Device and method for measuring the thickness of reverse annular flow liquid film in a rectangular narrow slit channel

Abstract

This invention relates to the field of two-phase flow experimental measurement, specifically to a device and method for measuring the thickness of an annular liquid film in a rectangular narrow slit channel. The provided device for measuring the thickness of an annular liquid film in a rectangular narrow slit channel includes: a rectangular flow channel experimental section, including a side plate and a visualization window, the side plate and the visualization window forming a medium flow channel; the visualization window including a first viewing area, a second viewing area, and a chamfer; and a measurement unit including multiple laser confocal measurement units for measuring the thickness of the annular liquid film in the medium flow channel; the multiple laser confocal measurement units are respectively arranged around the visualization window, and laser confocal measurement units are also arranged around the first viewing area, the second viewing area, and the chamfer. This invention can alleviate the shortcomings of current liquid film thickness testing methods, realizing multi-region, multi-point synchronous measurement of liquid film thickness in a rectangular flow channel, and improving the integrity and consistency of the measurement results.

Description

Technical Field

[0001] This invention belongs to the field of two-phase flow experimental measurement technology, and specifically relates to a device and method for measuring the thickness of a reverse annular flow liquid film in a rectangular narrow slit channel. Background Technology

[0002] Rectangular channels have a clear application background in engineering. For example, rectangular or narrow rectangular structures are often used in the cooling channels of plate fuel elements in nuclear reactors and in the heat dissipation channels of high heat flux density devices such as chips. Therefore, the gas-liquid two-phase flow and liquid film behavior within them have high research value. That is to say, gas-liquid two-phase flow is a very important topic in the field of nuclear power, especially the detection of gas-liquid two-phase flow parameters, which is of great significance for the study of heat transfer and hydraulic phenomena. Compared with circular channels, the flow and interface behavior of rectangular channels differ in different wall and corner regions, resulting in more obvious spatial non-uniformity of liquid film distribution and placing higher demands on experimental measurements.

[0003] Liquid films are an important component of common flow patterns; therefore, accurate measurement of liquid film thickness is of paramount importance for studying multiphase flow structures and their heat and mass transfer mechanisms. Among related technologies, the application of reverse-circulation film boiling experiments is relatively limited, mainly because reverse-circulation film boiling is relatively unstable, and constructing a relatively stable reverse-circulation flow pattern is a prerequisite for its measurement. Furthermore, existing experimental studies on reverse-circulation conditions typically employ different experimental setups, leading to differences in experimental section structure, boundary conditions, and measurement benchmarks under different operating conditions, resulting in poor comparability of experimental results.

[0004] In related technologies, regarding the construction of experimental sections, existing two-phase flow experimental platforms typically establish thermal boundary conditions using a heated metal wall and external heating. Regarding liquid film thickness measurement, based on different measurement principles, current methods mainly include conductivity methods, capacitance methods, differential pressure methods, and conventional visualization methods. However, existing liquid film thickness measurement methods have certain limitations in non-contact measurement, spatial resolution, and local fine measurement.

[0005] Therefore, in the measurement of liquid film thickness, it is necessary to address the shortcomings of existing methods such as conductivity, capacitance, differential pressure and conventional visualization in terms of spatial resolution and local fine measurement capabilities. Alternatively, it is also necessary to address the problems of incomplete liquid film distribution acquisition, insufficient consistency of multi-point measurement time, and poor comparability of experimental results under different working conditions in existing technologies. Summary of the Invention

[0006] The purpose of this invention is to provide a device and method for measuring the thickness of a reverse annular flow liquid film in a rectangular narrow slit channel. This method can alleviate the shortcomings of current liquid film thickness testing methods in terms of spatial resolution and local fine measurement capabilities, or solve the problems of incomplete liquid film distribution acquisition, insufficient consistency of multi-point measurement time, and poor comparability of experimental results under different working conditions.

[0007] To solve the above-mentioned technical problems, this application is implemented as follows: According to one aspect of this application, an embodiment of this application provides a measuring device for measuring the thickness of a reverse annular flow film within a rectangular narrow slit channel, the measuring device comprising: A rectangular flow channel experimental section includes a side plate and a visualization window, the side plate and the visualization window forming a medium flow channel, the visualization window including a first viewing area extending along a first direction and a second viewing area extending along a second direction, the first direction and the second direction being perpendicular to each other, and at least one corner of the visualization window having a chamfer; The measurement unit includes multiple laser confocal measurement units for measuring the thickness of the reverse annular flow film within the medium flow channel; Multiple laser confocal measurement units are respectively disposed around the periphery of the visualization window, and at least one laser confocal measurement unit is disposed around the periphery of the first viewing area, at least one laser confocal measurement unit is disposed around the periphery of the second viewing area, and at least one laser confocal measurement unit is disposed around the periphery of the chamfer.

[0008] In an optional embodiment, the area of ​​the first visible area is larger than the area of ​​the second visible area, the first visible area serves as the main measurement area, and a plurality of laser confocal measurement units are provided around the periphery of the first visible area.

[0009] In an optional embodiment, the rectangular flow channel experimental section further includes a heating block disposed in a portion of the rectangular flow channel experimental section; the first visible area is provided with a plurality of measurement holes corresponding to a plurality of laser confocal measurement units, the plurality of measurement holes including a first hole area and a second hole area, the first hole area being close to the heating block area; the spacing between the measurement holes in the first hole area is smaller than the spacing between the measurement holes in the second hole area.

[0010] In an optional embodiment, in the first direction, the spacing between the measuring holes in the first hole area is 10 mm to 20 mm; and / or, the spacing between the measuring holes in the second hole area is 20 mm to 40 mm.

[0011] In an optional embodiment, the measuring device further includes a measurement and control system, which includes a liquid film thickness data receiving module and a data acquisition and processing module. The liquid film thickness data receiving module is signal-connected to the laser confocal measurement unit and the data acquisition and processing module, respectively. The data acquisition and processing module is based on unified timing control to synchronously trigger and acquire data from each of the laser confocal measurement units, so that data from different spatial locations are acquired under the same time reference.

[0012] In an optional embodiment, the measurement and control system further includes a valve control module, a heating power control module, a temperature measurement module, a pressure measurement module, and a flow measurement module; the valve control module, the heating power control module, the temperature measurement module, the pressure measurement module, and the flow measurement module are respectively signal-connected to the data acquisition and processing module.

[0013] In an optional embodiment, the chamfer angle is 30° to 60°.

[0014] In an optional embodiment, the height of the chamfer is 5% to 10% of the height of the medium flow channel.

[0015] In an optional embodiment, the measuring device further includes: a circulation loop, a cross branch, and a heating unit, wherein the heating unit is used to heat the medium; the rectangular flow channel test section and the cross branch are connected to the circulation loop, and a flow path switching structure is provided at the rectangular flow channel test section and the cross branch to change the fluid flow path.

[0016] According to another aspect of this application, embodiments of this application provide a method for measuring the thickness of a reverse annular flow film within a rectangular narrow slit channel, the measurement method comprising: Multiple laser confocal measurement units are set around the visualization window of the rectangular flow channel experimental section. By setting laser confocal measurement units around the first visible area, the second visible area, and the chamfered area, the thickness of the reverse annular flow film in the rectangular flow channel experimental section can be measured synchronously in multiple areas and at multiple points.

[0017] In an optional embodiment, multiple laser confocal measurement units are triggered at the same time to achieve synchronous triggering and data acquisition at each measurement point through unified timing control, thereby obtaining spatial distribution information of the thickness of the anti-annular flow film under the same time reference.

[0018] The technical solution of this application has at least the following beneficial effects: In this application, the visualization window of the rectangular flow channel experimental section includes a first visible area, a second visible area, and a chamfer. By setting laser confocal measurement units in the first visible area, the second visible area, and the chamfer area respectively, a multi-region liquid film thickness measurement system covering the first visible area, the second visible area, and the chamfer area is constructed, thereby making up for the deficiency of the prior art that can only obtain local liquid film information and improving the completeness of liquid film spatial distribution measurement.

[0019] This invention enables simultaneous measurement of the thickness of the reverse annular flow film in a rectangular flow channel across multiple regions and points, improving the integrity and consistency of the measurement results. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 A schematic diagram of the rectangular flow channel experimental section in a measuring device for measuring the thickness of an annular liquid film in a rectangular narrow slit channel, provided in an embodiment of this application; Figure 2 A schematic diagram of the rectangular flow channel experimental section and measurement unit in a measuring device for measuring the thickness of an annular flow film in a rectangular narrow slit channel, provided in an embodiment of this application; Figure 3 A schematic diagram of the measurement point arrangement in a measuring device for measuring the thickness of an annular flow liquid film in a rectangular narrow slit channel, provided in an embodiment of this application; Figure 4 A schematic diagram of the experimental circuit in a device for measuring the thickness of an anti-annular flow film in a rectangular narrow slit channel, provided in an embodiment of this application; Figure 5 This application provides a schematic diagram of a measurement and control system in a device for measuring the thickness of an annular liquid film in a rectangular narrow slit channel.

[0022] Explanation of reference numerals in the attached figures: 10-Rectangular narrow slit test section; 110-Side plate; 120-Visualization window; 121-First visible area; 122-Second visible area; 123-Chamfer; 130-Medium flow channel; 140-Anti-annular flow film; 150-Pressure shell; 160-Heating cable; 170-Heating block; 171-Heating rod; 172-Thermocouple sheath; 180-Measuring hole; 181-First hole area; 182-Second hole area; 190-Measuring hole on the sidewall of the flow channel; 191-Corner measuring hole; 20-Laser confocal measurement unit; 30-Circulation loop; 310-Pump unit; 320-Preheater; 330-Mixer; 340-Heat exchanger; 350-Pressure stabilizer; 360-Flow meter; 370-Differential pressure gauge; 371-First pressure gauge; 372-Second pressure gauge; 373-Third pressure gauge; 381-First pneumatic valve; 382-Second pneumatic valve; 383-Third pneumatic valve; 391-First regulating valve; 392-Second regulating valve; 393-Third regulating valve; 40 - Crossing branch; 410 - First valve; 420 - Second valve; 430 - Third valve; 440 - Fourth valve; 50-Water tank. Detailed Implementation

[0023] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0025] Anti-annular flow is a two-phase flow pattern that occurs near high-temperature walls and is typically associated with boiling heat transfer and film boiling. In anti-annular flow, the liquid core (liquid spool) is located at the center of the channel, while vapor contacts the high-temperature heated wall in the form of a vapor film. This anti-annular flow pattern usually only appears after the heat flux density exceeds the critical heat flux density (CHF). When the wall temperature is extremely high, the liquid in contact with the wall instantly forms a vapor film, preventing the liquid from directly wetting the wall. Studying the thickness of the anti-annular flow is crucial for understanding the reflooding phase of a nuclear reactor loss-of-coolant accident, which is essential for reactor safety analysis.

[0026] In related technologies, experimental studies on anti-circular flow conditions are usually carried out using different experimental devices, which leads to differences in the experimental section structure, boundary conditions and measurement benchmarks under different conditions, resulting in poor comparability of experimental results.

[0027] In liquid film thickness measurement, while conductivity, capacitance, differential pressure, and conventional visualization methods have been applied to two-phase flow research, these methods have limitations in spatial resolution and local fine measurement capabilities. Furthermore, they also have limitations in non-contact measurement. Laser confocal measurement, as a non-contact optical measurement method, possesses high spatial resolution and good local measurement capabilities, making it suitable for fine acquisition of liquid film thickness. Especially for rapidly changing liquid film structures in unsteady vapor-liquid two-phase flows, laser confocal methods are more advantageous for obtaining local liquid film thickness information. Although laser confocal measurement offers non-contact and high resolution, current applications are mostly concentrated on single points or local areas, making it difficult to obtain complete spatial distribution information of liquid film thickness within rectangular flow channels. Particularly for rectangular channels, the sidewalls and corners are often difficult to measure directly due to geometric constraints and optical path limitations. Moreover, the flow and interface behavior in these areas differs from that of the main measurement wall, further limiting a complete understanding of the liquid film distribution characteristics.

[0028] Furthermore, under unsteady vapor-liquid two-phase flow conditions, the liquid film thickness changes rapidly over time. If the data from multiple measurement points lacks unified time control, inconsistencies in the time reference can easily arise, making it difficult to accurately reflect the spatial distribution and dynamic evolution of the liquid film.

[0029] Therefore, there is an urgent need for a device and method that can perform multi-region, multi-point, and synchronous measurement of liquid film thickness in a rectangular flow channel under multiple operating conditions within the same experimental section, in order to solve the problems of incomplete liquid film distribution acquisition, insufficient consistency of multi-point measurement time, and poor comparability of experimental results under different operating conditions in the existing technology.

[0030] Based on this, considering the engineering application background, the construction of the thermal boundary of the experimental section, and the requirements for fine liquid film measurement, adopting an electrically heated rectangular flow channel experimental section combined with laser confocal measurement is a reasonable technical basis for conducting multi-region measurement of liquid film thickness in unsteady vapor-liquid two-phase flow. Therefore, this invention proposes a device and method for measuring the thickness of liquid film in reverse annular flow within a rectangular narrow slit channel. This method can solve the problems of insufficient spatial resolution and local fine measurement capability in current liquid film thickness testing methods, as well as the problems of incomplete liquid film distribution acquisition, insufficient consistency of multi-point measurement time, and poor comparability of experimental results under different operating conditions. Specific technical solutions are described below.

[0031] refer to Figures 1 to 5 As shown, in some embodiments, a measuring device is provided for measuring the thickness of an anti-annular flow film within a rectangular narrow slit channel. The measuring device includes: The rectangular flow channel experimental section 10 includes a side plate 110 and a visualization window 120. The side plate 110 and the visualization window 120 form a medium flow channel 130. The visualization window 120 includes a first viewing area 121 extending along a first direction and a second viewing area 122 extending along a second direction. The first direction and the second direction are perpendicular to each other. At least one corner of the visualization window 120 has a chamfer 123. The measurement unit includes multiple laser confocal measurement units 20, used to measure the thickness of the anti-annular liquid film 140 within the medium flow channel 130. Multiple laser confocal measurement units 20 are respectively arranged around the visualization window 120, and at least one laser confocal measurement unit 20 is arranged around the first viewing area 121, at least one laser confocal measurement unit 20 is arranged around the second viewing area 122, and at least one laser confocal measurement unit 20 is arranged around the chamfer 123.

[0032] In this embodiment, the measuring device can be used to measure the thickness of the anti-annular flow film 140 within a rectangular narrow slit channel. The measuring device includes a rectangular flow channel experimental section 10 and a measuring unit. The measuring unit includes multiple laser confocal measuring units 20 for measuring the thickness of the anti-annular flow film 140. These multiple laser confocal measuring units 20 can be distributed across multiple areas of the visualization window 120, including the first viewing area 121, the second viewing area 122, and the chamfered area 123, forming a multi-area, all-around coverage measurement. In a preferred embodiment of the invention, the multiple laser confocal measuring units 20 are triggered and acquired simultaneously, i.e., multi-point synchronous acquisition is achieved through unified timing control.

[0033] Therefore, on the one hand, this embodiment uses laser confocal measurement to test the thickness of the reverse annular flow liquid film 140, which can solve the problems of the current rectangular narrow slit channel field where methods such as conductivity, capacitance, pressure difference and conventional visualization are insufficient in terms of non-contact measurement, spatial resolution and local fine measurement capabilities. It improves spatial resolution and local fine measurement capabilities, and realizes non-contact measurement, which is suitable for fine acquisition of liquid film thickness.

[0034] On the other hand, although some existing fields use laser confocal measurement to test liquid film thickness, current applications are mostly concentrated on single points or local areas, making it difficult to achieve multi-point spatial distribution measurement of liquid film thickness. Furthermore, the lack of unified timing control under multi-point conditions leads to insufficient consistency of measurement data at different locations in terms of time reference. This invention not only arranges a multi-point laser confocal measurement unit 20, sets a lateral measurement structure on the sidewall, and sets a chamfered structure 123 in the corner area to form an accessible measurement path, but also combines unified timing control to achieve synchronous acquisition of multiple measurement points. This improves the spatial integrity and temporal consistency of liquid film thickness measurement, thereby solving the problems of incomplete liquid film distribution acquisition, insufficient temporal consistency of multi-point measurements, and poor comparability of experimental results under different operating conditions in existing technologies.

[0035] In other words, current measurements of liquid film thickness in vapor-liquid two-phase flow are mostly concentrated in circular channels and under single operating conditions. While commonly used methods such as conductivity, capacitance, differential pressure, and conventional visualization are relatively simple to implement, they lack spatial resolution and fine local measurement capabilities, and are easily affected by disturbances under conditions of severe interface fluctuations. Although non-contact optical measurement methods such as laser confocalization can improve measurement accuracy, current applications are mostly concentrated on single points or local areas, making it difficult to achieve multi-point spatial distribution measurement of liquid film thickness. Furthermore, the lack of unified time-series control under multi-point conditions leads to insufficient consistency of measurement data across different locations in terms of time reference. In addition, for rectangular flow channels, due to their geometric asymmetry, the liquid film behavior in the sidewalls and corners differs from that in the main measurement area. However, due to limitations in the measurement optical path, these areas are usually difficult to effectively acquire, making it difficult for current measurement results to reflect the complete spatial distribution characteristics of the liquid film. Especially under unsteady conditions, the liquid film thickness changes rapidly over time; without multi-point synchronous measurement methods, it is difficult to accurately characterize its spatial distribution and dynamic evolution process. The multi-region synchronous measurement device and method for the thickness of a reverse annular flow liquid film in a rectangular narrow slit channel provided in this embodiment, by arranging a multi-point laser confocal measurement unit 20 on the main side wall, setting a lateral measurement structure on the side wall, and setting a chamfer 123 structure in the corner area to form an accessible measurement path, and by combining unified timing control to realize synchronous acquisition of multiple measurement points, can effectively improve the spatial integrity and temporal consistency of liquid film thickness measurement, thereby effectively solving the above-mentioned technical problems.

[0036] In this embodiment, the rectangular flow channel experimental section 10 may include a medium flow channel 130 enclosed by a side plate 110 and a visualization window 120, within which a reverse annular flow can be formed; wherein the visualization window 120 may include a first viewing area 121 and a second viewing area 122, the first viewing area 121 extending along a first direction and the second viewing area 122 extending along a second direction. As an example, the first direction may be the length direction of the rectangular flow channel experimental section 10, or the direction of medium flow, and the second direction may be the width direction or the height direction of the rectangular flow channel experimental section 10.

[0037] In the rectangular flow channel experimental section 10, the visualization window 120 can be used to observe the medium state inside the flow channel and can also serve as a detection window for non-contact measurement. For example, for a rectangular flow channel, it includes multiple sidewalls, where the first viewing area 121 can be the main sidewall of the visualization window 120, and the second viewing area 122 can be the remaining sidewalls of the visualization window 120. Relatively speaking, the sidewall area of ​​the first viewing area 121 is the largest. In this embodiment, the first viewing area 121 can be used as the main measurement area, while the second viewing area 122 and the chamfered area 123 serve as auxiliary measurement areas.

[0038] Furthermore, in this embodiment, to achieve an accessible measurement path, a chamfer 123 structure is provided in the corner area of ​​the visualization window 120 to form an accessible measurement path, making the corner position that was originally geometrically obscured an accessible optical measurement path, thereby realizing the acquisition of the liquid film thickness in the corner neighborhood. Optionally, a chamfer 123 is provided at the corner of the visualization window 120 near the side plate 110, and the number of chamfers 123 can be one to four, for example, the number of chamfers 123 can be one, two, three or four.

[0039] In some specific embodiments, the first visible area 121 serves as the main measurement area, and multiple laser confocal measurement units 20 are provided around the first visible area 121. That is, multiple laser confocal measurement units 20 are set around the first visible area 121 to obtain the spatial distribution information of the liquid film thickness.

[0040] The first viewing area 121 is the main sidewall of the visualization window 120, while the second viewing area 122 is the remaining sidewall of the visualization window 120. The cross-sectional area of ​​the first viewing area 121 is larger than that of the second viewing area 122. Multiple laser confocal measurement units 20 are provided around the periphery of the first viewing area 121, and one or more laser confocal measurement units 20 can be provided around the periphery of the second viewing area 122. One or more laser confocal measurement units 20 can also be provided around the periphery of the corner areas.

[0041] In some specific embodiments, multiple laser confocal measurement units 20 located in the first visible area 121, the second visible area 122, and the chamfer 123 are triggered to acquire data at the same time, that is, multi-point synchronous acquisition is achieved by combining unified timing control.

[0042] Therefore, the multi-region synchronous measurement device and method for liquid film thickness in a rectangular narrow-slit channel with reverse annular flow in this embodiment not only includes a rectangular flow channel experimental section 10 and a multi-point measurement unit, but also a data acquisition and processing unit. This device can achieve comparative measurement under different flow conditions through operating condition adjustment. In terms of liquid film thickness measurement, a multi-point laser confocal measurement unit 20 is arranged in the first visible area 121, i.e., the main sidewall of the flow channel, to obtain the spatial distribution information of the liquid film thickness. Lateral laser confocal measurement units 20 are set in the second visible area 122, i.e., the remaining sidewall of the flow channel, to expand the measurement range. A chamfer 123 structure is set in the corner area to form an accessible measurement path. Laser confocal measurement units 20 are set around the chamfer 123. Under the premise of meeting the confocal measurement requirements, the influence on the original flow is reduced, thereby realizing the unified acquisition of the liquid film thickness of the main sidewall, the remaining sidewall, and the corner area. Furthermore, each measurement unit is synchronously triggered and acquires data under unified timing control, enabling the liquid film thickness data at different spatial locations to be obtained under the same time reference and correlated with operating parameters, thereby obtaining the liquid film distribution and its evolution characteristics. Thus, this embodiment of the invention achieves multi-region, multi-point synchronous measurement of liquid film thickness within a rectangular flow channel, improving the completeness and consistency of the measurement results.

[0043] The apparatus and method provided in this invention can perform multi-region, multi-point, and synchronous measurement of the liquid film thickness in a rectangular flow channel under multiple operating conditions within the same experimental section. This can solve the problems of incomplete liquid film distribution acquisition, insufficient consistency of multi-point measurement time, and poor comparability of experimental results under different operating conditions in the prior art.

[0044] In some embodiments, the side plate 110 in the rectangular flow channel experimental section 10 described above includes an Inconel alloy plate. This Inconel alloy plate is connected to the visualization window 120.

[0045] In some embodiments, the rectangular flow channel test section 10 further includes a heating block 170 (also called a hot block), which is disposed in a portion of the rectangular flow channel test section 10.

[0046] In this embodiment, regarding the construction of the experimental section, the two-phase flow experimental platform can establish thermal boundary conditions using a metal heated wall surface and external heating. Incone alloy material possesses good high-temperature resistance, mechanical strength, and adaptability to electric heating, making it suitable for constructing electrically heated rectangular flow channel heated walls. The installation of heating blocks 170 in localized areas of the experimental section provides heat storage and temperature stabilization capabilities, reducing the impact of localized temperature fluctuations on experimental conditions after water flow. This helps maintain the stability of the thermal boundary conditions in the experimental section; specifically, the installation of heating blocks 170 facilitates the formation of anti-annular flow, thereby enabling more accurate measurement of the anti-annular flow liquid film thickness.

[0047] Optionally, the rectangular flow channel experimental section 10 also includes a pressure shell 150, which may be provided with the outer side of the side plate 110 to improve the strength and stability of the structure.

[0048] Optionally, the visualization window 120 can be made of quartz. The quartz visualization window 120 not only has excellent optical performance and good transparency, which is conducive to observation and detection, but also has excellent heat resistance and chemical stability, and high mechanical strength, which is conducive to ensuring the long-term stable operation of the device in complex environments.

[0049] As an example, the rectangular flow channel experimental section 10 mainly includes a pressure shell 150, a rectangular narrow-slit channel composed of Incone alloy plates (side plates 110), a quartz visualization window 120, and a heating block 170 structure disposed at a local location in the rectangular flow channel experimental section 10. Both ends of the rectangular flow channel experimental section 10 are connected to an external experimental loop, forming a bidirectional flow channel for the working fluid. The Incone alloy plates are heated by an external heating cable 160, ensuring the rectangular flow channel reaches predetermined thermal conditions before the experiment. Heating rods 171 are installed inside the heating block 170 to provide localized additional heating and heat storage capacity, and to maintain a relatively stable temperature in the corresponding area after water is introduced, thereby improving the stability of the thermal boundary conditions of the experimental section. Optionally, the rectangular flow channel experimental section 10 is equipped with multiple thermocouples and thermocouple sheaths 172.

[0050] In this embodiment, the rectangular narrow slit channel is equipped with a quartz visualization window 120, which can be used to provide an optical channel for the laser confocal measurement unit 20 in the main measurement area. Multiple sidewall measurement holes 190 are provided along the flow direction on the channel sidewall for arranging lateral laser measurement units to obtain sidewall liquid film thickness information. A chamfered structure 123 is provided in the corner area of ​​the channel, and corner measurement holes 191 are provided at corresponding positions, forming an accessible optical measurement path in the corner neighborhood. This minimizes the impact on the original flow structure while meeting the confocal measurement requirements, thereby enabling multi-region measurement of the liquid film thickness in the main measurement area, sidewall, and corner areas of the rectangular channel. Furthermore, by adjusting the flow direction of the liquid working fluid in the experimental section and coordinating with temperature control, different flow conditions can be switched within the same experimental section.

[0051] In this embodiment, for example, a corner measurement hole 191 is provided at the chamfer 123 of the visualization window 120 to form an accessible optical measurement path in the corner neighborhood, enabling the laser confocal measurement unit 20 located around the chamfer 123 to measure the liquid film thickness within the channel. A flow channel sidewall measurement hole 190 is provided in the second viewing area 122 of the visualization window 120, enabling the laser confocal measurement unit 20 located around the second viewing area 122 to measure the liquid film thickness within the channel.

[0052] In some embodiments, the first visible area 121 is provided with a plurality of measurement holes 180 corresponding to a plurality of laser confocal measurement units 20. The plurality of measurement holes 180 include a first hole area 181 and a second hole area 182. The first hole area 181 is close to the heating block 170 area. The spacing between the measurement holes in the first hole area 181 is smaller than the spacing between the measurement holes in the second hole area 182.

[0053] In this embodiment, the first viewing area 121 of the visualization window 120 is equipped with multiple measurement holes 180. Multiple measurement points are arranged in combination along the flow direction and channel width direction within the visualization area to obtain spatial distribution information of the liquid film thickness. Furthermore, each measurement point is synchronously measured through unified trigger control, ensuring that data from different locations are acquired at the same time reference, thus guaranteeing the temporal consistency of the spatial distribution results. Regarding the arrangement of measurement points, a denser arrangement is used near key observation areas, while a relatively sparse arrangement is used in other areas. For example, a denser arrangement is used near the heating block 170, while a relatively sparse arrangement is used in other areas. That is, the first hole area 181, near the heating block 170, uses a denser arrangement with smaller spacing between the measurement holes 180; while the remaining areas, namely the second hole area 182, use a relatively sparse arrangement with relatively larger spacing between the measurement holes 180.

[0054] In this embodiment, both the first orifice region 181 and the second orifice region 182 are provided with multiple measuring holes 180 in both the length and width directions. In some embodiments, in the first direction, such as the length direction of the flow channel cross-section, the spacing between the measuring holes in the first orifice region 181 is 10mm to 20mm; the spacing between the measuring holes in the second orifice region 182 is 20mm to 40mm. Further, the spacing between the measuring holes in the first orifice region 181 is 15mm to 20mm; the spacing between the measuring holes in the second orifice region 182 is 30mm to 35mm. For example, the spacing between the measuring holes in the first orifice region 181 is 15mm; the spacing between the measuring holes in the second orifice region 182 is 30mm. Optionally, in the width direction of the flow channel, the spacing between the measuring holes in the first orifice region 181 and the second orifice region 182 is the same; for example, in the width direction, the spacing between adjacent measuring holes 180 can be about 20mm.

[0055] Typically, but not limitingly, in this embodiment, the spacing between the measuring holes in the encrypted area, i.e., the first hole area 181, is 15 mm × 20 mm, and the spacing between the measuring points in the conventional area, i.e., the spacing between the measuring holes in the second hole area 182, is 30 mm × 20 mm.

[0056] Therefore, by combining the above-mentioned flow channel structure design with multi-point synchronous measurement, the spatial distribution information of liquid film thickness can be obtained at the same time, providing a data foundation for liquid film distribution reconstruction and its spatiotemporal evolution analysis.

[0057] In some embodiments, the angle of the chamfer 123 is 30° to 60°; as an example, the angle of the chamfer 123 can be 45°.

[0058] In some embodiments, the height of the chamfer 123 is 5% to 10% of the height of the medium flow channel 130. That is, the opening size of the chamfer 123 is 5% to 10% of the height of the medium flow channel 130.

[0059] Optionally, in this embodiment, the rectangular slit channel has a large aspect ratio structure. Typically, but not limited to, the rectangular slit channel has a width of 50 mm, a height of 3 mm, and a length of 1000 mm to form a stable thin liquid film flow and enhance the spatial distribution characteristics of the liquid film thickness in the flow direction and width direction.

[0060] In this embodiment, the laser confocal measurement unit 20 is disposed outside the quartz visualization window 120 of the rectangular flow channel experimental section 10, and performs non-contact measurement of the liquid film thickness within the rectangular narrow slit channel through the visualization window 120. The visualization window 120 has a chamfered corner structure 123 at the corners of the flow channel, making the originally geometrically obstructed corner positions accessible optical measurement paths, thereby enabling the acquisition of the liquid film thickness in the corner neighborhood. The size of the chamfered corner 123 can be determined according to the requirements of the laser confocal measurement optical path, minimizing the opening size while ensuring the passage of incident and reflected beams. Since the laser confocal measurement spot is small, the requirement for the opening size is low. In this embodiment, the opening size of the chamfered corner 123 only accounts for 5% to 10% of the channel height, so its influence is mainly limited to the corner neighborhood and does not change the flow pattern in the mainstream area.

[0061] In some embodiments, the measuring device further includes: a circulation loop 30, a cross branch 40, and a heating unit, wherein the heating unit is used to heat the medium; the rectangular flow channel test section 10 and the cross branch 40 are connected to the circulation loop 30, and a flow path switching structure is provided at the rectangular flow channel test section 10 and the cross branch 40 to change the fluid flow path.

[0062] In this embodiment, the measuring device may include a rectangular flow channel experimental section 10, a circulation loop 30, a cross branch 40, a heating unit (or a heating adjustment unit), and a measuring unit. It may also include a working condition construction and control unit. The rectangular flow channel experimental section 10 is connected to the circulation loop 30 via the main flow channel and the cross branch 40. Flow path switching structures are provided at both ends of the rectangular flow channel experimental section 10 and at the cross branch 40, which can be used to change the fluid flow path, thereby forming a reconfigurable flow channel.

[0063] By combining and controlling the above-mentioned flow path switching structure, different flow paths can be switched within the same experimental section, allowing the liquid working medium to flow in opposite directions within the experimental section. Combined with the heating adjustment unit to regulate the thermal boundary conditions, the flow direction and thermal boundary conditions can be changed in synergy. Thus, different vapor-liquid two-phase flow conditions can be constructed under a unified experimental structure and boundary condition control method, including the anti-annular flow condition and the vapor-liquid reverse flow restricted condition.

[0064] It should be noted that the embodiments of this application do not limit the devices, structures, or connection arrangements included in the loop 30, cross branch 40, etc., and related technologies can be referred to. The following is an exemplary example of the components of the loop 30 and cross branch 40, but it should be understood that its specific implementation is not limited thereto.

[0065] As an example, in some embodiments, the circulation loop 30 may be connected to a water tank 50, which can be used to provide medium water for conducting a flow boiling test. The circulation loop 30 may also be equipped with a pump set 310, a preheater 320, a mixer 330, a heat exchanger 340, and other device structures. The mixer 330 is connected to a pressure regulator 350, the pump set 310 is used to transport the medium water, the preheater 320 is used to preheat the medium water, and the heat exchanger 340 is used to achieve heat exchange of the medium. Optionally, the measuring device may include multiple valves (ordinary valves), pneumatic valves, regulating valves, a flow meter 360, a differential pressure gauge 370, pressure gauges, and other components. As an example, the pressure gauges may include a first pressure gauge 371, a second pressure gauge 372, and a third pressure gauge 373, which are respectively located at different positions within the measuring device. As an example, a pneumatic valve may include at least a first pneumatic valve 381, a second pneumatic valve 382, ​​and a third pneumatic valve 383; a valve may include at least a first valve 410, a second valve 420, a third valve 430, and a fourth valve 440; a regulating valve may include at least a first regulating valve 391, a second regulating valve 392, and a third regulating valve 393. Specific configurations of the aforementioned valves and pressure gauges can be found in [reference needed]. Figure 3 As shown. The arrangement of the first valve 410, the second valve 420, the third valve 430 and the fourth valve 440 can form a flow path switching structure.

[0066] For example, before the experiment begins, the first pneumatic valve 381 and the third pneumatic valve 383 are closed, the second valve 420 and the third valve 430 are closed, the second pneumatic valve 382 is opened, and the first valve 410 and the fourth valve 440 are opened. Water is supplied by the water tank 50. The water is transported by the pump set 310, preheated by the preheater 320, and then passes through the flow meter 360, the fourth valve 440, the second pneumatic valve 382, ​​and the first valve 410. After passing through the mixer 330 and the heat exchanger 340, the water circulates in the circulation loop 30. During the cycle, the second pneumatic valve 382 can be closed, the first pneumatic valve 381 and the third pneumatic valve 383 can be opened, and the second valve 420 and the third valve 430 can be closed, while the first valve 410 and the fourth valve 440 can be opened. Thus, the medium can enter the rectangular flow channel experimental section 10 through the preheater 320, the flow meter 360, the fourth valve 440, and the third pneumatic valve 383, and then flow out of the rectangular flow channel experimental section 10 and circulate in the circulation loop 30 through the first pneumatic valve 381. That is, under these conditions, the medium flows from bottom to top in the rectangular flow channel experimental section 10. In other cases, the first valve 410 and the fourth valve 440 can be closed, while the second valve 420 and the third valve 430 can be opened. In this way, the medium, after passing through the preheater 320 and the flow meter 360, flows downwards within the rectangular flow channel experimental section 10 after passing through the third valve 430 and the first pneumatic valve 381. Then, after exiting the rectangular flow channel experimental section 10, it flows through the third pneumatic valve 383 and the second valve 420, circulating in the circulation loop 30. This alters the fluid communication path, enabling the switching of different flow paths within the same experimental section, allowing the liquid working medium to flow in opposite directions within the experimental section.

[0067] In some embodiments, the measuring device further includes a measurement and control system, which includes a liquid film thickness data receiving module and a data acquisition and processing module. The liquid film thickness data receiving module is signal-connected to the laser confocal measurement unit 20 and the data acquisition and processing module, respectively. The data acquisition and processing module is based on unified timing control to synchronously trigger and acquire data from each laser confocal measurement unit 20, so that data from different spatial locations are acquired under the same time reference.

[0068] In some embodiments, the measurement and control system further includes a valve control module, a heating power control module, a temperature measurement module, a pressure measurement module, and a flow measurement module; the valve control module, heating power control module, temperature measurement module, pressure measurement module, and flow measurement module are respectively connected to the data acquisition and processing module via signals.

[0069] In this embodiment, the measurement and control system in the measuring device can be built based on a unified control program to achieve integrated management of multi-parameter synchronous measurement and data processing. Optionally, the measurement and control system includes a valve control module, a heating power control module, a temperature measurement module, a pressure measurement module, a flow measurement module, a liquid film thickness data receiving module, and a data acquisition and processing module. The liquid film thickness data receiving module is signal-connected to the laser confocal measurement unit 20. Each measurement module is used to acquire parameter information such as temperature, pressure, flow rate, and liquid film thickness during the experiment, and all measurement signals are uniformly connected to the data acquisition and processing module. Optionally, the data acquisition and processing module is based on unified timing control to synchronously trigger and acquire data for each measurement channel, so that data from different spatial locations and different physical quantities are acquired under the same time reference, thereby ensuring the temporal consistency of multi-parameter measurement results to meet the measurement requirements of rapid liquid film changes under unsteady vapor-liquid two-phase flow conditions. Further, the valve control module and the heating power control module are used to provide experimental condition regulation functions, providing stable and repeatable experimental conditions for multi-region, multi-point synchronous measurement by adjusting the flow path and thermal boundary conditions. In this embodiment, the measurement and control system manages the control signals and measurement data in a unified manner, realizing the coordinated operation of the measurement process and the adjustment of the working conditions, thereby improving the stability and consistency of the liquid film thickness measurement results.

[0070] Therefore, based on the above, the multi-region, multi-point synchronous measurement device for liquid film thickness under reverse annular flow conditions provided in this embodiment arranges multi-point laser confocal measurement units 20 within the same rectangular flow channel experimental section 10, and achieves synchronous triggering and data acquisition of each measurement point through unified timing control, thereby obtaining spatial distribution information of liquid film thickness under the same time reference. The rectangular flow channel experimental section 10 has a visualization window 120 in the main measurement area for optical measurement, a lateral measurement structure on the sidewall to expand the measurement range, and a chamfered structure in the corner area to form an accessible measurement path. Under the premise of meeting the requirements of the laser confocal measurement optical path, it achieves the acquisition of liquid film thickness in the corner neighborhood, thereby constructing a liquid film thickness measurement system covering different spatial regions. Furthermore, the measurement and control system performs unified synchronous acquisition and processing of multiple parameters such as liquid film thickness, temperature, pressure, and flow rate, enabling data from different physical quantities and different spatial locations to be acquired under the same time reference, thus ensuring the temporal consistency of the measurement results. Based on this, by setting up a reconfigurable flow channel structure and combining the control of flow direction and thermal boundary conditions, different working conditions can be constructed and switched, providing unified and stable experimental conditions for the above-mentioned multi-region, multi-point synchronous measurement, thereby obtaining comparable measurement results.

[0071] Accordingly, in some embodiments, a method for measuring the thickness of an annular flow film within a rectangular narrow slit channel is provided, the method comprising: Multiple laser confocal measurement units 20 are set around the visualization window 120 of the rectangular flow channel experimental section 10. By setting laser confocal measurement units 20 around the first visible area 121, the second visible area 122 and the chamfer 123 area respectively, the thickness of the reverse annular flow film 140 in the rectangular flow channel experimental section 10 can be measured synchronously in multiple areas and at multiple points.

[0072] In some embodiments, multiple laser confocal measurement units 20 are triggered at the same time to achieve synchronous triggering and data acquisition of each measurement point through unified timing control, thereby obtaining spatial distribution information of the thickness of the anti-annular flow film 140 under the same time reference.

[0073] It should be understood that the method for measuring the thickness of the anti-annular flow film in a rectangular narrow slit channel in this embodiment is based on the same inventive concept as the aforementioned measuring device for measuring the thickness of the anti-annular flow film in a rectangular narrow slit channel. Therefore, the method for measuring the thickness of the anti-annular flow film in a rectangular narrow slit channel has at least all the features and advantages of the aforementioned measuring device, which will not be repeated here.

[0074] Therefore, by arranging a multi-point laser confocal measurement unit 20 in the main measurement area of ​​the rectangular flow channel, and setting lateral measurement structures and chamfer measurement structures in the sidewall and corner areas respectively, a multi-region liquid film thickness measurement system covering the main measurement area, sidewall and corner areas is constructed. This makes up for the shortcomings of the prior art which can only obtain local liquid film information and improves the completeness of liquid film spatial distribution measurement.

[0075] This invention employs unified timing control for multiple measurement points to achieve synchronous triggering and acquisition of liquid film thickness data, enabling measurement results from different spatial locations to be acquired under the same time reference, thereby improving the temporal consistency and reliability of liquid film thickness measurement under unsteady conditions.

[0076] This invention provides a unified experimental condition for liquid film measurement under different operating conditions by enabling adjustable switching of flow path and thermal boundary conditions within the same rectangular flow channel experimental section 10, thereby improving the comparability of experimental results.

[0077] In the description of this invention, it should be noted that the terms "upper", "lower", "left", "right", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0078] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the term "installation" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for measuring the thickness of a reverse annular flow film within a rectangular narrow slit channel, characterized in that, The measuring device includes: A rectangular flow channel experimental section includes a side plate and a visualization window, the side plate and the visualization window forming a medium flow channel, the visualization window including a first viewing area extending along a first direction and a second viewing area extending along a second direction, the first direction and the second direction being perpendicular to each other, and at least one corner of the visualization window having a chamfer; The measurement unit includes multiple laser confocal measurement units for measuring the thickness of the reverse annular flow film within the medium flow channel; Multiple laser confocal measurement units are respectively disposed around the periphery of the visualization window, and at least one laser confocal measurement unit is disposed around the periphery of the first viewing area, at least one laser confocal measurement unit is disposed around the periphery of the second viewing area, and at least one laser confocal measurement unit is disposed around the periphery of the chamfer.

2. The measuring device for measuring the thickness of an annular flow film in a rectangular narrow slit channel according to claim 1, characterized in that, The area of ​​the first visible area is larger than the area of ​​the second visible area. The first visible area serves as the main measurement area, and multiple laser confocal measurement units are arranged around the periphery of the first visible area.

3. The measuring device for measuring the thickness of a reverse annular flow film in a rectangular narrow slit channel according to claim 2, characterized in that, The rectangular flow channel experimental section also includes a heating block, which is disposed in a portion of the rectangular flow channel experimental section. The first visible area is provided with a plurality of measurement holes corresponding to the plurality of laser confocal measurement units. The plurality of measurement holes include a first hole area and a second hole area, and the first hole area is close to the heating block area. The spacing between the measuring holes in the first hole area is smaller than the spacing between the measuring holes in the second hole area.

4. The measuring device for measuring the thickness of a reverse annular flow film in a rectangular narrow slit channel according to claim 3, characterized in that, In the first direction, the spacing between the measuring holes in the first hole area is 10mm to 20mm; and / or, the spacing between the measuring holes in the second hole area is 20mm to 40mm.

5. The measuring device for measuring the thickness of a reverse annular flow film in a rectangular narrow slit channel according to claim 1, characterized in that, The measuring device further includes: The measurement and control system includes a liquid film thickness data receiving module and a data acquisition and processing module. The liquid film thickness data receiving module is signal-connected to the laser confocal measurement unit and the data acquisition and processing module, respectively. The data acquisition and processing module is based on unified timing control to synchronously trigger and acquire data from each laser confocal measurement unit, so that data from different spatial locations can be acquired under the same time reference.

6. The measuring device for measuring the thickness of a reverse annular flow film in a rectangular narrow slit channel according to claim 5, characterized in that, The measurement and control system also includes a valve control module, a heating power control module, a temperature measurement module, a pressure measurement module, and a flow measurement module; The valve control module, the heating power control module, the temperature measurement module, the pressure measurement module, and the flow measurement module are respectively connected to the data acquisition and processing module.

7. The measuring device for measuring the thickness of a reverse annular flow film in a rectangular narrow slit channel according to any one of claims 1 to 6, characterized in that, The chamfer angle is 30° to 60°; And / or, the height of the chamfer is 5% to 10% of the height of the medium flow channel.

8. The measuring device for measuring the thickness of a reverse annular flow film in a rectangular narrow slit channel according to any one of claims 1 to 6, characterized in that, The measuring device further includes: a circulation loop, a cross branch, and a heating unit, wherein the heating unit is used to heat the medium; The rectangular flow channel experimental section and the intersecting branch are connected to the circulation loop. A flow path switching structure is set at the rectangular flow channel experimental section and the intersecting branch to change the fluid flow path.

9. A method for measuring the thickness of a reverse annular flow film in a rectangular narrow slit channel, characterized in that, The measurement method includes: Multiple laser confocal measurement units are set around the visualization window of the rectangular flow channel experimental section. By setting laser confocal measurement units around the first visible area, the second visible area, and the chamfered area, the thickness of the reverse annular flow film in the rectangular flow channel experimental section can be measured synchronously in multiple areas and at multiple points.

10. The method for measuring the thickness of an annular flow film in a rectangular narrow slit channel according to claim 9, characterized in that, Multiple laser confocal measurement units are triggered at the same time to achieve synchronous triggering and data acquisition at each measurement point through unified timing control, thereby obtaining spatial distribution information of the thickness of the anti-annular flow film under the same time reference.

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