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.

1 . A mixer for mixing first and second fluids, comprising: 
 a passageway along which a stream flows along an axis thereof, the stream comprising the first fluid, and the passageway comprising, in sequence in a 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.    
   
   
       2 . The mixer of  claim 1 , wherein the injector introduces the second fluid into the stream in the convergent section of the passageway.  
   
   
       3 . The mixer of  claim 1 , wherein the injector comprises at least one injection port in a peripheral wall of the passageway.  
   
   
       4 . The mixer of  claim 3 , wherein the injector comprises at least two injection ports of different sizes.  
   
   
       5 . The mixer of  claim 1 , wherein the injector introduces the second fluid at a plurality of locations along the passageway.  
   
   
       6 . The mixer of  claim 1 , wherein the injector introduces the second fluid in at least one direction which is transverse to the axis of the passageway.  
   
   
       7 . The mixer of  claim 1 , wherein the swirl generator has a swirl angle that varies as a function of distance from the axis.  
   
   
       8 . The mixer of  claim 7 , wherein the swirl angle varies such that there is at least one abrupt change in circumferential velocity of the stream about the axis, between one radial position and another.  
   
   
       9 . The mixer of  claim 1 , further comprising a central injection tube opening in the passageway upstream of the divergent section.  
   
   
       10 . The mixer of  claim 9 , wherein the swirl generator circumferentially surrounds the central injection tube.  
   
   
       11 . The mixer of  claim 1 , wherein upstream and downstream ends of the convergent section have a diameter ratio of less than 2.  
   
   
       12 . The mixer of  claim 1 , wherein the convergent section converges at an angle of at most 25° with respect to the axis of the passageway.  
   
   
       13 . The mixer of  claim 12 , wherein the angle is at least 10°.  
   
   
       14 . The mixer of  claim 12 , wherein the angle is at least 15°.  
   
   
       15 . The mixer of  claim 1 , wherein a peripheral wall of the passageway comprises a coating of a catalyst for quenching radicals that are precursors to ignition of a mixture of the first and second fluids.  
   
   
       16 . The mixer of  claim 1 , further comprising a flow straightener in the passageway downstream of the throat.  
   
   
       17 . The mixer of  claim 16 , wherein the flow straightener comprises channels with a hydraulic diameter of at most 5 mm.  
   
   
       18 . The mixer of  claim 16 , wherein the flow straightener carries a catalyst for quenching radicals.  
   
   
       19 . The mixer of  claim 16 , wherein the flow straightener has a length in the axial direction of at most 15 mm.  
   
   
       20 . The mixer of  claim 1 , wherein the passageway forms part of a combustion device.  
   
   
       21 . The mixer of  claim 20 , wherein the combustion device comprises a plurality of burners supplied with a mixture of the fluids by the passageway.  
   
   
       22 . The mixer of  claim 21 , wherein the burners form a burner sector, a downstream end portion of the passageway gradually changing cross-section into a sector of an annulus.  
   
   
       23 . A method of mixing fluids, comprising the sequential steps of: 
 (a) providing a stream comprising a first fluid and having an axis along which the stream flows;    (b) inducing swirl in the stream about an axis thereof;    (c) causing the stream to converge towards the axis; and    (d) causing the stream to diverge from the axis;    wherein a second fluid is introduced into the stream before step (d).    
   
   
       24 . The method of  claim 23 , wherein the second fluid is introduced into the stream in a direction that is transverse to the axis of the stream.  
   
   
       25 . The method of  claim 23 , wherein the second fluid is introduced into the stream during step (c).  
   
   
       26 . The method of  claim 25 , wherein the second fluid is introduced into the stream in a direction that is transverse to the axis of the stream.  
   
   
       27 . The method of  claim 23 , wherein a swirl angle of the swirl induced in step (b) varies as a function of distance from the axis.  
   
   
       28 . The method of claims  23 , wherein the swirl induced in step (b) is such that there is at least one abrupt change in circumferential velocity of the stream about the axis, between one radial position and another.  
   
   
       29 . The method of  claim 23 , further comprising introducing a fluid into a central region of the stream after step (b) and before step (d).  
   
   
       30 . The method of  claim 29 , wherein the fluid is the first fluid.  
   
   
       31 . The method of  claim 29 , wherein the fluid is the second fluid.  
   
   
       32 . The method of  claim 23 , wherein the first and second fluids are both introduced into a central region of the stream.  
   
   
       33 . The method of  claim 23 , further comprising straightening the flow of the stream after step (d).  
   
   
       34 . The method of  claim 23 , wherein at least one of the first and second fluids is a gas.  
   
   
       35 . The method of  claim 34 , wherein the first fluid is air and the second fluid is a combustible fluid.  
   
   
       36 . The method of  claim 34 , wherein the first fluid is a gas and the second fluid is a liquid.  
   
   
       37 . The method of  claim 36 , in which the first fluid is air and the second fluid is a combustible fluid.