Fluid mixing device with vortex generators

A mixing device for mixing two or more flowing fluids in a flow duct in which the fluids to be mixed flow along a dividing wall (22), includes a plurality of vortex generators mounted on a downstream end of the dividing wall. The vortex generators (9) have surfaces which project into the duct, and around which flow occurs freely. Each vortex generator includes two side surfaces connected at a lead connecting edge which stands perpendicularly to the dividing wall (22) and is the edge acted upon first by the flow. A top surface consists of two sectional top surfaces (1, 2) which are connected to one another via a top connecting edge (10). Downstream rear edges (5, 6) of the sectional top surfaces (1, 2) are oriented at an angle (.gamma.) with the dividing wall (22), as a result of which, the the rear edges (5, 6) lie on an opposite side of the dividing wall (22)), with respect to the side surfaces (11, 13). A base surface consists of two sectional base surfaces which are connected to one another by a base connecting edge and to the sectional top surfaces by the rear edges (5, 6).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a mixing device for mixing two or more fluids 
which can have the same or a dissimilar mass flow, the fluids to be mixed 
flowing along a dividing wall on whose downstream end a plurality of 
vortex generators having surfaces around which flow occurs freely are 
arranged, of which vortex generators a plurality are arranged next to one 
another, the side surfaces of the vortex generator being flush with one 
side of the dividing wall and enclosing with one another the sweepback 
angle, the longitudinally directed edges of the side surfaces running at a 
setting angle to the wall, and the two side surfaces enclosing with one 
another a connecting edge which preferably runs perpendicularly to the 
wall and is the edge acted upon first by the flow. 
2. Discussion of Background 
EP-A1-0 619 134, for example, discloses such mixing devices. In many 
sectors, such as, for example, chemicals, food or pharmaceuticals 
production, etc., fluids are required to be intimately mixed in the 
quickest way. The quality of the entire process mostly depends on the 
mixing quality achieved. The pressure drop during the mixing operation 
should at the same time remain within "reasonable" limits in order to keep 
down the process costs through low pumping work. 
SUMMARY OF THE INVENTION 
Accordingly, one object of the invention in a mixing device of the type 
mentioned at the beginning is to improve the intermixing. 
According to the invention, this is achieved in that 
a top surface consists of two sectional top surfaces, the longitudinally 
directed edges of the sectional top surfaces being flush with the edges of 
the side surfaces, and the sectional top surfaces being connected to one 
another via a connecting edge, 
the downstream rear edges of the sectional top surfaces enclose an angle 
with the dividing wall, as a result of which the rear edges, with respect 
to the side surfaces, come to lie essentially on the other side of the 
dividing wall, 
and a base surface consists of two sectional base surfaces which are 
connected to one another via a connecting edge and to the sectional top 
surfaces via the rear edges. 
The advantages of the invention may be seen, inter alia, in the fact that 
the downstream edge of the dividing wall is lengthened by the introduction 
of the rear edges rotated relative to the dividing wall. Consequently, the 
contact area of the flows to be mixed is increased on the one hand, and 
further vortices are generated on the other hand by the rear edges placed 
in the flow. These vortices assist and intensify the vortices of the 
vortex generator which are generated at the longitudinally directed edges. 
In addition, the intermixing of the flows to be mixed is increased, since 
the vortices propagate in the direction of the respectively opposite flow, 
as a result of which an interwoven flow pattern develops. 
From the fluidic point of view, the vortex-generator element has a very low 
pressure loss when flow occurs around it and it generates vortices without 
a wake zone. Finally, the element, due to its interior space, which is 
hollow as a rule, can be cooled in the most varied ways and by diverse 
means. 
It is especially expedient if the two side surfaces enclosing the sweepback 
angle .alpha. as well as the sectional top surfaces of the vortex 
generator are arranged symmetrically to a plane of symmetry, formed by an 
axis of symmetry and the connecting edge of the side surfaces. Vortices 
having identical swirl are thus generated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, wherein like reference numerals designate 
identical or corresponding parts throughout the several views, according 
to FIG. 1 a vortex generator 9 essentially comprises a plurality of 
triangular surfaces around which flow occurs freely. These are two 
sectional top surfaces 1, 2, two side surfaces 11, 13 and two sectional 
base surfaces (not visible in FIG. 1). In their longitudinal extent, these 
surfaces run at certain angles in the direction of flow. 
The two side surfaces 11 and 13 are each disposed perpendicularly on the 
associated top side 21 of a dividing wall 22, although this need not 
necessarily be the case. The side surfaces 11, 13, which consist of 
right-angled triangles, are fixed here by their longer leg to the dividing 
wall 22. They are oriented in such a way that they form a joint with their 
shorter leg while enclosing a sweepback angle .alpha.. The joint is 
designed as a sharp connecting edge 16 and is likewise disposed 
perpendicularly to the dividing wall 22. Incorporated in a duct, the 
cross-section of flow is scarcely impaired by obstruction on account of 
the sharp connecting edge. An intersection 8 which lies in the dividing 
wall is formed by the longer legs of the side surfaces 11, 13 and by the 
connecting edge 16. The two side surfaces 11, 13 enclosing the sweepback 
angle .alpha. are symmetrical in shape, size and orientation and are 
arranged on either side of a plane of symmetry which is formed by an axis 
17 of symmetry and the connecting edge 16. The axis 17 of symmetry is 
normally parallel to the duct axis and thus with the duct flow. 
An essentially longitudinally directed edge 12 of the sectional top surface 
1 is flush with the hypotenuse of the side surface 11 projecting into the 
flow duct. This longitudinal edge 12 runs at a setting angle .theta. to 
the wall 22. A downstream main edge 5 of the sectional top surface 1 lies 
in a plane perpendicular to the axis 17 of symmetry and is rotated by an 
angle .gamma. relative to the dividing wall 22 so that the rear edge 5 
comes to lie below the dividing wall. To assemble the vortex generator 9, 
therefore, slots have to be made in the dividing wall 22, or the dividing 
wall must be appropriately adapted. 
The sectional top surface 2 is symmetrical to the sectional top surface 1 
with regard to the plane of symmetry, formed by the axis 17 of symmetry 
and the connecting edge 16. Therefore a longitudinally directed edge 14 of 
the sectional top surface 2 is flush with the hypotenuse of the side 
surface 13 projecting into the flow duct. The longitudinal edge 14 runs at 
the setting angle .theta. to the wall 22. A rear edge 6 of the sectional 
top surface 2 likewise lies in the plane perpendicular to the axis 17 of 
symmetry and is rotated by the negative angle .gamma. relative to the 
dividing wall so that the rear edge 6 comes to lie below the dividing wall 
22. 
The second longitudinally directed edge of the sectional top surface 1 
forms with the second longitudinally directed edge of the sectional top 
surface 2 a connecting edge 10 which lies in the plane of symmetry formed 
by the axis 17 of symmetry and the connecting edge 16. The connecting edge 
10 forms with the rear edge 5 as well as with the rear edge 6 a point 7 
lying at the downstream end of the vortex generator 9. The longitudinal 
edges 12, 14 form together with the connecting edge 16 and the connecting 
edge 10 a point 18 lying at the upstream end of the vortex generator 9. 
According to FIG. 2, the triangular sectional base surface 3 is defined by 
the rear edge 5 and the intersection 8, and the triangular sectional base 
surface 4 is defined by the rear edge 6 and the intersection 8. A 
connecting edge 30 of the sectional base surfaces 3, 4 therefore extends 
from the point 7 up to the intersection 8. 
The vortex generator may of course also be produced without base surfaces, 
the dividing wall then performing the function of the base surfaces. To 
this end, the dividing wall must be of serrated configuration at its 
downstream end, in accordance with the sectional base surfaces. In order 
to further increase the contact area at the downstream end of the dividing 
wall, the rear edges of the vortex generator may also lie in various 
planes which do not run perpendicularly to the axis of symmetry. 
In FIGS. 3 and 4, a vortex generator 9' on the bottom side 20 of the 
dividing wall 22 and a vortex generator 9 on the top side 21 of the 
dividing wall are arranged next to one another. The vortex generator 9' is 
identical in shape and size to the vortex generator 9; the designations 
already used above for the vortex generator 9 are therefore also used for 
the vortex generator 9' but are provided with an apostrophe. The vortex 
generator 9 can be converted into the vortex generator 9' by a rotation of 
180.degree. about an axis 19 of rotation. The axis 19 of rotation lies in 
the dividing wall 22, is parallel to the axis 17 of symmetry and passes 
through the intersection of longitudinal edge 14 and rear edge 6. 
The connecting edge 16 of the two side surfaces 11, 13 always forms the 
upstream edge of the vortex generators 9, 9'. The sharp connecting edge 16 
is that location which is acted upon first by the duct flow. The rear 
edges 5, 6, 5', 6' of the top surfaces running transversely to the 
dividing wall 22 around which flow occurs are therefore the edges acted 
upon last by the duct flow. 
The vortex generators 9' may of course be of different design to the vortex 
generators 9, in which case the vortex generators are always of similar 
geometry to the basic configuration shown. This is advantageous, for 
example, for mixing physically different flows. 
The mode of operation of the vortex generator is as follows: when flow 
occurs around the edges 12 and 14, the flow is converted into a pair of 
oppositely running directed vortices. The vortex axes lie in the axis of 
the flow. The geometry of the vortex generators is selected in such a way 
that no backflow zones develop during the vortex generation. The vortices 
of the vortex generator 9 rotate above and along the top surfaces 1, 2 and 
head for the dividing wall 22 on which the vortex generator is mounted. 
The vortices of the vortex generator 9' rotate below and along the top 
surfaces and likewise head for the dividing wall 22. 
The swirl coefficient of the vortex is determined by appropriate selection 
of the setting angle .theta. and/or the sweepback angle .alpha.. As the 
angles increase, the vortex intensity or the swirl coefficient is 
increased, and the location of the vortex breakdown--provided this is 
actually desired--shifts upstream right into the region of the vortex 
generator itself. Depending on use, these two angles .theta. and .alpha. 
are predetermined by design conditions and by the process itself. Then 
only the height h of the connecting edge 16 has to be adapted. By the 
selection of the angle .gamma., the vortices are influenced in such a way 
that the larger .gamma. is selected to be, the better is the intermixing 
of the partial flows. However, the angle .gamma. cannot be selected to be 
of any desired magnitude, since the pressure drop also increases as 
.gamma. increases. 
It is pointed out that the shape of the dividing wall 22 around which flow 
occurs is not essential for the mode of operation of the invention. 
Instead of the straight shape of the dividing wall 22 shown in the 
figures, it could also be an annular or hexagonal or other cross-sectional 
shape. In the case of a curved dividing wall, the above statement that the 
side surfaces are disposed perpendicularly on the wall must of course be 
qualified. The decisive factor is that the connecting edge 16 lying on the 
line 17 of symmetry is disposed perpendicularly on the corresponding wall. 
In the case of annular walls, the connecting edge 16 would therefore be 
oriented radially. 
FIG. 5 shows a partial view of a duct having a fitted dividing wall 22. The 
cross-section through which flow occurs is subdivided by this dividing 
wall 22 into two sectional ducts having the duct heights H1 and H2. The 
top side 21 of the dividing wall 22 forms a duct wall of the top duct 41, 
and the bottom side 20 of the dividing wall 22 forms a duct wall of the 
bottom duct 42. The same medium could flow at a different velocity through 
the two ducts, or the media could be flowing fluids of different density 
or chemical composition which have to be mixed in the quickest way into a 
certain uniformly distributed concentration. 
In each case an identical number of vortex generators 9, 9' are lined up 
with gaps in between on the two duct walls 20 and 21 of the dividing wall. 
The height h1 of the elements 9 as well as the height h2 of the elements 
9' are, for example, about 90% of the associated duct heights H1 and H2. 
In FIG. 5 the flow takes place perpendicularly out of the drawing plane; 
the elements 9, 9' are oriented in such a way that the connecting edges 16 
are directed against the flow. The sense of rotation of the generated 
vortices in the region of the connecting edge is descending, i.e. heading 
toward the respective duct wall 20, 21 on which the vortex generator is 
arranged. At the end of the dividing wall 22, i.e. at the rear edges 5, 6, 
5', 6', the vortex flows generated on the two sides of the dividing wall 
22 are forced into one another, in the course of which the desired 
intermixing occurs. 
The vortices having identical swirl in the sectional ducts 41, 42 combine 
to make one large vortex having a uniform sense of rotation. The axis of 
rotation of this large vortex is essentially the axis 19 of rotation. 
The vortex generators 9, 9' can have different heights h1, h2 in the ducts 
41, 42 relative to the duct heights H1, H2. As a rule, the heights h1, h2 
of the connecting edges 16, 16' of the vortex generators 9, 9' will be 
matched to the respective duct heights H1, H2 in such a way that the 
generated vortices directly downstream of the vortex generator already 
attain such a size that the full duct height H1+H2 or the full height of 
the duct part allocated to the vortex generator is filled, which leads to 
a uniform distribution in the cross-section acted upon. A further 
criterion which can have an influence on the ratio h/H to be selected is 
the pressure drop which occurs when flow takes place around the vortex 
generator. It goes without saying that the pressure-loss coefficient also 
increases as the ratio h/H increases. 
The invention is of course not restricted to the exemplary embodiments and 
examples of use shown and described. Due to the specific design and 
dimensioning of the vortex generators, a simple means of controlling the 
mixing operation according to requirement at given flows is available. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.