A method for measuring air flow rate in a confined space

Abstract

The present invention discloses a method for measuring air flow rate in a confined space. Two gas flow meters of different types are selected as the first flow meter and the second flow meter respectively; in the target confined space, the air flow rate is tested simultaneously by the two gas flow meters to obtain test data; according to the test data, the measurement variances of the two gas flow meters are obtained respectively; in the target confined space, the air flow rate is measured formally by the two gas flow meters to obtain the instantaneous measurement values of the two gas flow meters respectively; according to the instantaneous measurement values and the measurement variances, the estimated value of the instantaneous gas flow rate is obtained; according to the estimated value, the gas flow rate measurement result is obtained; using the present invention can improve the accuracy of measuring the flow rate of gas with uneven convection field distribution in a confined space.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline air flow measurement, and particularly relates to a method for measuring air flow in a limited space. Background Art

[0002] Radionuclide substances usually exist in the air by attaching to aerosols in the air and mainly diffuse with the movement of the atmosphere. Since under normal environmental conditions, the activity concentration of radionuclides in the air is very low, it is difficult for general radiation measurement instruments to detect the weak changes in the activity concentration of radionuclides in the air. To accurately detect the activity concentration of radionuclides in the air in a short time, it is necessary to rely on an aerosol sampling device to collect a large amount of air in a short time, use an aerosol filter membrane to filter and collect aerosol particles in the air to make a sample to be measured, and then use a special radiation measurement instrument to measure and analyze the radionuclides. The aerosol sampling device needs to detect the instantaneous air flow in the air sampling pipeline in real time and dynamically adjust the power of the fan to ensure that the sampled air flow is stable within a predetermined range and provide the data of the final total air sampling volume for the aerosol sampling device.

[0003] In the construction of a radiation environment monitoring station, it is often necessary to integrate an aerosol sampling device and other radiation monitoring devices in a movable shelter, which will strictly limit the installation space of the aerosol sampling device and make the length of the straight pipe section of the air duct limited; moreover, when integrating and installing multiple devices in a narrow and cramped space, the sizes of the air duct components are inevitably different; these factors will cause the gas flow field distribution in the air duct to be uneven, resulting in a large measurement error of the gas flowmeter for air flow. And in actual use, the cleanliness of the air will also change with the changes of conditions such as the shelter deployment area and the use season, resulting in changes in the measurement errors when using a turbine gas flowmeter, a vortex street gas flowmeter or an ultrasonic gas flowmeter, further affecting the measurement accuracy of the air flow. Therefore, there is an urgent need for an air flow measurement method that can accurately detect the gas flow with uneven flow field distribution in a narrow and cramped space.

[0004] CN213114813U discloses a constant flow water supply control system, including: a PLC, an inverter, a water pump, a first flowmeter, a second flowmeter, a comparator, a data selector and a memory. It has functions of matching detection, correction and deviation correction, avoiding large deviations in the detection effect of the system due to changes in the detection scenario, thereby improving the system control accuracy and also improving the adaptability to different water qualities. However, this technical solution fails to solve the aforementioned gas flow measurement error caused by the uneven flow field distribution due to the installation of multiple air duct components of different specifications in a narrow and cramped space, nor can it solve the change in the gas flow measurement error caused by the change in air cleanliness. Summary of the Invention

[0005] In view of this, the present invention provides a method for measuring air flow rate in a limited space, which can improve the accuracy of measuring the flow rate of gas with uneven flow field distribution in a limited space.

[0006] In order to solve the above technical problems, the present invention is implemented as follows:

[0007] A method for measuring air flow rate in a limited space, which simultaneously selects two gas flow meters of different types as the first flow meter and the second flow meter respectively; performs a trial test on the air flow rate simultaneously with the two gas flow meters in the target limited space to obtain trial test data; obtains the measurement variances of the two gas flow meters respectively according to the trial test data; performs a formal measurement on the air flow rate simultaneously with the two gas flow meters in the target limited space to obtain the instantaneous measurement values of the two gas flow meters respectively; obtains an estimated value of the instantaneous gas flow rate according to the instantaneous measurement values and the measurement variances; and obtains a gas flow rate measurement result according to the estimated value.

[0008] Preferably, the estimated value is:

[0009]

[0010] Wherein, is the estimated value of the instantaneous gas flow rate; q f [k] is the instantaneous measurement value of the first flow meter, q v [k] is the instantaneous measurement value of the second flow meter; is the measurement variance of the first flow meter, is the measurement variance of the second flow meter.

[0011] Preferably, the method for obtaining the measurement variance is: performing a trial test simultaneously on the first flow meter, the second flow meter and a calibrated standard flow meter, and the trial test is to measure the instantaneous flow rate values of the first flow meter, the second flow meter and the standard flow meter respectively at different flow measurement points for multiple times to obtain:

[0012]

[0013] Wherein, e ij (1) is the indication error of the first flow meter at the jth measurement at the ith measurement point; e ij (2) is the indication error of the second flow meter at the jth measurement at the ith measurement point; q ij (1) is the instantaneous flow rate value of the first flow meter at the jth measurement at the ith measurement point; q ij (2)is the instantaneous flow rate value of the second flowmeter during the j-th measurement at the i-th measurement point; (q s ) ij is the instantaneous flow rate value of the standard flowmeter during the j-th measurement at the i-th measurement point; i is an integer from 1 to n, where n is the total number of measurement points, and j is an integer from 1 to m, where m is the total number of measurements at each measurement point;

[0014] The measurement variance of the first flowmeter and the measurement variance of the second flowmeter are:

[0015]

[0016] where is the mean of multiple measurement values of the first flowmeter at each measurement point, is the mean of multiple measurement values of the second flowmeter at each measurement point.

[0017] Preferably, the test is to install the first flowmeter and the second flowmeter in the target device, form a standard device with the standard flowmeter and the duct components meeting the measurement requirements of the standard flowmeter, connect the standard device to the target device, adjust the gas flow of the target device to a flow rate value for trial operation, wait for the target device to run until the fluid state is stable, and measure the instantaneous flow rate values of the first flowmeter, the second flowmeter, and the standard flowmeter at this measurement point multiple times; then change the gas flow of the target device multiple times and repeat the measurement at each measurement point to obtain multiple sets of instantaneous flow rate values.

[0018] Preferably, obtaining the gas flow measurement result according to the estimated value is:

[0019] The gas flow measurement result includes: the cumulative gas volume flow Q and the average gas volume flow In the target limited space at a set time step Δt, within a set time ΔT, the first flowmeter and the second flowmeter are used to simultaneously measure the air flow rate officially, and a total of x sets of readings are obtained, where x = ΔT / Δt + 1, which is the total number of times of reading the instantaneous measurement values of the two flowmeters within the time ΔT; the cumulative gas volume flow within the time ΔT The average gas volume flow within the time ΔT where is the estimated value of the gas instantaneous flow rate, and k is an integer from 1 to x, indicating that the estimated value is the k-th set of data within the time ΔT.

[0020] Preferably, the first flowmeter and the second flowmeter are respectively: an ultrasonic gas flowmeter and a vortex street gas flowmeter, or an ultrasonic gas flowmeter and a turbine gas flowmeter.

[0021] Beneficial effects:

[0022] 1. By simultaneously selecting two different types of gas flow meters, combining the measurement results of the two gas flow meters respectively, and obtaining the measurement estimated value through data processing, the present invention can minimize the measurement error as much as possible, make the measurement of air flow insensitive to a certain single error influence condition, and improve the accuracy of measuring the gas flow with uneven flow field distribution in a limited space.

[0023] 2. By constructing an algorithm for estimating gas flow value based on the measurement variances of the two flow meters, the present invention realizes the effective integration of the information obtained by the two different types of gas flow meters, thereby improving the accuracy of gas flow measurement.

[0024] 3. By conducting tests in the target device to obtain the measurement variance of the flow meter relative to the standard device in the corresponding narrow space, the present disclosure improves the measurement adaptability and measurement accuracy in the target limited space.

[0025] 4. By selecting an ultrasonic gas flow meter and a vortex street gas flow meter, or an ultrasonic gas flow meter and a turbine gas flow meter for measurement, the present invention can improve the measurement accuracy under the condition of uneven flow field distribution in a limited space while avoiding excessive measurement errors caused by poor air cleanliness. Description of the drawings

[0026] Figure 1 It is a schematic structural diagram of the flow measurement device based on the embodiment of the present invention;

[0027] Among them, 101 - sampling head, 102 - first intake pipe, 103 - ultrasonic gas flow meter, 104 - upper air box, 105 - aerosol filter membrane carrier plate, 106 - lower air box, 107 - second intake pipe, 108 - vortex street gas flow meter, 109 - elbow, 110 - high-power fan, 111 - sound absorption device. Detailed implementation manners

[0028] The following combines the drawings and gives embodiments to describe the present invention in detail.

[0029] The present invention provides a method for measuring air flow in a limited space, and its core idea is:

[0030] Select two gas flow meters of different types as the first flow meter and the second flow meter respectively; simultaneously detect the air flow with the two gas flow meters in the target limited space to obtain detection data; obtain the measurement variances of the two gas flow meters respectively according to the detection data; simultaneously measure the air flow with the two gas flow meters in the target limited space to obtain the instantaneous measurement values of the two gas flow meters respectively; obtain the estimated value of the instantaneous gas flow according to the instantaneous measurement value and the measurement variance; obtain the gas flow measurement result according to the estimated value.

[0031] Commonly used gas flow meters mainly include: differential pressure gas flow meters, ultrasonic gas flow meters, turbine gas flow meters, vortex street gas flow meters and positive displacement gas flow meters. Among them, the positive displacement gas flow meter has a complex structure and a large volume, and is not suitable for installation in a narrow mobile shelter, so it is not applicable to the present invention. The differential pressure gas flow meter has a large pressure loss for the gas. In order to improve the collection efficiency, the aerosol sampling device requires that the pressure loss of the equipment air duct should be as small as possible. Therefore, the differential pressure gas flow meter is also not applicable to the present invention.

[0032] The ultrasonic gas flow meter measures the gas flow velocity based on the following principle: when ultrasonic waves pass through a flowing fluid, within the same propagation distance, the propagation speeds in the downstream direction and the upstream direction are different. Within a wide range of flow Reynolds numbers, the time difference is proportional to the volume flow rate (average velocity) of the fluid to be measured in the pipeline. By measuring the time difference of the sound wave propagating in the same section of pipeline fluid in the downstream and upstream directions, the flow velocity of the pipeline fluid can be calculated. The advantages of the ultrasonic gas flow meter are non-flow-obstruction measurement and no pressure loss. Its disadvantage is that it has a high requirement for gas cleanliness, and there will be a large measurement error when the air cleanliness is not high.

[0033] The turbine gas flow meter measures the gas flow velocity based on the following principle: when the fluid flows through the turbine flow sensor, the turbine is forced to rotate under the thrust of the fluid, and its rotation speed is proportional to the average flow velocity of the pipeline. The turbine rotation periodically changes the magnetic resistance of the magnetoelectric converter, and the magnetic flux in the detection coil is periodically changed, generating a periodic electrical pulse signal. Within a certain range of flow Reynolds numbers, the electrical pulse signal is proportional to the volume flow rate of the fluid flowing through the turbine flow sensor. By measuring the electrical pulse signal, the gas flow rate can be calculated. The advantages of the turbine gas flow meter are high accuracy, good repeatability and small pressure loss. Its disadvantages are that it needs to be calibrated regularly and is greatly affected by the flow field distribution.

[0034] The vortex street gas flow meter measures the fluid flow rate by detecting the frequency of the vortices generated on both sides of a non-streamlined vortex generator. Its advantages are relatively high accuracy and small pressure loss. The disadvantage is that it requires a long straight pipe section and is not suitable for measurement at low Reynolds numbers.

[0035] It can be seen that there are three types of gas flow meters applicable to air flow measurement in a limited space: ultrasonic gas flow meters, turbine gas flow meters, and vortex street gas flow meters. Each of them has a certain measurement error, but the main influencing factors of the measurement errors of different types of gas flow meters are not the same. Therefore, the distributions of the measurement errors of different types of gas flow meters are not related to each other. In order to perform more accurate measurement, a gas flow meter often needs to limit the size of the straight duct. However, when the usage space of the flow meter is limited, it is often difficult to meet the size requirements of the duct. A relatively short straight duct will cause uneven distribution of the gas flow field in the area detected by the flow meter, thereby bringing errors. Especially for turbine gas flow meters and vortex street gas flow meters, the errors caused by the uneven distribution of the gas flow field will be more obvious. In contrast, an ultrasonic gas flow meter can detect the gas flow with uneven flow field distribution more accurately, but its accuracy is greatly affected by the gas cleanliness. Therefore, the present invention simultaneously selects two different types of gas flow meters, combines the measurement results of the two gas flow meters, and obtains a measurement estimate value through data processing, which can minimize the measurement error as much as possible, make the measurement of the air flow insensitive to a certain single error influence condition, and improve the accuracy of the measurement method for measuring the gas flow with uneven flow field distribution in a limited space.

[0036] The present invention will be further described in detail below with an embodiment.

[0037] As Figure 1 shown, the aerosol sampling device integrally installed in the movable cabin includes an air sampling head 101, a first intake pipe 102, an upper air box 104, an aerosol filter membrane carrier 105, a lower air box 106, a second intake pipe 107, an elbow 109, a high-power fan 110, an outlet pipe, and a silencing device 111. Only the air sampling head 101 and the silencing device 111 are installed outside the movable cabin, and the rest of the components are integrated inside the movable cabin. The installation space limits the size of the duct components and further makes the gas flow field in the duct unevenly distributed. For this operating condition, the air flow measurement method proposed by the present invention includes:

[0038] Step 1: Install an ultrasonic gas flow meter 103 at a suitable position in the middle of the first intake pipe 102, and install a vortex street gas flow meter 108 between the second intake pipe 107 and the elbow 109. The vortex street gas flow meter 108 here can also be a turbine gas flow meter.

[0039] Step 2: Operate the aerosol sampling device and measure the variances of the gas flow measurement results of the ultrasonic gas flow meter 103 and the vortex street gas flow meter 108 respectively. Step 2 specifically includes:

[0040] Step 201: Take a calibrated gas flowmeter, combine the calibrated gas flowmeter with the corresponding standard measurement environment (including air duct components of appropriate size) as the standard device, and connect the standard device to the outlet pipe. Adjust the gas flow of the aerosol sampling device to a flow value for trial measurement, and wait for the device to run until the fluid state is stable.

[0041] Step 202: Record the initial indications of the standard device, ultrasonic gas flowmeter 103, and vortex street gas flowmeter 108. At the same time, start the standard device, ultrasonic gas flowmeter 103, and vortex street gas flowmeter 108 for measurement. After running for a period of time according to the operation requirements, stop the measurement of the standard device, ultrasonic gas flowmeter 103, and vortex street gas flowmeter 108 at the same time, and record the final indications of the standard device, ultrasonic gas flowmeter 103, and vortex street gas flowmeter 108.

[0042] Step 203: Without changing the power of the aerosol sampling device, repeat Step 202 multiple times to conduct multiple measurements at the same flow measurement point; change the power of the aerosol sampling device multiple times and repeat Step 202 to conduct multiple measurements at different flow measurement points; and then calculate the instantaneous flow values of the standard device, ultrasonic gas flowmeter 103, and vortex street gas flowmeter 108 for multiple measurements at different flow measurement points respectively.

[0043] Step 204: The single indication error of the flowmeter showing the instantaneous flow value is calculated according to formula (I):

[0044]

[0045] where, e ij (1) is the indication error of the ultrasonic gas flowmeter 103 at the j-th measurement at the i-th measurement point; e ij (2) is the indication error of the vortex street gas flowmeter 108 at the j-th measurement at the i-th measurement point; q ij (1) is the instantaneous flow value of the ultrasonic gas flowmeter 103 at the j-th measurement at the i-th measurement point; q ij (2) is the instantaneous flow value of the vortex street gas flowmeter 108 at the j-th measurement at the i-th measurement point; (q s ) ij is the instantaneous flow value of the standard device at the j-th measurement at the i-th measurement point; i is an integer from 1 to n, n is the total number of measurement points, j is an integer from 1 to m, and m is the total number of measurements at each measurement point.

[0046] Step 205: Construct the error matrices E of the ultrasonic gas flowmeter 103 and the vortex street gas flowmeter 108 respectivelyij (1) and E ij (2) is as follows:

[0047]

[0048] wherein, R n×m represents an n×m matrix.

[0049] Step 206: Calculate the variance vectors and of the ultrasonic gas flowmeter 103 and the vortex street gas flowmeter 108 respectively, which are as follows:

[0050]

[0051] wherein, is the mean value of multiple measurement values of the ultrasonic gas flowmeter 103 at each measurement point, is the mean value of multiple measurement values of the vortex street gas flowmeter 108 at each measurement point.

[0052] Step 3: Officially operate the aerosol sampling device to make it in the stable flow sampling working mode. With the set time step △t, within the set time △T, use the ultrasonic gas flowmeter 103 and the vortex street gas flowmeter 108 to simultaneously measure the instantaneous air volume flow rate during the operation of the aerosol sampling device, and a total of x sets of readings are obtained. x is the total number of times of reading the instantaneous measurement values of the two flowmeters within the set time △T, and x = △T / △t + 1; the instantaneous measurement value of the ultrasonic gas flowmeter 103 is q f [k], and the instantaneous measurement value of the vortex street gas flowmeter 108 is q v [k], wherein, k is an integer from 1 to x, indicating that this value is the k-th group of data within the set time △T; select the variance value at the measurement point in the variance vector of the ultrasonic gas flowmeter 103 that is closest to q f [k] as Select the variance value at the measurement point in the variance vector of the vortex street gas flowmeter 108 that is closest to q v [k] as

[0053] Step 4: Calculate the estimated value of the instantaneous air volume flow rate during the operation of the aerosol sampling device of the variance where D represents the variance operation; introduce an intermediate variable p∈[0,1], and construct the function f(p) of the variance with respect to p as follows:

[0054]

[0055] Since the measurement errors of the two different types of gas flow meters are uncorrelated, then:

[0056]

[0057] Taking the second derivative with respect to p, we get:

[0058]

[0059] Obviously, Therefore, f(p) is a concave function in the interval p ∈ [0, 1]. Let We obtain the value of the extreme point p0 of the variance function f(p) as:

[0060]

[0061] Since f(p) is a concave function in the interval p ∈ [0, 1], the extreme point p0 of the variance function f(p) is the minimum point. That is to say, when p = p0, the value of f(p) is the smallest, that is, the estimated value Variance Is the smallest. Therefore, the measurement data of the two gas flow meters are optimally fused and processed according to the following formula, and the estimated value of the instantaneous air volume flow rate during the operation of the aerosol sampling device is calculated As:

[0062]

[0063] Step 5. According to the obtained estimated value of the instantaneous air volume flow rate Calculate the cumulative gas volume flow rate within the time ΔT And the average gas volume flow rate within the time ΔT

[0064] The method disclosed in the present invention makes full use of the uncorrelation of the measurement error distributions of the two different types of gas flow meters, and can reduce the gas flow measurement error caused by the uneven flow field distribution due to the installation of various different specifications of air duct components in a narrow and cramped space. The present invention can also be implemented by combining any other two of the three gas flow meters, and its specific steps are similar to those of this embodiment.

[0065] In summary, the above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for measuring air flow rate in a confined space, characterized in that, Select two gas flow meters of different types as the first flow meter and the second flow meter respectively; simultaneously test the air flow with the two gas flow meters in the target limited space to obtain test data; obtain the measurement variances of the two gas flow meters respectively according to the test data; simultaneously conduct formal measurement of the air flow with the two gas flow meters in the target limited space to obtain the instantaneous measurement values of the two gas flow meters respectively; obtain the estimated value of the gas instantaneous flow according to the instantaneous measurement value and the measurement variance; obtain the gas flow measurement result according to the estimated value.

2. The method for measuring air flow rate in a confined space according to claim 1, characterized in that, The estimated value is: Wherein, is the estimated value of the instantaneous gas flow rate; q f [k] is the instantaneous measured value of the first flowmeter, q v [k] is the instantaneous measured value of the second flowmeter; is the measurement variance of the first flowmeter, is the measurement variance of the second flowmeter.

3. The method for measuring air flow rate in a confined space according to claim 1, characterized in that, The way to obtain the measurement variance is: simultaneously conduct a test on the first flow meter, the second flow meter and a calibrated standard flow meter. The test is to measure the instantaneous flow values of the first flow meter, the second flow meter and the standard flow meter respectively at multiple measurement points with different flow rates, and obtain: where e ij (1) is the indication error of the first flowmeter at the j-th measurement of the i-th measurement point; e ij (2) is the indication error of the second flowmeter at the j-th measurement of the i-th measurement point; q ij (1) is the instantaneous flow rate value of the first flowmeter at the j-th measurement of the i-th measurement point; q ij (2) is the instantaneous flow rate value of the second flowmeter at the j-th measurement of the i-th measurement point; (q s ) ij is the instantaneous flow rate value of the standard flowmeter at the j-th measurement of the i-th measurement point; i is an integer from 1 to n, n is the total number of measurement points, j is an integer from 1 to m, and m is the total number of measurements for each measurement point; The measurement variance of the first flowmeter and the measurement variance of the second flowmeter are as follows: wherein, is the mean value of multiple measurement values of the first flowmeter at each measurement point, is the mean value of multiple measurement values of the second flowmeter at each measurement point.

4. The method for measuring air flow rate in a confined space according to claim 3, characterized in that, The test is to install the first flow meter and the second flow meter in the target device, form a standard device by the standard flow meter and the duct components meeting the measurement requirements of the standard flow meter, connect the standard device to the target device, adjust the gas flow of the target device to a flow value for trial operation, wait for the target device to run to a stable fluid state, and measure the instantaneous flow values of the first flow meter, the second flow meter and the standard flow meter at this measurement point multiple times; then change the gas flow of the target device multiple times and repeat the measurement at each measurement point to obtain multiple groups of instantaneous flow values.

5. The method for measuring air flow rate in a confined space according to claim 1, characterized in that, Obtaining the gas flow measurement result according to the estimated value is: The gas flow measurement results include: the cumulative volume flow rate Q of the gas and the average volume flow rate of the gas Within the target limited space, at a set time step Δt, within a set time ΔT, the air flow rate is officially measured simultaneously by the first flowmeter and the second flowmeter, and a total of x sets of readings are obtained, where x = ΔT / Δt + 1, which is the total number of times the instantaneous measurement values of the two flowmeters are read within the time ΔT; the cumulative volume flow rate of the gas within the time ΔT The average volume flow rate of the gas within the time ΔT wherein, is the estimated value of the instantaneous gas flow rate, and k is an integer from 1 to x, indicating that the estimated value is the k-th set of data within the time ΔT.

6. The method for measuring air flow rate in a confined space according to any one of claims 1-5, characterized in that, The first flow meter and the second flow meter are respectively: an ultrasonic gas flow meter and a vortex street gas flow meter, or an ultrasonic gas flow meter and a turbine gas flow meter.

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