Spherical three-dimensional electrical capacitance tomography device

Abstract

The utility model relates to the technical field of devices for measuring resistance, reactance, impedance or derived characteristics thereof, in particular to measurement of inductance or capacitance. According to the technical scheme, the spherical three-dimensional electrical capacitance tomography device comprises a spherical pole piece device composed of a plurality of electrode pieces and a spherical container, the pole piece device evenly clings to and wraps the outer surface of the spherical container, a spherical shielding cover is arranged on the outer side of the spherical container, round pipes are arranged on the two sides of the spherical container in the horizontal axial direction, and the round pipes are arranged on the outer side of the spherical container. The circular tube is coaxially matched with the flat welding flange, a closed space is formed by the interior of the shielding cover and the outer side of the spherical container, and the pole piece device is located in the closed space. The spherical three-dimensional electrical capacitance tomography imaging device solves the problems that in the prior art, the structure is complex, mounting and dismounting are inconvenient, precision is poor, and the detection effect is poor, and achieves the purposes of being high in precision, rapid in imaging and capable of giving phase distribution and phase volume fraction.

Description

Technical Field

[0001] This utility model relates to the technical field of devices for measuring resistance, reactance, impedance or their derived characteristics, and particularly to the measurement of inductance or capacitance. Background Technology

[0002] Cryogenic fluids have wide applications in industries such as chemical engineering, air separation, and refrigeration, involving critical issues of design optimization and operational safety. Fluids in cryogenic environments typically exhibit unique physical properties, such as significant differences in dielectric constants and thermal expansion characteristics. For the detection of two-phase flows of cryogenic fluids (such as liquid nitrogen and liquid oxygen), accurate measurement of phase distribution is crucial. Compared to room-temperature fluids (such as water / air), the gas-liquid dielectric constant ratio of cryogenic fluids (such as liquid nitrogen and liquid oxygen) is generally less than 1.5, making the imaging results extremely sensitive to measurement noise. In cryogenic environments, the shrinkage rates of metals and non-metals differ significantly, and traditional electrode mounting methods (such as bonding and ablation) can easily lead to loosening or even pipe rupture. Furthermore, non-metallic materials are prone to brittleness at low temperatures, placing higher demands on sensor design. Electrical Capacitance Tomography (ECT) technology measures the capacitance between electrode arrays and uses inversion algorithms to reconstruct the phase distribution image of the fluid. Capacitive sensors are crucial in ECT systems, with electrode arrays as their core component. Different electrode array arrangements can adapt to monitoring fluid phase distribution and phase content under different flow patterns and container shapes. The shielded electrodes and shielding covers within the sensor provide electromagnetic protection, preventing interference from external electric fields. Compared to other non-invasive measurement methods such as capacitance probes, radio frequency sensors, and particle image velocimeters, ECT offers advantages such as easy assembly, fast imaging speed, low cost, no interference with the flow field, and the ability to simultaneously obtain phase content and phase distribution data. It is suitable for monitoring two-phase flows of cryogenic fluids. For example, Chinese Patent CN111505066B discloses a three-dimensional capacitance tomography imaging device for cryogenic fluid flow within a Venturi tube. The technical solution is as follows: This invention discloses a three-dimensional capacitance tomography imaging device for monitoring the flow of cryogenic fluids (such as liquid nitrogen (~78K) and liquid oxygen (~90K)) within a Venturi tube. The device includes: a conductor rod, a metal shell, a Venturi tube, an electrode sleeve, electrode plates, and an annular connecting shell. This device incorporates electrode plates and electrode sleeves that fit snugly against the surface of the venturi tube, taking into account its variable diameter. It also features a corresponding wire connection structure and a shielding shell designed to address the shielding requirements of capacitance tomography. This cryogenic venturi tube three-dimensional capacitance tomography device has the following characteristics: simple and stable structure, easy assembly and disassembly with multiple reassemblies, and quick connection to other pipelines; it can be used in a wide range from room temperature to deep cryogenic temperatures, and offers good electromagnetic shielding. However, the aforementioned cryogenic fluid venturi tube three-dimensional capacitance tomography device cannot provide information on phase distribution and phase content, and may have blind zones and measurement errors in complex flow fields. Utility Model Content

[0003] This invention solves the problems of complex structure, inconvenient installation and disassembly, poor accuracy and poor detection effect in the prior art. This invention proposes a spherical three-dimensional capacitance tomography imaging device, which achieves the purpose of high accuracy, rapid imaging and the ability to provide phase distribution and phase content.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A spherical three-dimensional capacitance tomography device includes a spherical electrode assembly composed of several electrode sheets and a spherical container. The electrode assembly is uniformly and tightly wrapped around the outer surface of the spherical container. A spherical shield is provided on the outside of the spherical container. Circular tubes are opened on both sides of the horizontal axis of the spherical container. The circular tubes are coaxially fitted with flat-welded flanges. The inside of the shield and the outside of the spherical container form a closed space, and the electrode assembly is located within the closed space.

[0006] The advantages of this design are that the uniformly covered spherical electrode device ensures the uniformity of electrode distribution, improving the resolution and sensitivity of imaging; the spherical shielding provides electromagnetic shielding, reduces external interference, and ensures measurement accuracy; the enclosed space design effectively protects the electrode device, enabling it to work stably in low-temperature environments, while the coaxial cooperation between the round tube and the flange allows for the effective entry and exit of fluid.

[0007] Preferably, the electrode device is divided into a double-layer structure with mirror symmetry. Each layer includes half the number of electrode sheets. The two waists of a single electrode sheet are adjacent to the waists of the other two electrode sheets. The electrode sheets of each layer are arranged in a circle, and the central angle enclosed by the bottom edge is 360°, forming a hemispherical shape with a complete circumference. The electrode sheets of the two layers together form a spherical shape. The bending radius of the electrode device is equal to the outer diameter of the spherical container.

[0008] The advantages of this design are that the double-layer symmetrical structure ensures the balance and coverage of the electrode layout, avoids measurement blind spots, and improves the three-dimensional accuracy of imaging; the bending radius of the electrode sheet matches the outer diameter of the container, making the electrodes fit tightly, enhancing the consistency and stability of capacitance measurement, thereby improving the overall reliability of imaging.

[0009] Preferably, a quarter-circular through hole is opened on one bottom corner of half of the electrode plates on both sides of the spherical container. The diameter of the through hole is the same as the outer diameter of the circular tube. The four through holes are combined to form a circular through hole in the container, and the circular through hole in the container is coaxially fitted with the circular tube.

[0010] The advantages of this design are that the circular through-hole of the container is set with the same diameter as the circular pipe, which ensures the smooth flow of fluid and avoids the fluid flow being obstructed by the electrode plate; the symmetrical layout of the through-hole maintains the overall symmetry of the electrode device, reduces measurement errors, and facilitates the connection of the electrode device to the external pipeline, thereby improving the assembly and maintenance efficiency of the device.

[0011] Preferably, the shield is made of thin-walled metal, the shield fits the spherical container at the same center, the shield has a larger diameter than the spherical container, and the shield has circular through holes on both sides of the horizontal axis, the diameter of the circular through holes of the shield being the same as the outer diameter of the circular tube.

[0012] The advantages of this design are that the thin-walled metal shield provides effective electromagnetic shielding, reduces external electromagnetic interference, and improves measurement accuracy; the co-center fit with the spherical container ensures the symmetry and tight fit of the shield, further enhancing the shielding effect; and the circular through-hole with the same diameter as the circular tube ensures smooth fluid flow and avoids fluid flow obstruction caused by the shield design.

[0013] Preferably, the shield has a flange through hole on one side of its vertical axis, the flange through hole is coaxially fitted with the KF flange, and the shield is grounded.

[0014] The advantages of this design are that the coaxial fit of the KF flange facilitates quick connection and sealing between the shield and external equipment, improving the overall operability of the device; the grounding setting effectively dissipates and extracts electromagnetic waves, further reducing electromagnetic interference and ensuring the electromagnetic stability of the measurement environment, thereby improving the reliability and accuracy of the imaging system.

[0015] Preferably, the electrode device consists of 16 electrode plates, which are made of copper plates and are all spherical triangular inwardly curved thin sheets. The spherical triangle of the electrode plate is an isosceles triangle with a central angle of 90° corresponding to the two sides and a central angle of 45° corresponding to the base.

[0016] The advantages of this design are that the 16 electrode plates provide a high-density and uniform electrode layout, enhancing the resolution and sensitivity of capacitance measurements; the use of copper plates as electrode materials has good conductivity and low-temperature adaptability, ensuring the stability and durability of the electrodes in low-temperature environments; the design of the spherical triangular inward-curved thin sheet adapts to the curved surface of the spherical container, ensuring close contact and coverage of the electrodes, and improving the accuracy of imaging.

[0017] Preferably, the shielding cover includes upper and lower parts, with a ring structure extending horizontally between them, and a number of fixing bolts are evenly distributed on the ring structure.

[0018] The advantages of this design are that the separation of the upper and lower parts facilitates the installation and disassembly of the shielding cover, improving the convenience of maintenance and repair of the device; the evenly distributed fixing bolts on the ring structure ensure the stable fixation of the shielding cover, preventing displacement or loosening during operation, thereby maintaining the stability of the shielding effect; this modular design helps to adapt to various working environments and needs, enhancing the practicality of the device.

[0019] Preferably, the spherical container is made of polytetrafluoroethylene (PTFE).

[0020] The advantages of this design are that polytetrafluoroethylene (PTFE) has excellent low-temperature resistance and chemical stability, ensuring that the spherical container does not crack or break in deep cryogenic environments such as liquid nitrogen and liquid oxygen; its low dielectric constant helps to improve the contrast and sensitivity of capacitance tomography and improve the accuracy of measurement; in addition, the smooth surface of PTFE helps to reduce interference during fluid flow and ensures the stability and uniformity of the fluid state in the measurement area.

[0021] Compared with the prior art, the beneficial effects of this utility model are as follows.

[0022] 1. This invention features a large electrode coverage, ensuring uniform electrode distribution. This high-density electrode layout, combined with an advanced inversion algorithm, enables high-precision three-dimensional flow pattern imaging of two-phase flow of cryogenic fluids within a spherical container. Through the fully covered electrode device, the system can accurately capture and reconstruct the complex phase distribution and phase content within the fluid, significantly improving imaging resolution and sensitivity. This allows for more precise monitoring and analysis of the dynamic behavior of fluids in cryogenic environments in scientific research and industrial applications, thereby optimizing relevant process and operating parameters.

[0023] 2. This invention features a significant non-invasive characteristic. The electrode device is uniformly and tightly fitted to the outer surface of the spherical container, without interfering with the flow of the fluid within the measurement area. This design ensures that the natural flow of the fluid remains unaffected, guaranteeing the accuracy and reliability of the measurement data. Furthermore, the device employs a modular structure, allowing for easy assembly and disassembly of components such as the electrode assembly and shielding cover, greatly simplifying installation, maintenance, and repair. In addition, the system boasts a fast imaging speed, enabling real-time monitoring and meeting the demand for instant data in industrial production, thus improving monitoring efficiency and response speed.

[0024] 3. The spherical container of this invention is made of polytetrafluoroethylene (PTFE), which possesses excellent low-temperature resistance and chemical stability, ensuring that it will not crack or be damaged under extreme low-temperature conditions such as liquid nitrogen and liquid oxygen. Simultaneously, the low dielectric constant of PTFE helps improve the contrast and sensitivity of capacitance tomography, ensuring high measurement accuracy. Furthermore, the smooth surface of PTFE reduces interference during fluid flow, ensuring the stability and uniformity of the fluid state within the measurement area. This makes it particularly suitable for experimental environments requiring multiple large-scale temperature cycles without affecting imaging accuracy and extending the lifespan of the device. Attached Figure Description

[0025] Figure 1 This is a front view of a spherical three-dimensional capacitance tomography device according to the present invention.

[0026] Figure 2 This is a cross-sectional view (AA) of a spherical three-dimensional capacitance tomography device according to the present invention.

[0027] Figure 3 This is a partially enlarged cross-sectional view (Figure B) of the spherical three-dimensional capacitance tomography device of this utility model.

[0028] Illustration: 1. Electrode assembly, 2. Spherical container, 3. Shielding cover, 4. Flat welding flange, 5. KF flange, 6. Enclosed area. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this disclosure clearer, the embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings. The proportions of the components are not drawn to scale, and the proportions and dimensions shown in the drawings should not limit the essential technical solutions of this utility model. These embodiments do not exhaustively describe all details, nor do they limit this utility model to merely the specific embodiments described.

[0030] See Figure 1-3 As shown, a spherical three-dimensional capacitance tomography device includes a spherical electrode assembly composed of several electrode sheets and a spherical container. The electrode assembly is uniformly and tightly wrapped around the outer surface of the spherical container. A spherical shield is provided on the outside of the spherical container. Circular tubes are opened on both sides of the horizontal axis of the spherical container. The circular tubes are coaxially fitted with flat-welded flanges. The inside of the shield and the outside of the spherical container form a closed space, and the electrode assembly is located within the closed space.

[0031] like Figure 1 In one embodiment shown, Figure 1This is a front view of a spherical three-dimensional capacitance tomography device according to the present invention. The present invention relates to a spherical three-dimensional capacitance tomography device for use in low-temperature environments. Its main structure includes a spherical electrode assembly composed of several electrode plates and a spherical container. The spherical electrode assembly uniformly and tightly covers the outer surface of the spherical container, ensuring uniform electrode distribution and high coverage. A spherical shield made of thin-walled metal is provided on the outside of the spherical container. The shield aligns with the center of the spherical container and its diameter is larger than that of the spherical container to provide effective electromagnetic shielding and reduce the influence of external electromagnetic interference on the measurement.

[0032] The spherical container has circular tubes on both sides of its horizontal axis. These tubes are coaxially fitted with flat-welded flanges to ensure a stable and airtight connection. The interior of the shield and the exterior of the spherical container form a closed space, within which the electrode assembly is located, further protecting the electrode assembly for stable operation in low-temperature environments.

[0033] The electrode assembly employs a double-layer structure with mirror-symmetric dimensions, with each layer comprising half the number of electrode sheets. The two waist sections of each electrode sheet are adjacent to the waist sections of two other electrode sheets, forming a compact arrangement. The electrode sheets in each layer are arranged around a spherical container, with the central angle enclosed by the base edge being 360°, thus forming a hemispherical shape with a complete circumference. The two layers of electrode sheets together constitute a complete spherical shape, and the bending radius of the electrode assembly is equal to the outer diameter of the spherical container, ensuring that the electrode sheets fit tightly against the container surface.

[0034] On both sides of the spherical container, half of the electrode plates on each side have a quarter-circular through-hole at one bottom corner. The diameter of these through-holes is the same as the outer diameter of the circular tube, and four quarter-circular through-holes combine to form a complete circular through-hole. This circular through-hole is coaxially fitted with the circular tube to ensure smooth fluid flow into and out of the spherical container, without obstruction by the electrode plates.

[0035] The shielding cover is made of thin-walled metal material, providing highly efficient electromagnetic shielding capabilities. It effectively reduces external electromagnetic interference and improves measurement accuracy. The shielding cover fits concentrically with the spherical container, but its diameter is larger than the container's, further enhancing the shielding effect. Circular through-holes with the same outer diameter as the pipe are located on both sides of the horizontal axis of the shielding cover, ensuring unobstructed fluid flow. A flange through-hole is located on one side of the vertical axis of the shielding cover, coaxially fitting with a KF flange for easy connection and sealing with external equipment. Simultaneously, the shielding cover is grounded, effectively dissipating electromagnetic waves, further reducing electromagnetic interference, and ensuring the electromagnetic stability of the measurement environment.

[0036] In this embodiment, the electrode device consists of 16 electrode plates, all made of copper plates, which have good conductivity and low-temperature adaptability. The electrode plates are spherical triangular inward-curved thin sheets, specifically isosceles triangles, where the central angles corresponding to the two sides are 90° and the central angle corresponding to the base is 45°. This design ensures a tight fit and high coverage of the electrode plates on the surface of the spherical container, improving the sensitivity and accuracy of capacitance measurement.

[0037] The shielding cover consists of two parts, upper and lower, connected by a ring structure extending horizontally circumferentially. Several fixing bolts are evenly distributed on the ring structure to ensure a secure connection between the two parts and prevent displacement or loosening during operation. This separate design not only facilitates the installation and disassembly of the shielding cover, improving the convenience of maintenance and repair, but also enhances the adaptability of the device through modular design, making it suitable for various working environments and requirements.

[0038] The spherical container is made of polytetrafluoroethylene (PTFE), which possesses excellent low-temperature resistance and chemical stability. PTFE ensures that the container does not crack or break under extremely low temperatures such as liquid nitrogen and liquid oxygen. Its low dielectric constant also helps improve the contrast and sensitivity of capacitance tomography, ensuring high measurement accuracy. Furthermore, the smooth surface of PTFE reduces interference from fluid flow, guaranteeing the stability and uniformity of the fluid state within the measurement area. This makes it particularly suitable for experimental environments requiring multiple large-scale temperature cycles without affecting imaging accuracy and extending the lifespan of the apparatus.

[0039] This solution utilizes a dual-layer 16-electrode spherical three-dimensional capacitance tomography (ECVT) device for cryogenic environments, which offers several significant advantages through its precise structural design and high-quality material selection. Firstly, the electrode assembly employs a mirror-symmetrical dual-layer structure, with 16 high-density copper electrodes uniformly and tightly covering the outer surface of the spherical container, ensuring high uniformity and coverage of electrode distribution. This design significantly enhances the resolution and sensitivity of capacitance measurements, enabling the device to achieve high-precision three-dimensional flow pattern imaging of two-phase fluids within the spherical container under cryogenic conditions. Through advanced inversion algorithms, the system can accurately reconstruct the complex phase distribution and phase content within the fluid, providing detailed three-dimensional images and effectively supporting monitoring and analysis in scientific research and industrial processes.

[0040] Secondly, the non-invasive design of the device ensures the natural flow of fluid, without interfering with the fluid dynamics within the measurement area. This is achieved through the uniform and tight fit of the electrode assembly to the outer surface of the spherical container and the rationally designed 1 / 4 circular through-hole, ensuring smooth fluid entry and exit while maintaining the overall symmetry of the electrode assembly and reducing potential measurement errors. Furthermore, the spherical shield, made of thin-walled metal material, aligns perfectly with the spherical container, providing highly efficient electromagnetic shielding and further enhancing measurement accuracy. The modular design of the shield, including upper and lower sections and evenly distributed fixing bolts, makes the device easier to install, disassemble, and maintain, offering greater adaptability and enabling rapid response to various working environments and requirements, significantly improving the device's practicality and reliability.

[0041] Third, the device utilizes a spherical container made of polytetrafluoroethylene (PTFE), giving it wide temperature adaptability and enabling stable operation across a broad range from room temperature to deep cryogenics. PTFE not only possesses excellent low-temperature resistance and chemical stability, ensuring the container's safety and durability under extreme cryogenic conditions such as liquid nitrogen and liquid oxygen, but its low dielectric constant also helps improve the contrast and sensitivity of capacitance tomography, ensuring highly accurate measurement results. Furthermore, the smooth surface design of PTFE reduces interference during fluid flow, ensuring the stability and uniformity of the fluid state. This makes it particularly suitable for experimental environments requiring multiple large-scale temperature cycles, extending the device's lifespan and ensuring that measurement accuracy remains unaffected during repeated temperature cycles. These advantages make this device outstanding in industrial applications, especially for monitoring the internal flow conditions of containers such as spherical storage tanks. It provides highly efficient and accurate monitoring capabilities that traditional ECT sensors cannot achieve, significantly improving the control and optimization of industrial processes.

[0042] like Figure 2 and Figure 3 In one embodiment shown, Figure 2 This is a cross-sectional view of a spherical three-dimensional capacitance tomography imaging device according to the present invention. Figure 3This is a partially enlarged cross-sectional view of a spherical three-dimensional capacitance tomography device according to this utility model. The device includes the following components: an electrode assembly, a spherical container, a shielding cover, a flat welding flange, and a KF flange. The electrode assembly consists of a set of 16 electrode plates made of copper plate. All electrode plates are identical in shape, being thin, inwardly curved spherical triangles. A spherical triangle is defined as the shape formed by connecting three points on a sphere with three circular arcs. These three arcs are called the sides of the spherical triangle. The spherical triangle of the electrode plate is approximately an isosceles triangle, with the central angles corresponding to the two sides being 90° and the central angle corresponding to the base being 45°. The electrode assembly is configured as follows: it consists of a double-layer structure with mirror-symmetric upper and lower sections. Each layer contains eight electrode plates. The two sides of a single electrode plate are adjacent to the sides of the other two electrode plates. The eight electrode plates of each layer surround each other, and the central angle enclosed by the bottom edge reaches 360°, forming a hemispherical shape that is approximately a complete circle. The electrode plates of the other layer are arranged in the same way, also forming an approximately hemispherical shape. The two layers of electrode plates together form an approximately spherical shape. There is no overlapping area between the electrode plates, and the total span they cover is close to the entire sphere. Since the bending radius of the assembled electrode assembly is equal to the outer diameter of the spherical container, it can fit with the spherical container at the same center and uniformly and tightly cover the outer surface of the spherical container.

[0043] The spherical container is made of polytetrafluoroethylene (PTFE) with circular tubes on both sides of the horizontal axis for fluid entry and exit. These tubes are coaxially fitted with flat-welded flanges to connect to external pipes. Eight electrode plates have a quarter-circular through-hole on one bottom corner, with the diameter of the through-hole matching the outer diameter of the circular tubes on both sides of the spherical container. By arranging the electrode plates with these through-holes, two completely opposite circular through-holes can be formed, coaxially fitted with the circular tubes on both sides of the spherical container. The shield is a spherical shell structure made of thin-walled metal, with a diameter larger than the spherical container. The shield and the spherical container are fitted at the same center. Circular through-holes on both sides of the horizontal axis of the shield have the same diameter as the outer diameter of the pipes on both sides of the spherical container, coaxially fitted with the circular tubes on both sides of the spherical container. The interior of the shield and the exterior of the spherical container form a closed space enveloping the electrode plates. This closed space is insulated by vacuum to minimize heat leakage, ensuring that the small amount of evaporation of cryogenic fluids, such as liquid nitrogen and liquid oxygen, does not affect the experimental results.

[0044] The shielding cover is divided into upper and lower parts, with eight screw holes evenly distributed along the horizontal circumference. The screw holes and bolts are coaxially fitted to combine the upper and lower parts of the shielding cover. This is used to block external electromagnetic fields from interfering with the internal electrode plates of the shielding cover, and at the same time to prevent the electromagnetic fields generated by the internal electrode plates of the shielding cover from radiating outward.

[0045] The shielding cover has a through hole on one side of its vertical axis, which is coaxially fitted with the KF flange. The shielding cover needs to be grounded during operation. Grounding helps to draw out and dissipate electromagnetic waves, reducing electromagnetic wave reflection and interference.

[0046] In one embodiment, the device of this invention adopts a structure with a double-layer arrangement of 16 spherical triangular electrode plates. The measurement area is the inside of a spherical container, the cryogenic working fluid is liquid nitrogen-nitrogen gas, and two typical flow patterns, stratified flow and bubbly flow, are used for imaging. The specific usage is as follows:

[0047] According to the ECVT imaging principle shown in formula (1):

[0048] Y = S × g (1) In the above formula, Y is the normalized capacitance, S is the normalized sensitivity (i.e., the capacitance change corresponding to a change in the dielectric constant within the measurement region), and changes in the fluid phase distribution cause changes in the dielectric constant. g is the normalized dielectric constant. Both the normalized capacitance Y and the normalized sensitivity S can be obtained through numerical experiments. The normalized dielectric constant g can be obtained by combining the normalized capacitance Y and the normalized sensitivity S using an inversion algorithm. The flow pattern corresponds one-to-one with the distribution of the dielectric constant; therefore, the flow pattern of the measurement region can be simulated and plotted based on the normalized dielectric constant g.

[0049] The specific implementation method for obtaining the normalized capacitance value Y is as follows: First, the measurement area is set to an empty field state, that is, the entire measurement area is filled with nitrogen gas. An excitation potential of U is applied to electrode 1, while the other electrodes remain at 0 potential. At this time, the capacitance values ​​between electrode pairs 1-2, 1-3, ... 1-16 are calculated using finite element software. Then, an excitation potential U is applied to electrode 2, and the capacitance values ​​between electrodes 2-3, 2-4, ... 2-16 are calculated, and so on. It should be noted that the capacitance calculation is not repeated between pairs of electrodes; that is, after the capacitance between 1 and 2 is calculated, the capacitance value between 2 and 1 is not calculated again. When all 16 electrodes are excited in sequence, 120 independent capacitance values ​​can be obtained. Arranging them into a matrix according to the electrode numbering, this is the empty field capacitance C. e As shown in formula (2):

[0050]

[0051] Similarly, by setting the measurement area to a full-field state, i.e., the container is entirely filled with liquid nitrogen, the full-field capacitance C can be obtained by sequentially exciting the electrodes. f .

[0052] The measurement area was then set to laminar flow under typical flow conditions, that is, the measurement area was divided into two parts by a plane, filled with liquid nitrogen and nitrogen gas respectively, and the electrodes were excited sequentially to obtain the capacitance C of the laminar flow. c .

[0053] The normalized capacitance Y is calculated according to formula (3). c :

[0054]

[0055] Similarly, setting the measurement region as a typical flow pattern of bubble flow, an ellipsoid is randomly generated within the measurement region, with the interior of the ellipsoid filled with nitrogen gas and the remainder filled with liquid nitrogen. This allows the normalized capacitance Y of the bubble flow pattern to be obtained. p .

[0056] The specific implementation method for obtaining the normalized sensitivity S is as follows, according to the sensitivity field calculation formula (4):

[0057]

[0058] In formula (4), S ij (k) represents the sensitivity values ​​of the i-th electrode and the th electrode in the k-th grid, E i Let E be the electric field strength generated when the i-th electrode is excited by a single potential U. j Similarly, V is the three-dimensional space inside the entire spherical container, which is also the measurement area of ​​the experimental device. The three-dimensional space is divided into fine tetrahedral meshes using the finite element method. The electric field intensity of each grid corresponding to each electrode under the single excitation state of potential U is measured in turn. The sensitivity field between different electrode pairs corresponding to each grid is calculated according to formula (4), and then the normalized sensitivity S inside the entire spherical container is obtained.

[0059] The specific implementation method for obtaining the normalized capacitance value g is as follows: The Landweber inversion algorithm is used to achieve convergence through iteration. The calculation principle of Landweber is shown in the following formula (5):

[0060] g(n+1)=g(n)+λS T (Y-Sg(n)) (5)

[0061] In formula (5), g(n) represents the normalized dielectric constant in the nth iteration, and λ is a relaxation parameter used to adjust the convergence speed and stability of the Landweber inversion algorithm. The normalized capacitance value g is obtained through iterative calculation. The relative magnitude of g reflects whether the fluid is in the liquid phase or the gas phase under the corresponding grid. Under liquid nitrogen-nitrogen gas conditions, the dielectric constant of liquid nitrogen is higher than that of nitrogen gas under the same environmental conditions. Therefore, when g is higher, the fluid is in the liquid phase, and when g is lower, the fluid is in the gas phase. The value of g corresponds one-to-one with the geometric parameters of each finite element grid in the measurement area. The distribution law of g in the measurement area can be presented by drawing. It can be seen that the device of this utility model can achieve three-dimensional imaging while ensuring high imaging accuracy, especially the laminar flow inversion results, which can accurately restore the position and shape of the laminar flow interface, while effectively reducing the artifacts generated at the edge of the imaging area.

[0062] This utility model is not limited to the above-described embodiments. Any changes made to its shape or material composition, as long as the structural design provided by this utility model is adopted, are considered a variation of this utility model and should be regarded as within the protection scope of this utility model.

Claims

1. A spherical three-dimensional capacitance tomography imaging device, characterized in that, The device includes a spherical electrode assembly (1) composed of several electrode plates and a spherical container (2). The electrode assembly (1) is uniformly and tightly wrapped around the outer surface of the spherical container (2). A spherical shield (3) is provided on the outside of the spherical container (2). Circular tubes are opened on both sides of the horizontal axis of the spherical container (2). The circular tubes are coaxially fitted with a flat welding flange (4). The inside of the shield (3) and the outside of the spherical container (2) form a closed space. The electrode assembly (1) is located in the closed space.

2. The spherical three-dimensional capacitance tomography device according to claim 1, characterized in that, The electrode device (1) is divided into a double-layer structure with mirror symmetry. Each layer includes half of the number of electrode sheets. The two waists of a single electrode sheet are adjacent to the waists of the other two electrode sheets respectively. The electrode sheets of each layer are arranged in a circle, and the central angle enclosed by the bottom edge is 360°, forming a hemispherical shape with a complete circumference angle. The electrode sheets of the two layers together form a spherical shape. The bending radius of the electrode device (1) is equal to the outer diameter of the spherical container (2).

3. A spherical three-dimensional capacitance tomography device according to claim 1 or 2, characterized in that, The spherical container (2) has a 1 / 4 circular through hole on one side of the bottom corner of half of the electrode plates on both sides. The diameter of the through hole is the same as the outer diameter of the circular tube. The four through holes are combined to form a circular through hole in the container. The circular through hole in the container is coaxial with the circular tube.

4. The spherical three-dimensional capacitance tomography device according to claim 3, characterized in that, The shield (3) is made of thin metal wall. The shield (3) fits with the spherical container (2) at the same center and has a larger diameter than the spherical container (2). The shield (3) has circular through holes on both sides of the horizontal axis. The diameter of the circular through holes is the same as the outer diameter of the circular tube.

5. A spherical three-dimensional capacitance tomography imaging device according to claim 4, characterized in that, The shield (3) has a flange through hole on one side of its vertical axis. The flange through hole is coaxially fitted with the KF flange (5). The shield (3) is grounded.

6. A spherical three-dimensional capacitance tomography device according to claim 1 or 2, characterized in that, The electrode device (1) consists of 16 electrode plates. The electrode plates are made of copper plates and are all spherical triangular inwardly curved thin plates. The spherical triangle of the electrode plate is an isosceles triangle with the central angles corresponding to the two sides being 90° and the central angle corresponding to the base being 45°.

7. A spherical three-dimensional capacitance tomography device according to claim 4 or 5, characterized in that, The shield (3) includes upper and lower parts, with a ring structure extending horizontally between them, and a number of fixing bolts are evenly distributed on the ring structure.

8. A spherical three-dimensional capacitance tomography imaging device according to claim 7, characterized in that, The spherical container (2) is made of polytetrafluoroethylene.

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