Patent Publication Number: US-2021187449-A1

Title: Apparatus in the form of a unitary, single-piece structure configured to generate and mix ultra-fine gas bubbles into a high gas concentration aqueous solution

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of U.S. patent application Ser. No. 16/768,609, entitled “Apparatus in the Form of a Unitary, Single-Piece Structure Configured to Generate and Mix Ultra-Fine Gas Bubbles Into a High Gas Concentration Aqueous Solution,” filed on May 29, 2020, which is a U.S. national phase application of and claims priority to International Application No. PCT/US2019/034749, entitled “Apparatus in the Form of a Unitary, Single-Piece Structure Configured to Generate and Mix Ultra-Fine Gas Bubbles Into a High Gas Concentration Aqueous Solution,” filed on May 30, 2019, which claims the benefit of U.S. Provisional Application Ser. No. 62/679,702, entitled “Apparatus in the Form of a Unitary, Single-Piece Structure Configured to Generate and Mix Ultra-Fine Gas Bubbles into a High Gas Concentration Aqueous Solution,” filed on Jun. 1, 2018, each of which is expressly incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     Aspects of the present disclosure relates to liquid and gas systems and methods that generate ultra-fine bubbles and mix them into a highly concentrated aqueous solution. 
     BACKGROUND 
     Bubbles contained in a liquid are visible to the eyes when the bubble sizes are range from 6 to 29 microns. We can see bubbles in carbonated drinks or those coming from the air diffuser in a water tank. Bubbles with the size of a few millimeters in diameter show visible surfacing action in a liquid, and the presence of fine bubbles of dozens of microns in diameter can be confirmed with white turbidity in a liquid, because these bubbles are scattering substances. Bubbles in diameter smaller than the wavelength of light are called ultra-fine bubbles, and they are too small to see. Ultra-fine bubbles have several unique properties including long lifetime in liquid owing to their negatively charged surface, and high gas solubility into the liquid owing to their high internal pressure. These special features of ultra-fine bubbles have attracted attention from many industries such as food, cosmetics, chemical, medical, semi-conductor, soil and water remediation, aquaculture and agriculture. 
     SUMMARY 
     A mixing apparatus for generating and mixing gas bubbles, including for example, ultra-fine bubbles, into an aqueous solution includes a structure defining an interior fluid-flow chamber that extends along a longitudinal axis between an input port at a liquid input end and an output port at a liquid output end. The structure is characterized by a gas injection portion located upstream from the liquid output end and a mixing vane portion extending in the downstream direction from the gas injection portion. The gas injection portion defines a gas injection lumen and a first region of the interior fluid-flow chamber, while the mixing vane portion defines a second region of the interior fluid-flow chamber. The first region of the interior fluid-flow chamber includes a plurality of side fluid-path lumens that extend in the downstream direction alongside a first part of the gas injection lumen. This first part of the gas injection lumen, together with the side fluid-path lumens, merges with a downstream fluid-path lumen of the first region. The various lumens are arranged such that the first part of the gas injection lumen is closer to the longitudinal axis than any of the plurality of side fluid-path lumens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is perspective illustration of a fully assembled, multi-component ultra-fine bubble generating liquid/gas mixing apparatus having a gas injection component and a helical mixing vane component forming a structure defining an interior fluid-flow chamber extending along a longitudinal axis between a liquid input end and a liquid output end. 
         FIGS. 1B and 1C  are different perspective illustrations of the mixing apparatus of  FIG. 1A  disassembled and exploded to show the gas injection component and the helical mixing vane component. 
         FIG. 2  includes a side view illustration of the mixing apparatus of  FIG. 1A , and a scaled-up end-view illustration of the mixing apparatus, where the end view is from the perspective of the liquid input end. 
         FIG. 3  is a perspective cross-section illustration of the mixing apparatus of  FIG. 1A  taken along the x-y plane of  FIG. 1A , with portions of solid material absent to expose internal structures and components of the mixing apparatus. 
         FIG. 4  is a planar cross-section illustration of the fully assembled mixing apparatus of  FIG. 2  taken along the x-y plane of  FIG. 2 . 
         FIG. 5  is a perspective cross-section illustration of the fully assembled mixing apparatus of  FIG. 1A  taken along a x-z plane that is offset from the origin x-z plane, with portions of solid material absent to expose internal structures and components of the mixing apparatus. 
         FIG. 6  is a schematic plane representation of the interior fluid-flow chamber of the mixing apparatus of  FIG. 1A  taken along the x-z plane of  FIG. 1A  to show bifurcation of the interior fluid-flow chamber into multiple fluid-flow paths. 
         FIG. 7  is a schematic end-view representation of the interior fluid-flow chamber of the mixing apparatus of  FIG. 1A  from the perspective of the liquid input end and rotated 90 degrees clockwise. 
         FIG. 8  is a schematic cross-section representation of an alternate configuration of a helical mixing vane component having a series of individual helical vane sections. 
         FIG. 9  is perspective illustration of a unitary, single-piece mixing apparatus having a gas injection portion and a helical mixing vane portion together defining an interior fluid-flow chamber extending along a longitudinal axis between a liquid input end and a liquid output end. 
         FIG. 10  is a perspective cross-section illustration of the mixing apparatus of  FIG. 9  taken along the x-y plane and through the center of the mixing apparatus. 
         FIG. 11  is a planar cross-section illustration of the mixing apparatus of  FIG. 9  taken along an x-y plane and through the center of the mixing apparatus. 
         FIG. 12  is a planar cross-section illustration of the interior fluid-flow chamber of the mixing apparatus of  FIG. 9  taken along an x-z plane and through the gas injection portion to show bifurcation of the interior fluid-flow chamber into multiple fluid-flow paths. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. 
     Disclosed herein are different versions or embodiments of ultra-fine bubble generating liquid/gas mixing apparatuses. In one version, referred to as a “multi-component” mixing apparatus,” components of the apparatus are separately manufactured and coupled together with attaching hardware to form a complete apparatus. This version may also include some internal, removable components such as an O-ring gasket and gas inlet structure, e.g., diffuser. The multi-component version of the mixing apparatus allows for subsequent disassembly of the apparatus without destroying or damaging the structural integrity of the components. In another version, referred to as a “unitary, single-piece mixing apparatus,” the apparatus is a single unitary structure, where “single unitary” means that the mixing apparatus does not have any separate components parts that require assembly, and that the mixing apparatus cannot be taken apart or disassembled without damaging or destroying either of the structural integrity or functional integrity of the mixing apparatus. In other words, the mixing apparatus is a single piece structure with no separately attached external or internal components. 
     Multi-Component Mixing Apparatus 
     With reference to  FIGS. 1A-2 , a multi-component ultra-fine bubble generating liquid/gas mixing apparatus  100  (herein after referred to as a “mixing apparatus”) includes a gas injection component  104  and a mixing vane component  102 . In one configuration, the mixing vane component  102  is a variable-pitch helical mixing vane. Each of the gas injection component  104  and the mixing vane component  102  defines a respective region of an interior fluid-flow chamber that extends along a longitudinal axis  142  (also referred to herein as the “x axis”) between a liquid input end  134  and a liquid output end  138  of the mixing apparatus  100 . The interior fluid-flow chamber defines multiple fluid-path lumens that guide fluid through the mixing apparatus. Regarding the longitudinal axis  142 , while the example mixing apparatus  100  of  FIGS. 1A-2  has a linear longitudinal axis, other embodiments of the mixing apparatus may have non-linear longitudinal axes that curve. 
     Moving from left to right in  FIGS. 1A-2 , or in the downstream direction from the liquid input end  134  of the mixing apparatus  100  to the liquid output end  138 , the gas injection component  104  includes: a) the liquid input end through which liquid is input to the mixing apparatus, b) a gas input region  120  through which gas is injected into the mixing apparatus, and c) a downstream end  124  where the gas injection component couples to the mixing vane component  102 . 
     The gas input region  120  of the gas injection component  104  includes an inlet portion  112  having an opening  110  that is configured to be coupled with a tubular elbow fitting  106 . The tubular elbow fitting  106  defines a gas injection port  108  through which gas is injected into a gas injection lumen within the gas injection component  104 . The gas input region  120  also defines multiple fluid-path lumens  212   a ,  212   b  that form a first region of the interior fluid-flow chamber of the mixing apparatus  100 . As shown in  FIG. 2 , the fluid-path lumens  212   a ,  212   b  of the first region of the interior fluid-flow chamber are characterized by a C-shaped cross-section and accordingly are at times referred to herein as C-shaped lumens. 
     Continuing in the downstream direction, the mixing vane component  102  includes: a) an upstream end  144  where the mixing vane component couples with the gas injection component  104 , b) a helical region  146 , and c) the liquid output end  138  through which liquid/gas mixture exist the mixing apparatus  100 . The helical region  146  defines multiple fluid-path lumens, each lumen twisting around the longitudinal axis  142  to form a helical fluid-path lumen that guides fluid in the downstream direction toward the liquid output end  138  of the mixing apparatus  100 . The helical fluid-path lumens form a second region of the interior fluid-flow chamber of the mixing apparatus  100 . The helical fluid-path lumens of the second region of the fluid-flow chamber are equal in number with the C-shaped fluid path lumens of the first region of the fluid-flow chamber. For example, the mixing apparatus  100  of  FIGS. 1A-2  has two C-shaped fluid path lumens, each of which transitions to a corresponding helical fluid-path lumen. 
     In one configuration, each of the mixing vane component  102  and a gas injection component  104  may be separately manufactured as a single-piece, unitary component using 3D printing. In another configuration, each of the mixing vane component  102  and the gas injection component  104  may be separately manufactured using injection molding techniques. For example, separate molds may be used to form different portions of the mixing vane component  102  and the gas injection component  104  relative to the longitudinal axis  142  of the apparatus. In one implementation, each molded portion may be one half of the mixing vane component  102  and one half of the gas injection component  104  along the longitudinal axis  942 . 
     Once the mixing vane component  102  and a gas injection component  104  are manufactured, they are assembled with a gas inlet structure  114  and an O-ring  116  and secured together using various fastening components, e.g., nuts, bolts, washers, and a silicon sealant. The gas inlet structure  114  (also referred to herein as a muffler or a diffuser) provides a gas injection interface between gas received through the inlet portion  112  of the gas injection component  104  and the interior fluid-flow chamber of the mixing apparatus  100 . The O-ring  116  fits within an annular groove  122  (visible in  FIG. 1B ) formed in the downstream end  124  of the gas injection component  104 . The O-ring  116  provides a seal between liquid/gas mixture flowing through the interior fluid-flow chamber of the mixing apparatus  100  (which chamber passes through the inside of the O-ring) and any gap  128  that may exist between abutting surfaces  130 ,  132  of the mixing vane component  102  and the gas injection component  104  after assembly of the components. 
     After manufacture or manufacture and assembly, the mixing apparatus  100  may be encased in a sleeve. This may be accomplished by placing the mixing apparatus  100  in a heat-shrink tube; and then heating the tube to shrink into contact with the outer surface of the apparatus to thereby provide an impenetrable sleeve over the entire apparatus. 
     With reference to  FIGS. 2-5 , in one configuration the gas injection component  104  includes an outer wall  224  that surrounds a first geometric structure  202  and a second geometric structure  204  that is downstream from the first geometric structure. In one configuration the first geometric structure  202  is in the form of a solid cone and is thus referred to herein as “a conical structure,” and the second geometric structure is in the form of a hollow cylinder and is thus referred to herein as “a hollow cylindrical structure.” The conical structure  202  has a tip  220  that faces the liquid input end  134  of the mixing apparatus  100  and a base  222  opposite the tip. The conical structure  202  functions to constrict the flow of fluid into the gas injection component  104  just enough to maintain a constant back pressure. This reduces the voids in the water stream that may collect large gas bubbles. 
     The base  222  of the conical structure  202  transitions to the hollow cylindrical structure  204 . The interior of the hollow cylindrical structure  204  defines a first portion  206  of the gas injection lumen that extends along the length of the cylinder. Extending from the outer surface of the hollow cylindrical structure  204  are two wing structures  208   a ,  208   b  positioned on opposite sides of the cylinder. The wing structures  208   a ,  208   b  extend to and merge with an interior surface  210  (visible in  FIG. 2 , view A-A) of the outer wall  224  of the gas injection component  104 . 
     The space between the outer surfaces of the conical structure  202  and the hollow cylindrical structure  204  and the interior surface  210  of the outer wall  224  of the gas injection component  104  define the first region of the interior fluid-flow chamber. With reference to  FIG. 2 , view A-A, the wing structures  208   a ,  208   b  divide the space between the outer surface of the hollow cylindrical structure  204  and the interior surface  210  of the outer wall  224  to form a pair of separate fluid-path lumens  212   a ,  212   b , which extend along opposite sides of the gas injection component  104 . At this first region of the interior fluid-flow chamber, the fluid-path lumens  212   a ,  212   b  are generally C-shaped in cross section and extend from the base  222  of the conical structure  202  to the downstream end  124  of the gas injection component  104 . In this configuration, the first region of the interior fluid-flow chamber defined by the gas injection component  104  may be characterized as a “bifurcated” first region of the interior fluid-flow chamber. The space between surfaces that define the first region of the interior fluid-flow chamber may also be referred to as a “void”, where the void is defined by the absence of any solid material that forms the gas injection component  104 . 
     With reference to  FIGS. 6 and 7 , a first section  602  of the first region of the interior fluid-flow chamber defined by the gas injection component  104  or a gas injection portion extends between point “a” and point “b,”, and has a first interior radius at point “a” between the tip  220  of the conical structure  202  and the interior surface  210  of the gas injection component at point “a”. At the base  222  of the conical structure  202  the interior chamber or void bifurcates into two C-shaped fluid-path lumens  212   a ,  212   b . The width at the beginning of the C-shaped fluid-path lumens  212   a ,  212   b  is identified as point “b.” This width may be referred to as the radii of the void at point “b,” which corresponds to the interior radius of the gas injection component  104  from the center  608  of the gas injection component to the interior surface  210  of the gas injection component at point “b,” minus the portion of that radius that is filled with solid material. 
     A second section  604  of the first region of the interior fluid-flow chamber extends between point “b” and point “c” as shown in  FIG. 6 . Along the length of the second section  604 , the widths of the C-shaped fluid-path lumens  212   a ,  212   b  taper down in size relative to the width at point “b.” The width at the end of the C-shaped fluid-path lumens  212   a ,  212   b  is identified as point “c.” This width may be referred to as the radii of the void at point “c,” which corresponds to the interior radius of the gas injection component from the center  612  of the component to the interior surface  210  of the gas injection component  104  at point “c,” minus the portion of that radius that is filled with solid material. In one example configuration, the radii of the void at point “a” is approximately 0.91″, the width (or radii of the void) at point “b” is approximately 0.88″, and the width (or radii of the void) at point “c” is approximately 0.82″. 
     With reference to  FIGS. 3-5 , as previously mentioned, the interior of the hollow cylindrical structure  204  defines a first portion  206  of a gas injection lumen of the gas injection component  104 . This first portion  206  of the gas injection lumen extends along the longitudinal axis  142  of the mixing apparatus  100  from an upstream region of the hollow cylindrical structure  204  that is beneath the inlet portion  112  of the gas injection component  104  to a downstream region of the hollow cylindrical structure  204  at or near the downstream end  124  of the gas injection component. A gas inlet structure  114  extends from the downstream end of the hollow cylindrical structure. 
     In one configuration, the gas inlet structure  114  comprises a threaded base that screws into the first portion  206  of the gas injection lumen and a cap structure (also referred to as a muffler or a diffuser) that couples with the threaded base. The hollow interior  214  of the gas inlet structure  114  defines a second portion of the gas injection lumen. The cap structure includes a cylindrical sidewall and an end cap, each having a porous structure that permits injected gas to pass through. Alternatively, the gas inlet structure  114  may be configured as a simple Pitot type tube with holes passing through its sidewall and end cap. Configured as such the porous cap or Pitot tube allows for the injection of gas in multiple directions relative to the longitudinal axis  142  of the mixing apparatus  100 . For example, with reference to  FIG. 3 , gas may be injected from the interior of the gas inlet structure  114  into the surrounding interior fluid-flow chamber in a direction radially outward relative to the longitudinal axis  142  and/or downstream, in the direction of the longitudinal axis. 
     In another configuration, where the mixing apparatus  100  is manufactured as a single unitary structure, a separate gas inlet structure  114  is not present. Instead, the gas inlet structure  114  is formed as part of the downstream region of the hollow cylindrical structure  204 . For example, the downstream region of the hollow cylindrical structure  204  may comprise a reduced diameter portion that extends beyond the downstream end  124  of the gas injection component, which portion is formed to include a number of pores through which injected gas may pass in multiple directions relative to the longitudinal axis  142  of the mixing apparatus  100 , as described above. 
     In yet another configuration, to allow for unimpeded injection of gas, a gas inlet structure  114  is not included and gas is injected through the downstream end of the hollow cylindrical structure in the direction of the longitudinal axis and into the surrounding interior fluid-flow chamber. This configuration, an example of which is described further below with reference to  FIGS. 9-11 , avoids detrimental issues, e.g., clogging and corroding, that may arise with the gas inlet structure Eliminating the gas inlet structure also allows for the mixing apparatus to be 3D printed in one piece, thereby substantially reducing manufacturing costs. 
     The gas injection lumen of the gas injection component  104  includes a third portion  216  that extends between the base of the inlet portion  112  to the first portion  206  of the gas injection lumen. Extending in this manner, the third portion  216  passes through the outer wall  224  of the gas injection component  104 , through a wing structure  208   a , and through the wall of the cylinder structure  204  before it merges with the first portion  206  of the gas injection lumen. The first, second and third portions  206 ,  214 ,  216  of the gas injection lumen may have any of a number of cross-section shapes. In one configuration, the first portion  206  and second portion  214  are cylindrical, while the third portion  216  is rectangular. 
     In operation, as shown in  FIGS. 5 and 6 , a liquid stream input through the liquid input end  134  of the gas injection component  104  is initially displaced and separated by the conical structure  202 , with a first portion of the liquid being directed toward and into a first fluid-path lumen  212   a  to form a first liquid stream  402   a , and a second portion of the liquid being directed toward and into a second fluid-path lumen  212   b  to form a second liquid stream  402   b . The conical structure  202  and cylinder structure  204  thus function together to divide or expand a single stream of liquid into multiple liquid streams, e.g., two streams, as it passes through the gas injection component  104 , and prior to the liquid reaching the mixing vane component  102 . Because of this function, the gas injection component  104  may also be referred to as a “jet stream expander.” Expansion of a single liquid stream into multiple liquid streams maximizes the amount of contact between injected gas and the liquid flowing through the gas injection component  104 . Expansion into multiple liquid streams also allows the mixing vane component  102  to further compress and shear injected gas into ultra-fine bubbles of sub-micron size. 
     A method of mixing gas and liquid may include passing liquid through a venturi to create a low-pressure zone, thereby exposing a supply of gas to the low-pressure zone adjacent the venturi. This may allow low pressure suction to extract gas from the gas supply and expose the gas to more liquid before entering the mixing vane component  102 . With reference to  FIG. 6 , the change in diameter and the widths of the C-shaped fluid-path lumens  212   a ,  212   b  of the interior fluid-flow chamber along the length of the second section  604  of the gas injection component  104  defines a funnel or venturi. The venturi formed by the interior fluid-flow chamber in the area of the C-shaped fluid-path lumens  212   a ,  212   b  provides a gradual reduction in the cross-section area of the fluid-path lumens along the length of the lumens and focuses each of the first liquid stream  402   a  and the second liquid stream  402   b  liquid stream along their respective fluid-path lumen  212   a ,  212   b . The reduction in cross-section area of the C-shaped fluid-path lumens  212   a ,  212   b  increases the velocity of the liquid passing through the gas injection component  104  and creates a low pressure or suction area adjacent to the end of the C-shaped fluid-path lumens. 
     With reference to  FIG. 5 , as the first and second liquid streams  402   a ,  402   b  reach the end of their respective C-shaped fluid-path lumens  212   a ,  212   b  at the downstream end  124  of the gas injection component  104 , each liquid stream transitions into a respective helical fluid-path lumen  212   a ,  212   b  in the mixing vane component  102 . At this point, the liquid streams  402   a ,  402   b  surround the portion of the gas inlet structure  114  that extends into the mixing vane component  102 . Gas being injected into the gas injection component  104  through the gas injection port  108  passes through the gas inlet structure  114  and mixes with the surrounding liquid streams  402   a ,  402   b  to form an ultra-fine bubble liquid/gas mixture. At this point the liquid streams  402   a ,  402   b  are now liquid/gas mixture streams. 
     As described above, the gas inlet structure  114  through which gas exits may be configured to allow for the injection of gas in multiple directions relative to the longitudinal axis  142  of the mixing apparatus  100 , including radially outward relative to the longitudinal axis and downstream, in the direction of the longitudinal axis. Configured in this manner, the mixing apparatus  100  injects gas from a location close to the longitudinal axis  142 , into fluid that surrounds the location, as the fluid flows past the location. In other words, the mixing apparatus is configured to inject gas into liquid from the inside out. This is distinct from other mixing apparatuses that are configured to inject gas into liquid from the outside in, for example, through an annular structure surrounding a fluid-flow path, such as disclosed in U.S. Pat. No. 5,935,490. 
     With reference to  FIG. 6 , the upstream end  144  of the mixing vane component  102  where each of the liquid streams  402   a ,  402   b  transitions from a C-shaped fluid-path lumen to a helical fluid-path lumen, begins as an almost straight blade  610  to reduce back pressure and prevent fluid flow loss. The pitch of the helical fluid-path lumens of the mixing vane component  102  may increase from almost straight to several revolutions per inch over the length of the mixing vane component. The helical fluid-path lumens of the mixing vane component  102  gradually constricts the flow of the liquid/gas mixture and shears and compresses the gas into the liquid. The increased rate of revolutions of the helical fluid-path lumens accelerates the flow of the liquid/gas mixture and further mixes the liquid and gas to create a solution with abundant ultra-fine bubbles. 
     As the compressed liquid/gas mixture exits through the liquid output end  138  of the mixing apparatus  100 , the mixture is expanded slightly. This is done by attaching an exit tube (not shown) to the liquid output end  138 . The exit tube may have an internal diameter that is slightly larger than the internal diameter at the liquid output end  138  of the mixing vane component  102 . The enlarged internal diameter provided by the exit tube creates a vacuum effect that pulls the liquid/gas mixture forward through the liquid output end  138  and allows the spin of the liquid to stabilize before final discharge from the exit tube. This vacuum effect reduces back pressure on the liquid/gas mixture stream and flow loss associated with back pressure. As the compressed liquid/gas mixture passes through the liquid output end  138 , the previously compressed gas bubbles in the liquid/gas mixture expand and explode creating even smaller bubbles of sub-micron size. In one configuration, an exit tube (not shown) is coupled to the mixing vane component  102  at the liquid output end  138 . The exit tube is of a length sufficient to allow velocity and rotation of the liquid/gas mixture to slow to normal flow conditions before it discharges into to a tank, reservoir or surface body of water. The normal flow condition prevents high speed collisions and forces that will dislodge the trapped ultra-fine gas bubbles. 
     In one configuration, the mixing vane component  102  may include a series of individual helical vane sections, of equal or different length, separated by a distance of “d” that is void of any helical structure.  FIG. 8  is a schematic representation of a series of individual helical vane sections  802 ,  804 , where a first helical vane section  802  has a length greater than a second helical vane  804 . A series of helical vane sections may enable higher gas saturation with more gas injected in real time, while the increased pressure increases the gas transferred to the liquid. The separation distance “d” between adjacent helical vane sections  802 ,  804  that is void of any helical structure may be anywhere between a small fraction, e.g., one-sixteenth, of the inner diameter  808  of the adjacent mixing vane components  802 ,  804  to a multiple of the inner diameter. It has been found, however, that a separation distance  806  ranging from between one half of the inner diameter  808  to equal to the inner diameter is more effective in increasing the level of gas saturation. 
     With reference to  FIGS. 1A-8 , thus disclosed herein is a mixing apparatus  100  for generating and mixing gas bubbles into an aqueous solution. The mixing apparatus  100  includes a structure defining an interior fluid-flow chamber extending along a longitudinal axis  142  between a liquid input end  134  and a liquid output end  138 . The structure is characterized by a gas injection portion and a mixing vane portion. The gas injection portion is located downstream from the liquid input end  134  and upstream from the liquid output end  138 . The gas injection portion define a first region of the interior fluid-flow chamber and a gas injection lumen formed by first, second, and third portions  206 ,  214 ,  216 . The gas injection lumen  206 ,  214 ,  216  is surrounded by the interior fluid-flow chamber and extends along a length of the gas injection portion. The gas injection lumen  206 ,  214 ,  216  is configured to inject gas from the interior of the gas injection lumen into the surrounding interior fluid-flow chamber. The mixing vane portion extends in the downstream direction from the gas injection portion and defines a second region of the interior fluid-flow chamber. 
     The structure may be formed of separately manufactured components that are assembled. For example, the gas injection portion may be in the form of a gas injection component  104  and the mixing vane portion may be in the form of a mixing vane component  102 . Alternatively, the structure may be manufactured as a single component, portions of which respectively define a gas injection portion and a mixing vane portion. 
     The gas injection portion includes an outer wall  224  and a geometric structure  202 , e.g., a cone, surrounded by the outer wall. The geometric structure has a tip  220  facing the liquid input end  134  and a base  222  facing the liquid output end  138 . The gas injection portion also includes a hollow cylindrical structure  204 , e.g., a cylinder, that is also surrounded by the outer wall  224 . The hollow cylindrical structure  204  extends in the downstream direction from the base  222  of the geometric structure and has a hollow interior that defines a first portion  206  of the gas injection lumen. The outer wall  224  has an interior surface  210  and each of the geometric structure  202  and the hollow cylindrical structure  204  has an outer surface spaced apart from the interior surface  210 . The space between the interior surface  210  and the outer surfaces of the geometric structure  202  and the hollow cylindrical structure  204  defines the first region of the interior fluid-flow chamber. The space between the interior surface and the outer surfaces changes in dimension along the length of the gas injection portion. The change in dimension creates a venturi that creates a low-pressure zone for liquid that may allow low pressure suction to extract gas from the gas injection lumen  206 ,  214 ,  216  and expose the gas to more liquid before entering the mixing vane component  102 . 
     The hollow cylindrical structure  204  has a gas inlet structure  114  that extends from a downstream region of the hollow cylindrical structure. The gas inlet structure  114  has a hollow interior that defines a second portion  214  of the gas injection lumen. At least part of the second portion  214  of the gas injection lumen is configured to inject gas into the surrounding interior fluid-flow chamber in at least one of a plurality of directions relative to the longitudinal axis  142 . For example, the gas inlet structure  114  may inject gas radially outward relative to the longitudinal axis  142  and/or downstream, in the direction of the longitudinal axis. In one configuration, the gas inlet structure  114  includes a hollow cap structure having at least one of a porous cylindrical sidewall and a porous end cap through which gas may injected into the surrounding interior fluid-flow chamber. In another configuration, the gas inlet structure is a reduced diameter portion of the downstream region of the hollow cylindrical structure  204  that is formed to include a number of pores through which gas may injected into the surrounding interior fluid-flow chamber. 
     The first region of the interior fluid-flow chamber defined by the gas injection portion may include a plurality of separate fluid-path lumens  212   a ,  212   b . In one configuration, the plurality of separate fluid-path lumens  212   a ,  212   b  are partially defined by a pair of wing structures  208   a ,  208   b  that extend between the outer surface of the hollow cylindrical structure  204  and the interior surface  210  of the outer wall  224 . One of the wing structures  208   a ,  208   b  may define a third portion  216  of the gas injection lumen. For example, the gas injection portion may include an inlet portion  112  having a base, and the third portion  216  of the gas injection lumen may extend from the base of the inlet portion  112  through one of the pair of wing structures  208   a ,  208   b  and into the first portion  206  of the gas injection lumen defined by the hollow cylindrical structure  204 . 
     The plurality of separate fluid-path lumens  212   a ,  212   b  of the first region of the interior fluid-flow chamber are non-helical lumens. For example, the gas injection portion may define a pair of fluid-path lumens  212   a ,  212   b  having a C-shaped cross section that extend linearly along part of the gas injection portion. At the junction of the gas injection portion and the mixing vane portion, each of the separate non-helical fluid-path lumens  212   a ,  212   b  transition to a helical lumen of the second region of the interior fluid-flow chamber defined by the mixing vane portion. The mixing vane portion may include one helical vane region  802  or a plurality of helical vane regions  802 ,  804  arranged adjacently along the length of the mixing vane portion. In configurations having multiple helical vane regions, adjacent helical vane regions are separated by a separation distance  806  that defines an annular space between the adjacent helical vane regions. 
     Unitary, Single-Piece Configuration 
     With reference to  FIGS. 9-12 , a mixing apparatus  900  may be configured as a unitary, single-piece structure having no separate components parts, e.g., like the gas inlet structure, O-ring, nuts and bolts of the mixing apparatus configuration in  FIG. 1A-1C . The unitary, single-piece mixing apparatus  900  includes a gas injection portion  904  and a mixing vane portion  902 . In one configuration, the mixing vane portion  902  is a helical mixing vane. Each of the gas injection portion  904  and the mixing vane portion  902  defines a respective region of an interior fluid-flow chamber that extends along a longitudinal axis  942  (also referred to herein as the “x axis”) between an input port  1052  at a liquid input end  934  of the mixing apparatus  900  and an output port  1054  at a liquid output end  938  of the mixing apparatus  900 . The interior fluid-flow chamber defines multiple fluid-path lumens that guide fluid through the mixing apparatus. Regarding the longitudinal axis  942 , while the example mixing apparatus  900  of  FIGS. 9-12  has a linear longitudinal axis, other embodiments of the mixing apparatus may have non-linear longitudinal axes that curve. 
     Moving from left to right in  FIGS. 9, 10 and 11 , or in the downstream direction from the input port  1052  to the output port  1054 , the gas injection portion  904  includes: a) a liquid input end  934  that includes the input port  1052  through which liquid is input to the mixing apparatus, b) a gas input portion  920  through which gas is injected into the mixing apparatus, and c) a downstream end  924  where the gas injection portion transitions to the mixing vane portion  902 . The gas input portion  920  includes an inlet portion  912  having an opening  910  that is configured to be coupled with a tubular elbow fitting (not shown). The tubular elbow fitting defines a gas injection port through which gas is injected into a gas injection lumen within the gas injection portion  904 . 
     The gas injection portion  904  defines a first region of the interior fluid-flow chamber that includes multiple fluid-path lumens. With reference to  FIG. 11 , the interior of the liquid input end  934  defines an upstream tubular fluid-path lumen  1056  having a diameter that tapers down to the diameter of the gas input portion  920 . The upstream tubular fluid-path lumen  1056  extends into the gas input portion  920  where it bifurcates into separate fluid-path lumens, referred to herein as side fluid-path lumens. With reference to  FIG. 12 , these side fluid-path lumens  922   a ,  922   b  are characterized by a C-shaped cross-section and accordingly are at times referred to herein as C-shaped lumens. The C-shaped lumens  922   a ,  922   b  merge into and are in fluid communication with a downstream tubular fluid-path lumen  1038  defined by the interior of the downstream end  924  of the gas injection portion  904 . 
     Referring to  FIGS. 9, 10 and 11  and continuing in the downstream direction, the mixing vane portion  902  includes: a) an upstream end  944  where the mixing vane portion merges with the gas injection portion  904 , b) a helical region  946 , and c) the liquid output end  938  that includes the output port  1054  through which liquid/gas mixture exits the mixing apparatus  900 . As shown in  FIG. 10 , the helical region  946  defines multiple fluid-path lumens  1010   a ,  1010   b ,  1030   a ,  1030   b , each lumen twisting around the longitudinal axis  942  to form a helical fluid-path lumen that guides fluid in the downstream direction toward the liquid output end  938  of the mixing apparatus  900 . The helical fluid-path lumens  1010   a ,  1010   b ,  1030   a ,  1030   b , form a second region of the interior fluid-flow chamber of the mixing apparatus  900 . The helical fluid-path lumens  1010   a ,  1010   b ,  1030   a ,  1030   b , of the second region of the fluid-flow chamber are equal in number with the C-shaped fluid-path lumens  922   a ,  922   b  of the first region of the fluid-flow chamber. For example, the mixing apparatus  900  of  FIGS. 9-12  has two C-shaped side fluid-path lumens  922   a ,  922   b , two corresponding first helical fluid-path lumens  1010   a ,  1010   b , and two corresponding second helical fluid-path lumens  1030   a ,  1030   b.    
     In one configuration, the unitary, single-piece mixing apparatus  900  of  FIGS. 9-12  may be manufactured in its entirety as a single 3D printed object. In another configuration, different portions of the unitary, single-piece mixing apparatus  900  may be separately manufactured using injection molding techniques and then bonded together to form a unitary, single-piece mixing apparatus  900 . For example, separate molds may be used to form different portions of the mixing apparatus  900  relative to the longitudinal axis  942  of the apparatus. In one implementation, each molded portion may be one half of the mixing apparatus  900  along the longitudinal axis  942 . Regardless of how the unitary, single-piece mixing apparatus  900  is manufactured, the mixing apparatus is considered a single unitary structure, where “single unitary” means that the mixing apparatus does not have any separate components parts and that the mixing apparatus cannot be taken apart or disassembled without damaging or destroying either of the structural integrity or functional integrity of the mixing apparatus. In other words, the mixing apparatus  900  is a single piece of plastic with no separately attached external or internal components. 
     In any of the foregoing manufacturing configurations, after manufacture or manufacture and assembly, the mixing apparatus  900  may be encased in a sleeve. This may be accomplished by placing the mixing apparatus  900  in a heat-shrink tube; and then heating the tube to shrink into contact with the outer surface of the apparatus to thereby provide an impenetrable sleeve over the entire apparatus. 
     With continued reference to  FIGS. 10 and 11 , in one configuration the gas injection portion  904  includes an outer wall  1024  that surrounds a first geometric structure  1002  and a second geometric structure  1004  that extends in the downstream direction from the first geometric structure. The first geometric structure  1002  may be a solid cone having a solid surface that does not allow for the ingress of fluid. The second geometric structure  1004  may be a cylinder having a solid exterior surface that does not allow for the ingress of fluid. The second geometric structure  1004  is not entirely solid and includes a lumen that extends between an upstream end  1036  and a downstream opening  1034 . The lumen at the interior of the second geometric structure  1004  defines a first part  1006  of the gas injection lumen. 
     The first geometric structure  1002 , hereinafter referred to as the conical structure  1002 , has a tip  1020  that faces the liquid input port  1052  of the mixing apparatus  900  and a base  1022  opposite the tip. The base  1022  of the conical structure  1002  transitions to the second geometric structure  1004 , hereinafter referred to as the cylindrical structure  1004 . The conical structure  1002  functions to constrict the flow of fluid into and through the gas injection portion  904  just enough to maintain a constant back pressure. This reduces the voids in the water stream that may collect large gas bubbles. The space between the outer surfaces of the conical structure  1002  and the interior surface of the outer wall  1024  of the gas injection portion  904  define an upstream tubular fluid-path lumen  1056  of the first region of the interior fluid-flow chamber. 
     With reference to  FIGS. 10 and 12 , integral with and extending from the outer surface of the cylindrical structure  1004  are first and second wing structures  1008   a ,  1008   b  positioned on opposite sides of the cylinder. The first and second wing structures  1008   a ,  1008   b  extend to and merge or integrate with an interior surface of the outer wall  1024  of the gas injection portion  904 . “Integral” and “integrate with” in this context mean that the material forming the wing structures  1008   a ,  1008   b  is contiguous at one end with the material forming the cylindrical structure  1004 , and at the opposite end with the material forming the outer wall  1024 . In other words, the wing structures  1008   a ,  1008   b  are not separate parts that are adhered or bonded to the cylindrical structure  1004  and the outer wall  1024 . 
     With reference to  FIGS. 10, 11 and 12 , the first and second wing structures  1008   a ,  1008   b  divide the space between the outer surface of the cylindrical structure  1004  and the interior surface of the outer wall  1024  to define a pair of side fluid-path lumens  922   a ,  922   b  of the first region of the first region of the interior fluid-flow chamber. These side fluid-path lumens  922   a ,  922   b  extend along opposite sides of the gas injection portion  904 . In this area of the first region of the interior fluid-flow chamber, the fluid-path lumens  922   a ,  922   b  are generally C-shaped in cross section and extend from the base  1022  of the conical structure  1002  to the end of the cylindrical structure  1004 . The area of the first region of the interior fluid-flow chamber defined by the gas injection portion  904  may be characterized as a “bifurcated” area of the interior fluid-flow chamber. The side fluid-path lumens  922   a ,  922   b  merge into and are in fluid communication with a downstream tubular fluid-path lumen  1038  that is defined by a space bounded by the interior surface of the outer wall  1024 . The various spaces between surfaces that define the various areas of the first region of the interior fluid-flow chamber may also be referred to as “voids”, where a void is defined by the absence of any solid material that forms the gas injection portion  904 . 
     As previously mentioned, the interior of the cylindrical structure  1004  defines a first part  1006  of a gas injection lumen of the gas injection portion  904 . This first part  1006  of the gas injection lumen is in the form of a 90-degree elbow having a downstream opening  1034  at the end of the cylindrical structure  1004  and an upstream end  1036  that is beneath the inlet portion  912  of the gas injection portion  904 . The gas injection lumen merges into and is in fluid communication with the downstream tubular fluid-path lumen  1038  through the downstream opening  1034 . The gas injection lumen does not include any structure that would impede the flow of gas into the downstream tubular fluid-path lumen  1038 . For example, unlike the mixing apparatus of  FIGS. 1A-1C , there is no gas diffuser at the downstream opening  1034 . 
     The gas injection lumen of the gas injection portion  904  includes a second part  1016  that extends from the upstream end  1036  the first part  1006  through the inlet portion  912 . The second part  1016  of the gas injection lumen is arranged transverse to the first part  1006  and in one configuration, has an axis that extends generally perpendicular to the longitudinal axis of the first part. Extending in this manner, the second part  1016  of the gas injection lumen passes through a thickness of the outer wall  1024  of the gas injection portion  904 , through the first wing structure  1008   a , and through the wall of the cylinder structure  1004  before it merges with and comes into fluid communication with the first part  1006  of the gas injection lumen. The first and second parts  1006 ,  1016  of the gas injection lumen may have any of a number of cross-section shapes. In one configuration, the cross-section shape of each of the first part  1006  and the second part  1016  is cylindrical. 
     In operation, a liquid stream input through the liquid input end  934  of the gas injection portion  904  is initially displaced and separated by the conical structure  1002 , with a first portion of the liquid being directed toward and into a first fluid-path lumen  922   a  to form a first liquid stream  932   a , and a second portion of the liquid being directed toward and into a second fluid-path lumen  922   b  to form a second liquid stream  932   b . The conical structure  1002  and cylinder structure  1004  thus function together to divide or expand a single stream of liquid into multiple liquid streams, e.g., two streams, as it passes through the gas injection portion  904 , and prior to the liquid reaching the mixing vane portion  902 . Because of this function, the gas injection portion  904  may also be referred to as a “jet stream expander.” Expansion of a single liquid stream into multiple liquid streams maximizes the amount of contact between injected gas and the liquid flowing through the gas injection portion  904 . Expansion into multiple liquid streams also allows the mixing vane portion  902  to further compress and shear injected gas into ultra-fine bubbles of sub-micron size. 
     As the first and second liquid streams  932   a ,  932   b  reach the end of their respective C-shaped fluid-path lumens  922   a ,  922   b , the liquid streams empty into the downstream tubular fluid-path lumen  1038  where they merge. The downstream tubular fluid-path lumen  1038  has a length along the longitudinal axis  942  that defines a distance between the end of the C-shaped side fluid-path lumens  922   a ,  922   b  and the beginning of the helical fluid-path lumens  1010   a ,  1010   b . At this point, within the downstream tubular fluid-path lumen  1038 , the liquid side fluid-path lumens  922   a ,  922   b  is located in front of, i.e., downstream from, the downstream opening  1034  of the gas injection lumen. Gas being injected into the gas injection portion  904  through the gas injection opening  910  passes through the downstream opening  1034  into the downstream tubular fluid-path lumen  1038  and mixes with the liquid present in the downstream tubular fluid-path lumen to form an ultra-fine bubble liquid/gas mixture. The upstream pressure within the mixing apparatus  900  causes the liquid/gas mixture to bifurcate into a pair of liquid/gas mixture streams  1012   a ,  1012   b , each of which transitions into a respective helical fluid-path lumen  1010   a ,  1010   b  in the mixing vane portion  902 . 
     The arrangement of the first part  1006  of the gas injection lumen relative to the C-shaped fluid-path lumens  922   a ,  922   b  and the downstream tubular fluid-path lumen  1038  enables the injection of gas through the downstream opening  1034  into the downstream tubular fluid-path lumen in a same direction, e.g., downstream and aligned with or parallel to the longitudinal axis  942 , as the fluid flow through the C-shaped fluid-path lumens  922   a ,  922   b  into the downstream tubular fluid-path lumen  1038 . Configured in this manner, the mixing apparatus  900  injects gas from a location close to the center, longitudinal axis  942  of the mixing apparatus and thus distant from the inner wall of the mixing apparatus. This is distinct from other mixing apparatuses that are configured to inject gas into liquid at a location at to the inner wall, for example, through an annular structure adjacent an inner wall and surrounding a fluid-flow path, such as disclosed in U.S. Pat. No. 5,935,490. 
     With reference to  FIG. 11 , the upstream end  944  of the mixing vane portion  902 , where the liquid/gas fluid divides and enters the helical fluid-path lumens  1010   a ,  1010   b , begins as an almost straight blade to reduce back pressure and prevent fluid flow loss. The pitch of the helical fluid-path lumens  1010   a ,  1010   b  of the mixing vane portion  902  may be consistent or uniform along the length of the mixing vane portion. Alternatively, the pitch of the helical fluid-path lumens  1010   a ,  1010   b  of the mixing vane portion  902  may increase from almost straight to several revolutions per inch over the length of the mixing vane portion. The helical fluid-path lumens  1010   a ,  1010   b  of the mixing vane portion  902  constricts the flow of the liquid/gas mixture and shears and compresses the gas into the liquid. In the case of a helical vane having an increasing pitch, the increased rate of revolutions of the helical fluid-path lumens accelerates the flow of the liquid/gas mixture and further mixes the liquid and gas to create a solution with abundant ultra-fine bubbles. 
     Continuing with  FIG. 11 , the mixing vane portion  902  includes a series of individual helical vane sections  1040 ,  1042  of equal or different length, separated by a distance of “d” that is void of any helical structure. AS shown in  FIG. 10 , each helical vane section  1040 ,  1042  defines a same number of helical fluid-path lumens  1010   a ,  101   b ,  1030   a ,  1030   b . The distance “d” defines a gap in the mixing vane structure. A series of helical vane sections  1040 ,  1042  separated by a gap enables periodic merging and settling of liquid/gas mixture streams  1012   a ,  1012   b  and re-dividing thereof into separate liquid/gas steams. It has been found that the gap allows the spin of the liquid/gas mixture streams  1012   a ,  1012   b  resulting from a helical vane section  1040  to settle somewhat before the merged streams re-divide and accelerate into the next helical vane section  1042 . This settling followed by acceleration increases shearing and the generation of more ultra-fine bubbles. 
     The separation distance “d” between adjacent helical vane sections  1040 ,  1042  that is void of any helical structure may be anywhere between a small fraction, e.g., one-sixteenth, of the inner diameter  1044  of the mixing vane portion  902  to a multiple of the inner diameter. It has been found, however, that a separation distance “d” ranging from between one half of the inner diameter  1044  to equal to the inner diameter is more effective in increasing the level of gas saturation. In the configuration shown in  FIG. 10 , a first helical vane section  1040  and a second helical vane  1042  are of equal length. In other configurations, the helical vane section may be of different length. In other configurations, more than two helical vane sections may be present. 
     The direction of the twisting of the lumens within the helical vane sections about and along the length of the longitudinal axis may be counterclockwise or clockwise depending on the geographical region in which the mixing apparatus  900  will be used. For example, versions of the mixing apparatus  900  to be used in the northern hemisphere will include helical vane sections that twist in the clockwise direction, while those to be used in the southern hemisphere will include helical vane sections that twist in the counterclockwise direction. This results in a higher concentration of ultra-fine bubbles because there is less turbulence when the water flows in its natural direction. When water flows counter to the earths rotational effects the water “rolls” over itself as it flows. This creates a lot of “collision” inside the mixing apparatus. This collision reduces flow, increases pressure, and causes the turbulence that releases O2 molecules from the water. When water flows in its natural direction it avoids this collision, resulting in calmer water flow that increases velocity which increases the volume of the flow. This calm flow is actually higher than the standard flow tables you can get in a given pipe size. The higher flow velocity creates a slight vacuum at the injection point where the cross-sectional area is reduced just prior to the gas injection point. Also, a smaller pump using less energy can replace the larger pump needed to produce the same flow in a counter rotational example. 
     As the compressed liquid/gas mixture exits through the liquid output end  938  of the mixing apparatus  900 , the mixture is expanded slightly. This is done by attaching an exit tube (not shown) to the liquid output end  938 . The exit tube may have an internal diameter that is slightly larger than the internal diameter at the liquid output end  938  of the mixing vane portion  902 . The enlarged internal diameter provided by the exit tube creates a vacuum effect that pulls the liquid/gas mixture forward through the liquid output end  938  and allows the spin of the liquid to stabilize before final discharge from the exit tube. This vacuum effect reduces back pressure on the liquid/gas mixture stream and flow loss associated with back pressure. As the compressed liquid/gas mixture passes through the liquid output end  938 , the previously compressed gas bubbles in the liquid/gas mixture expand and explode creating even smaller bubbles of sub-micron size. In one configuration, an exit tube (not shown) is coupled to the mixing vane portion  902  at the liquid output end  938 . The exit tube is of a length sufficient to allow velocity and rotation of the liquid/gas mixture to slow to normal flow conditions before it discharges into to a tank, reservoir or surface body of water. The normal flow condition prevents high speed collisions and forces that will dislodge the trapped ultra-fine gas bubbles. 
     Another embodiment of a unitary, single-piece mixing apparatus may be modeled after the multi-component mixing apparatus described above with reference to  FIGS. 1A-8 . To this end, the mixing apparatus  100  may be 3D printed in its entirety as a unitary, single-piece object by 3D printing, instead of separately 3D printing a mixing vane component  102  and a gas injection component  104  and assembling them. In this embodiment, there is no O-ring  116  and manufacture of the gas inlet structure  114  is integrated with the 3D printing process. For example, the gas inlet structure  114  may be formed as an internal structure of a gas injection portion of the mixing apparatus  100 . Alternatively, the gas inlet structure  114  may not be included. 
     In other configuration, the mixing apparatus  100  may be manufactured using injection molding techniques. For example, separate molds may be used to form different portions of the mixing apparatus  100  relative to the longitudinal axis  142  of the apparatus. In one implementation, each molded portion corresponds one half of the mixing apparatus  100  along the longitudinal axis  142 . Once molded, the two halves may be bonded together to form a single assembly of the mixing apparatus  100 . 
     Thus, disclosed herein is a mixing apparatus  900  for generating and mixing gas bubbles, including for example, ultra-fine bubbles, into an aqueous solution. The mixing apparatus  900  includes a structure defining an interior fluid-flow chamber that extends along a longitudinal axis  942  between an input port  1052  at a liquid input end  934  and an output port  1054  at a liquid output end  938 . The structure is characterized by a gas injection portion  904  located upstream from the liquid output end  938  and a mixing vane portion  902  extending in the downstream direction from the gas injection portion. The gas injection portion  904  defines a gas injection lumen having a first part  1006  and a second part  1016 . The gas injection portion  904  also defined a first region of the interior fluid-flow chamber, while the mixing vane portion  902  defines a second region of the interior fluid-flow chamber. The first region of the interior fluid-flow chamber includes a plurality of side fluid-path lumens  922   a ,  922   b  that extend in the downstream direction alongside the first part  1006  of the gas injection lumen. This first part  1006  of the gas injection lumen, together with the side fluid-path lumens  922   a ,  922   b , merges with a downstream fluid-path lumen  1038  of the first region. The various lumens  922   a ,  922   b ,  1006  are arranged such that the first part  1006  of the gas injection lumen is closer to the longitudinal axis  942  than any of the plurality of side fluid-path lumens  922   a ,  922   b.    
     Manufacturing and Materials 
     The mixing apparatuses  100 ,  900  may be manufactured using 3D printing technology. For the multi-component version, each of the mixing vane component  102  and the gas injection component  104  may be separately manufactured as a unitary, single-piece object using 3D printing, and then assemble to form a mixing apparatus  100 . For the unitary, single-piece versions, the entirety of the mixing apparatus  100 ,  900  may be manufactured as a single object. 
     In either version, the mixing apparatus  100 ,  900  may be 3D printed using a plastic or a metallic material. Regarding plastics, the components may be 3D printed, for example, in nylon or a polycarbonate material, e.g., PVC, and/or other compatible filament with high tensile strength to withstand the force of water flowing at high speeds. The selected 3D print material should also be compatible with the chosen gas to be injected. For example, polycarbonate is rated for ozone, while nylon is not. With respect to metallic materials, the components may be 3D printed, for example, in stainless steel. 
     The mixing apparatuses  100 ,  900  may be manufactured using techniques other than 3D printing. For example, the mixing apparatuses  100 ,  900  may be manufactured using a number of injection molds to form separate portions of the assembly, which portions are then joined together to form a mixing apparatus  100 ,  900 . The portions may be formed of plastic and bonded together, or metal, e.g., coarse cast iron or aluminum, and welded together. 
     The mixing apparatuses  100 ,  900  may be manufactured in ½″, ¾″ and 1½″ sizes for use in varying systems, where the size corresponds to the interior diameter of the apparatus at the liquid input end and the liquid output end. Larger liquid flows may be accommodated by an array of liquid/gas mixing apparatuses enclosed in a larger pipe. In this configuration, a portion of a large liquid flow is divided into separate portions, each of which passes through a liquid/gas mixing apparatus. Testing of a ½″ size ultra-fine bubble generating liquid/gas mixing apparatus configured as disclosed herein, has generated ultra-fine bubbles having a size ˜100 nanometers and concentration of 265,000,000 bubbles per ml, as measured using a NanoSight NS300 particle analyzer. 
     The foregoing description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but instead are to be accorded the full scope consistent with the claim language. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims.