Patent Publication Number: US-7708453-B2

Title: Device for creating hydrodynamic cavitation in fluids

Description:
BACKGROUND OF THE INVENTION 
   One of the most promising courses for further technological development in chemical, pharmaceutical, cosmetic, refining, food products, and many other areas relates to the production of emulsions and dispersions having the smallest possible particle sizes and maximum size uniformity. Moreover, during the creation of new products and formulations, the challenge often involves the production of two, three, or more complex components in disperse systems containing particle sizes at the submicron level. Given the ever-increasing requirements placed on the quality of dispersion, traditional methods of dispersion that have been used for decades in technological processes have reached their limits. Attempts to overcome these limits by mere manipulation of these traditional technologies are often not effective. 
   Hydrodynamic cavitation is widely known as a method used to obtain free disperse systems, particularly lyosols, diluted suspensions, and emulsions. Such free disperse systems are fluidic systems wherein dispersed phase particles have no contacts, participate in random beat motion, and freely move by gravity. Such dispersion and emulsification effects are accomplished within the fluid flow due to cavitation effects produced by a change in geometry of the fluid flow. 
   The boiling point of a liquid is defined as the temperature at which the vapor pressure of the liquid is equal to the pressure of the atmosphere on the liquid. For pure compounds, the normal boiling point is defined as the boiling point at one standard atmosphere of pressure on the liquid. If the pressure on the liquid is reduced from one standard atmosphere, the boiling point observed for the compound is likewise reduced from that estimated for the pure compound. 
   Hydrodynamic cavitation is the formation of cavities and cavitation bubbles filled with a vapor-gas mixture inside the fluid flow or at the boundary of the baffle body resulting from a local pressure drop on the fluid. If during the process of movement of the fluid, the pressure decreases to a magnitude under which the fluid reaches its boiling point for the given temperature, then a great number of vapor-filled cavities and bubbles are formed. Insofar as the vapor-filled bubbles and cavities move together with the fluid flow, these bubbles and cavities may move into an elevated pressure zone. When these bubbles and cavities enter a zone having increased pressure, vapor condensation takes place within the cavities and bubbles, causing the cavities and bubbles to collapse almost instantaneously, which creates very large pressure impulses. The magnitude of the pressure impulses within the collapsing cavities and bubbles may reach 150,000 psi. The result of these high-pressure implosions is the formation of shock waves that emanate from the point of each collapsed bubble. Such high-impact loads result in the breakup of any medium found near the collapsing bubbles. 
   A dispersion process takes place when, during cavitation, the collapse of a cavitation bubble near the boundary of the phase separation of a solid particle suspended in a liquid results in the breakup of the suspension particle. An emulsification and homogenization process takes place when, during cavitation, the collapse of a cavitation bubble near the boundary of the phase separation of a liquid suspended or mixed with another liquid results in the breakup of drops of the disperse phase. Thus, the use of kinetic energy from collapsing cavitation bubbles and cavities, produced by hydrodynamic means, can be used for various mixing, emulsifying, homogenizing, and dispersing processes. 
   SUMMARY 
   A device for creating hydrodynamic cavitation in fluid is provided. The device includes a fluid passage having at least two local constrictions of flow provided in a parallel relationship therein, wherein each local constriction of flow configured to generate a hydrodynamic cavitation field downstream therefrom. 
   A method of creating hydrodynamic cavitation in fluid is also provided. The method includes the steps of providing a fluid passage having at least two local constrictions of flow provided in a parallel relationship therein and passing the fluid at a sufficient velocity through the at least two local constrictions of flow to generate a hydrodynamic cavitation field downstream from each local constriction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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. One of ordinary skill in the art will appreciate that one element may be designed as multiple elements or that multiple elements may be designed as one element. An element shown as an internal component of another element may be implemented as an external component and vice versa. 
     Further, in the accompanying drawings and description that follow, like parts are indicated throughout the drawings and description with the same reference numerals, respectively. The figures are not drawn to scale and the proportions of certain parts have been exaggerated for convenience of illustration. 
       FIG. 1  illustrates a longitudinal cross-sectional view of one embodiment of a device  10  for generating hydrodynamic cavitation in a fluid. 
       FIG. 2  illustrates a longitudinal cross-sectional view of an alternative embodiment of a device  200  for generating hydrodynamic cavitation in a fluid. 
       FIG. 3  illustrates one embodiment of a methodology for generating hydrodynamic cavitation in a fluid. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a longitudinal cross-sectional view of one embodiment of a device  10  for generating hydrodynamic cavitation in a fluid. The device  10  includes a first fluid passage or channel  15  having a longitudinal axis or centerline C L . The fluid passage  15  is defined by a wall  20  having an inner surface  25 . In the illustrated embodiment, the wall  20  is a cylindrical wall that defines a fluid passage having a circular cross-section. In alternative embodiments (not shown), the cross-section of the fluid passage  25  may take the form of other geometric shapes such as triangular, square, rectangular, pentagonal, hexagonal, or any other shape. In these alternative embodiments or the illustrated embodiment, the first fluid passage  15  may be defined by multiple walls or wall segments. For example, a fluid passage having a square cross-section is defined by four walls or wall segments. 
   As shown in  FIG. 1 , the first fluid passage  15  can further include an inlet  30  configured to introduce a fluid into the device  10  along a path represented by arrow A and an outlet  35  configured to permit the fluid to exit the device  10 . 
   With further reference to  FIG. 1 , the device  10  further includes a second fluid passage  40  disposed within the first fluid passage  15 . The second fluid passage  40  is defined by a wall  45  having an outer surface  50  and an inner surface  55 . In the illustrated embodiment, the wall  45  is a cylindrical wall that defines a second fluid passage having a circular cross-section. In alternative embodiments (not shown), the cross-section of the second fluid passage  40  may take the form of other geometric shapes such as triangular, square, rectangular, pentagonal, hexagonal, or any other shape. In these alternative embodiments or the illustrated embodiment, the second fluid passage  40  may be defined by multiple walls or wall segments. For example, a second fluid passage can have a triangular cross-section is defined by three walls or wall segments. 
   In this embodiment, the second fluid passage  40  is disposed coaxially within the first fluid passage  15  such that it shares the same centerline C L . Of course, it is possible that the second fluid passage  40  may not be disposed coaxially within the fluid passage  15 . 
   To retain the wall  45  that defines the second fluid passage  40  within the first fluid passage  15 , the wall  45  is connected or made integral with a plate  60  that is mounted to the wall  20  with screws or other attachment means. In the illustrated embodiment, the plate  60  is embodied as a disk when the fluid passage  15  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 first fluid passage  15 . The plate  60  includes one or more orifices  65  configured to permit fluid to pass therethrough. In alternative embodiments (not shown), a crosshead, post, propeller or any other structure that produces a minor loss of fluid pressure can be used to attach the wall  45 , which defines the second fluid passage  40 , to the wall  20 , which defines the first fluid passage  15 , instead of the plate  60  having orifices  65 . 
   The second fluid passage  40  is configured to divide the fluid flow in the device  10  into two primary streams—first stream S 1  and second stream S 2 . In this embodiment, the first stream S 1  flows between the outer surface  50  of the second fluid passage  40  and the inner surface of the first fluid passage  15 , while the second stream S 2  flows within the second fluid passage  40 . 
   Optionally, the wall  45  that defines the second fluid passage  40  may include orifices that provide fluid communication between the first stream S 1  and the second stream S 2  to assist in equalizing the flow rate between the first stream S 1  and the second stream S 2 . In the illustrated embodiment, the wall  45  that defines the second fluid passage  40  includes four orifices  70 . In alternative embodiments (not shown), the wall  45  that defines the second fluid passage  40  may include less than four orifices or more than four orifices. In the illustrated embodiment, the four orifices  70  have a circular cross-section. However, in alternative embodiments (not shown), one or more of the orifices  70  may take the form of another shape such as oval (e.g., a slot), triangular, square, rectangular, pentagonal, hexagonal, or any other geometric shape. In addition, the orifices  70  may be slotted or meshed. The dimensions of the orifices  70  may be such that the orifices  70  are sufficiently sized to equalize the flow rate, while not reducing the flow rate below a velocity that is conducive to generating hydrodynamic cavitation. 
   With further reference to  FIG. 1 , the wall  45 , which defines the second fluid passage  40  includes a projection  75  that extends radially outward therefrom, but spaced from the inner surface  25  of the wall  20 , which defines the first fluid stream S 1 . The projection  75  is configured to partially restrict fluid flow of the first fluid passage  15  and is hereinafter referred to as first baffle  75 . In the illustrated embodiment, the first baffle  75  includes a cylindrical portion  80  and a tapered portion  82  that confronts the fluid flow. 
   In the illustrated embodiment, the device  10  further includes a second baffle  84  disposed within the second fluid passage  40 , but spaced from the inner surface  55  of the wall  45 , which defines the second fluid passage  40 . The second baffle  84  includes a cylindrical portion  86  and a tapered portion  88  that confronts the fluid flow. 
   In this embodiment, the second baffle  84  is disposed coaxially within the second fluid passage  40  such that it shares the same center line C L . Of course, it is possible that the second baffle  84  may not be disposed coaxially within the second fluid passage  40 . 
   To retain the second baffle  84  within the second fluid passage  40 , the second baffle  84  is connected to a plate  90  via a shaft  92 . In alternative embodiments (not shown), the plate  90  can be embodied as a disk when the first fluid passage  15  has a circular cross-section, or the plate  90  can be embodied in a variety of shapes and configurations that correspond to the cross-section of the first fluid passage  15 . The plate  60  is mounted to the wall  20  with screws or other attachment means. The plate  90  includes a plurality of orifices  94  configured to permit fluid to pass therethrough. In alternative embodiments (not shown), a crosshead, post, propeller or any other structure that produces a minor loss of fluid pressure can be used to attach the second baffle  84  to the wall  20 , instead of the plate  90  having orifices  94 . 
   In the illustrated embodiment, the first baffle  75  is configured to generate a first hydrodynamic cavitation field  96  downstream therefrom via a first local constriction  97  of fluid flow formed between the outer surface of the cylindrical portion  80  of the first baffle  75  and the inner surface  25  of the wall  20 . Similarly, the second baffle  84  is configured to generate a second hydrodynamic cavitation field  98  downstream therefrom via a second local constriction  99  of fluid flow formed between the outer surface of the cylindrical portion  86  of the second baffle  84  and the inner surface  55  of the wall  45 . Since the first fluid passage  15  has a circular cross-section in the illustrated embodiment, the first and second local constrictions  96 ,  98  of flow are characterized as first and second annular orifices, respectively. However, it will be appreciated that if the cross-section of the first fluid passage  15  is any geometric shape other than circular, then each respective local constriction of flow may not be annular in shape. Likewise, if a baffle is not circular in cross-section, then each of the local constrictions of flow may not be annular in shape. 
   In the illustrated embodiment, the first local constriction  96  is defined by a first gap having a thickness G 1 , which is the space between the outer surface of the cylindrical portion  80  of the first baffle  75  and the inner surface  25  of the wall  20 . Similarly, the second local constriction  98  is defined by a second gap having a thickness G 2 , which is the space between the outer surface of the cylindrical portion  86  of the second baffle  84  and the inner surface  55  of the wall  45 . As shown in  FIG. 1 , the first gap thickness G 1  is substantially equal to the second gap thickness G 2 . In alternative embodiments (not shown), the first gap thickness G 1  may be different than the second gap thickness G 2 . A change in gap thickness can cause a change in flow rate and bubble size. However, the change in gap thickness does not affect the pressure drop in the device  10 , nor does it change the velocity of the fluid passing through the local constrictions of flow. 
   The gap thickness of each local constriction  96 ,  98 , or any local constriction of fluid flow discussed herein, is sufficiently dimensioned 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  96 ,  98 , 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 fluid passage. 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. 
   To vary the degree and character of the cavitation fields generated downstream from each of the baffles, one or both of the baffles  75 ,  84 , or any baffle discussed herein, can be embodied in a variety of different shapes and configurations other than the ones described above. For example, the first and second baffles  75 ,  84 , or any baffle discussed herein, can be embodied in the shapes and configurations disclosed in FIGS. 3a-3f of U.S. Pat. No. 6,035,897, the disclosure of which is hereby incorporated by reference in its entirety herein. Furthermore, it will be appreciated that other types of cavitation generators may be used instead of baffles. 
   In the illustrated embodiment, the first and second local constrictions  96 ,  98  are both aligned in a plane P, which is oriented substantially perpendicular to a plane passing through the centerline C L . Additionally, the first and second local constrictions  96 ,  98  are provided in a concentric relationship with each other. However, it is possible that the first and second local constrictions  96 ,  98  may be positioned such that they are not aligned in the same plane or provided in a concentric relationship with each other. In effect, the device  10  includes two local constrictions of fluid flow that are provided in a parallel relationship with respect to each other. 
     FIG. 2  illustrates a longitudinal cross-sectional view of an alternative embodiment of a device  200  for generating hydrodynamic cavitation in a fluid. The device  200  is similar to the device  10  illustrated in  FIG. 1  and described above, except that it includes another fluid passage  210  (hereinafter referred to as the “third fluid passage  210 ”) disposed within the first fluid passage  15  between the wall  20 , which defines the first fluid passage  15 , and the wall  45 , which defines the second fluid passage  40 . The third fluid passage  210  is defined by a wall  215  having an outer surface  220  and an inner surface  225 . 
   In this embodiment, the third fluid passage  210  is disposed coaxially within the first fluid passage  15  such that it shares the same longitudinal axis or centerline C L . Of course, it is possible that the third fluid passage  210  may not be disposed coaxially within the first fluid passage  15 . 
   To retain the wall  215  that defines the third fluid passage  210  within the first fluid passage  15 , the wall  215  is connected to or integral with a plate  230  that is mounted to the wall  20  with screws or other attachment means. In the illustrated embodiment, the plate  230  is embodied as a disk when the first fluid passage  15  has a circular cross-section, or the plate  230  can be embodied in a variety of shapes and configurations that can match the cross-section of the first fluid passage  15 . The plate  230  includes one or more orifices  235  configured to permit fluid to pass therethrough. In alternative embodiments (not shown), instead of the plate  230  having orifices  235 , a crosshead, post, propeller or any other structure that produces a minor loss of fluid pressure can be attached to the wall  215 , which defines the second fluid passage  210 , or to the wall  20 , which defines the fluid passage  15 . 
   The third fluid passage  210  is configured to divide the fluid flow in the device  200  into three primary streams—first stream S 1 , second stream S 2 , and third stream S 3 . In this embodiment, the first stream S 1  flows within the second fluid passage  40 , the second stream S 2  flows between the inner surface  225  of the third fluid passage  210  and the outer surface  50  of the second fluid passage  40 , and the third stream S 3  flows between the outer surface  220  of the third fluid passage  210  and the inner surface  25  of the first fluid passage  15 . 
   Optionally, the wall  215 , which defines the third fluid passage  210 , may include orifices similar to the ones described above to provide fluid communication between the first stream S 1  and the second stream S 2  and to assist in equalizing the flow rate between the first stream S 1  and the second stream S 2 . In the illustrated embodiment, the wall  215  includes several orifices  240 . The orifices  240  can be sufficiently sized to equalize the flow rate, while not reducing the flow rate below a velocity that is conducive to generating hydrodynamic cavitation. 
   With further reference to  FIG. 2 , the wall  215  includes a projection  245  that extends radially outward therefrom, but spaced from the inner surface  25  of the wall  20 , which defines the first fluid passage  15 . The projection  245  is configured to partially restrict the fluid flow of the third stream S 3  and is hereinafter referred to as “third baffle  245 .” In the illustrated embodiment, the third baffle  245  includes a cylindrical portion  250  and a tapered portion  255  that confronts the fluid flow. 
   In this embodiment, the third baffle  245  is configured to generate a third hydrodynamic cavitation field  260  downstream therefrom via a third local constriction  265  of fluid flow formed between the outer surface of the cylindrical portion  250  of the third baffle  245  and the inner surface  25  of the wall  20 , which defines the first fluid passage  15 . Since the first fluid passage  15  has a circular cross-section in the illustrated embodiment, the third local constriction  265  of flow is characterized as a third annular orifice. However, it will be appreciated that if the cross-section of the first fluid passage  15  is any geometric shape other than circular, then each respective local constriction of flow may not be annular in shape. Likewise, if a baffle is not circular in cross-section, then each of the local constrictions of flow may not be annular in shape. 
   In the illustrated embodiment, the third local constriction  265  is defined by a gap having a thickness G 3 , which is the space between the outer surface of the cylindrical portion  255  of the third baffle  250  and the inner surface  25  of the wall  20 . As shown in  FIG. 2 , the first, second, and third gap thicknesses G 1 , G 2 , G 3  are substantially equal to each other. In alternative embodiments (not shown), one or more of the gap thicknesses may differ from each other. 
   In the illustrated embodiment, the first, second, and third local constrictions  96 ,  98 ,  260  are all aligned in a plane P, which is oriented substantially perpendicular to a plane passing through the centerline C L . Additionally, the first and second local constrictions  96 ,  98 ,  260  are provided in a concentric relationship with each other. However, it is possible that the first, second, and third local constrictions  96 ,  98 ,  260  may be positioned such that they are not aligned in the same plane or provided in a concentric relationship with each other. 
   In effect, the device  200  includes three local constrictions of fluid flow (e.g., annular orifices in this case) that are provided in a parallel relationship with respect to each other, which can maximize the amount of processing area for a given gap thickness. In alternative embodiments (not shown), the device  200  described above and illustrated in  FIG. 1  can be modified to include three or more fluid passages having baffles provided thereon, thereby creating four or more local constrictions of flow within one fluid passage in a parallel relationship. 
   Illustrated in  FIG. 3  is one embodiment of a methodology associated with generating one or more stages of hydrodynamic cavitation in a fluid. The illustrated elements denote “processing blocks” and represent functions and/or actions taken for generating one or more stages of hydrodynamic cavitation. In one embodiment, the processing blocks may represent computer software instructions or groups of instructions that cause a computer or processor to perform the processing. It will be appreciated that the methodology may involve dynamic and flexible processes such that the illustrated blocks can be performed in other sequences different that the one shown and/or blocks may be combined or separated into multiple components. The foregoing applies to all methodologies described herein. 
   With reference to  FIG. 3 , the process  300  involves a hydrodynamic cavitation process. The process  300  includes providing a fluid passage having at least two local constrictions of flow provided in a parallel relationship therein (block  310 ) and passing the fluid at a sufficient velocity through the at least two local constrictions of flow to generate a hydrodynamic cavitation field downstream from each local constriction (block  320 ). 
   In practice, a practitioner may establish a particular set of conditions and/or factors that facilitate cavitation bubble formation and fluid mixing by empirically varying some or all of the factors that affect formation of cavitation bubbles and mixing of fluids. This establishment and optimization of conditions may be facilitated by use of the methods and devices described herein on a small scale. Once optimum conditions are established, the practitioner may desire to scale-up or increase the volume of fluids that can be processed by the methods and devices described herein. In one example, the practitioner may increase the number of second fluid passages provided in the fluid passage, thereby increasing the number of local constrictions of flow provided in a parallel arrangement. At times, the overall diameter of the outer most fluid passage can be increased to accommodate an increased number of second fluid passages. Under either scenario, the overall processing area increases, while the gap thicknesses of the local constrictions of flow remain the same. Therefore, high volumes of fluid can be processed with the same or similar quality as low volumes. 
   To the extent that the term “includes” or “including” is employed in the detailed description or the claims, it is intended to be inclusive in a manner similar to the term “comprising” as that term is interpreted when employed as a transitional word in a claim. Furthermore, to the extent that the term “or” is employed in the detailed description or claims (e.g., A or B) it is intended to mean “A or B or both”. When the applicants intend to indicate “only A or B but not both” then the term “only A or B but not both” will be employed. Thus, use of the term “or” herein is the inclusive, and not the exclusive use. See, Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995). Also, to the extent that the terms “in” or “into” are used in the specification or the claims, it is intended to additionally mean “on” or “onto.” Furthermore, to the extent the term “connect” is used in the specification or claims, it is intended to mean not only “directly connected to,” but also “indirectly connected to” such as connected through another component or components. 
   While example devices, methods, and so on have been illustrated by describing examples, and while the examples have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the devices, methods, and so on described herein. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention is not limited to the specific details, the representative devices, and illustrative examples shown and described. Thus, this application is intended to embrace alterations, modifications, and variations that fall within the scope of the appended claims. Furthermore, the preceding description is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined by the appended claims and their equivalents.