Silencer for gas ultrasonic flowmeter

Abstract

The silencer for the gas ultrasonic flowmeter comprises a shell and a rectifying element arranged in the shell, the rectifying element comprises a rectifying outer shell and a rectifying inner shell, small holes are distributed in the rectifying outer shell, the rectifying outer shell is formed by connecting multiple stages of cavities of the same structure, and the rectifying inner shell is formed by connecting multiple stages of cavities of the same structure. The cavity is formed by sequentially connecting an expansion section, a horizontal section and a contraction section in the airflow direction. Sound absorbing materials are filled between the shell and the rectification outer shell and inside the rectification inner shell, the rectification inner shell is located in the rectification outer shell, and an interlayer formed by the outer wall of the rectification inner shell and the inner wall of the rectification outer shell in parallel is an airflow channel. The silencer has a good sound absorption effect on high-frequency ultrasonic waves and is small in pressure loss.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrasonic flowmeters, and in particular relates to a muffler for a gas ultrasonic flowmeter. Background Art

[0002] In recent years, with the advancement of electronics, digital technology, and acoustic wedge materials, the technology for measuring fluid flow using ultrasonic pulses has rapidly developed. A variety of ultrasonic flowmeters, based on different principles and suitable for different locations, have emerged. Their applications span a wide range of sectors, from large gas transmission stations and gate stations, industrial users, to small processing workshops, restaurants, and hotels, and they are increasingly becoming the preferred instrument for flow measurement. The main sources of ultrasonic noise in pipeline gas production come from equipment such as regulating valves, throttle valves, pressure reducing valves, and pumps. This can adversely affect the flowmeter's accurate measurement. During design and installation, the flowmeter should be positioned as far away from noise sources as possible, or measures should be taken to eliminate noise interference.

[0003] Traditional tube- or plate-type mufflers, due to their oversized cross-sections, can experience high-frequency failure, a frequency lower than the ultrasonic frequency, resulting in the muffler failing to achieve its noise reduction goals. Conventional folded-plate mufflers, with high bends, can negatively impact gas dynamics by increasing flow resistance, leading to excessive pressure loss and failure to meet requirements. Low bends can cause the length to exceed installation requirements.

[0004] CN103487098B discloses a noise reduction and rectification device for a gas ultrasonic flowmeter. During the throttling process, mechanical energy of the gas is converted into acoustic energy, generating noise. This noise accompanies the gas as it enters the housing and passes through the air chamber, filter and rectifying element, compensating element, buffer air chamber, and secondary rectifying element. The filter and rectifying element of this device occupies too much space in the airflow path, resulting in a lack of a free passageway from the inlet to the outlet. The airflow must overcome the resistance of the filter and rectifying element to pass through it, resulting in significant airflow pressure loss. Furthermore, when the airflow volume is large and the flow velocity is high, significant regenerative noise may occur, reducing the noise reduction.

[0005] The muffler of CN103123786B includes a muffler connected to a pipe through which fluid passes. A boundary opening smaller than the internal cross-sectional area of ​​the muffler is formed on the boundary wall at the end of the muffler opposite the ultrasonic flowmeter. Furthermore, inside the muffler, a first central baffle, opposite the boundary opening, and a pair of first side baffles, opposite a pair of side openings formed between the first central baffle and the inner side of the muffler, are arranged alternately along the axial direction of the muffler. This muffler has baffles located perpendicular to the airflow direction at multiple locations within the pipe. When airflow encounters these baffles during its journey from inlet to outlet, it inevitably causes pressure loss. This repetition leads to significant pressure loss. Furthermore, the airflow path contains numerous continuous bends, each of which is a right angle, where the local pressure loss is maximized. This further exacerbates the already significant pressure loss. Furthermore, after the airflow returns from the pipe wall to the center, airflow from various directions collide near the pipe axis, further exacerbating the pressure loss. Multiple large-angle and right-angle airflow changes and airflow collisions near the axis intensify the rupture and shedding of the boundary layer. The entire flow process of the airflow in the pipe cannot form a stable laminar state, which cannot avoid causing regenerative noise and reducing the noise reduction amount. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a muffler for a gas ultrasonic flowmeter, which has a good sound absorption effect on high-frequency ultrasonic waves and a small pressure loss.

[0007] In order to achieve the purpose of the present invention, the technical solution adopted is: duct, and the like. The duct, or duct, of the second end of the second end is connected to the air inlet of the second end ...

[0008] The muffler of the present invention leads the airflow outward in the expansion section in a circumferential direction, with the aim of changing the co-directional propagation of the airflow and the sound flow, forming a propagation difference between the airflow and the sound flow, reducing the propagation of the sound flow driven by the airflow, and the undiverted sound energy is more absorbed by the sound-absorbing material of the rectifier inner shell. At the same time, there is no right-angle return in the direction of the airflow flow, and the bending path lengthens the propagation channel. There is no filtering obstruction in the channel, which reduces the regenerated noise and improves the noise reduction amount.

[0009] Adding a horizontal section between the expansion and contraction sections reduces the angle of change in airflow direction and reduces pressure loss. Simultaneously, the airflow through the horizontal section provides a smooth flow, reducing the regenerative noise from boundary layer shedding. The airflow turns inward in the contraction section, again creating a propagation difference between the air and sound streams. The sound energy that remains undiverted in the horizontal and contraction sections is absorbed further by the sound-absorbing material of the rectifier housing. The airflow then turns outward again through the expansion section, passing through multiple chambers in sequence. The multi-stage structure repeats this process, fully absorbing the sound energy. The number of chamber stages can be adjusted based on the desired noise reduction, and the air is ultimately discharged through the outlet, maintaining the same inlet and outlet directions.

[0010] During the airflow propagation process of the silencer of the present invention, the airflow flows in a metastable state in an unobstructed channel with a small angle change, with only a low pressure loss. The propagation of sound waves is decomposed into two paths at the entrance. One is linear propagation through the sound-absorbing material and then being absorbed. The other is propagation in the channel along with the airflow, but will enter the surrounding sound-absorbing material at an angle as small as possible to the direction of the sound-absorbing surface and be absorbed more.

[0011] The ends of the rectifier inner shell facing the air inlet pipe and the air outlet pipe are not flat, so as to avoid the air flow direction being reflected back by the flat surface.

[0012] The cross-sectional area of ​​the air flow channel of the present invention is not less than 1.2 times the cross-sectional area of ​​the air inlet. The pressure loss of the muffler can be equivalent to the pressure loss of the straight-through pipe, avoiding unnecessary pressure loss caused by too small a cross-sectional area.

[0013] In the present invention, the distance between the connecting point of adjacent chambers and the central axis is less than the distance between the central axis and the point of maximum inner diameter of the rectifier inner shell. This distance difference creates a certain obstruction within the channel, forcing airflow to flow through the expansion section of the next-stage chamber and not directly into the horizontal section of the next-stage chamber from the contraction section of the previous chamber without deflection. This causes the high-frequency ultrasonic noise to exceed the upper limit failure frequency.

[0014] Preferably, the difference between the two distances is 2-3 times the wavelength of the ultrasonic noise. This distance difference is the height difference between the connection point of adjacent chambers and the maximum inner diameter point of the rectifier inner shell relative to the central axis. During the noise propagation process, the air flow medium is constant, the ultrasonic frequency, wavelength and sound speed are constant, and only the intensity of the noise changes. This distance difference affects the noise reduction effect of the muffler. If it is less than 2 times, the noise reduction effect will be reduced due to the large channel width, especially causing high-frequency ultrasonic noise to fail; if it is higher than 3 times, it will have little effect on noise reduction, but will cause a rapid increase in pressure loss.

[0015] The sound absorbing material of the present invention is a porous sound absorbing material.

[0016] The inclination angle between the cavity wall of the expansion section and the contraction section and the horizontal section is not greater than 60 degrees. If the angle is greater than 60 degrees, the obstruction effect on the airflow is greater than the diversion effect on the sound flow, resulting in excessive pressure loss.

[0017] The perforation rate of the rectifier outer shell and the rectifier inner shell of the present invention is greater than 20%, so as to ensure that sound waves can pass through the shell layer without obstacles and be absorbed by the sound-absorbing material.

[0018] The beneficial effects of the present invention are: 1. The muffler of this invention features a cascaded disc design. During airflow propagation, the airflow flows in a metastable state within an unobstructed channel with small angle changes, resulting in minimal pressure loss. The airflow channel features multiple bends, altering the co-directional propagation of air and sound, creating a propagation difference between the air and sound streams and reducing the airflow's influence on the sound stream. With each bend, the sound wave is decomposed into two pathways: one is a straight line propagation through the sound-absorbing material, where it is absorbed; the other is a propagation path along with the airflow within the channel, but at an angle as small as possible to the direction of the sound-absorbing surface, where it enters the surrounding sound-absorbing material for greater absorption. The use of a multi-stage chamber rectifier ensures that sound waves are repeatedly and fully absorbed within the shortest possible linear distance. This allows for natural gas transmission. When the muffler shell length is ≤2 times its total diameter, and the installation requirements for mufflers for gas ultrasonic flowmeters are met, a two-stage cascade design achieves a noise reduction of ≥70dB, while maintaining a pressure loss of ≤20kPa.

[0019] 2. The cross-sectional area of ​​the airflow channel is controlled to be no less than 1.2 times the cross-sectional area of ​​the air inlet. Furthermore, the height difference between the connection point between adjacent chambers and the maximum inner diameter of the rectifier inner shell is 2-3 times the wavelength of ultrasonic noise. This airflow channel definition ensures that the airflow channel is neither too wide, thereby reducing noise reduction effectiveness, nor too narrow, thereby rapidly increasing pressure loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A cross-sectional view of a muffler for a gas ultrasonic flowmeter with a two-stage chamber cascade.

[0021] Figure 2A cross-sectional view of a muffler for a gas ultrasonic flowmeter with a three-stage chamber cascade.

[0022] Figure 3 The muffler structure and airflow trend diagram for a gas ultrasonic flowmeter with a two-stage chamber cascade.

[0023] Figure 4 This is a schematic diagram of the end face of the rectifier element of the muffler for the gas ultrasonic flowmeter of the present invention.

[0024] Figure 5 A three-dimensional cross-sectional diagram of a gas ultrasonic flowmeter with a two-stage chamber cascade.

[0025] Figure 6 The figure shows the comparison of the ultrasonic flowmeter's measurement values ​​at various measurement points between the present invention and the commercially available silencer.

[0026] Figure 7 The figure shows the signal-to-noise ratio comparison between the present invention and commercially available silencers at various measurement points.

[0027] Figure numerals: 1. Shell; 2. Fairing outer shell; 3. Fairing inner shell; 4. Sound-absorbing material; 5. Connecting rod; 6. Air flow channel; 7. Air inlet pipe, 8. Air outlet pipe, 11. Air inlet; 12. Air outlet; 21. Primary chamber; 22. Secondary chamber; 23. Tertiary chamber; 31. Expansion section; 32. Horizontal section; 33. Contraction section. DETAILED DESCRIPTION

[0028] In order to more clearly and in detail illustrate the purpose and technical solution of the present invention, the present invention is further described below through relevant examples. The following examples are only for specific illustration of the implementation method of the present invention and do not limit the scope of protection of the present invention. Example 1

[0029] like Figure 1 and 3-5, a silencer for a gas ultrasonic flowmeter comprises a shell 1 and a rectifier element arranged in the shell 1, one end of the shell 1 is connected to the air inlet pipe 7, and the other end is connected to the air outlet pipe 8, the rectifier element comprises a rectifier outer shell 2 and a rectifier inner shell 3 with small holes all over, the rectifier outer shell 2 is composed of two-stage chambers with the same structure, the chamber is composed of an expansion section 31, a horizontal section 32 and a contraction section 33 connected in sequence along the air flow direction, the expansion section air inlet 11 of the first chamber is connected to the air inlet pipe 7, the second chamber is connected to the air outlet pipe 7, and the second chamber is connected to the air outlet pipe 7. The contraction section air outlet 12 is connected to the air outlet pipe 8; the cavity wall of the expansion section 31 starts to spread outward from the air inlet, the cavity wall of the horizontal section 32 is parallel to the central axis of the shell 1, and the cavity wall of the contraction section 33 contracts toward the center and connects the expansion section 31 of the adjacent chamber; the space between the shell 1 and the fairing outer shell 2, as well as the interior of the fairing inner shell 3 are filled with sound-absorbing material 4, the fairing inner shell 3 is located in the fairing outer shell 2, and the outer wall of the fairing inner shell 3 and the inner wall of the fairing outer shell 2 are parallel to form an interlayer as the airflow channel 6.

[0030] A silencer is installed at the front end of the flowmeter, and the airflow undergoes noise reduction before entering the flowmeter. Airflow enters the expansion section 31 of the primary chamber 21 from the air inlet 11. It is initially deflected outward, changing the co-directional propagation of the airflow and acoustic flow, creating a propagation difference between the airflow and acoustic flow, reducing the airflow's influence on the acoustic flow. Undeflected acoustic energy is more absorbed by the sound-absorbing material 4 of the rectifier inner shell 3. Airflow then enters the horizontal section 32, reducing the angle of change in airflow direction and lowering pressure loss. This also smoothes the flow and reduces regenerative noise from boundary layer shedding. Airflow then deflects inward at the contraction section 33, again creating a propagation difference between the airflow and acoustic flow. Undeflected acoustic energy in the horizontal and contraction sections 32 and 33 is further absorbed by the sound-absorbing material 4 of the rectifier outer shell 2. Airflow then enters the secondary chamber 22, where it is deflected outward again at the expansion section. The airflow then flows through the two chambers in sequence, repeating the process in the two-stage structure before ultimately being discharged through the outlet, maintaining the same direction of airflow. Example 2

[0031] like Figure 2As shown, a silencer for a gas ultrasonic flowmeter comprises a housing 1 and a rectifying element arranged in the housing 1. One end of the housing 1 is connected to the air inlet pipe 7, and the other end is connected to the air outlet pipe 8. The rectifying element comprises a rectifying outer shell 2 and a rectifying inner shell 3 with small holes all over. The rectifying outer shell 2 is composed of three chambers with the same structure. The chamber is composed of an expansion section 31, a horizontal section 32 and a contraction section 33 connected in sequence along the air flow direction. The expansion section inlet 11 of the first chamber is connected to the air inlet pipe 7, and the third chamber is connected to the expansion section 32. The air outlet 12 of the contraction section is connected to the air outlet pipe 8; the cavity wall of the expansion section 31 starts to spread outward from the air inlet, the cavity wall of the horizontal section 32 is parallel to the central axis of the shell 1, and the cavity wall of the contraction section 33 contracts toward the center and connects the expansion section 31 of the adjacent chamber; the space between the shell 1 and the fairing outer shell 2, as well as the interior of the fairing inner shell 3 are filled with sound-absorbing material 4, the fairing inner shell 3 is located in the fairing outer shell 2, and the outer wall of the fairing inner shell 3 and the inner wall of the fairing outer shell 2 are parallel to form an interlayer as the airflow channel 6. Example 3

[0032] This embodiment is based on embodiment 1: The cross-sectional area of ​​the air flow channel 6 is 1.2 times the cross-sectional area of ​​the air inlet 11 .

[0033] The distance between the connection point of adjacent chambers and the central axis is less than the distance between the maximum inner diameter point of the rectifier inner shell and the central axis, and the difference between the two distances is twice the wavelength of the ultrasonic noise.

[0034] The two ends of the fairing inner shell 3 facing the air inlet pipe 7 and the air outlet pipe 8 are not flat. Example 4

[0035] This embodiment is based on embodiment 1: The cross-sectional area of ​​the air flow channel 6 is 1.5 times the cross-sectional area of ​​the air inlet 11 .

[0036] The distance between the connection point of adjacent chambers and the central axis is less than the distance between the maximum inner diameter point of the rectifier inner shell and the central axis, and the difference between the two distances is 2.5 times the wavelength of the ultrasonic noise.

[0037] The two ends of the fairing inner shell 3 facing the air inlet pipe 7 and the air outlet pipe 8 are not flat.

[0038] The inclination angle between the cavity walls of the expansion section 31 and the contraction section 33 and the horizontal section 32 is 60 degrees.

[0039] The sound absorbing material 4 is a porous sound absorbing material, which can be porous fiber sound absorbing material, porous medium or high density sound absorbing cotton, porous polyurethane foam or other sound absorbing materials.

[0040] The perforation rate of the fairing outer shell 2 and the fairing inner shell 3 is greater than 20%.

[0041] like Figure 3 and Figure 4 As shown, the fairing inner shell 3 is connected to the inner wall of the fairing outer shell 2 by arranging a connecting rod 5 on the outer surface. Example 5

[0042] This embodiment is based on embodiment 2: The cross-sectional area of ​​the air flow channel 6 is 1.6 times the cross-sectional area of ​​the air inlet 11 .

[0043] The distance between the connection point of adjacent chambers and the central axis is less than the distance between the maximum inner diameter point of the rectifier inner shell and the central axis, and the difference between the two distances is 3 times the wavelength of the ultrasonic noise.

[0044] The inclination angle between the cavity walls of the expansion section 31 and the contraction section 33 and the horizontal section 32 is 50 degrees.

[0045] The perforation rate of the fairing outer shell 2 and the fairing inner shell 3 is greater than 20%.

[0046] The two ends of the fairing inner shell 3 facing the air inlet pipe 7 and the air outlet pipe 8 are not flat.

[0047] The sound absorbing material 4 is a porous fiber sound absorbing material.

[0048] The noise reduction effect of the silencer of the present invention was compared with that of a commercially available flow meter-specific silencer. Two identical natural gas pipelines were assembled with the two silencers. The silencers were installed at the air inlet of the same type of ultrasonic flow meter. The noise reduction effects of the silencer of the present invention and the commercially available flow meter-specific silencer were compared. The two silencers were installed at the air inlet of the same type of ultrasonic flow meter. The noise reduction effects of the silencer of the present invention and the commercially available flow meter-specific silencer were compared. The two silencers were installed at the air inlet of the same type of ultrasonic flow meter. The noise reduction effects of the silencer of the present invention and the commercially available flow meter-specific silencer were compared. 3 / h) and other 9 test flow points, each flow point ran in the pipeline 20 times, and each flow value measured by the ultrasonic flowmeter at different measuring points was recorded, and then the signal-to-noise ratio (%) of the pipeline at the corresponding measuring point was further measured.

[0049] Depend on Figure 6 The test results show that the greater the gas flow rate, the greater the noise, which will affect the measurement accuracy of the flow meter. The gas flow rate of commercially available flow meters is between 200-300 m 3 / h, the measured value is no longer stable and begins to fluctuate, indicating that the measured value has lost its accuracy and exceeds the range of the flow meter. 3 / h gas flow, the measured value can still remain stable, the measurement repeatability is good, and the measurement result is reliable, indicating that the silencer has a significant noise reduction effect, greatly improving the accuracy of the flow meter, and can measure 650 m 3 / h flow rate can be accurately measured.

[0050] from Figure 7 As can be seen, at the same measurement point, the signal-to-noise ratio of the muffler of the present invention is also greater than that of commercially available mufflers, demonstrating that the muffler of the present invention is indeed more effective in reducing noise. Furthermore, the gas pressure at the inlet end of the muffler of the present invention is 59.3 kPa, and the gas pressure at the outlet end is 56.8 kPa, with a pressure difference of only 2.5 kPa, indicating minimal pressure loss. Furthermore, the muffler shell length is ≤2 times its total diameter. The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A muffler for a gas ultrasonic flowmeter, characterized in that: The vents are formed by venting the vents to the outside of the vent tube, and the vents are formed by venting the vent tube to the outside of the vent tube.

2. The muffler for a gas ultrasonic flowmeter according to claim 1, characterized in that: The two ends of the rectifier inner shell facing the air inlet pipe and the air outlet pipe are not flat.

3. The muffler for a gas ultrasonic flowmeter according to claim 1, characterized in that: The cross-sectional area of ​​the air flow channel is not less than 1.2 times the cross-sectional area of ​​the air inlet.

4. The muffler for a gas ultrasonic flowmeter according to claim 1, characterized in that: The distance between the connection point of adjacent chambers and the central axis is smaller than the distance between the maximum inner diameter point of the rectifier inner shell and the central axis.

5. The muffler for a gas ultrasonic flowmeter according to claim 4, characterized in that: The difference between the two distances is 2-3 times the wavelength of the ultrasonic noise.

6. The muffler for a gas ultrasonic flowmeter according to claim 1, characterized in that: The inclination angle between the cavity wall of the expansion section and the contraction section and the horizontal section is not greater than 60 degrees.

7. The muffler for a gas ultrasonic flowmeter according to claim 1, characterized in that: The sound absorbing material is a porous sound absorbing material.

8. The muffler for a gas ultrasonic flowmeter according to claim 1, characterized in that: The perforation rate of the fairing outer shell and the fairing inner shell is greater than 20%.

Images