Pipe joint, manufacturing method of pipe joint and using method of pipe joint

Abstract

The invention discloses a pipe joint, a manufacturing method of the pipe joint and a using method of the pipe joint, and relates to the technical field of fluid equipment. The pipe joint comprises a pipe joint main body, a temperature conducting rod and a fiber bragg grating, the pipe joint main body is provided with a fluid channel capable of circulating fluid and a mounting hole; the temperature conducting rod is mounted in the mounting hole; the temperature conducting rod is provided with a gap which is used for installing a fiber grating. The fiber bragg grating comprises a main fiber bragg grating and at least one auxiliary fiber bragg grating which are connected in series; the main fiber bragg grating is positioned at a gap recess at the communicating part of the temperature conducting rod and the fluid channel; the auxiliary fiber bragg grating is positioned near the main fiber bragg grating in the fiber; the gap is opened towards the fluid channel, and the gap is filled with a temperature conducting material for fixing the fiber bragg grating and conducting fluid temperature so as to ensure that the main fiber bragg grating and the auxiliary fiber bragg grating are in the same temperature field and different pressure strain fields; and the time difference of fluid pressure signals reflected by different main fiber gratings is compared to detect the pulsation and propagation direction of fluid in the pipe joint main body.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluid equipment, and particularly relates to a pipe joint, a manufacturing method of the pipe joint, and a using method of the pipe joint. Background Art

[0002] The elastic modulus of oil varies greatly in the range of 0.9 - 2.0 GPa, which often leads to slow response characteristics of the hydraulic system. Especially for long-distance transmission, for example, the hydraulic response of the previous flight control mechanism of an aircraft is slow and cannot meet the design requirements. Therefore, this is also one of the reasons why the aviation industry increasingly tends to use the electrical signal transmission of EHA electro-hydraulic actuators to replace the hydraulic transmission of long-distance hydraulic oil pipes. However, for conventional industrial systems, the cost of EHA electro-hydraulic actuators is high, and multiple pumping stations need to be established for control, resulting in the problem of repeated construction of multiple pumping stations even in a small working area. Because the working efficiency of the hydraulic system of each pumping station itself is not high, the overall efficiency of a valve-controlled system with a fixed-displacement pump driven by an electric motor is usually about 30%. Among them, the efficiency of an asynchronous motor is 80% - 87%, the volumetric efficiency of the fixed-displacement pump is 90% - 95%, and the maximum efficiency of the valve-controlled cylinder system is 38%. Without considering the overflow loss of the relief valve, 87% * 95% * 38% = 31.8%, resulting in a large amount of energy waste in multiple pumping stations, including the pumping stations of EHA electro-hydraulic actuators with shortened hydraulic pipelines. A new large-flow supply pump source without large overflow loss for centralized oil supply is needed. After that, when transporting to hydraulic equipment at a relatively long distance, it will cause a new problem that the end flow supply is insufficient due to the increased frictional loss of the long-distance transmission pipeline, resulting in slow equipment response. For this reason, an innovative development of hydraulic long-distance discrete high-speed transmission has emerged.

[0003] When the industrial conventional hydraulic oil is at about 20 MPa, its elastic modulus is basically stable around a certain stable value. For example, when the No. 46 hydraulic oil is at about 20 MPa, its elastic modulus is basically stable between 1.4 - 1.6 GPa. This stable characteristic provides the basis for the long-distance discrete transmission of hydraulic pressure. Generally speaking, from a macroscopic perspective, the elastic modulus is a measure of the ability of an object to resist elastic deformation. The larger its value, the greater the stress required to cause a certain elastic deformation in the material, that is, the greater the stiffness of the material. That is to say, under a certain stress, the elastic deformation is smaller. The nature of the modulus depends on the nature of the deformation. The modulus during shear deformation is called the shear modulus, denoted by G; the modulus during compressive deformation is called the compression modulus, denoted by K; in the case of uniaxial stress with tensile or compressive stress in one direction, the elastic modulus that can calculate the dimensional change of a rod made of an isotropic elastic material under tensile or compressive load is called the Young's modulus, denoted by E. The value of the Young's modulus of metal materials will have a fluctuation of 5% or more due to different alloy compositions, heat treatment states, cold plastic deformations, etc. However, generally speaking, the elastic modulus of metal materials is a mechanical property index that is not sensitive to the microstructure. Alloying, heat treatment (fiber structure), cold plastic deformation, etc. have little effect on the elastic modulus, and external factors such as temperature and loading rate also have little effect on it. Therefore, the elastic modulus of metals is generally regarded as a constant in general engineering applications. The effective bulk elastic modulus of the oil usually refers to the compression state, which is in the range of 0.9 - 2.0 GPa, far greater than the 5% change fluctuation and is not constant; there are many influencing factors for the comprehensive bulk elastic modulus of the oil, and the main factors include the gas content in the oil, oil pressure, oil temperature, container stiffness, and the contact situation between the oil and air, etc. The gas content is the most influential factor on the bulk elastic modulus of the oil. When air is mixed into the hydraulic oil, its compressibility will increase significantly. When the oil entrains 1% gas (in the form of bubbles), the elastic modulus drops to 35.6% of that of pure oil. However, when the initial gas content rate is the same and the pressure is higher than the air separation pressure, when the time when the pressure exceeds the air separation pressure is long enough, the air contained in the gas-liquid mixture is completely dissolved and the bulk elastic modulus basically remains unchanged. Moreover, generally in the common understanding, the bulk elastic modulus of the oil is little affected by pipeline accessories and the content of air dissolved in the oil and can be ignored. In this way, it is easy to control and achieve the stability of the elastic modulus required for the long-distance transmission of the oil.

[0004] From the formula of the bulk elastic modulus of the oil The reciprocal of, that is, the compressibility β of the oil = 1 / K = -ΔV / (VΔP). From the interpolation calculation of the experimental data in the attached Figure 3 It can be known that p = 20 MPa (the interpolation between 19.4425 - 20.7275 MPa is 20.0845 MPa). When the pressure (p + Δp) of a certain pipe end of the capacity V of the hydraulic pipeline for long-distance transmission impacts instantaneously, V hardly changes. The elastic modulus K of the No. 46 hydraulic oile The interpolation value, which is basically stable between 15.438 - 15.892 GPa, i.e., 15.665 GPa, usually occurs under the standby pressure condition of the hydraulic servo valve. Its response speed is relatively fast, that is, the response time is short. It not only has pressure gain but also flow gain.

[0005] It should be noted that the frequency characteristic of the electro-hydraulic flow servo valve is defined as: when the control current changes sinusoidally within a certain frequency range, the complex ratio of the no-load control flow of the valve to the control current. Generally, for a valve with 21 MPa and 30 L, its response is at 70 Hz. The reciprocal of the response frequency is the response time t = 1 / 70 = 0.014 s. Then, within less than 0.1 s, this impact reaches the other end. Even if the resolution of an ordinary mechanical pressure gauge can reach the measurement of Δp and the delay of the mechanical gauge is not considered, it is difficult for the human eye (usually the integration operation within 0.2 s) to capture and observe. Therefore, an electronic hydraulic gauge is needed for capture and resolution. As an important measurement tool, the main parameters of the pressure gauge include the range, accuracy, resolution, overload capacity, working temperature, etc. In conventional hydraulic transmission, there is generally hydraulic pulsation. However, for general electronic hydraulic gauges, such as piezoelectric pressure gauges, because the way of collecting signals belongs to the integration operation method of charge accumulation, there are certain limitations in capturing and resolving the high-frequency pressure pulsation existing in this hydraulic transmission. Therefore, there is an urgent need for a new type of sensor that can sensitively capture hydraulic pulsation signals.

[0006] Although the existing patent application number is CN202010132418.3, and the patent name is a composite sensor for detecting fluid parameters in a pipeline, which uses Bragg gratings for pressure signal acquisition and can effectively capture and resolve such pressure pulsation signals, the sensor has too many fiber Bragg gratings built-in, resulting in a high manufacturing cost. Using optical switches for signal acquisition and other factors also make the measurement cost high. Moreover, the gratings in the sensor of this patent use Bragg gratings with uniformly distributed grids, and it is necessary to measure reference signals (such as temperature, etc.) simultaneously to resolve the pressure. In order to prevent the acquisition of temperature signals from being affected by external stress, they are placed at specific positions in the sensor. Due to the current limitations of manufacturing processes, it is very difficult to make it small. Although the relatively large-sized sensor that can be made by this invention can be popularized and applied in large pipelines of other hazardous chemical fluids, it is very difficult to be popularized and applied in the construction machinery industry with smaller pipelines.

[0007] It is found in the experiment that the effective bandwidth of the chirped grating has the characteristic of changing with strain and being insensitive to temperature. Therefore, through this characteristic, the measurement of hydraulic pressure pulsation can be realized. In the experiment, the change of strain can be known by measuring the reflected light intensity of the chirped grating. The reflected light intensity ΔI R The relationship with strain Δε is: |ΔI R| = k(1 - k)σξΔε; where k is the splitting ratio, σ is the spectral density of the light source, ξ is a constant related to the fiber structure material, and Δε is the strain of the grating.

[0008] Therefore, there is an urgent need to design a new type of pipe joint that can be more compact and applicable to the acquisition of hydraulic pressure and pulsating signal in conventional fluids or new long-distance discrete transmissions, for the measurement of pressure pulsation and the connection of pulsating flow transmission in a long-distance discrete flow pipeline that can withstand a pressure of about 20 MPa. Summary of the Invention

[0009] The present invention provides a pipe joint, a manufacturing method of the pipe joint, and a using method of the pipe joint to solve the problem of a more compact pipe joint required for the acquisition of hydraulic pressure and pulsating signals in conventional fluids or new long-distance discrete transmissions, for the measurement of pressure pulsation in a long-distance discrete flow pipeline that can withstand about 20 MPa and the connection of pulsating flow transmission, and to provide a necessary basic component for the long-distance discrete transmission of conventional fluids or new fluids.

[0010] The technical solution adopted by the present invention is as follows:

[0011] A pipe joint includes a pipe joint body, a heat conduction rod, and a fiber Bragg grating;

[0012] The pipe joint body has a fluid passage through which the fluid can flow; at least one mounting hole is respectively opened on at least two cross-sections perpendicular to the axis of the fluid passage;

[0013] The heat conduction rod is installed in the mounting hole; the heat conduction rod is provided with a slit, the bottom of the slit coincides with or is parallel to the center of the heat conduction rod, and a concave groove is provided on the heat conduction rod at the axial center of the slit for corresponding to the main fiber Bragg grating;

[0014] The fiber Bragg grating includes a main fiber Bragg grating and at least one secondary fiber Bragg grating connected in series on a single optical fiber; the main fiber Bragg grating is located in the slit of the concave groove at the intersection of the heat conduction rod and the fluid passage, facilitating contact with the fluid in the fluid passage; the secondary fiber Bragg grating is located near the main fiber Bragg grating in the optical fiber and away from the fluid in the fluid passage, and is arranged in the slit of the heat conduction rod in the pipe joint body;

[0015] The slit of the heat conduction rod faces the fluid passage, and the slit is filled with a heat conduction material, which is used to fix the fiber Bragg grating and conduct the fluid temperature to ensure that the main fiber Bragg grating and the secondary fiber Bragg grating are in the same temperature field; the main fiber Bragg grating and the secondary fiber Bragg grating are in different pressure strain fields, thereby detecting the fluid pressure;

[0016] By comparing the magnitudes and time differences of the fluid pressure signals reflected by different main fiber Bragg gratings, it is used to detect the magnitude and propagation direction of the fluid pressure in the pipe joint body.

[0017] An additional technical feature of a pipe joint of the present invention is as follows:

[0018] A longitudinal through-gap for installing an optical fiber grating is machined from the outside to the inside along the longitudinal section of the temperature-conducting rod, and the depth of the gap is not greater than the diameter of the temperature-conducting rod.

[0019] The axis of the installation hole is perpendicular to the axis of the fluid passage and is spatially staggered from the axis of the fluid passage by a preset distance. The preset distance ensures that the installation hole penetrates the fluid passage, and the penetration height is not greater than the diameter of the temperature-conducting rod.

[0020] A plurality of installation holes extend in a direction perpendicular to the axial direction of the fluid passage; the plurality of installation holes are distributed on different cross-sections of the fluid passage;

[0021] The spacing of the plurality of installation holes in the axial direction is equidistant or non-equidistant, and is respectively used for different test systems.

[0022] Sealing grooves for installing sealing rings and bolt holes for high-pressure flange connection are provided in the coaxial rings at both ends of the fluid passage.

[0023] Filling holes are provided on both sides of the installation hole in the direction perpendicular to the axial direction of the fluid passage. The filling holes communicate with the installation hole, and the filling holes are used to fill annular brazing materials.

[0024] This application also relates to a manufacturing method of a pipe joint. Based on the above-mentioned pipe joint, the specific steps include:

[0025] Installing holes penetrating the pipe joint body are provided in the pipe joint body along the direction perpendicular to the fluid passage;

[0026] A fiber optic cable connecting a main fiber grating and at least one sub-fiber grating in series is pre-placed in the gap of the temperature-conducting rod;

[0027] The main fiber grating is fixed at the recessed groove of the gap of the temperature-conducting rod, and a sub-fiber grating is fixed in the gap on one side or both sides of the recessed groove of the temperature-conducting rod; the gap of the temperature-conducting rod is filled with strip solder, and the strip solder is not higher than the gap of the temperature-conducting rod, which is used to fix the fiber grating and can flow into the voids of the gap of the temperature-conducting rod through high temperature during sintering, so as to fill the gap, and further used to seal or conduct the temperature of the externally contacted fluid;

[0028] One end of the optical fiber and the temperature-conducting rod with the fiber grating fixed thereon are inserted from one end of the installation hole. First, ensure that the temperature-conducting rod is installed in place axially in the installation hole, so that the recessed groove of the temperature-conducting rod is located at the intersection of the temperature-conducting rod and the fluid passage;

[0029] Then rotate and adjust the temperature-conducting rod so that the gap opening faces the fluid passage and is perpendicular to the axis of the fluid passage of the pipe joint body;

[0030] Fill the filling holes at both ends of the pipe joint body with annular brazing filler metal. The annular brazing filler metal can flow through the high temperature during sintering and enter the gap between the heat conduction rod and the installation hole from the filling hole, so that the heat conduction rod is positioned in the pipe joint body, and the gap between the heat conduction rod and the installation hole is blocked and sealed.

[0031] Fill the gap of the heat conduction rod with strip brazing filler metal. Specifically, the strip brazing filler metal belongs to glass brazing filler metal, and the difference in thermal expansion coefficient from the optical fiber does not exceed 10%. Preferably, aluminum alloy or silver paste with good thermal conductivity is used as the strip brazing filler metal, so that the fiber grating is fixed at the bottom of the gap of the heat conduction rod, facilitating the acceptance of the temperature of the fluid in the fluid channel.

[0032] This application also relates to a method of using a pipe joint. Based on the above-mentioned pipe joint, it includes:

[0033] When the main fiber grating and the auxiliary fiber grating adopt the same specification of Bragg grating, by comparing the peak difference Δλ between the Bragg wavelengths of the reflected light or transmitted light between the main fiber grating and the auxiliary fiber grating in the same optical fiber in the same gap of the heat conduction rod, a one-to-one correspondence between Δλ and the fluid pressure P in the fluid channel is established, so as to realize the measurement of the fluid pressure.

[0034] By measuring the time difference or phase difference of the pressure signals measured by the main fiber grating and the auxiliary fiber grating at different positions in the fluid channel to judge the flow direction; or, only by collecting the time difference of the same pulsating pressure signal by the main fiber grating at different positions on the axis to judge the pulsating flow direction.

[0035] A method of using a pipe joint also includes: if only the main fiber grating is retained and the main fiber grating adopts a chirped grating, the change of strain can be known by measuring the reflected light intensity of the chirped grating;

[0036] Reflected light intensity ΔI R The relationship with strain Δε is: |ΔI R | = k(1 - k)σξΔε; where k is the splitting ratio, σ is the spectral density of the light source, ξ is a constant related to the optical fiber structure material, and Δε is the strain of the grating;

[0037] Since Δε and the fluid pressure ΔP in the fluid channel can be established through the reflected light intensity ΔI R Establish a corresponding relationship, so as to establish a corresponding relationship between ΔI R 、Δε and ΔP, so as to realize the measurement of the fluid pressure pulsation ΔP;

[0038] By measuring the time difference of the same pressure signal collected by the main fiber grating at different positions in the fluid channel to judge the pulsating flow direction.

[0039] Due to the adoption of the above technical solutions, the beneficial effects obtained by the present invention are:

[0040] 1. Compared with the pipe joint assembly for multi-parameter measurement of fluid involved in patent application number CN202010132410.7, the present application adopts a small number of gratings, the optical fiber can be reduced to an optimal two, the grating can be reduced to two, and there is no need to use an ellipsoidal shell that is difficult to make as a carrier. Only a metal rod with a gap that is easy to process is used as a carrier, which has a low production cost, is simpler and more practical to produce, and is conducive to popularization and application.

[0041] 2. Compared with conventional pressure sensors, the present application has a wider range of pressure detection, is more sensitive to pressure pulsations, is more conducive to capturing and detecting pressure signals in pulsating direct current hydraulic transmission, and is beneficial to the control and feedback calculation of hydraulic discrete transmission.

[0042] 3. The concentric circles of the pipe joint interface of this application adopt O-type sealing and flange connection, which can withstand pressure and impact above 20MPa.

[0043] 4. The diameter of the temperature conducting rod of the present application is less than 1 / 2 of the fluid channel, and the connection length and small gap between the temperature conducting rod and the pipe joint body can ensure sufficient sealing by brazing, and can withstand pulsating pressure and impact of more than 20MPa;

[0044] 5. The pipe joint body of the present application has a fluid channel through which fluid can flow; a plurality of mounting holes are staggeredly distributed along the axial direction of the fluid channel, a thermal conductive rod is installed in the mounting hole, and the main fiber grating is installed in the groove of the thermal conductive rod so as to be in contact with the fluid in the fluid channel; the auxiliary fiber grating is installed on one side of the thermal conductive rod; since the main grating is in contact with the fluid pressure through the softer strip solder, and the auxiliary grating is mainly bonded to the bottom of the gap of the thermal conductive rod and is located inside the pipe joint with high rigidity, the fluid pressure in the pipe joint is reduced due to the retreat of the softer strip solder, which makes the auxiliary grating The fluid pressure acts mainly through the thermal conductive rod and the pipe joint body with larger stiffness. The contact strain generated by the main grating is larger than that of the auxiliary grating and does not belong to the linear change of the same stiffness. Therefore, through the auxiliary comparison of the auxiliary grating, not only the interference of the fluid temperature or the vibration signal of the pipe joint body in the main grating can be removed, but also the pressure measurement range of the grating can be expanded, and the detection accuracy of the main grating for the fluid pressure can be improved; by comparing the signals of the main grating in the thermal conductive rod at least two places, it is used to detect the propagation direction of the fluid pulsation and the magnitude of the pulsation pressure amplitude in the pipe joint.

[0045] 6. In the present application, filling holes communicating with the mounting holes are provided on both sides along the axial direction perpendicular to the fluid passage. The filling holes are used to fill the annular brazing material, and the annular brazing material enters the gaps of the heat conduction rod and the gaps between the heat conduction rod and the inner wall of the fluid passage through the filling holes. By setting the width and length of the gaps and selecting the brazing material, the compatibility between the glass and the brazing material can be effectively improved, ensuring that the main fiber grating and the secondary fiber grating are limited in the correct positions of the heat conduction rod by the strip-shaped brazing material, and ensuring the sealing quality and long-term stability. Description of the Drawings

[0046] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0047] Figure 1 is a schematic structural diagram of a pipe joint under an embodiment of the present invention;

[0048] Figure 2 is Figure 1 a cross-sectional schematic diagram at A-A in

[0049] Figure 3 is the measured value of the bulk modulus of elasticity of hydraulic oil under different pressures;

[0050] Figure 4 is a typical curve of the relationship between the flow coefficient of the throttle hole and the Reynolds number;

[0051] In the figure,

[0052] 1, pipe joint; 2, fluid passage; 3, mounting hole; 4, main fiber grating; 5, secondary fiber grating; 6, heat conduction rod; 7, sealing groove; 8, recessed groove; 9, filling hole; 10, annular brazing material; 11, gap. Detailed Embodiments

[0053] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0054] In addition, in the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0055] In the present invention, unless otherwise clearly defined and limited, the terms "installed", "connected", "joined", "fixed", etc. shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or a communication connection; it may be directly connected, or indirectly connected through an intermediate medium, and may be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0056] In the present invention, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the description of this specification, the descriptions referring to terms such as "embodiment", "example", "an embodiment", "example" or "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0057] In order to more clearly illustrate the overall concept of the present invention, the following will be described in detail by way of examples in conjunction with the drawings of the specification.

[0058] Embodiment 1

[0059] This application relates to a pipe joint, as Figures 1-2 shown, including a pipe joint body, a heat conduction rod, and a fiber Bragg grating;

[0060] The pipe joint body has a fluid passage through which fluid can flow; at least one mounting hole is respectively opened on at least two vertical cross-sections perpendicular to the axis of the fluid passage;

[0061] The heat conduction rod is installed in the mounting hole; the heat conduction rod is provided with a slit, the bottom of the slit coincides with or is parallel to the center of the heat conduction rod, and a concave groove is provided on the heat conduction rod at the axial center of the slit for corresponding to the main fiber Bragg grating;

[0062] The fiber Bragg grating includes a main fiber Bragg grating and at least one auxiliary fiber Bragg grating connected in series on the same optical fiber; the main fiber Bragg grating is located in the slit of the concave groove at the intersection of the heat conduction rod and the fluid passage, so as to be in contact with the fluid in the fluid passage; the auxiliary fiber Bragg grating is located near the main fiber Bragg grating in the optical fiber and away from the fluid in the fluid passage, and is arranged in the slit of the heat conduction rod in the pipe joint body;

[0063] The gap opening of the heat conduction rod faces the fluid channel, and the gap is filled with a heat conduction material. The heat conduction material is used to fix the fiber Bragg grating and conduct the fluid temperature to ensure that the main fiber Bragg grating and the auxiliary fiber Bragg grating are in the same temperature field; the main fiber Bragg grating and the auxiliary fiber Bragg grating are in different pressure strain fields, and then the fluid pressure is detected; by comparing the fluid pressure signals or time differences reflected by different main fiber Bragg gratings, it is used to detect the fluid pulsation and propagation direction in the pipe joint body.

[0064] In this application, the heat conduction rod can be a cylindrical structure or a strip structure, and there is no specific limitation. The heat conduction rod is preferably a round rod structure, which can be easily formed by simple machining to reduce costs. A gap can be set in the middle of the heat conduction rod by wire cutting. The gap is used to place at least two series-connected gratings of the same specification. One main grating is set at a position in the fluid channel of the pipe joint body where the heat conduction rod can directly contact the liquid in the channel, and the other auxiliary grating is set at the part of the heat conduction rod brazed in the pipe joint body. Since the main grating contacts the fluid pressure through a softer strip-shaped brazing material, and after the auxiliary grating is brazed and sintered at the bottom of the gap of the heat conduction rod, its deformation changes with the deformation of the heat conduction rod. And the heat conduction rod where the auxiliary grating is located is included in the pipe joint body, and the pressure strain it receives mainly acts on the fluid pressure not through the softer strip-shaped brazing material but through the heat conduction rod and the pipe joint body with greater stiffness. The contact strain generated by the main grating is larger than that of the auxiliary grating and does not change linearly. Therefore, through the auxiliary comparison of the optical signal by the auxiliary grating for the main grating, not only can the interference of the fluid temperature or the vibration signal of the pipe joint body received by the main grating be removed, but also the pressure measurement range of the grating can be expanded, and the detection accuracy of the main grating for the fluid pressure can be improved; by comparing the signals of the main gratings in at least two heat conduction rods, it is used to detect the fluid pulsation propagation direction and the magnitude of the pulsation pressure amplitude in the pipe joint.

[0065] It is used to remove the interference of the fluid temperature or the vibration signal of the pipe joint body received by the main grating to improve the detection accuracy of the main grating for the fluid pressure; at least two through holes are respectively arranged at different cross-sectional positions in the axial direction in the fluid channel to accommodate the heat conduction rod, and by comparing the signals of the main gratings in at least two heat conduction rods, it is used to detect the fluid pulsation propagation direction and the magnitude of the pulsation pressure amplitude in the pipe joint.

[0066] From the formula of the bulk modulus of elasticity of the oil The reciprocal, that is, the compressibility β of the oil = 1 / K = -ΔV / (VΔP), where the bulk modulus of elasticity of the oil V is the volume of the oil, and the volume change amount of the oil under the pressure difference ΔP is ΔV. From Figure 3From the interpolation calculation of the experimental data, p = 20 MPa (the interpolation between 19.4425 and 20.7275 MPa is 20.0845 MPa). When the pressure (p + Δp) impacts instantaneously at one end of the long-distance hydraulic pipeline, the capacity V of the pipeline hardly changes. The elastic modulus Ke of No. 46 hydraulic oil is basically stable at the interpolation between 15.438 - 15.892 GPa, which is 15.665 GPa. At this time, the oil in the long-distance pipeline has been in a standby state of 20 MPa for a long time, and even if there are free bubbles in the oil, they will dissolve in the oil, thus maintaining the volume elastic modulus K of the oil e It is stable at 15.665 GPa and remains unchanged. That is to say, the volume elastic modulus of the oil has quasi-rigidity, and the elastic deformation amount can be calculated using the definition of the elastic modulus of metal, that is, the deformation amount ΔV / V = P / K e = 20 MPa / 15.665 GPa = 0.00127. For a pipeline with a diameter of 10 mm, the total length of the transmission pipeline installed between two hydraulic devices in two workshops is 140 m. Then, the total oil capacity in the pipeline is V = 140×1000×π / 4×10×10 = 10990000 (mm 3 ) ≈ 10.99 liters. At the pipe end with a pressure of 20 MPa, the maximum recoverable elastic pulse deformation amount ΔV = 0.00127×10990000 ≈ 13957 mm 3 = 13.957 milliliters (when the oil is compressed by slowly pressurizing at both ends of the pipeline, without considering the deformation of the pipeline, the volume of the oil that can be incorporated or pressed in). That is to say, in the oil with a capacity of V ≈ 10.99 liters, at 20 MPa, 13.957 milliliters / 10990 milliliters = 0.126% of the oil can be pressed in. The length of the pipeline with a diameter of 10 mm occupied by these pressed-in oils is ΔL = ΔV / (π / 4×10×10) = 13957 / (π / 4×10×10) ≈ 177.8 mm. Then, due to the restrictive effect of the steel pipe, the linear pressed-in amount growth in the 140 m long pipeline is ΔL / L = 177.8 mm / 140 m = 1.27%. The linear growth ΔL / L can also be regarded as a characterization related to the pulse decay rate (the decay change rate of the pulsation amplitude gradually decreasing during the process of the impact oil volume integrating into the oil in the pipeline). Then, if the pipeline diameter is increased from 10 mm to 20 mm, then, ΔL = ΔV / (π / 4×20×20) = 44.45 mm, ΔL / L = 44.45 mm / 140 m = 0.03%. Then, the pulse decay rate is greater, and the distance between the main grating optical fibers in the temperature guide rod can be set shorter

[0067] For a 140 m long pipeline with a diameter of 10 mm, assuming it is similar to a slender throttle hole, then its flow rate is proportional to the pressure difference, as follows:

[0068]

[0069] Among them, Q is the flow rate of the throttling orifice, d is the pipeline diameter, l is the pipeline length, μ = ρυ, μ is the dynamic viscosity of the oil in Pa·s, υ is the kinematic viscosity in m 2 / s, and ρ is the density in kg / m 3 . The kinematic viscosity υ of No. 46 hydraulic oil is generally 46 mm 2 / s, and the density ρ is 870 kg / m 3 (the density of No. 46 hydraulic oil is between 850 and 870 kg / m 3 ). Therefore, μ = 870×46 = 40 (mPa·s); A0 is the cross-sectional area of the throttling orifice outflow; the pressure difference △p is the pressure difference before and after the throttling orifice;

[0070] For the impact flow rate in this case, the flow rate of the throttling orifice outflow can be expressed by dividing the volume ΔV of the impact pulse by the impact duration Δt as:

[0071] Q = ΔV / Δt

[0072] Furthermore, when the impact duration Δt is relatively short, the change in the pulse rising pressure is:

[0073] Δp = K e ×ΔV / V

[0074] Assume that at 20 MPa, the pulsation Δp of the pipe end pressure generated by injecting 13.957 ml of oil into the oil volume V≈10.99 liters is Δp = K e ×ΔV / V = 15.665 GPa×13957 mm 3 / (10990000 / 1000000000) = 19.89 MPa. From the above formula, we can obtain:

[0075] The impact duration Δt = 128×μ×l×V / (K e ×π / 4×d×d×d×d) = 128×(40 / 1000)×140×(10990000 / 1000000000) / 15.665 GPa / (π / 4×0.01×0.01×0.01×0.01) ≈ 0.064 s, and the impact frequency f ≈ 15.6 Hz, with a relatively low frequency.

[0076] If calculated according to the highest frequency of 100 Hz of the digital switching valve of Guizhou Mangewei Fluid Intelligent Technology Co., Ltd. at present, the impact time Δt = 1 / 100 Hz = 0.01 s. Taking the maximum conduction volume ΔV' = the maximum elastic pulse deformation volume ΔV = 0.00127×10990000 ≈ 13957 mm3 = 13.957 ml to calculate the flow rate as:

[0077] Q max = 13.957 ml / 0.01 s = 1.39 L / s = 83.4 L / min;

[0078] Obviously, due to the influence of factors such as the friction of the pipe wall and the viscosity of the oil, there are effects such as throttling resistance, wall viscosity, and the length of the first bend. There is a flow saturation phenomenon in the pipeline flow. Moreover, the volume V' of the oil under instantaneous compression is different from the total oil volume V in the 140 m long pipeline under 20 MPa. From the formula Δp = K e ×ΔV / V', it can be seen that the smaller V' is, the larger the pulsation Δp of the impact pressure generated by the same ΔV is when K e remains unchanged. The pipeline not only has a high risk of fatigue failure but also a greater risk of pulse bursting. Therefore, it is possible to consider using the flow of small pressure difference and small flow rate through a thin-walled throttle hole so as not to cause the problem that the required pressure difference Δp = 19.89 MPa of the long throttle hole is likely to lead to pipeline fatigue failure.

[0079] The thin-walled throttle hole scheme at the transmitting end is as follows:

[0080] The pressure difference of the long throttle hole is proportional to the flow rate, while the flow rate Q through the thin-walled throttle hole is proportional to the square root of the pressure difference, as shown below:

[0081]

[0082] In the formula, Q is the outflow flow rate of the throttle hole, C d is the flow coefficient, A0 is the outflow cross-sectional area of the throttle hole, ρ is the liquid flow density, and the pressure difference △P is the pressure difference before and after the throttle hole.

[0083] Among them, regarding the flow coefficient C d Through experiments, the typical curve of the relationship between the throttle hole flow coefficient and the Reynolds number is as Figure 4 shown. According to the latest research conclusion on the flow coefficient C d in the conference paper "Re-study on the Cavitation Mechanism" of the ICFPMCE2024 conference:

[0084] The flow calculation formula derived from Bernoulli's equation:

[0085]

[0086] In the formula: C d is the flow correction coefficient; A0 is the flow area; ΔP is the pressure difference potential energy between the throttle holes; ρ is the liquid flow density;

[0087] The flow correction coefficient C d is always less than 100%. Then, if the flow coefficient C dSubstituting into the above formula, it can be seen that the pressure potential energy contained in the pressure difference ΔP inside the square root is not all converted into the kinetic energy of fluid flow. If it is a one-dimensional pipeline flow and the flow area A0 remains unchanged, in addition to a part of the pressure difference potential energy between the throttle holes being converted into fluid flow, another part still acts on the normal direction of the pipe wall through continuous thermal motion, indirectly providing a supporting force for the fluid in the flow direction of the throttle hole (if there is no such pressure difference supporting force to ensure flow, it will become a static communicating vessel, the fluid will no longer flow, and the pressure difference at both ends will be 0, and there is no need to accumulate pressure difference on the wall surfaces at both ends of the throttle hole). In fact, both parts of the energy are the thermal motion of fluid molecules. Therefore, under the average action of thermal motion, the two parts of the energy should be balanced, that is, each accounts for half of the pressure difference potential energy ΔP between the throttle holes (half is used to maintain the pressure difference head of the flow, and half is used for the flow of the fluid). Therefore, according to the above formula, the flow coefficient of the throttle hole will not exceed the square root of 1 / 2, that is, 0.707, and this inference is also consistent with Figure 4 the flow coefficient C of the throttle orifice in the typical curve of the relationship between the flow coefficient and the Reynolds number d , and is quite consistent with the typical experimental value of reaching the maximum value of 0.7, indicating that this method of calculating the flow coefficient by energy balance has a certain credibility.

[0088] For Figure 4 the flow coefficient C of the throttle orifice in the typical curve of the relationship between the flow coefficient and the Reynolds number d , after reaching 0.7, it decreases instead with the increase of the flow velocity and then gradually stabilizes at about 0.6, which indicates that in the flow of one-dimensional pipeline turbulent flow (tearing cavitation flow), in addition to a part of the pressure difference potential energy still acting on the normal direction of the pipe wall to provide a supporting force for the fluid flow direction, there are also two parts of the pressure difference potential energy that are respectively converted into the kinetic energy of fluid flow, and the oscillating energy generated by the continuous annihilation and generation of the cavities produced by high-speed tearing. These three parts of energy are still balanced and consistent at the molecular thermal motion level. Therefore, according to the balance principle of the three parts of energy, the pressure difference potential energy required for the flow of the fluid also only accounts for 1 / 3 of the pressure difference potential energy ΔP between the throttle holes. Therefore, the flow coefficient is:

[0089]

[0090] The above theoretically demonstrates the origin of the maximum value 0.7 and the stable value 0.6 of the flow coefficient from the perspective of the energy conversion balance of molecular thermal motion. And this inference fits well with the flow coefficients 0.7 and 0.6 reflected by the typical curve of the relationship between the flow coefficient and the Reynolds number obtained from experiments. Therefore, this further shows that the assumption of the present application regarding the tearing cavitation caused by too fast flow has further credibility. Figure 4 The typical curve of the relationship between the flow coefficient and the Reynolds number

[0091] According to the above research, the flow coefficient C of the throttle orifice d, after reaching 0.7, torn free bubbles will appear. Then, according to the significant impact of free bubbles on the elastic modulus of the oil fluid in the aforementioned research, which in turn affects the high-speed pulsed flow in this case, therefore, the flow coefficient C of the throttle orifice should be controlled d Reaching 0.7 is optimal, and the Reynolds number should be at least no greater than C d = 100 at 0.7.

[0092] In the experimental data Figure 4 when the flow velocity v = v c , assuming that the fluid molecules still maintain a close-packed rigid sphere structure, then, the average distance between molecules in the throttle orifice reaches the tearing (vaporization) distance r a , but in the three-dimensional space of the fluid, only the r in the one-dimensional flow direction a ≈ 10r0. Due to the approximate incompressibility of the fluid, the molecular distance in other directions basically remains no greater than r0, and the density ρ at the front end of the throttle orifice up ≈ ρ. Therefore, the fluid density in the throttle orifice drops by about 10 times, ρ down ≈ ρ / 10; thus, the pressure difference potential energy ΔP is not only used to ensure the flow velocity v = v in the throttle orifice c , but also, it is necessary to rely on the spatial confinement effect of the pipe wall to ensure that the molecular arrangement density ρ in the non-flow direction remains unchanged, and the energies of the two parts for maintaining the density difference and the flow are equal under the equalizing effect of molecular thermal motion. From the experimental data Figure 4 the flow coefficient C of the throttle orifice in d = sqrt(1 / 2) corresponds to the Reynolds number R e = 100, then the Reynolds number in the middle of the throttle orifice is:

[0093] R e临界 = 100 = ρ down v c d / μ

[0094] From the above formula, due to the critical existence of tearing cavitation, we assume that the oil fluid density is reduced by about 1 / 10. Usually, the oil fluid density used in our calculation of the Reynolds number R e is the average value at normal temperature and pressure. Therefore, the critical Reynolds number R found in the Reynolds experiment e usually takes a value of 2300, which is one order of magnitude larger and a coefficient of 2.3 times the critical Reynolds number of laminar flow and turbulent flow in the above Figure 4 research. Now, the method of setting the revision coefficient with experimental data is as follows: comparing the measured data of 2300 by Reynolds and the 100 obtained from typical experimental data, and taking the ratio of the two as the revision value for density or viscosity change. Then, with the Reynolds number R at C d = 0.7 e= 100 Calculate the maximum velocity at which the revised oil molecules flowing out of the throttle hole do not produce torn bubbles:

[0095] v max = (2300 / 100 × 100) × μ / ρ / d / = 2300υ / d

[0096] Substitute the kinematic viscosity υ = 46 mm 2 / s and d = 10 mm of No. 46 oil into the above formula, and the maximum flow velocity at which torn bubbles do not appear is v max = 2300 × 46 / 10 / 1000 = 10.58 m / s. For safety, we select v max as the designed value of the conventional pipeline flow velocity of 9 m / s. Then, the flow rate of the throttle hole outflow is:

[0097] Q = v max × π / 4 × d × d = 9 × π / 4 × 0.01 ×

[0098] 0.01 = 706 ml / s = 42 L / min < Q max 83.4 L / min,

[0099] which is approximately half of the flow rate calculated by the long throttle hole with the maximum allowable press-in amount. Therefore, the impact pressure will also be much lower than the state of Δp = 19.89 MPa.

[0100] In addition, from the above formula it can also be seen that the greater the pressure difference, the greater the impact flow rate. However, due to the influence of pipe wall friction and oil viscosity, etc., there is a flow saturation phenomenon in pipeline flow. After the flow coefficient C d = 0.7, although it can be stabilized at C d = 0.6 or so, which can bring convenience to the calculation, but problems such as the above-mentioned liquid flow cavitation and density reduction will occur, thus affecting the transmission loss caused by the reduction of the elastic modulus of the oil. Therefore, it is necessary to limit Q = v max × π / 4 × d × d = 42 L / min, and according to the pressure difference ΔP at the control transmitter can be calculated inversely:

[0101] ΔP = (v max / C d )^2 × ρ / 2 = (9 / 0.7)^2 × 870 / 2 = 71908 Pa = 0.07 MPa << Δ

[0102] p = 19.89 MPa;

[0103] Compared with 20 MPa, the differential pressure change Δp = 0.07 MPa is only 0.35% of 20 MPa. Such a small differential pressure can be emitted with only a small disturbance and is easy to achieve. Moreover, the fiber Bragg grating is sensitive to such a small differential pressure of 0.07 MPa. Therefore, the pipe joint of the present invention can be used in this new type of hydraulic discrete transmission scheme.

[0104] Regarding the innovation of this case: Compared with a pipe joint assembly for multi-parameter measurement of fluids involved in the patent application with the patent number CN202010132410.7, the number of gratings used in this application is small. The optical fibers can be reduced to two, and optimally two, and the gratings can be reduced to two. Moreover, instead of using a difficult-to-fabricate ellipsoidal housing as a carrier, only a metal rod with a slit that is easy to process and implement is used as a carrier, with low manufacturing cost, simpler and more practical production, which is conducive to popularization and application. It is more sensitive to pressure pulsation than conventional pressure sensors, which is more conducive to capturing and detecting pressure signals in pulsating DC hydraulic transmission, and is conducive to the control and feedback calculation of hydraulic discrete transmission. The pipe joint interface adopts an O-ring seal and flange connection method, which can withstand pressures and impacts above 20 MPa. In addition, the diameter of the heat-conducting rod is less than 1 / 2 of the fluid channel, and the connection length of the heat-conducting rod and the pipe joint body and the small slit, and the brazing sealing method adopted can ensure sufficient sealing and can withstand pressures and impacts above 20 MPa; the femtosecond grating used can withstand high temperatures of 1000 °C. The innovative use of a high-temperature (but lower than 1000 °C) brazing sealing method and fixing materials compatible with glass optical fibers provides an application method and scenario for the application of gratings in new fields.

[0105] As a preferred implementation manner, along the longitudinal section of the axis of the heat-conducting rod, a longitudinal through-slit for installing the fiber Bragg grating is machined from the outside to the inside, and the depth of the slit is not greater than the diameter of the heat-conducting rod.

[0106] Along the longitudinal section of the axis of the heat-conducting rod, a longitudinal through-slit for installing the fiber Bragg grating is machined from the outside to the inside by processes such as wire cutting or sawing. The depth of the slit is preferably a cylindrical structure, and the depth of the slit is not greater than the radius length of the heat-conducting rod to ensure a position for installing the main fiber Bragg grating is reserved.

[0107] The opening of the slit faces the fluid channel and is perpendicular to the axis of the fluid channel of the pipe joint; the part that hinders fluid flow is removed at the position where the heat-conducting rod communicates with the fluid channel, and after removal, the bottom of the slit of the heat-conducting rod is connected to the fluid channel or the connection distance between the bottom of the slit and the fluid channel is less than half of the depth of the slit.

[0108] Further preferably, the depth of the slit is the radius length of the cylindrical structure heat-conducting rod.

[0109] In use, after the installation holes are drilled, first use a little glue to bond the relative positions among the main fiber grating, the secondary fiber grating and the temperature conduction rod, and place them in the corresponding holes of the pipe joint body. Then, adjust the position of the main grating in the fluid channel of the pipe joint. Next, fill sufficient annular brazing filler metal into the annular brazing filler metal filling holes at both ends of the transverse hole of the pipe joint for installing the temperature conduction rod, which is used to fill the gap between the temperature conduction rod and the transverse hole of the pipe joint and the wire-cutting slot for installing the fiber grating on the temperature conduction rod during sintering. By setting the width and length of the gap, it can be ensured that the main grating is limited in the correct position on the temperature conduction rod by the brazing filler metal.

[0110] Since conventional gratings will be deleted or rewritten when exposed to high temperatures (such as exceeding 120 °C), therefore, the fiber grating in this case considers YOSC-FsFBG-15XX with high temperature tolerance. Because it belongs to the fiber grating written directly by femtosecond laser, which is different from the traditional fiber grating writing method, the fiber grating is written point by point on the fiber core directly through various transparent coating layers of the fiber by femtosecond laser. The fibers that can be written include from high-end special fibers to ordinary communication fibers. The fiber grating written directly by femtosecond laser itself has excellent stability, and the temperature resistance of the grating area reaches 1000 °C. Therefore, the conventional method of fixing the grating with glue is easily damaged because the bonding strength of the glue is difficult to withstand high pressure (such as 20 MPa). Brazing has a higher pressure resistance than glue, and the brazing process can be achieved at a temperature lower than 1000 °C. Therefore, in this case, when fixing the grating by the brazing process at 700 °C - 800 °C, the fiber grating written directly by femtosecond laser can be used.

[0111] As a preferred implementation manner, the axis of the installation hole is perpendicular to the axis of the fluid channel and is spatially staggered from the axis of the fluid channel by a preset distance. The preset distance ensures that the installation hole penetrates through the fluid channel, and the penetration height is not greater than the diameter of the temperature conduction rod. In this way, it can be ensured that most of the temperature conduction rod is buried deep in the pipe joint, and only the depression of the temperature conduction rod where the main grating is located is closest to the fluid in contact, and the fluid pressure felt is more direct than that of the secondary grating. In addition, because the temperature conducted to the secondary grating through brazing or the temperature conduction rod is in the same temperature field as the main grating, in this way, the wavelength change amount of the Bragg grating between the main grating and the secondary grating mainly reflects the stress change amount between the main grating and the secondary grating. Therefore, the pressure of the oil fluid can be obtained by comparing the wavelength change amount of the Bragg grating between the main grating and the secondary grating.

[0112] When they penetrate through each other, the installation hole and the fluid channel form an intersection line. Here, the intersection line is the common line of the surfaces of the two three-dimensional shapes and also the intersection line of the surfaces of the two three-dimensional shapes; the points on the intersection line are the common points of the two three-dimensional surfaces; the formed intersection line is continuous and does not separate from each other, avoiding the situation of two separate and discontinuous intersection lines formed by intersecting and penetrating.

[0113] As a preferred embodiment, a plurality of mounting holes extend in a direction perpendicular to the axial direction of the fluid passage; the plurality of mounting holes are distributed on different cross-sections of the fluid passage;

[0114] The spacing of the plurality of mounting holes in the axial direction is equidistant or non-equidistant, and is respectively used for different test systems.

[0115] The plurality of mounting holes extend in a direction perpendicular to the axial direction of the fluid passage, so that the mounting holes penetrate through the pipe joint body, which is convenient for installing the temperature guiding rod. Solder loading spaces are arranged at both ends of the mounting holes, which is convenient for placing the solder.

[0116] The arrangement of the plurality of mounting holes realizes the layout of the temperature guiding rods at different positions, so that the extraction of the pressure information at different positions before and after the fluid passage in the pipe joint can be realized, and the fluid pulsation propagation direction and the magnitude of the pulsation pressure amplitude in the pipe joint can be obtained.

[0117] The spacing of the plurality of mounting holes in the axial direction is equidistant or non-equidistant to achieve the estimation accuracy of different fluid pulse flows; the diameter of the mounting holes is generally smaller than the diameter of the fluid passage. The spacing between two of the mounting holes in the axial direction can be set differently according to different system pulsation conditions. The setting methods include either increasing the spacing through the connecting pipe, or shortening the spacing by increasing the flow-through diameter, or changing the response distance between the pulsations of the spacing by changing the emission flow of the system. By these methods of hardware change, they are applied to different systems to reduce the number of invalid data acquisitions and the duration of invalid calculations by the computer, so as to achieve the rapidity of signal acquisition and processing by the computer.

[0118] As a preferred embodiment, a sealing groove for installing a sealing ring and bolt holes for high-pressure flange connection are provided in the coaxial ring at both ends of the fluid passage.

[0119] The installation of the O-ring in the sealing grooves at both ends of the pipe joint and the flange connection can ensure that there is no leakage at the end face under a pressure impact of more than 20 MPA. The setting of the long distance and the small annular gap between the temperature guiding rod and the pipe joint can ensure that the brazing solder for high-temperature welding can withstand at least a pressure impact of more than 20 MPA without leakage at the gap.

[0120] If a pipe joint and pipeline with a nominal diameter of 10 mm are used, a 24-degree taper seal or a ferrule structure connection can also be adopted, which can also ensure that there is no leakage at the end face under a pressure impact of more than 20 MPa, and the transmission cost can be reduced.

[0121] As a preferred embodiment, filling holes are provided on both sides of the mounting holes in the direction perpendicular to the axial direction of the fluid passage. The filling holes communicate with the mounting holes, and the filling holes are used for filling annular brazing solder.

[0122] Filling holes communicating with the mounting holes are provided on both sides along the axial direction perpendicular to the fluid channel. The filling holes are used to fill the annular brazing material, and the annular brazing material enters the gaps of the heat conduction rod and the gaps between the heat conduction rod and the inner wall of the fluid channel through the filling holes. By setting the width or length of the gaps and selecting the brazing material, the compatibility between the glass and the brazing material can be effectively improved, ensuring that the main fiber grating and the auxiliary fiber grating are defined in the correct positions of the heat conduction rod by the strip brazing material, and ensuring the sealing quality and long-term stability.

[0123] The annular brazing material can be a glass brazing material. The composition of the glass brazing material is similar to that of the glass and its properties are close. Sealing can be completed through a common heat treatment step. The expansion coefficient of the product matches that of the base material, with high sealing strength, good airtightness, and good aging resistance. It is an excellent edge sealing material for vacuum glass. Among them, there are many metal materials suitable for sealing with glass in the glass brazing material, which can well realize the connection between the main fiber grating and the heat conduction rod and the connection between the auxiliary fiber grating and the heat conduction rod. The metal materials that can be used include aluminum alloy, silver paste, etc. These metal materials generally have a low melting point, good mechanical properties, and excellent corrosion resistance. During the sealing process, the molten metal material can fully wet the glass, and a good chemical bond is formed through element diffusion, thereby achieving effective sealing.

[0124] It should be noted that for the annular brazing material to achieve high-strength connection between the main fiber grating and the heat conduction rod and high-strength connection between the auxiliary fiber grating and the heat conduction rod, the key lies in two points. The first point is that the thermal expansion coefficients of the annular brazing material and the base material should be very close (the difference does not exceed 10%). During the sealing process, the expansion curves of the two should be as consistent as possible, otherwise cracks or chronic air leakage will occur at the sealing joint. The second point is that the annular brazing material must be able to wet the surface of the base material, which is another key condition for successful sealing. By increasing the surface roughness of the base material, the infiltration and curing effects of the brazing material can be further optimized, which can usually be achieved by methods such as sandpaper grinding or sandblasting. It can also be achieved by increasing the surface cleanliness of the base material, without impurities such as grease and dust. To ensure the surface cleanliness of the base material, methods such as solvent cleaning or mechanical grinding can be used.

[0125] Embodiment 2

[0126] This application also relates to a manufacturing method of a pipe joint. Based on the above-mentioned pipe joint, the specific steps include:

[0127] An installation hole penetrating the pipe joint body is opened in the pipe joint body along the direction perpendicular to the fluid channel;

[0128] Pre-place the optical fibers of a main fiber grating and at least one auxiliary fiber grating into the gaps of the heat conduction rod;

[0129] Fix the main fiber Bragg grating at the recessed groove of the heat conduction rod gap, and fix a secondary fiber Bragg grating in the gap on one side or both sides of the recessed groove of the heat conduction rod; fill the gap of the heat conduction rod with strip solder, and the strip solder is not higher than the gap of the heat conduction rod, which is used to fix the fiber Bragg grating and can flow into the void of the heat conduction rod gap through high temperature during sintering, so as to fill the gap, and then used to seal and conduct the temperature of the external contact fluid;

[0130] Insert one end of the optical fiber and the heat conduction rod with the fiber Bragg grating fixed correspondingly from one end of the installation hole. First, ensure that the heat conduction rod is installed in place axially in the installation hole, so that the recessed groove of the heat conduction rod is located at the intersection of the heat conduction rod and the fluid channel;

[0131] Then rotate and adjust the heat conduction rod so that the gap opening faces the fluid channel and is perpendicular to the axis of the fluid channel of the pipe joint body;

[0132] Fill the filling holes at both ends of the pipe joint body with annular brazing solder. The annular brazing solder can flow into the gap between the heat conduction rod and the installation hole from the filling hole through high temperature during sintering, so as to position the heat conduction rod in the pipe joint body and realize the plugging and sealing of the gap between the heat conduction rod and the installation hole.

[0133] The gap of the heat conduction rod is filled with strip solder. Specifically, the strip solder belongs to glass brazing solder, and the difference in thermal expansion coefficient from the optical fiber does not exceed 10%. Preferably, aluminum alloy or silver paste with good thermal conductivity is used as the strip solder, so that the fiber Bragg grating is fixed at the bottom of the gap of the heat conduction rod, facilitating the reception of the temperature of the fluid in the fluid channel.

[0134] Generally, the application of brazing in pipeline welding is a welding method that realizes metal connection by using a filler metal with a melting point lower than that of the base metal, melting the filler metal by heating, and then using the liquid filler metal to fill the gap of the solid workpiece. During the brazing process, the filler metal melts and fills the joint gap, and forms a firm metallurgical bond with the base metal after cooling. Its characteristics are: little influence on the physical and chemical properties of the base metal; small stress and deformation generated during the brazing process; relatively simple brazing equipment and small production investment. According to the melting point of the filler metal, brazing is divided into soft brazing and hard brazing: Soft brazing: The melting point of the filler metal is lower than 450°C, and the commonly used filler metal is tin-lead filler metal; Hard brazing: The melting point of the filler metal is higher than 450°C, and the commonly used filler metals are brass filler metal and silver-based filler metal, which are suitable for steel and copper alloy workpieces with greater stress.

[0135] Example 3

[0136] The present application also relates to a method of using a pipe joint. Based on the above pipe joint, by comparing the change in the Bragg wavelength of the reflected or transmitted light of the main grating and the auxiliary grating, a one-to-one correspondence with the fluid pressure in the fluid channel can be formed, thereby realizing the measurement of the fluid pressure; the time difference of the pressure signals measured by the main grating and the auxiliary grating on the optical fibers at different positions in the fluid channel can be used to determine the flow direction; or, only by collecting the time difference of the same pressure signal by the main grating at different positions on the axis, the flow direction can be determined. The specific steps are as follows:

[0137] From the formula The reciprocal of, that is, the compressibility β of the oil = 1 / K = -ΔV / (VΔP). From Figure 3 It can be seen that when the capacity V of the hydraulic pipeline with a long-distance transmission of p = 20 MPa is impacted instantaneously by the pressure (p + Δp) at a certain pipe end, V is almost unchanged. When the elastic modulus K of No. 46 hydraulic oil e Is basically stable between 1.468 - 1.6 GPa, the pressure P is between 18 - 22 MPa, that is, ΔP’ = 22 - 18 ≈ 4 MPa (pressure fluctuation ΔP / P = 4 / 20 = 20%), ΔK e ≈ 1.6 - 1.468 GPa = 132 MPa (elastic modulus fluctuation ΔK e / K e = 0.132 / 15.89 ≈ 8.3%), the elastic modulus hardly fluctuates, and K e Is stable at 15.89 GPa, not exceeding 10%. Then, for a pipeline with a diameter of 10 mm, the total length of the transmission pipeline installed between two hydraulic devices in two workshops is 140 m. Then, the total oil volume in the pipeline is V = 140×1000×π / 4×10×10 = 10990000 / 4 (mm 3 ) = 10.99 liters. At the pipe end of 20 MPa, a pulsating shock of ΔP = 0.07 MPa as calculated in Scheme 1 is generated, and the volume compression generated is ΔV = V×ΔP / -K e = 10990000 / 4 (mm 3 )×0.07 MPa / -15.89 GPa ≈ -48.4 (mm 3 ) = -0.048 ml. For a 10 mm pipeline, the cross-sectional area of the pipeline is 78.5 (mm 2 ), that is, the length l of the 10 mm diameter pipeline occupied by the oil volume compression generated by the pipe end pressure shock ΔP = 0.07 MPa is l = ΔV / 78.5 = 48.4 / 78.5 ≈ 0.6 mm, which means the length of the pulse is less than 1 mm.

[0138] Combined with the flow rate Q = v calculated in Scheme 1 max×π / 4×d×d = 9×π / 4×0.01×0.01 = 706 ml / s. Then, use Q = ΔV / Δt to calculate the acting time Δt = ΔV / Q = 0.048 ml / 706 ml / s = 0.068 μs.

[0139] Within such a short time, the impact pulsation in the 140 m transmission pipeline impacts once and quickly returns at the end. Then, together with the new pulse at the subsequent transmitting end, according to the law of conservation of matter, a Fibonacci sequence (also known as the golden ratio sequence, referring to such a sequence: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34,... In mathematics, the Fibonacci sequence is defined recursively as follows: F(0) = 0, F(1) = 1, F(n) = F(n - 1) + F(n - 2) (n ≥ 2, n ∈ N)) of pulses can be superimposed in the pipeline, quickly increasing the pressure in the pipeline. In this way, a pressure higher than that at the end receiving end (even if the original pressure at the end has reached 20 MPa) will be established at the pipeline end, thus forming a pulsed outflow that seemingly conducts at the speed of sound along the pipeline.

[0140] Assume that this conduction speed is the speed of sound c, and the pipeline length from the impact end to the other end is L = 140 m. Then, the speed of sound c = L / Δt = 140 m / 0.068 μs = 2.043×10e 6 m / s (0.68% of the speed of light). The accurate value of the speed of light is 299792458 m / s, 2.043×10e 6 ) Therefore, it can be considered that this impact motion is a macroscopic manifestation of the diffusion motion between oil molecules.

[0141] The pipeline length is L = 140 m, the diameter is Φ10, and the 46 - grade oil liquid density ρ = 870 kg / m^3 contained in the pipeline. The volume is:

[0142] V = 140×1000×π / 4×10×10 = 10990000 / 4 (mm 3 ) = 10.99 liters

[0143] For the calculation of Δt, the resonance frequency of the pipeline system is:

[0144] f = ω / 2π = sqrt(K e / M) / 2π = sqrt(15.89×1000000000 / (870×140×π / 4×

[0145] 0.01×0.01)) / 2π ≈ 6.5×10e 3 (Hz);

[0146] Among them, Ke is the bulk modulus K of No. 46 hydraulic oil under 20 MPa e = 15.89 GPa; M = ρV is the mass of the hydraulic oil, kg;

[0147] Δtresonance = 1 / f = 1.5×10e -4 s = 150 μs;

[0148] The propagation speed of resonance, the sound speed cresonance = L / Δtresonance = 140 m / 150 μs = 9.08×10e 5 , which is slower than the impact speed calculated by the above unidirectional flow by 0.908 / 2.043 = 0.44 ≈ 1 / 2 times and is 0.3% of the speed of light (the exact value of the speed of light is 299792458 m / s). Therefore, it can be considered that this resonant motion is caused by the unidirectional diffusion motion back and forth between the hydraulic oil molecules, similar to the reciprocating swing speed of a spring oscillator.

[0149] Among them, the mass M of the hydraulic oil in the 140 - meter pipeline with a diameter of 10 mm is M = 870 kg / m 3 ×π / 4×0.01×0.01, and the stiffness K of the 20 - MPa hydraulic oil is K = K e stabilizes at 15.89 GPa.

[0150] When the main fiber grating and the secondary fiber grating in the same temperature - guiding rod adopt the same - specification Bragg grating, by comparing the peak difference Δλ between the Bragg wavelengths of the reflected light or transmitted light between the main fiber grating and the secondary fiber grating of the temperature - guiding rod, a one - to - one correspondence between Δλ and the fluid pressure P within the range of the fluid channel is established, so as to realize the measurement of the fluid pressure.

[0151] For conventional hydraulic fluids, by measuring the time difference or phase difference of the pressure signals measured by the main fiber grating and the secondary fiber grating at different positions in the fluid channel to judge the flow direction; or, only by measuring the time difference of the same pulsating pressure signal collected by the main fiber grating at different positions on the axis to judge the pulsating flow direction.

[0152] If only the main fiber grating is retained and the main fiber grating adopts a chirped grating, the change of strain can be known by measuring the reflected light intensity of the chirped grating.

[0153] The reflected light intensity ΔI R has the following relationship with the strain Δε:

[0154] |ΔI R | = k(1 - k)σξΔε;

[0155] In the formula, k is the splitting ratio, σ is the spectral density of the light source, ξ is a constant related to the fiber structure material, and Δε is the strain of the grating.

[0156] Since Δε and the fluid pressure ΔP in the fluid channel can be correlated through the reflected light intensity ΔI R to establish a corresponding relationship, thereby by establishing the corresponding relationship among ΔI R , Δε and ΔP, the measurement of the fluid pressure pulsation ΔP can be realized.

[0157] By measuring the time difference of the same pulsating ΔP pressure signal collected by the main fiber Bragg gratings at different positions in the fluid channel, the pulsating flow direction can be determined.

[0158] What is not described in the present invention can be realized by adopting or referring to the existing technologies.

[0159] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the differences between each embodiment and other embodiments are emphasized.

[0160] The above description is only for the embodiments of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A pipe joint, characterized in that, It includes a pipe joint body, a temperature guiding rod, and a fiber Bragg grating; The pipe joint body has a fluid passage through which fluid can flow; at least one mounting hole is respectively provided on at least two cross-sections perpendicular to the axis of the fluid passage; The temperature guiding rod is installed in the mounting hole; the temperature guiding rod is provided with a slit, the bottom of the slit coincides with or is parallel to the center of the temperature guiding rod, and there is a concave groove on the temperature guiding rod at the axial center of the slit for corresponding to the main fiber Bragg grating; The fiber Bragg grating includes a main fiber Bragg grating and at least one auxiliary fiber Bragg grating connected in series on the same optical fiber; the main fiber Bragg grating is located in the slit of the concave groove at the intersection of the temperature guiding rod and the fluid passage, facilitating contact with the fluid in the fluid passage; the auxiliary fiber Bragg grating is located near the main fiber Bragg grating in the optical fiber and away from the fluid in the fluid passage, and is arranged in the slit of the temperature guiding rod in the pipe joint body; The opening of the slit of the temperature guiding rod faces the fluid passage, and the slit is filled with a temperature guiding material, which is used to fix the fiber Bragg grating and conduct the fluid temperature to ensure that the main fiber Bragg grating and the auxiliary fiber Bragg grating are in the same temperature field; the main fiber Bragg grating and the auxiliary fiber Bragg grating are in different pressure strain fields, thereby detecting the fluid pressure; By comparing the magnitudes and time differences of the fluid pressure signals reflected by different main fiber Bragg gratings, it is used to detect the magnitude and propagation direction of the fluid pressure in the pipe joint body.

2. The pipe joint according to claim 1, characterized in that, Along the longitudinal section of the axis of the temperature guiding rod, a longitudinal through slit for installing the fiber Bragg grating is machined from the outside to the inside, and the depth of the slit is not greater than the diameter of the temperature guiding rod.

3. A pipe joint according to claim 1, characterized in that, The axis of the mounting hole is perpendicular to the axis of the fluid passage and is spatially staggered from the axis of the fluid passage by a preset distance, and the preset distance ensures that the mounting hole penetrates through the fluid passage, and the penetration height is not greater than the diameter of the temperature guiding rod.

4. The pipe joint according to claim 3, characterized in that, Multiple mounting holes extend along the direction perpendicular to the axial direction of the fluid passage; the multiple mounting holes are distributed on different cross-sections of the fluid passage; The spacing of the multiple mounting holes in the axial direction is equidistant or non-equidistant, and is respectively used for different test systems.

5. A pipe joint according to claim 1, characterized in that, Sealing grooves for installing sealing rings and bolt holes for high-pressure flange connection are provided in the concentric rings at both ends of the fluid passage.

6. The pipe joint according to claim 1, wherein, Filling holes are provided on both sides of the mounting hole along the axial direction perpendicular to the fluid passage, and the filling holes communicate with the mounting hole, and the filling holes are used to fill annular brazing solder.

7. A manufacturing method of a pipe joint, based on the pipe joint according to any one of the above-mentioned claims 1-6, characterized in that, The specific steps include: A mounting hole penetrating through the pipe joint body is provided in the pipe joint body along the direction perpendicular to the fluid passage; The optical fiber in which a main fiber Bragg grating and at least one auxiliary fiber Bragg grating are connected in series is pre-placed in the slit of the temperature guiding rod; The main fiber Bragg grating is fixed at the concave groove of the slit of the temperature guiding rod, and an auxiliary fiber Bragg grating is fixed in the slit on one side or both sides of the concave groove of the temperature guiding rod; the slit of the temperature guiding rod is filled with strip solder, and the strip solder is not higher than the slit of the temperature guiding rod, which is used to fix the fiber Bragg grating and can flow into the voids of the slit of the temperature guiding rod through high temperature during sintering for filling the slit, and further for sealing or conducting the temperature of the externally contacted fluid; One end of the optical fiber and the temperature guiding rod with the fiber Bragg grating fixed correspondingly are inserted from one end of the mounting hole. First, ensure that the temperature guiding rod is installed in place axially in the mounting hole, so that the concave groove of the temperature guiding rod is located at the intersection of the temperature guiding rod and the fluid passage; Rotate the heat conduction rod again to make the gap opening face the fluid channel and be perpendicular to the axis of the fluid channel of the pipe joint body; Fill the filling holes at both ends of the pipe joint body with annular brazing solder. The annular brazing solder can flow through the high temperature during sintering from the filling holes into the gap between the heat conduction rod and the mounting hole, so as to position the heat conduction rod in the pipe joint body and realize the plugging and sealing of the gap between the heat conduction rod and the mounting hole.

8. The manufacturing method of a pipe joint according to claim 7, characterized in that, The gap of the heat conduction rod is filled with strip solder. Specifically, the strip solder belongs to glass brazing solder, and the difference in thermal expansion coefficient from the optical fiber does not exceed 10%. Preferably, aluminum alloy or silver paste with good thermal conductivity is used as the strip solder to fix the fiber grating at the bottom of the gap of the heat conduction rod, so as to facilitate receiving the temperature of the fluid in the fluid channel.

9. A method of using a pipe joint, based on the pipe joint according to any one of the above claims 1-6, characterized in that, It includes: When the main fiber grating and the secondary fiber grating in the same heat conduction rod adopt Bragg gratings of the same specification, by comparing the peak difference Δλ between the Bragg wavelengths of the reflected light or transmitted light between the main fiber grating and the secondary fiber grating of the heat conduction rod, a one-to-one correspondence between Δλ and the fluid pressure P within the range in the fluid channel is established, so as to realize the measurement of the fluid pressure; By measuring the time difference or phase difference of the pressure signals measured by the main fiber grating and the secondary fiber grating at different positions in the fluid channel to judge the flow direction; or, only by measuring the time difference of the same pulsating pressure signal collected by the main fiber grating at different positions on the axis to judge the pulsating flow direction.

10. The usage method of a pipe joint as described in claim 9, characterized in that, It also includes: If only the main fiber grating is retained and the main fiber grating adopts a chirped grating, the change of strain can be known by measuring the reflected light intensity of the chirped grating; Reflected light intensity ΔI R The relationship with strain Δε is: |ΔI R | = k(1 - k)σξΔε; where k is the splitting ratio, σ is the spectral density of the light source, ξ is a constant related to the fiber structure material, and Δε is the strain of the grating; Since Δε and the fluid pressure ΔP in the fluid channel can be correlated through the reflected light intensity ΔI R a corresponding relationship can be established, and by establishing the correspondence between ΔI R , Δε and ΔP, the measurement of the fluid pressure pulsation ΔP can be achieved; By measuring the time difference of the same pulsating ΔP pressure signal collected by the main fiber grating at different positions in the fluid channel to judge the pulsating flow direction.

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