Abstract:
A micro-nozzle for generating micro-bubbles. The micro-nozzle includes a liquid inlet forming a liquid path, a gas inlet, and a constricting wall positioned in the liquid path and shaped to abruptly constrict said liquid path to a width of less than approximately 20 um and then gradually diverge.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit under 35 USC 119(e) to U.S. Provisional Application No. 60/560,568, filed Apr. 8, 2004, which is incorporated by reference herein in its entirety. 

   STATEMENT REGARDING FEDERAL SPONSORED RESEARCH 
   N/A 
   BACKGROUND OF INVENTION 
   The present invention relates to devices, particularly nozzles, for producing very fine bubbles of gas in a liquid medium. 
   There are many uses for the production of very fine gas bubbles in a liquid medium. One such use is for the mechanical oxygenation of blood (as opposed to oxygenation by lungs or other biological processes). It is important for blood oxygenation devices that bubble size be sufficiently small and consistently be at or below the required size. Additionally, it is advantageous if the oxygenation device is sufficiently small that it can be inserted into the larger human veins. 
   SUMMARY OF INVENTION 
   The present invention provides a micro-nozzle for generating micro-bubbles. The micro-nozzle includes a liquid inlet forming a liquid path, a gas inlet, and a constricting wall positioned in the liquid path and shaped to abruptly constrict said liquid path to a width of less than approximately 20 um and then gradually diverge. 
   The present invention also includes a device for the generation of micro-bubbles. The device includes a device body and a plurality of micro-nozzles formed on the device body. The plurality of micro-nozzles have a liquid inlet forming a liquid path, a gas inlet, and a constricting wall positioned in the liquid path and shaped to abruptly constrict the liquid path to a width of less than approximately 20 um and then gradually diverge. Liquid and gas passages communicate through the device body with the liquid and gas inlets of the micro-nozzles. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a top view of one embodiment of the micro-nozzle of the present invention. 
       FIG. 1A  illustrates the micro-nozzle embodiment of  FIG. 1 , but formed with a symmetrical island structure. 
       FIG. 2  is a top view of another embodiment of the micro-nozzle of the present invention. 
       FIG. 3  illustrates the micro-nozzle embodiment of  FIG. 2 , but formed with a symmetrical island structure. 
       FIG. 4  is a side view of one embodiment of a micro-bubble generating device constructed of multiple nozzle disks. 
       FIG. 5  is a top view of a nozzle disk seen in  FIG. 4 . 
       FIG. 6A  is a top view of an enlarged section of a nozzle disk containing multiple micro-nozzles similar to that seen in  FIG. 3 . 
       FIGS. 6B ,  6 C and  6 D are sectional views of the nozzle disk seen in  6 A. 
       FIG. 6E  is a top view of an enlarged section of a nozzle disk containing multiple micro-nozzles similar to that seen in  FIG. 1A . 
   

   DETAILED DESCRIPTION OF INVENTION 
   The primary element of the micro-bubble generating device of the present invention is a novel micro-nozzle.  FIG. 1  illustrates one embodiment of the micro-nozzle  1  of the present invention. Micro-nozzle  1  will typically have a liquid inlet  3  which forms a liquid path  4  between bottom wall  10  and top wall  11 . In the embodiment of  FIG. 1 , top and bottom walls  11  and  10  are shown as shaded areas whereas the channel formed by liquid inlet  3  and liquid path  4  is unmarked. In the embodiment shown, the depth of this channel (i.e. the dimension perpendicular to the plane in which  FIG. 1  is drawn) may be approximately 10 um. Liquid path  4  generally flows undisturbed through the unconstricted region  13  until it approaches constriction point  12 . Unconstricted area  13  is “unconstricted” in the sense that is it substantially more open than constriction point  12  and generally conducive to uniform flow characteristics. For example, in the embodiment of  FIG. 1 , unconstricted area  13  is an uniform channel approximately 40 um wide. However, it may be advantageous to make unconstricted area  13  as wide as possible considering the overall nozzle size constraints. Unconstricted region  13  abruptly ends as the liquid path  4  encounters downward extending front wall or constricting wall  16  which extends downward to constriction point  12 . The actual width of the liquid path at constriction point  12  may vary. It is believed that there is a general correlation between the width of constriction point  12  and the size of the micro-bubble which exits micro-nozzle  1 . In order to produce micro-bubbles that are approximately 20 um or less in diameter, it is preferred that constriction point  12  should be no greater than approximately 20 um. Likewise, to produce micro-bubbles that are approximately 10 um or less in diameter, it is preferred that constriction point  12  should be no greater than approximately 10 um. 
   A gas path  6  will join liquid path  4  at gas inlet  5 . While not necessarily critical to all embodiments, a preferred embodiment of micro-nozzle  1  will position gas inlet  5  approximately at constriction point  12  and even more preferably at the beginning of constriction point  12 . The “beginning” of constriction point  12  is where fluid path  4  suddenly constricts from the unconstricted area  13 . In the embodiment of  FIG. 1  where constriction point  12  is 10 um, fluid inlet  3  width is approximately 40 um and gas inlet  5  is approximately 2 um. 
   As fluid path  4  continues past constriction point  12 , it enters divergent region  14 . Divergent region  14  is formed by diverging wall  9  inclining away from bottom wall  10 . The rate at which diverging wall  9  diverges may vary in different embodiments, but in one preferred embodiment, the angle “alpha” that diverging wall  9  makes relative to bottom wall  10  is less than about 45°. In a more preferred embodiment, angle alpha is 12° or less in order to promote laminar flow. In a preferred embodiment, divergent region  14  will extend for approximately 500 um or more beyond constriction point  12 . 
     FIG. 2  illustrates an alternative embodiment of micro-nozzle  1 . Here a diverging wall  9  takes a parabolic shape in the divergent region  14 . This parabolic shape in essence allows diverging wall  9  to smoothly transition from a divergence angel of 0° to 90°. As in  FIG. 1 , this embodiment positions gas inlet  5  at the beginning of constriction point  12  and sizes constriction point  12  and gas inlet  5  at 10 um and 2 um respectively. The gas inlet location is in a region where the Bernoulli equation suggest the lowest side-arm (static) pressure, e.g. the narrowest point of the constriction. Naturally, diverging wall  9  may take many different shapes. Alternative embodiments could include a semicircular constricting wall as suggested by dashed line  9   a.    
     FIG. 3  shows a compact double nozzle arrangement which comprises  FIG. 2  and its mirror image along the centerline A. Here dual diverging walls  9  are formed by island structure  15  in liquid path  4 , which in the embodiment shown is approximately 80 um in width (i.e. the liquid path  4 ). It can be seen that diverging walls  9  take a parabolic shape to form two constriction points  12   a  and  12   b . This symmetrical compact pattern lends itself to efficient replication on a large scale as shown below. Naturally those skilled in the art will recognize many variations of micro nozzles  1  seen in  FIGS. 1-3  and all such variations are within the scope of the present invention. For example,  FIG. 1A  illustrates an island structure formed of a pair of linear diverging walls such as seen in  FIG. 1 . 
   The rate at which fluid and gas are supplied to micro-nozzle  1  may also influence the size of bubbles generated. For example, with a micro-nozzle having the dimensions given relative to  FIGS. 1 and 2 , it is preferred to maintain a gas flow rate below approximately 1 uL/min and a fluid a fluid velocity of at least 0.33 m/sec. In one preferred embodiment, both the gas and fluid will be supplied at a pressure of approximately 2 p.s.i. It is also believed that employing saline as the liquid component facilitates smaller bubbles based on surface tension data. When the gas component is oxygen and the liquid is an oxygen saturated saline solution the bubble tends to remain filled with oxygen rather than experiencing an inrush of nitrogen. 
   Another aspect of the present invention is a device for generating micro-bubbles which incorporates micro-nozzle  1 . In one embodiment, the micro-bubble generator  20  will take a cylindrical shape and will be formed of a series of nozzle disks  21  stacked atop one another as suggested in  FIG. 4 . Each nozzle disk  21  will contain a plurality of nozzles  1  as seen in  FIG. 5  and will include a center opening which forms a liquid passage  7 .  FIG. 4  suggests how a continuous liquid passage  7  will be formed when a series of nozzle disks  21  are stacked atop one another.  FIGS. 6A-6D  better illustrate the details of how nozzles  1  will be formed on nozzle disk  21 .  FIG. 6A  shows an enlarged view of one arc or section of nozzle disk  21  which includes several nozzles  1 . Liquid paths  4  will be formed on disk  21  with divider wall structures  22  being left between adjacent liquid paths  4 . Each liquid path  4  will originate at and communicate with liquid passage  7 . The opposite end of each liquid path  4  will contain an island structure  15  forming two micro-nozzles  1  in the same manner as described in reference to  FIG. 3 . 
   Within each divider wall  22 , there will be a gas passage  8  formed through disk  21  and communicating with a restricted gas path  25  running down the upper half of divider wall  22 . Again viewing  FIG. 4 , it can be seen how gas passage  8  is a continuous channel through bubble generating device  20  when nozzle disks  21  are stacked. In the preferred embodiment seen in  FIG. 6A , it is shown how the restricted gas path  25  opens up to an enlarged chamber  24  which terminates at end walls  23 . However, a small cut running parallel to endwall  23  will separate divider walls  22  from end walls  23  and will form gas inlets  5  on each side of divider wall  22 . It is believed that the transition from restricted gas path  25  to the more open chambers  24 , together with the compressibility of the gas and resistance in restricted path  25 , induces an oscillatory effect which assists in the creation of discrete bubbles. In one preferred embodiment, nozzle disks  21  could be formed of poly methyl methacrylate (PMMA). Such PMMA nozzle disks  21  could be made through a conventional molding/stamping process such as disclosed in  Fundamentally of Microfabrication , Marc Madou, CRC Press, 1997, Chapter 6, which is incorporated by reference herein.  FIG. 6C  illustrates cross-section BB and how gas passages  8  will be formed through nozzle disk  21  between adjacent liquid paths  4 . It will be apparent from  FIG. 4  how the bottom of each nozzle disk  21  acts as a cover for the nozzle disk  21  below it. It can further be understood that when the nozzle disks  21  are in a stacked configuration such as shown in  FIG. 4 , the individual nozzle outlets  30  (see  FIG. 6A ) will be formed on (i.e., open onto) the outer surface of the cylindrical body of micro-bubble generator  20 .  FIG. 6D  illustrates how the gas path is restricted in the area of path  25 . The cross-section CC of  FIG. 6D  and AA of  FIG. 6B  suggest how the embodiment shown would have liquid paths 4 approximately 10 μm deep, with a 80 μm width similar to that shown in  FIG. 3 , and an overall disk thickness of 20-30 μm. Alternatively,  FIG. 6E  illustrates a structure similar to  6 A, but the island structure  15  is constructed in accordance with  FIGS. 1 and 1A  as opposed to  FIGS. 2 and 3 . 
   In the embodiment of  FIGS. 4-6 , nozzle disk  21  could be a plastic wafer or washer type structure with the various channels and structures creating micro-nozzles  2  being formed by conventional lithographical methods. Of course, nozzle disks  21  could be formed of any other material and any other machining technique which allowed the creation of the micro-nozzles  1 . Alignment of adjacent nozzle disks could be accomplished by placing an alignment tab or notch on the disks on the liquid inflow side (not shown in the figures) and using an jig for assembly. 
   The number of double micro-nozzles  1  on each nozzle disk  21  and the number of nozzle disks  21  stacked to form the bubble generation device  20  could vary greatly depending on various design parameters. As one illustrative example, if bubble generation device  20  is intended to oxygenate blood by being placed in a human vein, it may be considered that a 70 kg human at rest requires approximately 250 ml/min of oxygen (at 1 atmosphere pressure and 23° C.). It is calculated from the geometry that the STP gas volume of a 5 um radius bubble is 6.683×10 −9  ml, considering the surface tension. It is also believed that double micro-nozzle  1  embodiment shown in  FIG. 3  is capable of generating approximately 10,000 bubbles per second, thus requiring approximately 6.235×10 5  double micro-nozzles to meet the required oxygenation rate. A nozzle disk  21  approximately 0.25 inches in diameter is capable of containing approximately 90 double micro-nozzles around its perimeter, thus, 6.982×10 3  nozzle disks would be required. If each nozzle disk  21  is approximately 20 um thick, the overall bubble generating device  20  such as seen in  FIG. 4  will have a height “h” of approximately 5.45 inches. Alternatively, if designing for 15 um bubbles, then the device height may be reduced allowing the use of thicker, sturdier nozzle disks. For example, designing for 15 um bubbles and using thirty micron thick nozzle disks would allow construction of a micro-bubble generating device with a height of approximately 2.6 inches in length. 
   Although the present invention has been described in terms of specific embodiments, those skilled in the art will recognize many obvious variations and modifications. All such variations and modifications are intended to come within the scope of the following claims.