FIELD OF THE INVENTION
[0001] The present invention, in general, relates to apparatuses for generating nano-bubbles. Particularly, the invention relates to a two zone shearing based facility for air nanobubble generation. More particularly, the present invention relates to a continuous shear nanobubble generator configured to generate stable nanobubbles by passing pressurized air-water mixture on a custom designed shear member fixed at one end of said generator.
DESCRIPTION OF PRIOR ART
[0002] Systems for generating nanobubbles for industrial purposes are scarce. In the state of the art literature, generation of nanobubbles through pressurized water method is disclosed. But said method produces a mixture of micro bubbles and nanobubbles and it takes large number of cycling to obtain the desired nanobubble concentration. A further shortcoming of the system is that the nanobubble generation happens in a closed environment under controlled pressure and temperature. Under atmospheric conditions, the nanobubble concentration of the mixture may decrease significantly.
[0003] Another method found in prior art is high speed shearing, wherein liquid and gas is agitated into micro bubbles using ultrasonic waves, in a microbubble sonicator, to produce microbubble water. Said microbubble water along with gas r afldrwater- isj-suppijed^ntppay nanobjubbleygeneratorrat'pre.ssprerofrO^rl^MPa^at"" flow rate of 17 l/min, using a pump having 3600 rpm. Said nanobubble generator

is a circular member in which microbubble and gas water mixture spirals along the inner walls, wherein owing to the high centrifugal forces caused by the circulation, the microbubbles are separated (converted) into nanobubbles. Resultant nanobubble water mixture exits the generator through the outlet.
[0004] WO0197958 (A1) teaches a Fine Air Bubble Generator and Fine Air Bubble Generating Device with the Generator. But said invention mainly produces microbubbles and may not generate nanobubbles.
[0005] EP2552574 (A1) details a nanobubble generator and treatments. Here, the nano-bubbles are generated by forcing the ozone gas through submicron-sized porous material containing spherical porous material using an oscillating (pulsed) liquid injection. In regular use, however, the porous material may needed to be replaced regularly. Our invention does not need any pre oscillation of liquid for its operation, and is relatively clog free. It is also simple in construction.
[0006] US Pat No. 6382601 teaches a swirling fine bubble generator capable of generating micro-bubbles with diameter of not more than 20 um in industrial scale. But said invention is not designed to generate nanobubbles.
[0007] US Pat No. 8317165 details a nanobubble containing liquid producing apparatus and method. Said method uses two stage for producing nanobubble wherein in each stage, gas got to be supplied. Our invention is essentially a

single stage nano bubble generator, which is much simpler to construct and maintain.
[0008] EP 3124109 A1 teaches a nanobubble producing apparatus with which it is possible to obtain high-concentration nanobubbles that are minute and have a uniform diameter. However, in said invention, the micro bubble containing water are converted into nanobubbles by ultrasonic waves, wherein it needs a certain volume of pre-made micro bubble water to produce nanobubbles. Further, only a small quantity of water in reservoir can be converted to nanobubble water using this apparatus. Our invention does not need any micro bubble water to produce nanobubbles, and said system is scalable as well.
[0009] WO2005084718{A1) teaches a method of producing nanobubbles that remains in a solution for a long time, wherein the aforementioned object is achieved by applying physical irritation to microbubbles contained in a liquid so that the microbubbles are abruptly reduced in size. But said invention uses electro static discharge and recirculation for one hour for producing nanobubble. Our invention requires only less than 5 minutes of operation to produce nanobubbles. It is also simple and scalable.
[0010] From the foregoing, it becomes apparent that there is a need for a robust nanobubble generator that is capable of producing stable nanobubbles in atmospheric conditions.

[0011] Our invention proposes a continuous shear nanobubble generator configured to produce nanobubbles of diameter 500 nm or less. It is capable of producing higher concentration of nanobubbles in a given volume of water in less time.

SUMMARY OF THE INVENTION
[0012] It is therefore the primary objective of the present invention to propose a continuous shear nanobubble generator for producing stable nanobubbles.
[0013] It is another object of the invention to propose a continuous shear nanobubble generator that is configured to work in atmospheric conditions.
[0014] It is yet another object of the invention to propose a swirl nanobubble generator that is economical to manufacture and maintain.
[0015] It is a further object of the invention to propose a continuous shear nanobubble generator that is capable of generating a higher percentage of nanobubbles per cycle.
[0016] It is yet another object of the invention to propose a system configured to produce nanobubble water containing nanobubbles of diameter 500 nm or less.
[0017] Accordingly, our invention proposes a continuous shear nanobubble generator configured to generate nanobubbles by passing pressurised air-water mixture over a shearing surface, said nanobubble generator comprising of:
• a cylindrical hollow structure featuring a water inlet, at least one air inlet and an outlet; and ^Pi FT"rT*F'shB'af meffi^

extends towards the outlet.
[0018] Our invention also provides a system to generate nanobubble water, said system comprising of:
• a swirl tank filled with a fixed volume of water;
• continuous shear nanobubble generator positioned below the water level in the tank;
• centrifugal pump to draw and pressurise water from the tank, wherein said pressurised water is fed into the nanobubble generator through the water inlet; and
• means to compress air, wherein said air is injected into pressurised water in the nanobubble generator through the air inlet.
[0019] The other objectives, features, and advantages of the present invention will become more apparent from the ensuing detailed description of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF ACCOMPANYING FIGURES [0020] FIG.1 illustrates the nanobubble generator system. [0021] FIG.2 depicts the sectional view of nanobubble generator.

DETAILED DESCRIPTION OF INVENTION
[0022] The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. It should be understood that however the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the daims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail.
[0023] The preferred embodiment of the present invention teaches a two-zone shearing based system for air nanobubble generation (continuous shear nanobubble generator). Said system uses a fixed quantity of water drawn from a swirl tank to produce nanobubbles or nanobubble water. Nano-bubbles are tiny bubbles with a respective diameter of less than 1pm. The swirl tank can be of any shape even though a circular tank is efficient as the water tends to swirl in a circular tank, which helps in the generation of nanobubbles. Water to be turned into nanobubble water is taken from any source, provided said water is free of impurities that could lead to blockage in the system. One novel aspect of the invention is that the nanobubble generator works as an open system.

[0024] Referring to FIG.1, the water from the swirl tank is pressurised using a high speed recirculating pump (5) featuring a shear impeller, wherein said pressurised water is directed into the water inlet (3) of the continuous shear nanobubble generator (1). Further, high pressure compressed air is introduced into swirl stream of water through an air inlet (4) provided on the nanobubble generator. Said nanobubble swirl generator is positioned below the water level, in the swirl tank (7) as shown in the figure.
[0025] Owing to nigh pressure water swirl, the air stream gets compressed and is sheared by the shear member as the pressurized water flows towards the outlet, to produce micro and nanobubbles. The narrow neck also plays a part in accelerating the water and air, and hence in the generation of micro and nanobubbles. The water in the swirl tank is circulated multiple times through the nanobubble generator until the desired concentration of nanobubbles is obtained.
[0026] Referring to FIG.2, the nanobubble generator (1) is a partially closed
circular hollow structure featuring a water inlet (3), a shear member (2), one or
more air inlets and an outlet. The water inlet is connected to trie outlet of a high
pressure pump, wherein the pressurized water gets swirled inside the generator
owing to the circular cross section of said nanobubble generator. Further,
compressed air enters the swirl water stream in the nanobubble generator
chamber through the air inlet, wherein it gets further compressed due to the high
t-tf&Sa&ffltoES&mifrT EL7-M-1-ryrrrrT?» ~ 1 _____

[0027] A shearing member comprising of a solid divergent member is positioned towards the outlet as shown in FIG.2. The shear member has a flat face on which the compressed air stream strikes. The shear member is positioned in such a way that its flat face occupies about 2/3rd cross-section area of the cylindrical cross section. Said cross section area progressively decreases towards the outlet of the generator.
[0028] The impact of the air-water stream striking the shear member causes the air to shear resulting in the formation of micro, macro and nanobubbles. The presence of the shear member near the exit effectively reduces the area of the outlet therein accelerating the stream of water exiting the chamber. Said process is repeated until the desired nanobubble concentration in the swirl tank is obtained. One of the advantages of the present invention is that only less number of recirculation of water is required to generate nanobubbles in required volume compared to existing prior arts.
[0029] The steps of nano-bubble generation as per the preferred embodiment may be surmised as follows:
[0030] Step 1: The water in the swirl tank for nano-bubble generation is pressurised using a centrifugal pump and is fed into the continuous shear nanobubble generator through the water inlet.

[0032] Step 3: Air and water gets mixed in the chamber, wherein bubbles get sheared by the shearing member resulting in the formation on macro, micro and nanobubbles.
[0033] Step 4: The water in the tank is recirculated back into the nanobubble generator and the processes disclosed in steps 1, 2 and 3 are repeated until the desired concentration of the nanobubbles in the water is obtained.
The Nano-Bubble Generator
As per the preferred embodiment, the water inlet diameter is 10 mm, wherein water is pressurised using a centrifugal pump of 0.5 HP. The cross section measures 25.4 mm, and water chamber measures 50 mm in length. The
shearing member has a slight angle of around 2.5C and the compressed air outlet is 2 mm wide. The size of the generator was influenced by the water inlet pressure and compressed air pressure for conversion of the air into bubble efficiently without any loss. The nanobubble generator may be constructed in other sizes to create nanobubbles in different volumes, they are all included within the scope of the invention.
[0034] Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it

apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention unless they depart there from.

1. A continuous shear nanobubble generator (1) configured to generate
nanobubbles by passing pressurised air-water mixture over a shearing
surface, said nanobubble generator comprising of:
• a partially closed cylindrical hollow structure featuring a water inlet (3), at least one air inlet and an outlet; and
• shear member (2) fixed on the inner surface of said cylinder, wherein it extends towards the outlet.

2. The nanobubble generator as claimed in claim 1, wherein the water inlet is connected to the outlet of a high pressure pump (5).
3. The nanobubble generator as claimed in claim 1, wherein pressurized air is introduced into the cylindrical chamber through the at least one air inlet.
4. The nanobubble generator as daimed in claim 1, wherein the shear member has a flat face and a tapering edge, wherein it occupies 2/3rd of the internal cross section of the cylinder at its innermost tip.
5. A system to generate nanobubble water, said system comprising of:

• a swirl tank filled with a fixed volume of water;
• continuous shear nanobubble generator positioned below the water

• centrifugal pump to draw and pressurise water from the tank, wherein said pressurised water is fed into the nanobubble generator through the water inlet; and
• means to compress air, wherein said air is injected into pressurised water in the nanobubble generator through the air inlet.

6. The system as claimed in claim 5, wherein the water in the swirl tank is recirculated back into the nanobubble generator until the desired concentration of the nanobubbles in the water is obtained.
7. A method to produce and increase the concentration of nanobubbles in a given volume of water in a tank, said method comprising the steps of:

• drawing and pressurising water from the tank using centrifugal pump;
• supplying said pressurised water into the continuous shear nanobubble generator;
• injecting compressed air into said pressurised water in the nanobubble generator; and
• repeating the above said steps until the desired concentration of the nanobubbles in the water is obtained.

8. The method as claimed in claim 7, wherein the shearing of bubbles into nanobubbles happen on impact of pressurised air-water mixture on the shear member.