Patent Publication Number: US-9403132-B2

Title: Fluid mixer and fluid mixing method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application relates to and claims priority from International Application Ser. No. PCT/JP2011/079637 filed Dec. 21, 2011, the entire contents of which are incorporated herein by reference which in turn claims priority from JP Ser. No. 2011-167100 filed Jul. 29, 2011 and JP Ser. No. 2010-285833 filed Dec. 22, 2010. 
     TECHNICAL FIELD 
     The present invention relates to a fluid mixer and a fluid mixing method for mixing plural kinds of fluids. Here, fluid means liquid or gas. Fluid may also mean a liquid-liquid mixture, a liquid-gas mixture or a gas-gas mixture. Particularly, the present invention can refine and homogenize a dispersion phase of emulsion. Emulsion means a disperse system solution where both a dispersoid and a dispersion medium are in a liquid form. 
     BACKGROUND ART 
     Conventionally, as one mode of a fluid mixer, there has been known an emulsifying apparatus disclosed in patent literature 1. Such an emulsifying apparatus is configured as follows. To a dispersion phase flow path which extends linearly, a pair of continuous phase flow paths which extends in the direction orthogonal to the dispersion phase flow path is connected by way of a swirl flow path which swirls around an axis of the dispersion phase flow path and thereby a mixing flow path is formed coaxially with the dispersion phase flow path and downstream of the swirl flow path. 
     Due to such a constitution, a dispersion phase supplied through the dispersion phase flow path and a continuous phase supplied through the continuous phase flow path merge through the swirl flow path, and these phases are mixed with each other through the mixing flow path thus forming emulsion. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: JP-A-2009-279507 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the above-mentioned emulsifying apparatus is constituted by laminating a liquid introducing portion, a merged flow path portion, a mixing flow path portion and a liquid exit portion all of which have a plate shape. The flow path forming passages which are formed in the respective portions are connected with each other thus forming a dispersion phase flow path, a continuous phase flow path, a swirl flow path and a mixing flow path. In this manner, the structure is complicated and it is cumbersome to form the respective flow path forming passages. Accordingly, a manufacturing cost of the emulsifying apparatus is expensive, and a dispersion phase cannot be refined at a sub-micro level. 
     Accordingly, it is an object of the present invention to provide a fluid mixer and a fluid mixing method which can refine and homogenize a dispersion phase at a micro level or a sub-micro level at a low cost with the simple structure. 
     Solution to Problem 
     A fluid mixer according to the invention described in claim  1  is characterized in that a cylindrical mixer body having an opening portion on both ends thereof forms therein: an axial flow path in which a first fluid introduced into the axial flow path through the opening portion at one end is made to flow therethrough in the axial direction and the first fluid is made to exit from the opening portion at the other end; and a spiral flow path in which a second fluid introduced into the spiral flow path through a hole for introducing fluid into the mixer body formed in a peripheral wall of the mixer body is made to flow along an inner peripheral surface of the mixer body while being swirled in a spiral manner about an axis of the axial flow path so that the first fluid and the second fluid are mixed with each other and a mixture formed of the first fluid and the second fluid is made to exit from the opening portion at the other end. 
     Such a fluid mixer is, for example, arranged in the inside of a vessel which stores the second fluid which forms a continuous phase. The first fluid which forms a dispersion phase is made to flow through the axial flow path along the axial direction through the opening portion at one end to the opening portion at the other end of the mixer body (for example, the first fluid being sucked by a suction pump into the axial flow path from a side where the opening portion on the other end is formed). Due to such a constitution, pressure in the axial flow path can be reduced so that the second fluid can be introduced by suction into the mixer body through the hole for introducing fluid into the mixer body. Next, the second fluid introduced by suction into the mixer body through the hole for introducing fluid into the mixer body formed in the mixer body is made to form a swirl flow in a spiral manner through the spiral flow path around the first fluid which flows through the axial flow path so that the first fluid is sheared and dispersed over the whole region of the spiral flow path. As a result, the first fluid and the second fluid are uniformly mixed with each other. 
     In such an operation, the second fluid is made to form the swirl flow in a spiral manner about the axis of the axial flow path through the spiral flow path. That is, the second fluid is made to swirl while a swirling radius of the second fluid is gradually decreased toward the axis (center) from an outer peripheral side of the axial flow path. Accordingly, the swirl flow is accelerated on an axis side and applies a shearing action to the first fluid at a high speed and hence, the first fluid is dispersed finely and uniformly. 
     The fluid mixer according to the invention described in claim  2  is, in the fluid mixer according to the invention described in claim  1 , characterized in that an outer periphery of the mixer body is covered with a cover member with a predetermined gap maintained therebetween, a swirl flow path is formed in the inside of the cover member such that the second fluid introduced into the inside of the cover member through a hole for introducing fluid into the cover member formed in a peripheral wall of the cover member is made to flow along an inner peripheral surface of the cover member while being swirled about the axis of the axial flow path, and the second fluid is introduced into the hole for introducing fluid into the mixer body formed in the mixer body, and the first fluid which axially flows through the axial flow path and the second fluid which forms a swirl flow in a spiral manner around the first fluid are mixed with each other over the whole region of the spiral flow path, and a mixture of the first fluid and the second fluid is made to exit from the opening portion at the other end. 
     Such a fluid mixer is, for example, arranged in the inside of a vessel which stores the second fluid which forms a continuous phase. The first fluid which forms a dispersion phase is made to flow through the axial flow path along the axial direction through the opening portion at one end to the opening portion at the other end of the mixer body (for example, the first fluid being sucked by a suction pump into the axial flow path from the opening portion at the other end). Due to such a constitution, pressure in the axial flow path can be reduced so that the second fluid can be introduced by suction into the cover member from the cover introducing hole. Next, the second fluid introduced into the cover member is made to swirl through the swirl flow path and is also introduced by suction into the inside the mixer body through the hole for introducing fluid into the mixer body formed in the mixer body. Subsequently, the second fluid introduced by suction into the mixer body through the hole for introducing fluid into the mixer body formed in the mixer body is made to form a swirl flow in a spiral manner through the spiral flow path around the first fluid which flows through the axial flow path so that the first fluid is sheared and dispersed over the whole region of the spiral flow path. As a result, the first fluid and the second fluid are uniformly mixed with each other. 
     In such an operation, the second fluid is made to swirl about the axis of the axial flow path provisionally in the swirl flow path and, subsequently, is made to form the swirl flow in a spiral manner about the axis of the axial flow path through the spiral flow path. That is, the second fluid is made to swirl while gradually decreasing a swirling radius toward the axis (center) from an outer peripheral side of the axial flow path. Accordingly, the swirl flow is accelerated on an axis side and applies a shearing action to the first fluid at a high speed and hence, the first fluid is dispersed finely and uniformly. 
     Further, the fluid mixer can be constituted of the cylindrical mixer body having the opening portions on both ends thereof, and the cover member which covers the outer periphery of the mixer body with a predetermined gap maintained therebetween and hence, the fluid mixer which is light-weighted and has the simple structure can be manufactured at a low cost using a synthetic resin or the like. 
     The fluid mixer according to the invention described in claim  3  is, in the fluid mixer according to the invention described in claim  1  or  2 , characterized in that the mixer body includes: a proximal-end-side cylindrical portion which is formed with a diameter thereof gradually increasing toward the opening portion at the other end through the opening portion at one end; and a distal-end-side cylindrical portion which is formed with the approximately same diameter from a terminal end of the proximal-end-side cylindrical portion to the opening portion at the other end, a plurality of slit-like holes for introducing fluid into the mixer body which extend with a predetermined acute angle with respect to the longitudinal direction are formed in a peripheral wall of the distal-end-side cylindrical portion, and the respective holes for introducing fluid into the mixer body are arranged at intervals along a single imaginary spiral in the extending direction thereof. 
     In such a fluid mixer, the proximal-end-side cylindrical portion of the mixer body is formed such that the diameter of the proximal-end-side cylindrical portion is gradually increased, and the distal-end-side cylindrical portion of the mixer body is formed such that the diameter of the distal-end-side cylindrical portion is approximately equal from the terminal end of the proximal-end-side cylindrical portion to the opening portion at the other end thus making the second fluid form a swirl flow in a spiral manner in the distal-end-side cylindrical portion. Accordingly, the miscibility and the swirling property of the first fluid which is made to flow from the proximal-end-side cylindrical portion to the distal-end-side cylindrical portion and the second fluid which is made to form a swirl flow in a spiral manner in the distal-end-side cylindrical portion can be enhanced. 
     In forming the hole for introducing fluid into the mixer body, a plurality of slit-like holes for introducing fluid into the mixer body are formed in the peripheral wall of the distal-end-side cylindrical portion in such a manner that slit-like holes which extend while making a predetermined acute angle with respect to the longitudinal direction. The plurality of holes for introducing fluid into the mixer body are arranged along the single imaginary spiral. Accordingly, the second fluid which is introduced through the hole for introducing fluid into the mixer body is made to surely swirl in a spiral manner in the mixer body. 
     The fluid mixer according to the invention described in claim  4  is, in the fluid mixer according to the invention described in claim  2  or  3 , characterized in that a slit-like hole for introducing fluid into the cover member which extends along the longitudinal direction of the cover member is formed in a peripheral wall of the cover member. 
     In such a fluid mixer, the hole for introducing fluid into the cover member is formed in the peripheral wall of the cover member in a slit shape which extends in the longitudinal direction of the cover member. Accordingly, the second fluid which is introduced through the hole for introducing fluid into the cover member is made to flow along an inner peripheral surface of the cover member and is made to surely swirl. Accordingly, the second fluid which forms a continuous phase is changed to a spiral swirl flow on the inner periphery from a provisional swirl flow on the outer periphery thus forming a high-speed swirl flow and thereby the second fluid imparts a shearing and dispersion action on the first fluid which forms a dispersion phase. As a result, the first fluid is refined and homogenized at a sub-micro level. 
     A fluid mixing method according to the invention described in claim  5  is characterized in that a first fluid which flows through the axial flow path along the axial direction of an axial flow path, and a second fluid which forms a swirl flow through a swirl flow path and, thereafter, forms a swirl flow in a spiral manner through a spiral flow path on the outer periphery of the first fluid are mixed with each other while being made to flow in the axial direction of the axial flow path. 
     In such a fluid mixing method, the first fluid is made to flow through the axial flow path along the axial direction of the axial flow path, and the second fluid which forms a swirl flow provisionally on an outer periphery of the first fluid and, thereafter, forms a high-speed swirl flow in a spiral manner through the spiral flow path can be mixed to the first fluid while being made to flow in the axial direction of the axial flow path. As a result, the first fluid which forms a dispersion phase is refined and, at the same time, is uniformly dispersed into the second fluid which forms a continuous phase. 
     A fluid mixing method according to the invention described in claim  6  is, in the fluid mixing method according to the invention described in claim  5 , characterized in that, in the inside of a vessel which stores the second fluid therein, the first fluid is made to flow along the axial direction in the axial flow path thus reducing a pressure in the axial flow path and thereby the second fluid stored in the vessel is sucked into the axial flow path and is made to form a swirl flow in a spiral manner in the axial direction of the axial flow path. 
     In such a fluid mixing method, the pressure in the axial flow path is reduced by making the first fluid flow in the axial flow path along the axial direction so that the second fluid can be introduced into the axial flow path while being swirled and thereby a shearing and dispersion action is imparted on the first fluid. Accordingly, it is possible to favorably refine the first fluid which forms a dispersion phase, and it is also possible to favorably homogenize the second fluid which forms a continuous phase. Further, such a mixed fluid can be produced within a short time at a low cost. 
     Advantageous Effects of Invention 
     The present invention acquires the following advantageous effects. That is, the fluid mixing device according to the present invention has the simple structure, is light-weighted and compact, and can be manufactured at a low cost. Accordingly, the fluid mixing device according to the present invention can acquire an extremely advantageous effect with respect to a required initial cost. A cleaning operation and a maintenance operation of the fluid mixing device can be performed readily and easily. The fluid mixing method according to the present invention can efficiently shear and disperse the first fluid which forms a dispersion phase. Further, the first fluid can be refined and homogenized at a micro level or at a sub-micro level. Accordingly, a large amount of mixed fluid can be produced within a short time at a low cost. Particularly, according to the present invention, micro emulsion (emulsion at a micro order) can be produced by making two phases (liquid phase-liquid phase) swirl and mixed with each other at a high speed and hence, an emulsifying speed can be remarkably enhanced. Accordingly, the fluid mixing method according to the present invention is suitable for the mass production of emulsion within a short time at a low cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory view of a fluid mixing device according to the first embodiment. 
         FIG. 2  is an explanatory cross-sectional front view of a fluid mixer according to the first embodiment. 
         FIG. 3  is an explanatory view of a fluid mixing device according to the second embodiment. 
         FIG. 4  is an explanatory cross-sectional front view of a fluid mixer according to the second embodiment. 
         FIG. 5  is an explanatory cross-sectional right side view of the fluid mixer according to the second embodiment. 
         FIG. 6  is an explanatory front view of the fluid mixer according to the second embodiment. 
         FIG. 7  is a cross-sectional view taken along a line I-I in  FIG. 6 . 
         FIG. 8  is an explanatory front view of a mixer body. 
         FIG. 9  is an explanatory developed view of the mixer body. 
         FIG. 10  is an explanatory view of a hole for introducing fluid into a body. 
         FIG. 11  is an explanatory right side view of the mixer body. 
         FIG. 12  is an explanatory front view of a cover member. 
         FIG. 13  is a cross-sectional view taken along a line II-II in  FIG. 12 . 
         FIG. 14  is an explanatory cross-sectional front view of the first modification of the fluid mixing device according to the first embodiment. 
         FIG. 15  is an explanatory cross-sectional front view of the second modification of the fluid mixing device according to the first embodiment. 
         FIG. 16  is an explanatory cross-sectional front view of the third modification of the fluid mixing device according to the first embodiment. 
         FIG. 17  is an explanatory cross-sectional front view of a modification of the fluid mixer according to the second embodiment. 
         FIG. 18  is a cross-sectional view taken along a line in  FIG. 17 . 
         FIG. 19  is a graph showing a result of measurement of a size of oil droplets (particles) which form a dispersion phase in an emulsion produced by the mixer body. 
         FIG. 20  is a graph showing a result of measurement of a size of oil droplets (particles) which forma dispersion phase in an emulsion produced by the fluid mixer according to the present invention. 
         FIG. 21  is a view showing a microscope image of a micro emulsion into which an oleic acid is introduced. 
         FIG. 22  is a graph showing the particle size distribution of a micro emulsion into which an oleic acid is introduced by an amount of 50 ml/min using a fluid mixer having an acute angle θ 2  of 24°. 
         FIG. 23  is a graph showing the particle size distribution of a micro emulsion into which an oleic acid is introduced by an amount of 50 ml/min using a fluid mixer having an acute angle θ 2  of 15°. 
         FIG. 24  is a graph showing particle size distribution of a micro emulsion into which oleic acid is introduced by 50 ml/min using a fluid mixer having an acute angle θ 2  of 30°. 
         FIG. 25  is a graph showing the particle size distribution of a micro emulsion into which an oleic acid is introduced by an amount of 100 ml/min. 
         FIG. 26  is a graph showing the particle size distribution of a micro emulsion at a flow rate of 23 l/min. 
         FIG. 27  is a table showing the number of particles of an oleic acid. 
         FIG. 28  is a table indicating viscosities of various oils, and average particle sizes and the number of particles which are confirmed in the measurement of the particle size distribution. 
         FIG. 29  is a graph showing the particle size distribution of a micro emulsion produced using water and soybean oil. 
         FIG. 30  is a graph showing the particle size distribution of a micro emulsion produced using water and rapeseed oil. 
         FIG. 31  is a graph showing the particle size distribution of micro emulsion produced using water and corn oil. 
         FIG. 32  is a graph showing the particle size distribution of micro emulsion produced using water and olive oil. 
         FIG. 33  is a graph showing the particle size distribution of micro emulsion produced using water and camellia oil. 
         FIG. 34  is a photograph of micro-emulsified camellia oil (immediately after processing). 
         FIG. 35  is a photograph showing micro-emulsified camellia oil after a lapse of three months (being left for three months after processing). 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the present invention are explained in conjunction with drawings. 
     Symbol  1  shown in  FIG. 1  indicates a fluid mixing device according to the first embodiment, and the fluid mixing device  1  includes a fluid mixer  10  according to the first embodiment shown in  FIG. 2 . In  FIG. 3 , symbol  1  indicates a fluid mixer according to the second embodiment. The fluid mixing device  1  includes a fluid mixer  10  according to the second embodiment shown in  FIG. 4 . The fluid mixing device  1  according to the first embodiment and the fluid mixing device  1  according to the second embodiment are provided for mixing a first fluid F 1  and a second fluid F 2  as shown in  FIG. 1  and  FIG. 3  respectively. In the embodiments of the present invention, the explanation is made assuming that the first fluid F 1  is a liquid which forms a dispersion phase (oil, for example), and the second fluid F 2  is a liquid which forms a continuous phase (water, for example). 
     [Explanation of Fluid Mixing Device  1 ] 
     The fluid mixing device  1  according to the first embodiment (second embodiment) is, as shown in  FIG. 1  ( FIG. 3 ), configured such that the second fluid F 2  is stored in the vessel-shaped second fluid storing portion  2  having an open-ended upper surface. The fluid mixer  10  according to the first embodiment (second embodiment) is arranged in the second fluid F 2 . A first fluid storing portion  4  which stores the first fluid F 1  therein is communicably connected to one end side (proximal end side) of the fluid mixer  10  by way of a first communication pipe  3  which constitutes a first communication path. A suction port (not shown in the drawing) of a suction pump P is communicably connected to the other end side (distal end side) of the fluid mixer  10  by way of a second communication pipe  5  which constitutes a second communication path. A mixed fluid storing portion  7  which stores a mixed fluid F 3  therein is communicably connected to a discharge port (not shown in the drawing) of the suction pump P by way of a third communication pipe  6  which constitutes a third communication path. 
     Due to such a constitution, when the suction pump P performs a suction operation, the first fluid F 1  stored in the first fluid storing portion  4  is introduced into the fluid mixer  10  through the first communication pipe  3 , the second fluid F 2  stored in the second fluid storing portion  2  is introduced into the fluid mixer  10  where pressure is reduced by a suction effect, and the first fluid F 1  and the second fluid F 2  are mixed with each other in the fluid mixer  10  so that the third fluid F 3  is formed. The third fluid F 3  passes through the second communication pipe  5 , the suction pump P and the third communication pipe  6  sequentially and, then, is stored in the mixed fluid storing portion  7 . The mixed fluid F 3  can be suitably recovered from the mixed fluid storing portion  7 . 
     [Explanation of Fluid Mixer  10 ] 
     The fluid mixer  10  according to the first embodiment is, as shown in  FIG. 1  and  FIG. 2 , constituted of only a cylindrical mixer body  11  which has an opening portion on both ends thereof. The fluid mixer  10  according to the second embodiment is, as shown in  FIG. 3  and  FIG. 4 , configured such that an outer periphery of the mixer body  11  is covered with a cylindrical cover member  30  with a predetermined gap therebetween, and the mixer body  11  and the cover member  30  are arranged concentrically (duplicate cylindrical shape). The fluid mixer  10  according to the second embodiment is constituted such that the mixer body  11  is inserted into the inside of the cover member  30  in a detachable manner, and a proximal end portion of the mixer body  11  projects from the cover member  30 . The fluid mixer  10  is made of synthetic resin and has a small wall thickness so that the fluid mixer  10  is light-weighted. The fluid mixer  10  has the simple structure so that the fluid mixer  10  is manufactured at a low cost. Further, the mixer body  11  can be removed from the cover member  30  and hence, the fluid mixer  10  can be easily disassembled into several parts whereby the cleaning operation and the maintenance operation of the respective parts can be performed. 
     In the fluid mixer  10  according to the first embodiment shown in  FIG. 1  and  FIG. 2 , the first communication pipe  3  made of a flexible raw material is communicably connected to the mixer body  11  in a state where a distal end portion of the first communication pipe  3  is detachably fitted on a proximal end portion of the mixer body  11 . The second communication pipe  5  made of a flexible raw material is communicably connected to the mixer body  11  in a state where a proximal end portion of the second communication pipe  5  is detachably fitted on an outer peripheral surface of a distal end portion of the mixer body  11 . 
     The fluid mixer  10  according to the second embodiment is, as shown in  FIG. 3  and  FIG. 4 , configured such that the mixer body  11  and the first communication pipe  3  which is formed of a flexible raw material are communicably connected to each other in a state where a distal end portion of the first communication pipe  3  is detachably fitted on a proximal end portion of the mixer body  11 . The mixer body  11  and the second communication pipe  5  are communicably connected to each other in a state where a spacer  20  which is formed in a circular cylindrical shape using an elastic rubber material is fitted on an outer peripheral surface of a distal end portion of the mixer body  11 , and a proximal end portion of the second communication pipe  5  is detachably fitted between an outer peripheral surface of the spacer  20  and an inner peripheral surface of a distal end portion of the cover member  30 . 
     The fluid mixers  10  according to the first and second embodiments having such constitutions can be easily mounted on or dismounted from the first and second communication pipes  3 , and hence, the cleaning operation and the maintenance operation of the fluid mixers  10  can be easily performed. 
     [Explanation of Mixer Body  11 ] 
     As shown in  FIG. 8  to  FIG. 11 , the mixer body  11  is formed into a straight shape, and is constituted of: a proximal-end-side cylindrical portion  16 ; a circular-cylindrical-shaped distal-end-side cylindrical portion  17 , and a distal-end-side cylindrical portion  18 . The proximal-end-side cylindrical portion  16  is formed in a funnel shape with a diameter thereof gradually increased toward an opening portion  13  at the other end from an opening portion  12  at one end. The circular-cylindrical-shaped distal-end-side cylindrical portion  17  and the distal-end-side cylindrical portion  18  are formed with the approximately same diameter from a terminal end of the proximal-end-side cylindrical portion  16  to the opening portion  13  at the other end. Symbol L 1  indicates a longitudinal length of the mixer body  11 , and symbol L 2  indicates a longitudinal length of the proximal-end-side cylindrical portion  16 . Symbol θ 1  indicates an inclination angle of a peripheral surface of the proximal-end-side cylindrical portion  16 . Symbol D 1  indicates an inner diameter of the opening portion  12  at one end, symbol D 2  indicates an inner diameter of the opening portion  13  at the other end, and symbol D 3  indicates an inner diameter of the distal-end-side cylindrical portion  17 . 
     A peripheral wall of the distal-end-side cylindrical portion  17  is equidistantly divided into five parts in the axial direction such that the lengths L 3  to L 7  of five divided parts are equal in the axial direction. Slit-like holes  15  (in this embodiment, five holes) for introducing fluid into the mixer body which extend while making a predetermined acute angle θ 2  (for example, within a range from 20° to 30°) with respect to the longitudinal direction are formed in the peripheral wall of the distal-end-side cylindrical portion  17  within the lengths L 3  to L 7  in the axial direction respectively. The respective holes  15  for introducing fluid into the mixer body  11  are arranged along a single imaginary spiral S which is drawn on the peripheral wall of the distal-end-side cylindrical portion  17 , and are arranged at predetermined intervals in the extending direction of the single imaginary spiral S. As shown in  FIG. 9 , the single imaginary spiral S is drawn as an imaginary straight line in a state where the distal-end-side cylindrical portion  17  is developed, and the slit-like holes  15  for introducing fluid into the mixer body  11  are formed on the imaginary straight line at predetermined intervals. Further, in the original distal-end-side cylindrical portion  17  which is formed by being bent into a cylindrical shape, the imaginary straight line draws the single imaginary spiral S. Symbol L 8  indicates a length of the distal end cylindrical portion  18  in the axial direction. 
     Each hole  15  for introducing fluid into the mixer body  11  is formed such that a portion of a peripheral wall of the distal-end-side cylindrical portion  17  is cut on the single imaginary spiral S, and an edge portion  17   a  at one side end formed by cutting the opening portion  13  at the other end side in the circumferential direction is bent inward so that the hole  15  for introducing fluid into the mixer body  11  is opened while gradually increasing a diameter thereof toward the opening portion  13  at the other end side from the opening portion  12  at one end. Symbol W 1  indicates a maximum opening width of the hole  15  for introducing fluid into the mixer body  11 . 
     An outer surface of the edge portion  17   a  at one side end is bent in an outwardly projecting manner (in the radial direction of the distal-end-side cylindrical portion  17 ), and functions as an introducing guiding surface for the second fluid F 2  which is introduced from the hole  15  for introducing fluid into the mixer body  11 . On the other hand, an inner surface of the edge portion  17   a  at one side end functions as a swirl guiding surface for the second fluid F 2  which flows in a swirling manner. Accordingly, the edge portion  17   a  at one side end which forms each hole  15  for introducing fluid into the mixer body  11  which is arranged along the single imaginary spiral S surely guides swirling of the second fluid F 2  in a spiral manner. 
     As shown in  FIG. 2 , in the mixer body  11 , a straight-shaped axial flow path  14  which makes the first fluid F 1  introduced from the opening portion  12  at one end flow in the axial direction and exit from the opening portion  13  at the other end is formed. Further, a spiral flow path  19  is formed on a peripheral portion of the distal-end-side cylindrical portion  17  of the mixer body  11 . In the spiral flow path  19 , the second fluid F 2  which is introduced through the holes  15  for introducing fluid into the mixer body  11  is made to flow around the outer periphery of the axial flow path  14  about an axis of the axial flow path  14  along the inner peripheral surface of the distal-end-side cylindrical portion  17  while being swirled in a spiral manner. Then, the second fluid F 2  which flows through the spiral flow path  19  is mixed into the first fluid F 1  which flows through the axial flow path  14  by a dispersion-by-shearing action, and after mixing, the second fluid F 2  and the first fluid F 1  are made to exit from the opening portion  13  at the other end as a mixed fluid F 3 . 
     (Explanation of Cover Member  30 ) 
     As shown in  FIG. 6 ,  FIG. 7 ,  FIG. 12  and  FIG. 13 , the cover member  30  is formed in a straight shape, and is constituted of: a cover proximal-end cylindrical portion  33  which is formed in a funnel shape by gradually increasing a diameter thereof in the direction from the opening portion  31  at one end toward the opening portion  32  at the other end; a cylindrical cover body  34  which extends in the direction toward the opening portion  32  at the other end from a terminal end of the cover proximal-end cylindrical portion  33  while having the substantially same diameter; and a cylindrical cover distal-end cylindrical portion  35  which extends in the direction from the terminal end of the cover body  34  to the opening portion  32  at the other end. An intermediate portion of an outer peripheral surface of the proximal-end-side cylindrical portion  16  of the mixer body  11  is brought into contact with an inner peripheral portion of the opening portion  31  at one end. Symbol L 9  indicates a longitudinal length of the cover member  30 , symbol L 10  indicates an axial length of the cover proximal-end cylindrical portion  33 , symbol L 11  indicates a longitudinal length of the cover body  34 , and symbol L 12  indicates an axial length of the cover distal-end cylindrical portion  35 . Symbol D 4  indicates an inner diameter of the opening portion  31  at one end, and symbol D 5  indicates an inner diameter of the opening portion  32  at the other end. Symbol θ 3  indicates a peripheral-surface inclination angle of the cover proximal-end cylindrical portion  33 , and the relationship of θ 3 &gt;θ 1  is established between the peripheral-surface inclination angle θ 3  and the peripheral surface inclination angle θ 1 . 
     A plurality of (two in this embodiment) slit-like holes  36  for introducing fluid into the cover member  30  which extend straightly along the longitudinal direction are formed in the peripheral wall of the cover body  34  over the whole length of the cover body  34 . A pair of (two) holes  36  for introducing fluid into the cover member  30  is arranged at positions in point symmetry with respect to the axis of the cover member  30 . Each hole  36  for introducing fluid into the cover member  30  is formed such that a peripheral wall of the cover body  34  is cut straightly in the axial direction over the longitudinal length L 11  of the cover body  34 , and an edge portion  34   a  at one side end which has both ends thereof cut in the circumferential direction is bent inward so that the hole  36  for introducing fluid into the cover member  30  is formed in a state where the hole  36  opens in the direction toward the opening portion  13  at the other end from the opening portion  12  at one end while having the substantially same width. 
     In the edge portion  34   a  at one side end, an outer surface of the edge portion  34   a  at one side end which is bent in an outwardly projecting manner (in the radial direction of the cover body  34 ) and functions as an introducing guiding surface for the second fluid F 2  which is introduced from the outer introducing hole  36 , and an inner surface of the edge portion  34   a  at one side end functions as a swirling guiding surface for the second fluid F 2  which is made to form a swirl flow. Accordingly, the edge portions  34   a  at one side end which form the pair of holes  36  for introducing fluid into the cover member  30  arranged at positions in point symmetry surely guide the second fluid F 2  in a swirling manner. 
     Between an inner peripheral surface of the cover body  34  and an outer peripheral surface of the distal-end-side cylindrical portion  17  of the mixer body  11 , as shown in  FIG. 5 , a cylindrical swirl flow path  37  is formed while maintaining a predetermined gap W 3 , and the second fluid F 2  is made to form a swirl flow in the swirl flow path  37 . The predetermined gap W 3  which is a width of the swirl flow path  37  may be set to a value not more than an inner diameter of the mixer body  11  and not less than a half of the inner diameter of the mixer body  11 . The gap W 3  may preferably be set approximately equal to the inner diameter of the mixer body  11 . In the swirl flow path  37 , the second fluid F 2  which is introduced from the holes  36  for introducing fluid into the cover member  30  is made to flow while being swirled about the axis of the axial flow path  14  along the inner peripheral surface of the cover body  34 , and is introduced into the mixer body  11  through the holes  15  formed in the mixer body  11 . Symbol W 2  indicates a maximum opening width of the hole  36  for introducing fluid into the cover member  30 . 
     Within the longitudinal length L 11  of the holes  36  for introducing fluid into the cover member  30  which are formed in the peripheral wall of the cover body  34 , five holes  15  for introducing fluid into the mixer body  11  which are formed in the peripheral wall of the distal-end-side cylindrical portion  17  of the mixer body  11  are arranged, and the second fluid F 2  which is introduced into the cover body  34  through the holes  36  for introducing fluid into the cover member  30  is introduced into the mixer body  11  through five holes  15  for introducing fluid into the mixer body  11  while being swirled in the swirl flow path  37 . 
     Due to such a constitution, as shown in  FIG. 4  and  FIG. 5 , when the first fluid F 1  is made to flow through the axial flow path  14  in the mixer body  11  along the axial direction, a pressure in the axial flow path  14  in the mixer body  11  is reduced. Then, due to such a pressure reduction effect, the second fluid F 2  stored in the second fluid storing portion  2  is introduced into the cover body  34  while being swirled through the holes  36  for introducing fluid into the cover member  30  and is made to form a swirl flow in the swirl flow path  37  in the cover body  34 . Then, the second fluid F 2  which is made to form a swirl flow in the swirl flow path  37  is introduced into the mixer body  11  through the holes  15  for introducing fluid into the mixer body  11  and, at the same time, is made to form a swirl flow in a spiral manner around the first fluid F 1  which axially flows through the axial flow path  14  so that the second fluid F 2  is mixed with the first fluid F 1  in a swirling manner over the whole region of the spiral flow path  19 . In this manner, the first fluid F 1  and the second fluid F 2  are mixed with each other in a swirling manner thus producing the mixed fluid F 3 , and the mixed fluid F 3  is made to exit from the opening portion  13  at the other end. 
     The second fluid F 2  which forms a continuous phase is made to swirl about the axis of the axial flow path  14  provisionally in the swirl flow path  37  and, subsequently, is made to form the swirl flow in a spiral manner about the axis of the axial flow path  14  thorough the spiral flow path  19 . That is, the second fluid F 2  is made to swirl while gradually decreasing a swirling radius toward the axis (center) from an outer peripheral side of the axial flow path  14 . Accordingly, the second fluid F 2  which is made to swirl is accelerated on an axis side and applies a shearing action to the first fluid F 1  which forms a dispersion phase at a high speed. As a result, the first fluid F 1  is dispersed finely and is homogenized. Accordingly, the second fluid F 2  can be mixed to the first fluid F 1  in a swirling manner at a high speed whereby the first fluid F 1  and the second fluid F 2  can be uniformly mixed with each other. 
     Further, the proximal-end-side cylindrical portion  16  of the mixer body  11  is formed with a diameter thereof gradually increased and hence, the dispersibility of the first fluid F 1  which is made to flow through the proximal-end-side cylindrical portion  16  can be gradually enhanced. The distal-end-side cylindrical portion  17  is formed with the approximately same diameter from the terminal end of the proximal-end-side cylindrical portion  16  to the distal-end cylindrical portion  18 , and the second fluid F 2  is made to form the swirl flow in a spiral manner in the distal-end-side cylindrical portion  17  and hence, the miscibility and the swirling property of the first fluid F 1  which is made to flow from the proximal-end-side cylindrical portion  16  to the distal-end-side cylindrical portion  17  and the second fluid F 2  which is made to form a swirl flowing in a spiral manner in the distal-end-side cylindrical portion  17  can be enhanced. 
     With respect to the holes  15  for introducing fluid into the mixer body  11 , five slit-like holes  15  for introducing fluid into the mixer body  11  which extend with a predetermined acute angle θ 2  with respect to the longitudinal direction are formed in the peripheral wall of the distal-end-side cylindrical portion  17 , and five holes  15  for introducing fluid into the mixer body  11  are arranged along the single imaginary spiral S. Accordingly, the second fluid F 2  which is introduced through the holes  15  for introducing fluid into the mixer body  11  is made to surely swirl in a spiral manner in the mixer body  11 . Further, the holes  36  for introducing fluid into the cover member are formed in the peripheral wall of the cover body  34  in a slit shape which extends in the longitudinal direction of the cover body  34  and hence, the second fluid F 2  which is introduced from the holes  36  for introducing fluid into the cover member  30  is made to flow along the inner peripheral surface of the cover body  34  and is made to surely swirl. Accordingly, the second fluid F 2  which forms a continuous phase is changed to a spiral swirl flow on the inner periphery from a provisional swirl flow on the outer periphery thus forming a high-speed swirl flow and thereby the second fluid F 2  imparts a shearing and dispersion action on the first fluid F 1  which forms a dispersion phase. As a result, the first fluid F 1  is refined and homogenized at a sub-micro level. As described above, the fluid mixer  10  according to the first embodiment is characterized by including at least the axial flow path  14  and the spiral flow path  19 , and the fluid mixer  10  according to the second embodiment is characterized by including the swirl flow path  37  in addition to these flow paths  14 ,  19 . 
     In this embodiment, the explanation has been made with respect to a mode where the fluid mixing device  1  provided with the fluid mixer  10  according to the first embodiment or the second embodiment is configure to use a liquid as the first fluid F 1  and the second fluid F 2  respectively and to mix these liquids with each other. However, the fluid mixing device  1  provided with the fluid mixer  10  may be configured to mix a liquid and a gas with each other or to mix a gas and a gas with each other. Further, sizes and the like of respective parts which constitute the fluid mixer  10  may be set in conformity with viscosities and the like of the first and second fluids F 1 , F 2 . 
     Next, the modifications of the fluid mixing device  1 , the modifications of the second fluid storing portion  2 , and the modifications of the fluid mixer  10  are explained. Parts having constitutions in common with the parts explained in conjunction with the first embodiment are explained by giving the same symbols. 
     [Explanation of First Modification of Fluid Mixing Device  1 ] 
     The first modification of the fluid mixing device  1  is explained. That is,  FIG. 14  is an explanatory cross-sectional front view of the first modification of the fluid mixing device  1  according to the first embodiment. The fluid mixing device  1  according to the first modification is, as shown in  FIG. 14 , configured such that the fluid mixer  10  according to the first embodiment is surrounded by a second fluid storing portion  2  which is formed of a closed case provided in the first modification. That is, a portion of the mixer body  11  which is positioned between an outer peripheral surface of an intermediate portion of the proximal-end-side cylindrical portion  16  and an outer peripheral surface of a proximal end portion of the second communication pipe  5  is surrounded by the second fluid storing portion  2  of the first modification. The second fluid storing portion  2  of the first modification is formed of a circular cylindrical peripheral wall forming body  40 , a one-side end wall forming body  41  which is contiguously formed with one-side end portion of the peripheral wall forming body  40 , and the other-side end wall forming body  42  which is contiguously formed with the other-side end portion of the peripheral wall forming body  40 . The second fluid storing portion  2  can store the second fluid F 2  therein. Symbol  43  indicates a proximal-end-side mounting portion which is mounted on the peripheral surface of the intermediate portion of the proximal-end-side cylindrical portion  16 , and symbol  44  indicates a distal-end-side mounting portion which is mounted on the outer peripheral surface of a proximal end portion of the second communication pipe  5 . 
     A distal end portion of a second fluid supply pipe  45  is communicably connected to a proximal end side of the peripheral wall forming body  40 . An opening portion at distal end  46  of the second fluid supply pipe  45  is directed toward a downstream side at an inner peripheral surface of the peripheral wall forming body  40  so that the second fluid F 2  which is sucked and flown into the second fluid supply pipe  45  from the opening portion at distal end  46  is made to form a swirl flow in a spiral manner about an axis of the mixer body  11 . A proximal end portion of the second fluid supply pipe  45  is communicably connected to a second fluid accumulation source (not shown in the drawing). 
     Due to such a constitution, when the first fluid F 1  is sucked and flown into the mixer body  11 , a pressure in the mixer body  11  is reduced, the second fluid F 2  in the second fluid accumulation source is sucked and flown into the second fluid storing portion  2  from the opening portion at distal end  46  through the second fluid supply pipe  45 , and the sucked and flown second fluid F 2  is made to form a swirl flow in a spiral manner about the axis of the mixer body  11 . As a result, a provisional swirl flow path  37  is formed in the second fluid storing portion  2  according to the first modification, and the second fluid F 2  is sucked into the mixer body  11  through the hole  15  for introducing fluid into the mixer body  11  while being swirled. 
     [Explanation of Second Modification of Fluid Mixing Device  1 ] 
     The second modification of the fluid mixing device  1  is explained. That is,  FIG. 15  is an explanatory cross-sectional front view of the second modification of the fluid mixing device  1  according to the first embodiment. The fluid mixing device  1  according to the second modification has, as shown in FIG.  15 , the same basic constitution as the fluid mixing device  1  according to the above-mentioned first modification. However, the fluid mixing device  1  according to the second modification differs from the fluid mixing device  1  according to the first modification with respect to the following points. That is, in the second modification, the second fluid storing portion  2  is constituted such that a spiral swirl means  50  is arranged on an inner peripheral surface of the peripheral wall forming body  40 . Due to such a constitution, in the second modification, a provisional swirl flow path  37  is formed in the second fluid storing portion  2  so that the second fluid F 2  which is sucked and flown into the second fluid storing portion  2  is made to surely form a swirl flow in a spiral manner about the axis of the mixer body  11 . 
     That is, in the second modification, the second fluid storing portion  2  is configured such that, as the swirl means  50 , a strip-shaped swirl guiding member  51  is mounted on and along an inner peripheral surface of the circular cylindrical peripheral wall forming body  40  in a spiral manner about the axis of the peripheral wall forming body  40  and in a projecting manner toward the inside of the peripheral wall forming body  40 . In the second modification, the second fluid F 2  sucked and flown into the second fluid storing portion  2  is made to flow along side walls of the swirl guiding member  51  in a spiral manner about the axis of the peripheral wall forming body  40  and in a projecting manner toward the inside of the peripheral wall forming body  40  on the outer periphery of the mixer body  11 , and is surely sucked into the mixer body  11  through the holes  15  for introducing fluid into the mixer body  11  while being swirled. The second fluid storing portion  2  according to the second modification may be configured such that a recessed groove is formed on the inner peripheral surface of the circular cylindrical peripheral wall forming body  40  in a spiral manner about the axis of the peripheral wall forming body  40 , and the second fluid F 2  is made to form a swirl flow in a spiral manner along the recessed groove thus being sucked into the mixer body  11  through the holes  15  for introducing fluid into the mixer body  11  while being swirled. 
     As described above, in the second modification of the fluid mixing device  1 , by constituting the second fluid storing portion  2  in such a manner that the swirl means  50  is arranged in the second fluid storing portion  2  of the first modification, the second fluid storing portion  2  of the second modification can hold a swirl flow path forming function capable of surely forming the provisional swirl flow path  37 . That is, the second fluid storing portion  2  of the second modification also functions as the cover member  30  for maintaining the swirl flow path forming function. 
     [Explanation of Third Modification of Fluid Mixing Device  1 ] 
     The third modification of the fluid mixing device  1  is explained. That is,  FIG. 16  is an explanatory cross-sectional front view of the third modification of the fluid mixing device  1  according to the first embodiment. As shown in  FIG. 16 , in the fluid mixing device  1  according to the third modification, the fluid mixer  10  of the second embodiment is surrounded by a second fluid storing portion  2  of the third modification which is formed of a closed case. That is, in the third modification, the second fluid storing portion  2  is configured to surround a portion of the cover member  30  which is positioned between an outer peripheral surface of a proximal end portion of the cover proximal-end cylindrical portion  33  and an outer peripheral surface of a proximal end portion of the second communication pipe  5 . In the third modification, the second fluid storing portion  2  is constituted of: a circular cylindrical peripheral wall forming body  60 ; a one-side end wall forming body  61  which is contiguously formed on a one-side end portion of the peripheral wall forming body  60 ; and the other-side end wall forming body  62  which is contiguously formed on the other-side end portion of the peripheral wall forming body  60 . The second fluid storing portion  2  can store the second fluid F 2  therein. Symbol  63  indicates a proximal-end-side mounting portion which is mounted on a peripheral surface of an intermediate portion of the cover proximal-end cylindrical portion  33 , and symbol  64  indicates a distal-end-side mounting portion which is mounted on an outer peripheral surface of a proximal end portion of the cover distal-end cylindrical portion  35 . 
     A distal end portion of a second fluid supply pipe  65  is communicably connected to a proximal end side of the peripheral wall forming body  60 . An opening portion  66  which is formed on a distal end of the second fluid supply pipe  65  is directed toward a downstream side at an inner peripheral surface of the peripheral wall forming body  60  so that the second fluid F 2  which is sucked and flown into the second fluid supply pipe  65  from the opening portion  66  at a distal end is made to form a swirl flow in a spiral manner about an axis of the cover member  30 . A proximal end portion of the second fluid supply pipe  65  is communicably connected to a second fluid storing source (not shown in the drawing). 
     Due to such a constitution, when the first fluid F 1  is sucked and flown into the mixer body  11 , a pressure in the mixer body  11  is reduced, the second fluid F 2  in the second fluid storing source is sucked and flown into the second fluid storing portion  2  from the opening portion  66  at a distal end through the second fluid supply pipe  65 , and the sucked and flown second fluid F 2  is made to form a swirl flow in a spiral manner about the axis of the cover member  30 . As a result, a provisional swirl flow path  37  is formed in the second fluid storing portion  2  of the first modification, and the second fluid F 2  is sucked into the cover member  30  through the hole  36  for introducing fluid into the cover member  30  while being swirled. 
     [Explanation of Modification of Fluid Mixer  10  in the Form of Second Embodiment] 
     The modification of the fluid mixer  10  in the form of the second embodiment is explained. That is,  FIG. 17  is an explanatory cross-sectional front view of the modification of the fluid mixer  10  according to the second embodiment, and  FIG. 18  is a cross-sectional view taken along a line III-III in  FIG. 17 . The modification of the fluid mixer  10  according to the second embodiment is, as shown in  FIG. 17  and  FIG. 18 , configured such that a large number of holes  70  for introducing fluid into the cover member  30  which extend linearly in the tangential line direction of the inner peripheral surface of the cover body  34  and penetrate the cover body  34  are formed in the cover body  34 . That is, the holes  70  for introducing fluid into the cover member are formed in the cover body  34  at predetermined intervals in the axial direction of the cover body  34  and, at the same time, at predetermined intervals in the circumferential direction (in this embodiment, six holes  70  for introducing fluid into the cover member  30  being formed at intervals of 60° in the circumferential direction). The holes  70  for introducing fluid into the cover member  30  which are arranged adjacent to each other in the circumferential direction are arranged on an approximately imaginary spiral which extends in the axial direction on the outer peripheral surface of the cover body  34 . 
     Due to such a constitution, as shown in  FIG. 18 , the second fluid F 2  is sucked into the cover body  34  in the counterclockwise direction through the large number of respective holes  70  for introducing fluid into the cover member  30 . Further, in the swirl flow path  37  in the cover body  34 , the second fluid F 2  is made to forma swirl flow along the inner peripheral surface of the mixer body  11  in a spiral manner about the axis of the mixer body  11 . The second fluid F 2  which is made to form the swirl flow is sucked into the mixer body  11  through the holes  15  for introducing fluid into the mixer body  11  while being swirled in the counterclockwise direction. 
     Recently, the technique for producing micro emulsion has been shifting to a technique where fine grooves are formed on a substrate using a photo resist available in a semiconductor field and oil (or water) is extruded through the grooves thus producing micro emulsion. This technique has an advantage that emulsion which contains particles having a uniform particle size can be produced. However, the technique has drawbacks such as a drawback that a unit cost of fine working is expensive and a drawback that time efficiency in the production of emulsion is low. To the contrary, the fluid mixing device  1  according to this embodiment has advantages such as the production of micro emulsion at a low cost and high time efficiency in the production of micro emulsion. That is, only with a variable control of an output of a suction pump which sucks water and oil into the fluid mixing device  1 , the homogeneous micro emulsion can be produced in a wide range of amount from a small amount to a large amount and hence, the production of micro emulsion can be easily scaled up. Further, it is possible to produce micro emulsion which does not contain an emulsifying agent such as surfactant. That is, it is possible to produce micro emulsion having stability. 
     EXAMPLES 
     Example 1 
     In the example 1, an experiment for producing emulsion is performed using the fluid mixing device  1  according to the first embodiment shown in  FIG. 1 . That is, the experiment for producing emulsion is performed using the fluid mixer  10  according to the first embodiment. 
     In the example 1, the diameter D 2  is set to 12 mm (D 2 =12 mm), the diameter D 3  is set to 11 mm (D 3 =11 mm), the respective widths in the axial direction L 3  to L 7  are set to 15 mm (L 3  to L 7 =15 mm), the inclination angle of peripheral surface θ 1  is set to 7.5° (θ 1 =7.5°), the acute angle θ 2  is set to 24° (θ 2 =24°), and the maximum opening width W 1  is set to 1 mm (W 1 =1 mm). 
     Oil (edible oil) is used as the first fluid F 1  (dispersion phase), and city water is used as the second fluid F 2  (continuous phase). The displacement of the suction pump P is set to 23 l/min, and an introduced amount of oil is set to 100 ml/min. Emulsion is produced by 100 millimeter per minute under such conditions. 
     A size (particle size) of an oil droplet contained in emulsion produced in such an experiment is measured using a laser diffraction particle size distribution measuring device (SALD-2200 made by Shimadzu Corporation). The result of the measurement is shown in  FIG. 19 . 
     As shown in  FIG. 19  which is a graph, in case of the example 1, most of oil droplets contained in emulsion is refined into fine particles having a particle size within a range from 10 μm to 100 μm. 
     From this result of measurement, it is found that the mixer body  11  of this embodiment has the excellent performance that fine oil droplets at a micro level can be produced. 
     Example 2 
     In the example 2, an experiment for producing emulsion is performed using the fluid mixing device  1  according to the second embodiment shown in  FIG. 3 . That is, the fluid mixer  10  according to the second embodiment is assembled by mounting the cover member  30  on the mixer body  11  used in the experiment in the example 1, and the experiment for producing emulsion is performed using this fluid mixer  10 . 
     Here, with respect to the cover member  30  used in this example 2, the longitudinal length L 9  is set to 113 mm (L 9 =113 mm), the axial width L 10  is set to 14 mm (L 10 =14 mm), the longitudinal length L 11  is set to 83 mm (L 11 =83 mm), the axial width L 12  is set to 16 mm (L 12 =16 mm), the inner diameter D 4  is set to 7 mm (θ 4 =7 mm), the inner diameter D 5  is set to 28 mm (D 5 =28 mm), the inclination angle θ 3  of peripheral surface is set to 34° (θ 3 =34°), the maximum opening width W 2  is set to 1 mm (W 2 =1 mm), and the predetermined gap W 3  is set to 8 mm (W 3 =8 mm). 
     In the same manner as the example 1, oil (edible oil) is used as the first fluid F 1  (dispersion phase), and city water is used as the second fluid F 2  (continuous phase). The displacement of the suction pump P is set to 23 l/min, and an introduced amount of oil is set to 100 ml/min. Emulsion is produced under such conditions at a production rate of 100 ml/min. 
     A size (particle size) of oil droplets contained in emulsion produced in this experiment is measured using a laser diffraction particle size distribution measuring device (SALD-2200 made by Shimadzu Corporation). The result of the measurement is shown in  FIG. 20 . 
     As shown in a graph in  FIG. 20 , it is confirmed that most of oil droplets contained in emulsion mainly have a particle size of approximately 1 μm in case of the example 2. 
     From this result of measurement, it is found that the fluid mixer  10  of the second embodiment has the excellent performance that the fluid mixer  10  can produce extremely fine oil droplets at a sub micro level, and also has the excellent performance that the fluid mixer  10  can produce oil droplets having the uniform particle size. Further, from this result of measurement, it is also found that the fluid mixer  10  of the second embodiment has the extremely excellent emulsion production ability (fluid mixing ability). 
     Example 3 
     Next, an experiment substantially equal to the experiment in the example 2 is carried out using an oleic acid which is a main component of edible oil as an object to be emulsified. In this experiment, an experiment where an acute angle θ 2  is changed to 15° and an experiment where the acute angle θ 2  is changed to 30° are also carried out. Further, the viscosity of oil to be emulsified is focused as a physicochemical element, by focusing on, and the investigation is made using soybean oil, rapeseed oil, corn oil, olive oil and camellia oil which differ from each other in viscosity. As a dispersion solution, water (city water) is used. 
     To evaluate produced emulsions, particles are observed using a microscope (made by KEYENCE Corporation), a particle size is observed by a particle size distribution device (made by Shimadzu Corporation), and the number of particles is observed by a particle counter (made by Beckman Coulter, Inc.) respectively. 
     (Result and Consideration) 
     Oleic Acid 
     1)  FIG. 21  shows a microscope image and  FIG. 22  shows particle size distribution of micro emulsion when an oleic acid is introduced at a flow rate of 50 ml/min using the fluid mixer  10  where the acute angle θ 2  is set to 24° (production amount: 16 l/min). It is confirmed from  FIG. 21  that produced emulsion particles have a spherical shape (relatively large particles having a particle size of approximately 2 μm). It is also confirmed from  FIG. 22  that relatively homogenized emulsion having a peak in particle size at approximately 0.7 μm (mode size) is produced. The number of particles in the produced emulsion is counted using a particle counter, and it is confirmed that the number of particles in the produced emulsion is approximately 33×10 6 /ml (total amount of particles in emulsion having a particle size of 3 μm or less). 
     2) Micro emulsion is produced in the same manner as described above using the fluid mixer  10  where the acute angle θ 2  is set to 15°. The particle size distribution of the micro emulsion is shown in  FIG. 23 . It is confirmed from  FIG. 23  that relatively homogenized emulsion having a peak in particle size at approximately 0.178 μm (mode size) is produced. 
     3) Using the fluid mixer  10  where the acute angle θ 2  is set to 30°, micro emulsion is produced in the same manner as described above. The particle size distribution of the micro emulsion is shown in  FIG. 24 . It is confirmed from  FIG. 24  that relatively homogenized emulsion having a peak in particle size at approximately 0.708 μm (mode size) is produced. 
     Based on the above-mentioned results, it is confirmed that the fluid mixer  10  according to this embodiment is suitable for a micro emulsion technique. It is also confirmed that a mode size is decreased and made more uniform in the descending order of the acute angle, that is, in the order of 30°, 24° and 15°. It is understood that, the changing of the acute angle θ 2  influences a mode size of the first fluid F 1  which forms a dispersion phase. That is, it is understood that a particle size of the first fluid F 1  can be controlled to some extent by changing the acute angle θ 2 . 
     Next, to consider the application of the present invention to the actual industry, time efficiency in production of micro emulsion becomes important. As factors which largely influence time efficiency in production of micro emulsion, an amount of introduced (emulsified) oil and a suction pump pressure are named. These factors are studied hereinafter. 
     Amount of Introduced Oil (Oleic Acid) 
       FIG. 25  is a graph showing the result of measurement of particle size distribution which is performed under a condition that an amount of introduced oil (oleic acid) is increased to 100 ml/min from 50 ml/min. It is confirmed from  FIG. 25  that the particle size approximately equal to the particle size shown in  FIG. 22  is obtained. Although an introducing amount of oleic acid is increased to 130 ml/min, a large change is not confirmed in the particle size distribution. 
     On the other hand, it is confirmed that the number of particles is increased corresponding to an introduced amount of oil. 
     Pump Pressure 
     A suction pump pressure depends on a flow rate and hence, the pump pressure is evaluated based on a total flow rate using two kinds of suction pumps P under an environment where conditions such as diameters and lengths of the fluid mixer  10  and the pipes (first communication pipe  3  and the second communication pipe  5 ) are equal except for the suction pumps P (flow rate: 16 l/min and 23 l/min). 
       FIG. 26  shows the particle size distribution when an introduced amount of oleic acid is 50 ml/min and a flow rate of produced micro emulsion is 23 l/min. The peak of the particle size becomes approximately 0.5 μm which is smaller than the peak of particle size shown in  FIG. 22 . It is considered that this result is brought about by a fact that although the total flow rate is increased, an amount of introduced oleic acid is fixed and hence, only water (dispersion solvent) which is introduced simultaneously with oleic acid is increased, that is, a rate of amount of water which constitutes the dispersion solvent is increased with respect to the emulsified oleic acid and hence, an oleic-acid swirl dispersion force is enhanced. 
     On the other hand, it is confirmed that the number of particles is controlled by only an amount of introduced oleic acid when either pump (total flow rate) is used (see  FIG. 27 ). 
     Influence Exerted by Viscosity of Introduced Oil 
     When a fluid in a liquid phase and a fluid in a liquid phase are emulsified into micro emulsion by making use of a swirl mixed flow, a particle size and the like are more influenced by physiochemical elements than the compositions of the solutions. According to the experiment carried out in the example 3, viscosity of introduced oil is particularly evaluated. An average particle size and the number of particles which are confirmed in the measurement of viscosities and particle size distributions of various oils used in this embodiment are respectively shown in  FIG. 28 . Further, as examples of the measurement of particle size distribution,  FIG. 29  shows a measurement result when soybean oil is used,  FIG. 30  shows a measurement result when rapeseed oil is used,  FIG. 31  shows a measurement result when corn oil is used,  FIG. 32  shows a measurement result when olive oil is used, and  FIG. 33  shows a measurement result when camellia oil is used. 
     It is confirmed that the viscosity of oil hardly influences the average particle size, the number of particles and the like, and the particle size is controlled by a suction pump pressure, and the number of particles is controlled by an amount of introduced oil based on results including the result on the above-mentioned item, that is, oleic acid and introduced oil (oleic acid). 
     Stability 
       FIG. 34  shows a state of micro-emulsified camellia oil (immediately after processing), and  FIG. 35  shows a state of micro-emulsified camellia oil after three months elapse (left after processing for three months). It is confirmed that stable micro emulsion is produced without using an emulsifying agent such as a surfactant. 
     CONCLUSION 
     The micro-emulsifying technique which uses the fluid mixing device  1  is studied. As a result of the study, it is confirmed that the average particle size, the number of particles and the like of the produced emulsion are hardly influenced by the viscosity of the emulsion, and the particle size is controlled by a suction pump pressure, and the number of particles is controlled by an amount of introduced fluid. 
     EXPLANATION OF SYMBOLS 
     
         
           1 : fluid mixing device 
           2 : second fluid storing portion 
           3 : first communication pipe 
           4 : first fluid storing portion 
           7 : mixed fluid storing portion 
           10 : fluid mixer 
           11 : mixer body 
           12 : opening portion at one end 
           13 : opening portion at the other end 
           14 : axial flow path 
           15 : hole formed in the body for introducing fluid 
           16 : proximal-end-side cylindrical portion 
           17 : distal-end-side cylindrical portion 
           17   a : one-side edge portion 
           18 : distal-end cylindrical portion 
           19 : spiral flow passage 
           30 : cover member 
           34 : cover body 
           34   a : one-side edge portion