A flat flow channel and flow meter system with ultrasonic trap structure

Abstract

The present invention discloses a flat flow channel with an ultrasonic trap structure, wherein the cross section of the flat flow channel is a rectangle, and the length L of the cross section is greater than the height H; an ultrasonic sensor is arranged at the center of the upper and lower directions of the two side walls of the flat flow channel, respectively, and the axes of the two ultrasonic sensors are on the same straight line, and the angle between the axes and the flow direction of the flat flow channel is Φ; a plurality of strip grids are arranged along the flow direction on the upper and lower inner wall surfaces of the flat flow channel, and together with the corresponding inner wall surfaces, an ultrasonic trap structure is formed; the arrangement spacing d of the strip grids is 2λ~5λ, and the height of the strip grids is wherein λ is the ultrasonic wavelength emitted by the ultrasonic sensor, c is the medium sound velocity, ΔT is the delay time expected to be brought by the ultrasonic trap structure, and β is the incident angle of the ultrasonic signal incident on the trap structure. By using the present invention, the superposition problem of ultrasonic reflection signals and effective target signals in the flat flow channel can be effectively solved, and accurate measurement of gas flow can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of measuring instruments, and in particular to a flat flow channel and a flow meter system with an ultrasonic trap structure. Background Art

[0002] As people pay more and more attention to the environment, natural gas as a clean and environmentally friendly green energy has received more and more attention and application, and the natural gas industry will develop rapidly in the future. In order to meet the development needs of the natural gas industry, especially the development needs of gas companies for natural gas metering and pipeline distribution management, under the background of the development of information technology, ultrasonic gas flow meters have gradually played an increasingly important role in natural gas metering and distribution management.

[0003] At present, the flow meters used in natural gas metering and distribution management in China are mainly Roots meters and turbine meters. Both of these metering instruments are mechanical metering instruments and are difficult to get rid of the inherent weaknesses of mechanical meters. For example, they have high requirements on the quality of natural gas, are prone to getting stuck, require frequent maintenance and have high maintenance costs. At the same time, as the diameter of the natural gas transmission pipeline increases, the size, weight and price of the two mechanical metering instruments will increase significantly. These weaknesses have seriously restricted the development of natural gas metering and pipeline distribution management towards the direction of "precision, stability, intelligence and efficiency".

[0004] In order to overcome the shortcomings of mechanical metering instruments, ultrasonic flow meters have appeared in the prior art. The current flow meter flow channel design is mainly based on a flow channel with a circular cross-section, and there are also designs of flat flow channels with a rectangular cross-section. When the flow area is constant, compared with the circular flow channel, the flat flow channel has a smaller fixed size, which can limit the size of large eddies; at the same time, when the flow rate is constant, the Reynolds coefficient of the flattened flow channel fluid is higher and it is easier to enter the turbulent area. Therefore, a flat flow channel is conducive to the stability of the flow state.

[0005] For example, a Chinese patent document with publication number CN105043474A discloses a new flow channel structure for an ultrasonic flow meter, including a measuring flow channel body and two ultrasonic transducers. The measuring flow channel body is a rectangular parallelepiped, and the two ultrasonic transducers are simultaneously arranged on the front side or the rear side of the measuring flow channel body in the horizontal direction.

[0006] The Chinese patent document with publication number CN110285861A discloses an ultrasonic flowmeter, which includes a fluid chamber, an ultrasonic sensor, and a data acquisition and processing device; the fluid chamber is a through-going long tube, and the two ends of the tube are compressed and deformed from a circular tube toward the center of the tube to form a rectangular tube; the ultrasonic sensor is arranged on the side wall of the rectangular tube in the fluid chamber, and is data-connected to the data acquisition and processing device.

[0007] However, due to the problems of signal reflection and superposition of ultrasonic signals in conventional flat flow channels, flat flow channels suffer from problems such as signal attenuation and distortion in actual applications, which limits their scope of application. Summary of the invention

[0008] The present invention provides a flat flow channel with an ultrasonic trap structure, in which an ultrasonic trap structure is formed on the flow channel wall to delay, attenuate and offset the ultrasonic signal. The ultrasonic trap structure can effectively solve the problem of superposition of reflected signals and effective target signals of ultrasonic signals in conventional flat flow channels, and helps the flow meter system to achieve accurate measurement of gas flow.

[0009] A flat flow channel with an ultrasonic trap structure, wherein the cross section of the flat flow channel is a rectangle, and the length L of the cross section is greater than the height H; an ultrasonic sensor is arranged at the center of the two side walls in the upper and lower directions, respectively, the axes of the two ultrasonic sensors are on the same straight line, and the angle between the axes and the flow direction of the flat flow channel is Φ;

[0010] A plurality of strip grids are arranged on the upper and lower inner wall surfaces of the flat flow channel along the flow direction, and together with the corresponding inner wall surfaces, they form an ultrasonic trap structure; the ultrasonic trap structure is used to reflect the incident ultrasonic signal multiple times and cause attenuation, and at the same time, cause the emitted ultrasonic signal to produce a longitudinal displacement;

[0011] The arrangement spacing d of the strip grid is 2λ~5λ, and the height of the strip grid is Among them, λ is the wavelength of the ultrasonic wave emitted by the ultrasonic sensor, c is the sound velocity of the medium, ΔT is the delay time expected to be caused by the ultrasonic trap structure, and β is the incident angle of the ultrasonic signal incident on the trap structure.

[0012] In the present invention, multiple reflections of the signal in the trap structure will cause signal amplitude attenuation and longitudinal displacement, both of which can weaken the superposition effect formed at the receiving end by the signal that finally reaches the receiving end.

[0013] Preferably, the ratio of the length L to the height H of the cross section is not less than 3.

[0014] Theoretically, Φ≠90° is sufficient. In practical applications, preferably, the angle Φ between the axes of the two ultrasonic sensors and the longitudinal axis of the flat flow channel is 30° to 60°.

[0015] In practical applications, preferably, the heights of all the strip grids are unified to the height of the strip grid located in the middle.

[0016] Preferably, the thickness t of the strip grid is less than half of the ultrasonic wavelength λ emitted by the ultrasonic sensor, so as to prevent the ultrasonic signal from being effectively reflected at the top of the strip grid and reaching the ultrasonic sensor at the receiving end.

[0017] Alternatively, the top of the strip grid is designed to be other shapes that can prevent the ultrasonic signal from being reflected by the top of the grid and reaching the sensor at the receiving end.

[0018] Preferably, the length of the strip grid runs through the entire flat channel, and its shape is rectangular, or may be other shapes such as zigzag, wavy, etc., as long as it can effectively block the reflected ultrasonic signal to prevent it from reaching the receiving sensor.

[0019] Sufficient gaps should be left between the strip grids on the upper and lower inner walls for ultrasonic signal propagation to avoid affecting the effective propagation of ultrasonic signals along a straight path. Preferably, the spacing between the strip grids arranged on the upper and lower inner walls of the flat flow channel is not less than 0.6D, that is, H-2h≥0.6D.

[0020] While completing multiple reflections of the ultrasonic signal, the ultrasonic trap structure also causes attenuation of the ultrasonic signal. Even if the beam reaches the receiving end after being emitted, its intensity will be weakened. In addition, it also causes longitudinal displacement of the ultrasonic signal. Even if the beam reaches the wall where the receiving sensor is located after being emitted, it deviates from or even moves away from the effective receiving surface of the receiving sensor and cannot form a superposition with the effective target signal that is sufficient to affect the quality of the target effective signal.

[0021] The present invention also provides a flow meter system, including a measuring flow channel, wherein the measuring flow channel is composed of the above-mentioned flat flow channel with an ultrasonic trap structure; wherein the measuring flow channel is composed of one flat flow channel, or is composed of a plurality of flat flow channels superimposed on each other.

[0022] The flow meter system also includes a temperature sensor and a pressure sensor for completing the conversion of the gas operating flow rate to the standard flow rate.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention utilizes a carefully designed strip grid and the pipe wall in which it is located to form an ultrasonic trap structure that can delay, attenuate and offset the ultrasonic signal, effectively improving the reflection and superposition problem of the ultrasonic signal in the flat pipe. At the same time, with the help of the rectifying effect of the strip grid, the ultrasonic flow meter using the flat pipe can achieve higher metering performance.

[0025] In addition, the smaller size of the flat channel limits the size of the eddy current in the channel, thereby reducing the impact of the eddy current on the ultrasonic signal. Furthermore, the strip grid also has a rectifying effect, and due to the deeper depth of the grid, the flow capacity of a single channel is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1A schematic diagram of the ultrasonic trap structure and the incident, reflected and emitted signals in the ultrasonic trap structure in the present invention;

[0027] Figure 2 It is a schematic diagram of various incident, reflected and emitted events of ultrasonic signals in the ultrasonic trap structure;

[0028] Figure 3 It is a schematic diagram of the ultrasonic superposition principle after passing through an effective ultrasonic trap structure;

[0029] Figure 4 A schematic diagram of the delay of an ultrasonic signal injected into a flat flow channel using an ultrasonic trap structure;

[0030] Figure 5 Schematic diagram of the longitudinal deviation of the signal in a flat flow channel with an ultrasonic trap structure;

[0031] Figure 6 A schematic diagram of a flat channel structure and its parameters using an ultrasonic trap structure;

[0032] Figure 7 Schematic diagram of the superposition of three flat flow channels with ultrasonic trap structures. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0034] As a theoretical basis, the principle of using ultrasound to measure gas flow is briefly described as follows: The principle of using ultrasound to measure gas flow is the ultrasonic time difference method, which uses the (downstream) acceleration and (backstream) deceleration of the ultrasonic signal by the fluid, measures the propagation time of the ultrasonic wave in the downstream and backstream directions respectively, and then uses the difference between the two to calculate the medium flow rate, and finally obtains the medium flow rate. In other words, how to accurately identify the ultrasonic signal and accurately calculate the ultrasonic signal propagation time is the key to whether it can be accurately measured. In other words, all factors that affect the stable propagation of the ultrasonic signal will affect the measurement accuracy.

[0035] In the present invention, "ultrasonic trap structure" is defined as a physical structure that can cause ultrasonic waves injected into it to have a certain delay. The following analysis is based on the premise that ultrasonic signals in the flattened flow channel can be reflected on the upper and lower walls.

[0036] like Figure 1As shown in the figure, when the depth of adjacent strip grids gradually increases, the adjacent deep strip grids and the flow channel wall where they are located form a concave structure, which is called an "ultrasonic trap structure". When the ultrasonic signal is injected into the ultrasonic trap structure, multiple reflections can be formed in the structure, which correspondingly increases the propagation distance and then produces a certain delay effect on the ultrasonic wave. ( Figure 1 (This is only an indication)

[0037] like Figure 2 As shown, it is first assumed that Φ = 90° to simplify the description. According to the relationship between the depth h of the deep strip grid, the grid spacing d and the ultrasonic incident angle β, the reflected ultrasonic signal may return to the direction of the transmitting end, or continue to be emitted in the direction of the receiving end. The specific relationship can be summarized as follows:

[0038] when When the ultrasonic wave escapes from the wave trap, it continues to propagate toward the receiving sensor;

[0039] when When the ultrasonic wave escapes from the wave trap, it continues to propagate in the direction of the transmitting sensor.

[0040] When the h value is small (i.e., the k value is small), the ultrasonic signal is reflected less frequently between adjacent grids, and effective delay, attenuation, and offset cannot be formed. At this time, only the shielding effect of the strip grid on the ultrasonic signal can be utilized, and the ultrasonic trap effect cannot be achieved. When Φ≠90°, the above principle also applies.

[0041] It can be seen that when the position and depth of the strip grid are set improperly, the ultrasonic signal will still propagate toward the receiving sensor and superimpose with the target signal that reaches the receiving sensor along the ideal path. If the actual application is particularly sensitive to signal superposition, it will affect the precise measurement.

[0042] In the following description, the ultrasonic signal that propagates along an ideal straight path and reaches the receiving sensor and is used for calculating the ultrasonic propagation time is called the "target signal".

[0043] Theoretically, the height of h can be controlled to allow the ultrasonic signal to continue to propagate in the direction of the transmitting sensor instead of the receiving sensor after escaping the ultrasonic trap structure. However, in practical applications, since the ultrasonic wave is emitted radially within the beam angle range and there is air flow disturbance, it is unreliable to force all reflected ultrasonic signals to propagate in the direction of the transmitting end after escaping the ultrasonic trap structure through structural design.

[0044] However, when the h value is large enough (that is, the k value is large), the ultrasonic signal is reflected more times between adjacent grids, which can cause a larger delay, attenuation and offset. Even if the ultrasonic signal that escapes the trap continues to propagate toward the receiving sensor, it cannot be superimposed with the target signal to affect the measurement performance.

[0045] Based on this, the present invention proposes the idea of ​​actively delaying, attenuating and shifting the reflected ultrasonic signal, and delaying the reflected ultrasonic signal for a long enough time so that it cannot be superimposed with the target signal waveform. That is, by adjusting the grid depth h and the grid spacing d, the ultrasonic wave is reflected multiple times in the ultrasonic trap structure. Compared with the signal sound path along the ideal straight line path, the corresponding increased sound path is long enough, and the corresponding delay is also large enough. Even if the ultrasonic wave escapes the trap and reaches the receiving end, it cannot be superimposed with the target signal waveform. In addition, after passing through the wave trap structure, the ultrasonic signal will produce amplitude attenuation and longitudinal displacement due to multiple reflections, both of which will weaken the signal and also weaken the superposition effect of the ultrasonic signal.

[0046] The following combination Figure 3 Derivation is explained. Figure 3 As shown, f1(t) is the ultrasonic signal that directly reaches the receiving end sensor SB along the ideal path, and f2(t) is the ultrasonic signal that reaches the receiving end sensor SB after delay, attenuation and deviation of the ultrasonic trap structure. t0 is the time required for the ultrasonic signal to propagate from the transmitting sensor SA to the receiving sensor SB along the ideal path, and Δt is the delay time added by the ultrasonic wave propagating along the reflection path compared to the ideal path. (The reflection path includes the part outside the ultrasonic trap structure and the part inside the trap structure).

[0047] Then for the signal F(t) received at the receiving sensor SB, we have:

[0048] F(t)=f1(t), 0≤t≤t0+Δt…⑴Formula

[0049] F(t)=f1(t)+f2(t), t≥t0+Δt…(2) Formula

[0050] Generally speaking, the target signal used for time calculation is the shuttle-shaped ultrasonic signal in the area shown by f1(t). It can be seen that as long as the delay Δt is large enough, f2(t) can be far away from the target signal area and cannot be superimposed with the target signal, and thus cannot affect the measurement of time.

[0051] Based on this, it is assumed that the depth of the deep strip grid constituting the ultrasonic trap structure is h, the spacing between the grids is d, the corresponding ultrasonic wave propagation speed is c, the incident angle of the ultrasonic wave signal entering the ultrasonic trap structure is β, the angle between the ideal ultrasonic wave path and the longitudinal axis of the flow channel (gas flow direction) is Φ, and the total delay time Δt added by the signal along the reflection path to reach the receiving end sensor, where the time delay caused by n (n is a positive integer) reflections of the ultrasonic wave in the trap structure is Δt1, and the delay added to the path other than the ultrasonic trap structure on the reflection path is Δt2 (compared to the delay added to the ideal path), and Δt=Δt1+Δt2. Figure 4 shown.

[0052] To simplify the calculation, small errors will not be considered, and the approximate calculation is as follows:

[0053] The propagation distance of the signal in the wave trap is L1, and we have:

[0054] (n is the number of reflections, n is a positive integer greater than 1)

[0055] Then we have: (n is the number of reflections, and n is an integer greater than 1).

[0056] On the reflection path of the signal, excluding the sound path added in the ultrasonic trap structure, the sound path added compared to the ideal path is L2, which is:

[0057]

[0058] Then we have:

[0059] In summary:

[0060] (n is an integer greater than 1)

[0061] Assuming that the desired delay time is ΔT, when Δt≥ΔT is satisfied, even if the ultrasonic signal via the reflection path reaches the receiving end, it cannot be superimposed with the target signal. The wave trap structure can achieve the design purpose.

[0062] In order to increase the depth of the strip grid that constitutes the ultrasonic trap in a limited space, the grid depth is usually increased as much as possible while ensuring that the target signal propagates normally along the ideal path, that is, the value of H-2h tends to D. Considering that L>>D in the flat flow channel, Δt2 is sufficiently small compared to Δt1. To simplify the explanation, it can be considered that Δt2≈0. Then at this time:

[0063] (n is an integer greater than 1)

[0064] At this time, take Δt = ΔT, then:

[0065]

[0066] (n is an integer greater than 1)

[0067] Then the height h of the corresponding strip grid is:

[0068]

[0069] It can be seen that, in theory, when the incident angle β and the speed of sound are constant, the height h of the strip grid is only determined by the expected delay time ΔT. In practical applications, the spacing d of the strip grid should not be too small or too large. When d is small enough to approach the ultrasonic wavelength λ or even smaller than λ, even if the feasibility of the manufacturing process is not considered, the trap effect will be weakened or even fail; when d is too large, the wider the range of the incident angle β of the ultrasonic wave that can be incident into a trap structure, the greater the possibility of beam escape; at the same time, when h is constant, as d increases, the corresponding number of reflections decreases, which also reduces the attenuation effect of the ultrasonic trap structure on the ultrasonic signal incident therein. Therefore, the preferred spacing d is 2λ~5λ, and the specific spacing should be comprehensively considered and selected based on many factors such as the actual manufacturing process, the signal attenuation capability of the trap structure, and the flow stability capability of the grid.

[0070] Secondly, theoretically, the corresponding incident angle β is different depending on the position of the trap structure, which means that when ΔT is constant, the height of the grid at different positions is also different (because β is different at different positions). Combined with empirical data, in practical applications, the height of the trap structure can be unified as the height of the trap structure located in the middle of the upper and lower walls.

[0071] Theoretically, the design purpose can be achieved by placing ultrasonic trap structures in specific locations. In practical applications, the sensors used are all integrated transceiver sensors, and considering the actual manufacturing process and the flow constraint effect of the strip grid, on the basis of ensuring that sufficient signal channels are reserved, the above-mentioned wave trap structures can be preferably placed continuously on the upper and lower walls of the flow channel to achieve the purpose of effectively weakening / eliminating the influence of the signals reflected by the upper and lower walls on the target signal after reaching the receiving end and superimposed with the target signal.

[0072] In addition, due to the existence of the angle Φ between the sensor axis and the longitudinal axis of the flow channel and Φ≠90°, when the ultrasonic signal is reflected multiple times in the trap structure, the position offset of the signal along the longitudinal direction of the flow channel will also be generated. Figure 5As shown in the figure, for a more intuitive explanation, it is assumed that the horizontal incident angle β when the signal is incident on the trap structure is 0. It can be seen that as the number of transmissions increases, the longitudinal offset of the beam increases, and the beam is further away from the receiving sensor.

[0073] Figure 6 The schematic diagram of the flat flow channel with a wave trap structure designed according to the above design method. It should also be noted that the top width of the deep strip grid that constitutes the ultrasonic trap structure should be much smaller than the ultrasonic wavelength to prevent the ultrasonic wave from being effectively reflected at the top of the grid; or the top of the strip grid can be designed into other shapes that cannot effectively reflect the ultrasonic signal to the receiving end.

[0074] In addition, it should be noted that the spacing d of the deep strip grid should not be close to or even smaller than the ultrasonic wavelength, otherwise the effect of the wave trap structure will be weakened or even invalid.

[0075] Secondly, the length of the deep strip grid forming the wave trap structure preferably runs through the entire flow channel, which not only effectively delays, attenuates and deflects the signal, but also plays a role in stabilizing the flow state. However, its length does not necessarily have to run through the entire flow channel, as long as it can achieve effective delay of the ultrasonic signal.

[0076] Furthermore, the strip grid that constitutes the ultrasonic trap structure is preferably in the shape of a straight rectangular strip, but is not limited to this state. It can also be other shapes such as a broken line shape, a wave shape, etc., as long as it can effectively block the reflected ultrasonic signal from reaching the receiving sensor.

[0077] The flat flow channel designed according to the above flat flow channel design method is applied to the flow meter system, and the number of flow channels can be one or more, so as to realize the working flow measurement of the gas medium;

[0078] The flow meter system also includes the collection of medium temperature and pressure to complete the conversion of gas operating flow to standard flow.

[0079] like Figure 7 As shown in FIG. 1 , a schematic diagram of the superposition of three flat flow channels with ultrasonic trap structures is shown. It should be noted that the axes of the three sensor groups in the illustration are parallel, but this is not limited to the actual application, and the angles between the axes of the three sensor groups and the longitudinal axis of the flow channel are not necessarily consistent. In addition, flat flow channels of different sizes designed according to the above method can also be mixed and used in the same flow meter.

[0080] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A flat flow channel with an ultrasonic trap structure, characterized in that: The cross section of the flat flow channel is rectangular, and the length L of the cross section is greater than the height H. An ultrasonic sensor is arranged at the center of the two side walls in the upper and lower directions of each side wall of the flat flow channel. The axes of the two ultrasonic sensors are on the same straight line, and the angle between the axes and the flow direction of the flat flow channel is Φ. A plurality of strip grids are arranged on the upper and lower inner wall surfaces of the flat flow channel along the flow direction, and together with the corresponding inner wall surfaces, they form an ultrasonic trap structure; the ultrasonic trap structure is used to reflect the incident ultrasonic signal multiple times and cause attenuation, and at the same time, cause the emitted ultrasonic signal to produce a longitudinal displacement; The arrangement spacing d of the strip grid is 2λ~5λ, and the height of the strip grid is , where λ is the wavelength of the ultrasonic wave emitted by the ultrasonic sensor, c is the sound velocity of the medium, ∆T is the delay time expected to be caused by the ultrasonic trap structure, and β is the incident angle of the ultrasonic signal incident on the trap structure.

2. The flat flow channel with ultrasonic trap structure according to claim 1, characterized in that: The ratio of the length L to the height H of the cross section is not less than 3.

3. The flat flow channel with ultrasonic trap structure according to claim 1, characterized in that: The included angle Φ between the axes of the two ultrasonic sensors and the longitudinal axis of the flat flow channel is 30° to 60°.

4. The flat flow channel with ultrasonic trap structure according to claim 1, characterized in that: The heights of all the strip grilles are unified to the height of the strip grille located in the middle.

5. The flat flow channel with ultrasonic trap structure according to claim 1, characterized in that: The thickness t of the strip grid is less than half of the ultrasonic wavelength λ emitted by the ultrasonic sensor, so as to prevent the ultrasonic signal from being effectively reflected at the top of the strip grid and reaching the ultrasonic sensor at the receiving end.

6. The flat flow channel with ultrasonic trap structure according to claim 1, characterized in that: The length of the strip grid runs through the entire flat flow channel, and its shape is rectangular, folded line or wavy.

7. The flat flow channel with ultrasonic trap structure according to claim 1, characterized in that: The interval between the strip grids arranged on the upper and lower inner wall surfaces of the flat flow channel is not less than 0.6D, that is, H-2h≥0.6D, where D represents the effective radiation surface size of the ultrasonic sensor.

8. A flow meter system, comprising a measuring flow channel, characterized in that: The measuring flow channel is composed of a flat flow channel with an ultrasonic trap structure as described in any one of claims 1 to 7; wherein, the measuring flow channel is composed of one flat flow channel, or is composed of a plurality of flat flow channels superimposed on each other.

9. The flow meter system according to claim 8, characterized in that The flow meter system also includes a temperature sensor and a pressure sensor for completing the conversion of the gas operating flow rate to the standard flow rate.

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