Patent Publication Number: US-9421506-B2

Title: Static mixer

Description:
FIELD 
     The present disclosure relates to static mixers for use in conduits, and more particularly, to static mixers for mixing an injected fluid with a fluid flowing in the conduit. 
     BACKGROUND 
     Static mixers may be used to mix low viscosity fluid or fluids flowing in a pipe or conduit. Static mixers typically include an arrangement of fixed vanes or other elements that are mounted in a section of the conduit and arranged to impart turbulence to a fluid flowing in the conduit as the fluid flows around the vanes or other elements. Some static mixer designs may be relatively energy efficient in that they may impart the required amount of turbulence to fluid flow with a relatively small pressure drop in fluid flowing through the mixing elements. However, a disadvantage with such static mixers is that they may have long mixing lengths—they may require a significant amount of conduit length to effect a desired amount of mixing. 
     Other static mixer designs may provide “length efficient” mixing. This means that the static mixer effects a desired amount of mixing at a relatively short distance downstream of the static mixer. However, such static mixers may possess a disadvantage in that they may use more energy to effect the desired amount of mixing, which results in a higher pressure drop in the fluid flowing across the mixer. Accordingly, there is a need for a static mixer that provides thorough mixing of the fluids in the conduit in which it is mounted in a relatively short distance and at a pressure drop that may be relatively small compared to static mixers of comparable size and mixing effect. 
     Static mixers may be used to mix fluids having different physical properties, such as different viscosities. Such differences in physical properties may require the use of static mixers that are relatively long in comparison to the diameter of the conduit in which they are mounted, or which may require relatively long mixing distances. In some applications, it may be necessary to use multiple static mixer elements, arranged serially in a conduit. Accordingly, there is a need for a static mixer that is capable of mixing fluids having different physical properties, but is of a relatively short length, does not require a significant mixing distance downstream of the mixing element, and which can affect the desired amount of mixing with a single mixer element. 
     SUMMARY 
     In one embodiment, the disclosed static mixer may include a conduit section having a channel and an injector opening through an inner wall thereof, a tab having a main portion extending from the inner wall adjacent and downstream of the opening and extending radially inwardly and at an angle away from the opening in the downstream direction, and having at least one finger extending at a non-zero angle from the main portion, the main portion and the at least one finger being configured such that a second fluid injected through the injector opening and into a first fluid flowing through the conduit section flows radially along the main portion toward a center of the conduit section, and radially outward from the main portion along the at least one finger, whereby the first fluid and the second fluid are thoroughly mixed as a result of turbulence imparted by the tab to the first fluid and the second fluid. 
     In another embodiment, the disclosed static mixer may include an annular conduit section having a channel and an injector opening through an inner wall thereof, a tab having a main portion attached to and extending from the inner wall adjacent and downstream of the injector opening, and extending radially inwardly and at an angle away from the injector opening, and having a pair of opposing fingers extending from a terminal portion of the main portion, each of the opposing fingers extending at a non-zero angle from the main portion, the main portion having a concave shape extending longitudinally along the main portion and opening toward the injector opening, wherein the injector opening is positioned within a portion of the generally concave shape of the main portion, each of the opposing fingers having a generally concave shape extending longitudinally along the finger facing away from the injector opening, and the main portion and opposing fingers are configured such that a second fluid injected through the injector opening and into a first fluid flowing through the conduit section flows radially along the main portion toward a center of the conduit section, and radially outward from the main portion along each of the opposing fingers, whereby the first fluid and the second fluid are thoroughly mixed as a result of turbulence imparted by the tab to the first fluid and the second fluid. 
     In yet another embodiment, a method for mixing a first fluid flowing through a conduit with a second fluid is disclosed, the method may include providing a conduit section having an injector opening for injecting the second fluid, providing a tab in the conduit section having a main portion extending from an inner wall of the conduit section and downstream of the opening, and extending radially inwardly and at an angle away from the opening in a direction downstream of the flow of the first fluid, and at least one finger extending from the main portion, the finger having a generally concave shape facing in a downstream direction away from the opening, and causing a second fluid to flow through the injector opening and into flow of the first fluid in the conduit section, whereby the second fluid flows radially along the main portion toward a center of the conduit section, and radially along the at least one finger, and providing a rotating component to the second fluid by passing the second fluid around the at least one finger, whereby the second fluid is distributed over the conduit cross-section. 
     Other objects and advantages of the disclosed static mixer will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of the disclosed static mixer, viewed from downstream of the static mixer; 
         FIGS. 2A, 2B, 2C, and 2D  are, respectively, a downstream elevational view, an upstream elevational view, a side elevational view, and a top plan view of the tab of the static mixer of  FIG. 1 ; 
         FIG. 3  is a downstream elevational view of the static mixer of  FIG. 1 ; 
         FIG. 4  is a side elevation in section taken at line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a downstream elevational view of another embodiment of the disclosed static mixer; and 
         FIG. 6  is a side elevation in section of the static mixer of  FIG. 5 , taken at line  6 - 6  of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , an embodiment of the disclosed static mixer, generally designated  10 , may include a conduit section  12  that defines a channel  14  and includes an inner wall  16 . In an embodiment, the conduit section  12  may be circular in cross section, such that the inner wall  16  may be cylindrical in shape. In other embodiments, the conduit section  12  may be non-circular in cross section, such as oval, elliptical or irregular, or may have a polygonal shape in cross section. The conduit section  12  may include an injector passage  18  (see also  FIG. 4 ) that extends through a raised boss  20  in a generally radial direction and terminates in an injector opening  22  in the inner wall  16 . In embodiments, the raised boss  20  may take the form of a pipe nipple (shown), flanged pipe, or other piping attachment. The conduit section  16  may be made of plastic, such as polyvinyl chloride (PVC), or made of metal, such as copper, cast iron or stainless steel, or made of other material suitable for conveying the liquids selected to be mixed. 
     The static mixer  10  also may include a tab, generally designated  24 , that may be attached to the inner wall  16  of the conduit section  12  adjacent the injector opening  22  and extend toward a center of the channel  14 . In embodiments, the tab may be made of metal, such as stainless steel or other strong, non-corrosive metals, or of plastic, such as nylon. The tab  24  may be stamped, cast, or molded as a single piece, or built up of components. 
     The tab  24  may include a main portion  26  extending from the inner wall  16  adjacent and downstream of the opening  22  and extending radially inwardly and at an angle away from the opening in the downstream direction. In an embodiment, the angle may be a non-zero angle relative to a diameter of the conduit section  12 . The tab  24  also may include at least one finger, and in the embodiment shown the at least one finger may take the form of a pair of opposing fingers  28 ,  30 , extending at a non-zero angle from the main portion. In an embodiment, the main portion  26  of the tab  24  may terminate in the opposing fingers  28 ,  30 . 
     As shown in  FIGS. 2A, 2B, 2C, and 2D , the main portion  26  of the tab  24  may include an upper end  32  having a generally concave shape. The upper end  32  may be attached to the inner wall  16  (see  FIGS. 1 and 4 ). by welding, brazing, adhesives and other suitable means. The concave shape of the upper end  32  may extend from the inner wall  16  at least partially along the main portion  26 , and face toward the injector opening  22 . In an embodiment, the injector opening  22  may be positioned within a portion of the generally concave shape adjacent the upper end  32 , and preferably the injector opening is aligned with a centerline of the main portion  16  relative to a longitudinal direction of the channel  14  ( FIG. 1 ), as shown at A in  FIG. 2D . 
     In an embodiment, the main portion  26  of the tab  24  may include a substantially flat longitudinal central surface  34  that may extend from the upper end  32  and increase in width to a distal end  36 . The main portion  26  also may include edge surfaces  38 ,  40  extending adjacent opposing, diverging edges  42 ,  44  of the longitudinal central surface  34 . In an embodiment, the edge surfaces  38 ,  40  may be oriented at an angle to the longitudinal central surface  34  to form the concave shape, and/or in other embodiments, the edge surfaces may be arcuate in shape. In the embodiment shown in  FIGS. 2A-2D , the edge surfaces  38 ,  40  form the concave shape of the upper end  32 . In other embodiments, the tab  24  may include a main portion  26  that is configured to have a concave shape by continuously bending the main portion along a longitudinal centerline of the main portion. 
     As shown in  FIGS. 2A-2D , the fingers  28 ,  30  may have a generally concave shape extending longitudinally along the fingers, facing away from the injector opening  22  ( FIG. 4 ); that is, in a downstream direction. In an embodiment, the fingers  28 ,  30  extend outwardly from a terminal end  36  of the main portion  26 . In an embodiment, the fingers  28 ,  30  may be oriented such that they are bent in a downstream direction from a plane containing the main portion  26 , more specifically the substantially flat longitudinal central surface  34  of the main portion. 
     In an embodiment, the fingers  28 ,  30  may be similarly shaped, each having a substantially flat central portion  46  and a pair of ears  48 ,  50  extending along opposing, tapered longitudinal edges  52 ,  54  of the central portion  46 . In an embodiment, the ears  48 ,  50  may be arcuate in shape, and provide the downstream-facing concave shape to the ears. In an embodiment, as shown in  FIG. 2D , the ears  28 ,  30  may be oriented to extend in a downstream direction from the central surface  34  of the main portion  26  at an angle B of approximately 30°. 
     In other embodiments, the arcuate shape of the upper end  32  of the main portion  26  may have a radius of approximately 0.155 of the diameter of the interior wall  16  ( FIG. 1 ) of the conduit section  12 . The length of the longitudinal central surface  34  may be 0.80 of the diameter of the inner surface  16  of the conduit section  12 . As shown in  FIG. 2B , the opposing edges  42 ,  44  may taper at an angle C of approximately 25°. The maximum width of the longitudinal central surface  34 , measured at points  56 ,  58 , may be 0.25 of the diameter of the inner wall  16  of the conduit section  12 . 
     The ears  28 ,  30  may be skewed relative to the longitudinal central surface  34 , along lines  60 ,  62  and angle D of approximately 24°. The radius of the end surfaces  64  may be selected to be 0.055 of the diameter of the inner wall  16  of the conduit section  12 . The angle J of the opposing longitudinal edges  52 ,  54  may be selected to be 57.5°. However, it is within the scope of the disclosure to vary the foregoing angles and ratios to accommodate fluids of a given viscosity and flow rate of through the conduit section  12 . In embodiments, the tab  24  may be approximately ⅛ inches thick. The thickness of the tab  24  may be varied to be greater or lesser, depending upon such factors the volume flow rate of the liquids in the conduit, the viscosity of the liquids to be mixed, and presence and size of any particulate material in the liquids. 
     As shown in  FIGS. 5 and 6 , in an alternate embodiment of the static mixer, generally designated  10 ′, the conduit section  12 ′, which in an embodiment may be an annular conduit section, may include a tubular section  66 . A terminal portion of the opposing fingers  28 ,  30 , which in an embodiment are the end surfaces  64  of the opposing fingers, may be attached to the inner wall  16 ′ of the extension  66 . The attachment may be by adhesives, by brazing or welding, by mechanical connections such as pins or screws, or other attachment mechanisms. 
     An advantage of attaching the opposing fingers  28 ,  30  to the interior wall  16 ′ is that the tab  24  may be made of a thinner material since it will be supported at the ends  64  of the fingers  28 ,  30 , as well as at the upper end  32  of the main portion  26 . In the embodiment of  FIG. 6 , the tab  26  may be oriented to extend at a non-zero angle E to a diameter of the conduit cross section, wherein the non-zero angle is approximately 30°. 
     In operation, the static mixer  10 ,  10 ′ may be connected to a source  68  of a second fluid  70  under pressure by a supply line  72  that is connected to the boss  20 , as shown in  FIG. 4 . In an embodiment, the supply line  72  may include a conventional metering device (not shown) that controls the flow rate of the second fluid  70  through the supply line and into the conduit section  12 . In embodiments, the source  68  may retain the second fluid  70  in a pressurized container, and/or include a pump or other device to provide a desired pressure to the second fluid. In still other embodiments, the metering device may provide the requisite pressure to the second fluid  70  in supply line  72 . 
     In the embodiment shown, the conduit section  10  may be incorporated in a conduit  74  in which a first fluid  76  is flowing (see also the “Main Flow” arrow in  FIG. 1 ). The first fluid  76  and second fluid  70  may be of similar or dissimilar viscosities. The second fluid  70  enters the injector passage  18  (see also the “Injected Flow” arrow in  FIG. 1 ) from the supply line  72 . As the second fluid  70  leaves the injector opening  22 , it flows radially inwardly along the upstream side of the main portion  26  of the tab  24 , as indicated by arrows F in  FIG. 1 . Although constrained by the arcuate edge surfaces  38 ,  40 , some of the fluid flows around the main portion  26 , as indicated by arrows G and flows downstream. 
     The portion of the second fluid  70  ( FIG. 4 ) that travels the entire length of the main portion  26  of the tab  24  will flow from the terminal end  36  of the main portion. Some of the second fluid  70  will flow sidewardly along the upstream side of the fingers  28 ,  30 , and around the arcuate ears  48 ,  50 , as indicated by arrows H in  FIG. 1  in a downstream direction. The angle made by the main portion  26  to a diameter may provide optimal mixing of the second fluid  70  with the first fluid across an entire diameter of the conduit in which the conduit section  10 ,  10 ′ is mounted. 
     The overall concave shape of the main portion  26  of the tab  24  may impart mechanical strength of the main portion. Further, the concave shape may create a low pressure area behind (i.e., downstream of) the main portion  26  that may distribute the injectant (i.e., the second fluid  70 ) across the entire cross-section of the conduit section  10 ,  10 ′. Consequently, the area of highest energy dissipation may occur prior to or upstream of introduction of the injectant or second fluid  70  into the stream of the first fluid  76 . 
     With the disclosed static mixer  10 ,  10 ′, placement of the injector opening  22  upstream of the mixer element (the tab  24 ) the injectant is forced to flow through the high-energy dissipation region created by the mixer element. Having the injectant flow through the high-energy dissipation region may allow for more efficient mixing in terms of both effectiveness for a given mixer length and pressure drop when injecting a second fluid having different physical properties than the first fluid  76  flowing through the conduit  74 . Such differences in physical properties of the fluids  70 ,  76  may include differences in viscosity and in specific gravity. 
     While the forms of apparatus and methods herein described constitute preferred embodiments of the disclosed static mixer and static mixer operation, it is to be understood that the invention is not limited to these precise forms of apparatus and methods, and that changes may be made therein without departing from the scope of the invention.