Patent Publication Number: US-2010110824-A1

Title: Dispersion/stirring apparatus and dispersion tank

Description:
CROSS-REFERENCE TO PRIOR APPLICATION 
     This is the U.S. National Phase Application under 35 U.S.C. §371 of International Patent Application No. PCT/JP2008/058758 filed May 13, 2008, which claims the benefit of Japanese Patent Application No. 2007-132254 filed May 18, 2007, both of which are incorporated by reference herein. The International Application was published in Japanese on Nov. 27, 2008 as WO2008/143056 A1 under PCT Article 21(2). 
    
    
     TECHNICAL FIELD 
     The present invention relates to a dispersion/stirring apparatus used for dispersing and stirring a fluid. The invention further relates to a dispersion tank that uses the dispersion/stirring apparatus. 
     BACKGROUND OF THE INVENTION 
     In some industrial fields recently, such as the field of dispersing gas in liquid and stirring the resultant gas-liquid mixture, the demand is increasing for gas micronization in response to greater diversification of processes or in order to promote the efficiency and progress of related reactions. 
     An example of conventional dispersion/stirring apparatuses includes a liquid container, a star-shaped impeller disposed in the bottom part of the container, and a stationary unit containing the impeller, wherein the impeller is supported by a vertically extending shaft so as to rotate with the vertical shaft. A gas supply pipe is provided in the vicinity of the lower face of the impeller, and a gas outlet is provided at an outer circumferential part of the impeller. A liquid supply portion is provided in order to supply liquid to the end face of the impeller. The gas sucked into the impeller as a result of rotation of the impeller is released from the gas outlet into a flow path of the stationary unit and subsequently discharged into the liquid in the container through a pipe that is connected to the flow path of the stationary unit (e.g. See Japanese Laid-open Patent Publication No. 6-182379 (p 5, and FIGS. 1 and 2)). 
     However, a dispersion/stirring apparatus having such a structure described above, wherein bubbles discharged into the liquid have large diameters, is not capable of responding to the demand for micronizing the gas. 
     Examples of methods for micronizing a gas include those that require providing a pipeline with a Venturi tube. This method utilizes a phenomenon in which a gas contained in a liquid is micronized due to the difference in pressure between a constricted portion and an enlarged flow path portion when the liquid flows through a Venturi tube (e.g. See Japanese Laid-open Patent Publication No. 2007-843 (pp 3 and 4, and FIGS. 1 and 2)). 
     According to conventional methods and structures, however, using a Venturi tube requires a separate pump or the like to deliver the liquid into the Venturi tube, as well as a stirring device or other appropriate device so that the fluid containing ultrafine bubbles that is discharged from the Venturi tube into a reaction tank is uniformly dispersed into the tank. 
     As described above, conventional dispersion/stirring apparatus have a problem in that they are not capable of responding to the demand for micronizing the gas, because bubbles discharged into the liquid have large diameters. Another problem presented by conventional dispersion/stirring apparatuses is that using a Venturi tube requires a separate pump or the like to deliver the liquid into the Venturi tube, as well as a stirring device or other appropriate device so that the fluid containing ultrafine bubbles that is discharged from the Venturi tube into a reaction tank is uniformly dispersed into the reaction tank. In order to solve the problems described above, an object of the invention is to provide a dispersion/stirring apparatus that is capable of micronizing a fluid and also capable of dispersing and stirring the micronized fluid. Another object of the invention is to provide a dispersion tank equipped with this dispersion/stirring apparatus. 
     SUMMARY OF THE INVENTION 
     A dispersion/stirring apparatus according to the present invention has a rotation unit and includes a flow path and a flow path expansion portion. The flow path opens at an inner diameter side as well as an outer diameter side of the rotation unit, thereby enabling fluid communication between the exterior and the interior of the rotation unit. The flow path expansion portion is provided so that the flow path expands in the direction towards the outer diameter side of the rotation unit. 
     According to the present invention, the rotation unit of the dispersion/stirring apparatus as above includes a plurality of disks that face one another, and the flow path and the flow path expansion portion are provided between these disks. 
     According to the present invention, the dispersion/stirring apparatus includes a fixed member facing the rotation unit, and the flow path as well as the flow path expansion portion are provided between the rotation unit and the fixed member. According to the present invention, the flow path of the dispersion/stirring apparatus in any one of the above is provided with a porous member, at a location between the flow path expansion portion and the inner diameter side of the rotation unit. 
     According to the present invention, the rotation unit of the dispersion/stirring apparatus is provided with a centrifugal fin between either the inner diameter side and the flow path expansion portion or the outer diameter side and the flow path expansion portion, or between the inner diameter side and the flow path expansion portion, as well as between the outer diameter side and the flow path expansion portion. According to the present invention, an end of the rotation unit of the dispersion/stirring apparatus faces upward and is provided with a hole that communicates with the interior and the exterior of the rotation unit. 
     A dispersion/stirring apparatus according to the present invention has a rotation unit and a stationary unit provided outside the outer diameter side of the rotation unit, and includes a flow path and a flow path expansion portion. The flow path opens at an inner diameter side as well as an outer diameter side of the stationary unit, thereby enabling fluid communication of the exterior and the interior of the stationary unit. The flow path expansion portion is provided so that the flow path expands in the direction towards the outer diameter side of the stationary unit. According to the present invention, either one of or both the rotation unit and the stationary unit of the dispersion/stirring apparatus are provided with a porous member. The porous member provided in the stationary unit is positioned between the flow path expansion portion of the flow path and the inner diameter side of the stationary unit. 
     According to the present invention, the stationary unit of the dispersion/stirring apparatus as above covers the rotation unit, and a hole is formed in the top surface of the stationary unit. 
     According to the present invention, the dispersion/stirring apparatus includes a stirring fin provided outside the stationary unit and adapted to rotate integrally with the rotation unit. 
     According to the present invention, the dispersion/stirring apparatus includes a stirring fin provided on the outer surface of the rotation unit. 
     According to the present invention, the dispersion/stirring apparatus includes a canned motor for rotating the rotation unit. 
     A dispersion tank according to the present invention includes a tank for retaining a fluid, and a dispersion/stirring apparatus as described above. The dispersion/stirring apparatus is provided at least at the bottom or the side of the tank and adapted to disperse and stir into the fluid retained in the tank a fluid that is different from the fluid retained in the tank. 
     According to the present invention, the dispersion tank includes an external cyclic path and a pump. The external cyclic path serves to remove the fluid retained in the tank out of the tank and return the removed fluid into the tank. The pump serves to circulate the fluid retained in the tank through the external cyclic path. 
     A dispersion tank according to the present invention includes a tank, an external cyclic path, a pump, and a dispersion/stirring apparatus. The tank serves as a reservoir. The external cyclic path serves to remove the fluid retained in the tank out of the tank and return the remove fluid into the tank. The pump serves to circulate the fluid retained in the tank to the external cyclic path. The dispersion/stirring apparatus is provided in the external cyclic path and serves to disperse and stir into the fluid circulating through the external cyclic path a fluid that is different from the fluid circulating through the external cyclic path. 
     According to the present invention, the dispersion tank above includes a delivery path for delivering to a next process a part of the fluid discharged from the tank into the external cyclic path. 
     According to the present invention, the dispersion tank as in any one of the above embodiments includes a fluid supply path and a fluid cyclic path. The fluid supply path serves to supply a fluid, which is different from and has a specific gravity lower than that of the fluid retained in the tank, to the dispersion/stirring apparatus. The fluid cyclic path serves to return to the dispersion/stirring apparatus a fluid that is different from and has separated upward from the fluid retained in the tank. 
     The flow path expansion portion formed as a part of the flow path of the rotation unit has an effect similar to that of a Venturi tube. Therefore, the dispersion/stirring apparatus is capable of micronizing a fluid passing through the flow path and also capable of dispersing and stirring the micronized fluid. 
     The flow path expansion portion formed as a part of the flow path, which is provided between the plurality of disks of the rotation unit, has an effect similar to that of a Venturi tube. Therefore, while having the same effect as that of the dispersion/stirring apparatus above, this dispersion/stirring apparatus is capable of micronizing a fluid passing through the flow path and also capable of dispersing and stirring the micronized fluid. 
     According to the present invention, the flow path expansion portion formed as a part of the flow path, which is provided between the rotation unit and the fixed member, has an effect similar to that of a Venturi tube. Therefore, while having the same effect as that of the dispersion/stirring apparatus above, the dispersion/stirring apparatus of this embodiment of the present invention is capable of micronizing a fluid passing through the flow path and also capable of dispersing and stirring the micronized fluid. According to the present invention, the flow path is provided with a porous member at a location between the flow path expansion portion and the inner diameter side of the rotation unit. Therefore, while having the same effect as that of the dispersion/stirring apparatus as discussed above, the dispersion/stirring apparatus of the present invention is capable of ensuring satisfactory contact between two or more kinds of fluids and also increasing pressure in the diametrically inner part of the flow path with respect to the flow path expansion portion, i.e. the part between the flow path expansion portion and the inner diameter end of the flow path, thereby enabling dissolution of a fluid, resulting in more reliable micronization of a fluid passing through the flow path. 
     According to the present invention, the rotation unit is provided with a centrifugal fin between either the inner diameter side and the flow path expansion portion or the outer diameter side and the flow path expansion portion, or between the inner diameter side and the flow path expansion portion, as well as between the outer diameter side and the flow path expansion portion. Therefore, while having the same effect as that of the dispersion/stirring apparatus as above, the dispersion/stirring apparatus of the present invention ensures more reliable passage of a fluid without the need of a separate pump, because the rotation unit itself has functions and effects identical to those achieved by a centrifugal pump impeller. 
     An end of the rotation unit faces upward and is provided with a hole that communicates with the interior and the exterior of the rotation unit. Therefore, while having the same effect as that of the dispersion/stirring apparatus as in any one of the embodiments above, the dispersion/stirring apparatus of the present invention is capable of discharging gas remaining in the rotation unit from the hole. 
     Furthermore, should an excessive quantity of the fluid to be dispersed be fed, the excess fluid flows out of the rotation unit through the hole, consequently enabling monitoring of an appropriate amount of the supply of the fluid to be dispersed. 
     The flow path expansion portion formed as a part of the flow path of the stationary unit has an effect similar to that of a Venturi tube. Therefore, the dispersion/stirring apparatus is capable of micronizing a fluid discharged from the rotation unit and passing through the flow path of the stationary unit and also capable of dispersing and stirring the micronized fluid. 
     The flow path is provided with a porous member at a location between the flow path expansion portion and the inner diameter side of the stationary unit. Therefore, while having the same effect as that of the dispersion/stirring apparatus as discussed above, the dispersion/stirring apparatus of the present invention is capable of ensuring satisfactory contact between two or more kinds of fluids and also increasing pressure in the diametrically inner part of the flow path with respect to the flow path expansion portion, i.e. the part between the flow path expansion portion and the inner diameter end of the flow path, thereby enabling dissolution of a fluid, resulting in more reliable micronization of a fluid passing through the flow path. According to the present invention, a hole is formed in the top surface of the stationary unit covering the rotation unit. Therefore, while having the same effect as that of the dispersion/stirring apparatus as disclosed above, the dispersion/stirring apparatus of the present invention is capable of preventing the generation of cavitation as well as preventing failure of function of the rotation unit by discharging gas remaining in the stationary unit from the hole. Furthermore, should an excessive quantity of the fluid to be dispersed be fed, the excess fluid flows out of the rotation unit through the hole, consequently enabling monitoring of an appropriate amount of the supply of the fluid to be dispersed. 
     A stirring fin is provided outside the stationary unit and adapted to rotate integrally with the rotation unit. Therefore, while having the same effect as that of the dispersion/stirring apparatus as in any one of the above embodiments, the dispersion/stirring apparatus of the present embodiment enables more reliable stirring of a fluid without the need of a separate stirring device. 
     The rotation unit is provided with a stirring fin so that the rotation unit itself has a stirring function. Therefore, while having the same effect as above, the dispersion/stirring apparatus of the present invention enables more reliable stirring of a fluid without the need of a separate stirring device. 
     While having the same effect as that of the dispersion/stirring apparatus as claimed in any one of the embodiments above, the dispersion/stirring apparatus of the present invention is, because of characteristics of the canned motor, free from the problem of fluid leakage and, therefore, can be installed at any location and used in a high-temperature, high-pressure or high-vacuum system. 
     The tank of the dispersion tank is provided with a dispersion/stirring apparatus, which is capable of dispersing and stirring into the fluid retained in the tank a fluid that is different from the fluid retained in the tank. Furthermore, as the dispersion/stirring apparatus includes a canned motor, the dispersion/stirring apparatus can be positioned at the bottom or the side of the tank of the tank. Therefore, in cases where a motor is provided at the upper part of the tank, a maintenance space above the tank for performing maintenance would be unnecessary, such a maintenance space being otherwise required to remove the shaft of the dispersion/stirring apparatus. Furthermore, with a conventional dispersion tank, micronizing a fluid by using a Venturi tube requires a separate pump and a stirring device. However, as there is no need of a separate pump or a stirring device, the present invention is capable of realizing an inexpensive dispersion tank. 
     While having the same effect as that of the dispersion tank above, this dispersion tank enables more reliable stirring of the fluid retained in the tank, because of the effect of the external cyclic path in addition to the stirring function by the dispersion/stirring apparatus. 
     According to the present invention, the external cyclic path of the dispersion tank enables circulation and stirring of the fluid retained in the tank, and the dispersion/stirring apparatus provided in the external cyclic path disperses and stirs into the fluid circulating through the external cyclic path a fluid that is different from the fluid circulating through the external cyclic path. 
     While having the same effect as that of the dispersion tank above, the dispersion tank of the present invention is also capable of delivering, by means of the delivery path, to a next process a part of the fluid discharged from the tank into the external cyclic path. 
     While having the same effect as that of the dispersion tank as above, the dispersion tank of the present invention is capable of supplying, through the fluid supply path, a fluid, which is different from and has a specific gravity lower than that of the fluid retained in the tank, to the dispersing/stirring apparatus, and is also capable of returning, by means of the fluid cyclic path, to the dispersion/stirring apparatus a fluid that is different from and has separated upward from the fluid retained in the tank. Therefore, reuse of the fluid to be dispersed is possible, and the consumption efficiency of the fluid to be dispersed is improved, resulting in improved efficiency of the entire system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a dispersion/stirring apparatus and a dispersion tank according to an embodiment of the present invention. 
         FIG. 2  is a bottom view of a flow path of a rotation unit of the aforementioned dispersion/stirring apparatus. 
         FIG. 3  shows a dispersion/stirring apparatus according to another embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit is provided, and (b) is a bottom view illustrating the flow path of the rotation unit. 
         FIG. 4  shows a dispersion/stirring apparatus according to a further embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit is provided, and (b) is a bottom view illustrating the flow path of the rotation unit. 
         FIG. 5  shows a dispersion/stirring apparatus according to yet another embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit is provided, and (b) is a bottom view illustrating the flow path of the rotation unit. 
         FIG. 6  shows a dispersion/stirring apparatus according to an embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit is provided, and (b) is a bottom view illustrating the flow path of the rotation unit. 
         FIG. 7  shows a dispersion/stirring apparatus according to a further embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit is provided, and (b) is a bottom view illustrating the flow path of the rotation unit. 
         FIG. 8  shows a dispersion/stirring apparatus according to yet another embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit is provided, and (b) is a bottom view illustrating the flow path of the rotation unit. 
         FIG. 9  shows a dispersion/stirring apparatus according to an embodiment of the present invention and is a sectional view illustrating the part where the rotation unit is provided. 
         FIG. 10  shows a dispersion/stirring apparatus according to another embodiment of the present invention and is a sectional view illustrating the part where the rotation unit is provided. 
         FIG. 11  shows a dispersion/stirring apparatus according to a further embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit is provided, and (b) is a bottom view illustrating the flow path of the rotation unit. 
         FIG. 12  shows a dispersion/stirring apparatus according to an embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit is provided, and (b) is a bottom view illustrating the flow path of the rotation unit. 
         FIG. 13  shows a dispersion/stirring apparatus according to another embodiment of the present invention and is a sectional view illustrating the part where the rotation unit is provided. 
         FIG. 14  shows a dispersion/stirring apparatus according to a further embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit and the stationary unit are provided, and (b) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
         FIG. 15  shows a dispersion/stirring apparatus according to yet another embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit and the stationary unit are provided, and (b) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
         FIG. 16  shows a dispersion/stirring apparatus according to an embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit and the stationary unit are provided, and (b) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
         FIG. 17  shows a dispersion/stirring apparatus according to a further embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit and the stationary unit are provided, and (b) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
         FIG. 18  shows a dispersion/stirring apparatus according to another embodiment of the present invention, wherein (a) is a sectional view illustrating the part where the rotation unit and the stationary unit are provided, and (b) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
         FIG. 19  shows a dispersion/stirring apparatus according to an embodiment of the present invention and is a sectional view illustrating the part where the rotation unit and the stationary unit are provided. 
         FIG. 20  is a sectional view of a dispersion tank according to a further embodiment of the present invention. 
         FIG. 21  is a sectional view of a dispersion tank according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Next, the present invention is explained in detail hereunder, referring to the drawings. 
     An embodiment of the present invention is shown in  FIGS. 1 and 2 , wherein  FIG. 1  is a sectional view of a dispersion/stirring apparatus and a dispersion tank, and  FIG. 2  is a bottom view of a flow path of a rotation unit of the dispersion/stirring apparatus. 
     Referring to  FIG. 1 , the dispersion/stirring apparatus  11  includes a canned motor  12  and a rotation unit  13 , which is an impeller. 
     The canned motor  12  includes a rotor  16  and a rotary shaft  17 , which is inserted into the rotor  16  and fixed therein. A sleeve  18  and a thrust collar  20  are attached to the front end portion of the rotary shaft  17 , and a sleeve  19  and a thrust collar  21  are attached to the rear end portion of the rotary shaft  17 . The rotary shaft  17  is rotatably supported through the sleeves  18 , 19  and the thrust collars  20 , 21  by bearings  22 , 23 , which are respectively provided at the front end portion and the rear end portion of the rotary shaft  17 . The bearings  22 , 23  are inserted and fixed in a front bearing box  24  and a rear bearing box  25 , respectively. 
     The front bearing box  24  is fastened by means of a bolt  29  to the surface of a front flange  28  of a stator frame  27 , in which a stator  26  is placed and fixed. The rear bearing box  25  is fastened in a fluid-tight state by means of a bolt  32  to the rear end face  31  of the stator frame  27 , with a gasket  30  between the rear bearing box  25  and the rear end face  31 . 
     The rotor  16  includes a nonmagnetic rotor can  33 , which has a thin-walled cylindrical shape, and end plates  34  welded to the rotor can  33  in a fluid-tight state. The stator  26  includes a nonmagnetic stator can  35 , which has a thin-walled cylindrical shape and is welded to an end of the stator frame  27  in a fluid-tight state. The rotor  16  and the stator  26  are positioned so that the stator  26  surrounds the rotor  16  with a can gap  36  therebetween. 
     The rear bearing box  25  has a lubricating liquid inlet  37 , which is formed as an integral body with the rear bearing box  25 . A lubricating liquid flow path  38  is formed in the front flange  28  of the stator frame  27  and communicates with the front bearing box  24 . The front flange  28  is also provided with a lubricating liquid outlet  39 , which communicates with the lubricating liquid flow path  38 . 
     The rotary shaft  17  is provided with a mechanical seal. The mechanical seal includes a rotary ring  40  that is fixed to the rotary shaft  17  and adapted to rotate together with the rotary shaft  17 . The mechanical seal also includes a fixed ring  41  on which the rotating rotary ring  40  slides. The rotary ring  40  and the fixed ring  41  together form a shaft sealing portion  42 . Although the mechanical seal is used in this embodiment, the mechanical seal may be omitted, depending on conditions. Furthermore, it is also possible to use other sealing means, such as a gland packing, an O-ring, an oil seal, a VF seal, etc. 
     Through a fixed ring support  43 , the fixed ring  41  of the mechanical seal is fixed to a shaft sealing portion support  44 , which is fastened in a fluid-tight state by means of a bolt to the surface of the front flange  28  of the stator frame  27 . 
     A fluid passage forming member  46 , which is a hollow tubular member that forms a fluid passage  45 , is fastened by means of a bolt  47  to the shaft sealing portion support  44 . The fluid passage  45  is formed by the gap between the rotary shaft  17  and the fluid passage forming member  46 , and the gap between the fluid passage forming member  46  and the shaft sealing portion support  44 ; and a flow path formed in the shaft sealing portion support  44  and in the front flange  28  of the stator frame  27 . A fluid inlet  48  communicating with the fluid passage  45  is formed in the front flange  28  of the stator frame  27 . Between the end of the fluid passage forming member  46  and the rotary shaft  17 , a fluid outlet  49  communicating with the fluid passage  45  is formed at the inner diameter side of the rotation unit  13 . 
     Referring to  FIGS. 1 and 2 , the rotation unit  13  includes two disks  51 , 52 , between which a circumferentially uninterrupted flow path  53  is formed. A plurality of radially arranged centrifugal fins  54  for connecting the disks  51 , 52  are provided in the flow path  53 . The centrifugal fins  54  are positioned towards the center of the flow path  53 . 
     Tapered portions  51   a , 52   a  facing the flow path  53  are formed on the opposing surfaces of the respective disks  51 , 52 , at a location between centrifugal fins  54  and the outer diameter end of the disks  51 , 52 . The tapered portions  51   a , 52   a  are inclined so that the gap therebetween flares outward, towards the outer diameter end of the disks  51 , 52 . As a result, the flow path  53  includes a flow path contraction portion  55  around the centrifugal fins  54 , in other words at a location between the centrifugal fins  54  and the outer diameter end of the flow path  53 , and a flow path expansion portion  56  around the flow path contraction portion  55 , i.e. between the flow path reduction portion  55  and the outer diameter end of the flow path  53 . In other words, the flow path  53 , i.e. the gap between the disks  51 , 52 , narrows at the flow path contraction portion  55  in the direction towards the outer diameter end and expands at the flow path expansion portion  56  in the direction towards the outer diameter end. Furthermore, a minimum gap portion  57  at which the flow path  53 , i.e. the gap between the disks  51 , 52 , is the narrowest is provided between the flow path contraction portion  55  and the flow path expansion portion  56 . 
     One of the two disks, i.e. the disk  52 , is disposed closer to the canned motor  12  than is the other disk, i.e. the disk  51 . Formed in the central part of the disk  52  is a liquid inlet  59 , which is open to the outside of the disk  52 . 
     The disk  51  is positioned further from the canned motor  12  than is the disk  52 . A plurality of radially arranged stirring fins  60  are provided on and project from the externally facing planar surface of the disk  51 . A boss  61  attached to the rotary shaft  17  of the canned motor  12  is formed at the central part of the disk  51 . 
     The rotation unit  13  is fastened by means of a bolt  62  to the front end of the rotary shaft  17  of the canned motor  12 . Thus, the dispersion/stirring apparatus  11  comprises the canned motor  12  and the rotation unit  13 . 
     Referring to  FIG. 1 , a dispersion tank  65  includes a tank  66  for retaining a first fluid, such as a liquid. The dispersion tank  65  serves to disperse and stir in the first fluid a second fluid that is different from the first fluid. The second fluid contains at least one fluid that is a gas, a liquid that is not soluble in the liquid in the tank  66 , or a liquid that contains bubbles. The front flange  28  of the stator frame  27  of the canned motor  12  is fastened in a fluid-tight state by means of a bolt (not shown) to the bottom of the tank  66 , with a gasket  67  therebetween. Thus, the dispersion/stirring apparatus  11  is attached to the tank of the dispersion tank  65  in such a state that the rotation unit  13  is disposed in the tank  66 . 
     Next, how the dispersion/stirring apparatus  11  operates is explained, referring to  FIGS. 1 and 2 . 
     The explanation hereunder is given based on the assumption that the fluid retained in the tank  66  is a liquid and that the fluid to be dispersed and stirred in the liquid in the tank  66  by the dispersion/stirring apparatus  11  is a gas. 
     The lubricating liquid supplied to the canned motor  12  is introduced from the lubricating liquid inlet  37  to lubricate and cool the bearings  23  at the rear portion of the rotary shaft  17 . The lubricating liquid subsequently flows through the can gap  36  to cool the rotor  16  and the stator  26 , lubricates and cools the bearings  22  at the front portion of the rotary shaft  17 , and is then discharged from the lubricating liquid outlet  39 . 
     A minute part of the lubricating liquid serves to smooth rotational sliding of the rotary ring  40  on the fixed ring  41  of the mechanical seal and flows out of the shaft sealing portion  42  into the fluid passage  45 . In cases where the liquid in the tank  66  is used as the lubricating liquid, no problems occur should a part of the lubricating liquid flows out into the fluid passage  45 , in other words into the tank  66 . 
     When the gas is introduced from the fluid inlet  48 , the gas is fed through the fluid passage  45  into the central part of the rotation unit  13 . 
     When the rotary shaft  17  of the canned motor  12  rotates, the rotation unit  13 , too, rotates integrally with the rotary shaft  17  so that the liquid in the tank  66  is introduced from the liquid inlet  59  of the rotation unit  13 . As a result, the mixture of the gas and the liquid passes through the flow path contraction portion  55  and the flow path expansion portion  56  of the flow path  53  of the rotation unit  13  sequentially and is discharged out of the rotation unit  13 . When the mixture of the gas and the liquid passes through the flow path contraction portion  55  and subsequently through the flow path expansion portion  56 , the change of the dimension of the flow path causes a change in the flow velocity, and consequently the pressure, of the gas-liquid mixture, resulting in micronization of the gas in the liquid. 
     The degree of micronization of the gas largely depends on the flow velocity and quantity of the gas, as well as the respective dimensions of the flow path  53  at the minimum gap portion  57  and the flow path expansion portion  56 . For example, if the flow velocity of the gas exceeds a certain threshold, it is impossible to reduce bubbles of the gas to a sufficiently small diameter, resulting in insufficient micronization. Should this be the case, the diameter of bubbles to which the gas is micronized can be adjusted primarily by the respective dimensions of the flow path  53  at the minimum gap portion  57  and the flow path expansion portion  56 . Should the flow velocity of the gas be less than the threshold, the gas can be micronized into ultrafine bubbles of a sufficiently small dimension. 
     As described above, the flow path expansion portion  56  formed as a part of the flow path  53  of the rotation unit  13  has an effect similar to that of a Venturi tube so that the gas can be micronized as a result of the liquid containing the gas passing through the flow path  53  of the rotation unit  13 . Furthermore, as the disks  51 , 52  have functions and effects identical to those achieved by a pump impeller, the liquid can pass between the disks  51 , 52  without the need of a separate pump. 
     Furthermore, because of the centrifugal fins  54  provided at a location between the flow path expansion portion  56  and the inner diameter side of the rotation unit  13 , the rotation unit  13  itself has functions and effects identical to those achieved by a centrifugal pump impeller. Therefore, the rotation unit  13  is capable of passing the liquid therethrough even more reliably without the need of a separate pump. 
     Furthermore, the stirring fins  60  provided on the outer surface of the rotation unit  13  enable, without the need of a separate stirring device, greater reliability for stirring the gas-containing liquid in the tank  66 . 
     The outer surface of the rotation unit  13  on which the stirring fins  60  are provided is not limited to the externally facing planar surface of the disk  51  but also includes the externally facing planar surface of the disk  52  and the outer circumferential surfaces of the disks  51 , 52  so that the stirring fins  60  may be provided on any of these surfaces. 
     Next, another embodiment of the present invention is shown in  FIG. 3 , wherein  FIG. 3  ( a ) is a sectional view illustrating the part where the rotation unit is provided, and  FIG. 3  ( b ) is a bottom view illustrating the flow path of the rotation unit. 
     This embodiment has the same structure as found in the first embodiment shown in  FIGS. 1 and 2 , except that this embodiment does not include the stirring fins  60 . 
     Although the stirring fins  60  are not provided, the flow of the liquid discharged from the rotation unit  13  and the rotating disks  51 , 52  are capable of stirring the liquid in the tank  66 . 
     Depending on conditions, such as the property of the liquid in the tank  66 , dimensions of the tank  66 , etc., the present embodiment has sufficient functions and effects regardless of the absence of the stirring fins  60 . 
     Next, a further embodiment of the present invention is shown in  FIG. 4 , wherein  FIG. 4  ( a ) is a sectional view illustrating the part where the rotation unit is provided, and  FIG. 4  ( b ) is a bottom view illustrating the flow path of the rotation unit. 
     This embodiment has the same structure as found in the previous embodiment shown in  FIG. 3 , except that the centrifugal fins  54  are formed between the flow path expansion portion  56  and the outer diameter side of the rotation unit  13 . 
     The structure according to this embodiment of the invention is able to achieve the same functions and effects as can be done by the previous embodiment of the invention shown in  FIG. 3 . A particular benefit of this embodiment lies in that the centrifugal fins  54  formed closer to the outer diameter side of the rotation unit  13  generate greater centrifugal force and consequently produce improved centrifugal effect. 
     Next, an embodiment of the present invention is shown in  FIG. 5 , wherein  FIG. 5  ( a ) is a sectional view illustrating the part where the rotation unit is provided, and  FIG. 5  ( b ) is a bottom view illustrating the flow path of the rotation unit. 
     The embodiment has the same structure as found in the other embodiment shown in  FIG. 3 , except that the centrifugal fins  54  are formed between the inner diameter side and the flow path expansion portion  56 , as well as between the outer diameter side and the flow path expansion portion  56 . 
     Such a structure enables a mixture of liquid and gas to flow with greater reliability into the rotation unit  13 . A particular benefit of this embodiment lies in that the centrifugal fins  54  formed closer to the outer diameter side of the rotation unit  13  generate greater centrifugal force and consequently produce improved centrifugal effect. 
     Next, another embodiment of the present invention is shown in  FIG. 6 , wherein  FIG. 6  ( a ) is a sectional view illustrating the part where the rotation unit is provided, and  FIG. 6  ( b ) is a bottom view illustrating the flow path of the rotation unit. 
     This embodiment has the same structure as found in the embodiment shown in  FIGS. 1 and 2 , except that this fifth embodiment does not include the centrifugal fins  54  or the stirring fins  60 . In the case of this embodiment, providing a separate structure to connect the disks  51 , 52  together enables the disks  51 , 52  to be integrally rotated. 
     Although the centrifugal fins  54  are not provided, the rotation unit  13  achieves an effect identical to that by a pump so that the liquid can be introduced into the rotation unit  13  by rotating the rotation unit  13 . 
     Although the stirring fins  60  are not provided, the flow of the liquid discharged from the rotation unit  13  and the rotating disks  51 , 52  are capable of stirring the liquid in the tank  66 . 
     Depending on conditions, such as the property of the liquid in the tank  66 , dimensions of the tank  66 , etc., the present embodiment has sufficient functions and effects regardless of the absence of the centrifugal fins  54  and the stirring fins  60 . 
     Next, a further embodiment of the present invention is shown in  FIG. 7 , wherein  FIG. 7  ( a ) is a sectional view illustrating the part where the rotation unit is provided, and  FIG. 7  ( b ) is a bottom view illustrating the flow path of the rotation unit. 
     This embodiment has the same structure as found in the embodiment shown in  FIG. 3 , except that the disk  52  is separated from the disk  51  and formed as a fixed member  69  fixed to the fluid passage forming member  46  of the canned motor  12 . 
     The inner circumferential portion of the disk  52  that formed as the fixed member  69  is fixed to the fluid passage forming member  46 , and a plurality of liquid inlets  59  are formed near the inner circumferential portion of the disk  52 . 
     With the structure as above, driving the canned motor  12  rotates only the disk  51 , and the disk  52  does not rotate. However, a strong liquid shearing force field is generated in the flow path  53 , resulting in shearing flow, which, in addition to expanded flow caused by the flow path expansion portion  56 , enables micronizion of bubbles. 
     The same effects can be achieved by reversing the structure of the disks  51 , 52  of the embodiment, in other words providing the upper disk  51  as the fixed member  69  so that the lower disk  52  alone is capable of rotating. 
     The centrifugal fins  54  and/or the stirring fins  60  may be provided on the upper disk  51  of the rotation unit  13 , or, as in the fifth embodiment shown in  FIG. 6 , the rotation unit  13  may not be provided with centrifugal fins  54  or stirring fins  60 . 
     Next, an embodiment of the present invention is shown in  FIG. 8 , wherein  FIG. 8  ( a ) is a sectional view illustrating the part where the rotation unit is provided, and  FIG. 8  ( b ) is a bottom view illustrating the flow path of the rotation unit. 
     This embodiment has the same structure as found in the embodiment shown in  FIG. 3 , with the exception of a modification made to the flow path  53 . 
     According to this embodiment, the flow path expansion portion  56  is formed by providing only one of the disks, i.e. the lower disk  52 , with a tapered portion  52   a . This structure is able to not only achieve the same functions and effects as can be done by the above embodiment of the invention shown in  FIG. 3  but also provides a further benefit in that it facilitates production of the rotation unit  13 . 
     In  FIG. 8 , the lower disk  52  alone is provided with a tapered portion  52   a . However, a structure wherein the upper disk  51  alone is provided with a tapered portion achieves the same effects. 
     Next, an embodiment of the present invention is shown in  FIG. 9 , which is a sectional view illustrating the part where the rotation body is provided. 
     The embodiment has the same structure as found in the embodiment shown in  FIG. 3 , except that a guide portion  70  is provided along the outer circumferential surface of the fluid passage forming member  46 , which is a stationary portion facing the liquid inlet  59  of the rotation unit  13 . The guide portion  70  serves to guide and thereby facilitate flow of the liquid being introduced into the liquid inlet  59  as a result of rotation of the rotation unit  13 . 
     As the guide portion  70  enables the liquid to flow into the liquid inlet  59  of the rotation unit  13  smoothly, it is possible to increase the discharge rate of the liquid from the outer circumferential portion of the rotation unit  13 . Next, another embodiment of the present invention is shown in  FIG. 10 , which is a sectional view illustrating the part where the rotation body is provided. 
     This embodiment has the same structure as found in the embodiment shown in  FIG. 3 , except that a guide portion  70  is provided along the outer diameter end of the liquid inlet  59  of the rotation unit  13 . The guide portion  70  serves to guide and thereby facilitate flow of the liquid being introduced into the liquid inlet  59  as a result of rotation of the rotation unit  13 . 
     As the guide portion  70  enables the liquid to flow into the liquid inlet  59  of the rotation unit  13  smoothly, it is possible to increase the discharge rate of the liquid from the outer diameter portion of the rotation unit  13 . 
     Next, an embodiment of the present invention is shown in  FIG. 11 , wherein  FIG. 11  ( a ) is a sectional view illustrating the part where the rotation unit is provided, and  FIG. 11  ( b ) is a bottom view illustrating the flow paths of the rotation unit. 
     According to the embodiment, the space between the disks  51 , 52  is partitioned by a plurality of centrifugal fins  54  so as to form a plurality of flow paths  53  open at the inner diameter side as well as the outer diameter side of the rotation unit  13 . Each flow path  53  is provided with a flow path contraction portion  55 , a minimum gap portion  57 , and a flow path expansion portion  56 . 
     While having a uniform dimension with respect to the axial cross section of the rotation unit  13 , each flow path  53  has a flow path contraction portion  55  and a flow path expansion portion  56 , at which the dimension of the flow path  53  respectively decreases and increases in a direction towards the outer diameter side with respect to the diametrical cross section of the rotation unit  13 . 
     The structure described above is able to achieve the same functions and effects as can be done by the embodiment of the invention shown in  FIG. 3 . 
     Next, an embodiment of the present invention is shown in  FIG. 12 , wherein  FIG. 12  ( a ) is a sectional view illustrating the part where the rotation unit is provided, and  FIG. 12  ( b ) is a bottom view illustrating the flow paths of the rotation unit. 
     According to the embodiment, the rotation unit  13  has a rotation unit body  71  and a plurality of Venturi tubes  72 . The rotation unit body  71  has a boss  61  attached to the rotary shaft  17  of the canned motor  12 . Each Venturi tube projects from the outer peripheral surface of the rotation unit body  71  in a direction opposite the direction of rotation of the rotation unit  13 , which is indicated by the arrow in  FIG. 12  ( b ), along a tangential line. 
     The rotation unit body  71  is provided with a liquid inlet  59  communicating with the interior of the Venturi tubes  72 . Each Venturi tube  72  has a tubular flow path  53 , which opens at the inner diameter side as well as the outer diameter side of the rotation unit  13  and includes a flow path reduction portion  55 , a minimum gap portion  57 , and a flow path expansion portion  56 . 
     The structure as above produces a pump effect inside the Venturi tubes  72  for enabling a mixture of gas and liquid to flow therethrough and a stirring effect outside the Venturi tubes  72  for stirring the liquid in the tank  66 . 
     Furthermore, the Venturi tubes  72  may have any outer shape that is a cylindrical, square, rectangular, or any polygonal shape having more than four sides. However, Venturi tubes with a tubular shape having a polygonal cross section are capable of improving the stirring effect for stirring the liquid in the tank  66 . 
     Next, yet another embodiment of the present invention is shown in  FIG. 13 , which is a sectional view illustrating the part where the rotation body is provided. 
     The embodiment has the same structure as found in the embodiment shown in  FIG. 5 , except that a metal mesh  73  that serves as a porous member is provided as a circumferentially uninterrupted band, at a location between the flow path expansion portion  56  and the inner diameter side of the rotation unit  13 . The centrifugal fins  54  that are provided between the flow path expansion portion  56  and the inner diameter side in the embodiment shown in  FIG. 5  may be omitted or provided as in the embodiment. 
     The gas introduced from the fluid inlet  48  is fed from the fluid outlet  49  into the central part of the rotation unit  13 . The liquid in the tank  66  is introduced from the liquid inlet  59  of the rotation unit  13 , which is being rotated by driving the canned motor  12 . The mixture of the gas and the liquid subsequently is mixed at the metal mesh  73  and passes through the flow path contraction portion  55  and the flow path expansion portion  56  of the flow path  53  of the rotation unit  13  sequentially and is discharged out of the rotation unit  13 . 
     In addition to ensuring satisfactory contact between the gas and the liquid when their mixture passes through the metal mesh  73 , this structure presents a benefit in that centrifugal effect by the centrifugal fins  54  and the metal mesh  73  increases pressure in the diametrically inner part of the flow path  53  with respect to the flow path expansion portion  56 , i.e. the part between the flow path expansion portion  56  and the inner diameter end of the flow path  53 , thereby enabling pressure dissolution of the gas in the liquid. When the liquid containing the pressure-dissolved gas passes through the flow path  53 , the drop in pressure causes the gas that is supersaturated in the liquid to be generated as microbubbles, and the liquid saturated with the dissolved gas is discharged. 
     In order to ensure a sufficient discharge rate from the rotation unit  13  provided with the metal mesh  73 , it is desirable to enhance the centrifugal effect by, for example, arranging the centrifugal fins  54  at 45° intervals in the circumferential direction of the rotation unit  13 . 
     Furthermore, what serves as the porous member is not limited to a metal mesh  73 , and any other appropriate member, such as a plate with a plurality of holes formed therein may be used. 
     Next, another embodiment of the present invention is shown in  FIG. 14 , wherein  FIG. 14  ( a ) is a sectional view illustrating the part where the rotation unit and a stationary unit are provided, and  FIG. 14  ( b ) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
     According to the embodiment, the stationary unit  75  is provided outside the outer circumferential surface of the rotation unit  13 . 
     The rotation unit  13  includes two disks  51 , 52 , which face each other and thereby form a flow path therebetween, and a plurality of centrifugal fins  54  provided between the disks  51 , 52 . The central part of the disk  51 , which is further from the canned motor  12  than is the disk  52 , is open upward. The stationary unit  75  includes a stationary unit body  76 , which is formed as an integral body and also serves as the fluid passage forming member  46 . The stationary unit body has a rotation unit housing portion  77 , in which the rotation unit  13  is rotatably positioned. The stationary unit body  76  has a plurality of flow paths  53  extending from the interior of the rotation unit housing portion  77  and are open at the outer diameter side of the stationary unit body  76 . Each flow path  53  extends in a direction corresponding to the direction of rotation of the rotation unit  13 , which is indicated by the arrow in  FIG. 14  ( b ), along a tangential line. While having a uniform dimension with respect to the axial cross section, each flow path  53  has a flow path contraction portion  55  and a flow path expansion portion  56  at which the dimension of the flow path  53  respectively decreases and increases in a direction towards the outer diameter side with respect to the diametrical cross section. A liquid inlet  59  is formed at the upper part of the stationary unit  75 . A pipe  78  is connected through a stay  78   a  to the upper part of the stationary unit  75 . By a structure wherein the pipe  78  extends so that the upper end portion thereof reaches the upper part of the tank  66  and supported in that state, it is possible to feed the gas to the rotation unit  13  through the pipe  78 . In other words, the gas may be fed to the rotation unit  13  from either one of or both the lower part of the rotation unit  13 , at which the canned motor  12  is provided, and the upper part of the rotation unit  13 , at which the pipe  78  is provided. When the gas is fed through the pipe  78 , the aperture at the center of the disk  51 , at which the lower end of the pipe  78  is located, serves as a fluid outlet  49  through which the gas introduced from above is introduced into the rotation unit  13 . 
     The fluid passage  45  communicates with the flow paths  53  through the gap between the stationary unit body  76  and the disk  52  of the rotation unit  13 . One other fluid outlet  49  is formed between the stationary unit body  76  and the outer circumferential part of the disk  52  of the rotation unit  13 . With the structure as above, when the gas is introduced from the fluid inlet  48 , the gas is fed through the fluid passage  45  into the diametrically outer part of the rotation unit  13 . Or when the gas is introduced from the upper end of the pipe  78 , the gas is fed through the pipe  78  into the diametrically inner part of the rotation unit  13 . 
     When the rotation unit  13  rotates, the liquid in the tank  66  is sucked from the liquid inlet  59  of the rotation unit  13 . As a result, the mixture of the gas and the liquid fed into the rotation unit  13  is discharged into the flow paths  53  of the stationary unit  75 . When the mixture of the gas and the liquid passes through the flow path expansion portion  56  of each flow path  53 , the change of the dimension of the flow path causes a change in the flow velocity, and consequently the pressure, of the gas-liquid mixture, resulting in micronization of the gas in the liquid. 
     Furthermore, a liquid inlet  59  for introducing the liquid from the tank  66  may be provided below the stationary unit  75 . 
     Next, a further embodiment of the present invention is shown in  FIG. 15 , wherein  FIG. 15  ( a ) is a sectional view illustrating the part where the rotation unit and the stationary unit are provided, and  FIG. 15  ( b ) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
     The embodiment has the same structure as found in the embodiment shown in  FIG. 14 , except that the stationary unit has a plurality of Venturi tubes  79 , each of which projects from the outer peripheral surface of the stationary unit body  76  in a direction corresponding to the direction of rotation of the rotation unit  13 , which is indicated by the arrow in  FIG. 15  ( b ), along a tangential line. 
     Each Venturi tube  79  has a flow path  53 , which opens at the inner diameter side as well as the outer diameter side of the rotation unit  13  and includes a flow path contraction portion  55 , a minimum gap portion  57 , and a flow path expansion portion  56 . 
     The structure described above is able to achieve the same functions and effects as can be done by the embodiment of the invention shown in  FIG. 14 . 
     Next, an embodiment of the present invention is shown in  FIG. 16 , wherein  FIG. 16  ( a ) is a sectional view illustrating the part where the rotation unit and the stationary unit are provided, and  FIG. 16  ( b ) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
     The embodiment has the same structure as found in the embodiment shown in  FIG. 14 , except that the stationary unit includes two disks  82 , 83 , between which a circumferentially uninterrupted flow path  53  is formed. Tapered portions  82   a , 83   a  are formed on the opposing surfaces of the respective disks  82 , 83 . The tapered portions  82   a , 83   a  are inclined so that the gap therebetween flares outward, towards the outer diameter end of the disks  82 , 83 . As a result, the flow path  53  includes a flow path contraction portion  55 , a minimum gap portion  57 , and a flow path expansion portion  56 . 
     The structure described above is able to achieve the same functions and effects as can be done by the embodiment of the invention shown in  FIG. 14 . 
     The flow path of the stationary unit  75  may be provided with one tapered portion ( 82   a  or  83   a ), which is provided on either one of the disks  82 , 83 , as in the embodiment shown in  FIG. 8 . 
     Next, an embodiment of the present invention is shown in  FIG. 17 , wherein  FIG. 17  ( a ) is a sectional view illustrating the part where the rotation unit and the stationary unit are provided, and  FIG. 17  ( b ) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
     The embodiment has the same structure as found in the embodiment shown in  FIG. 16 , except that the upper disk  82  of the stationary unit  75  has a cover portion  86  for covering the top surface of the rotation unit  13  and that a plurality of liquid inlets  59  are formed near the inner circumferential portion of the lower disk  83 . Formed at the central part of the cover portion  86  are an indented portion  87 , which is formed in the bottom face of the cover portion  86 , and a hole  88  that passes through the indented portion  87  and is open to the top surface of the cover portion  86 . Another difference of the embodiment lies in that the rotation unit  13  includes one of the disks, i.e. the disk  51 , and a plurality of centrifugal fins  54 . 
     In cases where a dispersion tank  65  is equipped with a dispersion/stirring apparatus  11  having a structure described above, the tank  66  is empty at the initiation of the process, and when the liquid begins to be fed into the tank  66  to be retained therein, the gas remaining in the stationary unit  75  of the dispersion/stirring apparatus  11  can be discharged out of the stationary unit  75  from the hole  88 . As a result, it is possible to prevent the generation of cavitation or failure of function of the rotation unit  13 , which would otherwise occur due to the gas remaining in the stationary unit  75  during operation of the dispersion/stirring apparatus  11 . 
     Furthermore, should an excessive quantity of the gas be introduced from the liquid inlet  48  into the stationary unit  75 , the excess gas that cannot be dissolved or dispersed in the liquid flows out of the stationary unit  75  from the hole  88  of the stationary unit  75 . Therefore, it is possible to monitor an appropriate amount of the supply of gas by visually ascertaining whether gas flows out of the hole  88 . If it appears that gas is flowing out of the hole  88 , supply of the gas can be appropriately adjusted so that no excess gas will flow out. This feature is effective in preventing various problems, such as cavitation as well as malfunction of the rotation unit  13 , that are prone to occur in case of excessive supply of gas. 
     In any one of the embodiments shown in  FIGS. 1 to 13 , the same function and effects as those performed by the hole  88  formed in the stationary unit  75  described above can be achieved by a hole that communicates with the interior and the exterior of the rotation unit  13  and is formed at a location in the proximity of the center (for example, outside the boss  61  or at the boss  61 ) of the disk  51 , which is the upward-facing end of the rotation unit  13 . 
     Next, a further embodiment of the present invention is shown in  FIG. 18 , wherein  FIG. 18  ( a ) is a sectional view illustrating the part where the rotation unit and the stationary unit are provided, and  FIG. 18  ( b ) is a sectional view illustrating the flow paths of the rotation unit and the stationary unit viewed from the bottom side. 
     The embodiment has the same structure as found in the embodiment shown in  FIG. 17 , except that the rotary shaft  17  of the canned motor  12  extends to such a location as to pass through the stationary unit  75  and that a stirring fin unit  91  is attached to the front end of the rotary shaft  17  and adapted to rotate, outside the stationary unit  75 , integrally with the rotation unit  13 . 
     The stirring fin unit  91  includes a disk  92 . A plurality of radially arranged stirring fins  93  are provided on and project from the externally facing planar surface of the disk  92 , i.e. the surface facing away from the stationary unit  75 . A boss  94  attached to the rotary shaft  17  of the canned motor  12  is formed at the central part of the disk  92 . The stirring fin unit  91  is fastened, together with the rotation unit  13 , to the front end of the rotary shaft  17  of the canned motor  12  by fastening a bolt  62 . 
     Therefore, the stirring fins  93  of the stirring fin unit  91 , which is adapted to rotate outside the stationary unit  75  integrally with the rotation unit  13 , enables, without the need of a separate stirring device, greater reliability for stirring the gas-containing liquid in the tank  66 . 
     Next, an embodiment of the present invention is shown in  FIG. 19 , which is a sectional view illustrating the part where the rotation body and the stationary unit are provided. The embodiment has the same structure as found in the embodiment shown in  FIG. 17 , except that a metal mesh  73  that serves as a porous member is provided as a circumferentially uninterrupted band. The centrifugal fins of the rotation unit  13 , which are provided in the embodiment shown in  FIG. 17  may be omitted or provided as in the embodiment. 
     As a result of driving the canned motor  12 , the rotation unit  13  rotates so that the gas introduced from the fluid inlet  48  is fed from the fluid outlet  49  into the central part of the rotation unit  13 . The rotation unit  13  being rotated by driving the canned motor  12  causes the liquid in the tank  66  to be introduced from the liquid inlet  59  of the stationary unit  75 . The mixture of the gas and the liquid subsequently is mixed at the metal mesh  73  of the rotation unit  13  and passes through the flow path reduction portion  55  and the flow path expansion portion  56  of the flow path  53  of the stationary unit  75  sequentially and is discharged out of the stationary unit  75 . 
     In addition to ensuring satisfactory contact between the gas and the liquid when their mixture passes through the metal mesh  73 , this structure presents a benefit in that centrifugal effect by the metal mesh  73  increases pressure in the diametrically inner part of the flow path  53  with respect to the flow path expansion portion  56 , i.e. the part between the flow path expansion portion  56  and the inner diameter end of the flow path  53 , thereby enabling pressure dissolution of the gas in the liquid. When the liquid containing the pressure-dissolved gas passes through the flow path  53 , the drop in pressure causes the gas that is supersaturated in the liquid to be generated as microbubbles, and the liquid saturated with the dissolved gas is discharged. 
     The application of the metal mesh  73  is not limited to the structure described above, wherein the rotation unit  13  is provided with the metal mesh  73 . The metal mesh  73  may be provided at a location between the inner diameter side and the flow path expansion portion  56  of the flow path  53  of the stationary unit  75 . Furthermore, both the rotation unit  13  and the stationary unit  75  may respectively be provided with a metal mesh  73 . 
     Furthermore, what serves as the porous member is not limited to a metal mesh  73 , and any other appropriate member, such as a plate with a plurality of holes formed therein may be used. 
     Next, another embodiment of the present invention is shown in  FIG. 20 , which is a sectional view of a dispersion tank. According to the embodiment, an external cyclic path  97  connecting the bottom portion and the upper part of the side of the tank  66  is provided. The external cyclic path  97  is provided with a pump  98  that serves to introduce the liquid from the bottom of the tank  66  into the external cyclic path  97  and return the liquid from the external cyclic path  97  to the upper side of the tank  66 , thereby circulating the liquid. 
     A delivery path  99  is connected to the discharge side of the pump  98  of the external cyclic path  97  and serves to deliver to a next process a part of the gas-containing liquid in the external cyclic path  97  introduced from the tank  66 . The external cyclic path  97  and the delivery path  99  are respectively provided with valves  100 , 101 , which are respectively provided downstream from the point where the external cyclic path  97  and the delivery path  99  are connected. Flow rate adjustment by these valves  100 , 101  enables adjustment of delivery amount of the gas-containing liquid from the delivery path  99 . 
     By operating the pump  98  so as to introduce the gas-containing liquid from the bottom of the tank  66  into the external cyclic path  97  and return the liquid into the upper part of the tank  66 , the gas-containing liquid in the tank  66  can be stirred and mixed. 
     Therefore, the external cyclic path  97  in addition to the stirring function of the dispersion/stirring apparatus  11  enables more reliable stirring of the gas-containing liquid in the tank  66 . 
     Furthermore, the delivery path  99  enables a part of the gas-containing liquid that has been introduced from the tank  66  into the external cyclic path  97  to be delivered to a next process. At that time, connecting the delivery path  99  to the external cyclic path  97  enables the use of discharge pressure by the pump  98  for delivery of the liquid containing the gas. 
     As there are two or more kinds of fluids in the tank  66 , the liquid is retained in the lower part of the tank  66 , while the gas that cannot be dispersed in the liquid separates from the liquid resulting from the difference in specific gravity and is retained in the upper part of the tank  66 . Connected to the fluid inlet  48  of the dispersion/stirring apparatus  11  are a fluid supply path  102  and a fluid cyclic path  103 , which are respectively provided with valves  104 , 105 . The fluid supply path  102  serves to feed pressurized gas from the outside. The fluid cyclic path  103  shares a part of the fluid supply path  102  and serves to return the gas in the upper part of the tank  66  to the dispersion/stirring apparatus  11 . 
     A gas discharge path  106  for discharging the gas to the outside is connected to the upper part of the tank  66 . The gas discharge path  106  is provided with a valve  107 . 
     With the structure as above, the gas can be fed to the dispersion/stirring apparatus  11  through the fluid supply path  102 , while self-suction function resulting from rotation of the rotation unit  13  of the dispersion/stirring apparatus  11  enables the gas in the upper part of the tank  66  to be returned to the dispersion/stirring apparatus  11  through the fluid cyclic path  103  so as to be dispersed and stirred into the liquid in the tank  66 . Therefore, as reuse of the gas to be dispersed is possible, the consumption efficiency of the gas to be dispersed is improved, resulting in improved efficiency of the entire system. 
     Furthermore, in cases where a dispersion/stirring apparatus having a structure according to any one of the embodiments from the thirteenth to the fifteenth embodiments shown in  FIGS. 14 to 16 , the pipe  78  fixed to the stationary unit  75  of the dispersion/stirring apparatus  11  is arranged so that the upper end of the pipe  78  is positioned in the area of the upper part of the tank  66  where the gas is retained. With the structure as above, self-suction function resulting from rotation of the rotation unit  13  of the dispersion/stirring apparatus  11  enables the gas in the upper part of the tank  66  to be returned to the dispersion/stirring apparatus  11  through the pipe  78  so as to be dispersed and stirred into the liquid in the tank  66 . As a result, the pipe  78 , too, functions as a fluid cyclic path  103 . 
     Next, a embodiment of the present invention is shown in  FIG. 21 , which is a sectional view of a dispersion tank. The embodiment has the same structure as found in the embodiment shown in  FIG. 20 , except that the fluid cyclic path  97 , instead of the tank  66 , is provided with the dispersion/stirring apparatus  11 . To be more specific, a dispersion/stirring chamber  110  is formed at some point along the length of the fluid cyclic path  97 , between the pump  98  and the bottom of the tank  66 , and the rotation unit  13  of the dispersion/stirring apparatus  11  is positioned in the dispersion/stirring chamber  110 . 
     By operating the pump  98  so as to introduce the liquid from the bottom of the tank  66  into the external cyclic path  97  and return the liquid into the upper part of the tank  66 , the gas-containing liquid in the tank  66  can be stirred and mixed. 
     At that time, the dispersion/stirring apparatus  11  is capable of dispersing and stirring the gas into the liquid introduced into the fluid cyclic path  97 . 
     Furthermore, in cases where a part of the gas-containing liquid that has been introduced from the tank  66  into the external cyclic path  97  is delivered through the delivery path  99  to a next process, the dispersion/stirring apparatus disperses the gas into the liquid introduced into the fluid cyclic path  97  and stirs the resultant mixture, thereby ensuring reliable dispersion of the gas as well as delivery of the liquid containing the dispersed gas into the delivery path  99 . 
     A dispersion/stirring apparatus  11  that is provided with a rotation unit  13  and a stationary unit  75  may serve as the dispersion/stirring apparatus  11  used for this embodiment. The shapes of the flow path of the rotation unit  13  or the stationary unit  75  of the dispersion/stirring apparatus  11  according to the present invention are not limited to those explained as above referring to the embodiments of the invention, and any shape is permissible, provided that the flow path expansion portion  56  can be formed. 
     For example, it is not essential to provide the flow path  53  with a flow path contraction portion  55 . In another alternative structure, a passage portion having the same dimension as that of the minimum gap portion  57  may be provided in the diametrically inner part of the flow path  53 . It is also possible to provide a plurality of flow path expansion portions  56  in series arranged in a diametrical direction of the flow path  53  so as to increase even further the degree of micronization of the gas passing through the flow path  53 . Furthermore, in cases where the rotation unit  13  is provided with the flow path  53 , the flow path  53  may be formed diagonally so that a discharge port at the outer circumferential side of the flow path  53  is open at the outer diameter end of the disk  51  of the rotation unit  13 . It is also possible to provide a single rotary shaft  17  of the dispersion/stirring apparatus  11  with a plurality of rotation units  13  or a plurality of rotation units  13  and stationary units  75 . If such is the case, the quantity of the gas to be dispersed and stirred into the liquid can be increased. 
     The structure for feeding the fluid to the rotation unit  13  is not limited to those explained as above referring to the embodiments of the invention, and any structure is permissible, provided that the fluid can be fed without any problems. 
     The flow path  53  may be provided with, in the place of Venturi tubes, any other appropriate member, such as an orifice unit having numerous holes formed in the entire circumferential surface thereof, to micronize the gas. 
     The application of the dispersion/stirring apparatus  11  and the dispersion tank  65  having structures described above is not limited to dispersing and stirring a second fluid into a first fluid retained in the tank  66 , wherein the first fluid may be a liquid, and the second fluid is different from the first fluid and contains at least one fluid that is a gas, a liquid that is not soluble with the liquid in the tank  66 , or a liquid that contains bubbles. The dispersion/stirring apparatus  11  and the dispersion tank  65  are also applicable to dispersion of secondary particles, i.e. aggregations of primary particles, in a suspension liquid into primary particles, or micronization of liquid droplets in a dispersion liquid. 
     The present invention is applicable to, for example, dispersing and stirring a second fluid into a first fluid.