Patent Publication Number: US-8967852-B2

Title: Mixers for immiscible fluids

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to mixers for immiscible fluids, and more particularly to mixers for mixing fuel and water in gas turbine engines. 
     2. Description of Related Art 
     A variety of devices and methods are known in the art for injecting fuel into gas turbine engines. Of such devices, many are directed to injecting fuel into combustors of gas turbine engines while reducing undesirable emissions. Modern gas turbine engine designs use high temperature combustion for thermal efficiency throughout a range of engine operating conditions. High temperature combustion minimizes emissions of some undesired gaseous combustion products, such as carbon monoxide (CO) and unburned hydrocarbons (UHC), and particulates, among other things. However, high temperature combustion also tends to increase the production of nitrogen oxides (NO X ). Thus measures must be taken to provide thermally efficient operation within a temperature range that minimizes NO X , CO, and UHC. 
     One method often used to reduce unwanted NO X  emissions is to lower the temperature of combustion by injecting water into the combustor with the fuel. The water absorbs heat in the combustor, lowering the temperature of fuel combustion and reducing unwanted NO X  emissions. Injecting water into the combustor is particularly advantageous in non-flight applications such as industrial gas turbine engines, where water supplies are readily available. 
     Injecting water into the combustor of a gas turbine engine presents challenges related to uniform distribution of water and fuel within the combustor. Some approaches to this problem have been to provide fuel injectors for the fuel that are separate from the injectors for the water, or to provide both fuel and water circuits within each injector with separate injection ports for fuel and water. These approaches attempt to provide uniform spray patterns of both fuel and water within the combustor, but add to the complexity and cost of the engine and maintenance. Another approach has been to inject water and fuel simultaneously through a single set of injectors by mingling the water and fuel together in the fuel lines prior to injection. The problem with this approach is that hydrocarbon fuel oil and water are immiscible. Simply mingling the two fluids together in a fuel line does not result in a uniform distribution of the fuel-water mixture at the injectors, since the two fluids tend to arrive at the injectors in a highly unmixed state. 
     Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still an need in the art for mixers that allow for improved mixing of immiscible fluids. There also remains a need in the art for such mixers that are easy to make and use. The present invention provides a solution for these problems. 
     SUMMARY OF THE INVENTION 
     The subject invention is directed to a new and useful mixer for mixing immiscible fluids. The mixer includes a mixer housing defining a flow passage therethrough from a first fluid inlet to an outlet thereof. An upstream portion of the flow passage defines a main longitudinal axis. A second fluid inlet is defined in the mixer housing downstream of the first fluid inlet in fluid communication with the upstream portion of the flow passage. The second fluid inlet defines a secondary axis that is offset with respect to the main longitudinal axis of the flow passage to introduce fluid along a path that is offset with respect to the main longitudinal axis for inducing swirl on fluids introduced at the first and second fluid inlets. 
     In certain embodiments, the mixer also includes a mixer section having a flow constriction defined in a downstream portion of the flow passage with a flow area smaller than that of the upstream portion of the flow passage for enhancing turbulent mixing of fluids introduced at the first and second fluid inlets. The flow area of the flow constriction can define a centerline axis that is offset with respect to the main longitudinal axis of the flow passage. The mixer section can include two or more flow constrictions, wherein each flow constriction defines a centerline axis that is offset with respect to the centerline axis of the other flow constriction. Each flow constriction can be offset with respect to the main longitudinal axis of the flow passage. It is also contemplated that the centerline axis of each flow constriction can be offset in a direction opposite that of the centerline axis of the other flow constriction with respect to the main longitudinal axis of the flow passage. 
     In certain embodiments, an upstream one of two flow constrictions includes a beveled upstream inlet and a beveled downstream outlet to form a converging, diverging flow path therethrough for reducing pressure loss. Bevel features, chamfers, or filet radius features can be included on either or all flow constrictions. A downstream one of two flow constrictions can include opposed upstream and downstream faces that are oriented substantially perpendicular to the main longitudinal axis. The two flow constrictions can be separated by a spin chamber defined in the flow passage of the mixer housing, and the spin chamber can have a flow area substantially equal in size with that of the upstream portion of the flow passage. 
     The outlet of the mixer housing can define an outlet axis that is substantially concentric with the main longitudinal axis of the flow passage. It is also contemplated that the secondary axis defined by the second fluid inlet can be oriented substantially perpendicular, or on any other suitable angle, and offset with respect to the main longitudinal axis of the flow passage. The mixer can further include an outlet conduit mounted in fluid communication with the outlet of the mixer housing, wherein the outlet conduit includes a bend therein to promote mixing of fluids introduced in the first and second fluid inlets. 
     The invention also provides a mixer for mixing immiscible fluids wherein the second fluid inlet is defined in the mixer housing downstream of the first fluid inlet in fluid communication with the upstream portion of the flow passage, and a mixer section including a pair of flow constrictions is defined in a downstream portion of the flow passage. The flow constrictions each have a flow area smaller than that of the upstream portion of the flow passage for enhancing turbulent mixing of fluids introduced at the first and second fluid inlets. Each flow constriction defines a centerline axis that is offset with respect to the centerline axis of the other flow constriction. 
     The invention also provides a mixer for mixing immiscible fluids in which the second fluid inlet includes a swirl inducer. A mixer housing defines a flow passage therethrough from a first fluid inlet to an outlet thereof. The flow passage defines a main longitudinal axis. A second fluid inlet is defined in the mixer housing downstream of the first fluid inlet in fluid communication with the flow passage and oriented at an angle with respect to the main longitudinal axis. The second fluid inlet includes a swirl inducer for inducing swirl on fluids flowing through the flow passage. A flow constriction is defined in the flow passage downstream of the second fluid inlet having a flow area smaller than that of the flow passage upstream thereof for accelerating a swirling flow of fluids flowing through the flow passage to enhance turbulent mixing of fluids introduced at the first and second fluid inlets. 
     In certain embodiments, the swirl inducer includes a flow obstruction configured to direct flow through the second fluid inlet into the flow passage asymmetrically with respect to the main longitudinal axis. The flow obstruction of the second fluid inlet is configured to direct a single flow through the second fluid inlet into the flow passage that is predominantly offset with respect to the main longitudinal axis of the flow passage. 
     In accordance with certain embodiments, the swirl inducer includes a swirler mounted in the flow passage and configured to introduce fluid from the second fluid inlet into the flow passage through a plurality of swirl inlets defined through the swirler to impart swirl onto fluids flowing through the flow passage. The swirler can be a radial swirler and the swirl inlets can be radially offset with respect to the main longitudinal axis to impart swirl onto fluids flowing through the flow passage. It is also contemplated that the flow constriction and swirler can be substantially concentric with the main longitudinal axis of the flow passage. 
     These and other features of the systems and methods of the subject invention will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the devices and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a side elevation view of an exemplary embodiment of a mixer constructed in accordance with the present invention, showing two fluid inlets and an outlet for mixed fluids joined to an atomizer nozzle; 
         FIG. 2  is a perspective view of the mixer of  FIG. 1 , showing the offset fluid inlet for inducing swirl on the mixture of fluids within the mixer; 
         FIG. 3  is an exploded, partial cross-sectional perspective view of the mixer of  FIG. 1 , showing the mixer section downstream of the offset fluid inlet for inducing turbulence on the flow of mixed fluids in the mixer; 
         FIG. 4  is a cross-sectional end elevation view of the mixer of  FIG. 1 , showing the axis of the offset fluid inlet, which is offset with respect to the longitudinal axis of the main fluid passage of the mixer; 
         FIG. 5  is a cross-sectional side elevation view of a portion of the mixer of  FIG. 1 , showing the offset axes of the mixer section; 
         FIG. 6  is a cross-sectional perspective view of a portion of the mixer of  FIG. 1 , showing the flow obstructions in the mixer section; 
         FIG. 7  is a cross-sectional side elevation view of a portion of the mixer of  FIG. 1 , schematically showing swirling flow induced on the main fluid passage by the fluids entering the offset inlet; 
         FIG. 8  is a cross-sectional side elevation view of a portion of the mixer of  FIG. 1 , schematically showing swirling flow induced on the main fluid passage by the fluids entering the offset inlet; 
         FIG. 9  is a cross-sectional side elevation view of a portion of the mixer of  FIG. 1 , schematically showing the acceleration and turbulence imparted by the mixer section on the flow through the main fluid passage; 
         FIG. 10  is a perspective view of another exemplary embodiment of a mixer constructed in accordance with the present invention, showing the two fluid inlets and the fluid outlet; 
         FIG. 11  is a partially exploded perspective view of the mixer of  FIG. 10 , showing the flow obstruction insert and flow constriction insert; 
         FIG. 12  is a cross-sectional perspective view of the mixer of  FIG. 10 , showing the internal flow passage; 
         FIG. 13  is a partially cut away perspective view of another exemplary embodiment of a mixer constructed in accordance with the present invention, showing the two fluid inlets and the fluid outlet; 
         FIG. 14  is a partial cross-sectional perspective view of the mixer of  FIG. 13 , showing the radial swirler with radially offset swirl inlets; and 
         FIG. 15  is a cross-sectional end elevation view of a portion of the mixer of  FIG. 13 , showing the radial gap between the housing and the radial swirler. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject invention. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a mixer in accordance with the invention is shown in  FIG. 1  and is designated generally by reference character  100 . Other embodiments of mixers in accordance with the invention, or aspects thereof, are provided in  FIGS. 2-15 , as will be described. The systems of the invention can be used to mix fluids together, including immiscible fluids, for example for delivering a water/fuel oil emulsion to a fuel nozzle for a low NO X  gas turbine combustion system. 
     Referring now to  FIGS. 1-2 , mixer  100  has two inlets  106 ,  114  for receiving two different fluids, for example water and fuel, respectively. While discussed herein in the exemplary context of inlet  106  being used for water and inlet  114  being used for fuel, those skilled in the art will readily appreciate that the fluids received at each inlet can be switched, or that any other suitable fluids can be used without departing from the spirit and scope of the invention. Both of the different fluids are mixed throughout mixer  100  and the mixture is conveyed from outlet  108  through a conduit  138  to an atomizer  140 . 
     With reference now to  FIGS. 2-5 , mixer  100  includes a mixer housing  102  defining a flow passage  104  running therethrough from inlet  106  to outlet  108 . An upstream portion  110  of flow passage  104 , shown in  FIG. 5 , defines a main longitudinal axis  112 . A second fluid inlet  114  is defined in mixer housing  102  downstream of first fluid inlet  106  in fluid communication with upstream portion  110  of flow passage  104 . As can be seen in  FIG. 4 , second fluid inlet  114  defines a secondary axis  116  that is offset with respect to main longitudinal axis  112  of flow passage  104  to introduce fluid along a path that is offset with respect to main longitudinal axis  112  for inducing swirl on fluids introduced at first and second fluid inlets  106 ,  114 . Secondary axis  116  and second fluid inlet  114  are oriented substantially perpendicular to main longitudinal axis  112  of flow passage  104 , so inlets  106 ,  114  and outlet  108  form a T-shaped mixer configuration, as shown in  FIGS. 1 and 5 . 
     With reference to  FIGS. 3 and 5 , mixer  100  includes a non-coaxial mixer section  118  having a first flow constriction  120  defined in a downstream portion of flow passage  104  with a flow area smaller than that of upstream portion  110  of flow passage  104  for enhancing turbulent mixing of fluids introduced at first and second fluid inlets  106 ,  114 . The flow area of first flow constriction  120  defines a centerline axis  122  that is offset with respect to main longitudinal axis  112  of flow passage  104 , as indicated in  FIG. 5 . Mixer section  118  includes a second flow constriction  124  downstream of first flow constriction  120 . Second flow constriction  124  defines a centerline axis  126  that is offset with respect to centerline axis  122  of first flow constriction  120 . The respective flow area of each flow constriction  120 ,  124  is offset with respect to main longitudinal axis  112  of flow passage  104 . Flow constrictions  120 ,  124  are offset in opposite directions from each other with respect to main longitudinal axis  112 , i.e., the centerline axis  122 ,  126  of each flow constriction  120 ,  124  is offset in a direction opposite the direction the other flow constriction  120 ,  124  with respect to main longitudinal axis  112 . Those skilled in the art will readily appreciate that this 180° angular separation of the relative offset of axes  122 ,  126  achieves greater mixing than smaller angular separations, and that this is exemplary, as any other suitable angular separation can be used without departing from the spirit and scope of the invention. 
     Flow constriction  124  is provided as a disc with an off-center orifice formed therethrough, as shown in  FIG. 3 . The disc of flow constriction  124  can be assembled into housing  102  as a separate piece, properly oriented with respect to its offset axis  126  by mounting it between the main portion of housing  102  and outlet  108  by any suitable joining technique such as welding or brazing. 
     With reference now to  FIG. 6 , first flow constriction  120  includes a beveled upstream inlet  128  and a beveled downstream outlet  129  to form a converging, diverging flow path therethrough for reducing pressure loss. Second flow constriction  124  includes an upstream face  132  and an opposed downstream face  134  that are oriented substantially perpendicular to main longitudinal axis  112  to enhance turbulent mixing. Those skilled in the art will readily appreciate that any suitable combination of beveled features, chamfers, or filet radii may be used on the upstream and/or downstream portions of any or all of the flow constrictions to achieve an appropriate tradeoff between operational pressure drop, mixing levels, and cost of manufacturing for a given application. The two flow constrictions  120 ,  124  are separated by a spin chamber  136  defined in flow passage  104  of mixer housing  102 . Spin chamber  136  has a flow area substantially equal in size with that of upstream portion  110  of flow passage  104 . 
     Outlet  108  of mixer housing  102  defines an outlet axis that is substantially concentric with main longitudinal axis  112  of flow passage  104 . An outlet conduit  138  is mounted in fluid communication with outlet  108  of mixer housing  102 . As shown in  FIG. 1 , outlet conduit  138  advantageously includes an optional bend therein to promote mixing of fluids introduced in the first and second fluid inlets  106 ,  114  by the effect of Coriolis forces. Outlet conduit  138  connects flow passage  104  in fluid communication with an injector such as airblast atomizer  140 . As shown, the bend in conduit  138  is angled at about 90°, however it is contemplated that the bend can include any suitable amount of bend, including a helical bend with multiple revolutions, or no bend at all. 
     The flow patterns within mixer  100  are described with reference now to  FIGS. 7-9 . Since second inlet  114  is radially offset with respect to axis  112 , fluids flowing into mixer  100  through inlet  114  induce swirl on the flow within flow passage  104  downstream of inlet  114 . The swirling motion induced on the mixture, for example fuel and water, is indicated schematically in  FIGS. 7-8  by the swirl arrows in flow passage  104 . Introducing a perpendicular flow from second inlet  114  also results in momentum exchange between the fluids from inlets  106 ,  114  and generates turbulence which aids the initial mixing of the two fluids introduced at the respective inlets  106 ,  114 . This swirling motion from the offset axis of second inlet  114  induces swirl to further enhance preliminary mixing. 
     The swirling flow within flow passage  104  is accelerated through the converging-diverging constriction  120 , as indicated schematically by the arrows in  FIG. 9 , forming a high velocity jet that further enhances the swirl and mixing. As oriented in  FIG. 9 , constriction  120  forces the mixing flow downward, but the flow is forced to flow back upward within swirl chamber  136  by flow constriction  124 , where a second high velocity jet is formed. Downstream of flow constriction  124 , the flow is again forced downward to leave housing  102  via outlet  108 . Flowing through the offset axes within mixer section  118  contributes to turbulence and mixing, as the two jets formed in constrictions  120 ,  124  impinge on downstream internal structures. Axial acceleration in the two jets helps keep water and oil from separating centrifugally as the mixture swirls. 
     The abrupt upstream and downstream faces  132 ,  134  of constriction  124  give rise to eddies and turbulence downstream of constriction  124 , which further enhance mixing in the swirling flow through flow passage  104 . When used to mix fuel oil with water, for example, this impingement directly causes fuel oil breakup and mixing and generates additional freestream turbulence to enhance downstream mixing. While mixer  100  has been described above as an exemplary embodiment having two flow constrictions  120 ,  124 , those skilled in the art will readily appreciate that any suitable number of flow constrictions can be used without departing from the spirit and scope of the invention. Care should be used in selecting the number of flow constrictions for a given application, as too many flow constrictions can cause to an undesirable pressure drop and unnecessary increases in manufacturing costs. 
     As indicated above, the bend in conduit  138  adds to the mixing effectiveness by way of Coriolis forces. While the effects of offset second inlet  114 , mixer section  118 , and the bend in conduit  138  combine advantageously to enhance mixing, those skilled in the art will readily appreciate that one or more of these features can be omitted without departing from the spirit and scope of the invention. 
     Referring now to  FIGS. 10-12 , another exemplary embodiment of a mixer  200  is shown for mixing immiscible fluids in which the second fluid inlet includes a swirl inducer. As shown in  FIG. 12 , a mixer housing  202  defines a flow passage  204  therethrough from a first fluid inlet  206  to an outlet  208  thereof. Flow passage  204  defines a main longitudinal axis  212 , indicated in  FIG. 11 . A second fluid inlet  214  is defined in mixer housing  202  downstream of first fluid inlet  206  in fluid communication with flow passage  204  and oriented at a substantially perpendicular angle with respect to flow passage  204  and main longitudinal axis  212 . While described herein with exemplary embodiments having the second fluid inlet oriented perpendicular to the respective main longitudinal axis, those skilled in the art will readily appreciate that any other suitable angle can be used for the orientation of the second fluid inlet without departing from the spirit and scope of the invention. 
     With reference now to  FIGS. 11-12 , second fluid inlet  214  includes a swirl inducer, namely flow obstruction  215 , for inducing swirl on fluids flowing through flow passage  204 . Flow obstruction  215  is generally semi-circular and is configured to block off approximately one half of inlet  214  to direct flow through second fluid inlet  214  into flow passage  204  asymmetrically with respect to main longitudinal axis  212 . While second inlet  214  is itself substantially centered with respect to flow passage  204  and axis  212 , flow obstruction  215  directs a single flow through second fluid inlet  214  into the fluid passage  204  that is predominantly off-center with respect to fluid passage  204  and axis  212 . Those skilled in the art will readily appreciate that any suitable shape can be used for a flow obstruction  215  without departing from the spirit and scope of the invention. 
     A flow constriction  220 , similar to constriction  124  described above, is defined in flow passage  204  downstream of second fluid inlet  214 . Flow constriction  220  has a flow area therethrough that is smaller than that of flow passage  204  upstream thereof for accelerating a swirling flow of fluids flowing through flow passage  204  to enhance turbulent mixing of fluids introduced at the first and second fluid inlets  206 ,  214 . The flow area of flow constriction  220  defines a central axis  222  that is offset from main longitudinal axis  212 , to enhance mixing much as described above with respect to flow constriction  120 . The resulting flow pattern is much like that of mixer  100  described above. 
     Referring now to  FIGS. 13-15 , another exemplary embodiment of a mixer  300  is shown which includes a radial swirler. Mixer  300  includes a mixer housing  302 , flow passage  304 , first fluid inlet  306 , outlet  308 , main longitudinal axis  312 , and second fluid inlet  314  much as those described above with respect to mixer  200 . In mixer  300 , the swirl inducer includes a swirler  325  mounted in flow passage  304 . 
     Swirler  325  is a radial swirler configured to introduce fluid, such as water, from second fluid inlet  314  into flow passage  304  through a plurality of swirl inlets  327  defined through swirler  325  to impart swirl onto fluids flowing through flow passage  304 . Since fluid entering fluid passage  304  through second fluid inlet  314  must pass through swirl inlets  327 , which are radially offset with respect to main longitudinal axis  312 , swirl is imparted to fluids flowing through flow passage  304 . 
     Flow constriction  320  is similar to flow constriction  220  described above, but has a flow area therethrough that is substantially concentric with the respective main longitudinal axis. Swirler  325  is also substantially concentric with axis  312 . The resulting flow pattern is much like that of mixer  100  described above. Even though flow constriction  320  is not offset, it nonetheless enhances mixing by accelerating the swirling flow passing therethrough, increasing turbulence. Those skilled in the art will readily appreciate that flow constrictions that are either offset or concentric can be used to enhance mixing in any of the embodiments described above without departing from the spirit and scope of the invention. 
     As indicated in  FIG. 13 , mixer  100  is configured to receive fuel at first inlet  306  and water at second inlet  314 . Those skilled in the art will readily appreciate that water can be introduced at first inlet  306  and fuel can be introduced at second inlet  314 . Moreover, any other suitable fluids can be mixed without departing from the spirit and scope of the invention. 
     Computational fluid dynamics analyses used to investigate and demonstrate fuel and water mixing in a variety of geometric configurations has demonstrated that mixers constructed in accordance with the present invention provide a substantially uniform mixture that can be injected from injectors. Mixtures having a range of fuel volume fraction of around 32% to 39% at the outlet, where the ideal fraction of fuel by volume is 34%, have been demonstrated by the analysis. 
     While the mixers described herein have been explained in the exemplary context of assembling, brazing, and welding, those skilled in the art will readily appreciate that any suitable fabrication techniques can be used without departing from the spirit and scope of the invention. For example, direct metal laser sintering can be used to fabricate mixers in an additive manner. As further examples, inner diameter splines, posts, tapered bores, or any other suitable geometric approaches can also be used to form the turbulence generating features of mixers in accordance with the invention. 
     The methods and systems of the present invention, as described above and shown in the drawings, provide for mixing fluids with superior properties including enhanced mixing of immiscible liquids, for example. While the apparatus and methods of the subject invention have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject invention.