CN114739471A - Flow measurement system of medium in pipeline - Google Patents

Abstract

The invention discloses a flow measurement system for a medium in a pipeline, which relates to the technical field of flow measurement and structurally comprises a main flow system for conveying the medium and a bypass system connected with the main flow system; the main road system comprises a first pipeline; the bypass system comprises a second pipeline and detection equipment connected with the second pipeline, and the detection equipment comprises a heat source system and a first temperature measuring element and a second temperature measuring element which are arranged on two sides of the heat source system; the first temperature measuring element and the second temperature measuring element are respectively arranged on two sides of the heat source system and used for detecting the temperature of a medium in the second pipeline, and the liquid inlet and the liquid outlet of the second pipeline are communicated with the first pipeline.

Description

Flow measurement system of medium in pipeline

Technical Field

The invention relates to the technical field of flow measurement, in particular to a flow measurement system for a medium in a pipeline.

Background

Natural gas has been widely used as a clean energy source as a domestic residential energy source in developed countries, and the usage of natural gas in domestic residential energy sources has been significantly increased in recent years in developing countries. The mass flow measurement is a key part in the process from natural gas production to sale, and is a main basis for enterprises to perform market settlement, economic analysis and cost reduction. The natural gas flow measured in the household residence is extremely low, a diaphragm flowmeter is usually used, the diaphragm flowmeter is a positive displacement flowmeter, the measurement of mass flow is realized by pressure and temperature compensation, and the requirement of accurate measurement cannot be met. The thermal mass flowmeter can realize direct measurement of mass flow in a small pipeline and is not influenced by temperature and pressure. However, the stability, consistency and power consumption of thermal mass flowmeters limit their further applications, and the advent and development of micro-electromechanical technology (MEMS) provides solutions to the stability and consistency of thermal mass flowmeters, which can greatly reduce their power consumption. The thermal mass flowmeter based on the MEMS has the advantages of high response speed, small volume, low cost, batch preparation and the like, can realize accurate measurement in a wider flow ratio range, is less influenced by environmental change, and has wide application in the fields of automobiles, medicine, environmental monitoring, electronics, chemical industry and the like.

Many advantages of thermal mass flowmeters have attracted many researchers to study them, especially for optimizing the performance of thermal mass flowmeters. For example, through theoretical analysis of the thermal flow sensor by Lammerink et al, the geometric shape, the thermal conductivity and the thermal distribution of the sensor are given to influence the sensitivity and the measurement range of the sensor. The scholars of Sabat et al increase the number of the temperature sensors to increase the measurement range of the sensors, the scholars of Roh et al further study to obtain that the sensitivity linearly increases with the increase of the input power of the heating source, and the scholars of Kim et al study the transient and steady heat transfer in the sensor tube through the proposed numerical model to further analyze the sensitivity influence factors of the thermal mass flow meter. These are all relevant parameters of the sensor studied, and then optimize the performance of thermal mass flow meter. However, the thermal mass flow meter has many operations, such as circuit and structure design, besides the design of the sensor, which affect the performance of the thermal mass flow meter.

Thermal mass flowmeters can be classified into two types, insertion type and capillary type, according to the difference of measurement methods and structures. The measuring sensor of the plug-in thermal mass flowmeter is directly exposed in a measured medium, and is suitable for measuring fluid media with large pipe diameter and medium and high flow velocity. And capillary thermal mass flow meter shunts a part of mainstream to the bypass to measure the velocity of flow, is often used for the measurement of little pipe diameter, low velocity of flow. At present, the thermal mass flow meter is researched on the basis of a bypass-free plug-in structure, the capillary thermal mass flow meter with the bypass has obvious structural difference compared with the capillary thermal mass flow meter with the bypass, and performance influencing factors of the capillary thermal mass flow meter have own characteristics, so that the performance influencing factors of the capillary thermal mass flow meter need to be further researched. John G explains the working principle of the capillary tube thermal mass flow meter, Gord et al uses the capillary tube thermal mass flow meter for measuring residential natural gas, studies the sensitivity of the capillary tube thermal mass flow meter to methane, and finally simulates sample natural gas with the methane content of 94.38% to obtain the result with the uncertainty of 1.83%. Chaboki et al produced a capillary thermal gas mass flow meter, studied the role of the rectifier, and after placing the rectifier in the main flow channel of the capillary thermal gas mass flow meter, the linear range increased from 0-100SCCM to 0-500SCCM, and the linear degree of fit R2 increased from 0.96 to 0.99, but with the increase of the flow range, the measurement accuracy at lower flow rates would drop sharply. However, the article does not make further intensive study on the influence of the rectifier on the performance of the capillary gas mass flowmeter, and the optimization design of the rectifier has very important practical significance on improving the performance of the capillary gas mass flowmeter.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a flow measuring device for medium in a pipeline, and compared with the prior art, the flow monitoring device has higher sensitivity.

The invention is realized by the following technical scheme: a flow measuring device for medium in a pipeline structurally comprises a main flow system for conveying the medium and a bypass system connected with the main flow system; the main road system comprises a first pipeline; the bypass system comprises a second pipeline and detection equipment connected with the second pipeline, and the detection equipment comprises a heat source system and a first temperature measuring element and a second temperature measuring element which are arranged on two sides of the heat source system; the first temperature measuring element and the second temperature measuring element are respectively arranged on two sides of the heat source system and used for detecting the temperature of a medium in the second pipeline, and the liquid inlet and the liquid outlet of the second pipeline are communicated with the first pipeline.

Preferably, the distance between the first temperature measuring element and the heat source system is the same as the distance between the second temperature measuring element and the heat source system.

Preferably, the main path system further comprises two rectifying devices, the two first pipelines are connected through the rectifying devices, and the rectifying devices are used for combing the medium conveyed by the first pipeline on one side and then conveying the medium to the first pipeline on the other side.

Preferably, the rectifying device comprises a housing provided with a receiving cavity and at least two medium channels arranged inside the housing receiving cavity, wherein the medium channels are used for conveying media.

Preferably, the rectifying device comprises a housing provided with a receiving cavity and at least two medium channels arranged inside the housing receiving cavity, wherein the medium channels are used for conveying media.

Preferably, nine of the medium passages are arranged, one of the medium passages is arranged along the central axis position of the housing, and the remaining eight of the medium passages are arranged circumferentially around the medium passage at the central axis position.

Preferably, the medium channel comprises a through hole with a cylindrical inner wall, and the aperture of the inner wall of the through hole is two millimeters.

Preferably, the medium channel is provided with a sealing element, and the sealing element seals at least one through hole.

Preferably, the sealing element comprises a sealing plug and a projection connected with the side wall of the sealing plug, the medium channel further comprises a positioning groove arranged on one side of the through hole, and the positioning groove and the projection are correspondingly arranged; when the sealing plug seals the through hole, the convex block is embedded in the positioning groove.

Preferably, the push type switch is arranged in the positioning groove, nine warning devices are arranged on the outer surface of the shell, the warning devices are arranged in one-to-one correspondence with the push type switches, and one of the warning devices is controlled by the push type switches.

The invention discloses a flow measuring device for medium in a pipeline, which is compared with the prior art:

the invention designs a novel flow measuring device for medium in a pipeline based on the capillary thermal mass flowmeter principle, and develops analysis from singular points existing in a medium-low flow section in a calibration data result (mass flow-signal output value relation curve). Firstly, under the condition that the measured fluid medium and the related parameters of the sensor are determined, the influence of the bypass ratio on the flow measuring equipment is researched in a quantitative analysis and Fluent numerical analysis verification mode. A relation model of bypass ratio and sensitivity is established, and the generation reason of the singularity is explained. And then, according to the obtained relation model, placing tube bundle rectifiers with different apertures and hole numbers in a main flow channel of the flow measuring equipment, thereby adjusting the bypass ratio to optimize the performance of the flow measuring equipment.

Drawings

FIG. 1 is a schematic view of the construction of a flow measuring device according to the present invention;

FIG. 2 is a schematic view of the structure of the rectifying device of the present invention;

FIG. 3 is a schematic view of the structure of the sealing member of the present invention;

FIG. 4 is a schematic structural view of the detecting apparatus of the present invention;

FIG. 5 is a schematic view of the overall structure of the flow passage area of the MEMS gas meter;

FIG. 6 is a schematic diagram of a sensor temperature field distribution;

FIG. 7 is a schematic diagram of a thermal mass flowmeter flow measurement technique;

FIG. 8 is a graph of sensitivity definition;

FIG. 9 is a GNP sonic nozzle experimental data calibration platform;

FIG. 10 is a graph of mass flow versus signal output;

FIG. 11 is a graph of mass flow versus bypass ratio;

FIG. 12 is a model of sensitivity change due to bypass ratio;

FIG. 13 is a schematic diagram of a cross-sectional structure of 6 kinds of simulated rectifiers;

FIG. 14 is a graph of mass flow versus bypass ratio for an example embodiment;

FIG. 15 is a graph of mass flow versus bypass ratio as distinguished from the embodiment of FIG. 14;

FIG. 16 is a comparative graph of mass flow versus output signal curve optimization.

Detailed Description

The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.

As shown in fig. 1 to 4, the present invention discloses a flow measuring device for medium in a pipeline, which comprises a main flow system 1 for conveying medium and a bypass system 2 connected with the main flow system 1; the main road system 1 comprises a first pipeline 11; the bypass system 2 comprises a second pipe 21 and a detection device coupled to the second pipe 21, the detection device being arranged at a position a in fig. 1, the detection device comprising a heat source system 22 and a first temperature measuring element 23 and a second temperature measuring element 24 arranged on both sides of the heat source system 22; wherein, the first temperature measuring element 23 and the second temperature measuring element 24 are respectively arranged at two sides of the heat source system 22 to detect the temperature of the medium in the second pipeline 21, the liquid inlet and the liquid outlet of the second pipeline 11 are in a communication state with the first pipeline 11, the distance between the first temperature measuring element 23 and the heat source system 22 is the same as the distance between the second temperature measuring element 24 and the heat source system 22, the main pipeline system 1 further comprises a rectifying device 12, two first pipelines 11 are arranged, the two first pipelines 11 are connected through a rectifying device 12, the rectifying device 12 combs the medium conveyed by the first pipeline 11 at one side and conveys the medium to the first pipeline 11 at the other side, the rectifying device 12 comprises a housing 121 provided with a containing cavity and at least two medium channels 122 arranged inside the containing cavity of the housing 121, the medium channel 122 is used for conveying media, the rectifying device 12 comprises a housing 121 provided with a receiving cavity and at least two medium channels 122 arranged inside the receiving cavity of the housing 121, the medium channels 122 are used for conveying media, nine medium channels 122 are arranged, one medium channel 122 is arranged along the central axis position of the housing 121, the other eight medium channels 122 are arranged circumferentially around the medium channel 122 at the central axis position, the medium channel 122 comprises a through hole 1221 with a cylindrical inner wall, the inner wall hole diameter of the through hole 1221 is two millimeters, the sealing element 124 comprises a sealing plug 1241 and a lug 1242 connected with the side wall of the sealing plug 1241, the medium channel 122 further comprises a positioning groove 1222 arranged at one side of the through hole 1221, and the positioning groove 1222 and the lug 1242 are correspondingly arranged; when the sealing plug 1241 seals the through hole 1221, the protrusion 1242 is embedded in the positioning slot 1222, and the sensitivity of the present invention can be further adjusted by adjusting the number of the sealing members 124, a push switch is disposed in the positioning slot 1222, nine warning devices 123 are disposed on the outer surface of the housing 121, the warning devices 123 and the push switches are disposed in a one-to-one correspondence manner, one push switch controls one warning device 123, the warning device may be a warning light, and the number of the through holes 1221 through which a medium can be conveyed is determined by determining the state of the warning device.

The capillary tube type thermal mass flow meter separates the main flow through a specific structural design, a part of the medium flow is separated into the bypass, the capillary tube type thermal mass flow meter can measure the low flow rate flow, and the influence on the flow meter precision caused by the drift of an output signal due to the attachment of natural gas particle impurity dirt on a sensor chip in the measurement process can be avoided. Flow for MEMS gas meters developed hereinThe bulk medium is natural gas, the measurement target range is 0-100SLM, and therefore the capillary structure is selected as a research object. The MEMS gas meter structure is designed according to the JBT13567-2018 standard specification, and in addition, the maximum number of the designed flow meter bypass flow channel is smaller than 2400 according to the laminar flow condition inside the bypass flow channel where the MEMS gas meter sensor is located. In order to make the velocity distribution on the whole flow passage uniform and the convective heat transfer coefficient constant, the ratio of the inner diameter of the bypass flow passage to the total length is less than 0.01, fig. 5 shows the overall structural diagram of the flow passage region of the MEMS gas meter, as shown in the figure, the measured fluid is

Is split into two parts, i.e. a main flow part, while flowing through the measuring device

And a bypass portion

A rectifier is arranged in the middle of the main flow channel, and actual mass flow measurement does not occur in the main flow channel. The sensor and the circuit board used for measurement are arranged in the sensor channel of the bypass flow channel, and the measuring device mainly comprises two temperature sensors and a heating source.

For convenience of understanding, the present invention explains the measurement principle, as described above, the sensor (detection device) for the MEMS gas meter disclosed in the present invention structurally consists of three parts, one heat source and two temperature measuring elements, the two temperature measuring elements are respectively and symmetrically disposed on both sides of the heat source, the whole measurement device is placed in the bypass flow channel, fig. 6 is a schematic diagram of the distribution of the temperature field of the sensor, as shown in fig. 6(a), when the measurement sensor is at flow rate zero (Q), the measurement sensor is in a state where the flow rate is zero (Q)_m0), the distribution effect of the thermal field takes the heating body as the center and is symmetrically distributed; as shown in FIG. 6(b), (Q) is_mNot equal to 0) when the medium in the flow field flows towards one direction, the medium molecules in the flow field carry away heat from the surface of the heat source, so that the distribution effect of the heat field is deviated.

Based on the principle, when the flow rate of the medium is zero, the temperature field is normally distributed by taking the heater as the center; when the medium flow velocity is greater than zero, the temperature field that is normal distribution is destroyed, the field temperature distribution will deviate, the prior art personnel research the sensor that possesses two temperature measurement elements of a heat source and obtain the relation of temperature difference of the temperature measurement elements and the medium flow velocity:

ΔT＝T_h[exp(λ₁l₁)-exp(λ₂l₂)] (1)

in the formula: delta T is the temperature difference of the upstream and downstream temperature measuring resistors; t is_hIs the heating source temperature; l₁Is the distance from the heat source to the upstream temperature sensing element; l₂Is the distance from the heat source to the downstream temperature sensing element; lambda_1,2As a function of fluid flow rate, thermal conductivity, thermal diffusivity, and boundary layer thickness. T is_hAnd λ_1,2Can be further expressed as follows:

in which P is power, K_fIs the medium thermal conductivity, W_hIs the width of the heat source, L_hIs the heat source length, δ is the boundary layer thickness, V is the flow velocity, a is the fluid thermal diffusivity,

is a dimensionless factor, K_SiIs the sensor substrate thermal conductivity, T_dIs the thickness of the diaphragm. After the temperature difference between the two temperature measuring elements is measured, further, the mass flow rate of the fluid can be simply represented by the following formula:

in the formula: q_mIs the mass flow rate; c_pFor fluid mediaSpecific heat capacity; a is the heat transfer coefficient of the fluid medium; k₁Is the gauge factor.

As can be seen from the equations (1) to (4), the measured mass flow of the sensor channel is only related to the fluid flow velocity V of the sensor channel without considering the gas properties and environmental changes and the determination of related parameters of the sensor, the channel design of the flowmeter is a factor capable of influencing the distribution of the flow velocity V, as shown in FIG. 7, the laminar state of the measured medium of the sensor channel from zero flow velocity to a specific flow velocity, and the temperature difference Delta T of the temperature measuring resistors on the upstream and the downstream of the MEMS gas meter is almost the mass flow Q_mBeyond a certain flow rate or in the presence of turbulence, this dependence deviates from linearity, which makes it possible to manufacture a precise flow meter on a range of scales according to the principles described above. By defining this linear function (equation (5)), the mass flow rate is easily measured, and C is a calibration constant that should be specified separately for each working fluid.

The sensitivity is a main technical index for measuring the performance of the instrument, is an important parameter in the design of a capillary mass flowmeter, and is defined as follows:

the sensitivity of the MEMS gas meter is defined as the temperature difference delta T of the upstream and downstream temperature measuring resistors to the mass flow of the sensor channel

The rate of change of the change. Naturally, the greater the sensitivity, the more accurate the flow meter, and fig. 8 illustrates how the sensitivity is graphically defined.

However, for the MEMS gas meter herein, the mass flow rate that is not the sensor channel is ultimately desired

But rather the medium flow of the measured fluid

It is therefore necessary to introduce the bypass ratio concept here.

For the bypass ratio, as shown in fig. 5, the MEMS gas meter disclosed in the present invention is a bypass type structure, and the fluid to be measured is

Is split into two parts, i.e. main channel part, while flowing through the measuring device

And a bypass flow path portion

At this time, the bypass ratio (B) is defined as the total mass flow rate

And bypass flow path mass flow (sensor channel mass flow)

The ratio of (A) to (B) is

If the flow of the medium in the flow meter meets the conditions of incompressible flow and laminar flow, the total mass before and after the mass continuity equation is kept unchanged, namely:

in the formula (I), the compound is shown in the specification,

is mainly composed ofThe mass flow rate of the flow channel is,

for the mass flow of the bypass channel,

is the inlet mass flow.

The Bernoulli equation has the energy loss of the front end and the rear end in the main flow channel equal to the energy loss of the front end and the rear end in the bypass flow channel, and the Bernoulli equation comprises the following components:

∑h_fb＝∑h_fs (8)

where pi is the circumference ratio, D_sIs the effective diameter of the bypass flow passage, D_bIs the effective diameter of the main flow channel, h_fsFor energy losses in the bypass flow path, h_fbFor energy losses in the main flow channel, (L +. SIGMA L)_e)_sIs the sum of the bypass flow path length and the equivalent length, (L +. SIGMA L)_e)_bIs the sum of the length of the main flow channel and the equivalent length, lambda_b、λ_sCoefficient of friction, q, of the main flow pipe and the bypass flow channel, respectively_sQ flow rate of the medium in the bypass flow path_bIs the flow rate of the medium in the main flow channel. Further derivation is possible from equations (9) and (10):

it can be seen from the expressions (11) to (13) that if the bypass pipe is longer, the resistance coefficient is larger, and the pipe diameter is smaller, the flow rate in the bypass flow passage is smaller, and conversely, the flow rate in the main flow passage is larger, and the range is larger.

As can be seen from equation (13), when the structure and medium of the MEMS gas meter are determined, if the fluid velocity is uniformly distributed, the bypass ratio B is a constant theoretically. However, in practical situations, for small flow or high speed flows and most industrial pipelines, the velocity distribution of the fluid is affected by the fact that a reducer, a filter, an elbow and the like are encountered, the fluid is caused to form velocity vectors in multiple directions, and the fluid is disturbed, so that the bypass ratio is affected.

Further researching the influence of the bypass ratio on the performance of the gas meter, and analyzing the principle of the MEMS gas meter to obtain that the signal y output by the sensor is directly reflected by the temperature difference delta T of the upstream and downstream temperature measuring resistors and the medium flow of the sensor output signal y and the measured fluid is required to be obtained

The relationship between depends on two aspects:

a: sensor output signal y and sensor channel flow

Is mapped to

b: the bypass ratio B.

These two factors are independent, since a is determined only by the tiny area around the sensor in the sensor channel, and b is determined by the velocity profile of the sensor channel and the main flow channel. Therefore, a relational expression is obtained

Then, can pass through

Find out the relation

Considering the developed flow meter, the tiny area around the sensor in the sensor channel has been determined, and factor a is the same, so on a hardware level, it is only important to obtain b. By designing the velocity distribution of the bypass flow channel and the main flow channel, a proper bypass ratio is obtained, and the formula (13) can show that the effective diameter D of the bypass flow channel can be changed_sAnd main flow channel effective diameter D_bAnd then changing the bypass ratio B, the rectifier just has the function of changing the effective diameter D of the main flow channel_sAnd further, the flow velocity distribution of the bypass flow channel and the main flow channel is changed to realize the optimization of the bypass ratio. In practical application, the rectifier has the function of correcting the velocity distribution of the medium, and can remove the influences of vortexes, local secondary turbulence, asymmetry of a velocity distribution profile and the like generated in a flow field. Therefore, the rectifier is a reasonable choice by adding the rectifier in the main flow channel, the commonly used rectifier is provided with a perforated plate rectifier and a tube bundle rectifier, the perforated plate rectifier is usually in a shape of a perforated plate, the asymmetry of a flow field is improved through the perforated plate, and all the whole flow holes are in radial symmetry and uniform distribution. The tube bundle type rectifier, also called flow rectifier, is generally in a long and straight shape, can effectively reduce the vortex in the fluid and the interference of the upstream flow blocking piece to the flow state, and adjusts the flow state in the pipeline, so that the unstable airflow becomes the parallel and symmetrical fully developed turbulent flow velocity distribution required by metering. The ideal state of the gas flow field in the thermal mass flow meter refers to that the flow field laminar flow is distributed and parallel to the axis of the pipe section, the gas medium in the flow field is completely developed, the fluid speed in the cross section of the flow field is uniformly distributed, a tube bundle type gas rectifier is adopted to optimally adjust the distribution of the gas flow field in the flow meter, and the tube bundle type long straight form rectifier is adopted to set the flow field.

Considering the processing difficulty of the rectifier and the basic structure of the MEMS gas meter, the length of an initial rectifier channel to be tested is 25mm, the central aperture is 6mm, the edge aperture is 5mm, the hole distance between the central hole and the edge hole is 6mm, the number of the edge holes is 6, and the total number of the holes is 7. And the fact that singularities exist in a low-flow section is found in a calibration result of repeating the MEMS gas meter provided with the rectifier for multiple times.

The data calibration of the MEMS gas meter is carried out on a standard calibration experiment platform, the medium used for calibration is air in a standard state, the data calibration platform adopts a Hangzhou Tianma GNP sonic nozzle experiment platform (negative pressure method), the uncertainty is in the range of 0.5%, and the experiment is in the range of 0.016m³/h-6m³At different flow rates/h. The whole testing system mainly comprises a vacuum pump, a vacuum container, a header, a stagnation container, a critical flow venturi nozzle, a control valve group, a computer control system and the like, and is shown in fig. 9. The vacuum pump is an air source of the calibration device, the vacuum pump generates negative pressure by extracting air in the vacuum container, temperature and pressure sensors are arranged on each detection pipeline in the testing process, the temperature and pressure in the pipelines are detected in real time, and temperature sensors and pressure sensors capable of detecting the stagnation temperature and pressure of the nozzle are arranged in the stagnation container. Similarly, a pressure sensor for detecting the back pressure of the nozzle is installed in the collecting container. The vacuum pump operates to generate negative pressure, so that the nozzle works in a critical flow state. And according to the mass continuity equation, testing that the gas flow passing through the MEMS gas meter is equal to the gas flow passing through the nozzle.

Before the calibration is started, the MEMS gas meter is fixed on a sonic nozzle calibration platform, and then the calibration flow value and related parameters are set at the control end of the computer. After the calibration is started, the control software of the experimental platform reads the real-time flow value of the MEMS gas meter and calculates the real-time flow value, and then the average value is written into the MEMS gas meter. Before each flow point is calibrated, the system can be stably operated for a period of time, so that the airflow of the sonic nozzle reaches a stable state. And setting 19 flow calibration points according to the flow range of the MEMS gas meter. According to the measurement characteristics of the MEMS gas meter, in a small flow range: 0.016m³/h-1m³And h, more data calibration points are set, and the method is suitable for the large flow range: 1m³/h-6m³And h, setting fewer data calibration points. The calibration results are shown in FIG. 10, which shows that the calibration data tends to be linear as a whole, but 0.016m³/h-1m³The low flow velocity section has singularity, abnormal sensitivity and poor linear fitting degree, which causes the deviation of low flow velocity flow measurement, and the performance of the low flow velocity flow measurement is needed to be optimized, and the sensitivity of the MEMS gas meter is improved as much as possible.

Singular point of

The sensitivity of (1) is reduced with increasing flow velocity, as is the sensor channel flow

Curve of output y

As reflected. However, sometimes

The sensitivity of the MEMS gas meter is increased firstly and then is reduced normally along with the increase of the flow rate, which means a singularity, under the condition of not considering the factor a, the performance of the MEMS gas meter for the product is the bypass ratio B, and in order to collect mass flow data of a main flow channel and a bypass flow channel more conveniently, CFD software Fluent is used for carrying out numerical analysis on a fluid area of the MEMS gas meter.

In order to establish a bypass ratio-sensitivity relation model, a 1:1 fluid region numerical analysis model is established according to a calibration model of an MEMS gas meter, a medium is also set as air in a standard state, the air is assumed to be incompressible and to be in a stable state, the operating atmospheric pressure is simulated by using the urban gas operating pressure in JBT13567-2018 specification, the operating pressure is 3000pa, a standard k-epsilon model in Fluent is selected according to the maximum design value of a flow meter Raynaud number to carry out numerical solution, and the parameter setting is shown in Table 1. In order to verify the flow change condition of the flow meter in the low-flow section, the flow points are mainly concentrated on 0.016-1m 3/h. The data were numerically analyzed to obtain a mass flow-bypass ratio curve as shown in fig. 11.

TABLE 1

It is apparent from FIG. 11 that as the measured mass flow increases, the bypass ratio continues to decrease, at 0-1m³The flow section bypass ratio decreases rapidly with increasing flow. The bypass ratio B is reduced faster in the low flow section than in the high flow section because the pressure resistance of the main flow channel is increased faster than that of the bypass flow channel along with the increase of the flow speed, and the mass flow-bypass ratio graph in FIG. 11 is compared with the mass flow-signal output value relation graph in FIG. 10, so that the flow section corresponding to the abnormal sensitivity of the sensor is almost completely matched with the flow section corresponding to the rapid reduction and the gradual trend of the bypass ratio and is cut off at 16.67 SLM. From this, it can be concluded that it is true that the change in the bypass ratio causes a singularity in the low flow segment sensitivity anomaly.

In summary, it is demonstrated that there is a certain relationship between the bypass ratio and the sensitivity. A simple model between the bypass ratio and the sensitivity can be preliminarily established according to the input value mt-signal output value relation graph and the measured flow mt-bypass ratio B graph.

Assuming sensor channel flow in the low flow section

And output y is satisfied

s is sensitivity, which is a constant. Similarly, assume that there is a linear function with respect to the dependent variable bypass ratio B

When a is 0, it means that B is a constant, and when a is 0>0 means that the bypass ratio B follows the argument

Is increased when a is increased<0 means that the bypass ratio B follows the argument

Is increased and decreased.

The entire process of variation can be represented by fig. 12.

A summary of the above information can be made:

1. the constant B does not change the sensitivity K;

an increase in B leads to a decrease in sensitivity;

a decrease in B leads to an increase in sensitivity.

In the meter test, although the sensitivity of the low-flow section is increased by reducing B, the sensitivity is continuously reduced in the middle and high-flow ranges, and the contradiction causes the generation of singularity.

It is desirable that the input and output values of the sensor are designed to be linear over the range of the span, and the sensitivity is constant, so that the collected signal can truly express the actual value to be measured, but the bypass ratio-sensitivity relation model tells that the sensitivity is correlated with the bypass ratio, and the sensitivity is not linear but rapidly decreases in the low flow rate section. Considering the flow product, the following two objectives of changing the bypass ratio by designing different rectifier models to further optimize the performance of the MEMS gas meter are provided:

1. to eliminate or attenuate the singularity, the linear fit of the flow meter is improved in the low flow section, which allows the bypass ratio to be reduced as long as it is not reduced too quickly;

2. considering that the bypass ratio does not vary much for the medium and high flow sections, the signal output value 33000 and 52000 is a good output range for the sensor design herein, with the maximum output value 52000 corresponding to a bypass flow of approximately 1562.5 SCCM. Thus, when the meter designed herein is intended to reach the operating range of 100SLM full scale, a bypass ratio of 100SLM/1562.5SCCM of 64 is preferred, with the bypass ratio as close to 64 as possible to improve meter sensitivity.

The invention establishes a rectifier model according to two influence factors of the aperture and the number of holes respectively, designs 6 rectifier models with different specifications in total, has the central aperture equal to the edge aperture, mainly verifies the influence of different apertures and the number of holes on the bypass ratio, and finds the optimal rectifier scheme through the optimization of the bypass ratio. The rectifier is arranged in a main flow channel of the flow meter

The length of the rectifier channel is 25mm, the 6 rectifier models are respectively marked as 1# and 2# … … 6#,

in the form of a region of fluid,

as shown in fig. 13, as a non-fluid region. According to the structural characteristics and the aperture processing difficulty of the MEMS gas meter designed by the text, the maximum aperture is required<5mm, minimum pore diameter>The pitch between the centre hole and the edge hole was 6mm, 3 mm.

A1: 1 numerical analysis model is established according to a fluid area of an MEMS gas meter calibration model, wherein 6 rectifier simulation models shown in figure 13 are respectively adopted in a rectifier model part. And the solving model also selects a standard k-epsilon model in Fluent to simulate, the simulation parameters of the testing model are set as shown in table 1, and the numerical analysis result data is shown in table 2, wherein origin is an initial rectifier model.

As shown in table 2, in order to find the influence of the rectifier aperture and the number of holes on the bypass ratio, we first fix the size of the rectifier aperture by controlling variables, and first design the total number of holes as: 6-9 rectifier simulation models with 4 different hole numbers, then fixing the total hole number of the rectifier to 7, and designing the hole diameter as follows: 3mm, 4mm and 5mm rectifier simulation models with different apertures. Objectives 1 and 2 are the optimal design objectives for the rectifier.

TABLE 2

For the target 1, the linearity of the bypass ratio changing along with the measured flow can be reflected by calculating the ratio size of the maximum value to the minimum value of the bypass ratio, namely B _ max/B _ min, and the closer the ratio is to 1, the closer the bypass ratio and the sensitivity are to constants, which shows that in a low-flow section, the better the linear fitting degree is, and the singularity is easier to weaken. For target 2, the bypass ratio can be conveniently calculated by numerical analysis results.

In order to more vividly show the results in table 2, data can be shown in a graph form so as to facilitate subsequent analysis, fig. 14 shows the influence of the number of rectifier holes on the bypass ratio and B _ max/B _ min, fig. 15 shows the influence of the rectifier hole diameter on the bypass ratio and B _ max/B _ min, and only three sets of rectifier numerical simulation models of hole diameter factors are designed in consideration of the structural characteristics and hole diameter processing difficulty of the MEMS gas meter.

As shown in fig. 14, in the case of the same aperture (2 mm), the bypass ratio increases as the number of holes increases, but the value of B _ max/B _ min gradually decreases and becomes closer to 1, and when the total number of holes is 9, the bypass ratio is 65 when the flow rate reaches the full scale 100SLM, and is close to the ideal bypass ratio value 64, where B _ max/B _ min is 1.62. As shown in fig. 15, in the case of the same total number of holes (7), the values of the bypass ratio and B _ max/B _ min decrease with decreasing hole diameter, and at a hole diameter of 1.5mm, B _ max/B _ min is 1.18, where B _ max/B _ min is very close to 1, but unfortunately, the bypass ratio is 22 when the flow reaches the full range 100SLM, which is not less than the ideal value 64.

Combining the above analysis and the conclusion of the sensitivity-bypass ratio relation model, in a certain aperture and aperture range, the case of placing the tube bundle rectifier in the main flow channel of the MEMS gas meter is:

1. the number of holes is increased, the bypass ratio is increased, the linear fitting degree of a low-flow section is changed well, singularities are weakened more easily, and the sensitivity of the instrument is reduced;

2. the aperture is reduced, the bypass ratio is reduced, the linear fitting degree of a low-flow section is changed well, singularities are weakened more easily, and the sensitivity of the instrument is improved.

In consideration of the above analysis, the 4# rectifier simulation model is selected as the optimized test model, and the average value is obtained by performing multiple times of calibration by using the GNP sonic nozzle experimental data calibration method, so that the mass flow-output signal curve diagram shown in FIG. 16 is obtained, and it can be seen from the graph that the optimized rectifier model has the linear fitting degree R of the calibration result²The singularity of the low flow section is obviously weakened and the sensitivity is obviously improved from 0.9937 before optimization to 0.9972.

In summary, through the verification of the quantitative analysis and numerical analysis of the bypass ratio, a relation model of the bypass ratio and the sensitivity is established, in the meter test, although the sensitivity of the low-flow section is increased due to the reduction of B, the sensitivity is continuously reduced in the middle and high-flow ranges, and the contradiction causes the generation of singularity. The performance of the flow measuring device is optimized by adjusting the rectifier parameters to change the bypass ratio, so that the bypass ratio is slowly reduced in a low-flow section as much as possible, and the bypass ratio approaches to the ideal bypass ratio 64 of the instrument in the middle and high-flow sections. 6 rectifier numerical analysis models with different apertures and hole numbers are designed, wherein the numerical analysis result shows that in a certain aperture and hole number range, the bypass ratio is increased along with the increase of the hole number, singular points are easily weakened, but the sensitivity of the instrument is reduced; the aperture is reduced, the bypass ratio is reduced, the singularity is easier to weaken, and the sensitivity of the instrument is improved. Finally, a 4# rectifier model is selected for calibration experiment testing, calibration result data before and after the rectifier is compared and optimized, and the linear fitting degree R²The singularity of the low flow section is obviously weakened and the sensitivity is obviously improved from 0.9937 before optimization to 0.9972.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be able to cover the technical scope of the present invention and the equivalent alternatives or modifications according to the technical solution and the inventive concept of the present invention within the technical scope of the present invention.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in the process, method, article, or apparatus that comprises the element.

Claims (8)

1. A flow measuring system for a medium in a pipe, characterized by comprising a main flow system (1) for conveying the medium and a bypass system (2) coupled to the main flow system (1);

the main system (1) comprises a first pipe (11);

the bypass system (2) comprises a second pipeline (21) and a detection device connected with the second pipeline (21), wherein the detection device comprises a heat source system (22) and a first temperature measuring element (23) and a second temperature measuring element (24) which are arranged at two sides of the heat source system (22);

the first temperature measuring element (23) and the second temperature measuring element (24) are respectively arranged on two sides of the heat source system (22) to detect the temperature of a medium in the second pipeline (21), and a liquid inlet and a liquid outlet of the second pipeline (11) are communicated with the first pipeline (11).

2. A system for measuring the flow of a medium through a pipe according to claim 1, wherein the distance between the first temperature measuring element (23) and the heat source system (22) is the same as the distance between the second temperature measuring element (24) and the heat source system (22).

3. A system for measuring the flow of a medium in a pipe according to claim 2, characterized in that said main system (1) further comprises a rectifying device (12), two of said first pipes (11) being provided, two of said first pipes (11) being coupled by the rectifying device (12), said rectifying device (12) combing the medium delivered by the first pipe (11) on one side and delivering it to the first pipe (11) on the other side.

4. A flow measuring system for a medium in a pipe according to any of claims 1 to 3, characterised in that the rectifying device (12) comprises a housing (121) provided with a receiving chamber and at least two medium channels (122) arranged inside the receiving chamber of the housing (121), the medium channels (122) being adapted to conveying the medium.

5. A flow measuring system for a medium in a pipe according to claim 4, wherein nine medium passages (122) are arranged, one medium passage (122) is arranged along a central axial position of said housing (121), and the remaining eight medium passages (122) are arranged circumferentially around the medium passage (122) at the central axial position.

6. A flow measuring system for a medium in a pipe according to claim 5, wherein said medium passage (122) comprises a through hole (1221) having an inner wall arranged in a cylindrical shape, and an inner wall aperture of said through hole (1221) is two millimeters.

7. A system for measuring the flow of a medium in a pipe according to claim 6, wherein said medium passage (122) is provided with a sealing member (124), and said sealing member (124) seals at least one of said through holes (1221).

8. A system for measuring the flow of a medium in a pipe according to claim 7, wherein the sealing member (124) comprises a sealing plug (1241) and a projection (1242) coupled to a side wall of the sealing plug (1241), the medium passage (122) further comprises a positioning groove (1222) provided at one side of the through hole (1221), the positioning groove (1222) and the projection (1242) being provided correspondingly therebetween;

wherein, when the sealing plug (1241) seals the through hole (1221), the projection (1242) is embedded in the positioning groove (1222).

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