A method for detecting the flow coefficient of a Pitot tube differential pressure flow meter

Abstract

This invention provides a method for detecting the flow coefficient of a Pitot tube-type differential pressure flowmeter, relating to the field of instrumentation technology. Based on the geometry of the Pitot tube-type differential pressure flowmeter under test and the operating diameter range of the flow standard device, this invention fabricates a scaled-down test flowmeter of the Pitot tube-type differential pressure flowmeter under test; the flow standard device is used to detect the flow coefficient of the test flowmeter; finite element analysis is used to model the Pitot tube-type differential pressure flowmeter under test and the test flowmeter, analyzing the proportional relationship of the flow coefficients of the two flowmeters; based on the flow coefficient of the test flowmeter and the proportional relationship of the flow coefficients of the two flowmeters, the actual flow coefficient of the Pitot tube-type differential pressure flowmeter under test is calculated. This method can broaden the diameter range of Pitot tube-type differential pressure flowmeters that the flow standard device can detect, enabling the detection of the flow coefficient of large-diameter Pitot tube-type differential pressure flowmeters.

Description

Technical Field

[0001] This invention relates to the field of instrumentation technology, and in particular to a method for detecting the flow coefficient of a Pitot tube-type differential pressure flowmeter. Background Technology

[0002] Pitot tube differential pressure flow meters are a classic type of flow meter used for flow measurement in closed pipelines. When fluid flows through the flow meter, the pressure at the dynamic and static orifices changes. The flow rate is obtained by measuring the differential pressure between the dynamic and static orifices (i.e., the differential pressure output by the flow meter) and performing calculations. The flow rate coefficient of the flow meter is required when calculating the flow rate using the differential pressure between the dynamic and static orifices. Regarding the flow rate coefficient of pitot tube differential pressure flow meters, some research institutes have proposed using numerical simulation analysis. However, the reliability of the flow rate coefficient obtained solely from numerical analysis is low compared to the actual flow rate coefficient of the flow meter, and it cannot be used as a basis for manufacturers to assign values. Instrument manufacturers are hesitant to adopt this method. Currently, instrument manufacturers and metrology institutions obtain the flow coefficient of Pitot tube-type differential pressure flowmeters by using flow standard devices with the same pipe diameter. This method is highly reliable and is the only way for manufacturers and metrology institutions to test the flow coefficient of flowmeters. However, when the pipe diameter of the flowmeter exceeds the working pipe diameter range of the flow standard device, the flow coefficient of the flowmeter cannot be tested, which leads to the inability to guarantee the measurement accuracy of large-diameter Pitot tube-type differential pressure flowmeters used in industrial fields. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for detecting the flow coefficient of a Pitot tube differential pressure flow meter, which addresses the shortcomings of the prior art and ensures the measurement reliability of large-diameter Pitot tube differential pressure flow meters.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A method for detecting the flow coefficient of a Pitot tube-type differential pressure flowmeter includes: fabricating a scaled-down test flowmeter based on the geometry of the Pitot tube-type differential pressure flowmeter under test and the operating diameter range of a flow standard device; detecting the flow coefficient of the test flowmeter using the flow standard device; modeling the Pitot tube-type differential pressure flowmeter under test and the test flowmeter using finite element analysis to analyze the proportional relationship of the flow coefficients of the two flowmeters; and calculating the actual flow coefficient of the Pitot tube-type differential pressure flowmeter under test based on the flow coefficient of the test flowmeter and the proportional relationship of the flow coefficients of the two flowmeters.

[0006] Furthermore, the flow standard device is a standard flow generation device. A Pitot tube-type differential pressure flow meter is installed on the pipeline of the flow standard device, so that the standard flow generated by the flow standard device flows through the Pitot tube-type differential pressure flow meter. The Pitot tube-type differential pressure flow meter is detected based on the relationship between the output differential pressure value and the standard flow value. The expression for calculating the flow coefficient of the Pitot tube-type differential pressure flow meter is as follows:

[0007]

[0008] Where α is the flow coefficient, which is dimensionless; q V It is the instantaneous flow rate, m 3 / h; ρ is the density of the fluid medium used for detection, kg / m³ 3 Δp is the differential pressure output by the flow meter, in kPa; D is the diameter of the measuring tube of the flow meter, in mm; (1-ε) is the compression correction factor, dimensionless; for compressible fluids, at low Mach numbers, the compression correction factor is calculated using the following formula:

[0009]

[0010] Where γ is the specific heat ratio, which is dimensionless; p is the absolute static pressure of the fluid at the flow meter, in kPa.

[0011] Furthermore, the method for manufacturing the test flow meter is as follows: based on the ratio n between the pipe diameter of the Pitot tube differential pressure flow meter under test and the test pipe diameter of the flow standard device, a test flow meter with a reduction factor of n relative to the Pitot tube differential pressure flow meter under test is manufactured according to the design drawings of the Pitot tube differential pressure flow meter under test.

[0012] Furthermore, the method for detecting the flow coefficient of the test flowmeter using a flow standard device is as follows:

[0013] Install the test flow meter onto the flow standard device, and use the standard flow value q generated by the flow standard device. s The output differential pressure value Δp of the test flow meter s , density of the test medium ρ s The absolute static pressure p of the fluid at the test flow meter s The flow coefficient α of the test flowmeter was calculated using formulas (1) and (2). s .

[0014] Furthermore, in the modeling process of the finite element analysis method, a three-dimensional physical field model of the test flowmeter during the flow standard device detection process is constructed, as well as a three-dimensional physical field model of the tested Pitot tube differential pressure flowmeter during actual operation.

[0015] Furthermore, during the finite element analysis modeling process, the geometric dimensions of the test flowmeter and the tested Pitot tube differential pressure flowmeter are substituted into the constructed physical field model. The simulated medium type and inlet / outlet structure in the physical field model of the test flowmeter should be the same as the fluid medium type and inlet / outlet structure in the test flowmeter's detection process. Similarly, the simulated medium type and inlet / outlet structure in the physical field model of the tested Pitot tube differential pressure flowmeter should be the same as the medium type and inlet / outlet structure in the actual working operation of the tested Pitot tube differential pressure flowmeter. This ensures that the average flow velocity of the fluid flowing through the test flowmeter and the tested Pitot tube differential pressure flowmeter in the physical field model is the same as the average flow velocity of the test flowmeter when it is detected in the flow standard device. The differential pressure value Δp output by the test flowmeter and the tested Pitot tube differential pressure flowmeter are then simulated and calculated respectively. i 1. Detection of fluid medium density ρ i and the absolute static pressure p of the fluid at the flow meter i The simulated flow coefficient α of the test flowmeter is calculated using formulas (1) and (2). ms The simulated flow coefficient α of the tested Pitot tube differential pressure flowmeter mt .

[0016] Furthermore, the formula for calculating the actual flow coefficient of the tested Pitot tube differential pressure flowmeter is: α t =Cα s Where, C = α mt / α ms , is the correction factor for the instrument coefficient of the test flowmeter, that is, the ratio of the flow coefficient of the Pitot tube differential pressure flowmeter under test to the instrument coefficient of the test flowmeter.

[0017] The beneficial effects of adopting the above technical solution are as follows: the method for detecting the flow coefficient of Pitot tube differential pressure flowmeters provided by the present invention can broaden the range of diameters of Pitot tube differential pressure flowmeters that can be detected by the flow standard device, and realize the detection of the flow coefficient of large-diameter Pitot tube differential pressure flowmeters. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the Pitot tube differential pressure flowmeter provided in an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the installation and connection of the test flow meter in the flow standard device according to an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of the structure of the Pitot tube differential pressure flowmeter under test in the model provided in the embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of the structure of the test flow meter in the model provided in the embodiment of the present invention;

[0022] Figure 5 This is a structural schematic diagram of the cross-section of the verification test Pitot tube differential pressure flowmeter and the verification test Pitot tube differential pressure flowmeter sensor provided in an embodiment of the present invention.

[0023] In the diagram: 1. Pitot tube differential pressure flowmeter under test; 11. Sensor part of the Pitot tube differential pressure flowmeter under test; 2. Test flowmeter; 21. Sensor part of the test flowmeter; 3. Flow standard device; 4. Pitot tube differential pressure flowmeter under test in the model; 41. Inlet part of the Pitot tube differential pressure flowmeter in the model; 42. Outlet part of the Pitot tube differential pressure flowmeter in the model; 5. Test flowmeter in the model; 51. Inlet part of the test flowmeter in the model; 52. Outlet part of the test flowmeter in the model; 6. Pitot tube differential pressure flowmeter under test for verification; 7. Sensor part of the Pitot tube differential pressure flowmeter under test for verification. Detailed Implementation

[0024] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0025] The method for detecting the flow coefficient of a Pitot tube differential pressure flowmeter in this embodiment is as follows.

[0026] Based on the geometry of the Pitot tube differential pressure flowmeter under test and the operating diameter range of the flow standard device, a scaled-down test flowmeter is fabricated. The flow coefficient of the test flowmeter is then measured using the flow standard device. Simultaneously, finite element analysis is used to model both the Pitot tube differential pressure flowmeter under test and the test flowmeter, analyzing the proportional relationship between their flow coefficients. Finally, the flow coefficient of the Pitot tube differential pressure flowmeter under test is calculated based on the flow coefficient of the test flowmeter, thus enabling the detection of the flow coefficient of large-diameter Pitot tube differential pressure flowmeters.

[0027] A flow standard device is a standard flow generation device. A Pitot tube-type differential pressure flow meter is installed on the pipeline of the flow standard device, allowing the standard flow generated by the device to flow through the Pitot tube-type differential pressure flow meter. The flow meter is monitored based on the relationship between its output differential pressure value and the standard flow value. The expression for calculating the flow coefficient of the Pitot tube-type differential pressure flow meter is as follows:

[0028]

[0029] Where α is the flow coefficient, which is dimensionless; q V It is the instantaneous flow rate, m 3 / h; ρ is the density of the fluid medium used for detection, kg / m³ 3Δp is the differential pressure output by the flow meter, in kPa; D is the diameter of the measuring tube of the flow meter, in mm; (1-ε) is the compression correction factor, dimensionless; for compressible fluids, at low Mach numbers, the compression correction factor is calculated using the following formula:

[0030]

[0031] Where γ is the specific heat ratio, which is dimensionless and, for air, is 1.4 unless otherwise specified; p is the absolute static pressure of the fluid at the flow meter, in kPa.

[0032] Based on the ratio *n* between the pipe diameter of the Pitot tube differential pressure flowmeter under test and the test pipe diameter of the flow standard device, a test flowmeter with a reduction factor of *n* is fabricated according to the design drawings of the Pitot tube differential pressure flowmeter under test. The flow coefficient α of the test flowmeter is then measured using the flow standard device. s .

[0033] Since the geometric parameters of the test flowmeter and the tested Pitot tube-type differential pressure flowmeter are proportionally related, they have the same obstruction area ratio (i.e., the ratio of the sensor's obstruction area to the flow area). The pressure taps are also in the same relative position across the pipe's cross-sectional area. Ideally (i.e., when the average flow velocity through the test flowmeter and the tested Pitot tube-type differential pressure flowmeter is the same and the flow field distribution surface is the same), their output differential pressure values ​​are the same. However, due to differences between the actual dimensions of the finished product and the design, and because the flow field distribution surface of the tested Pitot tube-type differential pressure flowmeter and the test flowmeter cannot be completely identical, the flow coefficient of the tested Pitot tube-type differential pressure flowmeter differs from the instrument coefficient of the test flowmeter.

[0034] In order to obtain the ratio of the flow coefficient of the tested Pitot tube differential pressure flowmeter to the instrument coefficient of the test flowmeter (i.e., the correction coefficient of the instrument coefficient of the test flowmeter), a three-dimensional physical field model of the test flowmeter during the flow standard device detection process and a three-dimensional physical field model of the tested Pitot tube differential pressure flowmeter during actual operation are constructed using the finite element analysis method.

[0035] In the constructed physical field model, the geometric dimensions of the test flowmeter and the Pitot tube differential pressure flowmeter under test are substituted into the model. The simulated medium type and inlet / outlet structure in the physical field model of the test flowmeter should be the same as those of the fluid medium and inlet / outlet structure during the test flowmeter's detection process. Similarly, the simulated medium type and inlet / outlet structure in the physical field model of the Pitot tube differential pressure flowmeter under test should be the same as those of the fluid medium and inlet / outlet structure during the actual operation of the Pitot tube differential pressure flowmeter under test. The average flow velocity of the fluid flowing through the test flowmeter and the Pitot tube differential pressure flowmeter under test in the physical field model should be the same as the average flow velocity of the test flowmeter when it is tested in the flow standard device. The Δp of the test flowmeter and the Pitot tube differential pressure flowmeter under test are then simulated and calculated separately. i ρ i and p i The simulated flow coefficient α of the test flowmeter is calculated using formulas (1) and (2). ms The simulated flow coefficient α of the tested Pitot tube differential pressure flowmeter mt Because the correction factor for the instrument coefficient of the test flow meter is C = α. mt / α ms The flow coefficient of the tested Pitot tube differential pressure flowmeter is α. t =Cα s .

[0036] In summary, the working process of the flow coefficient detection method for Pitot tube-type differential pressure flowmeters proposed in this embodiment is as follows:

[0037] Step 1: Based on the design structure of the Pitot tube differential pressure flowmeter under test, fabricate a scaled-down test flowmeter. The scaling-down ratio is the ratio n between the diameter of the Pitot tube differential pressure flowmeter under test and the test diameter of the flow standard device.

[0038] Step 2: Install the test flow meter onto the flow standard device, and use the standard flow rate q generated by the flow standard device. s The output differential pressure value Δp of the testing machine s , density of the test medium ρ s The absolute static pressure p at the test flow meter s The instrument coefficient α of the testing machine is calculated using formulas (1) and (2). s .

[0039] Step 3: Based on the actual geometric dimensions, inlet and outlet structures, and fluid medium type of the tested Pitot tube differential pressure flowmeter and the test flowmeter, establish finite element three-dimensional physical simulation models of the tested Pitot tube differential pressure flowmeter during operation and the test flowmeter during testing. The average flow velocity of the fluid flowing through the tested Pitot tube differential pressure flowmeter and the test flowmeter in the model is the same as the average flow velocity of the test flowmeter when tested in the flow standard device. The Δp values ​​of the tested Pitot tube differential pressure flowmeter and the test flowmeter are obtained through physical simulation model analysis. i ρ i and p i The simulated flow coefficient α of the test flowmeter was calculated using formulas (1) and (2). ms The simulated flow coefficient α of the tested Pitot tube differential pressure flowmeter mt .

[0040] Step 4: Calculate the correction factor C = α for the instrument coefficient of the test flow meter. mt / α ms The flow coefficient α of the tested Pitot tube differential pressure flowmeter was calculated. t =Cα s .

[0041] like Figure 1 The diagram shown is a structural schematic of the tested Pitot tube type differential pressure flow meter 1, where 11 represents the corresponding flow sensor section. Figure 2 The diagram shows the installation and connection of the test flow meter 2 in the flow standard device 3. 21 represents the corresponding flow sensor. The test flow meter 2 and the tested Pitot tube differential pressure flow meter 1 are proportionally scaled. Figure 3 The diagram shown is a structural schematic of the Pitot tube differential pressure flowmeter 4 under test in the model. Figure 4 The diagram shown is a schematic representation of the test flow meter 5 in the model. Figure 5 The diagram shown is a cross-sectional schematic of the Pitot tube differential pressure flowmeter 6 and the sensor 7 of the Pitot tube differential pressure flowmeter used for verification.

[0042] according to Figure 5 The verification process involves fabricating a Pitot tube differential pressure flowmeter 6 and a Pitot tube differential pressure flowmeter sensor 7 for testing. The flowmeter 1 has a pipe diameter of 600 mm, and the test flowmeter 2 has a pipe diameter of 300 mm. The test flowmeter 2 is installed in a flow standard device 3 with a working pipe diameter of 300 mm to obtain the flow coefficient α of the test flowmeter 2. s =0.549.

[0043] Finite element analysis models of the tested Pitot tube differential pressure flowmeter 1 and the test flowmeter 2 were constructed. The dimensions of each part of the tested Pitot tube differential pressure flowmeter 4 and the test flowmeter 5 in the model are the same as the actual dimensions of the tested Pitot tube differential pressure flowmeter 1 and the test flowmeter 2. The inlet section 41 and outlet section 42 of the Pitot tube differential pressure flowmeter in the model have the same structure as the inlet and outlet sections of the tested Pitot tube differential pressure flowmeter 1 during operation. The inlet section 51 and outlet section 52 of the test flowmeter in the model have the same structure as the inlet and outlet sections of the test flowmeter 2 connected in the flow standard device 3. Based on the model, C = α was calculated. mt / α ms = 0.95156. Therefore, according to the method proposed in this embodiment, the flow coefficient of the tested Pitot tube differential pressure flowmeter 1 is α. t =Cα s =0.522.

[0044] The Pitot tube differential pressure flow meter 1 under test is installed on the flow standard device 3 with a working pipe diameter of 600 mm to obtain the actual flow coefficient α of the Pitot tube differential pressure flow meter 1 under test. t0 = 0.524. The method proposed in this embodiment yields the flow coefficient α of the tested Pitot tube differential pressure flowmeter. t The actual flow coefficient α of the tested Pitot tube differential pressure flowmeter 1 t0 The relative error was -0.38%, reaching a level less than ±1%.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for detecting the flow coefficient of a Pitot tube-type differential pressure flowmeter, characterized in that: The method describes the following steps: Based on the geometry of the Pitot tube differential pressure flowmeter under test and the operating diameter range of the flow standard device, a test flowmeter is fabricated that is proportionally scaled down from the Pitot tube differential pressure flowmeter under test; the flow coefficient of the test flowmeter is detected using the flow standard device; the test flowmeter and the Pitot tube differential pressure flowmeter are modeled using the finite element analysis method to analyze the proportional relationship of the flow coefficients of the two flowmeters; and the actual flow coefficient of the Pitot tube differential pressure flowmeter under test is calculated based on the flow coefficient of the test flowmeter and the proportional relationship of the flow coefficients of the two flowmeters. The flow standard device is a standard flow generation device. A Pitot tube-type differential pressure flow meter is installed on the pipeline of the flow standard device, so that the standard flow generated by the flow standard device flows through the Pitot tube-type differential pressure flow meter. The Pitot tube-type differential pressure flow meter is detected based on the relationship between the output differential pressure value and the standard flow value. The expression for calculating the flow coefficient of the Pitot tube-type differential pressure flow meter is as follows: （1）； Where α is the flow coefficient, which is dimensionless; q V It is the instantaneous flow rate, m 3 / h; ρ is the density of the fluid medium used for testing, kg / m³ 3 Δp is the differential pressure output by the flow meter, in kPa; D is the diameter of the measuring tube of the flow meter, in mm; (1-ε) is the compression correction factor, dimensionless; for compressible fluids, at low Mach numbers, the compression correction factor is calculated using the following formula: （2）； Where γ is the specific heat ratio, which is dimensionless; p is the absolute static pressure of the fluid at the flow meter, in kPa.

2. The method for detecting the flow coefficient of a Pitot tube-type differential pressure flowmeter according to claim 1, characterized in that: The method for manufacturing the test flow meter is as follows: based on the ratio n between the pipe diameter of the Pitot tube differential pressure flow meter under test and the test pipe diameter of the flow standard device, and according to the design drawings of the Pitot tube differential pressure flow meter under test, a test flow meter with a reduction factor of n relative to the Pitot tube differential pressure flow meter under test is manufactured.

3. The method for detecting the flow coefficient of a Pitot tube-type differential pressure flowmeter according to claim 2, characterized in that: The method for detecting the flow coefficient of the test flow meter using a flow standard device is as follows: Install the test flow meter onto the flow standard device, and use the standard flow value q generated by the flow standard device. s The output differential pressure value Δp of the test flow meter s , density of the test medium ρ s The absolute static pressure p of the fluid at the test flow meter s The flow coefficient α of the test flowmeter is calculated using formulas (1) and (2). s .

4. The method for detecting the flow coefficient of a Pitot tube-type differential pressure flowmeter according to claim 3, characterized in that: In the modeling process of the finite element analysis method, a three-dimensional physical field model of the test flowmeter during the flow standard device detection process and a three-dimensional physical field model of the Pitot tube differential pressure flowmeter under test during actual operation are constructed.

5. The method for detecting the flow coefficient of a Pitot tube-type differential pressure flowmeter according to claim 4, characterized in that: In the finite element analysis modeling process, the geometric dimensions of the test flowmeter and the Pitot tube differential pressure flowmeter under test are substituted into the constructed physical field model. The simulated medium type and inlet / outlet structure in the physical field model of the test flowmeter should be the same as the fluid medium type and inlet / outlet structure in the test flowmeter's detection process. Similarly, the simulated medium type and inlet / outlet structure in the physical field model of the Pitot tube differential pressure flowmeter under test should be the same as the medium type and inlet / outlet structure in the actual working operation of the Pitot tube differential pressure flowmeter under test. This ensures that the average flow velocity of the fluid flowing through the test flowmeter and the Pitot tube differential pressure flowmeter in the physical field model is the same as the average flow velocity of the test flowmeter when it is detected in the flow standard device. The differential pressure value Δp output by the test flowmeter and the Pitot tube differential pressure flowmeter under test are then simulated and calculated separately. i 1. Detection of fluid medium density ρ i and the absolute static pressure p of the fluid at the flow meter i The simulated flow coefficient α of the test flowmeter is calculated using formulas (1) and (2). ms The simulated flow coefficient α of the tested Pitot tube differential pressure flowmeter mt .

6. The method for detecting the flow coefficient of a Pitot tube-type differential pressure flowmeter according to claim 5, characterized in that: The formula for calculating the actual flow coefficient of the tested Pitot tube differential pressure flowmeter is: α t =Cα s Where C=α mt / α ms , is the correction factor for the instrument coefficient of the test flowmeter, that is, the ratio of the flow coefficient of the Pitot tube differential pressure flowmeter under test to the instrument coefficient of the test flowmeter.

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