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  MixerUSPTO Application #: 20060035183Title: Mixer Abstract: A mixer for mixing first and second fluids has a passageway along which a stream comprising the first fluid flows along an axis of the passageway. The passageway has, in sequence in the downstream direction, a convergent section, a throat, and a divergent section. An injector introduces the second fluid into the stream in the passageway upstream of the divergent section. A swirl generator in the passageway is upstream of the convergent section. (end of abstract) Agent: Steptoe & Johnson LLP - Washington, DC, US Inventors: Richard Carroni, Timothy Griffin USPTO Applicaton #: 20060035183 - Class: 431007000 (USPTO) Related Patent Categories: Combustion, Process Of Combustion Or Burner Operation, In A Porous Body Or Bed, E.g., Surface Combustion, Etc. The Patent Description & Claims data below is from USPTO Patent Application 20060035183. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of the U.S. National Stage designation of co-pending International Patent Application PCT/EP2004/050074 filed Feb. 3, 2004, which claims priority to Great Britain patent application no. 0303495.6 filed Feb. 14, 2003, and the entire contents of these applications are expressly incorporated herein by reference thereto. FIELD OF THE INVENTION [0002] This invention relates to a mixer and a method for mixing first and second fluids. The two fluids may be gases, e.g. air and a combustible gas, or a gas and a liquid, e.g. air and a liquid fuel, or liquids. The mixer may, in particular, form part of a combustion device. BACKGROUND OF THE INVENTION [0003] A number of applications require that separate fluid streams be thoroughly mixed. One such application is catalytic combustion, where the fuel and air must be very well mixed prior to entry in the catalyst. This requirement also holds true for conventional lean-premix burners. However, current mixing techniques generally do not achieve homogeneous mixtures, and therefore the resulting combustion process is non-uniform; large temperature variations are observed, and significant NOx emissions associated with high-temperature areas are recorded. [0004] Attaining high levels of mixedness between fluids is normally accompanied by large, undesirable pressure losses. The most promising option to date is that involving counter-swirling flows. However, complex aerodynamic designs (i.e. aerofoil sections) are essential components of such units, because the structures generating swirl must not form wakes including recirculation zones (which can lead to flashback and severe damage); furthermore, there is scope for significant improvement in mixing quality. For certain applications, e.g. those involving catalytic units, the catalyst inlet velocity distribution must be as uniform as possible; this is a difficult objective for conventional mixers which employ swirling flows. A further problem with many units is that of flashback, i.e. the phenomenon which entails a homogeneous flame moving upstream and into the mixer, often resulting in damage. [0005] Venturi injectors are relatively simple devices for attaining reasonable mixing; however, the quality falls short of that achieved by the swirl-based concepts. Venturi units rely upon low local pressures to draw additive fluid into a carrier fluid; mixing is attained by virtue of the shear layer across the longitudinal jet of fluid, whose principal velocity component is axial. U.S. Pat. No. 4,123,800 describes a mixer in which a certain degree of twisting motion is imparted to the flow downstream of the Venturi constriction, to further aid in mixing, by means of skewed grooves machined into the walls of the divergent section downstream of a throat section into which the additive fluid is injected. However, this twisting motion is only imparted near the walls, without significantly affecting the bulk of the flow, and does not meaningfully assist the mixing process. SUMMARY OF THE INVENTION [0006] The present invention provides a passageway along which a stream comprising the first fluid flows along an axis of the passageway, the passageway having, in sequence in the downstream direction, a convergent section, a throat, and a divergent section; an injector for introducing the second fluid into the stream in the passageway upstream of the divergent section; and a swirl generator in the passageway upstream of the convergent section. [0007] The invention also provides a method of mixing fluids, comprising the sequential steps of: [0008] (a) providing a stream comprising a first fluid and having an axis along which the stream flows, [0009] (b) inducing swirl in the stream about its axis, [0010] (c) causing the stream to converge towards its axis, and [0011] (d) causing the stream to diverge from its axis, The method including introducing a second fluid into the stream before step (d). BRIEF DESCRIPTION OF THE DRAWINGS [0012] The invention will be described further, by way of example only, with reference to the accompanying drawing, in which: [0013] FIG. 1 is a schematic axial section through one embodiment of a mixer; [0014] FIG. 2 is a graph of angular velocity, .omega., in the circumferential direction against radial distance, r, from the axis of a swirling stream created in a preferred embodiment of the mixer; [0015] FIG. 3 shows the angular velocity field produced by the swirling stream having the radial distribution of angular velocity shown in FIG. 2; [0016] FIG. 4a is a cross-section through the convergent section of a mixer, showing one possible arrangement of injectors; [0017] FIG. 4b in a view similar to FIG. 4a, showing another possible arrangement of injectors; [0018] FIG. 5 is a schematic axial section through a mixer combined with a burner sector; [0019] FIG. 6 is an inlet end view of the mixer in FIG. 5; and [0020] FIG. 7 is an outlet end view of the burner sector. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0021] The mixer illustrated in FIG. 1 comprises a passageway 1 having an axis 2 along which a stream of air (the carrier fluid or first fluid) flows in the direction of the arrow 3. The passageway 1 has an upstream end portion or inlet section 4 which is cylindrical, a convergent section 6 which is conical and which converges at an angle .theta. with respect to the axis 2, a divergent section 7 which is conical and diverges at an angle a with respect to the axis 2, and a downstream end portion or outlet section 8 which is cylindrical. The passageway has a throat 9 between the convergent and divergent sections 6, 7; in the embodiment illustrated, the throat 9 is of negligible axial length. The convergent section 6, throat 9, and divergent section 7 together constitute a Venturi section. [0022] An injector comprising a plurality of injection ports 11 in the peripheral wall 12 of the passageway 1 introduces fuel (the additive fluid or second fluid) into the stream in the convergent section 6 at multiple locations along and around the axis 2. If the additive fluid is a liquid, it can be injected as sprays, and droplet atomisation and penetration can be enhanced by using high-pressure injectors. Continue reading... Full patent description for Mixer Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Mixer patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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