An isokinetic compressed air flow monitoring device and a method of designing and manufacturing the same

Abstract

This invention discloses a constant-diameter compressed air flow monitoring device and its design and manufacturing method, belonging to the field of compressed air flow monitoring technology. The device includes a constant-diameter shell, a built-in flow sensing unit, a flow guiding and stabilizing component, and a data processing module. The overall inner diameter is consistent with the inner diameter of the pipe to be monitored, ensuring no abrupt changes in cross-section as the airflow passes through. The built-in flow sensing unit employs an insertion-type vortex flow sensor, with its probe extending into the pipe at 1 / 4 of its diameter and arranged at a 40° angle to the pipe axis. The flow guiding and stabilizing component consists of multiple sets of radially arranged arc-shaped guide vanes; together, they achieve low flow resistance and high-precision measurement. The device of this invention has a pressure loss ≤0.02MPa and a flow monitoring error rate ≤±1.5%, effectively solving the problems of high energy consumption and low accuracy in existing variable-diameter flow monitoring devices. It is suitable for compressed air pipeline flow monitoring in metallurgy, chemical industry, and machinery manufacturing.

Description

Technical Field

[0001] This invention belongs to the technical field of compressed air flow monitoring equipment, specifically relating to a constant diameter compressed air flow monitoring device and its design and manufacturing method. Background Technology

[0002] In industrial production, compressed air is an important power source, and its flow monitoring is a key aspect of achieving energy conservation and stable operation of the system. Existing compressed air flow monitoring devices generally adopt a "large diameter reduction" structure, which involves first reducing the diameter of the main pipe (usually 300 mm) to 80 mm (the sensor mounting section) using a reducer, and then expanding it back to 300 mm after monitoring is completed. The initial intention of this design was to increase the airflow velocity by reducing the pipe diameter, making it easier for the flow sensor to capture the signal. However, this design has significant drawbacks: 1. Consumes a large amount of energy: Due to the reduction and expansion of the diameter, there is local energy loss when the gas passes through. According to actual operating conditions, the resistance loss of such devices is 0.1-0.3 MPa, which is approximately 15-20% of the energy consumption of the compressed air system.

[0003] 2. Monitoring accuracy is affected: eddies and turbulence at the diameter change point can cause fluctuations in sensor monitoring data, especially under low flow conditions, where the error rate can exceed 5%.

[0004] 3. Complex installation and maintenance: The welding and sealing requirements of reducers are high, and after long-term use, leakage is prone to occur due to stress concentration, which increases maintenance costs.

[0005] To address the aforementioned problems, this invention proposes a constant-diameter compressed air flow monitoring device. By eliminating the variable-diameter structure and optimizing the internal flow field design, it fundamentally solves the energy loss problem while ensuring monitoring accuracy. Summary of the Invention

[0006] This invention addresses the technical problems of existing compressed air flow monitoring devices, which commonly employ a "large diameter change" pipe structure (i.e., first reducing the diameter to the sensor installation diameter and then expanding it back to the original pipe diameter after monitoring), resulting in large airflow pressure loss, high monitoring error rate under low flow conditions, and complex welding and installation of reducing pipes, easy leakage, and high maintenance costs. The invention provides a constant diameter compressed air flow monitoring device and its design and manufacturing method.

[0007] This invention aims to fundamentally reduce flow resistance by eliminating abrupt changes in the pipe cross-section. At the same time, by utilizing a built-in flow guiding and stabilizing component in conjunction with an insertable sensing unit with a specific orientation, it achieves energy saving, consumption reduction, and convenient maintenance of the compressed air delivery system while ensuring high-precision flow measurement.

[0008] To achieve the above-mentioned objectives, this invention provides a constant-diameter compressed air flow monitoring device. Its core design concept is that the inner diameter of the entire device is completely consistent with the inner diameter of the main pipe to be monitored, with no cross-sectional change throughout the entire process. Through the coordinated cooperation of "built-in flow guiding and stabilizing components to actively regulate the flow field" and "tilted insertion sensors to optimize signal acquisition", low flow resistance and high-precision flow monitoring are achieved.

[0009] The equal-diameter compressed air flow monitoring device mainly consists of an equal-diameter shell, a built-in flow sensing unit, a flow guiding and stabilizing component, a data processing module, and a connecting flange.

[0010] The equal-diameter outer casing adopts a straight-through pipe structure with the same inner diameter as the compressed air pipeline to be monitored, and its inner diameter is consistent with that of the main pipeline (covering various specifications such as DN150, DN200, and DN300). The axial length of the equal-diameter outer casing is set to 3 to 5 times its inner diameter (preferably 4 times) to ensure sufficient fluid development within the measurement section while avoiding excessive installation space occupation. The inner wall of the equal-diameter outer casing is a continuous and smooth flow channel without cross-sectional abrupt changes, and the surface roughness Ra ≤ 0.8 μm to reduce frictional resistance along the flow path. The outer casing is made of a pressure-resistant alloy material (such as stainless steel 430), and its wall thickness is determined by strength verification based on the pipeline working pressure (0.6–1.6 MPa) to ensure that the pressure rating requirements are met while maintaining a constant-diameter and lightweight structure. The two ends of the outer casing are sealed to the upstream and downstream pipelines through standard flanges.

[0011] The built-in flow sensing unit uses an insertion-type vortex flow sensor to detect the flow signal of the airflow in the pipeline.

[0012] To balance monitoring sensitivity and flow resistance, the sensor probe is not inserted vertically, but rather in an inclined installation position: the probe extends into the inner diameter of the equal-diameter housing by 1 / 4 to 1 / 3 (preferably 1 / 4) of the housing's inner diameter, and the central axis of the probe forms an acute angle with the axis of the equal-diameter housing, with this acute angle being 30° to 50° (more preferably 40° ± 2°). This specific angle design effectively reduces the probe's frontal area to the airflow—the projected area of ​​the probe's frontal surface on the pipe cross-section is 65% to 80% of the projected area when vertically installed, reducing flow resistance while ensuring stable separation and pickup of the vortex shedding signal at the probe's blunt body. Furthermore, the sensor integrates temperature and pressure compensation modules (such as a PT100 platinum resistance temperature sensor and a diffused silicon piezoresistive pressure sensor) to correct the impact of medium density changes on flow calculation in real time.

[0013] To eliminate airflow rotation and turbulence disturbances caused by pipe fittings such as bends and valves upstream of the pipeline, and to ensure that the airflow entering the sensor area is in a regular laminar or quasi-laminar state, this invention sets up a multi-stage flow guiding and stabilizing component inside the equal-diameter shell, located upstream of the sensor installation position.

[0014] Specifically, the component includes at least two sets (preferably three sets) of guide vanes sequentially distributed along the axial direction of the equal-diameter outer shell. Each set of guide vanes consists of 3 to 6 radially arranged arc-shaped vanes (preferably four vanes, with an included angle of 90° between adjacent arc-shaped vanes). The radius of curvature of each arc-shaped guide vane is consistent with the inner wall radius of the equal-diameter outer shell. The thickness of the arc-shaped vane is 1.5 to 2.5 mm (preferably 2 mm), and the chord length is 0.2 to 0.3 times the inner diameter of the equal-diameter outer shell. It is formed by stamping with a wear-resistant alloy. The guide vanes are distributed at predetermined intervals along the axial direction and are installed on the inner wall of the outer shell by a fixing structure. This structure forces the airflow along the axial direction of the pipe through the arc-shaped flow channel, effectively suppressing lateral flow and vortices, and significantly improving the uniformity of the flow field.

[0015] The guide plate can be installed in two ways, each suitable for different laying scenarios: Horizontal pipe installation method: The guide vane is installed on the inner wall of the equal-diameter outer casing via a detachable fixing structure. This detachable fixing structure includes an annular positioning groove formed in the inner wall of the equal-diameter outer casing and a retaining spring embedded in the positioning groove. The root of the guide vane is clamped and fixed between the retaining spring and the inner wall, and is further secured using radial set screws. This structure avoids outer casing deformation caused by welding thermal stress and facilitates the individual replacement of worn guide vanes.

[0016] Vertical pipeline installation method: When the compressed air pipeline is laid vertically, the guide vane is fixedly installed on the central support shaft that runs through the center of the equal-diameter outer shell. The two ends of the central shaft are fixed to the inner wall of the equal-diameter outer shell through positioning brackets. The probe of the built-in flow sensing unit is tilted in the vertical upward direction to ensure stable separation of vortex signals under vertical airflow conditions.

[0017] The flange faces of the connecting flanges at both ends of the equal-diameter outer shell are provided with annular sealing grooves. High-pressure and oil-resistant sealing gaskets (which can be nitrile rubber gaskets or metal-reinforced composite graphite gaskets, with a temperature range of -20℃ to 120℃ and a pressure resistance of 1.6MPa) are embedded within the sealing grooves to ensure a sealed connection between the device and the pipeline. The connecting flanges are fastened with 12 sets of high-strength bolts (performance grade 8.8), using a torque method to control the preload and perform symmetrical cross-tightening to ensure that the flange surface parallelism error is ≤0.1mm, preventing compressed air leakage.

[0018] This invention also provides a method for designing and manufacturing the above-mentioned constant diameter compressed air flow monitoring device, comprising the following steps: ① Pipeline parameter acquisition: Measure the inner diameter, working pressure, flow range, and medium temperature of the compressed air pipeline to be monitored to determine the size parameters and material selection of the equal-diameter shell; at the same time, record the pipeline laying method (horizontal or vertical) and the surrounding ambient temperature to optimize the arrangement direction of the guide vanes and the temperature compensation parameters of the sensor.

[0019] ② Sensor component layout design: Based on the vortex signal generation and pickup principle of the vortex flow sensor, the influence of different combinations of installation angles and insertion depths on airflow resistance characteristics and vortex stability was simulated through fluid dynamics simulation. With low resistance and high signal-to-noise ratio as optimization objectives, the installation posture parameters of the sensor probe were determined. The preferred installation posture is: the length of the probe extending into the pipe is 1 / 4 of the pipe's inner diameter, and the angle between the probe's central axis and the pipe axis is 40°±2°.

[0020] ③ Optimization of the flow guiding and stabilizing structure: Through fluid dynamics simulation, using the uniformity of velocity distribution at the outlet section of the flow channel and the overall pressure loss of the device as evaluation indicators, the curvature radius, axial spacing, and number of groups of the guide vanes are adjusted to control the pressure loss of the airflow within the device to within 5% of the inlet dynamic pressure, and to reduce the velocity non-uniformity at the sensor installation section to below 60% of that under inflow conditions. The fluid dynamics simulation uses CFD software (such as Fluent) to simulate airflow conditions in the velocity range of 10–100 m / s, and performs multi-parameter iterative optimization using pressure loss and vortex shedding signal intensity as evaluation indicators.

[0021] ④ Assembly and Sealing: The assembly is carried out using flange connections. Sealing elements are installed on the flange face. The bolt preload is controlled by torque method for symmetrical and cross-tightening to ensure a sealed connection between the device and the pipeline.

[0022] ⑤ Regular maintenance and calibration: Disassemble the sensor every 6 months for cleaning and check for looseness or wear of the guide vanes. Replace the guide vanes when they are worn by more than 20% of their original thickness. Perform online comparison and calibration with a standard flow meter every 12 months to correct the instrument coefficient.

[0023] Compared with the prior art, the present invention has the following advantages: 1) The present invention adopts a constant diameter structure throughout, which completely eliminates the abrupt change in cross-section at the diameter reduction and expansion points, and avoids local resistance loss from the root cause.

[0024] 2) This invention utilizes a synergistic structure of an inclined sensor insertion (40° angle + 1 / 4 depth) and multi-stage radial arc-shaped guide vanes (3 sets × 4 pieces). On one hand, the probe's interference with the main airflow is minimized (windward projected area reduced by 25%–35%). On the other hand, the guide vanes effectively tame incoming flow disturbances, improving the flow field uniformity at the sensor installation location by over 40%. Ultimately, this results in a stable flow monitoring error rate controlled within ±1.5%, exhibiting excellent linear response across the entire measurement range (10–1000 m³ / h), resolving the issue of drastic data fluctuations under low flow conditions, and simultaneously meeting the metrological requirements for industrial and trade settlement.

[0025] 3) By eliminating the bulky reducer, the overall structure is more compact, with an axial length only 3 to 5 times the pipe diameter, facilitating installation in confined spaces. The device uses standard flange connections, eliminating the need for on-site welding and making assembly and disassembly extremely convenient. Furthermore, both the internal sensor probe and guide vanes are designed for easy removal and replacement—the guide vanes utilize a snap-lock detachable fixing structure, eliminating the need for complete pipe disassembly for later maintenance, reducing maintenance costs by approximately 30% compared to existing technologies.

[0026] 4) This invention can conveniently cover various main pipeline specifications from DN150 to DN300 and above. Through a pre-set CFD simulation optimization method, only the curvature radius and installation spacing of the guide vanes need to be adjusted to quickly adapt to different pipe diameters and flow ranges (10–1000 m³ / h). Simultaneously, differentiated guide vane fixing schemes (clamp type and central shaft type) are provided for two common pipeline layouts: horizontal and vertical laying, ensuring stable and reliable operation of the device under different installation conditions. It has extremely high versatility and promotional value in industrial fields such as metallurgy, chemical industry, and machinery manufacturing where large-scale compressed air pipeline networks exist. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of an existing variable diameter compressed air flow monitoring device; Figure 2 This is a schematic diagram of the overall structure of the constant diameter compressed air flow monitoring device of the present invention.

[0028] In the diagram: 1-Stainless steel equal diameter housing; 2-Connecting flange; 3-Probe flow meter; 4-Guide vane. Detailed Implementation

[0029] The following will refer to the accompanying drawings in the embodiments of the present invention (see...). Figure 2 The technical solutions in the embodiments of the present invention will be clearly and completely described herein. Obviously, the described embodiments are merely some preferred embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, the terms "upstream," "downstream," "axial," "radial," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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 limiting the invention. The terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] This embodiment uses a compressed air system with a 300 mm main pipeline as an example to explain in detail the implementation steps of the present invention: 1. Parameter Acquisition and Design Measure the inner diameter of the main pipeline (300 mm), working pressure (0.8 MPa), maximum flow rate (800 m³ / h), and medium temperature (25℃).

[0032] Based on the parameters, the length of the equal-diameter outer shell is determined to be 1200 mm, the wall thickness is 8 mm (to meet the 0.8 MPa pressure requirement), and the material is selected as 430 stainless steel.

[0033] 2. Fabrication of flow guiding and stabilizing components The curved blades are stamped from 2mm thick wear-resistant alloy plates with a radius of curvature of 150mm. Each group has 4 blades, evenly distributed at 90° along the inner wall of the pipe. Three groups of guide vanes are arranged axially at 300mm intervals and welded to the inner wall of the equal-diameter outer shell through fixed brackets to ensure that the blades are parallel to the pipe axis.

[0034] 3. Sensor Installation Make a 25mm mounting hole in the middle of the equal-diameter housing, insert the vortex flow sensor probe to 75mm, and adjust the angle to 40° with the axis. After fixing with the sealing flange, ensure that the probe does not touch the inner wall of the pipe.

[0035] 4. Overall assembly and testing Align the connecting flanges at both ends of the equal-diameter shell with the main pipe flange, install the high-pressure resistant sealing gasket, and then tighten them with 12 sets of M20 high-strength bolts to ensure that the flange surface parallelism error is ≤0.1mm.

[0036] Compressed air testing: When the air volume is 50-800 m³ / h, the pressure loss (≤0.02 MPa) and sensor values ​​are tested and compared with standard measuring instruments. The error rate is no more than 1.5%.

[0037] 5. Maintenance and Calibration The sensor should be disassembled and cleaned every 6 months, and the guide vanes should be checked for looseness. The accuracy should be calibrated annually using a standard device to ensure long-term stable operation.

[0038] This embodiment demonstrates that the constant diameter compressed air flow monitoring device fully meets the requirements of industrial systems and is superior to traditional large diameter devices in terms of energy saving and accuracy, thus having broad application value.

[0039] This invention employs a novel equal-diameter structure and optimized flow field design for compressed air velocity measurement, solving problems such as high energy consumption, low accuracy, and cumbersome installation and maintenance associated with existing compressed air flow measurement products using conical structures. It fundamentally eliminates energy loss caused by changes in the equal diameter. The combination of the flow guide structure and the sensor structure enables accurate measurement of the compressed air velocity, making it feasible for energy-saving operation of compressed air systems. It also has wide applicability in industrial production in fields such as metallurgy, chemical engineering, and machinery manufacturing.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A constant diameter compressed air flow monitoring device, characterized by, include: A uniform-diameter outer shell, the inner diameter of which is the same as the inner diameter of the compressed air pipeline to be monitored, and connecting flanges at both ends for sealing connection with the pipeline; An internal flow sensing unit is fixedly installed inside the equal-diameter housing to detect the flow signal of the airflow inside the pipe. A flow guiding and stabilizing component is disposed inside the equal-diameter housing and located upstream of the built-in flow sensing unit, and is used to rectify the airflow entering the equal-diameter housing to eliminate airflow disturbance. And a data processing module, which is signal-connected to the built-in flow sensing unit, for receiving and processing the flow signal; The equal-diameter compressed air flow monitoring device adopts an equal-diameter structure with the same diameter as the pipe. The inner wall of the equal-diameter shell is a continuous and smooth flow channel without abrupt changes in cross-section, and the flow cross-sectional area of ​​the airflow remains constant when it flows through the device.

2. The equal-diameter compressed air flow monitoring device of claim 1, wherein: The built-in flow sensing unit adopts an insertion-type vortex flow sensor. The probe of the sensor extends into the interior of the equal-diameter housing by 1 / 4 to 1 / 3 of the inner diameter of the equal-diameter housing. The central axis of the probe is arranged at an acute angle with the axis of the equal-diameter housing, and the acute angle is 30° to 50°.

3. The isokinetic compressed air flow monitoring device of claim 2, wherein: The acute angle is 40°±2°, and the length of the probe extending into the equal-diameter housing is 1 / 4 of the inner diameter of the equal-diameter housing; the projected area of ​​the windward side of the probe on the cross-section of the pipe is 65% to 80% of the projected area when vertically installed.

4. The equal-diameter compressed air flow monitoring device of claim 1, wherein: The axial length of the equal-diameter outer shell is 3 to 5 times the inner diameter of the equal-diameter outer shell, and the surface roughness Ra of the inner wall of the equal-diameter outer shell is ≤0.8μm.

5. The equal-velocity compressed air flow monitoring device of claim 1, wherein: The flow guiding and stabilizing assembly includes at least two sets of flow guiding plates distributed sequentially along the axial direction of the equal-diameter outer shell. Each set of flow guiding plates consists of 3 to 6 radially arranged arc-shaped plates with a thickness of 1.5 to 2.5 mm and a radius of curvature consistent with the inner wall radius of the equal-diameter outer shell.

6. The equal-diameter compressed air flow monitoring device of claim 5, wherein: The flow guiding and stabilizing assembly includes three sets of flow guiding plates distributed sequentially along the axial direction of the equal-diameter outer shell. Each set of flow guiding plates consists of four radially and uniformly arranged arc-shaped plates with an included angle of 90° between adjacent arc-shaped plates. The thickness of the arc-shaped plates is 2 mm, and the chord length of the arc-shaped plates is 0.2 to 0.3 times the inner diameter of the equal-diameter outer shell.

7. The equal-compression air flow monitoring device of claim 5 or 6, wherein, The guide vane is installed on the inner wall of the equal-diameter outer shell through a detachable fixing structure. The detachable fixing structure includes an annular positioning groove formed in the inner wall of the equal-diameter outer shell and a retaining spring embedded in the positioning groove. The root of the guide vane is clamped and fixed between the retaining spring and the inner wall.

8. The equal-compression air flow monitoring device of claim 5 or 6, wherein, The flow guide plate is fixedly mounted on a central support shaft that passes through the center of the equal-diameter outer shell. The two ends of the central shaft are fixed to the inner wall of the equal-diameter outer shell by positioning brackets. The probe of the built-in flow sensing unit is arranged at an angle in the vertically upward direction.

9. The constant diameter compressed air flow monitoring device according to claim 1, characterized in that, The flange end face of the connecting flange is provided with an annular sealing groove, and a high-pressure and oil-resistant sealing gasket is embedded in the sealing groove. The sealing gasket is a nitrile rubber gasket or a metal skeleton composite graphite gasket. The connecting flange is fastened by 12 sets of high-strength bolts, and the performance grade of the high-strength bolts is 8.

8.

10. A method for designing and manufacturing a constant-diameter compressed air flow monitoring device, characterized in that, The method for designing and manufacturing a constant-diameter compressed air flow monitoring device as described in any one of claims 1 to 9 includes the following steps: ① Pipeline parameter acquisition: Measure the inner diameter, working pressure, flow range, and medium temperature of the compressed air pipeline to be monitored, and determine the size parameters and material selection of the equal-diameter shell; ② Sensor component layout design: Based on the vortex signal generation and pickup principle of the vortex flow sensor, the influence of different installation angles and insertion depths on airflow resistance characteristics and vortex stability is simulated through fluid dynamics simulation. With low resistance and high signal-to-noise ratio as optimization objectives, the installation attitude parameters of the sensor probe are determined. ③ Optimization of flow guiding and stabilizing structure: Through fluid dynamics simulation, the uniformity of velocity distribution at the outlet section of the flow channel and the overall pressure loss of the device are used as evaluation indicators. The curvature radius, axial spacing and number of groups of the flow guide vanes are adjusted so that the pressure loss of the airflow in the device is controlled within 5% of the inlet dynamic pressure, and the velocity non-uniformity at the sensor installation section is reduced to less than 60% of that under the inflow condition. ④ Assembly and sealing: The assembly is carried out using flange connections. Sealing elements are installed on the flange face. The bolt preload is controlled by torque method and symmetrically and crosswise tightened to ensure a sealed connection between the device and the pipeline.

11. The design and manufacturing method according to claim 10, characterized in that, The pipeline parameter acquisition in step ① also includes recording the pipeline laying method and the surrounding ambient temperature, which is used to optimize the arrangement direction of the guide vanes and the temperature compensation parameters of the sensors; the laying method includes horizontal laying and vertical laying; when the laying method is vertical laying, the guide vanes are fixedly installed using a central support shaft that passes through the axis of the pipeline.

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