Microbubble generator

Abstract

To provide a technology that can generate a larger amount of fine air bubbles in a fine air bubble generation device.SOLUTION: A fine air bubble generation device includes: an inflow part into which a gas dissolved water flows; an outflow part from which the gas dissolved water flows out; and a fine air bubble generation part provided between the inflow part and the outflow part. The fine air bubble generation part includes: a venturi part including a diameter decreasing passage in which a passage diameter decreases from the upstream to the downstream, and a diameter increasing passage in which the passage diameter increases from the upstream to the downstream; an outflow passage for causing the gas dissolved water flowing out from the venturi part to flow out from the fine air bubble generation part; and a return passage which connects a middle part of the outflow passage with the venturi part.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The technology disclosed in this specification relates to a fine bubble generator.

Background Art

[0002] Patent Document 1 discloses a fine bubble generator including an inflow section into which gas-dissolved water flows, an outflow section from which the gas-dissolved water flows out, and a fine bubble generation section provided between the inflow section and the outflow section. The fine bubble generation section includes a reduced-diameter flow path that decreases in diameter from upstream to downstream, and an enlarged-diameter flow path that is provided downstream of the reduced-diameter flow path and increases in diameter from upstream to downstream.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the fine bubble generator of Patent Document 1, water in which gas is dissolved (hereinafter sometimes referred to as "gas-dissolved water") passes through the reduced-diameter flow path, whereby the flow velocity increases and as a result, the pressure is reduced. When the gas-dissolved water is depressurized, bubbles are generated. Next, the gas-dissolved water is gradually pressurized as it passes through the enlarged-diameter flow path. When the gas-dissolved water after bubbles are generated by depressurization is pressurized, the bubbles contained in the gas-dissolved water split into fine bubbles. Thus, in the fine bubble generator of Patent Document 1, fine bubbles are generated by the fine bubble generation section. However, in the fine bubble generator of Patent Document 1, a situation occurs in which the amount of fine bubbles generated by the fine bubble generator is insufficient.

[0005] This specification provides a technology capable of generating a large amount of fine bubbles.

Means for Solving the Problems

[0006] The fine bubble generator disclosed by this specification includes an inflow part into which gas-dissolved water flows, an outflow part from which the gas-dissolved water flows out, and a fine bubble generation part provided between the inflow part and the outflow part. The fine bubble generation part includes a Venturi part including a reduced-diameter flow path whose flow path diameter decreases from upstream to downstream and an expanded-diameter flow path whose flow path diameter increases from upstream to downstream, an outflow flow path for causing the gas-dissolved water flowing out from the Venturi part to flow out from the fine bubble generation part, and a reflux flow path connecting a middle part of the outflow flow path and the Venturi part.

[0007] According to the above configuration, the gas-dissolved water flowing into the fine bubble generator flows into the reduced-diameter flow path of the Venturi part of the fine bubble generation part. The gas-dissolved water increases in flow velocity by passing through the reduced-diameter flow path and is thus depressurized as a result. When the gas-dissolved water is depressurized, bubbles are generated. Next, the gas-dissolved water is gradually pressurized by passing through the expanded-diameter flow path. When the gas-dissolved water after bubbles are generated by depressurization is pressurized, the bubbles contained in the gas-dissolved water split into fine bubbles. Then, the gas-dissolved water containing fine bubbles flows out from the fine bubble generation part via the outflow flow path. In the Venturi part, a negative pressure is generated (Venturi effect) due to the flow of the gas-dissolved water inside the Venturi part. And the reflux flow path connects a middle part of the outflow flow path and the Venturi part. For this reason, a part of the gas-dissolved water flowing through the outflow flow path is sucked into the reflux flow path by the negative pressure generated in the Venturi part. And the gas-dissolved water sucked into the reflux flow path flows back into the Venturi part. By passing through the Venturi part again, the fine bubbles in the gas-dissolved water become finer bubbles and the amount of fine bubbles increases. Therefore, a large amount of fine bubbles can be generated.

[0008] In one or more embodiments, the Venturi portion may further include a constant-diameter flow path that connects the downstream end of the converging flow path and the upstream end of the diverging flow path. The flow path of the constant-diameter flow path may be the same as the flow path at the downstream end of the converging flow path. The reflux flow path may be connected near the downstream end of the constant-diameter flow path.

[0009] In the Venturi portion, the flow velocity of the gas-dissolved water near the downstream end of the constant-diameter flow path is the fastest. Therefore, the largest negative pressure is generated near the downstream end of the constant-diameter flow path. According to the above configuration, the reflux flow path is connected near the downstream end of the constant-diameter flow path. Therefore, the amount of gas-dissolved water sucked from the outflow flow path into the reflux flow path can be increased. As a result, the amount of gas-dissolved water reflowing into the Venturi portion increases, and more fine bubbles can be generated.

[0010] In one or more embodiments, the outflow flow path may be provided with a guide wall portion that guides the gas-dissolved water flowing through the outflow flow path into the reflux flow path on the downstream side of the portion where the reflux flow path is connected.

[0011] According to the above configuration, the gas-dissolved water flowing through the outflow flow path is more likely to be sucked into the reflux flow path by the guide wall portion. Therefore, the amount of gas-dissolved water sucked from the outflow flow path into the reflux flow path can be increased. As a result, the amount of gas-dissolved water reflowing into the Venturi portion increases, and more fine bubbles can be generated.

[0012] In one or more embodiments, the fine bubble generation portion may further include a collision wall portion that faces the opening at the downstream end of the diverging flow path and against which the water flowing out of the diverging flow path collides, and a side wall portion that extends from the collision wall portion toward the Venturi portion side and surrounds at least a part of the Venturi portion. The outflow flow path may include a first outflow flow path defined between the collision wall portion and the opening at the downstream end of the diverging flow path, and a second outflow flow path that is a flow path downstream of the first outflow flow path and is defined between the Venturi portion and the side wall portion. The reflux flow path may be connected in the middle of the second outflow flow path.

[0013] According to the above configuration, the gas-dissolved water flowing out from the diffusion flow path collides with the collision wall portion. When the gas-dissolved water collides with the collision wall portion, the fine bubbles in the gas-dissolved water are split into finer bubbles, and the amount of fine bubbles increases. Further, since the reflux flow path is connected to the middle of the second outflow flow path on the downstream side of the first outflow flow path, the gas-dissolved water sucked into the reflux flow path and re-flowing into the Venturi portion collides with the collision wall portion again by flowing out from the diffusion flow path. As a result, the fine bubbles in the gas-dissolved water are split into even finer bubbles, and the amount of fine bubbles becomes even larger.

[0014] Also, according to the above configuration, the gas-dissolved water flowing in the Venturi portion in the first direction flows in the second outflow flow path defined between the side wall portion and the Venturi portion in the second direction opposite to the first direction after colliding with the collision wall portion. According to such a configuration, compared with a configuration in which the fine bubble generation portion does not include the side wall portion, the length of the fine bubble generation portion along the first direction can be shortened, and the fine bubble generator can be miniaturized.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

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Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0016] (Example) (Configuration of the hot water supply system 2; FIG. 1) The hot water supply system 2 shown in FIG. 1 heats the water supplied from a water supply source 4 such as a water supply pipe, and supplies the water heated to a desired temperature to a faucet 6 installed in a kitchen or the like, or a bathtub 8 arranged in a bathroom. Further, the hot water supply system 2 can reheat the water in the bathtub 8.

[0017] The hot water supply system 2 includes a first heat source machine 10, a second heat source machine 12, and a combustion chamber 14. The first heat source machine 10 is a heat source machine used for supplying hot water to the faucet 6 and filling the bathtub 8. The second heat source machine 12 is a heat source machine used for reheating the water in the bathtub 8. The interior of the combustion chamber 14 is partitioned by a partition wall portion 16 into a first combustion chamber 18 and a second combustion chamber 20. The first heat source machine 10 is accommodated in the first combustion chamber 18, and the second heat source machine 12 is accommodated in the second combustion chamber 20.

[0018] The first heat source machine 10 includes a first burner 22 and a first heat exchanger 24. The second heat source machine 12 includes a second burner 26 and a second heat exchanger 28.

[0019] The upstream end of the first heat exchanger 24 of the first heat source machine 10 is connected to the downstream end of the water supply line 30. Water is supplied from the water supply source 4 to the upstream end of the water supply line 30. The downstream end of the first heat exchanger 24 is connected to the upstream end of the hot water supply line 32. The water supply line 30 and the hot water supply line 32 are connected by a bypass line 34. A bypass servo 36 is provided at the connection point between the water supply line 30 and the bypass line 34. The bypass servo 36 adjusts the ratio of the flow rate of water sent from the water supply line 30 to the first heat source machine 10 and the flow rate of water sent from the water supply line 30 to the bypass line 34. At the connection point between the bypass line 34 and the hot water supply line 32, the low-temperature water passing through the water supply line 30 and the bypass line 34 and the high-temperature water passing through the water supply line 30, the first heat source machine 10, and the hot water supply line 32 are mixed. A water volume sensor 38 and a water volume servo 40 are provided in the water supply line 30 upstream of the bypass servo 36. The water volume sensor 38 detects the flow rate of water flowing through the water supply line 30. The water volume servo 40 adjusts the flow rate of water flowing through the water supply line 30. A heat exchanger outlet thermistor 42 is provided in the hot water supply line 32 upstream of the connection point with the bypass line 34.

[0020] The upstream end of the hot water pouring line 50 is connected to the hot water supply line 32 downstream of the connection point of the bypass line 34. A hot water supply thermistor 44 is provided at the connection point between the hot water supply line 32 and the hot water pouring line 50. A fine bubble generator 46 is provided between the connection point of the hot water supply line 32 and the bypass line 34 and the connection point of the hot water supply line 32 and the hot water pouring line 50. The fine bubble generator 46 will be described in detail later. Hereinafter, the water passage of the hot water supply line 32 upstream of the fine bubble generator 46 may be described as the first hot water supply line 32a, and the water passage of the hot water supply line 32 downstream of the fine bubble generator 46 may be described as the second hot water supply line 32b.

[0021] The downstream end of the filling path 50 is connected to the upstream end of the reheating return path 60 and the downstream end of the first bathtub circulation path 62. The downstream end of the reheating return path 60 is connected to the upstream end of the second heat exchanger 28. The upstream end of the first bathtub circulation path 62 is connected to the bathtub 8. A filling control valve 52 and a check valve 54 are provided in the filling path 50. The filling control valve 52 opens and closes the filling path 50. The check valve 54 allows the flow of water from the upstream side to the downstream side of the filling path 50 and prohibits the flow of water from the downstream side to the upstream side of the filling path 50. A bathtub return thermistor 64 is provided at the connection point of the filling path 50, the reheating return path 60, and the first bathtub circulation path 62. A circulation pump 66 is provided in the reheating return path 60.

[0022] The downstream end of the second heat exchanger 28 of the second heat source unit 12 is connected to the upstream end of the second bathtub circulation path 68. The downstream end of the second bathtub circulation path 68 is connected to the bathtub 8. A bathtub forward thermistor 70 is provided in the second bathtub circulation path 68.

[0023] When the hot water supply system 2 supplies hot water to the faucet 6, the first burner 22 of the first heat source unit 10 burns with the filling control valve 52 closed. In this case, the water supplied from the water supply source 4 to the water supply path 30 is heated by heat exchange in the first heat exchanger 24 and then supplied from the hot water supply path 32 to the faucet 6. By adjusting the combustion amount of the first burner 22 of the first heat source unit 10 and the opening degree of the bypass servo 36, the temperature of the water flowing through the hot water supply path 32 can be adjusted to a desired temperature.

[0024] When the hot water supply system 2 fills the bathtub 8 with hot water, the first burner 22 of the first heat source machine 10 burns with the hot water supply control valve 52 open. In this case, the water supplied from the water supply source 4 to the water supply passage 30 is heated by heat exchange in the first heat exchanger 24 and then flows into the hot water filling passage 50 from the hot water supply passage 32. At this time, the temperature of the water is adjusted to a desired temperature by adjusting the combustion amount of the first burner 22 of the first heat source machine 10 and the opening degree of the bypass servo 36. The water that has flowed into the hot water filling passage 50 flows into the bathtub 8 via the first bathtub circulation passage 62 and also flows into the bathtub 8 via the reheating forward passage 60 and the second bathtub circulation passage 68.

[0025] When the hot water supply system 2 reheats the bathtub 8, the circulation pump 66 is driven with the hot water supply control valve 52 closed, and the second burner 26 of the second heat source machine 12 burns. In this case, the water in the bathtub 8 flows into the first bathtub circulation passage 62 and is sent to the second heat source machine 12 via the reheating forward passage 60. The water sent to the second heat source machine 12 is heated by heat exchange in the second heat exchanger 28 and then flows into the second bathtub circulation passage 68. At this time, the temperature of the water is adjusted to a desired temperature by adjusting the combustion amount of the second burner 26 of the second heat source machine 12. The water that has flowed into the second bathtub circulation passage 68 is returned to the bathtub 8.

[0026] (Configuration of the microbubble generator 46; FIGS. 2 to 12) Next, with reference to FIGS. 2 to 12, the fine bubble generator 46 provided in the hot water supply path 32 will be described. As shown in FIG. 2, the fine bubble generator 46 includes a main body case 100, an inflow portion 102, and an outflow portion 104. The main body case 100 has a cylindrical shape. As shown in FIG. 3, the inflow portion 102 is fixed to the first end portion 100a of the main body case 100 by a screw (not shown). An inlet 102a is formed in the inflow portion 102. The inflow portion 102 is connected to the downstream end of the first hot water supply path 32a (see FIG. 1). The outflow portion 104 is fixed to the second end portion 100b of the main body case 100 by a screw (not shown). An outlet 104a is formed in the outflow portion 104. The outflow portion 104 is connected to the upstream end of the second hot water supply path 32b (see FIG. 1). Hereinafter, the direction in which water flows from the first hot water supply path 32a into the inflow portion 102 will be described as the "first direction", and the direction opposite to the first direction will be described as the "second direction". That is, the right direction and the left direction in FIG. 3 are the "first direction" and the "second direction", respectively.

[0027] The main body case 100 houses two fine bubble generating portions 110. The two fine bubble generating portions 110 are provided along the central axis A of the fine bubble generator 46. Hereinafter, the central axis A of the fine bubble generator 46 may be simply described as the "central axis A".

[0028] (Configuration of the fine bubble generating portion 110; FIGS. 3 to 12) Next, with reference to FIGS. 3 to 12, the fine bubble generating portion 110 will be described. As shown in FIGS. 5 and 6, the fine bubble generating portion 110 includes a first main body portion 120, a second main body portion 122, and a third main body portion 124. The first main body portion 120, the second main body portion 122, and the third main body portion 124 are provided along the central axis A. The first main body portion 120, the second main body portion 122, and the third main body portion 124 are provided in the order of the first main body portion 120, the second main body portion 122, and the third main body portion 124 from the second direction to the first direction.

[0029] As shown in FIGS. 5 and 6, the first main body portion 120 includes a first flange portion 130, a cylindrical portion 132, five flow path portions 134a to 134e, and an outer peripheral portion 136. As shown in FIG. 3, the diameter of the cylindrical portion 132 decreases as it extends in the first direction. The first flange portion 130 extends radially outward of the central axis A from the end portion on the second direction side of the cylindrical portion 132. The outer diameter of the first flange portion 130 is the same as the inner diameter of the main body case 100.

[0030] As shown in FIGS. 7 and 8, the five flow path portions 134a to 134e are arranged at equal intervals along the circumferential direction of the central axis A. Hereinafter, the flow path portions 134a to 134e may be collectively referred to simply as the "flow path portion 134". As shown in FIG. 3, the flow path portion 134 extends in the first direction from the end portion on the first direction side of the cylindrical portion 132. The flow path portion 134 extends parallel to the central axis A. The reduced-diameter flow paths 138a to 138e and the equal-diameter flow paths 140a to 140e are provided in the flow path portions 134a to 134e. Hereinafter, the reduced-diameter flow paths 138a to 138e and the equal-diameter flow paths 140a to 140e may be collectively referred to simply as the "reduced-diameter flow path 138" and the "equal-diameter flow path 140", respectively. The flow path diameter of the reduced-diameter flow path 138 decreases as it goes toward the first direction side. The water flowing into the flow path portion 134 flows through the reduced-diameter flow path 138 in the first direction side. Therefore, the flow path diameter of the reduced-diameter flow path 138 decreases from the upstream to the downstream. The flow path diameter of the end portion on the second direction side of the reduced-diameter flow path 138 is smaller than the flow path diameter of the inlet 102a of the inflow portion 102. The end portion on the second direction side (i.e., the upstream end) of the equal-diameter flow path 140 is connected to the end portion on the first direction side (i.e., the downstream end) of the reduced-diameter flow path 138. Further, the end portion on the first direction side (i.e., the downstream end) of the equal-diameter flow path 140 is connected to the end portion on the second direction side (i.e., the upstream end portion) of the enlarged-diameter flow path 156 described later. The flow path diameter of the equal-diameter flow path 140 is constant in the direction parallel to the central axis A. The flow path diameter of the equal-diameter flow path 140 is the same as the flow path diameter of the end portion on the first direction side (i.e., the downstream end) of the reduced-diameter flow path 138. In this embodiment, the five reduced-diameter flow paths 138a to 138e have the same shape, but at least one of the five reduced-diameter flow paths 138a to 138e may have a different shape. Also, in this embodiment, the five equal-diameter flow paths 140a to 140e have the same shape, but at least one of the five equal-diameter flow paths 140a to 140e may have a different shape.

[0031] As shown in FIG. 3, the outer peripheral portion 136 extends in the first direction from the end portion on the first direction side of the cylindrical portion 132. As shown in FIG. 8, the outer peripheral portion 136 surrounds the coaxial flow path 140 on the radially outer side of the central axis A. The outer shape of the outer peripheral portion 136 is constituted by five arc shapes. The diameter of the arc shape is larger than the diameter of the coaxial flow path 140. As shown in FIG. 3, the end portion on the first direction side of the outer peripheral portion 136 is located on the first direction side of the end portion on the first direction side of the coaxial flow path 140.

[0032] As shown in FIGS. 5 and 6, the second main body portion 122 includes an inner case portion 150 and five second flange portions 152a to 152e. Hereinafter, the five second flange portions 152a to 152e may be collectively referred to simply as the "second flange portion 152". As shown in FIG. 6, the outer shape of the inner case portion 150 is constituted by five arc shapes. The inner case portion 150 is provided with a connection flow path 154 and five expanded flow paths 156a to 156e. Hereinafter, the five expanded flow paths 156a to 156e may be collectively referred to simply as the "expanded flow path 156". The connection flow path 154 is provided at the central portion of the inner case portion 150 and extends along the central axis A. As shown in FIG. 3, the flow path diameter of the connection flow path 154 is constant. As shown in FIG. 9, the expanded flow path 156 is provided on the radially outer side of the connection flow path 154. The expanded flow paths 156 are arranged at equal intervals along the circumferential direction of the central axis A. As shown in FIG. 3, the five expanded flow paths 156a to 156e are respectively arranged on the first direction side of the five same-diameter flow paths 140a to 140e of the first main body portion 120 and correspond to each of the five same-diameter flow paths 140a to 140e. The flow path diameter of the expanded flow path 156 increases as it goes in the first direction. Note that the water flowing into the second main body portion 122 flows through the expanded flow path 156 toward the first direction side. Therefore, the flow path diameter of the expanded flow path 156 expands from the upstream to the downstream. The flow path diameter of the end portion of the expanded flow path 156 on the second direction side is larger than the flow path diameter of the same-diameter flow path 140. In the direction of the central axis A, the position of the end portion of the expanded flow path 156 on the second direction side coincides with the position of the flow path diameter of the same-diameter flow path 140 on the first direction side. And a gap is formed between the expanded flow path 156 and the same-diameter flow path 140 at the end portion of the expanded flow path 156 on the second direction side. Also, the end portion (i.e., the end portion 122a on the second direction side of the second main body portion 122) of the expanded flow path 156 is provided radially inward of the outer peripheral portion 136 of the first main body portion 120. In the direction of the central axis A, the end portion 122a of the second main body portion 122 is located on the first direction side of the inner end portion 120a of the first main body portion 120. The inner end portion 120a of the first main body portion 120 is provided radially inward of the outer peripheral portion 136.Therefore, a gap is formed between the end portion 122a of the second main body portion 122 and the inner end portion 120a of the first main body portion 120 in the direction of the central axis A. Also, the flow path diameter of the end portion (i.e., the downstream end) on the first direction side of the diffuser flow path 156 is the same as the flow path diameter of the end portion (i.e., the upstream end) on the second direction side of the reduced-diameter flow path 138 of the first main body portion 120. In this embodiment, the reduced-diameter flow path 138, the equal-diameter flow path 140, and the diffuser flow path 156 constitute a Venturi portion. Therefore, hereinafter, the reduced-diameter flow path 138, the equal-diameter flow path 140, and the diffuser flow path 156 may be collectively referred to as the "Venturi portion". Note that in this embodiment, the five diffuser flow paths 156a to 156e have the same shape, but at least one of the five diffuser flow paths 156a to 156e may have a different shape.

[0033] As shown in FIG. 6, the second flange portion 152 extends radially outward from the end portion on the second direction side of the inner case portion 150. As shown in FIG. 9, the five second flange portions 152a to 152e are respectively provided radially outside the five diffuser flow paths 156a to 156e. As shown in FIGS. 6 and 9, through holes 158a to 158e are provided at the end portion on the second direction side of the inner case portion 150. Hereinafter, the five through holes 158a to 158e may be collectively referred to simply as the "through hole 158". The five through holes 158a to 158e are respectively provided between the five diffuser flow paths 156a to 156e and the five second flange portions 152a to 152e. As shown in FIG. 3, the end portion on the first direction side of the through hole 158 is located on the first direction side of the end portion on the first direction side of the second flange portion 152.

[0034] As shown in FIGS. 5 and 6, the third main body portion 124 includes a bottom wall portion 170, a cylindrical portion 172 extending in the second direction from the outer edge of the bottom wall portion 170, and an extension portion 174 extending in the first direction from the surface of the bottom wall portion 170 on the first direction side. The bottom wall portion 170 has a disk shape. As shown in FIG. 3, the bottom wall portion 170 faces the opening at the end (i.e., the downstream end) on the first direction side of the expanded flow path 156 of the second main body portion 122. The outer diameter of the bottom wall portion 170 is smaller than the inner diameter of the main body case 100. The outer diameter of the cylindrical portion 172 is the same as the outer diameter of the bottom wall portion 170. The cylindrical portion 172 is provided on the radially outer side of the second main body portion 122.

[0035] On the surface of the bottom wall portion 170 on the second direction side, protruding portions 176a to 176c protruding in the second direction are provided. As shown in FIG. 11, the protruding portions 176a to 176c are provided in the radially outer direction in the order of the protruding portion 176a, the protruding portion 176b, and the protruding portion 176c in the radial direction of the central axis A. The protruding portions 176a to 176c are each composed of four arc shapes. As shown in FIG. 3, the ends on the second direction side of the protruding portions 176a to 176c are located on the first direction side of the end on the first direction side of the inner case portion 150. As shown in FIGS. 5 and 11, five notches 178a to 178e are provided at the end on the second direction side of the cylindrical portion 172. The five notches 178a to 178e are arranged at equal intervals along the circumferential direction of the central axis A. Hereinafter, the five notches 178a to 178e may be collectively referred to simply as "notch 178". As shown in FIG. 12, the five notches 178a to 178e are provided at positions corresponding to the five second flange portions 152a to 152e, respectively. In a state where the second flange portion 152 enters the notch 178, an opening 188 is formed between the end on the second direction side of the cylindrical portion 172 and two adjacent second flange portions 152 in the circumferential direction.

[0036] As shown in FIGS. 5, 6, 11, and 12, four first water receiving portions 180 and four second water receiving portions 182 are connected to the outer peripheral wall portion 172a of the cylindrical portion 172. In FIGS. 11 and 12, for ease of understanding, the four first water receiving portions 180 are shown in gray. The first water receiving portion 180 and the second water receiving portion 182 extend radially outward from the outer peripheral wall portion 172a. As shown in FIG. 4, the first water receiving portion 180 includes a circumferential wall portion 180a extending along the outer peripheral surface of the cylindrical portion 172 in the circumferential direction, and an axial extension portion 180b extending from the circumferential end of the circumferential wall portion 180a toward the second direction side. The axial extension portion 180b is inclined in a direction away from the central portion of the circumferential wall portion 180a as it goes toward the second direction side. The first water receiving portion 180 is provided on the first direction side rather than the second water receiving portion 182. The second water receiving portion 182 is provided between adjacent first water receiving portions 180 in the circumferential direction. The second water receiving portion 182 includes a circumferential wall portion 182a extending along the outer peripheral surface of the cylindrical portion 172 in the circumferential direction, and an axial extension portion 182b extending from the circumferential end of the circumferential wall portion 182a toward the first direction side. The axial extension portion 182b is inclined in a direction away from the central portion of the circumferential wall portion 182a as it goes toward the first direction side. As shown in FIG. 3, the first water receiving portion 180 and the second water receiving portion 182 are in contact with the inner peripheral wall portion 100c of the main body case 100.

[0037] As shown in FIG. 6, the extension portion 174 includes a cylindrical portion 184 and four radially extending portions 186. The central axis of the cylindrical portion 184 coincides with the central axis A. As shown in FIG. 3, the outer diameter of the cylindrical portion 184 is smaller than the outer diameter of the bottom wall portion 170. The radially extending portions 186 extend radially outward from the cylindrical portion 184 in a radial direction. The four radially extending portions 186 are arranged at equal intervals along the circumferential direction of the central axis A.

[0038] Note that the fine bubble generating portion 110 on the second direction side and the fine bubble generating portion 110 on the first direction side have the same shape and configuration, but are arranged such that the circumferential positions of the reduced diameter flow path 138 and the like are different when viewed in the direction of the central axis A.

[0039] Next, with reference to FIGS. 3 and 4, the fine bubbles generated by the fine bubble generator 46 will be described. The solid arrows in FIGS. 3 and 4 indicate the direction of water flow. The fine bubble generator 46 of this embodiment generates fine bubbles by utilizing the air contained in the water supplied from a water supply source 4 such as a waterworks. The water supplied from the waterworks contains dissolved air (oxygen, carbon dioxide, nitrogen, etc.). Hereinafter, the water in which air is dissolved will be referred to as "air-dissolved water". Further, hereinafter, the description will be made assuming a situation where the callan 6 is operated by the user. As shown in FIG. 1, when the callan 6 is operated by the user, the first burner 22 of the first heat source machine 10 burns with the hot water supply control valve 52 closed. The air-dissolved water supplied from the water supply source 4 to the water supply passage 30 is heated by heat exchange in the first heat exchanger 24 and then flows into the fine bubble generator 46 via the first hot water supply passage 32a.

[0040] Before describing the fine bubbles generated by the fine bubble generator 46, the reason why the fine bubble generator 46 is provided in the first hot water supply passage 32a will be explained. The dissolved air amount indicating the amount of air that can be dissolved in water decreases as the temperature of the water increases. And the closer the amount of air dissolved in water is to the dissolved air amount, the easier it is for bubbles to be generated. Although it will be described in detail later, in the fine bubble generator 46, fine bubbles are generated by generating bubbles in the air-dissolved water and making the bubbles finer. For this reason, the more bubbles are generated in the air-dissolved water, the more the amount of fine bubbles can be increased. For such a reason, in this embodiment, the fine bubble generator 46 is provided in the first hot water supply passage 32a through which the water heated by the first heat source machine 10 flows.

[0041] As shown in FIG. 3, the air-dissolved water that has flowed into the fine bubble generator 46 flows into the fine bubble generator 110 on the second direction side among the two fine bubble generation units 110 via the inlet 102a of the inflow unit 102. The air-dissolved water that has flowed into the fine bubble generation unit 110 flows into the reduced-diameter flow path 138 of the flow path unit 134. The air-dissolved water that has flowed into the reduced-diameter flow path 138 increases in flow velocity by passing through the reduced-diameter flow path 138, and as a result, is depressurized. When the air-dissolved water is depressurized, bubbles are generated. The air-dissolved water that has passed through the reduced-diameter flow path 138 flows into the same-diameter flow path 140. The flow velocity of the water that has flowed into the same-diameter flow path 140 stabilizes by passing through the same-diameter flow path 140. Then, the air-dissolved water that has passed through the same-diameter flow path 140 flows into the enlarged-diameter flow path 156 of the inner case portion 150 of the second main body portion 122. The air-dissolved water that has flowed into the enlarged-diameter flow path 156 decreases in flow velocity by passing through the enlarged-diameter flow path 156, and as a result, is pressurized. When the air-dissolved water containing bubbles after the bubbles are generated by depressurization is pressurized, the bubbles contained in the air-dissolved water split into fine bubbles. The water that has passed through the enlarged-diameter flow path 156 flows out toward the bottom wall portion 170 of the third main body portion 124. That is, the water that has passed through the enlarged-diameter flow path 156 flows out into the first outflow flow path OP1 defined between the end portion on the first direction side of the inner case portion 150 and the bottom wall portion 170. The air-dissolved water that has flowed out into the first outflow flow path OP1 collides with the bottom wall portion 170 and the protruding portions 176a to 176c. When the air-dissolved water collides with the bottom wall portion 170 and the protruding portions 176a to 176c, the fine bubbles in the air-dissolved water split into finer bubbles, and the amount of fine bubbles increases.

[0042] When the air-dissolved water flows through the Venturi portion, a negative pressure is generated in the Venturi portion. In particular, a large negative pressure is generated in the vicinity of the end portion (i.e., the downstream end) on the first direction side of the same flow path 140. As described above, a gap is formed between the Venturi-expanded flow path 156 and the same flow path 140 at the end portion on the second direction side of the Venturi-expanded flow path 156. Also, in the direction of the central axis A, a gap is formed between the end portion 122a of the second main body portion 122 and the inner end portion 120a of the first main body portion 120. And the vicinity of the end portion on the first direction side of the same flow path 140 and the first outflow flow path OP1 communicate with each other through the connection flow path 154, the gap between the inner end portion 120a on the first direction side of the first main body portion 120 and the end portion 122a on the second direction side of the second main body portion 122, and the gap between the Venturi-expanded flow path 156 and the same flow path 140. Hereinafter, the connection flow path 154, the gap between the inner end portion 120a on the first direction side of the first main body portion 120 and the end portion 122a on the second direction side of the second main body portion 122, and the gap between the Venturi-expanded flow path 156 and the same flow path 140 may be collectively referred to as the "first reflux flow path 160". Due to the negative pressure generated in the vicinity of the end portion on the first direction side of the same flow path 140, a part of the air-dissolved water that collides with the bottom wall portion 170 and the protruding portions 176a to 176c is sucked into the first reflux flow path 160 (specifically, the connection flow path 154). And the air-dissolved water sucked into the first reflux flow path 160 reflows into the Venturi-expanded flow path 156 via the first reflux flow path 160. The air-dissolved water that has reflowed into the Venturi-expanded flow path 156 passes through the Venturi-expanded flow path 156, and as a result, the flow velocity decreases again and the pressure increases. Thereby, the bubbles contained in the air-dissolved water are split into finer microbubbles. Also, the air-dissolved water that has passed through the Venturi-expanded flow path 156 again collides with the bottom wall portion 170 and the protruding portions 176a to 176c. Also by this, the bubbles contained in the air-dissolved water are split into finer microbubbles. Note that the vicinity of the end portion (i.e., the downstream end) on the first direction side of the same flow path 140 means the first direction side (i.e., the downstream side) rather than the central portion in the direction of the central axis A of the same flow path 140, and the second direction side (i.e., the upstream side) rather than the central portion in the direction of the central axis A of the Venturi-expanded flow path 156.Also, among the vicinity of the end portion on the first direction side of the same flow path 140, a larger negative pressure is generated at the end portion on the first direction side (i.e., the downstream end) of the same flow path 140 and at the end portion on the second direction side (i.e., the upstream end) of the expanded flow path 156. For this reason, by connecting the first reflux flow path 160 to the end portion on the first direction side (i.e., the downstream end) of the same flow path 140 and the end portion on the second direction side (i.e., the upstream end) of the expanded flow path 156, more air-dissolved water is sucked into the first reflux flow path 160 (specifically, the connection flow path 154).

[0043] Also, a part of the air-dissolved water that has collided with the bottom wall portion 170 and the protruding portions 176a to 176c flows into a second outflow flow path OP2 defined between the outer wall portion of the inner case portion 150 of the second main body portion 122 and the inner wall portion of the cylindrical portion 172 of the third main body portion 124. The water that has flowed into the second outflow flow path OP2 flows from the first direction side to the second direction side within the second outflow flow path OP2 and reaches the end portion on the second direction side of the inner case portion 150.

[0044] As shown in FIGS. 3 and 12, a second flange portion 152 is provided at the end portion on the second direction side of the inner case portion 150. When the air-dissolved water reaching the portion where the second flange portion 152 is provided among the end portions on the second direction side of the inner case portion 150 comes into contact with the second flange portion 152, the flow of the air-dissolved water is blocked. A through hole 158 is provided on the first direction side (i.e., the upstream side) of the second flange portion 152. That is, the through hole 158 is provided in the middle of the second outflow channel OP2. As described above, a gap is formed between the expanded flow path 156 and the same flow path 140 at the end portion on the second direction side of the expanded flow path 156. Also, a gap is formed between the end portion 122a of the second main body portion 122 and the inner end portion 120a of the first main body portion 120 in the direction of the central axis A. And the gap formed between the expanded flow path 156 and the same flow path 140 and the gap formed between the end portion 122a of the second main body portion 122 and the inner end portion 120a of the first main body portion 120 communicate with each other. For this reason, the vicinity of the end portion on the first direction side (i.e., the downstream end) of the same flow path 140 and the middle of the second outflow channel OP2 communicate with each other through the through hole 158, the gap between the inner end portion 120a on the first direction side of the first main body portion 120 and the end portion 122a on the second direction side of the second main body portion 122, and the gap between the expanded flow path 156 and the same flow path 140. Hereinafter, the through hole 158, the gap between the inner end portion 120a on the first direction side of the first main body portion 120 and the end portion 122a on the second direction side of the second main body portion 122, and the gap between the expanded flow path 156 and the same flow path 140 may be collectively referred to as the "second reflux channel 162". As described above, a large negative pressure is generated in the vicinity of the end portion on the first direction side (i.e., the downstream end) of the same flow path 140. For this reason, a part of the air-dissolved water blocked by the second flange portion 152 is sucked into the second reflux channel 162 (specifically, the through hole 158) by the negative pressure generated in the vicinity of the end portion on the first direction side of the same flow path 140. Then, the air-dissolved water sucked into the second reflux channel 162 reflows into the expanded flow path 156 via the second reflux channel 162. Similar to the air-dissolved water that reflows into the expanded flow path 156 via the first reflux channel 160, the fine bubbles in the air-dissolved water that reflows into the expanded flow path 156 via the second reflux channel 162 are also further refined.

[0045] In addition, the air-dissolved water that reaches the portion where the opening 188 (see FIG. 12) is formed among the end portions on the second-direction side of the inner case portion 150 flows out to the outside of the cylindrical portion 172 through the opening 188. Then, the air-dissolved water that has flowed out to the outside of the cylindrical portion 172 flows into a third outflow channel OP3 defined between the outer peripheral wall portion 172a of the cylindrical portion 172 and the inner peripheral wall portion 100c of the main body case 100.

[0046] As shown in FIG. 4, the air-dissolved water that has flowed into the third outflow channel OP3 collides with the surface on the second-direction side of the circumferential wall portion 182a of the second water receiving portion 182. When the air-dissolved water collides with the circumferential wall portion 182a, the fine bubbles in the air-dissolved water split into finer bubbles, and the amount of the fine bubbles increases. Then, the air-dissolved water flows from the second direction side to the first direction side along the surface on the second-direction side of the second water receiving portion 182 and collides with the surface on the second-direction side of the circumferential wall portion 180a of the first water receiving portion 180. When the air-dissolved water collides with the circumferential wall portion 180a, the fine bubbles in the air-dissolved water split into finer bubbles, and the amount of the fine bubbles increases. The air-dissolved water that has collided with the first water receiving portion 180 flows from the second direction side to the first direction side along the surface on the second-direction side of the first water receiving portion 180 and collides with the surface on the first-direction side of the circumferential wall portion 182a of the second water receiving portion 182. When the air-dissolved water collides with the circumferential wall portion 182a, the fine bubbles in the air-dissolved water split into finer bubbles, and the amount of the fine bubbles increases. The air-dissolved water that has collided with the circumferential wall portion 182a flows from the second direction side to the first direction side, flows out from the fine bubble generation portion 110 on the second direction side, and flows into the fine bubble generation portion 110 on the first direction side.

[0047] As described above, the air-dissolved water flows out from the fine bubble generation unit 110 by flowing through the first outflow channel OP1, the second outflow channel OP2, and the third outflow channel OP3. Hereinafter, the first outflow channel OP1, the second outflow channel OP2, and the third outflow channel OP3 may be collectively referred to simply as the "outflow channel". Then, a part of the air-dissolved water flowing through the outflow channel flows back into the diffusion channel 156 through the first reflux channel 160 connecting the middle of the outflow channel and the end on the first direction side of the same-flow channel 140, and the second reflux channel 162. When the air-dissolved water flows back into the diffusion channel 156, the fine bubbles in the air-dissolved water are further refined, and a large number of fine bubbles are generated.

[0048] As described above, the air-dissolved water passes through a total of two fine bubble generation units 110. As a result, the fine bubbles in the air-dissolved water are refined, and a large number of fine bubbles are generated.

[0049] According to the above configuration, as shown in FIG. 3, the fine bubble generator 46 includes an inflow portion 102 into which the air-dissolved water flows, an outflow portion 104 from which the air-dissolved water flows out, and a fine bubble generation portion 110 provided between the inflow portion 102 and the outflow portion 104. The fine bubble generation portion 110 includes a venturi portion including a reduced-diameter flow path 138 whose flow path diameter decreases from upstream to downstream, and an enlarged-diameter flow path 156 provided downstream of the reduced-diameter flow path 138 and having a flow path diameter that increases from upstream to downstream, an outflow flow path (i.e., the first outflow flow path OP1, the second outflow flow path OP2, and the third outflow flow path OP3) provided downstream of the venturi portion for allowing the air-dissolved water to flow out from the fine bubble generation portion 110, a first reflux flow path 160 connecting the middle of the outflow flow path and the venturi portion, and a second reflux flow path 162. The air-dissolved water flowing into the fine bubble generator 46 flows into the reduced-diameter flow path 138 of the venturi portion of the fine bubble generation portion 110. The air-dissolved water increases in flow velocity as it passes through the reduced-diameter flow path 138, and as a result, is depressurized. Bubbles are generated when the air-dissolved water is depressurized. Next, the air-dissolved water is gradually pressurized as it passes through the enlarged-diameter flow path 156. When the air-dissolved water containing bubbles after the bubbles are generated by depressurization is pressurized, the bubbles contained in the air-dissolved water split into fine bubbles. Then, the air-dissolved water containing fine bubbles flows out from the fine bubble generation portion 110 via the outflow flow path. In the venturi portion, a negative pressure is generated (Venturi effect) as the air-dissolved water flows through the venturi portion. The first reflux flow path 160 and the second reflux flow path 162 connect the middle of the outflow flow path and the venturi portion. Therefore, a part of the air-dissolved water flowing through the outflow flow path is sucked into the first reflux flow path 160 and the second reflux flow path 162 due to the negative pressure generated in the venturi portion. The air-dissolved water sucked into the first reflux flow path 160 and the second reflux flow path 162 reflows into the venturi portion. As the air-dissolved water passes through the venturi portion again, the fine bubbles in the air-dissolved water become finer bubbles and the amount of fine bubbles increases. Therefore, a large amount of fine bubbles can be generated.

[0050] Also, as shown in FIG. 3, the venturi portion further includes a constant flow path 140 that connects the end portion (i.e., the downstream end) on the first direction side of the converging flow path 138 and the end portion (i.e., the upstream end) on the second direction side of the diverging flow path 156, and the flow path of the constant flow path 140 is the same as the flow path of the end portion (i.e., the downstream end) on the first direction side of the converging flow path 138. The first reflux flow path 160 and the second reflux flow path 162 are connected in the vicinity of the end portion on the first direction side (i.e., in the vicinity of the downstream end) of the constant flow path 140. In the venturi portion, the flow velocity of the air-dissolved water in the vicinity of the end portion on the first direction side of the constant flow path 140 is the fastest. Therefore, the largest negative pressure is generated in the vicinity of the end portion (i.e., the downstream end) on the first direction side of the constant flow path 140. According to the above configuration, the first reflux flow path 160 and the second reflux flow path 162 are connected in the vicinity of the end portion on the first direction side of the constant flow path 140. Therefore, the amount of air-dissolved water sucked from the outflow flow path into the first reflux flow path 160 and the second reflux flow path 162 can be increased. As a result, the amount of air-dissolved water reflowing into the venturi portion increases, and more fine bubbles can be generated as a result.

[0051] In one or more embodiments, as shown in FIG. 3, in the outflow flow path, a second flange portion 152 is provided on the downstream side of the portion where the second reflux flow path 162 is connected, for guiding the air-dissolved water flowing in the outflow flow path to the second reflux flow path 162. According to the above configuration, the air-dissolved water flowing in the outflow flow path is easily sucked into the second reflux flow path 162 by the second flange portion 152. Therefore, the amount of air-dissolved water sucked from the outflow flow path into the second reflux flow path 162 can be increased. As a result, the amount of air-dissolved water reflowing into the venturi portion increases, and more fine bubbles can be generated as a result.

[0052] Also, as shown in FIG. 3, the fine bubble generation unit 110 further includes a bottom wall portion 170 that faces the opening at the end (i.e., the downstream end) on the first direction side of the diffuser channel 156 and against which the water flowing out from the diffuser channel 156 collides, and a cylindrical portion 172 that extends from the bottom wall portion 170 toward the venturi portion side (the second direction side) and surrounds at least a part of the venturi portion. The outflow channel includes a first outflow channel OP1 defined between the bottom wall portion 170 and the opening at the end (i.e., the downstream end) on the first direction side of the diffuser channel 156, and a channel on the downstream side of the first outflow channel OP1, which is a second outflow channel OP2 defined between the venturi portion and the cylindrical portion 172. The second reflux channel 162 is connected in the middle of the second outflow channel OP2. According to the above configuration, the air-dissolved water flowing out from the diffuser channel 156 collides with the bottom wall portion 170. When the air-dissolved water collides with the bottom wall portion 170, the fine bubbles in the air-dissolved water are split into finer bubbles, and the amount of fine bubbles increases. Also, since the second reflux channel 162 is connected in the middle of the second outflow channel OP2 on the downstream side of the first outflow channel OP1, the air-dissolved water sucked into the second reflux channel 162 and reflowing into the venturi portion collides with the bottom wall portion 170 again by flowing out from the diffuser channel 156. As a result, the fine bubbles in the air-dissolved water are split into even finer bubbles, and the amount of fine bubbles becomes even larger.

[0053] Also, in the above configuration, the air-dissolved water flowing in the venturi portion in the first direction and flowing out from the venturi portion collides with the bottom wall portion 170 and then flows in the second direction opposite to the first direction through the second outflow channel OP2 defined between the cylindrical portion 172 and the venturi portion. According to such a configuration, compared with the configuration in which the fine bubble generation unit 110 does not include the cylindrical portion 172, the length of the fine bubble generation unit 110 along the first direction can be shortened, and the fine bubble generator 46 can be miniaturized.

[0054] (Corresponding relationship) The first reflux channel 160 and the second reflux channel 162 are examples of "reflux channels". The second flange portion 152 is an example of a "guide wall portion". The bottom wall portion 170 is an example of a "collision wall portion". The cylindrical portion 172 is an example of a "side wall portion".

[0055] As described above in detail for each embodiment, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

[0056] (First Modification Example) The position where the fine bubble generator 46 is provided is not limited to the first hot water supply path 32a. The fine bubble generator 46 may be provided in the water supply path 30, the water filling path 50, the supplementary heating forward path 60, the first bathtub circulation path 62, or the second bathtub circulation path 68.

[0057] (Second Modification Example) In the above hot water supply system 2, fine bubbles are generated by utilizing the air contained in the water supplied from a water supply source 4 such as a water supply. In the modification example, the hot water supply system 2 may be provided with an air-dissolved water generator that dissolves the air taken in from the outside into the water. Then, the air-dissolved water generated by the air-dissolved water generator may be supplied to the fine bubble generator 46. Further, in another modification example, an air introduction passage for introducing air from the outside may be provided in the co-current flow path 140 of the fine bubble generation unit 110. Also, instead of air, gases such as carbon dioxide gas, hydrogen, and oxygen may be dissolved in the water.

[0058] (Third Modification Example) The fine bubble generator 46 may be provided with one fine bubble generation unit 110 or may be provided with three or more fine bubble generation units 110.

[0059] (Fourth Modification Example) The positions where the first reflux channel 160 and the second reflux channel 162 are connected to the Venturi section are not limited to the vicinity of the end on the first direction side of the same flow channel 140. For example, the first reflux channel 160 and the second reflux channel 162 may be connected to the reduced diameter channel 138, may be connected to the same flow channel 140 upstream of the vicinity of the end on the first direction side of the same flow channel 140, or may be connected to the expanded diameter channel 156.

[0060] (Fifth Modification Example) The Venturi section may not include the same flow channel 140.

[0061] (Sixth Modification Example) The fine bubble generation section 110 may not include the second flange section 152. That is, the “guide wall section” can be omitted.

[0062] (Seventh Modification Example) The fine bubble generation section 110 may not include the bottom wall section 170 and the cylindrical section 172. That is, the “collision wall section” and the “side wall section” can be omitted. In this modification example, the air-dissolved water flowing out from the Venturi section (specifically, the expanded diameter channel 156) flows in the first direction.

[0063] (Eighth Modification Example) The fine bubble generation section 110 may not include the cylindrical section 172. That is, the “side wall section” can be omitted. In this modification example, the air-dissolved water flowing out from the Venturi section (specifically, the expanded diameter channel 156) collides with the bottom wall section 170 and then flows in the first direction. In this modification example, the second reflux channel 162 may be connected to the middle of the outflow channel on the downstream side (that is, the first direction side) of the bottom wall section 170.

[0064] The technical elements described in this specification or the drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Also, the technologies exemplified in this specification or the drawings can achieve multiple purposes simultaneously, and achieving one of those purposes itself has technical utility.

Description of Reference Numerals

[0065] 2: Hot water supply system 4: Water supply source 6: Faucet 8: Bathtub 10: First heat source machine 12: Second heat source machine 14: Combustion chamber 16: Partition wall part 18: First combustion chamber 20: Second combustion chamber 22: First burner 24: First heat exchanger 26: Second burner 28: Second heat exchanger 30: Water supply path 32: Hot water supply path 32a: First hot water supply path 32b: Second hot water supply path 34: Bypass path 36: Bypass servo 38: Water volume sensor 40: Water volume servo 42: Heat exchanger outlet thermistor 44: Hot water supply thermistor 46: Microbubble generator 50: Water pouring path 52: Water pouring control valve 54: Check valve 60: Supplementary heating forward path 62: First bathtub circulation path 64: Bathtub return thermistor 66: Circulation pump 68: Second bathtub circulation path 70: Bathtub forward thermistor 100: Main body case 100a: First end 100b: Second end 100c: Inner peripheral wall part 102: Inflow part 102a: Inlet 104: Outflow part 104a: Outlet 110: Microbubble generation part 120: First main body part 120a: Inner end 122: Second main body part 122a: End part on the second direction side 124: Third main body part 130: First flange part 132: Cylindrical part 134a - 134e: Flow path parts 136: Outer peripheral part 138a - 138e: Reducing flow paths 140a - 140e: Equal - diameter flow paths 150: Inner case part 152a - 152e: Second flange parts 154: Connecting flow path 156a - 156e: Expanding flow paths 158a - 158e: Through - holes 160: First reflux flow path 162: Second reflux flow path 170: Bottom wall part 172: Cylindrical part 172a: Outer peripheral wall part 174: Extension part 176a: Protrusion part 176b: Protrusion part 176c: Protrusion part 178a - 178e: Notch parts 180: First water receiving part 180a: Circumferential wall part 180b: Axial extension part 182: Second water receiving part 182a: Circumferential wall part 182b: Axial extension part 184: Cylindrical part 186: Radial extension part 188: Opening part A: Central axis OP1: First outflow flow path OP2: Second outflow flow path OP3: Third outflow flow path

Claims

1. A fine bubble generator, comprising: an inflow section into which gas-dissolved water flows in; an outflow section from which the gas-dissolved water flows out; a fine bubble generation section provided between the inflow section and the outflow section, wherein the fine bubble generation section is a plurality of venturi sections arranged around the central axis of the fine bubble generator, and each of the plurality of venturi sections includes a reduced-diameter flow path whose flow path diameter decreases from upstream to downstream, and an enlarged-diameter flow path whose flow path diameter increases from upstream to downstream; a collision wall section facing the opening at the downstream end of the enlarged-diameter flow path of each of the plurality of venturi sections and against which the water flowing out from the enlarged-diameter flow path collides; an outflow flow path for allowing the gas-dissolved water flowing out from the plurality of venturi sections to flow out from the fine bubble generation section, the outflow flow path including a first outflow flow path defined between the collision wall section and the opening at the downstream end of the enlarged-diameter flow path; a reflux flow path connecting a middle portion of the outflow flow path and the plurality of venturi sections, the reflux flow path being arranged inside the plurality of venturi sections and including a first reflux flow path connecting a middle portion of the first outflow flow path and the plurality of venturi sections; A fine bubble generator comprising the above.

2. The fine bubble generation section further includes a side wall section extending from the collision wall section toward the plurality of venturi sections and surrounding at least a part of the plurality of venturi sections, the outflow flow path is a flow path on the downstream side of the first outflow flow path and further includes a second outflow flow path defined between the plurality of venturi sections and the side wall section, each of the plurality of venturi sections is provided with a through hole in its outer peripheral wall, The fine bubble generator according to claim 1, wherein the reflux flow path further includes a second reflux flow path connected to a middle portion of the second outflow flow path through the through hole.

3. The fine bubble generator according to claim 2, wherein a guide wall section for guiding the gas-dissolved water flowing in the second outflow flow path to the second reflux flow path is provided in the second outflow flow path on the downstream side of the portion where the second reflux flow path is connected.

4. Each of the plurality of venturi sections further includes a constant-diameter flow path connecting the downstream end of the reduced-diameter flow path and the upstream end of the enlarged-diameter flow path and having a constant flow path diameter. The flow path of the same flow path is the same as the flow path at the downstream end of the reduced flow path, The recirculation flow path is connected in the vicinity of the downstream end of the same flow path. The fine bubble generator according to any one of claims 1 to 3.

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