Mixer device

Abstract

The present invention relates to a mixer device for distributing and evaporating a liquid introduced into a gas flow, in particular into an exhaust-gas flow, wherein the mixer device comprises at least one mixer vane (14a) which influences the flow direction of the gas flow. The mixer vane has a first vane (14a′) portion and a second vane portion (14a″) which are arranged in series in the flow direction of the gas flow, which vane portions are designed so that the first vane portion diverts the gas flow approaching the mixer device such that said gas flow has a first swirl component imparted thereto, and so that the second vane portion subsequently diverts the gas flow such that said gas flow has a second swirl component imparted thereto, wherein the first swirl component and the second swirl component oppose one another.

Claims

1. A mixer device for distributing and vaporizing a liquid introduced into one of a gas flow and an exhaust gas flow, wherein the mixer device comprises at least one mixer blade (14a 14b) which influences the flow direction of the gas flow and which has a first blade section (14a′) and a second blade section (14a′″, 14b′″), said first blade section and said second blade section being arranged behind one another in the flow direction of the gas flow and being configured such that the first blade section (14a′) deflects the gas flow flowing onto the mixer device such that said gas flow receives a first swirl component and such that the second blade section (14a′″, 14b′″) subsequently deflects the gas flow such that it receives a second swirl component, wherein the first swirl component and the second swirl component are opposite to one another, further comprising a third blade section arranged in the axial direction between the first blade section and the second blade section and wherein said third blade section is configured as one of a plane that extends in substantially the axial direction of the mixer device.

2. The mixer device in accordance with claim 1, wherein the first swirl component and the second swirl component are of different amounts.

3. The mixer device in accordance with claim 1, wherein at least one of the first blade section (14a′) and the second blade section (14a′″, 14b′″) are inclined or curved with respect to a center axis (M) of the mixer device and wherein optionally at least one of the first blade section (14a′) and the second blade section (14a′″, 14b′″) have different angles of inclination or curvatures with respect to the center axis (M).

4. The mixer device in accordance with claim 1, wherein at least one of the first blade section (14a′) and the second blade section (14a′″, 14b′″) forms a plane.

5. The mixer device in accordance with claim 1, wherein at least one of an angle of inclination (N1) of the first blade section (14a′) amounts to no more than 25° at least at its upstream end with respect to the center axis and an angle of inclination (N2) of the second blade section (14a′″, 14b′″) amounts to no more than 35° at least at its downstream end with respect to the center axis (M).

6. The mixer device in accordance with claim 1, wherein at least one of the first blade section and the second blade section (14b′″) comprises at least two segments (19) which have different angles of inclination or curvatures with respect to the center axis (M).

7. The mixer device in accordance with claim 1, wherein a transition region between one of the first blade section (14a′) and the second blade section (14a′″), the first blade section (14a′) and the third blade section (14a″), and the third blade section (14a′) and the second blade section (14a′″) is a straight edge (B1 or B2) inclined with respect to a center axis (M) of the mixer device.

8. The mixer device in accordance with claim 1, wherein the mixer blade (14a, 14b, 14c, 14d, 14e, 14f) extends from a center axis (M) of the mixer device in a substantially radial direction toward one of a housing (12) and a ring shaped housing.

9. The mixer device in accordance with claim 1, wherein a plurality of mixer blades (14a, 14b, 14c, 14d, 14e, 14f) are provided which are arranged one of distributed and uniformly distributed in the peripheral direction of the mixer device.

Description

(1) The present invention will be explained in the following purely by way of example with reference to advantageous embodiments and to the enclosed drawings. There are shown:

(2) FIG. 1 a perspective view of a first embodiment of a mixer device in accordance with the invention in a view obliquely from the front—viewed in the flow direction of the gas flow;

(3) FIGS. 2 to 4 the embodiment of FIG. 1 in a perspective view obliquely from behind, in a view from the front and in a view from the rear respectively;

(4) FIG. 5 a mixer blade of the mixer device in accordance with FIG. 1 in a perspective view;

(5) FIG. 6 the mixer blade of FIG. 5 in a side view;

(6) FIG. 7 a perspective view of a second embodiment of a mixer device in accordance with the invention;

(7) FIGS. 8 to 10 different perspective views of a third embodiment of a mixer device in accordance with the invention;

(8) FIGS. 11 and 12 different perspective views of a fourth embodiment of a mixer device in accordance with the invention;

(9) FIGS. 13 and 14 different perspective views of a fifth embodiment of a mixer device in accordance with the invention; and

(10) FIGS. 15 and 16 different perspective views of a sixth embodiment of a mixer device in accordance with the invention.

(11) FIG. 1 shows a mixer device 10a which, for example, is used in an exhaust train of a motor vehicle to vaporize in the exhaust gas flow a urea solution introduced in the exhaust gas flow and to distribute it as homogenously as possible. The mixer device 10a comprises a ring-shaped housing 12 and a plurality of mixer blades 14a uniformly distributed about a center axis M in the peripheral direction. The mixer blades 14a have blade sections 14a′, 14a″ and 14a′″ which are each essentially planar. The blade sections 14a′, 14a″ and 14a′″ are inclined with respect to one another to defect a gas flow flowing onto the mixer device 10a, for example, essentially axially—i.e. parallel to the center axis M. The aim is thereby to obtain a gas flow which is as homogeneous as possible and in which suitable conditions are present for the chemical reactions required for efficient emission control. The blade sections 14a′, 14a″, 14a′″ effect the following in detail:

(12) First, the gas flow is defected by the blade sections 14a′ so that a swirl is imparted to the flow. I.e. the blade sections 14a′ have the effect that the gas flow receives a movement component in the peripheral direction. On the deflection of the gas flow, a number of the droplets contained in the gas flow—so-called primary droplets—impact the blade sections 14a′ and at least partly vaporize there since the mixer blades 14a were heated by the hot exhaust gas flow. Some of the primary droplets burst on the blade sections 14a′, whereby secondary droplets are formed which are again hurled into the exhaust gas flow. Some primary droplets are also reflected at the blade sections 14a′. It is understood that mixed forms of the above-described droplet-mixer blade interactions can also occur.

(13) The mixer blades 14a can generally have a profile at their gas inlet side to achieve a deposition of the droplets on the inlet side of the mixer device 10a. In the present case, the mixer blades 14a, however, do not have any profile on the inlet side.

(14) The blade sections 14a′ are inclined both relative to the center axis M and relative to radial directions perpendicular thereto. In contrast to this, the blade sections 14a″ only extend in the radial and axial directions. The blade sections 14a″ effect a repeat deflection of the gas flow, whereby further collisions of the liquid droplets in the gas flow with the mixer blades 14a are provoked. The blade sections 14a′″ adjoin the blade sections 14a″ downstream and they are in turn inclined with respect to the blade sections 14a″—and also with respect to the blade sections 14a′. The gas flow thereby undergoes a swirl reversal, i.e. the swirl of the gas flow produced at the inlet side is reversed by the blade sections 14a′″ since a new tangential component is imparted to the gas flow by its angled alignment.

(15) The spatial arrangement and configuration of the blade sections 14a′″ can in particular be clearly seen in FIG. 2. The blade sections 14a′″ have slits 16 which effect a regulation of the temperature distribution by a local influencing of the thermal conductivity of the mixer blades 14a in order in particular to avoid the initially described disadvantageous effects in connection with a “film boiling”. As a flanking measure or instead of the slits, materials can also be used in specific regions of the mixer blades which have a reduced thermal conductivity such as a ceramic material—for instance ZrO.sub.2—or an increased thermal conductivity. In addition, the thickness of the mixer blades 14a can be reduced, for example to thicknesses below 1 mm. Direct thickened material portions can also be a suitable means for influencing the thermal conductivity. Additionally or alternatively, porous material can be used—for the mixer blade as a whole or also only locally—such as porous stainless steel sheets produced from structural paper or porous sheets produced from sintered wire mesh. Perforated stainless steel sheets—the perforations can be produced by means of laser perforation processes—or holed stainless steel sheets can likewise be configured in simple manner such that the desired temperature distribution is adopted at the surface of the mixer blades 14 in operation.

(16) FIGS. 3 and 4 show a front view and a rear view respectively—with respect to the flow direction of the exhaust gas—of the mixer device 10a for illustrating its design.

(17) FIG. 5 shows a mixer blade 14a in a perspective view. The dashed lines indicate the shape of a blank 18 which is shaped by suitable shaping processes to form the mixer blade 14a.

(18) The blank 18 is a substantially planar sheet metal part which was cut to the desired external shape and was provided with slits 16. An outer edge 18a is connected to the housing 12 in the installation position of the mixer blade 14a, whereas an inner edge 18b is located in the region of the center axis M in the installation position. Starting from the blank 18, only two bending processes are required to produce the mixer blade 14a. For this purpose, the blade section 14a′ is bent over along a bending edge B1 relative to the blade section 14a″. The second bending process relates to the blade section 14a′″ which is bent over along a second bend edge B2.

(19) FIG. 6 illustrates the deflection of the exhaust gas flow by the mixer blade 14a. The exhaust gas flow is marked by arrows in this respect. It can be seen that the blade section 14a′ first effects a deflection of the exhaust gas flow which imparts a tangential component with respect to the center axis M, which is directed upwardly in FIG. 6, to the exhaust gas flow. The blade section 14a′″ in contrast has the effect that the exhaust gas flow has an essentially axial direction for a short path distance before a deflection of the exhaust gas flow caused by the blade section 14a′″ again produces a tangential flow component which is opposite to the tangential component produced by the blade section 14a′, but which is not necessarily of the same amount as it.

(20) The side view of the mixer blade 14a also shows inclination angles N1, N2 of the blade sections 14a′ and 14a′″ respectively. The angle of inclination N1 is the inclination of the blade section 14a′ in a tangential plane—the image plane of FIG. 6 which is arranged perpendicular to the radial extent of the mixer blade 14a—relative to the center axis M, whereas the angle of inclination N2 is the tangential component of the inclination of the blade section 14a′″ relative to the center axis M.

(21) In other words, the angle N1 is the angle which a gas particle entering into the mixer device 10a “sees” in the tangential direction. In order largely to avoid relevant flow separations, the angle of inclination N1 should amount to no more than 25°. In the case shown of a planar blade section 14a′, the latter is inclined in the described manner at each point with respect to the arrow H which is shown upstream of the mixer blade 14a and which indicates a main flow direction flowing onto the mixer blade 14a. With a curved inlet-side blade section, what is important is that a corresponding angle of inclination N1 is present at least in the region of an inlet-side edge K1. I.e. a tangent at the surface of the blade section in the region of the edge K1 should include an angle of no more than 25° with the center axis M in a projection comparable with FIG. 6.

(22) The same applies analogously to the angle of inclination N2 and to an outlet-side edge K2 of the blade section 14a′″. The angle of inclination N2 should as a rule not exceed 35° in order to keep the counter pressure low which is caused by the mixer device. It is, however, understood that the angles N1, N2 can also be larger than 25° and 35° respectively in special cases.

(23) As stated above, the angular positions of the blade sections 14a′. 14a′″ with respect to the exhaust gas flow are comparatively small to avoid flow separations and dead water zones resulting therefrom and thus to minimize the counter-pressure produced by the mixer device 10a.

(24) The configuration of the blade sections 14a′, 14a″. 14a′″ can be adapted to the respective circumstances. The geometry and the position of the bending edges B1, B2 relative to the edges 18a, 18b can, for example, be varied to produce the desired flow profile. Further parameters which can be varied are, for example, the angles by which the blade sections 14a′ and 14a′″ respectively are bent over with respect to the blade section 14a″. Deviating from the embodiment shown, the edges B1 and/or B2 can be replaced by curved regions. In particular when a transition region between the blade sections 14a″ and 14a′ is less abrupt and has a comparatively “gentle” or curved extent, flow separations can be avoided in this region.

(25) The geometry of the mixer blade 14a has the consequence that an influencing of the gas flow caused by it is a function of the spacing from the center axis M. In the present case, the gas flow is deflected less in a region about the center axis M than in regions disposed radially further outwardly.

(26) FIG. 7 shows a modification 10b of the mixer device 10a. The mixer device 10b has mixer blades 14b which are similar to the mixer blades 14a at the inlet side. Outlet-side blade sections 14b′″ of the mixer blades 14b have, unlike the blade sections 14a′ of the mixer blades 14a, segments 20 which are inclined alternatingly with respect to one another in order to achieve a greater turbulence of the gas flow at the outlet side and thus ultimately a better homogenization of the gas flow. The segments 20 produce different outlet angles of part flows of the gas flow as well as of the liquid droplets still possibly contained in the part flows. The different outlet angles effect an increased turbulence which contributes to an improved mixing of the exhaust gas flow in the wake of the mixer device 10b.

(27) FIGS. 8 to 10 show an embodiment 10c of a mixer device whose mixer blades 14c are arranged in a frame 20 fastened in the housing 12. The mixer blades 14c are ordered—figuratively speaking—in a similar manner to petals in a uniform distribution about the center axis M. As can be seen from FIG. 8, which shows a perspective view of the mixer device 10c obliquely from behind, the mixer blades 14c are provided at their outlet-side end with slits 16 which are provided for influencing the thermal conduction. The mixer blades 14c have blade sections 14c′, 14c″ and 14c′″—see FIG. 10—which have different angles of inclination relative to the gas flow flowing onto the mixer device 10c. However, they do not effect any swirl reversal, but the swirl produced by the inlet-side blade sections 14c′ is rather successively amplified by the blade sections 14c″, 14c″. This multistage swirl production is accompanied by a comparatively small counter-pressure production and nevertheless delivers good mixing results and vaporization results since this construction also has an improved droplet-mixer blade interaction in comparison with conventional mixer devices.

(28) FIG. 11 shows a mixer device 10d having mixer blades 14d which each comprise a substantially planar blade section 14d′ which does not have any significant inclination with respect to the onflowing gas and a curved blade section 14d′″. The mixer blades 14d are provided with slits 16 open downstream such as can in particular also be seen from FIG. 12. The length of the slits decreases from the center axis M toward the housing 12.

(29) The mixer blades 14d are in close contact in the region about the center axis M. However, they are not welded or soldered together in as comprehensive a manner as possible, but are rather only held together by an auxiliary assembly weld site 22. On the assembly of the mixer device 10d, the mixer blades 14d are first fixed relative to one another by the weld site 22. The weld site 22 is a simple weld point which connects the mixer blades 14d at the inlet side in a point-like manner and localized in the region of the center axis M. The mixer blades 14d are not connected to one another apart from the weld site 22. Thermomechanical stresses can thereby be at least partly eliminated. The localized weld site 22 does not prevent the outlet ends of the mixer blades 14d from carrying out relative movements also in the region of the center axis M. These movements compensate the temperature expansion of the mixer blades 14d, which ultimately prevents their connections to the housing 12 from being put under excessive stress.

(30) Joins 24 are provided—as can in particular be seen in FIG. 11—which are open at the inlet side and which end in a hole-like end section 24′ to improve the mechanical decoupling of the mixer blades 14d. The joins 24 are arranged comparatively close to the center axis M and allow a large decoupling—with respect to thermomechanical stresses—of the weld site 22 from the outer connection of the mixer blades 14d due to the spatial proximity of the joins to the weld site 22.

(31) FIGS. 13 and 14 show a mixer device 10e whose mixer blades 14e have a somewhat different geometry, in particular with respect to the planar blade sections 14e′ and the curved blade sections 14e″, than the mixer blades 14d of the mixer device 10d. As with the mixer device 10d, the mixer blades 14e of the mixer device 10e are only connected to one another in the region of the center axis M by an auxiliary assembly weld site 22. To increase the movability of the mixer blades 14e relative to one another and thus to be able better to eliminate thermomechanical stresses, the mixer blades 14e are likewise each provided with joins 24 which are, however, disposed closer to the center axis M in comparison with the joins 24 of the mixer device 10d. It is understood that the position and the configuration of the joins 24 can be adapted so that thermomechanical stresses are admittedly compensated as best as possible, but without the stability of the respective mixer device being simultaneously compromised.

(32) FIGS. 15 and 16 show a mixer device 10f which is similar to the mixer device 10e in a number of aspects. However, the mixer blades 14f of the mixer device 10f are provided with slits 16, 16′ which are alternatingly open at the inlet side or at the outlet side so that a suitable temperature distribution is formed in their operation, in particular at the surface of the mixer blades 14f, to avoid the initially discussed problems.

(33) The concept of the auxiliary assembly weld point 22 and of the joins 24 was admittedly only described in connection with the mixer devices 10d, 10e; however, this concept can also easily be transferred to the mixer devices 10a, 10, 10c, 10f.

REFERENCE NUMERAL LIST

(34) 10a, 10b, 10c, 10d, 10e, 10f mixer device

(35) 12 housing

(36) 14a, 14b, 14c, 14d, 14e, 14f mixer blade

(37) 10a′, 10a″, 14a′″, 14b″, 14c′,

(38) 14c″, 14d′, 14d″, 14e′, 14e″ blade section

(39) 16, 16′ slit

(40) 18 blank

(41) 18a outer edge

(42) 18b inner edge

(43) 20 frame

(44) 22 auxiliary assembly weld site

(45) 24′″ join

(46) 24 end section

(47) M center axis

(48) B1, B2 bending edge

(49) N1, N2 angle of inclination

(50) H main flow direction

(51) K1 inlet-side edge

(52) K2 outlet-side edge