Method for measuring air volume within cross-section of air duct in non-uniform wind field

Abstract

The present invention provides a method for measuring air volume within the cross-section of an air duct in a non-uniform wind field, comprising: by using an electrical signal of a rotating speed measurement unit corresponding to at least one of speed measurement fans of different specifications arranged within the cross-section of an air duct in a non-uniform wind field, counting rotations of the speed measurement fan, and then by means of processing of a monitoring analysis unit, calculating a rotating speed value and converting the rotating speed value into circumferential wind speed; on the basis of the circumferential wind speed, and the outer diameter and flow calibration factor of the speed measurement fan, calculating air volume in a plane area measured by the speed measurement fan; repeating said steps to respectively calculate air volume in plane areas measured by the remaining speed measurement fans, and then calculating an area-weighted average of all the speed measurement fans, i.e., the air volume within the cross-section of the whole air duct. On the basis of the torque generated by the wind speed of wind going through the plane covered by the average blade surfaces of the speed measurement fans, as well as on the basis of the average wind speed of wind going through the cross-sectional area covered by the blades and generated by weighted averaging upon the wind passing through the rotating shafts of the speed measurement fans, a weighted value is calculated according to area, thereby using a similar method to obtain the average wind speed on the basis of overall data of a plurality of speed measurement fans, so as to accurately measure air volume within the cross-section of the air duct in the non-uniform wind field.

Description

A method for measuring air volume in a cross section of an air duct in a non-uniform wind field Technical Field

[0001] The present invention belongs to the technical field of air volume measurement, and relates to an air volume measurement method based on a speed measuring fan, and in particular to an air volume measurement method within an air duct cross section in a non-uniform wind field based on a speed measuring fan. Background Art

[0002] According to Chapter 6, pages 166 and 167, of the China Electric Power Press's "Practical Handbook of Flow Measurement" (August 2017, ISBN 978-7-5198-0722-1), requirements for air flow measurement points in the ducts of large coal-fired boilers include a 30-50D straight pipe section and fully developed turbulent flow velocity distribution within the duct. However, in reality, the cross-sectional diameter, width, or height of large coal-fired boilers ranges from 4 to 8 meters, and in engineering designs, the straight pipe section can only be 1 to 3D, significantly different from the 30-50D straight pipe section requirement in the handbook. This means that the duct vortex cannot fully develop into turbulent flow, as required by the measurement requirement.

[0003] Currently, the most widely used air flow measurement technology for large coal-fired boilers is to measure the air flow using weighted coefficients, such as geometrically averaged fixed-point sampling within the duct cross-section. These technologies include one-dimensional (various bar types), two-dimensional (matrix), one-dimensional, and two-dimensional insert-type fixed-point air flow measurement devices. Sampling is performed in duct sections where turbulence is not fully developed. Practice has shown that existing technologies, which employ geometrically symmetrical or uniformly distributed sampling and indifferent pressure averaging, cannot represent the average wind speed across the duct cross-section of large coal-fired boilers, resulting in inaccurate air flow measurement within the duct. Furthermore, existing air flow measurement technologies are prone to dust clogging, preventing coal-fired generators from accurately achieving or approaching their optimal air-to-coal ratio during operation. This significantly reduces the safety and economic efficiency of coal-fired boiler combustion, increases nitrogen oxide production, and leads to higher environmental costs. This severely restricts the flexible power generation capabilities of coal-fired generators, impacts the economic benefits of peak-shaving electricity prices, and compromises the stable operation of the entire power grid. Furthermore, existing air flow measurement technologies are relatively expensive. Summary of the Invention

[0004] In order to solve the problems in the prior art of measuring wind speed in air ducts of large coal-fired boilers (i.e., air ducts with non-uniform wind fields) using geometrically averaged points, resulting in inaccurate air volume measurement, easy dust clogging, complex structure, high installation cost, and large wind resistance, the present invention provides an air volume measurement method for measuring air volume in a cross-section of an air duct with non-uniform wind fields, which is accurate, non-clogging, low-cost, and low-wind resistance, comprising the following steps:

[0005] Step 1: Using the electrical signals of the speed measurement units corresponding to at least one speed-measuring fan of different specifications set in the cross-section of the wind duct of the non-uniform wind field, the rotations of the speed-measuring fans are counted and a pulse sequence is generated. The speed values ​​are then converted into the circular wind speed through the conversion processing of the monitoring and analysis unit. The calculation formula is as follows:

[0006]

[0007] in,

[0008] μ2——the circumferential linear velocity of the outer diameter of the speed measuring fan, in m / s;

[0009] n——the number of revolutions per minute of the speed measuring fan, unit: / s;

[0010] D2——the outer diameter of the speed measuring fan, in m;

[0011] Step 2: Based on the calculated circumferential velocity μ2, and according to the outer diameter D2 and flow calibration coefficient Q1 of the speed measuring fan, the air volumes L1, L2, L3, ..., LN within the plane area sensed by the speed measuring fan are calculated respectively. The formula is as follows:

[0012]

[0013] in,

[0014] Li——the calculated air volume of the i-th speed-measuring fan, in m 3 / s;

[0015] D2——the outer diameter of the speed measuring fan, in m;

[0016] Q1———Flow calibration coefficient, which is related to the shape and working conditions of the speed measuring fan;

[0017] Step 3: Based on the calculated air volumes L1, L2, L3, ..., LN and the proportions S1, S2 ... SN of the rotating cross-sectional area of ​​each fan blade of the speed-measuring fan to the total cross-sectional area, the air volume of the entire sensing air duct cross-section is calculated. The calculation formula is as follows:

[0018] L=L1*S1+L2*S2+ L3*S3+ …+ LN*SN

[0019] N——The number of speed measuring fans of different specifications set in the cross section of the wind duct in the non-uniform wind field;

[0020] S1, S2, S3, ..., SN are the proportions of the rotating cross-sectional area of ​​the entire fan blade of several speed-testing fans of different specifications to the total cross-sectional area;

[0021] The speed measuring fan is an unpowered fan.

[0022] Preferably, within the non-uniform wind field air duct cross section, a guide plate with a peak-shaped windward surface is respectively provided between the speed measuring fans and between the fans and the air duct wall of the non-uniform wind field air duct cross section.

[0023] Preferably, at least two speed measuring fans of different specifications and speed measuring units for respectively monitoring them are provided in the cross section of the wind duct of the non-uniform wind field.

[0024] Preferably, the speed measuring fan includes fan blades, fan blade handles and a rotating shaft; an external fixed bearing is also provided at a corresponding position on the special-shaped steel frame on which the speed measuring fan is provided; and the rotating shaft is axially embedded in the external fixed bearing.

[0025] Preferably, the speed measuring unit includes a permanent magnet element provided at the outer end of one of the blades of the speed measuring fan and a magnetic counter provided outside the speed measuring fan and at a corresponding position thereto; wherein the magnetic counter is arranged on the special-shaped steel frame, and the magnetic counter is electrically connected to the monitoring and analysis units respectively.

[0026] Preferably, the material of the speed measuring fan blades is carbon fiber, titanium alloy, silicon carbide, aluminum, iron, acrylic, plastic, solid wood or plywood; the number of the speed measuring fan blades is an odd number greater than 1.

[0027] Preferably, the number of blades of the speed measuring fan is three, five, seven, nine or eleven.

[0028] The present invention utilizes at least one speed-measuring fan of different specifications to be set up in the cross-section of the air duct in a non-uniform wind field (for example, a square air duct can also be provided with a large speed-measuring fan and small speed-measuring fans of the same specifications at the four corners). The torque is generated by the wind speed of the plane reached by the average fan blade surface, and the average wind speed of the cross-section reached by the fan blade is generated after averaging and weighting by its rotating shaft. The area-weighted average value, i.e., the air volume of the entire air duct cross-section, is then calculated. The invention has the advantages of low cost, excellent dynamic average speed performance, low wind resistance (i.e., it rotates in the direction of the flow without obstruction), accurate real-time dynamic measurement, and easy project implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 is a schematic diagram of the arrangement of a three-blade speed measuring fan in a square air duct cross section in an air volume measurement device based on a speed measuring fan according to a first embodiment;

[0030] FIG2 is a schematic diagram of the arrangement of the special-shaped steel frame 3 shown in FIG1 within the cross section of the square air duct;

[0031] FIG3 is an enlarged schematic cross-sectional view of a node where a speed measuring fan is provided in the special-shaped steel frame 3 shown in FIG2 ;

[0032] FIG4 is an enlarged schematic cross-sectional view of the special-shaped steel bars in the special-shaped steel frame 3 shown in FIG2 ;

[0033] FIG5 is a schematic diagram of the three-dimensional structure of the speed measuring fan 2 shown in FIG1 ;

[0034] FIG6 is a front view of the right-angle guide plate shown in FIG1 ;

[0035] FIG7 is a schematic cross-sectional view taken along line AA of the right-angle guide plate shown in FIG6 ;

[0036] FIG8 is a front view of the side guide plate shown in FIG1 ;

[0037] FIG9 is a schematic cross-sectional view taken along line BB of the side guide plate shown in FIG8 ;

[0038] FIG10 is a front view of the central guide plate shown in FIG1 ;

[0039] FIG11 is a schematic cross-sectional view of the central guide plate shown in FIG10 taken along the CC direction;

[0040] FIG12 is a schematic diagram of an air volume measurement system based on the speed measurement fan shown in FIG1 ;

[0041] FIG13 is a schematic diagram showing the arrangement of a three-blade speed measuring fan in a square air duct cross section in an air volume measurement device based on a speed measuring fan according to a second embodiment;

[0042] FIG14 is a schematic diagram of the arrangement of the special-shaped steel frame 3' shown in FIG13 within the cross section of the square air duct;

[0043] FIG15 is a flow chart of a method for measuring air volume in a square air duct cross section with a non-uniform wind field, in which several speed-measuring fans of the same specification are arranged; and

[0044] FIG16 is a flow chart of an air volume measurement method in which several speed-measuring fans of different specifications are arranged in a square air duct cross section in a non-uniform wind field.

[0045] Description of the numbers in the figure:

[0046] 1. Square air duct wall; 2. Speed ​​measuring fan, 21. Fan blade, 22. Permanent magnet element, 23. Fan blade handle, 24. Rotating shaft; 3. Special-shaped steel frame, 31. Special-shaped steel bar, 32. External fixed bearing, 4. Guide plate, 4A. Right-angle guide plate, 4B. Side guide plate, 4C. Center guide plate, 5. Magnetic counter. DETAILED DESCRIPTION

[0047] The following describes the present invention in detail by taking the arrangement of a three-blade speed measuring fan in a square air duct cross section in a non-uniform wind field as an example and combining the accompanying drawings and specific embodiments. Example 1

[0048] As shown in Figures 1-11, it is a schematic diagram of the arrangement of a three-blade speed measuring fan in a square air duct cross section of a non-uniform wind field in an air volume measurement device based on a speed measuring fan; and an air volume measurement system based thereon, as shown in Figure 12. The air volume measurement device includes four groups of speed measuring fans 2 and magnetic counters 5 thereof, each of which has a permanent magnet element 22 at the outer end of a blade 21, and a monitoring and analysis unit, uniformly distributed on a special-shaped steel frame 3 in a square air duct cross section of a non-uniform wind field; in order to prevent air leakage between the speed measuring fans 21 and between the square air duct wall 1 of the non-uniform wind field, a guide plate with a peak-shaped windward surface is also provided between them (i.e., a right-angle guide plate 4A (its structural schematic diagram is shown in Figures 6 and 7), a side guide plate 4B (its structural schematic diagram is shown in Figures 8 and 9), and a center guide plate 4C (its structural schematic diagram is shown in Figures 10 and 11)); wherein the magnetic counter 5 is respectively connected to the monitoring and analysis unit. The unit is electrically connected; the speed measuring fan includes blades 21, a blade handle 23 and a rotating shaft 24, wherein the blades 21 are evenly distributed on the outer periphery of one side of the blade handle 23, and the rotating shaft 24 is arranged at the center of the axis on the other side of the blade handle 23 (its structural schematic diagram is shown in Figure 5); the special-shaped steel frame 3 (its layout schematic diagram is shown in Figure 2) is a grid-like frame composed of special-shaped steel bars 31 (its cross-sectional structural schematic diagram is shown in Figure 4) according to the arrangement of the evenly distributed speed measuring fans (based on the principle of minimizing the wind resistance within the measurement cross section), and an external fixed bearing 32 is provided at the corresponding position of the evenly distributed speed measuring fan on it; the rotating shaft 24 is axially embedded in the external fixed bearing 32 (its structural schematic diagram is shown in Figure 3). The position of the non-uniform wind field square air duct cross section of the above-mentioned three-blade speed measuring fan can be at any longitudinal position of the air duct, and is not restricted by the length of the straight air duct required by the existing design specifications.

[0049] The speed measuring unit comprises a permanent magnet element arranged at the outer end of one of the blades of the speed measuring fan and a magnetic counter arranged outside the speed measuring fan and at a corresponding position thereto.

[0050] How it works:

[0051] Four three-blade speed measuring fans are evenly distributed in the cross-section of the wind duct in the non-uniform wind field. Due to the different positions of each speed measuring fan, the wind speed in the sensing area is different; each blade 21 of each speed measuring fan senses the wind speed at the cross-sectional position within the area where it is located: the same blade senses different wind speeds at different points in the measurement area (non-uniform wind duct wind field); in this way, different rotational torques will be generated at the corresponding points of the blade 21, and the rotational force average of the first rotational thrust will be achieved through the surface of the blade 21; then the three blades 21 form different wind speed rotational thrusts and then pass through the blade handle 23 connected to them to perform secondary rotational thrust self-average on the rotating shaft 24; finally, the real-time speed of the speed measuring fan is obtained, which represents the average wind speed in the plane covered by the speed measuring fan; at the same time, the average speed is monitored in real time by the permanent magnet element 22 installed on the outer end of a blade 21 of the speed measuring fan, and the magnetic counter 5 set on the square air duct wall monitors its number of rotations per minute, and the number of rotations per minute of the speed measuring fan is transmitted to the monitoring and analysis unit in real time.

[0052] The air volume calculation method for four speed-measuring fans of the same specification evenly distributed in the square air duct cross section of the above non-uniform wind field is as follows (as shown in Figure 15):

[0053] Step 1: Using the electrical signal of the speed measurement unit corresponding to at least one speed-measuring fan of the same specification set in the cross-section of the wind duct of the non-uniform wind field, the rotation of the speed-measuring fan is counted and a pulse sequence is generated. The speed value is then converted into the circular wind speed μ2 through the conversion processing of the monitoring and analysis unit. The calculation formula is as follows:

[0054]

[0055] in,

[0056] μ2——the circumferential wind speed of the outer diameter of the speed measuring fan, in m / s;

[0057] n——the number of revolutions per minute of the speed measuring fan, unit: / s;

[0058] D2——the outer diameter of the speed measuring fan, in m;

[0059] Step 2: Based on the calculated circumferential wind speed μ2, and the outer diameter D2 and flow calibration coefficient Q1 of the speed measuring fan, the air volumes L1, L2, L3, ..., LN in the plane area sensed by the speed measuring fan are calculated respectively. The formula is as follows:

[0060]

[0061] in,

[0062] Li——the calculated air volume of the i-th speed-measuring fan, in m 3 / s;

[0063] D2——the outer diameter of the speed measuring fan, in m;

[0064] Q1———Flow calibration coefficient, which is related to the shape and working conditions of the speed measuring fan;

[0065] The speed measuring range and accuracy of the speed measuring fan are as follows: the general accuracy can only reach 0.1m / s, and the maximum range can reach 50m / s.

[0066] Step 3: Calculate the air volume of the entire sensing air duct cross section using the following formula:

[0067]

[0068] in,

[0069] N is the number of speed-measuring fans of the same specification uniformly distributed in the cross section of the air duct in the non-uniform wind field. In this embodiment, N is 4.

[0070] In this embodiment, the speed measuring fan is an unpowered fan, which can calculate the average wind speed of the plane reached by the average fan blade surface. The average values ​​of different speed measuring fans are weighted to calculate the average wind speed of the plane, thereby accurately calculating the air volume in the cross section of the wind duct in the non-uniform wind field.

[0071] In this embodiment, the speed-measuring fans may be unpowered fans of the same specifications or unpowered fans of different specifications.

[0072] In this embodiment, the fan blades can be made of carbon fiber blades, titanium alloy blades, silicon carbide blades, aluminum blades, iron blades, acrylic blades, plastic blades, solid wood blades, and plywood blades. To ensure stable operation of the speed measuring fan, the number of blades of the speed measuring fan is an odd number greater than 1, such as three, five, seven, nine, eleven, or more blades, depending on the wind speed in the non-uniform wind field and wind duct.

[0073] In this embodiment, the speed measuring fan is an unpowered fan. The more speed measuring fans are arranged in the cross-section of the air duct in the measured non-uniform wind field, the closer the comprehensive average wind speed of each speed measuring fan will be to the average wind speed in the measured cross-section. At the same time, in order to prevent air leakage between the blades of each speed measuring fan and between the blades of each speed measuring fan and the wall of the air duct in the non-uniform wind field during the rotation of each speed measuring fan, a guide plate with a windward surface in the shape of a mountain peak is designed between them to achieve the purpose of full wind speed measurement and fixed speed measuring fans.

[0074] The air flow measurement device of the present invention is simple and easy to use. It accurately measures the average wind speed within the cross-section of a non-uniform wind field duct by averaging the wind speed of each blade in the tachometer fan and averaging the wind speed across the matrix group of tachometer fans. This overcomes the stringent design specification requirement that the straight pipe section for air flow measurement in large coal-fired boiler ducts be 30-50 degrees. It is particularly suitable for measuring air flow in large coal-fired boiler ducts with no straight sections or variable diameters. This effectively solves the global problem of inaccurate air flow measurement in non-uniform wind field ducts caused by turbulence, vortices, and other phenomena.

[0075] In addition to the overall layout selection design of a plurality of speed measuring fans uniformly distributed in the air duct and the speed measuring fan with a guide plate having a peak-shaped windward surface, the present embodiment can also be: the overall layout design is carried out according to factors such as the geometric shape of the air duct cross section, the error of the air volume measured by the overall layout selection design scheme of the speed measuring fan in the air duct cross section, and the size of the wind resistance of the overall layout selection design scheme of the speed measuring fan in the air duct cross section; for example, a speed measuring fan with a blade of the same size as the circular radius is set for an air duct with a non-uniform wind field cross section, and then the speed measuring fan with a blade of the same size as the circular radius is set according to the measurement error and the wind resistance. The other specification parameters of the speed measuring fan except its outer diameter are selected as small (minimizing the wind resistance as much as possible while satisfying the measurement error); for a duct with a square cross section in a non-uniform wind field, a speed measuring fan with an inscribed circle in the square is set, and a speed measuring fan of the same specification is arranged at each of the four corners between the speed measuring fan and the square duct wall, or a guide plate with a mountain-shaped windward surface is filled in each corner (wherein the other specification parameters of the speed measuring fan except its outer diameter are selected: overall measurement error and wind resistance (minimizing the wind resistance as much as possible while satisfying the overall measurement error)). The overall layout design scheme for the square duct with a non-uniform wind field cross section mentioned above: one large speed measuring fan and four small speed measuring fans, and the air volume (i.e., the average wind speed value of the duct) measurement method (calculation method) is as follows (as shown in Figure 16):

[0076] First, calculate the air volume of each speed-measuring fan (one large speed-measuring fan and four small speed-measuring fans) based on steps 1 and 2 of the air volume calculation method for four speed-measuring fans of the same specification evenly distributed within the cross-section of a square air duct in a non-uniform wind field;

[0077] Then multiply the calculated air volume of each speed-measuring fan by the proportion of the entire fan blade rotating cross-sectional area of ​​each speed-measuring fan in the entire air duct cross-sectional area to obtain the average air speed value of the air duct (assuming the air volume value of the large speed-measuring fan is LA1, the proportion SA1 of its entire fan blade rotating cross-sectional area in the entire air duct cross-sectional area is 0.8, and the air volume values ​​of the four small speed-measuring fans are La1, La2, La3, and La4 respectively, and the proportions sa1, sa2, sa3, and sa4 of their respective entire fan blade rotating cross-sectional areas in the entire air duct cross-sectional area are all 0.05):

[0078] The average wind speed value of the air duct = the sum of the air volume value of each speed-measuring fan multiplied by the proportion of the entire fan blade rotating cross-sectional area of ​​each speed-measuring fan in the entire air duct cross-sectional area

[0079] =LA1*SA1+La1*sa1+ La2*sa2+ La3*sa3+ La4*sa4

[0080] =LA1*0.8+ La1*0.05+ La2*0.05+ La3*0.05+ La4*0.05

[0081] For example, an air duct with a rectangular cross-section in a non-uniform wind field is provided with two speed-measuring fans inscribed in the rectangle, and a speed-measuring fan of the same specification is arranged at each of the four corners between the two speed-measuring fans and the rectangular air duct wall, or each is filled with a guide plate with a peak-shaped windward surface (of course, the above two adjacent corner areas can be provided with only one speed-measuring fan or additionally with a guide plate with a peak-shaped windward surface. For the selection of other specification parameters of the speed-measuring fan except its outer diameter and the calculation of the average wind speed value of the air duct, please refer to the above-mentioned air duct calculation method for the air duct with a square cross-section in a non-uniform wind field).

[0082] The measurement error of the overall layout selection and design scheme of the speed measurement fan within the air duct cross section in this embodiment can be determined according to the following three methods:

[0083] 1. Computer simulation The air duct model is determined by computer;

[0084] 2. Indirect determination based on laboratory simulation of actual air duct experiments;

[0085] 3. Install in the actual air duct and calibrate with standard measuring instruments to determine the actual measurement (the air volume measuring device is also a measuring instrument and must be calibrated by a calibration agency before it can be used. As long as the measurement error of the air volume measuring device in this embodiment is within the calibration range).

[0086] The technical solution of this embodiment is easier to implement in actual engineering implementation and installation, and its practicality is stronger; at the same time, compared with the existing uniform tube air volume measuring device, multi-point insertion air volume measuring device, especially the existing Pitot tube air volume flowmeter or Venturi air volume flowmeter and the big data air volume measurement system composed thereof (such as Chinese Patent No. CN2022227521229 Patent Name: A Air Volume Measurement System for Air Ducts in Non-uniform Wind Fields, Chinese Patent CN2022227517134 Patent Name: A Air Volume Measurement System Based on Big Data Analysis), a back-purge device is required to prevent dust from clogging the air volume flowmeter. Dust will not cause clogging problems, and accurate measurements can be made in real time and dynamically, with low cost and easy operation and maintenance. In addition, compared with the wing-type air volume measuring device in the prior art, there is almost no wind resistance loss. Example 2

[0087] As shown in Figure 13, this is a schematic diagram of the arrangement of two three-blade speed measuring fans in a square air duct cross-section of a non-uniform wind field in an air volume measurement device based on a speed measuring fan; the difference from Example 1 is that the two three-blade speed measuring fans are installed at the position of the data average wind speed point in the square air duct cross-section of the non-uniform wind field, and there is no need to set a guide plate with a peak-shaped windward surface between the speed measuring fans 2 and between the speed measuring fans 2 and the square air duct wall 1 of the non-uniform wind field; since the speed measuring fans are irregularly arranged in the square air duct cross-section of the non-uniform wind field, the structure of the special-shaped steel frame 3' that fixes them is also changed accordingly, as shown in Figure 14; for the remaining structural parts, please refer to the corresponding parts of Example 1.

[0088] How it works:

[0089] In this embodiment, the speed measuring fan is an unpowered fan, which is set at the position of the data average wind speed point in the square air duct cross-section of the non-uniform wind field. By weighting the wind speed of the plane reached by the self-average fan blade surface, the average value of the two speed measuring fans can directly calculate the average wind speed in the square air duct cross-section of the non-uniform wind field, thereby accurately measuring the wind volume in the square air duct cross-section of the non-uniform wind field; or directly using the self-average wind speed of one of the speed measuring fans, the wind volume in the square air duct cross-section of the non-uniform wind field can also be accurately measured.

[0090] In this embodiment, the number of speed-measuring fans is determined based on the number of data-average wind speed points within a square air duct cross-section in a non-uniform wind field, with at least one speed-measuring fan provided. Furthermore, a speed-measuring fan of specific specifications (primarily referring to parameters such as blade material, blade shape and size, and number of blades) is selected based on the average wind speed value. Specifically, after the average wind speed position is determined, the smaller the speed-measuring fan's dimensions, the more accurate the air volume measurement within the non-uniform wind field cross-section. This method for determining data-average wind speed points within a non-uniform wind field cross-section has been disclosed in a Chinese patent (Patent No. CN2022112805951, titled "Method for Determining Data-Average Wind Speed ​​Points within a Non-Uniform Wind Field Cross-Section"). A speed measuring fan is directly set at the data average wind speed point. Since the speed measuring fan can measure the wind speed of the plane reached by the average fan blade surface, the position error of the speed measuring fan in the cross section of the non-uniform wind field duct does not need to be particularly precise, and the air volume in the square air duct cross section of the non-uniform wind field can be accurately measured. In this way, the technical solution of this embodiment is easier to implement in actual engineering implementation and installation, and its practicality is stronger; at the same time, compared with the existing uniform pipe air volume measurement device, multi-point insertion air volume measurement device, especially the existing Bar-type air volume flowmeter or Venturi-type The air volume flow meter and the big data air volume measurement system it constitutes (such as Chinese patent number CN2022227521229, patent name: an air volume measurement system for an air duct in a non-uniform wind field, and Chinese patent CN2022227517134, patent name: an air volume measurement system based on big data analysis) must also be equipped with a back-purge device to prevent dust from clogging the air volume flow meter. This will prevent clogging problems caused by dust, and its structure is simple and the installation cost is low. In addition, compared with the wing-type air volume measurement device in the prior art, there is almost no wind resistance loss. In addition, in order to prevent the failure of one of the speed measuring fans or the speed measuring unit (the speed measuring unit includes a permanent magnet element provided at the outer end of one of the blades of the speed measuring fan and a magnetic counter provided at the outer edge of the speed measuring fan and at a corresponding position), a speed measuring fan can be respectively provided at two or more data average wind speed points within the cross-section of the square air duct in the non-uniform wind field, and speed measuring units can be used to monitor them respectively. The specific specifications of the speed measuring fans should be basically the same (the reason is that the wind speeds at the data average wind speed points within the cross-section of the square air duct in the non-uniform wind field are approximately equal within the allowable range of air volume measurement error).

[0091] After confirming the three average wind speed points according to the technical solution disclosed in the Chinese patent (patent number CN2022112805951, patent name: method for determining the average wind speed value points of data within the cross-section of a wind duct in a non-uniform wind field), a counter-verification experiment on the accuracy of its air volume measurement was conducted using a standard wind tunnel experimental device (this standard wind tunnel experimental device is the wind tunnel experimental device of the Baoji Branch of Xi'an Zhongwang Measurement and Control Instrument Co., Ltd., designed and manufactured by Chongqing Lantian Instrument Co., Ltd., and calibrated by Chongqing Metrology and Quality Inspection Institute. The calibration was performed using a Pitot tube flowmeter, and the air duct was designed with a 1:1 actual air duct outer dimension, that is, the experimental air duct disclosed in the Chinese patent (patent number CN2022112805951, patent name: method for determining the average wind speed value points of data within the cross-section of a wind duct in a non-uniform wind field) with a 1:1 ratio to the actual air duct). The experimental time was August 16, 2023, and the experimental process is as follows:

[0092] Step 1: Use the standard measuring instruments in Table 1 to calibrate the seven different wind speeds at the three average wind speed points mentioned above. The corresponding recorded data are shown in Table 2.

[0093] Table 1: List of main standard measuring instruments used in calibration:

[0094]

[0095] Step 2: First, use a dual-throat air velocity measuring device (Xi'an Zhongwang Measurement and Control Instrument Co., Ltd. dual-throat air volume measuring device: Model AFM-110) to measure the differential pressure values ​​at the three average wind speed points mentioned above under seven different wind speed conditions. Then use a fan anemometer (Germany Testo Mini Anemometer, Model TESTO 410-1) to measure and verify the wind speed at the three average wind speed points mentioned above under seven different wind speed conditions. The records are as follows:

[0096] Table 2: Measurement data record table of three measurement methods: standard calibration measurement section wind speed (Pitot tube) - throat diameter (traditional differential pressure) - fan anemometer (speed measuring fan)

[0097]

[0098] Note: The calibration section reference wind speed measuring instruments are calibrated by the national traceability agency and are within the validity period. The calibration section reference wind speed measurement results are used as the comparison standard for the measurement results of the double-throat diameter wind speed measuring device (differential pressure type) and the fan flow meter. The measurement results of the double-throat diameter wind speed measuring device and the fan flow meter are their actual measurement data.

[0099] Step 3: Calculate the error between the wind speeds at the three average wind speed points in the air duct and the average wind speed of the three average wind speed points (according to the corresponding reference wind speed (one of the seven wind speeds mentioned above) and the corresponding average wind speed point, and the percentage of the conversion based on the calibrated reference wind speed measurement result), see Table 3.

[0100] Table 3: Average wind speed at three average wind speed points, and the error conversion table between the wind speed at three average wind speed points and the average wind speed at three average wind speed points

[0101]

[0102]

[0103] The error values ​​in Table 3 are calculated by subtracting the average wind speed value of the three points from the wind speed value at each point, dividing by the maximum wind speed (17.52), and multiplying by 100. The three error values ​​are then averaged, and the average error values ​​all reach above level 0.6, that is, the wind volume measurement accuracy reaches above level 0.6.

[0104] The above experiments prove that the fan flow meter (speed measuring fan) verifies the results at the above three average wind speed points and seven different wind speeds, and its air volume measurement accuracy reaches above level 0.6, which is far better than the 2% accuracy requirement of the national industrial secondary flow measurement standard stipulated by the standard.

[0105] In this embodiment, the fan blade material can be selected from carbon fiber fan blades, titanium alloy fan blades, silicon carbide fan blades, aluminum fan blades, iron fan blades, acrylic fan blades, plastic fan blades, solid wood fan blades and plywood fan blades.

[0106] In order to ensure stable operation of the speed measuring fan, the number of fan blades of the speed measuring fan is selected to be an odd number greater than 1 according to the wind speed in the non-uniform wind field and wind duct, such as three, five, seven, nine, eleven or more fan blades.

[0107] The inventive point of the present invention is: 1) using a number of speed measuring fans of the same specification in the cross-section of the air duct in a non-uniform wind field (such as a large speed measuring fan in a square air duct and guide plates with peak-shaped windward surfaces at the four corners, or the speed measuring fans in the square air duct as in Example 1: four speed measuring fans of the same specification and guide plates with peak-shaped windward surfaces between them and between the air duct walls) or a number of speed measuring fans of different specifications (such as a rectangular air duct or other irregular air duct, a square air duct can also be provided with a large speed measuring fan and small speed measuring fans of the same specification at the four corners), generating torque through the wind speed of the plane reached by their self-average fan blade surface, and the average wind speed of the fan blade reached by the average weighted average of its rotating shaft, and then dynamically calculating the weighted average value or area weighted average value, that is, the air volume of the entire air duct cross-section, thereby accurately measuring the air volume in the cross-section of the air duct in the non-uniform wind field by using technical means similar to the overall data average wind speed. 2) By directly setting a speed measuring fan at the data average wind speed point in the cross section of the wind duct in the non-uniform wind field, the wind speed of the plane reached by the self-average fan blade surface of the speed measuring fan is used. There is no need to use the average value of each speed measuring fan to weight and dynamically calculate the average wind speed of the entire cross section in real time. Therefore, a technical means similar to the data average wind speed can be used to conveniently and accurately measure the air volume in the cross section of the wind duct in the non-uniform wind field. This breaks the drawback of the geometric average designed to replace the inaccurate cross-sectional wind speed measurement required by previous domestic and international specifications for very long straight pipe sections that cannot be met. The above describes the present invention by taking the wind volume measurement device based on the speed measuring fan arranged in the cross section of the square wind duct in the non-uniform wind field as an example in conjunction with the accompanying drawings, but it can be understood that those skilled in the art can make changes or improvements to the present invention without departing from the essential spirit and scope of the present invention, but all should fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for measuring the air volume in a cross section of an air duct in a non-uniform wind field, characterized in that: The steps include: Step 1: Using the electrical signal of the speed measurement unit corresponding to at least one speed measuring fan of different specifications set in the cross section of the wind duct of the non-uniform wind field, the rotation of the speed measuring fan is counted and a pulse sequence is generated. Then, the speed value is obtained through the conversion processing of the monitoring and analysis unit and converted into the circular wind speed. The calculation formula is as follows: in, μ2——Circumferential linear velocity of the outer diameter of the speed measuring fan, in m / s; n——the number of revolutions per minute of the speed measuring fan, unit: / s; D2——the outer diameter of the speed measuring fan, in m; Step 2: According to the circumferential velocity μ2 calculated above, and according to the outer diameter D2 and flow calibration coefficient Q1 of the speed measuring fan, the air volumes L1, L2, L3, ..., LN in the plane area sensed by the speed measuring fan are calculated respectively, and the formula is as follows: in, Li———Calculated air volume of the i-th speed-measuring fan, in m 3 / s; D2——The outer diameter of the speed measuring fan, in m; Q1——Flow calibration coefficient, which is related to the shape and working condition of the speed measuring fan; Step 3: Based on the above-calculated air volumes L1, L2, L3, ..., LN and the proportions S1, S2 ... SN of the entire blade rotation cross-sectional area of ​​each speed measuring fan in the entire cross-sectional area; calculate the air volume of the entire sensing air duct cross-sectional area, and the calculation formula is as follows: L=L1*S1+L2*S2+ L3*S3+ …+ LN*SN Among them, N——The number of speed measuring fans of different specifications set in the cross section of the wind duct in the non-uniform wind field; S1, S2, S3, ..., SN——respectively represent the proportion of the rotating cross-sectional area of ​​the entire blade of a number of speed-testing fans of different specifications to the entire cross-sectional area; The speed measuring fan is an unpowered fan.

2. The air volume measurement method according to claim 1, characterized in that: In the non-uniform wind field air duct cross section, a guide plate with a peak-shaped windward surface is respectively arranged between the speed measuring fans and between the air duct wall of the non-uniform wind field air duct cross section.

3. The air volume measurement method according to claim 1 or 2, characterized in that: At least two speed measuring fans of different specifications and speed measuring units for respectively monitoring the fans are arranged in the cross section of the wind channel of the non-uniform wind field.

4. The air volume measurement method according to claim 1 or 2, characterized in that: The speed measuring fan comprises fan blades, a fan blade handle and a rotating shaft; an external fixed bearing is also arranged at a corresponding position on the special-shaped steel frame on which the speed measuring fan is arranged; and the rotating shaft is axially embedded in the external fixed bearing.

5. The air volume measurement method according to claim 4, characterized in that: The speed measurement unit includes a permanent magnet element arranged at the outer end of one of the blades of the speed measuring fan and a magnetic counter arranged outside the speed measuring fan and at a corresponding position thereto; wherein the magnetic counter is arranged on the special-shaped steel frame, and the magnetic counter is electrically connected to the monitoring and analysis units respectively.

6. The air volume measurement method according to claim 3, characterized in that: The speed measuring fan comprises fan blades, a fan blade handle and a rotating shaft; an external fixed bearing is also arranged at a corresponding position on the special-shaped steel frame on which the speed measuring fan is arranged; and the rotating shaft is axially embedded in the external fixed bearing.

7. The air volume measurement method according to claim 6, characterized in that: The speed measurement unit includes a permanent magnet element arranged at the outer end of one of the blades of the speed measuring fan and a magnetic counter arranged outside the speed measuring fan and at a corresponding position thereto; wherein the magnetic counter is arranged on the special-shaped steel frame, and the magnetic counter is electrically connected to the monitoring and analysis units respectively.

8. The air volume measurement method according to claim 1, 2, 5, 6 or 7, characterized in that: The material of the speed measuring fan blades is selected from carbon fiber, titanium alloy, silicon carbide, aluminum, iron, acrylic, plastic, solid wood or plywood; the number of the speed measuring fan blades is an odd number greater than 1.

9. The air volume measurement method according to claim 8, characterized in that: The number of blades of the speed measuring fan is selected to be three, five, seven, nine or eleven.

10. The air volume measurement method according to claim 3, characterized in that: The material of the speed measuring fan blades is selected from carbon fiber, titanium alloy, silicon carbide, aluminum, iron, acrylic, plastic, solid wood or plywood; the number of the speed measuring fan blades is an odd number greater than 1.

11. The air volume measurement method according to claim 4, characterized in that: The material of the speed measuring fan blades is selected from carbon fiber, titanium alloy, silicon carbide, aluminum, iron, acrylic, plastic, solid wood or plywood; the number of the speed measuring fan blades is an odd number greater than 1.

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