A low start-up flow rate differential pressure optical fiber grating flow sensor

Abstract

A kind of low start-up flow differential pressure type fiber grating flow sensor, first main pipe and second main pipe are detachably connected with nozzle, the end of first main pipe and second main pipe is provided with joint, first main pipe side wall is machined with first pressure tapping, first pressure tapping is provided with first straight pipe sleeve, first straight pipe sleeve is connected with sensing assembly by steel pipe assembly and is communicated, second main pipe side wall is machined with second pressure tapping, and the aperture of second pressure tapping is same with first pressure tapping, second pressure tapping is provided with second straight pipe sleeve, and sensing assembly is supported and connected with second straight pipe sleeve by pipe assembly and is communicated with sensing assembly.The present application adopts double fiber grating structure to compensate temperature, eliminates the cross-sensitivity problem of temperature strain, and the double fiber grating structure is combined with differential pressure sensing structure, which significantly improves the sensitivity, meets the measurement requirements of small flow, has low start-up flow, fast response, corrosion resistance and other advantages.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of measurement or testing, and particularly relates to a fiber grating flow sensor. BACKGROUND

[0002] Flow is an important indicator parameter in modern industrial production, and accurate measurement of flow data is crucial to improve industrial productivity. Although the traditional electric flowmeter has been widely used, it has certain limitations, such as high start-up flow, inability to measure high-temperature and high-pressure fluids, and susceptibility to external electromagnetic interference. Compared with traditional electric flowmeters, fiber grating flow sensors have the advantages of anti-electromagnetic interference, low loss, high temperature resistance, high pressure resistance, and corrosion resistance, making them more suitable for parameter measurement in harsh environments. The principle of the differential pressure type flow sensor based on Bragg grating is that when the fluid passes through the throttling element, a pressure difference is generated before and after the throttling element. The pressure difference is transmitted to the pressure-taking pipe through the pressure-taking hole and acts on the metal diaphragm, causing the metal diaphragm to deform and the center wavelength of the Bragg grating pasted on the metal diaphragm to change, thereby achieving the purpose of measuring flow.

[0003] Chinese Patent No. CN202648714U discloses a "micro tube diameter high pressure nozzle flow device based on fiber grating micro pressure difference sensing", which uses a diaphragm fixed at one end of the pressure-taking cavity and connected by threads. This fixing method has some problems. For example, the two end pressure-taking cavities are easy to drive the grating during rotation, causing damage to the fiber grating. The fiber grating sensor is fixed on one side of the alloy diaphragm, and the fiber grating sensor does not have temperature compensation function, has low sensitivity and inaccurate measurement due to temperature influence, and is only suitable for high pressure flow measurement. The nozzle of the device is fixed in a hexagonal thick wall pipe, and the range is fixed and cannot be changed.

[0004] Chinese Patent No. CN102095451A, entitled "Fiber Grating Liquid Flow Sensor with Temperature Compensation", discloses that elastic tongues are pasted on both sides of the fiber grating. During measurement, the elastic tongues are directly placed into the liquid pipeline for measurement, which is a target type flow sensor. The elastic tongues are directly driven to deform by the impact of the fluid on one side. The disadvantage of this structure is short service life, uneven stress due to fluid impact fluctuation, large data error obtained by testing, easy to fall off, and damage to the pipeline after falling off. Due to the difference between the diaphragm type and the elastic tongue type structures, the double grating temperature compensation of the diaphragm type structure is more difficult to achieve than the elastic tongue type, which is also the reason why the traditional differential pressure type diaphragm structure does not have double grating temperature compensation.

[0005] At present, there is an urgent need for a fiber grating flow sensor with low start-up flow measurement, high sensitivity and high accuracy. SUMMARY

[0006] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a low-starting-flow differential pressure diaphragm fiber grating flow sensor which is reasonable in design, compact in structure, high in sensitivity and measurement accuracy, replaceable in range, and long in service life.

[0007] The technical solution adopted to solve the above technical problems is: a low-starting-flow differential pressure fiber grating flow sensor, a nozzle is detachably connected between a first main pipeline and a second main pipeline, the end portions of the first main pipeline and the second main pipeline are provided with joints, a first pressure tapping hole is processed on the side wall of the first main pipeline, a first straight pipe sleeve is arranged on the first pressure tapping hole, the first straight pipe sleeve is connected in communication with a sensing assembly through a steel pipeline assembly, a second pressure tapping hole is processed on the side wall of the second main pipeline, the second pressure tapping hole has the same diameter as the first pressure tapping hole, a second straight pipe sleeve is arranged on the second pressure tapping hole, the second straight pipe sleeve supports the sensing assembly and is connected in communication with the sensing assembly through a pipeline assembly; the sensing assembly is an annular mounting seat which is threadedly connected between a first sealing cover and a second sealing cover, a metal diaphragm and an annular gasket are arranged on one side of the annular mounting seat from inside to outside, the metal diaphragm divides a cavity formed by the first sealing cover, the second sealing cover and the annular mounting seat into independent first pressure tapping cavities and second pressure tapping cavities which have the same volume, the first pressure tapping cavities are in communication with the first pressure tapping holes a, the second pressure tapping cavities are in communication with the second pressure tapping holes, a first fiber mounting hole is radially processed on the annular mounting seat on one side of the metal diaphragm, a first optical fiber is mounted in the first fiber mounting hole, a first grating is inscribed on the first optical fiber, the portion of the first optical fiber on which the first grating is inscribed is encapsulated on one side of the metal diaphragm through high-temperature glue, a second fiber mounting hole is radially processed on the annular mounting seat on the other side of the metal diaphragm, a second optical fiber is mounted in the second fiber mounting hole, a second grating is inscribed on the second optical fiber, the portion of the second optical fiber on which the second grating is inscribed is encapsulated on the other side of the metal diaphragm through high-temperature glue, and the first fiber mounting hole and the second fiber mounting hole are sealed through high-temperature glue.

[0008] As a preferred technical solution, the diameter of the first pressure tapping hole is 2-6 mm.

[0009] As a preferred technical solution, an annular boss is processed on the inner wall of the middle part of the annular mounting seat, a metal diaphragm and an annular gasket are sequentially arranged on one side of the annular boss from inside to outside, the metal diaphragm is pasted on the side of the annular boss through glue, two symmetrical positioning holes are processed on the side of the boss on which the metal diaphragm is pasted, two positioning columns which match the positioning holes are processed on the annular gasket, and the positioning columns are located in the positioning holes; internal threads are processed on both sides of the annular boss of the annular mounting seat, and are used for connecting the first sealing cover and the second sealing cover.

[0010] As a preferred technical solution, the grating area length of the first grating is the same as that of the second grating, and the center wavelengths are not equal.

[0011] As a preferred technical solution, the metal diaphragm has a thickness of 0.3-0.5 mm and is made of copper or stainless steel.

[0012] As a preferred technical solution, the nozzle is an ISA1932 standard nozzle.

[0013] As a preferred technical solution, the pipe assembly is provided with a connecting pipe connected to the two ends of the elbow sleeve.

[0014] As a preferred technical solution, the nozzle is connected to the first main pipe and the second main pipe through flanges.

[0015] The present application has the following advantages:

[0016] The present application is provided with a threaded connection between the first sealing cover and the second sealing cover, and a ring-shaped mounting seat is arranged between the first sealing cover and the second sealing cover. A metal diaphragm is arranged in the middle of one side of the ring-shaped mounting seat from the inside to the outside. The metal diaphragm divides the cavity formed by the first sealing cover, the second sealing cover and the ring-shaped mounting seat into a first pressure taking cavity and a second pressure taking cavity which are independent and have the same volume. First and second optical fibers are arranged on the ring-shaped mounting seat on both sides of the metal diaphragm. A portion of the first optical fiber inscribed with a first grating is packaged on one side of the metal diaphragm by high-temperature glue, and a portion of the second optical fiber inscribed with a second grating is packaged on the other side of the metal diaphragm by high-temperature glue. The metal diaphragm is isolated from the first sealing cover by the ring-shaped gasket. The ring-shaped mounting seat prevents the optical fiber grating from directly contacting the sealing cover, thereby avoiding the problem of damage to the optical fiber grating caused by rotation during installation. The ring-shaped mounting seat is threadedly connected between the first sealing cover and the second sealing cover, which facilitates the packaging of the double optical fiber grating and overcomes the defect that the membrane is directly connected to the fixed cover on one side in the prior art "Micro-pipe diameter high-pressure nozzle flow device based on optical fiber grating micro-pressure difference sensing".

[0017] The present application uses a double optical fiber grating structure for temperature compensation, eliminating the cross-sensitivity problem of temperature strain. The double optical fiber grating structure combined with the differential pressure sensing structure significantly improves the sensitivity and meets the measurement requirements of small flow. The present application is suitable for complex downhole testing requirements and has the advantages of low start-up flow, fast response and corrosion resistance, etc., and realizes real-time monitoring of low start-up fluid flow in oil and gas wells. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a structural schematic diagram of the present application.

[0019] Figure 2 is a mounting schematic diagram of the first optical fiber 8 of the present application.

[0020] Figure 3 is a mounting schematic diagram of the second optical fiber 10 of the present application.

[0021] Wherein: the first main pipe 1; the first straight pipe sleeve 2; the pipe assembly 3; the first sealing cover 4; the annular mounting seat 5; the annular gasket 6; the metal diaphragm 7; the first optical fiber 8; the second sealing cover 9; the second optical fiber 10; the second straight pipe sleeve 11; the second main pipe 12; the nozzle 13; the joint 14; the first grating 15; the second grating 16; the first pressure tapping hole a; the second pressure tapping hole b; DETAILED DESCRIPTION

[0022] The application will be further described in detail below in combination with the drawings and examples, but the application is not limited to the following embodiments.

[0023] Example 1

[0024] In Figure 1 , 2 , 3, the low start-up flow differential pressure type optical fiber grating flow sensor of the embodiment is provided with a nozzle 13 between the first main pipe 1 and the second main pipe 12 through a flange connection, and the range replacement is realized by replacing nozzles 13 of different sizes. The nozzle 13 of the embodiment is an ISA1932 standard nozzle, the throat diameter of the nozzle 13 is 15.516 mm, the diameter ratio is 0.597, the end portions of the first main pipe 1 and the second main pipe 12 are provided with joints 14 for being connected with the measured pipe, the first main pipe 1 is provided with a first pressure tapping hole a on the side wall, the hole diameter of the first pressure tapping hole a is 4 mm, the first straight pipe sleeve 2 is welded on the first pressure tapping hole a, the first straight pipe sleeve 2 is connected with the sensing assembly through the steel pipe assembly 3, the second main pipe 12 is provided with a second pressure tapping hole b on the side wall, the hole diameter of the second pressure tapping hole b is the same as that of the first pressure tapping hole a, the second straight pipe sleeve 11 is welded on the second pressure tapping hole b, the second straight pipe sleeve 11 supports the sensing assembly through the pipe assembly 3 and is connected with the other end of the sensing assembly.

[0025] The sensing assembly of the embodiment is that the annular mounting seat 5 is threadedly connected between the first sealing cover 4 and the second sealing cover 9, an annular boss is processed on the inner wall of the middle part of the annular mounting seat 5, a metal diaphragm 7 and an annular gasket 6 are sequentially arranged from inside to outside on the left side surface of the annular boss, the annular gasket 6 is used for protecting the metal diaphragm 7, the thickness of the metal diaphragm 7 is 0.4 mm, the material of the metal diaphragm 7 is copper, the metal diaphragm 7 is glued on the side surface of the annular boss, two symmetrical positioning holes are processed on the side surface of the boss to which the metal diaphragm 7 is glued, two positioning columns matched with the positioning holes are processed on the annular gasket 6, the positioning columns are located in the positioning holes, inner threads are processed on the two sides of the annular boss of the annular mounting seat 5, which are used for connecting the first sealing cover 4 and the second sealing cover 9, the metal diaphragm 7 divides the cavity formed by the first sealing cover 4, the second sealing cover 9 and the annular mounting seat 5 into independent and same-volume first pressure taking cavities and second pressure taking cavities, the first pressure taking cavities are communicated with the first pressure taking holes a, the second pressure taking cavities are communicated with the second pressure taking holes b, a first optical fiber mounting hole is radially processed on the annular mounting seat 5 on one side of the metal diaphragm 7, a first optical fiber 8 is mounted in the first optical fiber mounting hole, a first grating 15 is engraved on the first optical fiber 8, the grating area length of the first grating 15 is 5 mm, and the center wavelength is 1531.906 nm, the part of the first optical fiber 8 on which the first grating 15 is engraved is encapsulated on one side surface of the metal diaphragm 7 by high-temperature glue, a second optical fiber mounting hole is radially processed on the annular mounting seat 5 on the other side of the metal diaphragm 7, a second optical fiber 10 is mounted in the second optical fiber mounting hole, a second grating 16 is engraved on the second optical fiber 10, the grating area length of the second grating 16 is 5 mm, and the center wavelength is 1538.017 nm, the part of the second optical fiber 10 on which the second grating 16 is engraved is encapsulated on the other side surface of the metal diaphragm 7 by high-temperature glue, and the first optical fiber mounting hole and the second optical fiber mounting hole are sealed by high-temperature glue.

[0026] The pipeline assembly 3 of the embodiment is that connecting pipes are connected at the two ends of the elbow pipe clamp.

[0027] The working principle of the embodiment is as follows:

[0028] The application is installed on the measured pipeline, the fluid in the pipeline passes through the nozzle 13 between the first main pipeline 1 and the second main pipeline 12, so that the fluid entering the first pressure taking hole a and the second pressure taking hole b forms a pressure difference, the fluid entering the first pressure taking hole a passes through the pipeline into the first pressure taking cavity and acts on the metal diaphragm 7, the fluid entering the second pressure taking hole b passes through the pipeline into the second pressure taking cavity and acts on the metal diaphragm 7, the metal diaphragm 7 deforms, thereby causing the center wavelength drift of the first grating 15 and the second grating 16, the fluid flow is measured in a differential form, and the difference Δλ between the center wavelength drifts of the first grating 15 and the second grating 16 is 21 related to the measured volumetric flow Q v as follows:

[0029]

[0030] In the formula, A0 is the minimum diameter end area of the nozzle 13, A0 = 15.5 mm, β is the throat diameter ratio of the nozzle 13, β = 0.597, t is the thickness of the metal diaphragm 7, t = 0.4 mm, E is the Young's modulus of the diaphragm material, E = 2 x 10 11 P a v is the Poisson ratio, v = 0.32, P e is the effective photoelastic coefficient of the optical fiber, P e = 0.22, and K is a constant introduced in equivalent representation of the average strain suffered by the optical fiber grating.

[0031] The present application eliminates the cross-sensitivity problem of temperature strain and improves the sensitivity.

[0032] Example 2

[0033] In this embodiment, the nozzle 13 is connected between the first main pipe 1 and the second main pipe 12 through a flange, the throat diameter of the nozzle 13 is 18.576 mm, the diameter ratio is 0.599, the first pressure tapping hole a is processed on the side wall of the first main pipe 1, the hole diameter of the first pressure tapping hole a is 2 mm, the second pressure tapping hole b is processed on the side wall of the second main pipe 12, the hole diameter of the second pressure tapping hole b is the same as that of the first pressure tapping hole a, the first straight pipe sleeve 2 is welded on the first pressure tapping hole a, the first straight pipe sleeve 2 is connected in communication with the sensing assembly through the steel pipe assembly 3, the second pressure tapping hole b is processed on the side wall of the second main pipe 12, the hole diameter of the second pressure tapping hole b is the same as that of the first pressure tapping hole a, the second straight pipe sleeve 11 is welded on the second pressure tapping hole b, the second straight pipe sleeve 11 is connected in communication with the sensing assembly through the pipe assembly 3. The sensing assembly is an annular mounting seat 5 threadedly connected between the first sealing cover 4 and the second sealing cover 9, an annular boss is processed on the inner wall of the middle part of the annular mounting seat 5, a metal diaphragm 7 and an annular gasket 6 are sequentially arranged from inside to outside on the left side surface of the annular boss, the annular gasket 6 is used for protecting the metal diaphragm 7, the thickness of the metal diaphragm 7 is 0.3 mm, and the material is 304 stainless steel. The other components and the connection relationship of the components are the same as those of Example 1.

[0034] Example 3

[0035] In the embodiment, the nozzle 13 is connected between the first main pipeline 1 and the second main pipeline 12 through flanges, the throat diameter of the nozzle 13 is 21.526 mm, the diameter ratio is 0.598, the first pressure tapping hole a is processed on the side wall of the first main pipeline 1, the hole diameter of the first pressure tapping hole a is 6 mm, the second pressure tapping hole b is processed on the side wall of the second main pipeline 12, the hole diameter of the second pressure tapping hole b is the same as that of the first pressure tapping hole a, the first straight pipe sleeve 2 is welded on the first pressure tapping hole a, the first straight pipe sleeve 2 is connected with the sensing assembly through the steel pipeline assembly 3, the second pressure tapping hole b is processed on the side wall of the second main pipeline 12, the hole diameter of the second pressure tapping hole b is the same as that of the first pressure tapping hole a, the second straight pipe sleeve 11 is welded on the second pressure tapping hole b, the second straight pipe sleeve 11 is connected with the sensing assembly through the pipeline assembly 3 and is connected with the other end of the sensing assembly. The sensing assembly is that the annular mounting seat 5 is threadedly connected between the first sealing cover 4 and the second sealing cover 9, the inner wall of the middle part of the annular mounting seat 5 is processed with an annular boss, the left side surface of the annular boss is sequentially provided with a metal diaphragm 7 and an annular gasket 6 from inside to outside, the annular gasket 6 is used for protecting the metal diaphragm 7, the thickness of the metal diaphragm 7 is 0.5 mm, and the material is 304 stainless steel. The connection relationship of other components is the same as that of the embodiment 1.

Claims

1. A fiber Bragg grating flow sensor for low start-up flow differential pressure, characterized in that... The first main pipe and the second main pipe are detachably connected with a nozzle, the end of the first main pipe and the end of the second main pipe are provided with a joint, a first pressure tapping hole is processed on the side wall of the first main pipe, a first straight pipe sleeve is arranged on the first pressure tapping hole, the first straight pipe sleeve is connected with a sensing assembly through a steel pipe assembly, a second pressure tapping hole is processed on the side wall of the second main pipe, the diameter of the second pressure tapping hole is the same as that of the first pressure tapping hole, a second straight pipe sleeve is arranged on the second pressure tapping hole, the second straight pipe sleeve supports a sensing assembly and is connected with the sensing assembly; the sensing assembly is an annular mounting seat which is threadedly connected between a first sealing cover and a second sealing cover, a metal diaphragm and an annular gasket are arranged on one side of the annular mounting seat from inside to outside, the metal diaphragm divides the cavity formed by the first sealing cover, the second sealing cover and the annular mounting seat into a first pressure tapping cavity and a second pressure tapping cavity which are independent and have the same volume, the first pressure tapping cavity is connected with the first pressure tapping hole a, the second pressure tapping cavity is connected with the second pressure tapping hole, a first fiber installation hole is radially processed on one side of the annular mounting seat of the metal diaphragm, a first optical fiber is installed in the first fiber installation hole, a first grating is written on the first optical fiber, the part of the first optical fiber on which the first grating is written is packaged on one side of the metal diaphragm through high-temperature glue, a second fiber installation hole is radially processed on the other side of the annular mounting seat of the metal diaphragm, a second optical fiber is installed in the second fiber installation hole, a second grating is written on the second optical fiber, the part of the second optical fiber on which the second grating is written is packaged on the other side of the metal diaphragm through high-temperature glue, and the first fiber installation hole and the second fiber installation hole are sealed through high-temperature glue; An annular boss is processed on the inner wall of the middle part of the annular mounting seat, the metal diaphragm is pasted on the side of the annular boss, two symmetrical positioning holes are processed on one side of the boss to which the metal diaphragm is pasted, two positioning columns matched with the positioning holes are processed on the annular gasket, and the positioning columns are located in the positioning holes; internal threads are processed on both sides of the annular boss of the annular mounting seat, and are used for being connected with the first sealing cover and the second sealing cover; The thickness of the metal diaphragm is 0.3-0.5 mm, and the material is copper or stainless steel.

2. The low start-up flow rate differential pressure optical fiber grating flow sensor of claim 1, wherein The diameter of the first pressure tapping hole is 2-6 mm.

3. The low start-up flow rate differential pressure optical fiber grating flow sensor of claim 1, wherein The grating area length of the first grating is the same as that of the second grating, and the center wavelengths are not equal.

4. The low start-up flow rate differential pressure optical fiber grating flow sensor of claim 1, wherein The nozzle is an ISA1932 standard nozzle.

5. The low start-up flow rate differential pressure optical fiber grating flow sensor of claim 1, wherein The pipe assembly is a connecting pipe connected at both ends of a bend pipe sleeve.

6. The low-startup-flow differential pressure fiber optic grating flow sensor of claim 1, wherein The nozzle is connected with the first main pipe and the second main pipe through flanges.

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