Pipe joint

Abstract

The utility model discloses a 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; by comparing the time difference of fluid pressure signals reflected by different main fiber gratings, the conventional fluid pulsation and propagation direction in the pipe joint main body can be detected.

Description

Technical Field

[0001] This utility model belongs to the field of fluid equipment technology, and specifically relates to a pipe connector. Background Technology

[0002] The elastic modulus of hydraulic fluid varies greatly from 0.9 to 2.0 GPa, which often leads to slow response characteristics of hydraulic systems, especially when used for long-distance transmission. For example, the hydraulic response of traditional aircraft flight control mechanisms is slow and fails to meet design requirements. Therefore, this is one of the reasons why the aviation industry is increasingly inclined 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, EHA electro-hydraulic actuators are costly and require multiple pump stations for operation. This leads to redundant construction of multiple pump stations even in a small work area. The efficiency of each pump station's hydraulic system is inherently low; the overall efficiency of a motor-driven fixed displacement pump's valve control system is typically around 30%, with the asynchronous motor at 80%–87%, the fixed displacement pump at 90%–95% volumetric efficiency, and the valve-controlled cylinder system at a maximum efficiency of 38%. Without considering overflow losses from the relief valve, this is 87% * 95% * 38% = 31.8%. This results in significant energy waste at multiple pump stations, including those with shortened hydraulic pipelines for EHA electro-hydraulic actuators. A new centralized, high-flow-rate pump source with no overflow losses is needed. Furthermore, the pumps need to be supplied to distant hydraulic equipment, which leads to increased friction losses along long-distance pipelines, resulting in insufficient flow at the end of the pipeline and slower equipment response. Therefore, an innovative development of long-distance discrete high-speed hydraulic transmission has emerged.

[0003] Industrial hydraulic oils typically exhibit a stable elastic modulus around 20 MPa; for example, the elastic modulus of No. 46 hydraulic oil remains relatively stable between 1.4 and 1.6 GPa at around 20 MPa. This stable characteristic provides a foundation for long-distance discrete hydraulic transmission. Generally speaking, from a macroscopic perspective, the elastic modulus measures an object's resistance to elastic deformation. A higher value indicates a greater stress required for elastic deformation, meaning greater material stiffness and less elastic deformation under a given stress. The properties of the modulus depend on the nature of the deformation. The modulus under shear deformation is called the shear modulus, denoted by G; the modulus under compressive deformation is called the compressive modulus, denoted by K; and the elastic modulus, denoted by E, is used to calculate the dimensional changes of a rod made of isotropic elastic material under tensile or compressive loads in the case of uniaxial stress with tensile or compressive stress in one direction. The Young's modulus of metallic materials can fluctuate by 5% or more depending on alloy composition, heat treatment state, and cold plastic deformation. However, generally speaking, the elastic modulus of metallic materials is a mechanical property that is insensitive to microstructure. Alloying, heat treatment (fibrous structure), and cold plastic deformation have relatively small effects on the elastic modulus, and external factors such as temperature and loading rate also have little impact. Therefore, the elastic modulus of metals is generally considered a constant in engineering applications. In contrast, the effective bulk elastic modulus of oil, usually referring to the compressible state, fluctuates by much more than 5% within the range of 0.9–2.0 GPa, and is not constant. Many factors influence the overall bulk elastic modulus of oil, primarily including the gas content, oil pressure, oil temperature, container stiffness, and the contact conditions between the oil and air. Gas content is the most significant factor affecting the bulk elastic modulus of oil. When air is mixed into hydraulic oil, its compressibility increases significantly. When the oil contains 1% gas (in the form of bubbles), the elastic modulus drops to 35.6% of that of pure oil. However, with the same initial gas content and a pressure higher than the air separation pressure, the air in the gas-liquid mixture completely dissolves after a sufficiently long period of pressure exceeding the air separation pressure, and the bulk elastic modulus remains essentially unchanged. Furthermore, it is generally accepted that the bulk elastic modulus of hydraulic oil is minimally affected by pipeline accessories and the amount of air dissolved in the oil, and can be ignored. Therefore, the stability of the elastic modulus required for long-distance oil transmission is easily controlled and achieved.

[0004] From the formula for the bulk elastic modulus of oil The reciprocal of the value, i.e., the compressibility of the oil. From the interpolation calculations of the experimental data in the table, we know that p = 20MPa (the interpolation between 19.4425 and 20.7275MPa is 20.0845MPa). The capacity V of the long-distance hydraulic pipeline remains almost unchanged at the instant of pressure (p + Δp) impact at a certain pipe end. The elastic modulus of hydraulic oil No. 46... K eThe interpolation value of 15.665 GPa, which is basically stable between 15.438 and 15.892 GPa, is usually under the standby pressure condition of the hydraulic servo valve. Its response speed is relatively fast, that is, the response time is short, and there is not only pressure gain but also flow gain.

[0005] It should be noted that the frequency characteristic of an electro-hydraulic flow servo valve is defined as the complex ratio of the valve's no-load control flow rate to the control current when the control current undergoes a sinusoidal change within a certain frequency range. A typical 21MPa 30L valve responds at 70Hz, and the reciprocal of its response frequency is the response time t = 1 / 70 = 0.014s. Therefore, this impact reaches the other end in less than 0.1s. Even if a regular mechanical pressure gauge can achieve a resolution of Δp, and disregarding the delay of the mechanical gauge, it is difficult for the human eye (typically performing integral calculations within 0.2s) to detect and observe. Therefore, an electronic hydraulic gauge is needed to capture and distinguish this impact. As an important measuring tool, pressure gauges have key parameters such as range, accuracy, resolution, overload capacity, and operating temperature. Hydraulic pulsations are common in conventional hydraulic transmission. However, conventional electronic hydraulic gauges, such as piezoelectric pressure gauges, have limitations in capturing and distinguishing high-frequency pressure pulsations in hydraulic transmission because they acquire signals through charge accumulation integration. Therefore, there is an urgent need for new sensors that can sensitively capture hydraulic pulsation signals.

[0006] Although the existing patent application CN202010132418.3, entitled "A Composite Sensor for Detecting Fluid Parameters in Pipelines," uses Bragg gratings for pressure signal acquisition, which can effectively capture and distinguish such pressure pulsation signals, its sensor incorporates too many fiber gratings, resulting in high manufacturing costs. The use of optical switches for signal acquisition further increases measurement costs. Moreover, the gratings in this patented sensor are uniformly distributed Bragg gratings, requiring simultaneous measurement of reference signals (such as temperature) to distinguish pressure. To prevent temperature signal acquisition from being affected by external stress, the gratings are placed in specific locations within the sensor. Due to current manufacturing limitations, it is difficult to make them compact. While this utility model's larger sensor can be widely applied in large pipelines for other hazardous chemical fluids, its application in the engineering machinery industry, with its smaller pipelines, is difficult to promote.

[0007] Experiments revealed that the effective bandwidth of the chirped grating varies with strain but is insensitive to temperature. This characteristic can be used to measure hydraulic pressure pulsations. In the experiment, the strain variation was determined by measuring the reflected light intensity of the chirped grating. The reflected light intensity ΔI... R The relationship with strain Δε is: 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 fitting that is more compact and suitable for the acquisition of hydraulic pressure and pulsation signals in conventional fluid or novel long-distance discrete transmission, for the measurement of pressure pulsation in long-distance discrete flow pipelines at around 20MPa and for pipeline connections for pulsation flow transmission. Utility Model Content

[0009] This invention provides a pipe connector that offers a more compact design for acquiring hydraulic pressure and pulsation signals in long-distance discrete fluid transmission. It is used for measuring pressure pulsations within long-distance discrete flow pipelines at approximately 20 MPa and for connecting pipelines that facilitate pulsating flow transmission. This provides a necessary basic component for long-distance discrete fluid transmission.

[0010] The technical solution adopted in this utility model is as follows:

[0011] A pipe fitting includes a pipe fitting body, a temperature-conducting rod, and a fiber optic grating;

[0012] The pipe fitting body has a fluid channel through which fluid can flow; at least one mounting hole is provided on at least two cross sections along the axis perpendicular to the fluid channel.

[0013] A temperature-conducting rod is installed in the mounting hole; the temperature-conducting rod has a slit, the bottom of the slit coincides with or is parallel to the center of the temperature-conducting rod, and the temperature-conducting rod at the axial center of the slit has a recessed groove to correspond to the main fiber grating.

[0014] A fiber optic grating comprises a main fiber optic grating and at least one secondary fiber optic grating connected in series. The main fiber optic grating is located in the gap of the recessed groove where the temperature-conducting rod intersects with the fluid channel, facilitating contact with the fluid in the fluid channel. The secondary fiber optic grating is located near the main fiber optic grating in the fiber and away from the fluid in the fluid channel, and is disposed in the gap of the temperature-conducting rod within the pipe fitting body.

[0015] The opening of the temperature-conducting rod faces the fluid channel, and the gap is filled with a temperature-conducting material. The temperature-conducting material is used to fix the fiber grating and conduct fluid temperature to ensure that the main fiber grating and the secondary fiber grating are in the same temperature field. The main fiber grating and the secondary fiber grating are in different pressure and strain fields, thereby detecting fluid pressure.

[0016] By comparing the magnitude and time difference of the fluid pressure signal reflected by different master fiber gratings, the magnitude and propagation direction of the fluid pressure inside the pipe fitting body can be detected.

[0017] The pipe fitting of this utility model also has the following additional technical features:

[0018] A longitudinal through-slit for installing a fiber optic grating is machined from the outside to the inside along the longitudinal section of the temperature-conducting rod. The depth of the slit is no greater than the diameter of the temperature-conducting rod.

[0019] The axis of the mounting hole is perpendicular to the axis of the fluid channel and intersects the axis of the fluid channel by a preset distance. The preset distance ensures that the mounting hole and the fluid channel penetrate each other, and the height of penetration is not greater than the diameter of the temperature conducting rod.

[0020] Multiple mounting holes extend along an axial direction perpendicular to the fluid channel; multiple mounting holes are distributed on different cross-sections of the fluid channel;

[0021] Multiple mounting holes are spaced equidistantly or non-equidistantly along the axial direction, and are used for different testing systems.

[0022] A sealing groove for installing a sealing ring and bolt holes for high-pressure flange connection are provided in the coaxial rings at both ends of the fluid channel.

[0023] Filling holes are provided on both sides of the mounting hole along the axial direction perpendicular to the fluid channel. The filling holes are connected to the mounting hole and are used to fill the annular brazing filler.

[0024] This application also relates to a method for manufacturing a pipe fitting, based on the aforementioned pipe fitting, the specific steps of which include:

[0025] An installation hole is made inside the pipe fitting body in a direction perpendicular to the fluid channel, penetrating the pipe fitting body.

[0026] Beforehand, insert one fiber of a main fiber Bragg grating and at least one fiber of a secondary fiber Bragg grating into the gap of the temperature-conducting rod.

[0027] The main fiber grating is fixed in the recessed groove of the temperature-conducting rod, and a secondary fiber grating is fixed in the gap on one or both sides of the recessed groove of the temperature-conducting rod. The gap of the temperature-conducting rod is filled with strip solder, which is not higher than the gap of the temperature-conducting rod. It is used to fix the fiber grating and can flow into the gap of the temperature-conducting rod through high temperature during sintering to fill the gap, thereby sealing and conducting the temperature of the external contact fluid.

[0028] Insert one end of the optical fiber and the corresponding temperature-conducting rod with the fiber grating fixed in place into one end of the mounting hole. First, ensure that the temperature-conducting rod is installed in the axial direction of the mounting hole so that the groove of the temperature-conducting rod is located at the intersection of the temperature-conducting rod and the fluid channel.

[0029] Then rotate and adjust the temperature guide rod so that the slit opening faces the fluid channel and is perpendicular to the axis of the fluid channel of the pipe fitting body;

[0030] The filling holes at both ends of the pipe fitting body are filled with annular brazing filler. During sintering, the annular brazing filler can flow from the filling holes into the gap between the temperature-conducting rod and the mounting hole through high temperature, thereby positioning the temperature-conducting rod inside the pipe fitting body and sealing the gap between the temperature-conducting rod and the mounting hole.

[0031] The gaps of the temperature-conducting rod are filled with strip solder, specifically, the strip solder is a glass brazing solder, and the difference in thermal expansion coefficient between it and 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 grating is fixed at the bottom of the gap of the temperature-conducting rod, which is convenient for receiving the temperature of the fluid in the fluid channel.

[0032] This application also relates to a method of using a pipe fitting, based on the above-described pipe fitting, comprising:

[0033] If the main fiber grating and the secondary fiber grating are Bragg gratings of the same specification, by comparing the peak difference Δλ between the reflected or transmitted light of the main fiber grating and the secondary fiber grating in the same fiber in the same temperature guide bar gap, a one-to-one correspondence between Δλ and the fluid pressure P in the fluid channel is established, thereby realizing the measurement of fluid pressure.

[0034] The flow direction can be determined 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; or, the pulsating flow direction can be determined by measuring the time difference of the same pulsating pressure signal collected by the main fiber grating at different positions on the axis.

[0035] A method of using a pipe connector further includes: if only the main fiber grating is retained and the main fiber grating is a chirped grating, the strain change 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: 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.

[0037] Because Δε and the fluid pressure ΔP in the fluid channel can be correlated with the reflected light intensity ΔI R By establishing a correspondence between ΔIR, Δε, and ΔP, the fluid pressure pulsation ΔP can be measured.

[0038] The direction of pulsating flow is determined by measuring the time difference between the acquisition of the same pressure signal by the main fiber optic grating at different locations in the fluid channel.

[0039] Due to the adoption of the above technical solution, the beneficial effects achieved by this utility model are as follows:

[0040] 1. Compared with the pipe fitting assembly for multi-parameter fluid measurement disclosed in patent application number CN202010132410.7, this application uses fewer gratings, reduces the number of optical fibers to two, and reduces the number of gratings to two, resulting in lower manufacturing costs, simpler and more practical manufacturing, and is more conducive to widespread application.

[0041] 2. Compared with conventional pressure sensors, this application is more sensitive to pressure pulsations, which is more conducive to capturing and detecting pressure signals in pulsating DC hydraulic transmission, and is beneficial to the control and feedback calculation of hydraulic discrete transmission.

[0042] 3. The pipe fitting interface of this application adopts O-ring sealing and flange connection with concentric circles, which can withstand pressure and impact of more than 20MPa.

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

[0044] 5. The pipe fitting body of this application has a fluid channel through which fluid can flow; multiple mounting holes are staggered along the axial direction of the fluid channel, and a temperature-conducting rod is installed in the mounting hole. The main fiber grating is installed in the groove of the temperature-conducting rod and can contact the fluid in the fluid channel; the secondary fiber grating is installed on one side inside the temperature-conducting rod; it is used to remove interference from the fluid temperature or vibration signal of the pipe fitting body in the main grating, so as to improve the detection accuracy of the main grating for fluid pressure; by comparing the signals of the main grating in at least two temperature-conducting rods, it is used to detect the direction of fluid pulsation propagation and the magnitude of pulsation pressure amplitude in the pipe fitting.

[0045] 6. In this application, filling holes communicating with mounting holes are provided on both sides along the axial direction perpendicular to the fluid channel. These filling holes are used to fill with annular brazing filler metal, which enters the gaps in the temperature-conducting rod and the gaps between the temperature-conducting rod and the inner wall of the fluid channel through the filling holes. By setting the gap width and length, 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 correctly positioned on the temperature-conducting rod by the strip brazing filler metal, and ensuring sealing quality and long-term stability. Attached Figure Description

[0046] The accompanying drawings, which are included to provide a further understanding of the present invention and constitute a part of this invention, illustrate exemplary embodiments of the present invention and, together with the description thereof, serve to explain the present invention and do not constitute an undue limitation thereof. In the drawings:

[0047] Figure 1 This is a schematic diagram of the structure of a pipe connector according to one embodiment of the present invention;

[0048] Figure 2 for Figure 1 Schematic diagram of the cross section at point AA;

[0049] Figure 3 This is a typical curve showing the relationship between the orifice flow coefficient and the Reynolds number;

[0050] In the picture,

[0051] 1. Pipe fitting; 2. Fluid channel; 3. Mounting hole; 4. Main fiber grating; 5. Secondary fiber grating; 6. Temperature guide rod; 7. Sealing groove; 8. Recessed groove; 9. Filling hole; 10. Annular brazing filler; 11. Gap. Detailed Implementation

[0052] Many specific details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0053] Furthermore, it should be understood in the description of this utility model that the terms "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", 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 utility model 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 utility model.

[0054] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0055] In this invention, unless otherwise expressly specified and limited, the first feature "on" or "below" the second feature may be in direct contact with the first and second features, or indirect contact through an intermediate medium. In the description of this specification, references to terms such as "implementation," "example," "aspect," or "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0056] To more clearly illustrate the overall concept of this utility model, a detailed description will be provided below with reference to the accompanying drawings.

[0057] This application relates to a pipe fitting 1, such as Figures 1-2 As shown, it includes the main body of the pipe connector 1, the temperature conducting rod 6, and the fiber optic grating;

[0058] The pipe fitting 1 body has a fluid channel 2 through which fluid can flow; at least one mounting hole 3 is provided on at least two vertical cross sections along the axis of the vertical fluid channel 2.

[0059] A temperature-conducting rod 6 is installed in the mounting hole 3; the temperature-conducting rod 6 has a slit 11, the bottom of the slit 11 coincides with or is parallel to the center of the temperature-conducting rod 6, and the temperature-conducting rod 6 at the axial center of the slit 11 has a recessed groove 8 for corresponding to the main fiber grating 4.

[0060] The fiber optic grating comprises a main fiber grating 4 and at least one secondary fiber grating 5 connected in series. The main fiber grating 4 is located in the gap 11 of the groove 8 where the temperature-conducting rod 6 intersects with the fluid channel 2, facilitating contact with the fluid in the fluid channel 2. The secondary fiber grating 5 is located near the main fiber grating 4 in the optical fiber and away from the fluid in the fluid channel 2, and is disposed in the gap 11 of the temperature-conducting rod 6 within the main body of the pipe connector 1.

[0061] The opening of the slit 11 of the temperature-conducting rod 6 faces the fluid channel 2. The slit 11 is filled with a temperature-conducting material, which is used to fix the fiber grating and conduct fluid temperature to ensure that the main fiber grating 4 and the secondary fiber grating 5 are in the same temperature field. The main fiber grating 4 and the secondary fiber grating 5 are in different pressure and strain fields, thereby detecting fluid pressure. By comparing the fluid pressure signals or time differences reflected by different main fiber gratings 4, the fluid pulsation and propagation direction in the main body of the pipe joint 1 can be detected.

[0062] In this application, the temperature-conducting rod 6 can be a cylindrical structure or a strip structure, and the specific shape is not limited. The temperature-conducting rod 6 is preferably a cylindrical structure, which can be easily formed through simple machining to reduce costs. A slit 11 can be set in the middle of the temperature-conducting rod 6 using wire cutting. The slit 11 is used to place at least two gratings of the same specification connected in series. One main grating is located in the fluid channel 2 within the body of the pipe connector 1, where it can directly contact the liquid in the channel. The other auxiliary grating is located in the part of the temperature-conducting rod 6 brazed to the inside of the body of the pipe connector 1, used to remove interference from the fluid temperature or vibration signal of the pipe connector 1 body on the main grating, thereby improving the detection accuracy of the fluid pressure by the main grating. At least two through holes are respectively set at different cross-sectional positions in the axial direction within the fluid channel 2 to accommodate the temperature-conducting rod 6. By comparing the signals of the main grating in at least two locations of the temperature-conducting rod 6, the direction of fluid pulsation propagation and the magnitude of the pulsation pressure amplitude within the pipe connector 1 can be detected.

[0063] Table 1 Measured values ​​of hydraulic oil volumetric elastic modulus under different pressures

[0064]

[0065] From the reciprocal of the formula for the bulk modulus of hydraulic fluid, i.e., the compressibility of the fluid, and the interpolation calculation of the experimental data in Table 1, we know that p = 20 MPa (the interpolation between 19.4425 and 20.7275 MPa is 20.0845 MPa). For a long-distance hydraulic pipeline, the capacity V remains almost unchanged at the instant of pressure (p + Δp) impact at a certain pipe end. The elastic modulus K of hydraulic oil No. 46... e The interpolated value, approximately 15.665 GPa, remains relatively stable between 15.438 and 15.892 GPa. At this point, the oil in the long-distance transmission pipeline, having been in a standby state at 20 MPa for an extended period, will dissolve any free air bubbles present, thus maintaining the oil's bulk elastic modulus at a constant 15.665 GPa. In other words, the oil's bulk elastic modulus exhibits quasi-rigidity, allowing the calculation of elastic deformation using the definition of the elastic modulus of metals: deformation ΔV / V = P / K. e =20MPa / 15.665GPa=0.00127. Therefore, for a pipeline with a diameter of 10mm, the total length of the transmission pipeline between the two hydraulic devices in the two workshops is 140m. The total oil capacity in the pipeline is V=140×1000×π / 4×10×10=10990000 (mm²). 3 With a pressure of approximately 10.99 liters, at a pipe end of 20 MPa, the maximum recoverable elastic pulse deformation ΔV = 0.00127 × 10⁹⁹⁰⁰⁰⁰⁰⁰ ≈ 13957 mm can occur. 3=13.957 ml, which means that in an oil volume of V≈10.99 liters, at 20 MPa, 13.957 ml / 10990 ml = 0.126% of the oil can be injected. This injected oil will occupy a pipe length of 10 mm diameter of ΔL = ΔV / (π / 4 × 10 × 10) = 13957 / (π / 4 × 10 × 10) = 177.8 mm. Due to the limiting effect of the steel pipe, the linear increase in the average length of the pipe is ΔL / L = 177.8 mm / 140 m = 1.27%. The linear increase of ΔL / L can also be considered a characteristic of the pulse attenuation rate. If the pipe diameter is increased from 10mm to 20mm, then ΔL=ΔV / (π / 4×20×20)=44.45mm, ΔL / L=44.45mm / 140m=0.03%. Therefore, the pulse attenuation rate is smaller, and the distance between the main grating fibers in the temperature guide bar can be set shorter.

[0066] A 140m long pipeline with a 10mm diameter, assuming it is similar to a narrow orifice, then its flow rate is directly proportional to the pressure difference, as shown below:

[0067]

[0068] Where Q is the outflow rate from the throttling orifice, d is the pipe diameter, l is the pipe length, μ = ρυ, μ is the dynamic viscosity of the oil (Pa·s), and υ is the kinematic viscosity (m). 2 / s, ρ is density kg / m 3 The kinematic viscosity υ of No. 46 hydraulic oil is generally 46 mm. 2 / s, ρ density is 0.85kg / L (the density of No. 46 hydraulic oil is 850~870kg / m³). 3 (between), so μ = 0.85 × 46 = 39.1 (mPa·s); A0 is the cross-sectional area of ​​the throttling orifice outlet; pressure difference ΔP is the pressure difference before and after the throttling orifice;

[0069] For the impact flow rate in this case, the outflow flow rate from the throttling orifice can be expressed as: the volume of the impact pulse ΔV divided by the impact duration Δt.

[0070] Q=ΔV / Δt

[0071] Furthermore, when the impact duration Δt is short, the change in pulse rising pressure is:

[0072] Δp=K e ×ΔV / V

[0073] From the above formula, we can obtain:

[0074] Impact duration Δt = 128μ × l × V / (K e×π / 4×d×d×d×d)=128×(39.1 / 1000)×140×(10990000 / 1000000000) / 15.665GPa / (π / 4×0.01×0.01×0.01×0.01)≈4.26×10e 15 (hours), then the change in pulse pressure Δp = 128μ×l×ΔV / (π / 4×d×d×d×d) / Δt will also be infinitesimal.

[0075] Therefore, the impinging flow in a 140m long pipe with a diameter of only 10mm cannot be assumed to be similar to a narrow orifice. That is, laminar flow with infinitesimal pressure changes can exist in a 140m long pipe with a diameter of only 10mm over a long period of time. If an instantaneous impinging flow is to be formed, it cannot be generated by a long orifice.

[0076] In a macroscopic space, the molecules of a medium are relatively stationary. Energy is transferred only through the exchange of momentum Δmc via impact. Generally, the speed of sound c remains constant; only the mass Δm is conducted through changes in the medium's density. Assuming the average density of the oil in the pipeline is ρ, the increased oil density at the impact end leads to a local increase in density due to the oil impacting out but not being conducted away. The high-density oil, due to the high-speed thermal diffusion of its molecules, will conduct the impact along the pipeline at the speed of sound c. The pipeline length from the impact end to the other end is L. Then, the time difference between the impact received at the other end is Δt = L / c.

[0077] Assuming the propagation speed of the impact compression wave in the hydraulic oil is the speed of sound c, approximately 1472 m / s, and the total length of the transmission pipeline between the two hydraulic devices in the two workshops is 140 m, then Δt = 140 / 1472 = 0.095 s. The impact reaches the other end in less than 0.1 s. To achieve the maximum transmission amount equal to the maximum elastic pulse deformation ΔV = 0.00127 × 10⁹⁹⁰⁰⁰⁰⁰⁰⁰ ≈ 13957 mm,... 3 How is 13.957 ml achieved? It requires flow through a thin-walled throttling orifice. The method is as follows:

[0078] Based on the highest frequency of 100Hz currently used by the digital switching valve of Guizhou Mangewei Fluid Intelligent Technology Co., Ltd., the impact time Δt = 1 / 100Hz = 0.01s, and the maximum conduction ΔV' = maximum elastic pulse deformation ΔV = 0.00127 × 10990000 ≈ 13957mm. 3 =13.957 ml, calculated flow rate is:

[0079] Q max =13.957ml / 0.01s=1.39L / s=83.4L / min;

[0080] Obviously, due to the influence of pipe wall friction and oil viscosity, the flow in the pipeline is subject to flow saturation. Therefore, it is not easy to achieve a pipe with a diameter of 10mm. Therefore, in order to increase the flow rate, the pipe diameter can be increased, thereby forming a thin-walled throttling orifice structure.

[0081] To avoid the direct proportionality between pressure difference and flow rate in long orifices, we first calculate the flow rate q through a thin-walled orifice based on energy conservation and Bernoulli's equation. This flow rate q is proportional to the square root of the pressure difference, as shown below:

[0082]

[0083] Where Q is the outflow rate from the throttling orifice, and C d ρ is the flow coefficient, typically a maximum of 0.7; A0 is the cross-sectional area of ​​the orifice outlet; ρ is the fluid density; and ΔP is the pressure difference across the orifice.

[0084] Among them, regarding the flow coefficient C d Experiments have yielded a typical curve showing the relationship between the orifice flow coefficient and the Reynolds number, as follows: Figure 3 As shown, according to the paper "Re-examination of Cavitation Mechanism" from the ICFPMCE2024 conference, regarding the flow coefficient C... d The latest research findings are as follows:

[0085] The flow rate calculation formula derived from Bernoulli's equation:

[0086]

[0087] In the formula: C d ρ is the flow rate correction factor; A0 is the flow area; ΔP is the pressure difference potential energy between the orifices; ρ is the fluid density.

[0088] Flow revision factor C d If the total is less than 100%, then if the flow coefficient C is... d Substituting this into the above formula, it can be seen that the pressure potential energy contained in the pressure difference ΔP within the square root is not entirely converted into the kinetic energy of the fluid flow. If the flow is considered as a one-dimensional pipe, with the flow area A0 remaining constant, the pressure difference potential energy between the orifices, besides being partially converted into fluid flow, still acts on the pipe wall in the normal direction through continuous thermal motion, indirectly providing the fluid with a supporting force in the flow direction of the orifices. (Without this pressure difference supporting force to ensure flow, one scenario is that it becomes a static communicating vessel, where the fluid no longer flows and the pressure difference between the two ends is 0; another is that it flows in an open one-dimensional flow tube, such as a river, where the pressure head difference between the two ends directly acts on the fluid flow, thus forming a...) Figure 3The parabolic shape of the flow coefficient before 0.7 increases with increasing pressure or velocity (without needing a pressure difference to accumulate on the walls at both ends of the orifice). The energy in both parts is essentially the thermal motion of fluid molecules. Therefore, under the average effect of thermal motion, the energy in both parts should be balanced, each accounting for half of the pressure difference potential energy ΔP between the orifices (half for the pressure head maintaining flow, half for fluid flow). Therefore, according to the above formula, the orifice flow coefficient will not exceed the square root of 1 / 2, i.e., 0.707, and this deduction is consistent with... Figure 3 The flow coefficient C at the throttling orifice in a typical curve relating flow coefficient to Reynolds number. d The results are comparable to the typical experimental value of 0.7, indicating that this method of calculating the flow coefficient using energy balance has a certain degree of reliability.

[0089] right Figure 3 The flow coefficient C at the throttling orifice in a typical curve relating flow rate coefficient to Reynolds number. d After reaching 0.7, the pressure difference potential energy decreases with increasing flow velocity, then gradually stabilizes at around 0.6. This indicates that in one-dimensional turbulent flow (torn cavitation flow) in a pipe, besides a portion of the pressure difference potential energy acting on the pipe wall in the normal direction to provide support in the direction of fluid flow, two other portions of the pressure difference potential energy are converted into fluid flow kinetic energy and oscillation energy generated by the continuous annihilation of cavitation bubbles produced by high-speed tearing. These three portions of energy remain balanced at the molecular thermal motion level. Therefore, according to the principle of energy balance, the pressure difference potential energy required for fluid flow only accounts for 1 / 3 of the pressure difference potential energy ΔP between the orifices. Therefore, the flow coefficient is:

[0090]

[0091] The above theoretical explanation, based on the energy conversion from the equilibrium of molecular thermal motion, provides the origin of the maximum value of the flow coefficient (0.7) and the stable value (0.6). Furthermore, this conclusion is consistent with the results obtained experimentally. Figure 3 The typical curves showing the relationship between flow coefficient and Reynolds number reflect a good fit for flow coefficients of 0.7 and 0.6, which further demonstrates the credibility of this application's hypothesis regarding tearing cavitation caused by excessively fast flow.

[0092] Based on the above research, the flow coefficient C of the throttling orifice... d Once the flow coefficient reaches 0.7, tearing free cavitation will occur. Based on the aforementioned research, free cavitation significantly affects the elastic modulus of the oil, thus impacting the high-speed pulsating flow in this case. Therefore, the flow coefficient C of the throttling orifice should be controlled. d Achieving 0.7 is optimal; the Reynolds number should be at least no greater than C. d =100 at 0.7.

[0093] In experimental data Figure 3 In the middle, when the flow velocity v = v c Assuming that the fluid molecules maintain a close-packed, rigid spherical structure, then the average distance between molecules in the orifice reaches the tearing (vaporization) distance r. a However, because the fluid's three-dimensional space only has one dimension r in the flow direction... a ≈10r0, due to the approximate incompressibility of the fluid, the molecular distance in other directions remains basically no greater than r0, and the density ρ at the front end of the orifice is... up ≈ρ, therefore, the fluid density in the orifice decreases by about 10 times, ρ down ≈ρ / 10; therefore, the pressure difference potential energy ΔP is not only used to ensure the flow velocity v=v in the throttling orifice. c Furthermore, the spatial confinement of the tube wall is necessary to ensure that the molecular density ρ in the non-flow direction remains constant. The energy required to maintain both the density difference and the flow is equal under the equilibration effect of molecular thermal motion, as shown in experimental data. Figure 3 The flow coefficient C of the throttling orifice d =sqrt(1 / 2) corresponds to the Reynolds number R. e =100, then the Reynolds number in the middle of the orifice is:

[0094]

[0095] From the above formula, the critical existence of tearing cavitation leads to a decrease in oil density of approximately 1 / 10. Typically, the Reynolds number R we calculate... e The oil density used is the average value under normal temperature and pressure, such as the critical Reynolds number R. e A value of 2300 is better than the above. Figure 3 The critical Reynolds number for laminar and turbulent flow in the study is 100, which is an order of magnitude larger and 2.3 times greater. Comparing the Reynolds number measured at 2300 with that obtained from typical experimental data, the ratio of these two values ​​is used as a revision value for density or viscosity changes. (C...) d The Reynolds number R at =0.7 e =100 The velocity of the flow out of the throttle orifice is calculated as follows:

[0096] v max =(2300 / 100×100)×μ / ρ / d / =2300υ / d

[0097] Substituting the kinematic viscosity of oil No. 46, υ = 46 mm² / s, and d = 10 mm, into the above formula, we can obtain the maximum flow velocity without tearing bubbles as v. max =2300×46 / 10 / 1000=10.58m / s, to be on the safe side, we choose v max =9m / s, then the outflow rate from the throttle orifice is:

[0098] Q=v max ×π / 4×d×d=9×π / 4×0.01×0.01=706ml / s=42L / min max 83.4 L / min

[0099] Furthermore, from the above formula It can also be seen that the greater the pressure difference, the greater the impact flow should be. However, due to factors such as pipe wall friction and oil viscosity, the pipeline flow exhibits flow saturation. Although the flow coefficient remains stable at C... d A value of around 0.6 can simplify calculations, but it leads to the aforementioned problems of fluid cavitation and density reduction, which in turn affects the transmission loss caused by the decrease in the elastic modulus of the oil. Therefore, it is necessary to control the pressure difference ΔP at the transmitting end; from Q=v max ×π / 4×d×d=42 liters / min It can be calculated in reverse:

[0100] ΔP = (v max / C d )^2×ρ / 2=(9 / 0.7)^2×870 / 2=71908Pa=0.07MPa

[0101] Compared to 20 MPa, the pressure difference change is only 0.35%. Such a large pressure difference can be emitted with only a small disturbance, which is easy to achieve.

[0102] Compared to the pipe fitting assembly for multi-parameter fluid measurement disclosed in patent application CN202010132410.7, this application uses fewer gratings, reducing the number of optical fibers to two (ideally two) and the number of gratings to two. Furthermore, it eliminates the need for a difficult-to-manufacture ellipsoidal shell as a carrier, using only an easily fabricated, slit metal rod, resulting in lower manufacturing costs, simpler and more practical production, and greater ease of application. It is more sensitive to pressure pulsations than conventional pressure sensors, making it better suited for capturing and detecting pressure signals in pulsating DC hydraulic transmission, thus facilitating control and feedback calculations in discrete hydraulic transmission. The pipe fitting interface uses O-ring seals and flange connections, capable of withstanding pressures and impacts exceeding 20 MPa. In addition, the diameter of the temperature-conducting rod is less than half the diameter of the fluid channel, and the connection length between the temperature-conducting rod and the pipe fitting body, along with the small gap, ensures sufficient sealing and allows it to withstand pressures and impacts exceeding 20 MPa.

[0103] In a preferred embodiment, a longitudinal through-slit 11 for installing a fiber optic grating is machined from the outside to the inside along the longitudinal section of the temperature-conducting rod 6. The depth of the slit 11 is not greater than the diameter of the temperature-conducting rod 6.

[0104] ​Along the longitudinal section of the temperature-conducting rod 6, a longitudinal through-slit 11 for installing the fiber optic grating is processed from the outside to the inside using wire cutting or sawing. The depth of the slit 11 is preferably cylindrical, and the depth of the slit 11 is not greater than the radius of the temperature-conducting rod 6, so as to ensure that the position for installing the main fiber optic grating 4 is reserved.

[0105] The opening of the slit 11 faces the fluid channel 2 and is perpendicular to the axis of the fluid channel 2 of the pipe joint 1; the part that obstructs the flow of fluid is cut off at the position where the temperature-conducting rod 6 intersects with the fluid channel 2, so that after the cut-off, the bottom of the slit 11 of the temperature-conducting rod 6 is connected to the fluid channel 2 or the connection distance between the bottom of the slit 11 and the fluid channel 2 is less than half the depth of the slit 11.

[0106] More preferably, the depth of the gap 11 is the radius length of the cylindrical heat-conducting rod 6.

[0107] During use, after drilling the mounting hole 3, first glue the main fiber grating 4, the secondary fiber grating 5 and the temperature guide rod 6 together, and place them in the corresponding holes of the pipe connector 1. Then adjust the position of the main grating in the fluid channel 2 of the pipe connector 1. Then fill the annular brazing filler 10 holes 9 at both ends of the transverse hole of the pipe connector 1 where the temperature guide rod 6 is installed with sufficient annular brazing filler 10. This is used to fill the gap between the temperature guide rod 6 and the transverse hole of the pipe connector 1 and the wire cut groove of the temperature guide rod 6 for installing the fiber grating during sintering. By setting the width and length of the gap 11, it can be ensured that the main grating is slightly constrained by the brazing filler in the correct position of the temperature guide rod 6.

[0108] In a preferred embodiment, the axis of the mounting hole 3 is perpendicular to the axis of the fluid channel 2 and spatially offset from the axis of the fluid channel 2 by a predetermined distance. This predetermined distance ensures that the mounting hole 3 penetrates the fluid channel 2, and the height of the penetration is no greater than the diameter of the temperature-conducting rod 6. This ensures that the temperature-conducting rod 6 is mostly embedded deep within the pipe joint 1, with only the recessed area of ​​the temperature-conducting rod 6 where the main grating is located having the closest contact with the fluid, thus experiencing the fluid pressure most directly. Therefore, the temperature transmitted to the secondary grating via brazing or the temperature-conducting rod 6 is in the same temperature field as the main grating. By comparing the wavelength variation of the Bragg grating between the main and secondary gratings, the oil pressure can be obtained.

[0109] When they intersect, the mounting hole 3 and the fluid channel 2 form an intersection line. Here, the intersection line is the common line of the two solid surfaces and also the boundary line between the two solid surfaces. The points on the intersection line are the common points of the two solid surfaces. The intersection lines formed are not separated from each other, avoiding the situation where two separate intersection lines are formed by crossing each other.

[0110] In a preferred embodiment, a plurality of mounting holes 3 extend in a direction perpendicular to the axial direction of the fluid channel 2; the plurality of mounting holes 3 are distributed on different cross sections of the fluid channel 2;

[0111] Multiple mounting holes 3 are spaced equidistantly or non-equidistantly along the axial direction, respectively used for different testing systems.

[0112] Multiple mounting holes 3 extend along the axial direction perpendicular to the fluid channel 2, so that the mounting holes 3 penetrate the main body of the pipe joint 1, which facilitates the installation of the temperature conducting rod 6. The mounting holes 3 are provided with brazing filler spaces at both ends to facilitate the placement of brazing filler.

[0113] The multiple mounting holes 3 allow for the placement of the temperature-conducting rod 6 at different positions. This enables the extraction of pressure information from different positions before and after the fluid channel 2 within the pipe joint 1, thereby obtaining the direction of fluid pulsation propagation and the magnitude of the pulsation pressure amplitude within the pipe joint 1.

[0114] The mounting holes 3 are spaced equidistantly or non-equidistantly along the axial direction to achieve different estimation accuracy for fluid pulse flow rates; the diameter of the mounting holes 3 is generally smaller than the diameter of the fluid channel 2. The spacing between two mounting holes 3 along the axial direction can be set differently according to different system pulsation conditions, facilitating rapid processing of computer-acquired data.

[0115] In a preferred embodiment, a sealing groove 7 for installing a sealing ring and bolt holes for high-pressure flange connection are provided in the coaxial rings at both ends of the fluid channel 2.

[0116] The O-ring seals and flange connections installed in the sealing grooves at both ends of the pipe joint 1 can ensure that there is no leakage at the end face under pressure impact of more than 20MPA. The long distance between the temperature conducting rod 6 and the pipe joint 1 and the small annular gap 11 can ensure that the brazing material of high-temperature welding can withstand pressure impact of at least 20MPA without leakage in the gap 11.

[0117] In a preferred embodiment, filling holes 9 are provided on both sides of the mounting hole 3 in the axial direction perpendicular to the fluid channel 2. The filling holes 9 communicate with the mounting hole 3 and are used to fill the annular brazing filler 10.

[0118] Filling holes 9, communicating with mounting holes 3, are provided on both sides along the axial direction perpendicular to the fluid channel 2. The filling holes 9 are used to fill with annular brazing filler 10, which enters the gap 11 of the temperature-conducting rod 6 and the gap between the temperature-conducting rod 6 and the inner wall of the fluid channel 2 through the filling holes 9. By setting the width and length of the gap 11 and selecting the brazing material, the compatibility between the glass and the brazing material can be effectively improved, ensuring that the main fiber grating 4 and the secondary fiber grating 5 are correctly positioned on the temperature-conducting rod 6 by the strip brazing filler, and ensuring sealing quality and long-term stability.

[0119] The annular brazing filler 10 can be made of glass brazing filler. Glass brazing filler has a composition and properties similar to glass, allowing for sealing through a single, ordinary heat treatment step. Its coefficient of thermal expansion matches the substrate, resulting in high sealing strength, good airtightness, and excellent aging resistance, making it a good sealing material for vacuum glass. Many metal materials are suitable for sealing with glass brazing filler, effectively connecting the main fiber grating 4 to the temperature-conducting rod 6, as well as the secondary fiber grating 5 to the temperature-conducting rod 6. Suitable metal materials include indium alloys, Kovar alloys, aluminum alloys, and silver paste. These metal materials generally have low melting points, good mechanical properties, and excellent corrosion resistance. During the sealing process, the molten metal material fully wets the glass, forming a good chemical bond through element diffusion, thus achieving an effective seal.

[0120] It is important to note that the key to achieving a high-strength connection between the main fiber grating 4 and the temperature-conducting rod 6, and between the secondary fiber grating 5 and the temperature-conducting rod 6, lies in two points. First, the coefficients of thermal expansion of the annular brazing material and the substrate must be very close (the difference should not exceed 10%). During the sealing process, their expansion curves should be as consistent as possible; otherwise, the seal may crack or experience chronic leakage. Second, the annular brazing material 10 must be able to wet the substrate surface; this is another crucial condition for successful sealing. Increasing the surface roughness of the substrate can further optimize the wetting and curing effect of the brazing material, which is typically achieved through sanding or sandblasting. Alternatively, increasing the cleanliness of the substrate surface, ensuring it is free of grease, dust, and other impurities, can be achieved through solvent cleaning or mechanical polishing.

[0121] For any parts not mentioned in this utility model, existing technologies can be used or referenced.

[0122] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0123] The above description is merely an embodiment of this utility model and is not intended to limit the scope of this utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this utility model should be included within the scope of the claims of this utility model.

Claims

1. A pipe fitting, characterized in that, Includes the pipe fitting body, temperature conducting rod, and fiber optic grating; The pipe fitting body has a fluid channel through which fluid can flow; at least one mounting hole is provided on at least two cross sections along the axis perpendicular to the fluid channel. The temperature-conducting rod is installed in the mounting hole; the temperature-conducting rod has a slit, the bottom of the slit coincides with or is parallel to the center of the temperature-conducting rod, and the temperature-conducting rod at the axial center of the slit has a recessed groove for corresponding to the main fiber grating. The fiber grating includes a main fiber grating and at least one secondary fiber grating connected in series. The main fiber grating is located in the gap of the recessed groove where the temperature-conducting rod intersects with the fluid channel, which facilitates contact with the fluid in the fluid channel. The secondary fiber grating is located near the main fiber grating in the fiber and away from the fluid in the fluid channel, and is located in the gap of the temperature-conducting rod inside the pipe joint body. The opening of the temperature-conducting rod faces the fluid channel, and the gap is filled with a temperature-conducting material. The temperature-conducting material is used to fix the fiber grating and conduct fluid temperature to ensure that the main fiber grating and the secondary fiber grating are in the same temperature field. The main fiber grating and the secondary fiber grating are in different pressure and strain fields, thereby detecting fluid pressure. By comparing the magnitude and time difference of the fluid pressure signal reflected by different master fiber gratings, the magnitude and propagation direction of the fluid pressure inside the pipe fitting body can be detected.

2. A pipe fitting as described in claim 1, characterized in that, A longitudinal through-slit for installing a fiber optic grating is machined from the outside to the inside along the longitudinal section of the temperature-conducting rod. The depth of the slit is no greater than the diameter of the temperature-conducting rod.

3. A pipe fitting as described in claim 1, characterized in that, The axis of the mounting hole is perpendicular to the axis of the fluid channel and intersects the axis of the fluid channel by a preset distance. The preset distance ensures that the mounting hole and the fluid channel penetrate each other, and the height of penetration is not greater than the diameter of the temperature conducting rod.

4. A pipe fitting as described in claim 3, characterized in that, Multiple mounting holes extend along an axial direction perpendicular to the fluid channel.

5. A pipe fitting as described in claim 4, characterized in that, Multiple mounting holes are distributed on different cross sections of the fluid channel.

6. A pipe fitting as described in claim 5, characterized in that, Multiple mounting holes are spaced equidistantly or non-equidistantly along the axial direction, and are used for different testing systems.

7. A pipe fitting as described in claim 1, characterized in that, A sealing groove for installing a sealing ring and bolt holes for high-pressure flange connection are provided in the coaxial rings at both ends of the fluid channel.

8. A pipe fitting as described in claim 1, characterized in that, Filling holes are provided on both sides of the mounting hole along the axial direction perpendicular to the fluid channel. The filling holes are connected to the mounting hole and are used to fill the annular brazing filler.

9. A pipe fitting as described in claim 8, characterized in that, The difference between the coefficient of thermal expansion of the annular brazing filler and the coefficient of thermal expansion of the pipe fitting body shall not exceed 10%.

10. A pipe fitting as described in claim 1, characterized in that, The gap depth is equal to the radius of the heat-conducting rod.

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