Cryogenic fluid electrical capacitance tomography device

Abstract

The utility model discloses a low-temperature fluid electrical capacitance tomography imaging device, which overcomes the problems that an electrical capacitance tomography sensor in the prior art is difficult to acquire real flow pattern distribution quantitative data and can only measure a single flow pattern during low-temperature fluid measurement, and comprises an insulating measurement pipeline and a flow pattern test pipe, the outer wall of the insulation measuring pipeline is sleeved with a supporting piece, a flexible electrode is arranged between the insulation measuring pipeline and the supporting piece, a shielding cover is arranged on the surface of the supporting piece, one end of the insulation measuring pipeline is provided with a first positioning hole plate, and the other end of the insulation measuring pipeline is provided with a second positioning hole plate. And the flow pattern test tube is vertically inserted from the positioning hole of the first positioning hole plate and is inserted into the corresponding positioning hole of the second positioning hole plate. A group of replaceable pore plates with precise hole positions are adopted to realize switching of different flow patterns at low temperature and obtain quantitative data of real image distribution.

Description

Technical Field

[0001] The utility model relates to the technical fields of cryogenic refrigeration engineering and sensor science and technology, and particularly relates to a cryogenic fluid capacitance tomography device. Background Technique

[0002] Cryogenic fluids are extremely prone to gas-liquid two-phase flow, such as Taylor bubbles formed during the filling process of liquid hydrogen and liquid oxygen propellants, cavitation phenomena in engine turbo pumps, and local boiling during LNG unloading. The two-phase flow makes the flow and heat transfer mechanisms complex, resulting in water hammer and pressure rise, etc., increasing the uncertainty of the process and even endangering the stable operation and safety of the system. Therefore, real-time monitoring of the phase distribution of cryogenic fluids is of great significance for in-depth study of two-phase flow heat transfer and flow mechanisms, and is also an important parameter to ensure the stable and efficient operation of industrial systems.

[0003] Electrical Capacitance Tomography (ECT) is a non-invasive, non-contact, low-cost phase distribution and volume fraction measurement technology, which has been widely used in the petroleum industry, fluidized beds, flame detection and other fields. And due to its advantages of small heat leakage and applicability to microgravity environments, etc., it has great application potential in propellant tank monitoring and LNG transfer pipeline measurement.

[0004] As a non-invasive measurement method, the electrodes of the ECT sensor are usually arranged on the outer wall of the container. Due to the inherent non-uniform sensitivity distribution of ECT, the capacitance signals on the electrodes are sensitive to dielectric changes at different positions to different degrees; the relative dielectric constant of cryogenic fluids is generally between 1 and 2, which is nearly an order of magnitude smaller than that of normal temperature fluids, making the boundary capacitance more easily interfered by noise and affecting the spatial resolution far from the electrodes; at the same time, since ECT is a non-linear, soft-field measurement method, the change of dielectric distribution will also affect the sensitive field, further causing non-uniform distribution of spatial resolution, and making it difficult to use the spatial resolution evaluation method of linear imaging systems for ECT systems. Summary of the Invention

[0005] The purpose of the utility model is to overcome the problem that it is difficult to obtain quantitative data of the true flow pattern distribution and only single flow patterns can be measured when a capacitance tomography sensor measures cryogenic fluids in the prior art, and provides a cryogenic fluid capacitance tomography device. A set of orifice plates that are replaceable and have precisely machined holes are used to achieve the switching of different flow patterns at low temperatures and obtain quantitative data of the true image distribution. The device has a simple structure, can be quickly disassembled and assembled, has a low processing cost, high structural reliability, can be used in a large temperature range from room temperature to deep cryogenic temperature, and is applicable to various cryogenic fluids.

[0006] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0007] A low-temperature fluid capacitance tomography device includes an insulating measurement pipeline and a flow pattern test tube. A support is sleeved on the outer wall of the insulating measurement pipeline. A flexible electrode is arranged between the insulating measurement pipeline and the support. A shielding cover is arranged on the surface of the support. A first positioning orifice plate is arranged at one end of the insulating measurement pipeline, and a second positioning orifice plate is arranged at the other end of the insulating measurement pipeline. The flow pattern test tube vertically inserts into the positioning orifice of the first positioning orifice plate and is inserted into the corresponding positioning orifice of the second positioning orifice plate.

[0008] The first positioning orifice plate and the second positioning orifice plate have exactly the same shape. During the test, the flexible electrode is connected to a capacitance acquisition circuit and a computer by a shielded wire. The imaging device is placed in a foam box filled with liquid nitrogen. After cooling is completed and the temperature is stable, the measured low-temperature fluid is poured into the flow pattern test tube. The flexible electrode forms a sensitive field around the flow pattern test tube to sense the change in the dielectric constant of the liquid nitrogen in the flow pattern test tube, and the capacitance acquisition circuit is used to collect the change in the capacitance value of the flexible electrode. By replacing the positioning orifice plate and the insertion hole position of the flow pattern test tube, the measurement of different flow patterns can be realized, and the measurement of single-liquid-column and double-liquid-column flow patterns with different parameters can be realized. The device has a simple structure, can be quickly disassembled and assembled, has a low processing cost, is convenient to operate during measurement, and the measurement data is accurate and effective. It can be used in a relatively large range from room temperature to deep low temperature. Multiple large-amplitude temperature cycles do not affect the measurement accuracy, and it has high positioning accuracy and good electromagnetic shielding effect.

[0009] Preferably, a top connecting piece is arranged between one end of the insulating measurement pipeline and the first positioning orifice plate, and a bottom connecting piece is arranged between the other end of the insulating measurement pipeline and the second positioning orifice plate.

[0010] Preferably, the support includes two fitting semi-circular ring structures. The inner and outer ring arcs of the semi-circular ring structure are less than 180°. Through holes with the same number as the number of pole pieces of the flexible electrode are arranged in the axial direction of the support.

[0011] Preferably, a stud is arranged between the bottom connecting piece and the insulating measurement pipeline.

[0012] Preferably, the insulating measurement pipeline is a polytetrafluoroethylene circular tubular straight pipe, and flanges are arranged at both ends of the polytetrafluoroethylene circular tubular straight pipe.

[0013] Preferably, both the top connecting piece and the bottom connecting piece are annular structures with the same outer diameter as the flange of the insulating measurement pipeline. The inner side of the annular structure is an annular boss, and positioning keys are arranged on the annular boss.

[0014] Preferably, square pole pieces are evenly distributed inside the flexible electrode.

[0015] Preferably, positioning grooves that fit with the positioning keys of the top connector / bottom connector are provided at the edges of the first positioning orifice plate and the second positioning orifice plate.

[0016] Preferably, the flow pattern test tube is a single-pass polytetrafluoroethylene tube or a quartz tube, and a boss is provided at the orifice of the flow pattern test tube.

[0017] Preferably, the shielding cover is a square copper plate, and the square copper plate is curled and covered on the surface of the support member.

[0018] Therefore, the utility model has the following beneficial effects:

[0019] 1. By customizing and replacing different orifice plates, the measurement of single-liquid-column and double-liquid-column flow patterns with different parameters can be achieved. Before measurement, the position of the middle hole of the orifice plate and the diameter of the flow pattern test tube are precisely machined, solving the difficulty of obtaining quantitative data on the true flow pattern distribution during low-temperature fluid measurement.

[0020] 2. The split design is adopted, reducing the processing difficulty. At the same time, the orifice plate, flow pattern test tube, and measurement pipeline are non-rigidly connected, greatly alleviating the operation difficulty during low-temperature measurement, and also avoiding structural deformation and fitting errors caused by different thermal expansion coefficients of different materials at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of the electrical capacitance tomography device in the utility model.

[0022] Figure 2 is the main view of the flexible electrode deployment of the electrical capacitance tomography device in the utility model.

[0023] Figure 3 is the left view of the electrical capacitance tomography device in the utility model.

[0024] Figure 4 is the sectional view taken along the line A-A of the electrical capacitance tomography device in the utility model.

[0025] Figure 5 is the schematic assembly diagram of the flexible electrode of the electrical capacitance tomography device in the utility model.

[0026] In the figure: 1. Flow pattern test tube; 2. First positioning orifice plate; 3. Shielding cover; 4. Bottom connector; 5. Stud; 6. Insulated measurement pipeline; 7. Support member; 8. Top connector; 9. Flexible electrode; 10. Pole piece; 11. Axial shielding; 12. Second positioning orifice plate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The following further describes the utility model in detail in conjunction with the drawings and the specific embodiments:

[0028] Embodiment 1:

[0029] This embodiment is a low-temperature fluid capacitance tomography device, and its structure is as Figure 1 shown, including a flow pattern test tube 1, a first positioning orifice plate 2, a shielding cover 3, a bottom connecting piece 4, a stud 5, an insulating measurement pipeline 6, a support 7, a top connecting piece 8, a flexible electrode 9, and a second positioning orifice plate 12. The first positioning orifice plate and the second positioning orifice plate have exactly the same shape. The top connecting piece is installed on the left side of the insulating measurement pipeline, and the bottom connecting piece is installed on the right side of the insulating measurement pipeline. The first positioning orifice plate is installed on the top connecting piece, and the second positioning orifice plate is installed on the bottom connecting piece. The stud is installed between the bottom connecting piece and the insulating measurement pipeline; the flexible electrode is tightly wrapped around the outer surface of the insulating measurement pipeline, the support is coaxially and fixedly installed on the outer wall of the insulating measurement pipeline, and the flexible electrode is located between the support and the insulating measurement pipeline. The shielding cover is installed on the surface of the support; the flow pattern test tube is vertically inserted into the positioning hole of the upper positioning orifice plate and inserted into the corresponding positioning hole of the lower orifice plate.

[0030] During the test, the flexible electrode is connected to the capacitance acquisition circuit and the computer using a shielded wire. The imaging device is placed in a foam box filled with the low-temperature fluid to be measured. After cooling is completed and the temperature is stable, the low-temperature fluid to be measured is poured into the flow pattern test tube. The flexible electrode forms a sensitive field around the flow pattern test tube, senses the change in the dielectric constant of the liquid nitrogen in the flow pattern test tube, and uses the capacitance acquisition circuit to collect the change in the capacitance value of the flexible electrode. By changing the positioning orifice plate and the insertion hole position of the flow pattern test tube, the measurement of different flow patterns can be realized, and the measurement of single-liquid-column and double-liquid-column flow patterns with different parameters can be realized. The device has a simple structure, can be quickly disassembled and assembled, has a low processing cost, is convenient to operate during measurement, and the measurement data is accurate and effective. It can be used in a large range from room temperature to deep low temperature, and multiple large-amplitude temperature cycles do not affect the measurement accuracy. It has high positioning accuracy and good electromagnetic shielding effect.

[0031] It should be noted that the low-temperature fluid capacitance tomography device provided in this embodiment can only form a sensitive field around the object to be measured and sense the change in the dielectric constant of the low-temperature fluid to be measured. The subsequent data processing process is not within the protection scope of this application. After the collected capacitance data is filtered, transformed, and amplified by the data acquisition system, it is transmitted to the imaging computer; the computer uses the corresponding image reconstruction algorithm to invert the dielectric distribution map of the object field to be measured based on the measured capacitance value and display it in a visual way, which also belongs to the prior art.

[0032] The following further elaborates on the solution of this embodiment in detail. Specifically:

[0033] In this embodiment, the insulation measurement pipeline is a straight polytetrafluoroethylene round tube. The two ends of the straight polytetrafluoroethylene round tube are open. The flow pattern test tube is inserted from the inside of the insulation measurement pipeline. Flanges are provided at both the left and right ends of the insulation measurement pipeline. The top connector is connected to the flange at the left end of the insulation measurement pipeline, and the bottom connector is connected to the flange at the right end of the insulation measurement pipeline.

[0034] Further, after the bottom connector inserts the stud, it is connected to the flange at the left end of the insulation measurement pipeline.

[0035] It should be noted that Figure 1 the electrical capacitance tomography device is placed horizontally in []. During measurement, the electrical capacitance tomography device can be placed vertically. At this time, the left end is the top end and the right end is the bottom end.

[0036] As Figure 2 shown, the flexible electrode internally contains a plurality of pole pieces 10 that are evenly and spaced apart. Axial shields 11 are provided at both ends. The support member is axially located at the axial shield of the flexible electrode.

[0037] Further, the pole pieces are square pole pieces.

[0038] The support member is a cylindrical structure composed of two semi-circular ring structures made of polytetrafluoroethylene. The inner ring radius of the semi-circular ring structure is equal to the outer diameter of the insulation measurement pipeline. The inner and outer ring arcs of the semi-circular ring structure are slightly less than 180°. Through holes with the same number as the pole pieces are provided in the axial direction of the semi-circular ring structure.

[0039] The shielding cover is a rectangular copper plate that is curled and covers the surface of the support member.

[0040] The top connector and the bottom connector are of a ring structure. The outer diameter of the ring structure is the same as the outer diameter of the flange of the insulation measurement pipeline. The inner sides of the top connector and the bottom connector are of a ring-shaped boss structure, that is, the inner diameter of the small half part is smaller than the inner diameter of the upper half part. A positioning key is machined on the ring-shaped boss.

[0041] Further, both the first positioning hole plate and the second positioning hole plate are transparent acrylic round plates. Taking the first positioning hole plate as an example, the diameter of the first positioning hole plate is slightly smaller than the inner diameter above the ring-shaped boss of the top connector. Positioning holes are provided on the first positioning hole plate, and positioning grooves with the same size as the positioning key of the top connector are provided at the edge of the first positioning hole plate. The second positioning hole plate has exactly the same structure as the first positioning hole plate. These two positioning hole plates with the same hole positions need to be used in combination during measurement.

[0042] Further, the flow pattern test tube is a single-pass tetrafluoro or quartz tube. The outer diameter of the flow pattern test tube is equal to the diameter of the positioning hole of the first positioning hole plate / the second positioning hole plate. A boss is machined at the pipe orifice of the flow pattern test tube.

[0043] This embodiment provides a low-temperature fluid capacitance tomography device. By customizing and replacing different orifice plates, the measurement of single-liquid-column and double-liquid-column flow patterns with different parameters can be achieved. Before measurement, the positions of the holes in the orifice plate and the diameter of the flow pattern test tube are precisely machined, solving the difficulty of obtaining quantitative data on the true flow pattern distribution during low-temperature fluid measurement. The split design is adopted, reducing the processing difficulty. At the same time, the orifice plate, flow pattern test tube, and measurement pipeline are non-rigidly connected, greatly alleviating the operation difficulty during low-temperature measurement and also avoiding structural deformation and fitting errors caused by different thermal expansion coefficients of different materials at low temperatures.

[0044] Embodiment Two:

[0045] This embodiment provides a low-temperature fluid capacitance tomography device for further optimizing and explaining Embodiment One.

[0046] The low-temperature fluid capacitance tomography device provided in this embodiment adopts an 8-electrode imaging scheme. The low-temperature working medium is saturated liquid nitrogen-nitrogen (77K) at 1 atm. The flexible electrodes are wrapped and adhered to the outer wall surface of the insulated measurement pipeline through DW-3-1 low-temperature glue. This low-temperature glue can work in the range of -296 to 60 degrees Celsius. The flexible electrodes integrate measurement electrodes, axial shielding, and internal circuits, and there are pads left on each pole piece and the shield. The insulated measurement pipeline is made of polytetrafluoroethylene, with flanges at both ends of the insulated measurement pipeline, and the pipeline diameter is 100 mm.

[0047] During use, after assembling the low-temperature fluid capacitance tomography device, it is immersed in a foam box filled with liquid nitrogen (first introduce precooled gaseous working medium (such as cold nitrogen, cold oxygen) to complete the pre-cooling of the device to prevent brittle fracture caused by sudden cooling of the device). The capacitance tomography device is connected to the capacitance acquisition circuit and the imaging upper computer through shielded wires and data lines. The bottom of the foam box is liquid nitrogen, and the space above the liquid level is filled with low-temperature nitrogen.

[0048] After the capacitance tomography device is immersed for a period of time to complete the cooling, install the first positioning orifice plate above the annular boss of the top connector, install the second positioning orifice plate on the annular boss of the bottom connector, pour liquid nitrogen into the flow pattern test tube, then insert the flow pattern test tube into the insulated measurement pipeline from one of the positioning holes of the first positioning orifice plate and insert it out from the corresponding positioning hole of the second positioning orifice plate, and then start the measurement.

[0049] A set of replaceable orifice plates with precisely machined hole positions is used to achieve the switching of different flow patterns at low temperatures and obtain quantitative data on the true image distribution; the device has a simple structure and low processing cost, and all accessories can be repeatedly installed and disassembled; the structural reliability is high, and it can be used in a large temperature range from room temperature to deep low temperature, and is applicable to various low-temperature fluids.

[0050] Embodiment Three:

[0051] This embodiment provides a low-temperature fluid capacitance tomography device to further optimize and explain Embodiment 1.

[0052] For the low-temperature fluid capacitance tomography device provided in this embodiment, the support members are all made of polytetrafluoroethylene semi-circular ring structures, which still have good mechanical properties at low temperatures and are machined by a numerical control machine tool. Eight shielded wire through-holes are reserved in the axial direction of the semi-circular ring structure. The inner ring radius of the semi-circular ring structure is equal to the outer diameter of the insulation measurement pipeline, and the inner and outer ring arcs of the semi-circular ring structure are slightly less than 180°.

[0053] After the flexible electrodes are coated, four support members are coaxially installed at both ends of the flexible electrodes. The shielded wires pass through the through-holes on the support members. The shielded wire model is RG316. One end is welded to the surface of the flexible electrode pad, and the other end is an SMB female head, which is connected to the signal acquisition device. Subsequently, the shield is curled and wrapped around the outer wall of the support member, and a metal clamp is used for fastening.

[0054] Embodiment 4:

[0055] This embodiment provides a low-temperature fluid capacitance tomography device to further optimize and explain Embodiment 1.

[0056] For the low-temperature fluid capacitance tomography device provided in this embodiment, the top connector and the bottom connector are both welded by two aluminum alloy rings with the same outer diameter and different inner diameters. The difference in the inner diameters forms a boss structure, and the upper ring is machined with a positioning key. The top connector is fixedly connected to the left flange of the insulation measurement pipeline through bolts, and studs are added between the bottom connector and the right flange of the insulation measurement pipeline to ensure sufficient operating space.

[0057] Embodiment 5:

[0058] This embodiment provides a low-temperature fluid capacitance tomography device, which is a specific application of the low-temperature fluid capacitance tomography device provided in Embodiment 1.

[0059] Using the low-temperature fluid capacitance tomography device provided in Embodiment 1 for measurement, the measurement steps include:

[0060] (1) Coating the flexible electrodes on the outer wall surface of the insulation measurement pipeline, welding the coaxial shielded wire signal lines to the pads of the flexible electrodes, welding the shield layer to the axial shield pads of the flexible electrodes. After the shielded wires pass through the through-holes on the support members, the support members, the shield, the top, the bottom connectors, and the studs are sequentially connected and fixed.

[0061] (2) Connecting the low-temperature fluid capacitance tomography device and the capacitance acquisition circuit and the upper computer through the shielded wires.

[0062] (3) Immerse the cryogenic fluid capacitance tomography device in a foam box filled with liquid nitrogen. After cooling is complete and the temperature is stable, place the first positioning orifice plate on the boss of the top connector, place the second positioning orifice plate on the boss of the bottom connector, pour liquid nitrogen into the flow pattern test tube, insert the flow pattern test tube into one of the positioning holes of the first positioning orifice plate, then pass through the inside of the insulation measurement pipeline and insert it out from the corresponding positioning hole of the second positioning orifice plate.

[0063] (4) Sequentially excite the electrodes of the flexible electrode and collect capacitance signals, and transmit the collected capacitance signals to the host computer for phase distribution inversion. The capacitance value changes between electrode pairs are measured and recorded, and these changes reflect the distribution of the dielectric constant inside the measured cryogenic fluid.

[0064] Further, with the shielding cover and the axial shielding of the flexible electrode grounded, sequentially excite each electrode of the flexible electrode to obtain 28 independent capacitance measurement values.

[0065] For the capacitance tomography relationship imaging device provided in the first embodiment, it only needs the capacitance value of the electrode pairs of the flexible electrode to change according to the distribution of the dielectric constant of the liquid to be measured in the flow pattern test tube. The subsequent specific processing process is not within the scope of the first embodiment. And the host computer uses the corresponding image reconstruction algorithm to invert the dielectric distribution map of the fluid to be measured based on the capacitance data measured by the capacitance tomography device, which also belongs to the prior art.

[0066] (5) Realize the measurement of different cryogenic flow patterns by changing the insertion hole positions of the positioning orifice plate and the flow pattern test pipeline. After completing a set of flow pattern measurements, immerse the entire capacitance tomography device again to prevent rewarming.

[0067] The above-described embodiments are only a preferred solution of the present invention, and do not impose any form of limitation on the present invention. There are other variations and modifications without exceeding the technical solutions recorded in the claims.

Claims

1. A low-temperature fluid capacitance tomography device, characterized in that, It includes an insulation measurement pipeline and a flow pattern test tube. A support is sleeved on the outer wall of the insulation measurement pipeline. A flexible electrode is arranged between the insulation measurement pipeline and the support. A shielding cover is arranged on the surface of the support. One end of the insulation measurement pipeline is provided with a first positioning orifice plate, and the other end of the insulation measurement pipeline is provided with a second positioning orifice plate. The flow pattern test tube is vertically inserted through the positioning hole of the first positioning orifice plate and inserted into the corresponding positioning hole of the second positioning orifice plate.

2. The low-temperature fluid capacitance tomography device according to claim 1, characterized in that A top connector is arranged between one end of the insulation measurement pipeline and the first positioning orifice plate, and a bottom connector is arranged between the other end of the insulation measurement pipeline and the second positioning orifice plate.

3. A low-temperature fluid capacitance tomography device according to claim 1 or 2, characterized in that, The support includes a semi-circular ring structure, the radian of the inner and outer rings of the semi-circular ring structure is less than 180°, and through holes with the same number as the number of pole pieces of the flexible electrode are arranged in the axial direction of the support.

4. A cryogenic fluid electrical capacitance tomography device according to claim 2, characterized in that, A stud is arranged between the bottom connector and the insulation measurement pipeline.

5. A low-temperature fluid electrical capacitance tomography device according to claim 1 or 2 or 4, characterized in that, The insulation measurement pipeline is a polytetrafluoroethylene circular tubular straight pipe, and flanges are arranged at both ends of the polytetrafluoroethylene circular tubular straight pipe.

6. A low-temperature fluid electrical capacitance tomography device according to claim 2 or 4, characterized in that Both the top connector and the bottom connector are annular structures with the same outer diameter as the flange of the insulation measurement pipeline. The inner side of the annular structure is an annular boss, and positioning keys are arranged on the annular boss.

7. A cryogenic fluid electrical capacitance tomography device according to claim 1 or 2, characterized in that, Uniformly distributed square pole pieces are arranged inside the flexible electrode.

8. A cryogenic fluid electrical capacitance tomography device according to claim 2 or 4, characterized in that Positioning grooves that fit with the positioning keys of the top connector / bottom connector are arranged at the edges of the first positioning orifice plate and the second positioning orifice plate.

9. A low-temperature fluid electrical capacitance tomography device according to claim 1 or 2 or 4, characterized in that The flow pattern test tube is a single-pass polytetrafluoroethylene tube or a quartz tube, and a boss is arranged at the pipe orifice of the flow pattern test tube.

10. A cryogenic fluid electrical capacitance tomography device according to claim 1 or 2 or 4, characterized in that The shielding cover is a square copper plate, and the square copper plate is curled and covered on the surface of the support.

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