DISPOSITIF STATIQUE DE MELANGE D'ECOULEMENT DE FLUIDE

STATIC FLUID FLOW MIXING APPARATUS

Abrégé français

Conduit de mélangeur statique comprenant un conduit allongé longitudinalement pourvu d'onglets disposés de manière à avoir leurs premiers bords respectifs adjacents à la paroi du conduit et des seconds bords opposés respectifs espacés radialement vers l'intérieur par rapport à la paroi du conduit. Ces onglets peuvent servir de déflecteur de fluide, de sorte qu'avec l'écoulement du fluide à travers le conduit, de plus fortes pressions de fluide se font sentir contre les faces amont des onglets par rapport à des pressions de fluide réduites contre leurs faces aval. La différence de pression qui en résulte dans le fluide adjacent, respectivement, aux faces mutuellement opposées de chacun des onglets provoque un écoulement longitudinal de fluide à travers le conduit par dessus et au-delà de chacun desdits onglets, qui sera dévié. Le résultat de cette déviation est l'introduction d'une composante de courant transversal radial dans l'écoulement de fluide longitudinal à travers le conduit. En particulier, le mélangeur comprend également un corps central s'étendant généralement coaxialement le long d'au moins une partie de l'étendue longitudinale du conduit et définissant, entre la surface du corps central et la paroi du conduit, un espace annulaire limitant l'écoulement transversal radial. L'invention décrit également un procédé incluant le mélange statique sur une étendue longitudinale de volume à mélanger de section annulaire, dans lequel le mélange par force latérale radiale dans un écoulement longitudinal de fluide est le résultat de la déviation d'écoulement opérée par des onglets faisant dévier un écoulement de fluide longitudinal à partir d'une surface limite de confinement de fluide à travers un espace stérile de section annulaire vers une surface limite intérieure.

Abrégé anglais

A static mixer conduit 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. These tabs
redirect fluid flow to
introduce a radial cross-flow component to the longitudinal flow of fluid
through the conduit. A
central body extending generally coaxially along at least a portion of the
longitudinal extent of
the conduit defines between it and the conduit wall, an annular space
confining the radial
cross-flow.

Revendications

-7-
We claim:
1. A static mixer conduit comprising a longitudinally elongated
conduit having tabs that are secured to a conduit wall and
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, 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 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, and
wherein said mixer further comprises a central body
extending generally coaxially along at least a portion of
the longitudinal extent of said conduit and defining between
said central body and said conduit wall, an annular space.
2. A static mixer conduit comprising a longitudinally elongated
conduit having tabs that are secured to a conduit wall and
that are arranged with respective first edges adjacent said
conduit wall, and respective opposed second edges that are
spaced inwardly from the conduit wall, 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 said fluid adjacent, respectively,
mutually opposed faces of each of said tabs causes a
longitudinal flow of fluid through said conduit over and

-8-
past each said tab, to be redirected, thereby resulting in
the addition of a cross-flow component to the longitudinal
flow of fluid through said mixer conduit, and wherein said
mixer conduit further comprises a motionless central body
extending generally coaxially along at least a portion of
said longitudinally elongated conduit.
3. The static mixer conduit of claim 2, wherein the central
body comprises a cross-flow filter element.
4. The static mixer conduit of any one of claims 1-3, wherein
the central body comprises a heat transfer body adapted to
exchange heat with the fluid passing through the conduit.
5. A static mixer conduit 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, 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 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, and wherein said mixer, further comprises a
motionless central body, comprising a cross-flow filter
element, extending generally coaxially along at least a
portion of the longitudinal extent of said conduit and
defining between said central body and said conduit wall, an
annular space.

-9-
6. A method comprising static mixing, over a longitudinal
extent of a mixing volume having an annular cross-section,
wherein radial cross-stream mixing and in a longitudinal fluid
flow results from flow-directing tabs redirecting a
longitudinal flow from an outer, containment boundary
surface to which tabs are secured, comprising redirecting
said longitudinal flow across an intervening space having an
annular cross-section towards a motionless inner boundary
surface.
7. The method according to claim 6, wherein 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 tab to deflect the generally longitudinal fluid
flow inwardly from the fluid containment boundary surface,
across the intervening annular space towards said inner
boundary surface.
8. A method comprising static mixing, over a longitudinal
extent of a mixing volume having an annular cross-section,
wherein radial cross-stream mixing in a longitudinal fluid
flow results from flow-directing tabs redirecting a
longitudinal flow from an outer, fluid containment boundary
surface,
wherein 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 tab to
deflect the generally longitudinal fluid flow inwardly from
the fluid containment boundary surface, across the
intervening annular space towards said inner boundary
surface,
wherein the fluid flow over the edges of each said
tab results in the flow being deflected inwardly and

-10-
upwardly along an inclined surface of each said tab, to
thereby generate a pair of tip 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 said
two boundary surfaces, comprising redirecting said
longitudinal flow across an intervening space having an
annular cross-section towards a motionless inner boundary
surface.
9. A flow-through reactor for treating a fluid therein, said
reactor comprising:
A) a fluid conducting channel;
B) a central body providing an inner boundary surface
substantially centrally located within said channel;
and
C) static fluid-dynamic-effector means positioned in said
channel for deflecting the flow of a fluid through said
channel, said effector means comprising a plurality of
motionless, ramped tabs having inclined surfaces and
trailing downstream edges directed inwardly into said
channel toward said inner boundary surface to permit a
longitudinal fluid flow in a space between said
downstream edges and said inner boundary surface, said
tabs providing cross-stream mixing in said longitudinal
fluid flow by deflecting said fluid over said edges of
each of said tabs inwardly and upwardly along said
inclined surface toward said inner boundary surface
thereby generating a pair of tip vortices in said
longitudinal fluid flow past each tab, each vortex of
each of said pair of tip vortices being mutually
opposed in rotation about an axis of rotation oriented

-11-
along said longitudinal fluid flow and along said space
between said edges and said inner boundary surface.
10. The reactor of claim 9, wherein the central body is a heat
transfer body.
11. The reactor of claim 9 or 10, wherein the central body is a
cross-flow filter element.
12. A method for treating a fluid comprising flowing said fluid
through a flow-through reactor, said reactor comprising:
A) a fluid conducting channel;
B) a central body providing an inner boundary surface
substantially centrally located within said channel;
and
C) static fluid-dynamic-effector means positioned in said
channel for deflecting the flow of a fluid through said
channel; said effector means comprising a plurality of
motionless, ramped tabs having inclined surfaces and
trailing downstream edges directed inwardly into said
channel toward said inner boundary surface to permit a
longitudinal fluid flow in a space between said
downstream edges and said inner boundary surface, said
tabs providing cross-stream mixing in said longitudinal
fluid flow by deflecting said fluid over said edges of
each of said tabs inwardly and upwardly along said
inclined surface toward said inner boundary surface
thereby generating a pair of tip vortices in said
longitudinal fluid flow past each tab, each vortex of
each of said pair of tip vortices being mutually
opposed in rotation about an axis of rotation oriented
along said longitudinal fluid flow and along said space
between said edges and said inner boundary surface.

-12-
13. The method of claim 1-2, wherein the central body is a heat
transfer body.
14. The method of claim 12 or 13, wherein, the central body is a
cross-flow filter element

Description

CA 02221158 1997-11-13
WO 96/35506 PCT/CA96/00302
- 1 -
Static Fluid Flow Mixing Apparatus
TECffiNICAL FIELD :
The present invention relates to static mixers, and
especially to static mixers having both radial and
longitudinal flow in an elongated fluid-mixing conduit.
BACKGROUND OF ART :
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.
In a departure from that more typical approach, US
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 patented 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 occur in a conduit under turbulent fluid flow
conditions.
DISCLOSURE OF INVENTION:
In accordance with the present invention there is
3S provided a further improvement in static mixers - one in
$d BSTiTltiE SHEET (RULE 261

CA 02221158 1997-11-13
WO 96/35506 PCT/CA96/00302
- 2 -
which 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
centre of the conduit.
In a particularly preferred embodiment according to
the present invention, there is provided a static mixer
conduit in which 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 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.
The present invention further includes an improved
method, in which the static mixing is performed over a
longitudinal extent of a mixing volume having an annular
cross-section. More specifically, the 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.

CA 02221158 2003-04-09
... 3 --
Preferably, the tabs are ramped and arranc.~ed in. the fluid flow
between the respective boundary surfaces, to cause the fluid to
flow over the edges of each such tab to d~-,flect the generally
longitudinal f luid flow i:nward:l y f roiri ttie fluid containment
boundary surface, across the intervenir.;,g ,.~:-pace (having the
aforesaid annular cross-section), towards an inner boundary
surface. 'I'he inner boundary surface def.ixlF_s a volume which but
for the presence of that surface, would p r.mit passage of a
central longitudinal flow of non uni.fozm ~:luid mixing.
In a particularly preferred form tiie fluid flow over the
edges of each tab results in the flow be-ir:~~.g 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.
In accordance with another aspect of the invention there
is provided a static mixer conduit including a longitudinally
elongated conduit having tabs that are ;-~ec.ured to a conduit
wall and 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. The tabs are
operable as fluid foils which, with flu::ad flowing through the
mixer conduit, have greater flu.id pressi.zres manifest against
their upstream faces and reduced fluid pressures against their
downstream faces. A resultant pressure difference in the fluid
adjacent, respectively, the mutual:ly opposi~ec:i faces of each of
the tabs causes a longitudinal flow of fluid through the
conduit over and past each tab, to be redirected, resulting in
the addition of a radial crUss--flow component to the
longitudirial flow of' fluid through the conduit. The mixer
further includes a central body extending generally coaxially
along at least a portion of the longitudinal extent of the

CA 02221158 2003-04-09
3 a
conduit and defiriirig an annular spacf:- between the central body
and the conduit wal.l.
In accordance with another aspect :::>f the invention there
is provided a static tnixer conduit inc~7udiia(,.1 a lorlgitudinally
elongated conduit having tabs that are ~:sec ..ired to a conduit
wall and that are arranged with respectIve first edges adjacent
the conduit wall, and respective opposed second edges that are
spaced inwardly from the conduit wal.:l.. ':Che tabs are operable
as fluid foils which, wi t h. fluid f lowing through the mixer
conduit, have greater fluid pressures manifest against their
upstream faces and reduced fluid pressures against their
downstream faces. A resul t:ant pressuz:'e c:ii fterence in the fluid
adjacent, respectively, mutually opposed faces of each of the
tabs causes a longitudinal flow of fluid through the conduit
over and past each tab, to be redirectec:9., resulting in the
addition of a cross-flow component tiM> the Longitudinal flow of
f:l.uid through the mixer condui.t. The mixer conduit further
includes a motionless central body extendi:ng generally
coaxially along at least a portion of tlae longitudinally
elongated conduit.
In accordance with another aspect of t-he invention there
is provided a static mixer conduit including a longitudinally
e:Longated conduit having tabs that are arranged with respective
first edges adjacent the conduit wall, and respecti.ve opposed
second edges that are spaced radially inwardly from the conduit
wall. The tabs are operable as fluid foils which, with fluid
f:Lowing through said mixer conduit:, have greater fluid
pressures manifest against their u.pstream faces and reduced
fluid pressures against their downstream faces. 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 the conduit over and past
each tab, to be redirected, resulting in the addition of a
radial cross-flow component to the longituiiinal flow of fluid

CA 02221158 2003-04-09
3b .
through the conduit_ The inixer further :irrcludes a motionless
ceritral body, inc:Luding d~~rosE~, f lc~w .Ei.Lt-,tr element, extending
gerierally coaxial:Ly along at lt:.aast a poa._t:ion of the
longitudinal extent. of trle co:czdl.z.it: araca dei ining an annular
space between the central body and t.he, 4.-(-)n.duit wall.
In accordance with another aspect of t'rie invention there
is provided a method including static rn:a..xing over a
longitudinal exterit of a mixing volume having an annular cross-
section, where radial cross-stx-eam ma.x:iric; in a 1.ongit:udinal
fluid flow results from f low-direct. inc:l t:,A;,s redirect:ing a
longitudinal flow from an outer, fluid containment boundary
surface to which tabs are secured, by redirecting the
longitudinal flow across ari intervening space having an annular
cross-section towards a motionless inner boundary surface.
In accordance with another aspect r.,i: the invention there
iis provided a method inc:luding static mi.x.ing, over a
longitudinal extent of a mixing volume having an annular cross-
section, wherein radial cross-stream mixing in a longitudinal
fluid flow results from ilow-directing t..abs redirecting a
longitudinal flow from an outer, fluid containment boundary
surface by redirecting tlie longitudinal flow across an
intervening space having an aririular, c.ross-secti.on towards a
motionless inner boundarv surface. The tabs may be ramped and
arranged in the fluid flow between the :reslaective boundary
surfaces, to cause the fluid to flow over the edges of each tab
to deflect the generally longitudinal fluid flow inwardly from
the fluid containment boundary surface, ac:k-oss the irrtervening
annular space towards the inner boundary surface. The fluid
f:Low over the edges of each tab results in the flow being
deflected inwardly and upwardly along an inclined surface of
each tab, to generate a pair of tip vortices in the fluid flow
past each tab. The vortices associated witii each pair have
mutually opposed rotat.ioris about an axis of rotation oriented
generally along the longitudinal. "stream-w.ise" fluid flow

CA 02221158 2003-04-09
- ic -
direction, along the annular space between the two boundary
surfaces.
In accordance with anothel aspect:()1= the invention there
is provided a flow-through rea(..,t::c>r for t:reating a fluid. The
reactor includes: A) a fluid conducting channel ; B) a central
body providing an inner boundary surface substantially
centrally located within the channel; arid ;.,1 static fluid-
dynamic-effector mearis positioned in t.hf:_, channel for deflecting
the flow of a fluid through the channe~l. 'Trie effect(Dr means
include a plurality of mot:ion::le.:>s, ramped tabs having inclined
surfaces and trailing downstream edges c,:lirected inwardly into
the channel toward the inner boundary surface to permit a
longitudinal fluid flow in a space between the downstream edges
and the inner boundary surface. The tabs provide cross-stream
mixin(g in the longitudinal fla.zid flow by deflecting the fluid
over the edges of eack-i of the tabs inwardly and upwardly along
the inclined surface toward the inner boundary surface,
generating a pair of tip vortices in the longitudinal fluid
flow past each tab, each vortex of each of the pair of tip
v(Drtices being mutually opposed in rotation about an axis of
rotation oriented along the longitudinal fl.uid flow and along
the space between the edges and the inner boundary surface.
In accordance with another aspect of the invention there
is provided a method for treating a fluid by flowing the fluid
through a flow-through reactor. The reactor includes: A) a
fluid conducting channel; E) a central body providing an inner
b(Dundary surface substantially centrally located within the
channel; and C) static f,~~.ui.d-dynarnic-effector means positioned
in the channel for deflecting the flow of a fluid through the
channel. The effector means include a plurality of motionless,
ramped tabs having inclined surfaces and trailing downstream
edges directed inwardly into the channel tcDward the iriner
boundary surface to permit a longitudina.:l f'luid flow in a space
between the downstream edges and, the inner boundary surface.

CA 02221158 2003-04-09
3 d The tabs provide cross-stream niixirig :in t:he longitudinal fluid
flow by deflecting the fluid over the edq(~:~s of each of the tabs
inwardly and upwardly along the inclined surface toward the
inner boundary surface thereby generatiaig a pair of tip
vortices in the lon.gitud.ina:l. :flui.d flow past, each tab, each
vortex of each of the pa:ii:, of tip vort:::i.c:es being mutually
opposed in rotation about an axis c-~f rot.at:ion oriented along
the longitudinal fluid flow and along the space between the
edges and the inner boundary surface.
In alternative embodiments of the ~.r~,-~r.i.ous aspects of the
invention, the central body of t::he stat.i(- mixer condi,zit. may
include a cross-flow filter element, or niay include a heat
t:ransfer body adapted to exchange heat with the fluid passing
t'zrough the conduit.
BRIEF DESCRIPTION OF DRAWINGS:
Figure 1 is an elevated, longitudinal cross-section
through a static mixer according t.c) the combination of the
present invention;
Figure 2 is an elevated, transverse cross-section taken
through line 2-2 of the rnixer depicted in Figure 1;
Figure 3 is a reproduction of th.e view illustrated in
Figure 2, but further including representative fluid
stream lines, to illustrate radial cross--flow patterns;
and,
Figure 4 is a cut-away perspective view illustrating
vortex flow downstream of a single, representative tab.

CA 02221158 2005-08-19
- 4 -
HEST MODE(S) FOR CARRYING OUT TH8 INVMTION
AND INDUS'T'RIAL APPLIGAHILITY :
(Note: The apparatus disclosed and illustrated in US
4,929,088 - Smith, (dar.ed March 29, 1990), is useful as a
component of the present invention, as well as
the method described i.n US
4,981,368 - Smith, (dated January 1, 1991).
2.0
iteforring now to Figures 1, 2 and 3, there is
illustrated an embodiment according to the pxesent
tnvention, in which a static tnixer. 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.
In the illustrated embodiment, that region forms
between diametricall.y==opposed, radia:l.lyWconvergerYt,
cross=strcanm mixing flowb (see Figure 3, in particular)
within conduit 4.
Static mixer 1 comprises conduit 4, in which tabs 2
are each arranged with respecti=re, (leading, upstream)
edges 6 adjacent the conduit wall, and respective,
(trailing, downstream) opposed edges 7 that are spaced
radially inwardly from the conduit wa1l. 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 Figure 1) and reduced fluid
pressures against their downstream faces 9(see Figure 1).
This pressure dif.ference in the fluid adjacent,
respectiv2ely, 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),

CA 02221158 1997-11-13
WO 96/35506 PCT/CA96/00302
- 5 -
thereby resulting in the addition of a radial cross-flow
component to the longitudinal flow of fluid through the
conduit 4.
With body 5 occupying the zone of relatively poor
mixing as described above, 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.
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
an manufacturer to not only secure improved mixing as
aforesaid, but to also 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 US 4,929,088, is true for both that boundary
surface, and for the heat exchange surface of the central
body S.
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.
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 cross-section towards the inner

CA 02221158 1997-11-13
WO 96/35506 PCT/CA96/00302
- 6 - ~
boundary surface defining the outermost extent of central
body S. 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 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 5, circumscribes a
volume which but for the presence of that surface, would
permit passage of a central longitudinal flow of
substantial, relatively non-uniform mixing.
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.

Dessin représentatif