Abstract:
A device and method for generating micro bubbles in a liquid. The method comprises the steps of: providing a flow-through channel containing at least two local constrictions of flow therein; passing the liquid at a velocity of at least at least 12 m/sec through a first local constriction of flow to create a first hydrodynamic cavitation field downstream from the first local constriction of flow; introducing a gas into the liquid in the first local constriction of flow, thereby creating gas-filled cavitation bubbles; collapsing the gas-filled cavitation bubbles formed in the first hydrodynamic cavitation field to dissolve the gas into the liquid, thereby forming a gas-saturated liquid; passing the gas-saturated liquid through a second local constriction of flow to create a second hydrodynamic cavitation field downstream from the second local constriction of flow; and extracting the dissolved gas from the gas-saturated liquid, thereby generating micro bubbles in the liquid.

Description:
RELATED APPLICATION  
       [0001]     This application is a continuation-in-part application of U.S. Ser. No. 10/461,698 filed on Jun. 13, 2003. 
     
    
     BACKGROUND  
       [0002]     The present invention relates to a device and process for generating micro bubbles in a liquid using hydrodynamic cavitation.  
         [0003]     Because micro bubbles have a greater surface area than larger bubbles, micro bubbles can be used in a variety of applications. For example, micro bubbles can be used in mineral recovery applications utilizing the floatation method where particles of minerals can be fixed to floating micro bubbles to bring them to the surface. Other applications include using micro bubbles as carriers of oxidizing agents to treat contaminated groundwater or using micro bubbles in the treatment of waste water. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     In the accompanying drawings which are incorporated in and constitute a part of the specification, embodiments of a device and method are illustrated which, together with the detailed description given below, serve to describe example embodiments of the device and method. It will be appreciated that the illustrated boundaries of elements (e.g., boxes or groups of boxes) in the figures represent one example of the boundaries. Also, it will be appreciated that one element may be designed as multiple elements or that multiple elements may be designed as one element. Furthermore, an element shown as an internal component of another element may be implemented as an external component and vice versa.  
         [0005]     Like elements are indicated throughout the specification and drawings with the same reference numerals, respectively. Moreover, the drawings are not drawn to scale and the proportions of certain parts have been exaggerated for convenience of illustration.  
         [0006]      FIG. 1  is a longitudinal cross-section of one embodiment of a hydrodynamic cavitation device  10  for generating micro bubbles in a liquid;  
         [0007]      FIG. 2  is a longitudinal cross-section of another embodiment of a hydrodynamic cavitation device  200  for generating micro bubbles in a liquid;  
         [0008]      FIG. 3  is a longitudinal cross-section of another embodiment of a hydrodynamic cavitation device  300  for generating micro bubbles in a liquid;  
         [0009]      FIG. 4  is a longitudinal cross-section of another embodiment of a hydrodynamic cavitation device  400  for generating micro bubbles in a liquid; and  
         [0010]      FIG. 5  is a longitudinal cross-section of another embodiment of a hydrodynamic cavitation device  500  for generating micro bubbles in a liquid. 
     
    
     DETAILED DESCRIPTION  
       [0011]     Illustrated in  FIG. 1  is a longitudinal cross-section of one embodiment of a hydrodynamic cavitation device  10  for generating micro bubbles in a liquid. The device  10  includes a wall  15  having an inner surface  20  that defines a flow-through channel or chamber  25  having a centerline C L . For example, the wall  15  can be a cylindrical wall that defines a flow-through channel having a circular cross-section. It will be appreciated that the cross-section of flow-through channel  25  may take the form of other geometric shapes such as square, rectangular, hexagonal, or any other complex shape. The flow-through channel  25  can further include an inlet  30  configured to introduce a liquid into the device  10  along a path represented by arrow A and an outlet  35  configured to exit the liquid from the device  10 .  
         [0012]     With further reference to  FIG. 1 , in one embodiment, the device  10  can further include multiple cavitation generators that generate a cavitation field downstream from each cavitation generator. For example, the device  10  can include two stages of hydrodynamic cavitation where a first cavitation generator can be a first baffle  40  and a second cavitation generator can be a second baffle  45 . It will be appreciated that any number of stages of hydrodynamic cavitation can be provided within the flow-through channel  25 . Furthermore, it will be appreciated that other types of cavitation generators may be used instead of baffles such as a Venturi tube, nozzle, orifice of any desired shape, or slot.  
         [0013]     In one embodiment, the second baffle  45  is positioned within the flow-through channel downstream from the first baffle  40 . For example, the first and second baffles  40 ,  45  can be positioned substantially along the centerline CL of the flow-through channel  25  such that the first baffle  40  is substantially coaxial with the second baffle  45 .  
         [0014]     To vary the degree and character of the cavitation fields generated downstream from the first and second baffles  40 ,  45 , the first and second baffles  40 ,  45  can be embodied in a variety of different shapes and configurations. For example, the first and second baffles  40 ,  45  can be conically shaped where the first and second baffles  40 ,  45  each include a conically-shaped surface  50   a,    50   b,  respectively, that extends into a cylindrically-shaped surface  55   a,    55   b,  respectively. The first and second baffles  40 ,  45  can be oriented such that the conically-shaped portions  50   a,    50   b,  respectively, confront the fluid flow. It will be appreciated that the first and second baffles  40 ,  45  can be embodied in other shapes and configurations such as the ones disclosed in U.S. Pat. No. 5,969,207, issued on Oct. 19, 1999, which is hereby incorporated by reference in its entirety herein. Of course, it will be appreciated that the first baffle  40  can be embodied in one shape and configuration, while the second baffle  45  can be embodied in a different shape and configuration.  
         [0015]     To retain the first baffle  40  within the flow-through channel  25 , the first baffle  40  can be connected to a plate  60  via a shaft  65 . It will be appreciated that the plate  60  can be embodied as a disk when the flow-through channel  25  has a circular cross-section, or the plate  60  can be embodied in a variety of shapes and configurations that can match the cross-section of the flow-through channel  25 . The plate  60  can be mounted to the inside surface  20  of the wall  15  with screws or any other attachment means. The plate  60  can include a plurality of orifices  70  configured to permit liquid to pass therethrough. It will be appreciated that that a crosshead, post, propeller or any other fixture that produces a minor loss of liquid pressure can be used instead of the plate  60  having orifices  70 . To retain the second baffle  45  within the flow-through channel  25 , the second baffle  45  can be connected to the first baffle  40  via a stem or shaft  75  or any other attachment means.  
         [0016]     In one embodiment, the first and second baffles  40 ,  45  can be configured to be removable and replaceable by baffles embodied in a variety of different shapes and configurations. It will be appreciated that the first and second baffles  40 ,  45  can be removably mounted to the stems  65 ,  75 , respectively, in any acceptable fashion. For example, each baffle  40 ,  45  can threadly engage each stem  65 ,  75 , respectively.  
         [0017]     In one embodiment, the first baffle  40  can be configured to generate a first hydrodynamic cavitation field  80  downstream from the first baffle  40  via a first local constriction  85  of liquid flow. For example, the first local constriction  85  of liquid flow can be an area defined between the inner surface  20  of the wall  15  and the cylindrically-shaped surface  55   a  of the first baffle  40 . Also, the second baffle  45  can be configured to generate a second hydrodynamic cavitation field  90  downstream from the second baffle  45  via a second local constriction  95  of liquid flow. For example, the second local constriction  95  can be an area defined between the inner surface  20  of the wall  15  and the cylindrically-shaped surface  55   b  of the second baffle  45 . Thus, if the flow-through channel  25  has a circular cross-section, the first and second local constrictions  85 ,  95  of liquid flow can be characterized as first and second annular orifices, respectively. It will be appreciated that if the cross-section of the flow-through channel  25  is any geometric shape other than circular, then each local constriction of flow may not be annular in shape. Likewise, if a baffle is not circular in cross-section, then each corresponding local constriction of flow may not be annular in shape.  
         [0018]     In one embodiment, the size of each local constriction  85 ,  95  is sufficient to increase the velocity of the fluid flow to a minimum velocity necessary to achieve hydrodynamic cavitation (hereafter the “minimum cavitation velocity”), which is dictated by the physical properties of the fluid being processed (e.g., viscosity, temperature, etc.). For example, the size of each local constriction  85 ,  95 , or any local constriction of fluid flow discussed herein, can be dimensioned in such a manner so that the cross-section area of each local constriction of fluid flow would be at most about 0.6 times the diameter or major diameter of the cross-section of the flow-through channel. The minimum cavitation velocity of a fluid is about 12 m/sec. On average, and for most hydrodynamic fluids, the minimum cavitation velocity is about 18 m/sec.  
         [0019]     With further reference to  FIG. 1 , the flow-through channel  25  can further include a port  97  for introducing a gas into the flow-through channel  25  along a path represented by arrow B. For example, the gas can be air, oxygen, nitrogen, hydrogen, ozone, or steam. In one embodiment, the port  97  can be disposed in the wall  15  and positioned adjacent the first local constriction  85  of flow to permit the introduction of the gas into the liquid in the first local constriction  85  of flow. For example, the gas can be introduced into the liquid in a region of reduced liquid pressure in the first local constriction  85  of flow. It will be appreciated that the port  97  can be disposed in the wall  15  anywhere along the axial length first local constriction  85  of flow. Furthermore, it will be appreciated that any number of ports can be provided in the wall  15  to introduce gas into the first local constriction  85  or the port  97  can be embodied as a slot to introduce gas into the first local constriction  85 .  
         [0020]     In operation of the device  10  illustrated in  FIG. 1 , the liquid enters the flow-through channel  25  via the inlet  30  and moves through the orifices  70  in the plate  60  along the fluid path A. The liquid can be fed through the flow-through channel  25  and maintained at any flow rate sufficient to generate a hydrodynamic cavitation field downstream from both the first and second baffles  40 ,  45 . As the liquid moves through the flow-through channel  25 , the gas is introduced into the first local constriction  85  via the port  97 , thereby mixing the gas with the liquid as the liquid passes through the first local constriction  85 . The gas can be introduced into the liquid in the first local constriction  85  and maintained at a flow rate that is different from the liquid flow rate and sufficient to control the collapse of cavitation bubbles formed in the hydrodynamic cavitation field. For example, a ratio between the gas volumetric flow rate and the liquid volumetric flow rate is about 0.1 or less. In other words, the ratio between the liquid volumetric flow rate and the gas volumetric flow rate can be at least about 10.  
         [0021]     While passing through the first local constriction  85 , the velocity of the liquid increases to the minimum cavitation velocity for the particular fluid being processed. The increased velocity of the liquid forms the first hydrodynamic cavitation field  80  downstream from the first baffle  40 , thereby generating cavitation bubbles that grow when mixed with the gas to form gas micro bubbles. Upon reaching an elevated static pressure zone, the gas micro bubbles can be partially or completely collapsed (or squeezed) thereby dissolving the gas into the liquid to form a gas-saturated liquid.  
         [0022]     Once the gas micro bubbles are generated after the first stage of hydrodynamic cavitation, the gas-saturated liquid continues to move towards the second baffle  45 . While passing through the second local constriction  95 , the velocity of the gas-saturated liquid increases to a minimum cavitation velocity of the liquid. The increased velocity of the gas-saturated liquid, forms the second hydrodynamic cavitation field  90  downstream from the second baffle  45  thereby generating cavitation bubbles. Upon reaching an elevated static pressure zone, a vacuum is created in the second hydrodynamic cavitation field  90  to extract the dissolved gas from the gas-saturated liquid, thereby generating micro bubbles. These micro bubbles are smaller in size and more uniform than the micro bubbles produced after the first stage of hydrodynamic cavitation. The liquid and micro bubbles then exits the flow-through channel  25  via the outlet  35 .  
         [0023]     Illustrated in  FIG. 2  is a longitudinal cross-section of another embodiment of a hydrodynamic cavitation device  200  for generating micro bubbles in a liquid. The device  200  includes a wall  215  having an inner surface  220  that defines a flow-through channel or chamber  225  having a centerline C L . For example, the wall  215  can be a cylindrical wall that defines a flow-through channel having a circular cross-section. It will be appreciated that the cross-section of flow-through channel  225  may take the form of other geometric shapes such as square, rectangular, hexagonal, or any other complex shape. The flow-through channel  225  can further include an inlet  230  configured to introduce a liquid into the device  200  along a path represented by arrow A and an outlet  235  configured to exit the liquid from the device  200 .  
         [0024]     With further reference to  FIG. 2 , in one embodiment, the device  200  can further include multiple cavitation generators that generate a cavitation field downstream from each cavitation generator. For example, the device  200  can include two stages of hydrodynamic cavitation where a first cavitation generator can be a first plate  240  having an orifice  245  disposed therein to produce a first local constriction of liquid flow and a second cavitation generator can be a second plate  250  having an orifice  255  disposed therein to produce a second local constriction of liquid flow. It will be appreciated that any number of stages of hydrodynamic cavitation can be provided within the flow-through channel  225 . Furthermore, it will be appreciated that other types of cavitation generators may be used instead of plates having orifices disposed therein such as baffles. As discussed above, the size of the local constrictions of flow are sufficient to increase the velocity of the liquid flow to the minimum cavitation velocity for the fluid being processed.  
         [0025]     Each plate  240 ,  250  can be mounted to the wall  215  with screws or any other attachment means to retain each plate  240 ,  250  in the flow-through channel  225 . In another embodiment, the first and second plates  240 ,  250  can include multiple orifices disposed therein to produce multiple local constrictions of fluid flow. It will be appreciated that each plate can be embodied as a disk when the flow-through channel  225  has a circular cross-section, or each plate can be embodied in a variety of shapes and configurations that can match the cross-section of the flow-through channel  225 .  
         [0026]     In one embodiment, the second plate  250  is positioned within the flow-through channel downstream from the first plate  240 . For example, the first and second plates  240 ,  250  can be positioned substantially along the centerline CL of the flow-through channel  225  such that the orifice  245  in the first plate  240  is substantially coaxial with the orifice in the second plate  250 .  
         [0027]     To vary the degree and character of the cavitation fields generated downstream from the first and second plates  240 ,  250 , the orifices  245 ,  255  can be embodied in a variety of different shapes and configurations. The shape and configuration of each orifice  245 ,  255  can significantly affect the character of the cavitation flow and, correspondingly, the quality of crystallization. In one embodiment, the orifices  245 ,  255  can have a circular cross-section. It will be appreciated that each orifice  245 ,  255  can be configured in the shape of a Venturi tube, nozzle, orifice of any desired shape, or slot. Further, it will be appreciated that the orifices  245 ,  255  can be embodied in other shapes and configurations such as the ones disclosed in U.S. Pat. No. 5,969,207, which is hereby incorporated by reference in its entirety herein. Of course, it will be appreciated that the orifice  245  disposed in the first plate  240  can be embodied in one shape and configuration, while the orifice  255  disposed in the second plate  250  can be embodied in a different shape and configuration.  
         [0028]     In one embodiment, the orifice  245  disposed in the first plate  240  can be configured to generate a first hydrodynamic cavitation field  260  downstream from the orifice  245 . Likewise, the orifice  255  disposed in the second plate  250  can be configured to generate a second hydrodynamic cavitation field  265  downstream from the orifice  255 .  
         [0029]     With further reference to  FIG. 2 , the flow-through channel  225  can further include a port  270  for introducing a gas into the flow-through channel  225  along a path represented by arrow B. For example, the gas can be air, oxygen, nitrogen, hydrogen, ozone, or steam. In one embodiment, the port  270  can be disposed in the wall  215  and extended through the plate  240  to permit the introduction of the gas into the liquid in the first local constriction of flow. For example, the gas can be introduced into the liquid in a region of reduced liquid pressure in the first local constriction of flow. It will be appreciated that the port  270  can be disposed in the wall  215  anywhere along the axial length of the orifice  245  disposed in the first plate  240 . Furthermore, it will be appreciated that any number of ports can be provided in the wall  215  to introduce gas into the orifice  245  disposed in the first plate  240  or the port  270  can be embodied as a slot to introduce gas into the orifice  245  disposed in the first plate  240 .  
         [0030]     In operation of the device  200  illustrated in  FIG. 2 , the liquid is fed into the flow-through channel  225  via the inlet  230  along the path A. The liquid can be fed through the flow-through channel  225  and maintained at any flow rate sufficient to generate a hydrodynamic cavitation field downstream from both the first and second plates  240 ,  250 . As the liquid moves through the flow-through channel  225 , the gas is introduced into the orifice  245  disposed in the first plate  240  via the port  270  thereby mixing the gas with the liquid as the liquid passes through the orifice  245  disposed in the first plate  240 . The gas can be introduced into the liquid in the orifice  245  disposed in the first plate  240  and maintained at a flow rate that is different from the liquid flow rate and sufficient to control the collapse of cavitation bubbles formed in the hydrodynamic cavitation field. For example, a ratio between the volumetric gas flow rate and the volumetric liquid flow rate is about  0 . 1  or less. In other words, the ratio between the volumetric liquid flow rate and the volumetric gas flow rate can be at least about 10.  
         [0031]     While passing through the orifice  245  disposed in the first plate  240 , the velocity of the liquid increases to a minimum cavitation velocity for the particular liquid being processed. The increased velocity of the liquid forms the first hydrodynamic cavitation field  260  downstream from the first plate  240 , thereby generating cavitation bubbles that grow when mixed with the gas to form gas micro bubbles. Upon reaching an elevated static pressure zone, the gas micro bubbles can be partially or completely collapsed (or squeezed), thereby dissolving the gas into the liquid to form a gas-structured liquid.  
         [0032]     Once the gas micro bubbles are generated after the first stage of hydrodynamic cavitation, the gas-saturated liquid continue to move towards the second plate  250 . While passing through the orifice  255  disposed in the second plate  250 , the velocity of the gas-saturated liquid increases to the minimum cavitation velocity of the liquid. The increased velocity of the gas-saturated liquid forms the second hydrodynamic cavitation field  265  downstream from the second plate  250 , thereby generating cavitation bubbles. Upon reaching an elevated static pressure zone, a vacuum is created in the second hydrodynamic cavitation field  265  to extract the dissolved gas from the gas-saturated liquid thereby generating micro bubbles. These micro bubbles are smaller in size and more uniform than the micro bubbles produced after the first stage of hydrodynamic cavitation. The liquid and micro bubbles then exits the flow-through channel  225  via the outlet  235 .  
         [0033]     Illustrated in  FIG. 3  is a longitudinal cross-section of another embodiment of a hydrodynamic cavitation device  300  for generating micro bubbles in a liquid. The device  300  includes a wall  315  having an inner surface  320  that defines a flow-through channel or chamber  325  having a centerline C L . The flow-through channel  325  can further include an inlet  330  configured to introduce a liquid into the device  300  along a path represented by arrow A and an outlet  335  configured to exit the liquid from the device  300 .  
         [0034]     With further reference to  FIG. 3 , in one embodiment, the device  300  can further include multiple cavitation generators that generate a cavitation field downstream from each cavitation generator. For example, the device  300  can include two stages of hydrodynamic cavitation where a first cavitation generator can be a baffle  340  and a second cavitation generator can be a plate  345  having an orifice  350  disposed therein to produce a local constriction of liquid flow. It will be appreciated that the plate  355  can be embodied as a disk when the flow-through channel  325  has a circular cross-section, or the plate  355  can be embodied in a variety of shapes and configurations that can match the cross-section of the flow-through channel  325 . Further, it will be appreciated that any number of stages of hydrodynamic cavitation can be provided within the flow-through channel  325 . As discussed above, the size of the local constrictions of flow are sufficient to increase the velocity of the fluid flow to a minimum cavitation velocity for the fluid being processed.  
         [0035]     In one embodiment, the plate  345  is positioned within the flow-through channel downstream from the baffle  340 . For example, the baffle  340  and the plate  345  can be positioned substantially along the centerline CL of the flow-through channel  325  such that the baffle  340  is substantially coaxial with the orifice  350  disposed in the plate  345 .  
         [0036]     To retain the baffle  340  within the flow-through channel  325 , the baffle  340  can be connected to a plate  355  via a stem or shaft  360 . It will be appreciated that the plate  355  can be embodied as a disk when the flow-through channel  325  has a circular cross-section, or the plate  355  can be embodied in a variety of shapes and configurations that can match the cross-section of the flow-through channel  325 . The plate  355  can be mounted to the inside surface  320  of the wall  315  with screws or any other attachment means. The plate  355  can include a plurality of orifices  365  configured to permit liquid to pass therethrough. To retain the plate  345  within the flow-through channel  325 , the plate  345  can be connected to the wall  315  with screws or any other attachment means.  
         [0037]     In one embodiment, the baffle  340  can be configured to generate a first hydrodynamic cavitation field  370  downstream from the baffle  340  via a first local constriction  375  of liquid flow. For example, the first local constriction  375  of liquid flow can be an area defined between the inner surface  320  of the wall  315  and an outside surface of the baffle  340 . Also, the orifice  350  disposed in the plate  345  can be configured to generate a second hydrodynamic cavitation field  380  downstream from the orifice  350 .  
         [0038]     With further reference to  FIG. 3 , the flow-through channel  325  can further include a port  385  for introducing a gas into the flow-through channel  325  along a path represented by arrow B. In one embodiment, the port  385  can be disposed in the wall  315  and positioned adjacent the first local constriction  375  of flow to permit the introduction of the gas into the liquid in the first local constriction  375  of flow. For example, the gas can be introduced into the liquid in a region of reduced liquid pressure in the first local constriction of flow. It will be appreciated that the port  385  can be disposed in the wall  315  anywhere along the axial length first local constriction  375  of flow. Furthermore, it will be appreciated that any number of ports can be provided in the wall  315  to introduce the gas into the first local constriction  375  or the port  385  can be embodied as a slot to introduce the gas into the first local constriction  375 .  
         [0039]     In operation of the device  300  illustrated in  FIG. 3 , the liquid enters the flow-through channel  325  via the inlet  330  and moves through the orifices  365  in the plate  360  along the path A. The liquid can be fed through the flow-through channel  325  and maintained at any flow rate sufficient to generate a hydrodynamic cavitation field downstream from both the first and second cavitation generators. As the liquid moves through the flow-through channel  325 , the gas is introduced into the first local constriction  375  via the port  385  thereby mixing the gas with the liquid as the liquid passes through the first local constriction  375 . The gas can be introduced into the liquid in the first local constriction  375  and maintained at a flow rate that is different from the liquid flow rate and sufficient to control the collapse of cavitation bubbles formed in the hydrodynamic cavitation field. For example, a ratio between the gas volumetric flow rate and the liquid volumetric flow rate is about 0.1 or less. In other words, the ratio between the liquid volumetric flow rate and the gas volumetric flow rate can be at least about 10.  
         [0040]     While passing through the first local constriction  375 , the velocity of the liquid increases to a minimum cavitation velocity for the particular liquid being processed. The increased velocity of the liquid forms the first hydrodynamic cavitation field  370  downstream from the baffle  340 , thereby generating cavitation bubbles that grow when mixed with the gas to form gas micro bubbles. Upon reaching an elevated static pressure zone, the gas micro bubbles can be partially or completely collapsed (or squeezed), thereby dissolving the gas into the liquid to form a gas-saturated liquid.  
         [0041]     Once the gas micro bubbles are generated after the first stage of hydrodynamic cavitation, the gas-saturated liquid continues to move towards the plate  350 . While passing through the orifice  350  disposed in the plate  345 , the velocity of the gas-saturated liquid increases to the minimum cavitation velocity of the liquid. The increased velocity of the gas-saturated liquid forms the second hydrodynamic cavitation field  380  downstream from the plate  345 , thereby generating cavitation bubbles. Upon reaching an elevated static pressure zone, a vacuum is created in the second hydrodynamic cavitation field  380  to extract the dissolved gas from the gas-saturated liquid, thereby generating micro bubbles. The micro bubbles are smaller in size and more uniform than the micro bubbles produced after the first stage of hydrodynamic cavitation. The liquid and micro bubbles then exit the flow-through channel  325  via the outlet  335 .  
         [0042]     Illustrated in  FIG. 4  is a longitudinal cross-section of another embodiment of a hydrodynamic cavitation device  400  for generating micro bubbles in a liquid. The device  400  includes a wall  415  having an inner surface  420  that defines a flow-through channel or chamber  425  having a centerline C L . The flow-through channel  425  can further include an inlet  430  configured to introduce a liquid into the device  400  along a path represented by arrow A and an outlet  435  configured to exit the liquid from the device  400 . i 
         [0043]     With further reference to  FIG. 4 , in one embodiment, the device  400  can further include multiple cavitation generators that generate a cavitation field downstream from each cavitation generator. For example, the device  400  can include two stages of hydrodynamic cavitation where a first cavitation generator can be a plate  440  having an orifice  445  disposed therein to produce a local constriction of liquid flow and a second cavitation generator can be a baffle  450 . It will be appreciated that the plate  455  can be embodied as a disk when the flow-through channel  325  has a circular cross-section, or the plate  455  can be embodied in a variety of shapes and configurations that can match the cross-section of the flow-through channel  325 . Further, it will be appreciated that any number of stages of hydrodynamic cavitation can be provided within the flow-through channel  425 . As discussed above, the size of the local constrictions of flow are sufficient to increase the velocity of the fluid flow to a minimum cavitation velocity for the fluid being processed.  
         [0044]     In one embodiment, the plate  440  is positioned within the flow-through channel upstream from the baffle  450 . For example, the plate  440  and the baffle  450  can be positioned substantially along the centerline CL of the flow-through channel  425  such that the baffle  450  is substantially coaxial with the orifice  445  disposed in the plate  440 .  
         [0045]     To retain the plate  440  within the flow-through channel  425 , the plate  440  can be connected to the wall  415  with screws or any other attachment means. To retain the baffle  450  within the flow-through channel  425 , the baffle  450  can be connected to a plate  455  via a stem or shaft  460 . It will be appreciated that the plate  455  can be embodied as a disk when the flow-through channel  425  has a circular cross-section, or the plate  455  can be embodied in a variety of shapes and configurations that can match the cross-section of the flow-through channel  425 . The plate  455  can be mounted to the inside surface  420  of the wall  415  with screws or any other attachment means. The plate  455  can include a plurality of orifices  465  configured to permit liquid to pass therethrough.  
         [0046]     In one embodiment, the orifice  445  disposed in the plate  450  can be configured to generate a first hydrodynamic cavitation field  470  downstream from the orifice  245 . Also, the baffle  450  can be configured to generate a second hydrodynamic cavitation field  475  downstream from the baffle  450  via a local constriction  480  of liquid flow. For example, the local constriction  475  of liquid flow can be an area defined between the inner surface  420  of the wall  415  and an outside surface of the baffle  450 .  
         [0047]     With further reference to  FIG. 4 , the flow-through channel  425  can further include a port  485  for introducing a gas into the flow-through channel  425  along a path represented by arrow B. In one embodiment, the port  485  can be disposed in the wall  415  and extended through the plate  440  to permit the introduction of the gas into the liquid in the local constriction  480  of flow. For example, the gas can be introduced into the liquid in a region of reduced liquid pressure in the first local constriction  480  of flow. It will be appreciated that the port  485  can be disposed in the wall  415  anywhere along the axial length of the orifice  445  disposed in the plate  440 . Furthermore, it will be appreciated that any number of ports can be provided in the wall  415  to introduce gas into the orifice  445  disposed in the plate  440  or the port  485  can be embodied as a slot to introduce gas into the orifice  445  disposed in the plate  440 .  
         [0048]     In operation of the device  400  illustrated in  FIG. 4 , the liquid is fed into the flow-through channel  425  via the inlet  430  along the path A. The liquid can be fed through the flow-through channel  425  and maintained at any flow rate sufficient to generate a hydrodynamic cavitation field downstream from both the first and second cavitation generators. As the liquid moves through the flow-through channel  425 , the gas is introduced into the orifice  445  disposed in the plate  440  via the port  485  thereby mixing the gas with the liquid as the liquid passes through the orifice  445 . The gas can be introduced into the liquid in the orifice  445  disposed in the plate  440  and maintained at a flow rate that is different from the liquid flow rate and sufficient to control the collapse of cavitation bubbles formed in the hydrodynamic cavitation field. For example, a ratio between the gas volumetric flow rate and the liquid volumetric flow rate is about 0.1 or less. In other words, the ratio between the liquid volumetric flow rate and the gas volumetric flow rate can be at least about 10.  
         [0049]     While passing through the orifice  445  disposed in the plate  440 , the velocity of the liquid increases to a minimum cavitation velocity for the particular liquid being processed. The increased velocity of the liquid forms the first hydrodynamic cavitation field  470  downstream from the plate  440 , thereby generating cavitation bubbles that grow when mixed with the gas to form gas micro bubbles. Upon reaching an elevated static pressure zone, the gas micro bubbles can be partially or completely collapsed (or squeezed), thereby dissolving the gas into the liquid to form a gas-saturated liquid.  
         [0050]     Once the gas micro bubbles are generated after the first stage of hydrodynamic cavitation, the gas-saturated liquid continues to move towards the baffle  450 . While passing through the local constriction  480  of flow, the velocity of the gas-saturated liquid increases to the minimum cavitation velocity of the liquid. The increased velocity of the gas-saturated liquid forms the second hydrodynamic cavitation field  475  downstream from the baffle  450 , thereby generating cavitation bubbles. Upon reaching an elevated static pressure zone, a vacuum is created in the second hydrodynamic cavitation field  475  to extract the dissolved gas from the gas-saturated liquid thereby generating micro bubbles. These micro bubbles are smaller in size and more uniform than the micro bubbles produced after the first stage of hydrodynamic cavitation. The liquid and micro bubbles then exit the flow-through channel  425  via the outlet  435 .  
         [0051]     Illustrated in  FIG. 5  is a longitudinal cross-section of another embodiment of a hydrodynamic cavitation device  500  for generating micro bubbles in a liquid. The device  500  includes a wall  515  having an inner surface  520  that defines a flow-through channel or chamber  525  having a centerline C L . The flow-through channel  525  can further include an inlet  530  configured to introduce a liquid into the device  500  along a path represented by arrow A and an outlet  535  configured to exit the liquid from the device  500 .  
         [0052]     With further reference to  FIG. 5 , in one embodiment, the device  500  can further include multiple cavitation generators that generate a cavitation field downstream from each cavitation generator. For example, the device  500  can include two stages of hydrodynamic cavitation where a first cavitation generator can be a first baffle  540  and a second cavitation generator can be a second baffle  345 . It will be appreciated that any number of stages of hydrodynamic cavitation can be provided within the flow-through channel  525 .  
         [0053]     In one embodiment, the first baffle  545  is positioned within the flow-through channel  525  downstream from the first baffle  540 . For example, the first and second baffles  540 ,  545  can be positioned substantially along the centerline CL of the flow-through channel  525  such that the first baffle  540  is substantially coaxial with the second baffle  545 .  
         [0054]     To vary the degree and character of the cavitation fields generated downstream from the first and second baffles  540 ,  545 , the first and second baffles  540 ,  545  can be embodied in a variety of different shapes and configurations. It will be appreciated that the first and second baffles  540 ,  545  can be embodied in other shapes and configurations such as the ones disclosed in U.S. Pat. No. 5,969,207, issued on Oct. 19, 1999, which is hereby incorporated by reference in its entirety herein. Of course, it will be appreciated that the first baffle  540  can be embodied in one shape and configuration, while the second baffle  545  can be embodied in a different shape and configuration.  
         [0055]     To retain the first baffle  540  within the flow-through channel  525 , the first baffle  540  can be connected to a plate  550  via a stem or shaft  555 . The plate  550  can be mounted to the inside surface  520  of the wall  515  with screws or any other attachment means. The plate  550  can include at least one orifice  560  configured to permit liquid to pass therethrough. To retain the second baffle  545  within the flow-through channel  525 , the second baffle  545  can be connected to the first baffle  540  via a stem or shaft  565  or any other attachment means.  
         [0056]     In one embodiment, the first baffle  540  can be configured to generate a first hydrodynamic cavitation field  570  downstream from the first baffle  540  via a first local constriction  575  of liquid flow. For example, the first local constriction  575  of liquid flow can be an area defined between the inner surface  520  of the wall  515  and an outside surface of the first baffle  540 . Also, the second baffle  545  can be configured to generate a second hydrodynamic cavitation field  580  downstream from the second baffle  545  via a second local constriction  585  of liquid flow. For example, the second local constriction  585  can be an area defined between the inner surface  520  of the wall  515  and an outside surface of the second baffle  545 . As discussed above, the size of the local constrictions  575 ,  585  of flow are sufficient to increase the velocity of the fluid flow to a minimum cavitation velocity for the fluid being processed.  
         [0057]     With further reference to  FIG. 5 , the flow-through channel  525  can further include a fluid passage  590  for introducing a gas into the flow-through channel  525  along a path represented by arrow B. In one embodiment, the port  590  can be disposed in the wall  515  to permit the introduction of the gas into the liquid in the first local constriction  575  of flow. For example, the gas can be introduced into the liquid in a region of reduced liquid pressure in the first local constriction  575  of flow. Beginning at the wall  515 , the fluid passage  590  extends through the plate  550 , the stem  555 , and at least partially into the first baffle  540 . It will be appreciated that the fluid passage  595  can be embodied in any shape or path. In the first baffle  540 , the fluid passage terminates into at least one port  595  that extends radially from the C L  of the first baffle  540  and exits in the first local constriction  575  of flow. Furthermore, it will be appreciated that the port  595  can be disposed in the first baffle  540  anywhere along the axial length of the first local constriction  575  of flow. Furthermore, it will be appreciated that any number of ports can be provided in the first baffle to introduce gas into the first local constriction  575  of flow or the port  595  can be embodied as a slot to introduce gas into the first local constriction  575  of flow.  
         [0058]     In operation of the device  500  illustrated in  FIG. 5 , the liquid enters the flow-through channel  525  via the inlet  530  and moves through the at least one orifice  560  in the plate  550  along the path A. The liquid can be fed through the flow-through channel  525  and maintained at any flow rate sufficient to generate a hydrodynamic cavitation field downstream from both the first and second baffles  540 ,  545 . As the liquid moves through the flow-through channel  525 , the gas is introduced into the first local constriction  575  via the port  590  and the passage  595  thereby mixing the gas with the liquid as the liquid passes through the first local constriction  575 . The gas can be introduced into the liquid in the first local constriction  575  and maintained at a flow rate that is different from the liquid flow rate and sufficient to control the collapse of cavitation bubbles formed in the hydrodynamic cavitation field. For example, a ratio between the gas volumetric flow rate and the liquid volumetric flow rate is about 0.1 or less. In other words, the ratio between the liquid volumetric flow rate and the gas volumetric flow rate can be at least about 10.  
         [0059]     While passing through the first local constriction  575 , the velocity of the liquid increases to a minimum cavitation velocity for the particular liquid being processed. The increased velocity of the liquid forms the first hydrodynamic cavitation field  580  downstream from the first baffle  540 , thereby generating cavitation bubbles that grow when mixed with the gas to form gas micro bubbles. Upon reaching an elevated static pressure zone, the bubbles can be partially or completely collapsed (or squeezed), thereby dissolving the gas into the liquid to form a gas-saturated liquid.  
         [0060]     Once the gas micro bubbles are generated after the first stage of hydrodynamic cavitation, the gas-saturated liquid continues to move towards the second baffle  545 . While passing through the second local constriction  585 , the velocity of the gas-saturated liquid increases to the minimum cavitation velocity of the liquid. The increased velocity of the gas-saturated liquid forms the second hydrodynamic cavitation field  580  downstream from the second baffle  545 , thereby generating cavitation bubbles. Upon reaching an elevated static pressure zone, a vacuum is created in the second hydrodynamic cavitation field  580  to extract the dissolved gas from the gas-saturated liquid, thereby generating micro bubbles. The micro bubbles are smaller in size and more uniform than the micro bubbles produced after the first stage of hydrodynamic cavitation. The liquid and micro bubbles then exit the flow-through channel  525  via the outlet  535 .  
         [0061]     The following examples are given for the purpose of illustrating the present invention and should not be construed as limitations on the scope or spirit of the instant invention.  
       EXAMPLE 1  
       [0062]     The following example of a method of generating micro bubbles in liquid was carried out in a device substantially similar to the device  200  as shown in  FIG. 2 , except that the device included only one stage of hydrodynamic cavitation. Water was fed, via a high pressure pump, through the flow-through channel  225 , at a velocity of 30.12 meters per second (m/sec) and a flow rate of 5.68 liter per minute (l/min). Air was introduced, via a compressor, into the flow-through channel  225  via the port  270  in the first local constriction of flow  245  at a flow rate of 0.094 standard liters per minute (sl/min). Accordingly, the volume ratio of the air flow rate to the water flow rate was 0.017. The combined water and air then passed through the local constriction of flow  245  creating hydrodynamic cavitation to thereby effectuate the generation of micro bubbles. The resultant bubble size of the micro bubbles was between 5,000 and 7,000 microns.  
       EXAMPLE 2  
       [0063]     The following example of a method of generating micro bubbles in liquid was carried out in a device substantially similar to the device  200  as shown in  FIG. 2 , which included two stages of hydrodynamic cavitation. Water was fed, via a high pressure pump, through the flow-through channel  225 , at a velocity of 30.12 m/sec and a flow rate of 5.68 l/min. Air was introduced, via a compressor, into the flow-through channel  225  via the port  270  in the first local constriction of flow  245  at a flow rate of 0.566 sl/min. Accordingly, the volume ratio of the air flow rate to the water flow rate was 0.100. The combined water and air then passed through the first and second local constrictions of flow  245 ,  255  creating hydrodynamic cavitation to thereby effectuate the generation of micro bubbles. The resultant bubble size of the micro bubbles was between 200 and 300 microns.  
         [0064]     The method above was repeated in the device  200 , except that the gas flow rate was changed. The results are illustrated in Chart 1 below.  
                               CHART 1                                   Volume ratio -               Liquid Flow   Gas Flow Rate   gas flow rate   Bubble size       Test   Rate (l/min)   (sl/min)   to liquid flow rate   microns                   1   5.68   0.472   0.080   100-200       2   5.68   0.080   0.014   100-200       3   5.68   0.047   0.008   100-200       4   5.68   0.033   0.006   100-200                  
 
       EXAMPLE 3  
       [0065]     The following example of a method of generating micro bubbles in liquid was carried out in a device substantially similar to the device  200  as shown in  FIG. 2 , except that the device included only one stage of hydrodynamic cavitation. Water was fed, via a high pressure pump, through the flow-through channel  225 , at a velocity of 46.21 m/sec and a flow rate of 8.71 l/min. Air was introduced, via a compressor, into the flow-through channel  225  via the port  270  in the first local constriction of flow  245  at a flow rate of 0.212 standard sl/min. Accordingly, the volume ratio of the air flow rate to the water flow rate was 0.024. The combined water and air then passed through the local constriction of flow  245  creating hydrodynamic cavitation to thereby effectuate the generation of micro bubbles. The resultant bubble size of the micro bubbles was between 5,000 and 7,000 microns.  
       EXAMPLE 4  
       [0066]     The following example of a method of generating micro bubbles in liquid was carried out in a device substantially similar to the device  200  as shown in  FIG. 2 , which included two stages of hydrodynamic cavitation. Water was fed, via a high pressure pump, through the flow-through channel  225 , at a velocity of 46.21 m/sec and a flow rate of 8.71 l/min. Air was introduced, via a compressor, into the flow-through channel  225  via the port  270  in the first local constriction of flow  245  at a flow rate of 0.614 sl/min. Accordingly, the volume ratio of the air flow rate to the water flow rate is 0.070. The combined water and air then passed through the first and second local constrictions of flow  245 ,  255  creating hydrodynamic cavitation to thereby effectuate the generation of micro bubbles. The resultant bubble size of the micro bubbles was between 200 and 300 microns.  
         [0067]     The method above was repeated in the device  200 , except that the gas flow rate was changed. The results are illustrated in Chart 2 below.  
                               CHART 2                                   Volume ratio -               Liquid Flow   Gas Flow Rate   gas flow rate   Bubble size       Test   Rate (l/min)   (sl/min)   to liquid flow rate   (microns)                   1   8.71   0.472   0.054   100-200       2   8.71   0.234   0.027   100-200       3   8.71   0.080   0.009   100-200       4   8.71   0.047   0.005   100-200       5   8.71   0.033   0.004   100-200                  
 
       EXAMPLE 5  
       [0068]     The following example of a method of generating micro bubbles in liquid was carried out in a device substantially similar to the device  200  as shown in  FIG. 2 , except that the device included only one stage of hydrodynamic cavitation. Water was fed, via a high pressure pump, through the flow-through channel  225 , at a velocity of 60.48 m/sec and a flow rate of 11.4 l/min. Air was introduced, via a compressor, into the flow-through channel  225  via the port  270  in the first local constriction of flow  245  at a flow rate of 0.236 sl/min. Accordingly, the volume ratio of the air flow rate to the water flow rate is 0.021. The combined water and air then passed through the local constriction of flow  245  creating hydrodynamic cavitation to thereby effectuate the generation of micro bubbles. The resultant bubble size of the micro bubbles was between 5,000 and 8,000 microns.  
       EXAMPLE 6  
       [0069]     The following example of a method of generating micro bubbles in liquid was carried out in a device substantially similar to the device  200  as shown in  FIG. 2 , which included two stages of hydrodynamic cavitation. Water was fed, via a high pressure pump, through the flow-through channel  225 , at a velocity of 60.48 m/sec and a flow rate of 11.4 l/min. Air was introduced, via a compressor, into the flow-through channel  225  via the port  270  in the first local constriction of flow  245  at a flow rate of 0.991 sl/min. Accordingly, the volume ratio of the air flow rate to the water flow rate is 0.087. The combined water and air then passed through the first and second local constrictions of flow  245 ,  255  creating hydrodynamic cavitation to thereby effectuate the generation of micro bubbles. The resultant bubble size of the micro bubbles was between 200 and 300 microns.  
         [0070]     The method above was repeated in the device  200 , except that the gas flow rate was changed. The results are illustrated in Chart 3 below.  
                               CHART 3                                   Volume ratio -   Bubble           Liquid Flow   Gas Flow Rate   gas flow   size       Test   Rate (l/min)   (sl/min)   rate to liquid flow rate   (microns)                   1   11.4   0.520   0.046   100-200       2   11.4   0.378   0.033   100-200       3   11.4   0.189   0.017   100-200       4   11.4   0.094   0.008   100-200       5   11.4   0.057   0.005   100-200       6   11.4   0.024   0.002   100-200                  
 
         [0071]     Although the invention has been described with reference to the preferred embodiments, it will be apparent to one skilled in the art that variations and modifications are contemplated within the spirit and scope of the invention. The drawings and description of the preferred embodiments are made by way of example rather than to limit the scope of the invention, and it is intended to cover within the spirit and scope of the invention all such changes and modifications.