A device for preparing plasma-activated water by underwater bubble discharge

Abstract

The application provides a device for preparing plasma-activated water by underwater bubble discharge, which adopts an asymmetric electrode off-axis structure, the axis of a high-voltage electrode is below the axis of an outer medium tube, and the high-voltage electrode is tightly nested by the inner medium tube, and the ground electrode is arranged at the bottom end of the water tank. The application forms a strong non-uniform electric field in the discharge area, reduces the discharge requirement and enhances the concentration of active species generated in the medium tube under the same electrode and medium size and the same power supply condition. The gas outlet hole of the outer medium tube adopts a micro-bubble generating structure, the micro-pore is located directly below the off-axis, so that the plasma can be quickly blown out with the gas and directly enter the liquid phase to react with water molecules to generate RONS. And the discharge occurs on one side of the micro-pore, which reduces energy loss and improves the preparation efficiency of PAW.

Description

Technical Field

[0001] This invention belongs to the field of plasma-activated water preparation, and relates to an apparatus for preparing plasma-activated water by underwater bubble discharge. Background Technology

[0002] Plasma-activated water (PAW), with its products exhibiting significant transient and broad-spectrum bioactivity, presents a promising green solution for a wide range of biotechnological applications, from water purification to biomedicine. In agriculture, PAW is used to improve seed germination rates and seedling growth, and to treat fungal infections in plants. In the biomedical field, PAW applications include biofilm removal, wound healing, bacterial and viral inactivation, dentistry, and cancer treatment.

[0003] The biochemical activity of PAW is directly related to the presence of highly active substances in solution, especially long-lived substances such as nitrite (NO2). - ), nitrates (NO3) - Hydrogen peroxide (H2O2) and ozone (O3), as well as short-lived substances such as hydroxyl radicals (•OH) and superoxide radicals (•O2). − ), peroxynitrite (ONOO) − PAW (Polymerase Injection) exhibits excellent effects in sterilization, disinfection, fruit and vegetable cleaning, seed germination, and food preservation. However, the chemical properties and relative concentration of RONS (Reactive Oxygen Species) in solution are closely related to the reactor structure. Using different reactors during water treatment will cause changes in PAW parameters, thus affecting the application of PAW in agriculture and biomedicine. Currently, the mainstream methods for preparing PAW include plasma jetting, sliding arc discharge, and coaxial DBD (Diverterless Discharge). Although these types of discharge plasmas can transport RONS from the gaseous plasma to the liquid phase, they generally suffer from drawbacks such as low mass transfer efficiency, limited single-pass processing capacity, insufficient plasma-liquid contact, high power requirements, demanding power supply requirements, and complex structures.

[0004] For example, the concentration of active particles generated in a coaxial DBD reactor is limited by the wall thickness of the inner dielectric tube and the inner diameter of the outer dielectric tube. The wall thickness of the inner dielectric tube determines the discharge voltage; excessive thickness places higher demands on the power supply, while insufficient thickness can easily break down the inner dielectric tube, leading to filamentary discharge and uneven discharge. The inner diameter of the outer dielectric tube determines the concentration of active particles and the mass transfer efficiency. A larger inner diameter results in a larger discharge gap, reducing the discharge intensity and thus decreasing the activity and yield of species in the plasma. Furthermore, a larger gap increases the time it takes for active species to enter the aqueous phase, which is detrimental to the reaction of short-lived species with water. A smaller inner diameter allows for uniform discharge within the dielectric tube, but the generated active species can only be transported to the liquid phase via gas flow on the perforated side, while the unperforated portion of the outer dielectric tube inevitably results in excess discharge. In a sliding arc reactor, ROS is mainly generated during discharge because O3 is rapidly quenched at the high temperature of the sliding arc, resulting in a low ROS concentration in the solution. Simultaneously, the heat transfer during discharge also hinders its scaling up. In the preparation of PAW (Polyhydroplasma Arsenide) using a needle-water electrode structure, the high-pressure needle electrode is prone to corrosion, and the amount processed at one time is very small, resulting in high energy loss. This limits the efficiency of plasma activation and hinders the development of PAW applications. Summary of the Invention

[0005] 1. The technical problem to be solved:

[0006] Currently, common PAW preparation devices are severely affected by the conductivity of water, making it impossible to maintain stable discharge for extended periods. This results in energy waste, rapid heating, low mass transfer efficiency, and limited single-batch processing capacity.

[0007] 2. Technical Solution:

[0008] To address the above problems, this invention provides an underwater bubble discharge plasma activation preparation method comprising a plasma source, a water tank, and a driving power supply. The plasma source is located below the water surface and employs an asymmetric off-axis electrode structure. It also includes an outer dielectric tube and an inner dielectric tube, with a 1 mm discharge gap between them. The inner dielectric tube extends from the water tank through the water tank wall and support columns at both ends. A high-voltage electrode is tightly nested within the inner dielectric tube. A ground electrode is positioned at the bottom of the pool. The axis of the high-voltage electrode is parallel to, but does not coincide with, the axis of the outer dielectric tube.

[0009] The central axis of the inner medium tube is located below the central axis of the outer medium tube.

[0010] The external dielectric tube is located directly below the high-voltage electrode and has multiple microbubble openings.

[0011] The multiple microbubble pores are formed at 0.05 mm intervals every 4 mm below the axis of the external medium tube.

[0012] It also includes a gas flow controller, through which gas is injected into the plasma source. The injected air is ionized by an electric field within a 1mm discharge gap. The generated plasma is carried by the gas flow through micropores into the liquid.

[0013] The water tank has openings on both sides near the bottom, with the diameter of the openings being the same as the outer diameter of the outer medium pipe. A sealing rubber ring covers the openings on the outside of the openings. A support column is located outside the sealing rubber ring, and the support column has an annular hole. The outer annular hole is in the same position as the opening and has the same diameter. The distance between the outer side of the inner annular ring and the inner side of the outer annular ring is the same as the thickness of the outer medium pipe. A through hole is opened in the inner annular ring at the position of the inner medium pipe, and the diameter of the through hole is the same as the outer diameter of the inner medium pipe.

[0014] It also includes multiple set screws that pass through the tank wall to press the sealing collar.

[0015] It also includes a water valve, which is located above the water tank for adding untreated water.

[0016] It also includes a water outlet valve, which is located at the water outlet at the bottom of the water tank.

[0017] 3. Beneficial effects:

[0018] This invention employs underwater bubble discharge, and the activated water preparation device utilizes an asymmetrical off-axis electrode structure, with the axis of the high-voltage electrode positioned below the axis of the outer dielectric tube. This electrode structure creates a strong non-uniform electric field in the discharge region, reducing discharge requirements and enhancing the concentration of active species generated within the dielectric tube under the same electrode and dielectric dimensions and power supply conditions. For example, under the same processing conditions, compared to a coaxial structure, the off-axis electrode structure results in a higher concentration of NO3- in the treated PAW. - The concentration was increased from 105 mg / L to 140.6 mg / L, an increase of 34%. Furthermore, the aperture size of the outer dielectric tube plays a crucial role in increasing the contact between the plasma plume and water. This invention employs a microbubble generation structure, with micropores located directly below the high-voltage electrode, allowing the plasma to be rapidly blown out with the gas and directly enter the liquid phase to react with water molecules to generate RONS. Moreover, the discharge occurs on one side of the micropores, reducing energy loss and improving the preparation efficiency of PAW. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the PAW preparation system.

[0020] Figure 2 This is a schematic diagram of the plasma source as a whole.

[0021] Figure 3 This is a schematic diagram of the internal cross-section of the plasma source.

[0022] Figure 4 It is an external medium tube with a microporous structure.

[0023] Figure 5 This is a comparison diagram of the electric field distribution of two plasma sources.

[0024] Figure 6 This is a schematic diagram of the outer and inner dielectric layers.

[0025] Explanation of reference numerals in the attached diagram: 1. Water tank; 2. Gas flow controller; 3. Plasma source; 4. Water outlet valve; 5. Power supply; 6. Grounding electrode; 7. Water inlet valve; 8. High voltage electrode; 9. Sealing rubber ring; 10. Set screw; 11. Outer medium tube; 12. Support column; 13. Air inlet; 14. Inner medium tube; 15. Microbubble pore. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] like Figures 1-3 As shown, an apparatus for preparing plasma-activated water by underwater bubble discharge includes a plasma source 3, a water tank 1, and a driving power supply 5. The plasma source 3 is located below the water surface during use. The electrodes employ an asymmetrical off-axis structure, with the axis of the high-voltage electrode below the axis of the outer dielectric tube 11 and enclosed by an inner dielectric tube 14. A 1mm discharge gap exists between the outer and inner dielectric tubes. The inner dielectric tube 14 extends from the water tank 1 through the water tank wall and support column 12 at both ends. To further improve discharge stability, the high-voltage electrode 8 is tightly nested within the inner dielectric tube 14. The ground electrode 6 is located at the bottom of the water tank. The central axis of the inner dielectric layer 14 is parallel to, but not coincident with, the central axis of the outer dielectric layer 11. Figure 6 As shown, this structure is named the asymmetric off-axis structure.

[0028] The asymmetric off-axis structure concentrates the discharge on one side of the off-axis, resulting in a stronger electric field at a lower voltage and improved energy utilization. This electrode structure creates a strong non-uniform electric field in the discharge region, enhancing the concentration of active species in the PAW under the same electrode and dielectric dimensions and power supply conditions.

[0029] In one embodiment, the central axis of the inner dielectric layer 14 is located below the central axis of the outer dielectric layer 11. The outer dielectric layer 14, located directly below the high-voltage electrode 8, is provided with a plurality of microbubble pores 15. Plasma is generated in the discharge gap of the plasma source 3 and enters the aqueous solution through the microbubble pores 15 with the gas flow, forming a uniform and dense bubble flow in the aqueous solution. This invention employs a microbubble generating structure, with the microbubbles located directly below the off-axis structure, allowing the plasma to be rapidly blown out with the gas and directly enter the liquid phase to react with water molecules to generate RONS. Furthermore, the discharge occurs on one side of the microbubbles, reducing energy loss and improving the preparation efficiency of PAW.

[0030] The electrode adopts an asymmetric off-axis structure, which creates a strong non-uniform electric field in the discharge region, reduces the discharge voltage, and allows for a wider selection of driving power sources. Currently, most reported PAW production reactors are excited by AC power, but AC power inevitably causes problems such as local overheating of the discharge channel, plasma instability, and high energy consumption.

[0031] In one embodiment, the power supply 5 driving the plasma source 3 can be any one of a nanosecond pulse power supply, a microsecond pulse power supply, or a solar-driven pulse power supply.

[0032] In one embodiment, the high-voltage electrode 8 can be made of conductive materials such as stainless steel or tungsten. The inner dielectric tube has a wall thickness of 1 mm and can be made of inorganic materials such as glass or quartz tube. A top view of the microbubble structure is shown below. Figure 4 As shown, the microbubble openings are located directly below the high-voltage electrode 8, with 80 micropores, each with a diameter of 0.05 mm and a spacing of 4 mm.

[0033] In one embodiment, the water tank 1 has openings on both sides near the bottom, with the diameter of the openings being the same as the outer diameter of the outer medium pipe 11. A sealing rubber ring 9 is provided on the outside of the openings to cover them. A support column 12 is used to fix the inner medium pipe 14 and the outer medium pipe 11. The support column 12 is located outside the sealing rubber ring 9. The support column 12 has an annular hole. The outer annular hole and the opening are in the same position and have the same diameter. The distance between the outer side of the inner annular ring and the inner side of the outer annular ring is the same as the thickness of the outer medium pipe. A through hole is provided in the inner annular ring at the position of the inner medium pipe 14. The diameter of the through hole is the same as the outer diameter of the inner medium pipe 14.

[0034] Water tank 1 is used to hold the water to be treated. It has a rectangular structure with openings on both sides near the bottom. The diameter of these openings is the same as the outer diameter of the external medium pipe 11, facilitating insertion of the external medium pipe into the water tank. The sealing rubber rings 9 prevent water from leaking out from the openings on both sides of the water tank, serving a sealing function.

[0035] In one embodiment, the support column is 3D printed with a thickness of 10mm and has a through hole slightly below the center for inserting and fixing the inner medium tube 14. A circular hole with a depth of 7mm is made with the center of the support column 12 as the center and the outer diameter of the outer medium tube 11 as the diameter. This circular hole facilitates the insertion of the outer medium tube 11 into the support column 12 and serves a fixing function.

[0036] The set screw 10 is used to press the support column 12 against the sealing rubber ring 9, so that the sealing rubber ring 9 fits better against the openings on both sides of the water tank, thus preventing water leakage from the water tank.

[0037] In one embodiment, a gas flow controller 2 is further included to control the flow rate of air entering the reaction system; the gas is injected into the plasma source 3 through the flow controller, and the injected air is ionized by an electric field within a 1 mm discharge gap. The generated plasma is then carried by the gas flow through micropores 15 into the liquid.

[0038] In one embodiment, a water valve 7 is also included for adding untreated water; and an outlet valve 4 is included for discharging treated PAW outside the system for storage.

[0039] The plasma source 3 electrode of this invention adopts an asymmetric off-axis structure. Before operation, water must first be added to the water tank 1 through the water inlet valve 7, with the water level higher than the plasma source 3. At the same time, the water to be treated is in contact with the ground electrode 6. Then, air is introduced through the air inlet 13, and the air flow rate can operate normally at the minimum flow rate of 1L / min. Then, the high voltage electrode 8 is connected to the power supply 5. By adjusting the output voltage, the plasma is generated in the 1mm discharge gap. Finally, the plasma generated in the gap is directly carried into the liquid phase through the micropores by the airflow, thus efficiently completing the preparation of PAW.

[0040] The plasma-activated water preparation device of this invention mainly comprises three parts: a plasma source 3, a water tank 1, and a power supply 5. The main plasma reactor has an asymmetric off-axis electrode structure, and the discharge mode is underwater asymmetric off-axis porous dielectric barrier discharge. The space between the dielectric layers and sealed by the two end supports serves as a gas chamber. An air inlet 13 is opened in one of the supports, allowing air or other gases to enter the gas chamber. Microbubbles generated through micropores 15 then allow the plasma generated in the air gap to directly enter the solution in the water tank 1. A stainless steel rod, serving as a high-voltage electrode 8, is fixed in the inner dielectric tube 14, which is surrounded by an outer dielectric tube 11. The two dielectric tubes are arranged asymmetrically off-axis. Figure 5 The electric field of the two arrangement methods was simulated and compared using COMSOL simulation software. The electric field strength around the outer dielectric tube of the coaxial DBD device was 4.6 × 10⁻⁶. 6 V / m decreased to 1.25×10 6V / m. The asymmetric electrode arrangement still maintains a high electric field strength (5.79 × 10⁻⁶) near the micropores. 6 The electric field strength on the outer wall of the inner dielectric tube (V / m) shows that this asymmetric off-axis arrangement can enhance the electric field in the plasma generation region, making discharge easier. Therefore, under the same power supply parameters, the off-axis electrode arrangement can concentrate the generation of more active species, improving the generation efficiency of active species and avoiding the reduction in discharge intensity caused by the weakening of the electric field during discharge of the coaxial DBD structure, which would otherwise result in a lower concentration of active species and energy waste.

[0041] The process of preparing PAW begins by installing a plasma source 3 in a water tank 1, then introducing gas and adding an appropriate amount of water to the tank. The discharge first occurs in a 1mm discharge gap. After the plasma is generated, it flows through the micropores 15 in the device into the aqueous solution along with the air in the gas chamber, where a series of reactions occur to achieve efficient PAW preparation.

[0042] This device can be driven by nanosecond pulse power, microsecond pulse power, or solar-powered pulse power. After the circuit is connected, air is introduced into the gas chamber. Under the influence of a strong electric field, the gas is broken down to generate nitrogen oxides, including ·OH, ·O, O3, H2O2, and NO2. - NO3 - Active species, such as gas, interact with the liquid phase as they are blown into it to generate PAW.

Claims

1. An underwater bubble discharge device for preparing plasma-activated water, comprising a plasma source (3), a water tank (1), and a driving power source (5), the plasma source (3) being located below the water surface when in use, adopting an electrode asymmetric off-axis structure, further comprising an outer dielectric tube (11) and an inner dielectric tube (14), a discharge gap of 1 mm existing between the outer dielectric tube (11) and the inner dielectric tube (14), the inner dielectric tube (14) extending out of the water tank through the water tank wall and a support column (12) at both ends, a high-voltage electrode (8) being tightly nested by the inner dielectric tube (14), and a ground electrode being arranged at the bottom end of the water tank (1), characterized in that: The axis of the high-voltage electrode (8) is parallel to the axis of the outer medium tube (11), but not coincident. The central axis of the inner medium tube (14) is located below the central axis of the outer medium tube (11), and multiple microbubble openings (15) are provided below the axis of the outer medium tube (11).

2. The apparatus for preparing plasma-activated water by underwater bubble discharge as described in claim 1, characterized in that: Multiple microbubble openings (15) are located directly below the high-voltage electrode (8), forming micropores of 0.05 mm every 4 mm along the lower part of the outer dielectric tube axis.

3. The apparatus for preparing plasma-activated water by underwater bubble discharge as described in claim 1, characterized in that: It also includes a gas flow controller (2), through which gas is injected into the plasma source (3). The injected air is ionized by the electric field in the 1mm discharge gap, and the generated plasma enters the liquid through the microbubble opening (15) with the airflow.

4. The apparatus for preparing plasma-activated water by underwater bubble discharge as described in claim 1, characterized in that: The water tank has openings on both sides near the bottom, with the diameter of the openings being the same as the outer diameter of the outer medium pipe (11). A sealing rubber ring (9) is provided on the outside of the openings to cover the openings. A support column (12) is set on the outside of the sealing rubber ring (9). The support column (12) has a circular hole, with the outer circular hole being in the same position as the outer medium pipe, having the same diameter and thickness. A through hole is opened in the inner ring at the position corresponding to the inner medium pipe (14), with the diameter of the through hole being the same as the outer diameter of the inner medium pipe (14).

5. The apparatus for preparing plasma-activated water by underwater bubble discharge as described in claim 4, characterized in that: It also includes a plurality of set screws (10) that pass through the tank wall to press against the sealing rubber ring (9).

6. The apparatus for preparing plasma-activated water by underwater bubble discharge as described in claim 1, characterized in that: It also includes a water valve (7), which is located above the water tank (1) for adding untreated water.

7. The apparatus for preparing plasma-activated water by underwater bubble discharge as described in claim 1, characterized in that: It also includes a water outlet valve (4), which is located at the water outlet at the bottom of the water tank (1).

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