually opposed rotations, about an axis of rotation oriented generally along the longitudinal "stream-wise" fluid flow direction, along the annular space between the two boundary surfaces.

i BRIEF DESCRIPTION OF DRAWINGS [0013] ee ~FIG. 1 is an elevated, longitudinal cross'section through a static mixer according to the present invention; FIG. 2 is an elevated, transverse cross-section taken through line 2--2 of the mixer depicted in FIG. 1; FIG. 3 is a reproduction of the view illustrated in FIG. 2, but further including representative fluid stream lines, to illustrate radial cross-flow patterns; and, [H:]00987.doc:SaF FIG. 4 is a cut-away perspective view illustrating vortex flow downstream of a single, representative tab.

BEST MODE(S) FOR CARRYING OUT THE INVENTION AND INDUSTRIAL APPLICABILITY [0014] Referring now to FIGS. 1, 2 and 3, there is illustrated an embodiment according to the present invention, in which a static mixer 1, includes a series of tabs 2 that are secured to the side walls 3 of a conduit 4. A central body 5 is arranged in co-axially aligned relation, centrally within the interior of conduit 4, where it occupies a region of inefficient mixing.

[0015] In the illustrated embodiment, that region forms between diametrically-opposed, radially-convergent, cross-stream mixing flows (see FIG. 3, in particular) within conduit 4.

[0016] Static mixer 1 comprises conduit 4, in which tabs 2 are each arranged with 9.

respective (leading, upstream) edges 6 adjacent the conduit wall, and respective (trailing, downstream) opposed edges 7 that are spaced radially inwardly from the conduit wall 3.

Tabs 2 operate as fluid foils which, with fluid flowing through the mixer, have greater fluid pressures manifest against their upstream faces 8 (see FIG. 1) and reduced fluid 25 pressures against their downstream faces 9 (see FIG. This pressure difference in the fluid adjacent, respectively, the mutually opposed faces of each of the tabs then causes the longitudinal flow over and past each tab to be redirected (as is illustrated by the various flow streamlines that are shown in the various figures), thereby resulting in the addition of a radial cross-flow component to the longitudinal flow of fluid through the conduit 4.

[0017] With body 5 occupying the zone of relatively poor mixing as described above, 0 the fluid itself is precluded from forming eddies in that zone, in which the fluid would not be as thoroughly admixed with the balance of the fluid flow.

[ll:I 00987.doc:SaF [0018] In a particularly preferred embodiment, body 5 comprises a heat transfer body adapted to exchange heat with the fluid passing through the conduit. This allows a manufacturer to not only to secure improved mixing as aforesaid, but also to increase the amount of heat exchange surface available to alter the temperature of the fluid flow. This is particularly advantageous since the benefit of avoiding boundary layer "insulation" effects as discussed in relation to the boundary surface described in U.S.-A-4,929,088, is true for both that boundary surface and for the heat exchange surface of the central body [0019] In a further embodiment according to the present invention, the central body 5 is a cross-flow filter element. As will be apparent to persons skilled in the art, in light of the present invention, the boundary layer advantages associated with thermal transfer are applicable in achieving cross-flow filtration advantages too.

[0020] In operation, the improved static mixing according to the present invention is performed over a longitudinal extent of a mixing volume having an annular cross-section located between the central body 5 and side walls 3 of conduit 4. More specifically, there is cross-stream mixing in the longitudinal fluid flow through the present apparatus, in which tabs 2 redirect a longitudinal fluid flow from the outer, fluid containment, boundary surface of side walls 3, across an intervening space having an annular crosssection towards the inner boundary surface defining the outermost extent of central body Preferably, tabs 2 are ramped and arranged in the fluid flow between the respective boundary surfaces of side walls 3 and central body 5 to cause the fluid to flow over the 25 edges of each tab 2 to deflect the generally longitudinal fluid flow radially inwardly from the fluid containment boundary surface of side wall 3, across the intervening space (having the aforesaid annular cross-section), towards an inner boundary surface defined by the outermost surface of central body 5. The inner boundary surface of central body circumscribes a volume that, which but for the presence of that surface, would permit 30 passage of a central longitudinal flow of substantial, relatively non-uniform mixing.

[0021] As can be seen from all Figures 1 to 4, in the shown embodiment, the sides of the ramped portions of the tabs 2 converge towards the edge 7.

[H:]00987.doc:SaF [0022] In a particularly preferred form the fluid flow over the edges of each tab results in the flow being deflected inward and up the inclined surface of the tab to generate a pair of tip vortices in the fluid flow past each tab. The vortices of each such pair have mutually opposed rotations, about an axis of rotation oriented generally along the longitudinal "stream-wise" fluid flow direction, along the annular space between the two boundary surfaces.

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Claims (8)

1. A static mixer comprising a longitudinally elongated conduit having tabs that are arranged with respective first edges adjacent the conduit wall, and respective opposed second edges that are spaced radially inwardly from the conduit wall, said mixer further comprising a central body extending generally coaxially along at least a portion of the longitudinal extent of said conduit and defining between said central body's surface and said conduit wall, an annular space, wherein said tabs are operable as fluid foils which, with fluid flowing through said mixer conduit, have greater fluid pressures manifest against their upstream faces and reduced fluid pressures against their downstream faces, and wherein a resultant pressure difference in the fluid adjacent, respectively, the mutally opposed faces of each of the tabs causes a longitudinal flow of fluid through said conduit over and past each said tab, to o be redirected, thereby resulting in the addition of a radial cross-flow component to the longitudinal flow of fluid through the conduit. 9090*: cna

2. The static mixer as claimed in claim 1 characterized in that said 0 central body comprises a heat transfer body, adapted to exchange heat with the fluid passing through the conduit.

3. The static mixer as claimed in claim 1 or 2, characterized in that said ooo central body is a cross-flow filter element.

4. The static mixer as claimed in claim 1, 2 or 3, characterized in that 0 0 said tabs are ramped. 0 s

5. The static mixer as claimed in claim 4, characterized in that the sides of the ramped portions of the tabs are converging towards the second edges.

6. Use of the static mixer as claimed in any one of claims 1 to 5 for mixing a fluid flowing through said conduit, wherein radial cross-stream mixing results from said flow redirecting tabs redirecting a longitudinal fluid flow from the conduit wall across an intervening space of annular cross-section towards the surface of the inner body.

7. Use as claimed in claim 6, characterized in that said tabs are ramped and arranged in the fluid flow between the respective boundary surfaces, to cause the fluid to flow over the edges of each said tabs to deflect the generally longitudinal fluid flow inwardly from the fluid containment boundary surface, across the intervening annular space towards said inner boundary surface. [R:\LIBLL] 10096.doc:SSL

8. Use as claimed in claim 7, characterized in that the fluid flow over the edges of each said tabs results in the flow being deflected inwardly and upwardly along an inclined surface of each said tab, to thereby generate a pair of tip vortices in the fluid flow past each tab, and wherein said vortices associated with each said pair have mutually opposed rotations about an axis of rotation oriented generally along the longitudinal "stream-wise" fluid flow direction, along the annular space between two boundary surfaces. Dated 25 September, 2000 Labatt Brewing Company Limited Patent Attorneys for the Applicant S: SPRUSON FERGUSON [R\LIBLL 10096.doc:SSL