JP6067201B2 - Fine bubble generating method, fine bubble generating device, etc. - Google Patents

Description

  The present invention relates to a fine bubble generating apparatus, a fine bubble generating method, and the like that generate fine bubbles by precipitating dissolved gas from gas-dissolved water.

  Microbubbles with a diameter of about 0.1-100 μm have characteristics such as a large specific surface area, high internal pressure, and adsorptive properties, so various effects such as purification, physiological activity, and drag reduction are expected. Therefore, studies are underway for its application.

  For example, the above-mentioned fine bubbles are generated in hot water in a bathtub to make it cloudy, giving a taste like a milk bath, and obtaining bathing effects comparable to hot springs such as a moisturizing effect on the skin. ing.

  In the fine bubble generator described in Patent Document 1, hot water sucked from the bathtub by the operation of the circulation pump is sprayed from the spray nozzle into the gas-liquid dissolution tank, and the air stored in the gas-liquid dissolution tank and the outside It mixes with the air taken in from and produces gas-liquid dissolution bath water. Then, the generated gas-liquid dissolving bath water is discharged toward the bathtub, and when the gas-liquid dissolving bath water passes through the pressure reducing valve, the pressure is released and fine bubbles are generated by the expansion of the air that has been dissolved under pressure in the hot water. Is generated.

  With regard to such a fine bubble generating device, Patent Literature 2 discloses a fine bubble generator that generates fine bubbles using liquid cavitation and reduces the amount of energy consumed by a pump.

  The fine bubble generator described in Patent Document 2 includes a large tube diameter portion and a small tube diameter portion, and the end surface and the inner peripheral surface of the small tube diameter portion form corners in the longitudinal section of the fine bubble generator. However, the end face of the small pipe diameter part is in contact with the large diameter flow path of the large pipe diameter part. In this microbubble generator, the flow velocity of the liquid introduced into the small-diameter channel of the small tube diameter portion increases rapidly as the channel cross-sectional area rapidly decreases, and as a result, the static pressure of the liquid decreases. Cavitation can be generated even with small power. In addition, vortices are generated in the liquid as it collides with the corners, and the pressure of the liquid is lowest in the vicinity of the corners, and cavitation is likely to occur.

  Therefore, the fine bubble generator can generate cavitation without using a pump that discharges a high-pressure and large-flow liquid, and realizes a reduction in energy consumption of the pump.

JP-A-2005-329100 JP 2008-23515 A

  Although it is also desired for the fine bubble generator to adjust the size and number of bubbles according to the application, etc., in the fine bubble generator described in Patent Document 2, it is necessary to adjust the bubble diameter and number. Not considered. It is required as an improvement point to adjust the generation of fine bubbles according to the use of fine bubbles.

  The present invention has been made in view of the circumstances as described above, and a fine bubble generating method and a fine bubble generating device capable of generating fine bubbles having an optimum bubble diameter and number density according to the use, etc. Another object is to provide a method for adjusting and designing the bubble diameter and number density.

As a result of intensive studies on the case where fine bubbles are generated by decompression in a pressure-dissolution type fine bubble generator, the present inventors have found that gas-dissolved water flowing through the flow path in the fine bubble generation unit that generates fine bubbles The knowledge that the diameter and number density of the fine bubbles can be adjusted by changing at least one of the flow velocity and the pressure was obtained, and the present invention was completed.

  That is, the present invention has the following features in order to solve the above problems.

In the first invention, a gas is dissolved in water under a pressurized condition to generate gas-dissolved water, and then a fine bubble generating part formed by connecting a contracted part having a smaller cross-sectional area than the introducing part and the introducing part. Gas dissolved water was supplied to the gas, and the gas dissolved water was depressurized by passing through the contracted part, thereby generating cavitation to precipitate dissolved gas in the gas dissolved water, generating fine bubbles, and generated by cavitation. It is a fine bubble generating device that discharges bubbles, and it is possible to reduce the diameter of the fine bubbles in the water generated by cavitation by adjusting the flow rate of the dissolved gas flowing through the contraction portion to be slow. together, by adjusting to the gas flow rate dissolving water flowing in the vena contracta is fast, it is possible to increase the size of the fine bubbles in the water generated by cavitation Is characterized in that the flow rate adjusting means.

According to a second aspect of the present invention, in the first aspect, the flow velocity of the gas-liquid dissolved water to be changed by the flow velocity adjusting means is equal to or higher than the lowest flow velocity at which cavitation occurs, and the lowest lower limit at which supercavitation occurs It is characterized by being within the range of less than the flow velocity of.

According to a third invention, in the feature of the first or second invention, the flow velocity adjusting means changes a cross-sectional area of the contraction portion or the introduction portion .

According to the first aspect of the invention, since the flow rate adjusting means for changing the flow rate of the dissolved gas flowing through the contracted flow portion in the fine bubble generating portion is provided, the fine bubbles having the bubble diameter and number density according to the flow rate are provided. It is possible to generate optimal microbubbles according to the application.

According to the second aspect, the flow rate of the contraction flow portion by the flow rate adjusting means Ru is adjusted, or the lower limit of the flow rate cavitation occurs, there is a range of less than the lower limit of the flow rate super cavitation occurs Therefore, it is possible to more reliably generate fine bubbles having a bubble diameter or number density corresponding to the flow rate. Moreover, since cavitation occurs reliably, it is possible to reliably generate fine bubbles in a sufficient amount.

According to the third aspect of the invention, in addition to the effects of the first or second aspect of the invention, the flow rate adjusting means changes the cross-sectional area of the contraction part or the introduction part, so that it is easy to control the flow rate of the dissolved gas water. Can be done. Moreover, the design of the flow rate adjusting means is facilitated.

It is the block diagram which showed one Embodiment of the fine bubble generator of this invention, the fine bubble generation method, etc. FIG. It is the figure which modeled and showed the principle in the fine bubble generator of this invention, the fine bubble generation method, etc. It is the graph which showed the change of the flow rate of gas dissolution water, and the fine bubble diameter. It is the graph which showed the relationship between the change of the flow rate of gas dissolution water, and the number density of a fine bubble. It is the graph which showed the water temperature change of the initial flow velocity of a fine bubble, the flow velocity at the time of the minimum fine bubble diameter, and the flow velocity at the time of bubble number density saturation. It is the figure which showed the relationship between the change of the flow rate of gas dissolution water, and the generation | occurrence | production state of a fine bubble.

  As described above, FIG. 1 shows a fine bubble generator, a fine bubble generation method, a bubble diameter adjustment method, a fine bubble number density adjustment method, a bubble diameter design method, and a fine bubble number density setting according to the present invention. 1 is a block diagram illustrating an embodiment of a method.

  This embodiment is specifically realized as a fine bubble generating bathtub that generates fine bubbles in hot water in the bathtub.

  In the fine bubble generating bathtub 1a as the fine bubble generating device 1, the bathtub 3 for storing hot water 2 is provided with a hot water inlet 4 and a discharge port 5 on the side surface. The bathtub 3 also includes an air inlet 7 in the flange portion 6 that forms the upper surface portion. The suction port 4 of the bathtub 3 is connected to the suction side 9 a of the pump 9 through the water distribution pipe 8. The discharge side 9 b of the pump 9 is connected to the suction side 110 a of the gas dissolving device 110 as the gas dissolving unit 11 in the fine bubble generating device 1 through the inflow pipe 10. The discharge side 110 b of the gas dissolving device 110 is connected to the fine bubble generating unit 13 through the outflow pipe 12, and the fine bubble generating unit 13 is connected to the discharge port 5 through the water distribution pipe 14. The air suction port 7 communicates with the inflow pipe 10 through the air pipe 15. A check valve 16 is provided in the middle of the air pipe 15.

  In the fine bubble generating bathtub 1a, the fine bubble generating portion 13 is formed by connecting the introduction portion 13a and the contracted flow portion 13b having a smaller cross-sectional area than the introduction portion 13a as shown in FIG. Further, as shown in FIG. 1, the fine bubble generating unit 13 is provided with an adjusting valve 18 that constitutes the flow velocity adjusting means 17. The connecting portion between the introduction portion 13a and the contracted flow portion 13b forms a corner portion 13c with the end face of the contracted flow portion 13b opened outward, so that cavitation is likely to occur. The regulating valve 18 changes the cross-sectional area of the contraction part 13b or the introduction part 13a in the fine bubble generating part 13, and when the opening degree is large, the cross-sectional area of the flow path is large, and when the opening degree is small, the flow passage The cross-sectional area becomes smaller. The adjustment valve 18 is provided with a control means 19 for adjusting the opening thereof, and the control means 19 constitutes a flow rate control means 17 together with the adjustment valve 18. The control means 19 can employ an automatic control system according to an electrical signal or a manual control system such as a water tap.

  In the fine bubble generating bathtub 1 a, the hot water 2 in the bathtub 3 is sucked from the suction port 4 by the operation of the pump 9, and sent out to the gas dissolving device 110 through the water distribution pipe 8 and the inflow pipe 10. The hot water 2 is ejected from the suction side 110 a into the tank provided in the gas dissolving device 110, mixed with the air stored in the tank and the air in the bathroom sucked from the air suction port 7, and the air in the hot water 2 Dissolves to produce gas-dissolved water. The gas-dissolved water in which air is dissolved to a predetermined concentration flows out from the discharge side 110b and is sent out to the outflow pipe 12. When passing through the contracted portion 13b, the pressure decreases, cavitation occurs below the saturated water vapor pressure, dissolved gas in the gas dissolved water precipitates due to a boiling phenomenon, and fine bubbles are generated. The generated fine bubbles flow through the water distribution pipe 14 together with the hot water 2, are discharged into the bathtub 3 through the discharge port 5, and are mixed with the hot water 2 stored in the bathtub 3.

  The hot water 2 in the bathtub 3 circulates by the operation of the pump 9, and this circulation is repeated to increase the amount of fine bubbles in the hot water 2 in the bathtub 3, and the hot water 2 in the bathtub 3 becomes cloudy due to the fine bubbles, and the milk Give a taste like a bath.

  There are no particular limitations on the pump 9 and the gas dissolving device 110 that can be employed in the fine bubble generating bathtub 1a. For example, a centrifugal pump is exemplified as the pump 9. As the gas dissolving device 110, any device can be adopted as long as air can be dissolved in water.

  Further, the suction port 4 and the discharge port 5 in the fine bubble generating bathtub 1 a can be incorporated as a single nozzle unit or the like and attached to the wall portion of the bathtub 2. In this case, the control of the opening degree of the adjusting valve 18, which will be described later, is realized as a change in the opening area of the nozzle unit.

  And in the fine bubble generation bathtub 1a, the flow rate adjustment means 17 comprised from the adjustment valve 18 and the control means 19 changes the flow rate of the gas dissolved water which flows through the contraction part 13b in the fine bubble generation part 13. FIG. Specifically, the flow rate adjusting means 17 slows the flow rate of the dissolved gas flowing through the flow path by changing the cross-sectional area of the contracted flow portion 13b or the introduction portion 13a in the fine bubble generating portion 13. Or make it faster. The opening degree of the regulating valve 18 is controlled by the control means 19. For example, when the adjustment valve 18 is provided so as to change the cross-sectional area on the side of the contraction part 13 b, the cross-sectional area of the contraction part 13 b is small when the opening degree is small. As a result, the flow rate of the gas-dissolved water in the contracted flow portion 13b is increased, and the flow rate of the gas-dissolved water flowing through the contracted flow portion 13b is increased. When the flow rate is increased in this manner, the amount of generated fine bubbles increases, and the number density of fine bubbles in the hot water 2 increases. On the other hand, when the opening degree of the regulating valve 18 is large, the cross-sectional area of the contracted portion 13b increases, and as a result, the flow rate of the dissolved gas in the contracted portion 13b becomes slow. When the flow rate becomes slow, the diameter of the fine bubbles in the hot water 2 becomes small, and the floating time in the hot water 2 becomes long.

  When the regulating valve 18 is provided so as to change the cross-sectional area on the introduction part 13a side, when the opening degree is small, the cross-sectional area of the introduction part 13a becomes small, and the flow rate of the gas dissolved water in the introduction part 13a is the same. The flow rate of the gas dissolved water in the contracted flow part 13b becomes slow. When the flow rate becomes slow, the diameter of the fine bubbles in the hot water 2 becomes small, and the floating time in the hot water 2 becomes long. On the other hand, when the opening degree of the regulating valve 18 is large, the cross-sectional area of the introduction part 13a is large, and as a result, the flow rate of the dissolved gas in the contracted flow part 13b is increased. As the flow rate increases, the amount of fine bubbles generated increases and the number density of fine bubbles in the hot water 2 increases.

  Note that the change in the flow rate of the dissolved gas water in the contracted flow part 13 b can also be performed by controlling the output of the pump 9 that supplies the dissolved gas water to the fine bubble generating part 13. In this case, when it is desired to reduce the diameter of the fine bubbles and increase the floating time in the water, the output of the pump 9 is decreased to reduce the flow velocity, and when the diameter of the fine bubbles in the water is increased, the pump 9 Increase the output to increase the flow rate. In this way, the bubble diameter can be adjusted.

  The change in the diameter and number density of the fine bubbles accompanying the change in the flow rate of the gas-dissolved water described above is based on the following experimental verification and analysis.

  FIG. 3 and FIG. 4 show the relationship between the change in the flow rate of the gas-dissolved water obtained by the experiment and the fine bubble diameter, and the relationship between the change in the flow rate of the gas-dissolved water and the number density of the fine bubbles, respectively. These relationships are the results of experiments in which the cross-sectional area of the introduction portion 13a and the flow rate of the pump 9 are constant, and the flow velocity of the contraction portion 13b is changed by changing the cross-sectional area of the contraction portion 13b. In addition, the three graphs in the figure are the evaluation results when the gas dissolution amounts are different. In FIG. 3, the Sauter average bubble diameter is used as the fine bubble diameter.

  As shown in FIG. 3, when the flow velocity u2 of the contracted flow portion 13b is 10.5-12 m / s, the diameter of the fine bubbles rapidly decreases as the flow velocity increases. Thereafter, it becomes almost minimum at 12 m / s, and when it becomes faster than 12.5 m / s, the fine bubble diameter gradually increases. Also, as shown in FIG. 4, the number density is extremely low when the flow velocity u2 is 10.5-11 m / s, but the number density increases rapidly as the flow velocity increases at 11-13 m / s, When it exceeds 13 m / s, it becomes almost constant.

  From these experimental results, it is considered that the adjustment range of the flow velocity u2 of the gas dissolved water in the contracted flow portion 13b is suitably 11-13 m / s, preferably 11.5-13 m / s. . That is, as shown in FIG. 3 and FIG. 4, the bubble diameter can be increased or decreased within the above flow velocity range, and the diameter of the fine bubbles is reduced at a low speed of 11.5-12.5 m / s. The floating time of fine bubbles can be lengthened. In the case of a high speed of 12.5 m / s or more, the diameter of the fine bubbles can be increased, the amount of fine bubbles generated is increased, and the number density of the fine bubbles is increased. By applying such a result to the design of the fine bubble generator and adjusting the flow rate of the dissolved gas water, it is possible to realize a fine bubble generator capable of generating fine bubbles having a desired diameter and number density. it can.

  Moreover, the flow state of the gas dissolved water in the contracted flow part 13b was photographed using a high-speed video camera, and the result of confirming the occurrence of cavitation is shown in FIG.

  When the flow velocity u2 is 11 m / s, cavitation occurs in the flow path. On the other hand, the area of cavitation is relatively small, and the ratio of occupying the channel inlet is also relatively small. Also, the amount of fine bubbles deposited on the downstream side is relatively small.

  When the flow velocity u2 is 11.5, 12, or 12.5 m / s, the cavitation region expands as the flow velocity increases, and the proportion of the flow path inlet increases. The amount of fine bubbles deposited on the downstream side also increases.

  When the flow velocity u2 is 13 m / s, the cavitation region occupies almost the entire area, and almost the entire flow path inlet is occupied by the gas. The amount of fine bubbles deposited on the downstream side is considerably large. On the other hand, the enlargement of the cavitation region is almost saturated, and a cavity filled with water vapor is formed in the flow path, and super cavitation in which bubbles broken off at the downstream end of the cavity are discharged from the flow path as fine bubbles is generated. Occurred.

  Therefore, 11-13 m / s, which is considered to be appropriate as the change range of the flow rate of the dissolved gas flowing through the flow path, is a range that is equal to or higher than the lowest flow rate at which cavitation occurs and less than the lowest flow rate at which super cavitation occurs. It corresponds to.

  As described above, when the regulating valve 18 capable of changing the flow velocity by changing the cross-sectional area of the contracted flow portion 13b or the introduction portion 13a in the fine bubble generating portion 13 is used, water is supplied to the gas dissolving portion 13. For example, even if the discharge pressure of the pump 9 is made constant without controlling the output of the pump 9, the flow rate of the dissolved gas in the contracted flow portion 13b can be changed. When it is desired to reduce the diameter of the fine bubbles and increase the floating time in water, the flow rate of the gas dissolved water flowing through the contracted portion 13b is decreased, and the diameter of the fine bubbles in water is increased or the number density of the fine bubbles. Is increased, the flow rate of the dissolved gas flowing in the contracted flow portion 13b is increased. Therefore, adjustment to the generation of the optimum fine bubbles according to the use of the fine bubbles can be performed without controlling the output of the pump 9, and the energy consumption of the pump 9 can be further reduced. As a result, the size of the tank provided in the gas dissolving unit 11 such as the gas dissolving device 110 can be designed according to the application, and the miniaturized bubble generation bathtub 1a and the like promote the miniaturization of the tank.

  The principle of the present invention will be described below with reference to FIG.

  In FIG. 2, reference signs A <b> 1 and A <b> 2 indicate cross-sectional areas of the gas-dissolved water flow paths. Further, other symbols shown in FIG. 2 and parameters in the following mathematical formulas are as follows.

P1: Pressure of the introduction part 13a P2: Pressure of the contraction part 13b Pv: Saturated water vapor pressure u1: Flow rate of the introduction part 13a u2: Flow rate of the contraction part 13b ρ: Density Bernoulli's theorem (p + 1 / 2ρu ² + ρgh = const. )Than,
P1 + 1 / 2ρu1 ² = P2 + 1 / 2ρu2 ² (1)
P1-P2 = 1 / 2ρ (u2 ² −u1 ² ) (2)
On the other hand, as a condition for generating fine bubbles, considering that the pressure is equal to or lower than the saturated water vapor pressure and cavitation occurs,
(P1-Pv) / (P1-P2) ≦ 1 (3)
From equations (2) and (3),
(P1-Pv) / (1 / 2ρu2 ² ) ≦ 1 (4)
The value represented by the left side of Equation (4) is a cavitation coefficient Cv, which is a coefficient representing the ease of occurrence of cavitation. A larger Cv indicates that cavitation is more likely to occur. In particular, when cavitation is likely to occur, Cv takes a value of 1 or more.

  From the equation (4), it can be seen that Cv changes by changing the flow velocity u2 of the gas-dissolved water in the contracted portion.

In addition, due to the conservation of mass,
u1 = (A2 / A1) u2 (5)
Therefore,
Cv = (P1-Pv) / (1 / 2ρ (1- (A2 / A1) ² ) u2 ² ) (6)
From equation (6)
u2 = ((P1-Pv) / (Cv × ρ / 2 × (1- (A2 / A1) ² ))) ^(1/2) (7)
The condition for generating cavitation is A1 >> A2, that is, (A2 / A1) ² << 1.
u2 = ((P1-Pv) / (Cv × ρ / 2)) ^(1/2) (8)
From the experiment, it was confirmed that when the water temperature is 25 ° C., the initial flow velocity of the fine bubbles, the flow velocity at which the fine bubble diameter is minimized, and the flow velocity at which the number density of the bubbles is saturated are 11, 12.5, and 13 m / s, respectively. Has been. From these results, the cavitation coefficient Cv of the initial flow velocity of the fine bubbles, the flow velocity at which the fine bubble diameter is minimum, and the flow velocity at which the number density of bubbles is saturated is calculated. Cv and Cv when the bubble number density is saturated are 1.627, 1.367, and 1.165 in this order. Based on the cavitation coefficient Cv and the pressure condition P1 of the introduction portion 13a, the flow velocity condition for generating fine bubbles can be expressed by the following equation from the equation (8).

Initial flow velocity of fine bubbles: u2 = ((P1-Pv) / (1.627 × ρ / 2)) ^(1/2)
Flow velocity at the minimum fine bubble diameter: u2 = ((P1-Pv) / (1.367 × ρ / 2)) ^(1/2)
Flow velocity when the bubble number density is saturated: u2 = ((P1-Pv) / (1.165 × ρ / 2)) ^(1/2)
The result of calculating the flow velocity from the saturated vapor pressure at each water temperature is shown in FIG. When the flow rate of the gas-dissolved water in the contracted portion 13b is changed in the flow velocity range between the curve of the initial flow velocity of the fine bubbles and the flow velocity curve when the bubble number density is saturated, the diameter and number density of the fine bubbles in the water It becomes possible to adjust at least one of these.

  In addition, this invention is not limited to the fine bubble generation bathtub shown in FIG. It can be realized in various devices according to the use of fine bubbles. Further, the flow rate adjusting means can be configured as, for example, a venturi other than the adjusting valve and the control means shown in FIG.

DESCRIPTION OF SYMBOLS 1 Fine bubble generator 9 Pump 11 Gas melt | dissolution part 13 Fine bubble generation part 13a Introduction part 13b Shrinkage part 17 Flow velocity adjustment means

Claims (3)

After dissolving gas in water under pressure and generating gas-dissolved water, gas dissolved water is supplied to the microbubble generation part formed by connecting the introduction part and the contracted part with a smaller cross-sectional area than the introduction part Then, when the gas dissolved water is depressurized by passing through the contracted flow part, cavitation is generated to precipitate the dissolved gas in the gas dissolved water, generating fine bubbles, and discharging the bubbles generated by cavitation A generator,
By adjusting the flow rate of the dissolved gas flowing through the contracted part to be slow, the diameter of the fine bubbles in the water generated by cavitation can be reduced, and the flow rate of the dissolved gas flowing through the contracted part is reduced. A fine bubble generating device, characterized in that a flow rate adjusting means capable of increasing the diameter of the fine bubbles in water generated by cavitation by adjusting so as to be faster is provided.   The flow rate of the gas-liquid dissolved water constricted portion adjusted by the flow rate adjusting means is not less than the lowest flow rate at which cavitation occurs and is less than the lowest flow rate at which super cavitation occurs. Item 2. The fine bubble generator according to Item 1.   The microbubble generator according to claim 1 or 2, wherein the flow velocity adjusting means changes a cross-sectional area of the contracted flow portion or the introduction portion.