CN112985528B - Device and method for measuring unstable liquid flow in a closed pipeline - Google Patents

Abstract

The invention belongs to the technical field of liquid flow measurement, and particularly discloses a device and a method for measuring unstable liquid flow in a closed pipeline; comprises a pipeline, wherein a water inlet and a first water outlet are respectively arranged at two ends of the pipeline; a standard meter electromagnetic flowmeter is also arranged on the pipeline, and a weighing method flow measuring mechanism is arranged between the standard meter electromagnetic flowmeter and the water inlet; a flow stabilizer is arranged between the standard meter electromagnetic flowmeter and the first water outlet; an ultrasonic flowmeter is arranged between the flow stabilizer and the first water outlet.

Description

Device and method for measuring unstable liquid flow in a closed pipeline

technical field

The invention belongs to the technical field of liquid flow measurement, and in particular relates to a device for measuring unstable liquid in a closed pipeline and a measurement method thereof.

Background technique

Closed pipeline fluid metering is a very important part of industrial process control. Flow measurement problems generally come from the measurement and control requirements of full pipeline fluid, and most flow sensors are based on the flow measurement method of the full pipeline state. However, with the continuous increase of industrial and agricultural production and social water consumption, in the fields of sewage discharge flow monitoring and water resources transportation measurement, there are more and more demands on the measurement of flow instability and non-full pipe flow. In recent years, my country has paid more and more attention to the safety and management of water resources transportation and discharge. The water supply and drainage pipelines of the water resource system are often in a state of partial fullness and unstable flow. If there is a lack of corresponding flow measurement methods and devices, it is obviously difficult to meet the energy-saving and emission-reduction monitoring requirements of pipeline water supply and drainage flow management.

Unstable flow and partially filled fluid have the characteristics of water flow movement on the free surface. In view of this characteristic, the open channel is one of the commonly used measurement methods at present. Open channels have achieved certain results in some water conservancy projects, but there are certain limitations in the measurement of non-full pipe flow. Open channels cannot be used in sewage treatment, especially in toxic and harmful sewage treatment. Another method of measuring partially filled fluid is: "level meter + flow meter". However, the use of multiple sensors to solve partial pipe measurement has problems such as high cost, difficulty in later maintenance, and inability to measure in real time. Especially when measuring toxic and harmful fluids, the use of multiple sensors is greatly restricted. There are also ultrasonic flowmeters, which claim to be able to measure the flow in the "partially full pipe" state at the time of sales, but when the flow rate is low, the flow rate is unstable, and the liquid level is lower than 50% of the total liquid level, it cannot be accurately measured. Measurement.

When the flow rate is unstable, or even the pipeline is not full, the key technology to be solved is the relationship between the flow rate and the change of the liquid level of the partially filled pipe (generally considering the range of fluid fullness from 10% to 100%). The invention proposes a device and a method for accurately measuring the flow rate at an industrial site, aiming at the state of unstable fluid flow and partial full pipe when the pipeline is closed.

Contents of the invention

The object of the present invention is to provide a measuring device and a measuring method for an unstable liquid in a closed pipeline with accurate measurement in a part-full pipe state.

Based on above-mentioned purpose, the present invention adopts following technical scheme:

A device for measuring unstable flow in a closed pipeline, comprising a pipeline, the two ends of the pipeline are respectively provided with a water inlet and a first water outlet; A weighing method flow measurement mechanism is set; a flow stabilizer is set between the standard meter electromagnetic flowmeter and the first water outlet; an ultrasonic flowmeter is set between the flow stabilizer and the first water outlet; the ultrasonic flowmeter is connected to the first water outlet A glass window is arranged between the water ports, and the flow stabilizer, the ultrasonic flowmeter and the glass window are all arranged on the pipeline.

Further, four pairs of capacitor electrodes are laid up and down on the insulating tube wall of the standard meter electromagnetic flowmeter, and the four pairs of capacitor electrodes are evenly distributed around the insulating tube wall; any capacitor electrode is arc-shaped, and the central opening angle of any capacitor electrode is uniform. is 40°, and the gap between any two adjacent capacitor electrodes is equal; four consecutive capacitor electrodes are positive plates, and the four capacitor electrodes opposite to the positive plates are negative plates, and the positive plates and negative plates are respectively located in the insulating tube The upper and lower sides of the wall; a shielding cover is arranged outside the ring formed by the capacitance electrodes.

Further, the flow stabilizer includes a cuboid-shaped first water tank, the bottom of the first water tank is provided with a water inlet pipe, and the water inlet pipe includes a vertical pipe, and the bottom end of the vertical pipe is connected to the pipeline on the side of the first water tank near the electromagnetic flowmeter of the standard meter Connected, the top of the vertical pipe is connected with an elbow, the elbow is a downwardly curved arc-shaped pipe; the end of the elbow away from the vertical pipe is provided with a liquid inlet, and the liquid inlet is located at the bottom of the first water tank; A liquid outlet is provided above the liquid port, and the liquid outlet is arranged above the elbow, and the liquid outlet communicates with the pipe on the side of the first water tank away from the standard meter electromagnetic flowmeter; the first water tank is provided with a plurality of orifices Any throttling orifice plate is provided with evenly distributed through holes; the throttling orifice plate includes a horizontal plate arranged parallel to the bottom surface of the first water tank, and any horizontal plate is sealed with the four side walls of the first water tank connection; the throttling orifice plate also includes a vertical plate arranged vertically to the horizontal plate, any vertical plate is in sealing connection with the bottom end and the side wall of the first water tank, and the vertical plate is in unsealed connection with the top of the first water tank; The vertical boards include crosswise horizontal boards and longitudinal boards; the top of the first water tank is provided with a breathing valve.

Further, the ultrasonic flowmeter is clamped on the pipeline; the glass window is transparent tubular, both ends of the glass window are connected to the pipeline, a liquid level scale is arranged on the glass window, and a capacitive liquid level switch is arranged inside the glass window.

Further, the excitation system of the standard meter electromagnetic flowmeter is a low-frequency square wave excitation; the standard meter electromagnetic flowmeter is provided with a filter circuit.

Further, the gravimetric flow measurement mechanism includes a commutator connected to the pipeline, the commutator is provided with a second water outlet and a third water outlet, and a second water outlet communicating with the second water outlet is provided below the second water outlet. Two water tanks; a load-bearing container connected to the third water outlet is arranged below the third water outlet, and an electronic scale is arranged below the load-bearing container, and the electronic scale is used to weigh the weight of the load-bearing container; the second water tank is far away from one end of the commutator and The pipeline is connected, and a pipeline pump is arranged on the pipeline on the side away from the commutator of the second water tank.

Further, a metal bellows is arranged between the commutator and the water inlet, and both ends of the metal bellows are connected to the pipeline; a manual valve is arranged on the pipeline between the second water tank and the pipeline pump, and the standard gauge electromagnetic flowmeter and A manual valve is arranged on the pipeline between the flow stabilizers.

Further, the standard meter electromagnetic flowmeter is provided with a control system, the control system is used to receive capacitance value information, and the control system is connected with an LED warning light.

The measurement method of the above-mentioned measuring device for unstable flow in a closed pipeline is characterized in that it includes the following steps,

Step 1, connect the part to be tested with the water inlet and the first water outlet, and the liquid flows through the water inlet to the weighing method flow measuring mechanism, pipeline pump, standard meter electromagnetic flowmeter, flow stabilizer, ultrasonic flowmeter, glass window and first water outlet;

Step 2, measure the capacitance value C of the electrode of the standard meter electromagnetic flowmeter, calculate the liquid level height of the liquid in the pipeline through the capacitance value C, and calculate the flow rate Q1 of the liquid in the pipeline through the liquid level height value of the liquid in the pipeline;

Step 3, use the weighing method flow measuring mechanism to measure the flow Q2 of the liquid in the pipeline for a period of time; observe the liquid level through the glass window, when the liquid level is greater than 50% of the pipeline, measure the flow Q3 through the ultrasonic flowmeter, and Q3 is compared with Q1.

Compared with the prior art, the present invention has the following beneficial effects:

The metal bellows can buffer the impact on the electronic scale under different fullness and reduce the error of the electronic scale under the weighing method.

The flow rate of the measured fluid is usually in a state of low pressure or no pressure. When the pressure loss is small and the total head loss of the device changes at any time, a high-precision electronic scale is selected to ensure the uncertainty of the overall device.

The glass window with a scale is equipped with a capacitive liquid level switch for monitoring different liquid levels at any time, and the liquid level can also be observed through the scale on the glass window. The values of the two can be compared to reduce the uncertainty of liquid level measurement.

The ultrasonic flowmeter is directly clamped on the pipeline without disassembling the pipeline. When the fullness is (50-100)%, the reading of the ultrasonic flowmeter can be compared with the standard meter to reduce the reading uncertainty of the standard meter.

There is a shielding cover outside the capacitance electrode, which is used to prevent interference to the measurement electrode.

Capacitive electrodes are evenly laid outside the insulating pipe wall. In terms of size design, each capacitor electrode has the same size and the gap between two electrodes is also the same. This design is to measure the change of the liquid level to the greatest extent, and to ensure that the measurement of the fullness is lower than 50%. Theoretically, the more the number of capacitive electrodes, the more the capacitance value between the two plates can be measured, the higher the measurement accuracy and the accuracy will be improved. However, if the number of capacitive electrodes is increased, the design of the hardware circuit will be more complicated in terms of specific implementation, and its production cost will be increased at the same time. The design of 4 pairs of capacitive electrodes and the central opening angle of 40 degrees in the present invention not only ensures the accuracy of measurement, but also reduces the complexity and cost in terms of hardware circuit design and implementation.

Standard meter electromagnetic flowmeter, the excitation system adopts low-frequency square wave excitation, and the excitation circuit designed by follower circuit and inverting circuit is shown in the attached drawing. The choice of excitation method directly affects the accuracy of measurement. In the case of unstable fluid flow, finding a stable and uniform magnetic field is an effective way to ensure the sensitivity of the device. DC excitation is prone to polarization, and AC excitation reduces the signal-to-noise ratio. The low-frequency square wave excitation provides a relatively uniform magnetic field for the standard meter electromagnetic flowmeter, and at the same time avoids the shortcomings of DC excitation and AC excitation. From the perspective of the whole process, the magnetic field generated by the low-frequency rectangular wave is in the process of periodic change, which is an alternating signal, which is convenient for later amplification and processing.

The flow stabilizer is a rectangular parallelepiped. In order to ensure the smooth flow of the fluid in the pipe and the requirements of the partial liquid level in order to obtain better measurement results, a layered design is adopted, and a breathing valve is installed at the top of the device. The breathing valve ensures the circulation of internal liquid and air, and ensures the overflow of fluid when the pipe is full. The interior adopts a throttle orifice. When the flow rate is unstable and the flow rate is not full, the flow rate and flow rate inside the device are unstable, causing very large errors in the measurement. The lower edge and both side edges of the orifice plate are sealed and connected with the inside of the device box. The liquid inlet is communicated with the liquid outlet, but not on a horizontal plane, and the liquid inlet of the elbow structure is placed at the bottom of the device. When the liquid level gradually rises from a low place, it gradually fills each unit in the device, and the unit is the gap between adjacent horizontal plates, and the interface between the fluid and the air maintains a relatively steady rise or fall during the whole process.

The flow stabilizer is a plurality of vertical plates intersected with horizontal plates to form n small water storage partitions. When water flows in, the water storage compartment will be gradually filled, ensuring the stability of the water level.

Description of drawings

Fig. 1 is a structural diagram of a liquid flow instability measuring device according to Embodiment 1 of the present invention;

2 is a schematic diagram of a glass window in Embodiment 1 of the present invention;

Fig. 3 is the structural representation of the standard meter electromagnetic flowmeter of embodiment 1 of the present invention;

Fig. 4 is the circuit diagram of the excitation excitation module of the standard meter electromagnetic flowmeter in Embodiment 1 of the present invention;

FIG. 5 is a schematic structural view of a flow stabilizer according to Embodiment 1 of the present invention;

6 is a circuit diagram of a filter module of a standard meter electromagnetic flowmeter in Embodiment 1 of the present invention;

Fig. 7 is a schematic diagram of the distribution of capacitive electrodes of the standard meter electromagnetic flowmeter according to Embodiment 1 of the present invention.

In the figure: DN50 bellows 1, DN50 glass window 2, ultrasonic flowmeter 3, DN20 manual valve 4, standard meter electromagnetic flowmeter 5, pipeline pump 6, DN40 manual valve 7, second water tank 8, electronic scale 9, load-bearing container 10. Commutator 11, flow stabilizer 12, first water tank 13, elbow pipe 14, vertical pipe 15, water inlet 16, first water outlet 17, second water outlet 18, third water outlet 19, pipeline 20, Support 21 , shielding case 22 , capacitor electrode 23 , liquid 24 , insulating pipe wall 25 , and throttling orifice plate 26 .

Detailed ways

Example 1

The invention is a device capable of measuring the flow of a partial pipe which integrates the standard meter method and the static mass method. Flow range: (1~800)m ³ /h, fluid fullness range is 10%~100%. The expanded uncertainty of the device under the static mass method is 0.06%, and the expanded uncertainty of the device under the standard table method is 0.2%. Among them, the standard meter adopts an electromagnetic electromagnetic flowmeter, and the electrodes of the flowmeter adopt 4 pairs of capacitive electrodes. The standard table can obtain the relationship between the liquid level and the average flow rate, and then obtain the liquid 24 flow rate.

A device for measuring unstable flow liquid 24 in a closed pipeline 20, as shown in Figure 1, includes a pipeline 20, the pipeline 20 is arranged on a support 21, and the two ends of the pipeline 20 are respectively provided with a water inlet 16 and a first water outlet 17; 20 is also provided with a standard meter electromagnetic flowmeter 5, a weighing flow measurement mechanism is arranged between the standard meter electromagnetic flowmeter 5 and the water inlet 16; a flow rate is arranged between the standard meter electromagnetic flowmeter 5 and the first water outlet 17 A stabilizer 12; an ultrasonic flowmeter 3 is arranged between the flow stabilizer 12 and the first water outlet 17; a DN50 glass window 2 is arranged between the ultrasonic flowmeter 3 and the first water outlet 17.

As shown in Figure 1, a DN50 bellows 1 is provided between the commutator 11 and the water inlet 16 of the weighing method flow measurement mechanism, and both ends of the DN50 bellows 1 are connected to the pipeline 20, and the DN50 bellows 1 is filled with different Under the high degree, it can buffer the impact force on the electronic scale 9, and reduce the error of the electronic scale 9 under the weighing method; the pipeline 20 between the second water tank 8 and the pipeline pump 6 is provided with a DN40 manual valve 7, and the standard gauge electromagnetic A DN20 manual valve 4 is provided on the pipeline 20 between the flow meter 5 and the flow stabilizer 12 .

As shown in Figure 1, the weighing method flow measurement mechanism includes a commutator 11 connected to the pipeline 20, the commutator 11 is provided with a second water outlet 18 and a third water outlet 19, and the second water outlet 18 is provided below There is a second water tank 8 communicating with the second water outlet 18; a load-bearing container 10 communicating with the third water outlet 19 is provided below the third water outlet 19, and an electronic scale 9 is arranged below the load-bearing container 10, and the electronic scale 9 is used for Weigh the weight of the load-bearing container 10; the electronic scale 9 selects the MSE524S type balance of Germany Sartorius Company. The resolution of MSE524S is 0.1mg, the precision is 1mg, and the accuracy level is Class I. The flow rate of the measured fluid is usually in a state of low pressure or no pressure. When the pressure loss is small and the total head loss of the device changes at any time, a high-precision electronic scale 9 is selected to ensure the uncertainty of the overall device. The end of the second water tank 8 away from the commutator 11 communicates with the pipeline 20 , and the pipeline pump 6 is arranged on the pipeline 20 on the side of the second water tank 8 away from the commutator 11 .

Further, the ultrasonic flowmeter 3 is clamped on the pipeline 20; the clamp-on ultrasonic flowmeter 3 is directly clamped on the pipeline 20 without disassembling the pipeline 20. When the fullness is (50-100)%, the ultrasonic flowmeter 3 The reading can be compared with the standard table to reduce the reading uncertainty of the standard table.

As shown in Figure 1 and Figure 2, the DN50 glass window 2 is transparent tubular, both ends of the DN50 glass window 2 are connected to the pipeline 20, the DN50 glass window 2 is provided with a liquid level scale, and the DN50 glass window 2 is provided with a Capacitive level switch. The DN50 glass window 2 with scale has a capacitive liquid level switch inside, which is used to monitor different liquid levels at any time, and the liquid level can also be observed through the scale on the DN50 glass window 2. The values of the two can be compared to reduce the uncertainty of liquid level measurement.

As shown in Figure 2, T is the DN50 glass window 2, L1...Ln+1 is the liquid level switch at different liquid levels, the fluid outflow end of the DN50 glass window 2 is connected to the instrument to be tested, and the other end is connected to the ultrasonic flowmeter 3. The fluid input end of the ultrasonic flowmeter 3 is connected with a flow stabilizer 12 .

As shown in Figure 3, four pairs of capacitor electrodes 23 are laid outside the insulating tube wall 25 of the standard meter electromagnetic flowmeter 5, and the four pairs of capacitor electrodes 23 are evenly distributed around the insulating tube wall 25; any capacitor electrode 23 is arc-shaped, The central opening angle of any capacitive electrode 23 is 40°, and the gap between any adjacent two capacitive electrodes 23 is equal; four continuous capacitive electrodes 23 are positive plates, and the four capacitive electrodes 23 opposite to the positive plate It is a negative plate, and the positive plate and the negative plate are respectively located on the upper and lower sides of the lining; the capacitor electrode 23 is provided with a shielding cover 22; LED warning lights are connected; the control system is also used to receive information from the liquid level switch in the DN50 glass window 2.

The standard meter electromagnetic flowmeter 5 adopts 4 pairs of capacitors. The capacitance value between two capacitor electrodes 23 is obtained through the existing technology, and the average flow rate related to the liquid level is obtained after being processed by the control system, and then the fluid flow in the pipe is obtained.

The outer wall of the insulating pipe wall 25 of the sensor of the standard meter electromagnetic flowmeter 5 is laid with 4 pairs of capacitive electrodes 23 , and the central opening angle of each arc electrode is 40 degrees. There is a shielding cover 22 outside the sensor to prevent interference to the measuring electrodes.

The capacitive electrodes 23 of the standard meter electromagnetic flowmeter 5 are evenly laid outside the insulating pipe wall 25, and the size of each capacitive electrode 23 is the same in size design and the gap between two electrodes is also the same. This design is to measure the change of the liquid level to the greatest extent, and to ensure that the measurement of the fullness is lower than 50%. Theoretically, the more the capacitive electrodes 23 are, the more capacitance values between the two plates can be measured, the higher the measurement accuracy and the accuracy will be improved. However, if the number of capacitive electrodes 23 is increased, the design of the hardware circuit will be more complicated in terms of specific implementation, and its production cost will be increased at the same time. The design of 4 pairs of capacitive electrodes 23 in the present invention and the central opening angle of 40 degrees not only ensures the accuracy of measurement, but also reduces the complexity and cost in terms of hardware circuit design and implementation.

Furthermore, the excitation system of the standard meter electromagnetic flowmeter 5 adopts a low-frequency square wave excitation, and the excitation circuit designed with a follower circuit and an inverting circuit is shown in Fig. 4 . The choice of excitation method directly affects the accuracy of measurement. In the case of unstable fluid flow, finding a stable and uniform magnetic field is an effective way to ensure the sensitivity of the device. DC excitation is prone to polarization, and AC excitation reduces the signal-to-noise ratio. While the low-frequency square wave excitation provides a more uniform magnetic field for the standard meter electromagnetic flowmeter 5, it avoids the shortcomings of DC excitation and AC excitation. From the perspective of the whole process, the magnetic field generated by the low-frequency rectangular wave is in the process of periodic change, which is an alternating signal, which is convenient for later amplification and processing.

As shown in Figure 6, the standard meter electromagnetic flowmeter 5 uses a filter circuit, which guarantees a certain response speed and strong anti-interference ability. S1a, S1b and S2a, S2b are synchronous switches. When S1a, S1b, S2a, and S2b are disconnected, the input signal does not charge the capacitor, and the capacitor only maintains the potential at this time. When S1a and S1b are closed, the signal charges the capacitor from top to bottom. When S2a and S2b are closed, the signal charges the capacitor from top to bottom.

As shown in Figure 5, the flow stabilizer 12 includes a cuboid first water tank 13, the bottom of the first water tank 13 is provided with a water inlet pipe, the water inlet pipe includes a vertical pipe 15, and the bottom end of the vertical pipe 15 is close to the first water tank 13 The pipeline 20 on one side of the standard meter electromagnetic flowmeter 5 is connected, and the top of the vertical pipe 15 is connected with an elbow 14; Bottom; the top of the liquid inlet is provided with a liquid outlet, and the liquid outlet communicates with the first water tank 13 away from the pipeline 20 on the side of the standard meter electromagnetic flowmeter 5; the first water tank 13 is provided with a plurality of throttling orifice plates 26, Any throttling orifice 26 is provided with uniformly distributed through holes; the throttling orifice 26 includes a horizontal plate arranged parallel to the bottom surface of the first water tank 13, and any horizontal plate is connected to the four sides of the first water tank 13. Wall sealing connection; throttle orifice plate 26 also includes a vertical plate vertically arranged with the horizontal plate, any vertical plate is all sealed with the bottom end and the side wall of the first water tank 13, and the vertical plate includes a transverse plate arranged crosswise And longitudinal plate; The top of the first tank 13 is provided with a breather valve.

The flow stabilizer 12 is a cuboid. In order to ensure the smooth flow of the fluid in the pipe and the requirements of the partial liquid level, and to obtain better measurement results, a layered design is adopted, and a breathing valve is arranged at the top of the device. The breathing valve ensures the circulation of the internal liquid 24 and the air, and ensures the overflow of the fluid when the pipe is full. A throttling orifice 26 is used inside. When the flow rate is unstable and the flow rate is not full, the flow rate and flow rate inside the device are unstable, causing very large errors in the measurement. The lower edge and both side edges of the orifice plate are sealed and connected with the inside of the device box. The liquid inlet is communicated with the liquid outlet, but not on a horizontal plane, and the liquid outlet of the elbow 14 structure is placed at the bottom of the device. When the liquid level gradually rises from a low place, and gradually fills each layer of units in the device, the interface between the fluid and the air maintains a relatively stable rise or fall state throughout the process. The flow stabilizer 12 has a very important effect on the accurate measurement of the standard meter. The flow stabilizer 12 is a plurality of vertical plates and horizontal plates intersected to form n small water storage partitions. When water flows in, the water storage compartment will be gradually filled, ensuring the stability of the water level.

When the device measures the unstable (not full pipe) liquid 24, the measured part is communicated with the water inlet of the pipeline 20 and the first water outlet 17; water is pumped from the water tank to the pipeline 20 by the pipeline pump, and the water flows through the measured Flow meter and flow working standard, compare the output flow of the two, so as to determine the measurement accuracy and repeatability of the tested flow meter.

Example 2

The measurement method of the measuring device for the unstable liquid 24 in the closed pipeline 20 includes the following steps,

Step 1, the part to be tested is communicated with the water inlet 16 and the first water outlet 17, the liquid 24 flows to the commutator 11 of the weighing method flow measurement mechanism sequentially through the water inlet 16, and the liquid 24 will flow through the commutator 11 respectively to The weighing container or the second water tank 8, the pipeline pump 6 extracts the liquid 24 in the second water tank 8, the liquid 24 flows to the standard meter electromagnetic flowmeter 5, and when the liquid 24 flows into the standard meter electromagnetic flowmeter 5, the partial pipe standard meter electromagnetic The flow meter 5 starts to measure the fluid. When the flow rate is small and the liquid level is low, the measured fluid cannot fill the measuring pipe 20, and the traditional liquid 24 measuring instrument cannot perform accurate measurement. When the flow rate is low and the liquid level is not full of the measuring pipe 20, the average flow velocity has a certain relationship with the liquid level. Therefore, to obtain accurate parameters of the flow velocity is a key technology to solve the measurement of the partial electromagnetic flowmeter. When the liquid 24 flows through the water flow stabilizer 12, as shown in Figure 5, the liquid 24 flows in from the elbow 14 below, passes through the throttling orifice 26, and there is a breathing valve above the orifice to communicate with the air. The liquid 24 slowly fills each orifice plate from a low liquid level. During the whole process, the liquid level rises steadily, and then the liquid flows through the flow stabilizer 12, the ultrasonic flowmeter 3, the DN50 glass window 2 and the first outlet in sequence. Shuikou17.

Step 2, inside the sensor, that is, inside the insulating tube wall 25, the relative permittivity ε _{1 of the fluid, the relative permittivity ε 2 of} the air, the volume of the fluid in the insulating tube wall 25 is V1, and the insulating tube wall 25 occupied by the air is V1. The volume inside the pipe wall 25 is V2, and the equivalent relative permittivity ε

ε＝(V ₁ /V)·ε ₁ +(V ₂ /V)·ε ₂ (1)

ε=[(VV ₂ )]·ε ₁ +(V ₂ /V)·ε ₂ =(V ₂ /V)·(ε ₂ −ε ₁ ) (2)

where V is the total volume of the two-phase flow:

V＝V ₁ +V ₂ (3)

Define the discrete phase concentration as:

β ₂ =V ₂ /V (4)

The capacitance measurement value C can be obtained as:

C=K·ε=K·f(V ₂ /V)=K·f(β ₂ ) (5)

In the formula, K is a coefficient, and K is related to the electrical characteristics of air and liquid 24, and the structural characteristics of the insulating pipe wall 25, etc.

When the liquid level is different, the cross-sectional area of the liquid 24 in the tube is different, the volume of the liquid 24 in the tube is different, and the equivalent relative permittivity of the two substances is different, so the capacitance value between the two electrode plates changes. The relationship between the capacitance value and the liquid level in the insulating tube is established through the above formula.

The relationship between the capacitance and the liquid level is established to measure the capacitance values at different heights of the partially filled pipe flowing liquid 24, and realize the measurement of the liquid level parameters of the partially filled pipe electromagnetic flowmeter.

When the tube is full, the induced potential E of the sensor is:

为液体24的平均流速；D为有效测量管径，当满管时D为绝缘管壁25的内径。In the formula, B is the magnetic induction intensity;

is the average flow velocity of the liquid 24; D is the effective measurement pipe diameter, and D is the inner diameter of the insulating pipe wall 25 when the pipe is full.

When the liquid level is low, D in formula (1) is related to the liquid level h.

The actual flow value of the fluid flowing through the pipe:

为液体24的平均流速In the formula, Q is the actual flow in the insulating pipe wall 25; A is the cross-sectional area of the liquid 24 flowing through the insulating pipe wall 20;

is the average velocity of the liquid 24

In the formula, h is the height of the liquid level, and D is the inner diameter of the insulating pipe wall 25

As shown in Figure 3, standard meter electromagnetic flowmeters use capacitive electrodes. The liquid level parameter measured by the capacitive electromagnetic flowmeter of the present invention calculates the flow velocity signals under different liquid levels according to the weight function. Four pairs of capacitor plates are arranged between the measuring tube and the lining, and the conductive liquid 24 flowing in the tube and the measuring tube lining are used as the medium of the capacitor. When the height of the liquid 24 flowing through the insulating tube wall 25 changes, the angle of the equivalent capacitance between the pole plate and the liquid 24 also changes, and the capacitance value between the capacitor electrodes 23 also changes. The height of the liquid level determines the capacitance value between the two plates of the capacitor. In order to calculate the relationship between liquid level and capacitance, the calculation model shown in Figure 7 is constructed. The 4 pairs of capacitive electrodes 23 are numbered: 1, 1'; 2, 2'; 3, 3'; 4, 4'. The relationship between geometric quantities can be obtained from Figure 7:

d=R(cosβ--cosα) (9)

a=R(sinα-sin(β) (10)

In the formula, R is the radius of the inner wall of the insulating pipe wall 20 .

The capacitance value C per unit length of the symmetrical circular arc column plate capacitor can be obtained through the geometric relationship (9)-(10):

In the formula, ε ₀ is the relative permittivity.

Therefore, when the liquid level h is different, α and β change, and the value between the capacitance electrodes 23 changes (formula (6)). At this time, the capacitance value measured between the two capacitance electrodes 23 also changes, so that the distance between the plates is established. Capacitance value C and the functional relationship between the liquid level height h flowing through the insulating pipe wall 20 of the partially filled pipe, measure the capacitance value, calculate the liquid level height h of the liquid 24 in the insulating pipe wall 25 through the capacitance value C, and pass the insulating pipe wall 25 The liquid level height value h of the inner liquid 24 calculates the flow rate Q1 of the liquid 24 in the insulating pipe wall 25 .

Step 3, use the weighing method flow measuring mechanism to measure the flow Q2 of the liquid 24 in the pipeline 20 for a period of time; when the flow unstable liquid measuring device starts to work, the liquid level can be observed through the DN50 glass window 2 of Fig. 2, and at the same time Trigger and start the liquid level switch, and record the liquid level through the control system in Figure 3. When the flow rate of the liquid 24 reaches a certain height, that is, the liquid level exceeds 50%, the reading Q3 of the ultrasonic flowmeter 3 can be compared with the reading Q1 of the standard meter, and the reading of the standard meter is calibrated after comparison.

When the device breaks down, for example, the measurement cannot be realized or the liquid 24 does not realize the internal circulation of the system, the control system cannot receive the capacitance value, and the standard meter electromagnetic flowmeter in Figure 3 sends out an alarm signal and reminds through the LED.

The measurement is complete. The measured data can be displayed through the display terminal (as shown in Figure 3), and can also be transmitted and shared with other devices through the communication port.

The error of the existing non-full pipe flow device in China is about 15%, while the experimental device works continuously for one day, the measured data and actual output are shown in the table below. It can be seen from the table below that compared with the error of about 5%, the measurement accuracy has been greatly improved.

Actual flow (m³) Test traffic (m³) error(%) 27.34 25.97 5.01 28.56 27.27 4.59 25.61 24.37 4.92 25.69 24.33 5.08 26.65 23.60 4.26 24.37 23.14 5.04 22.34 21.21 5.06

Claims (4)

1. a device for measuring unstable liquid flow in a closed pipeline, characterized in that it comprises a pipeline, and the two ends of the pipeline are respectively provided with a water inlet and a first water outlet; said pipeline is also provided with a standard meter electromagnetic flowmeter, said A gravimetric flow measurement mechanism is set between the standard gauge electromagnetic flowmeter and the water inlet; a flow stabilizer is set between the standard gauge electromagnetic flowmeter and the first water outlet; between the flow stabilizer and the first water outlet An ultrasonic flowmeter is arranged in between; four pairs of capacitor electrodes are laid up and down on the insulating pipe wall of the standard meter electromagnetic flowmeter, and the four pairs of capacitor electrodes are evenly distributed around the insulating pipe wall; any of the capacitor electrodes is arc-shaped , the central opening angle of any capacitor electrode is 40°, and the gaps between any two adjacent capacitor electrodes are equal; four continuous capacitor electrodes are positive plates, and the four capacitor electrodes opposite to the positive plates are The negative plate, the positive plate and the negative plate are respectively located on the upper and lower sides of the insulating pipe wall; a shielding cover is arranged outside the ring formed by the capacitor electrodes; the flow stabilizer includes a first water tank, and the bottom of the first water tank is provided with a Water inlet pipe, the water inlet pipe includes a vertical pipe, the bottom end of the vertical pipe communicates with the pipeline on the side of the first water tank near the standard meter electromagnetic flowmeter, and the top of the vertical pipe is connected with an elbow; the elbow One end away from the vertical pipe is provided with a liquid inlet, and the liquid inlet is located at the bottom of the first water tank; a liquid outlet is arranged above the liquid inlet, and the liquid outlet and the first water tank are far away from the standard meter electromagnetic The pipeline on one side of the flow meter is connected; the first water tank is provided with a plurality of throttling orifice plates, and any of the throttling orifice plates is provided with uniformly distributed through holes; the throttling orifice plate includes A horizontal plate arranged parallel to the bottom surface of the water tank, any one of the horizontal plates is sealed and connected with the inner side wall of the first water tank; the throttle orifice plate also includes a vertical plate vertically arranged The straight plates are all in sealing connection with the bottom end and the side wall of the first water tank, and the vertical plates include transverse plates and longitudinal plates arranged crosswise; a breathing valve is arranged on the top of the first water tank; the ultrasonic flowmeter clamps On the pipeline; the excitation system of the standard meter electromagnetic flowmeter is a low-frequency square wave excitation; the standard meter electromagnetic flowmeter is provided with a filter circuit; the weighing method flow measurement mechanism includes a commutator connected to the pipeline, The commutator is provided with a second water outlet and a third water outlet, and a second water tank communicating with the second water outlet is provided below the second water outlet; a second water tank connected with the second water outlet is provided below the third water outlet A load-bearing container connected to the third water outlet, an electronic scale is arranged below the load-bearing container; the end of the second water tank away from the commutator is connected to the pipeline, and the pipeline on the side of the second water tank away from the commutator is provided with pipeline pump; the side of the commutator close to the water inlet is provided with a metal bellows, both ends of the metal bellows are connected to the pipeline; the pipeline between the second water tank and the pipeline pump is provided with a manual valve , the pipeline between the standard meter electromagnetic flowmeter and the flow stabilizer is provided with a manual valve. 2 . The device for measuring unstable liquid in a closed pipeline according to claim 1 , wherein a control system is arranged in the standard meter electromagnetic flowmeter, and the control system is connected with an LED warning light. 3 . 3. A measuring method for an unstable liquid flow measuring device in a closed pipeline, based on the device according to claim 1, characterized in that it comprises the following steps, Step 1. Connect the part to be tested with the water inlet and the first water outlet. The liquid flows through the water inlet to the commutator of the weighing method flow measurement mechanism, and the liquid will flow to the weighing container or the second water tank respectively through the commutator. The pipeline pump pumps out the liquid in the second water tank, the liquid flows to the electromagnetic flowmeter of the standard meter, and then the liquid flows through the flow stabilizer, the ultrasonic flowmeter and the first water outlet in sequence; Step 2, measure the capacitance value C of the electrode of the standard meter electromagnetic flowmeter, calculate the liquid level height of the liquid in the pipeline through the capacitance value C, and calculate the flow rate Q1 of the liquid in the pipeline through the liquid level height value of the liquid in the pipeline; Step 3: Measure the flow Q2 of the liquid in the pipeline for a period of time using a weighing method flow measurement mechanism; when the liquid level is greater than 50% of the pipeline, measure the flow Q3 with an ultrasonic flowmeter, and compare Q3 with Q1. 4. the measurement method of flow instability liquid measuring device in the closed pipeline as claimed in claim 3, it is characterized in that, in step 2, when liquid level height is different, the liquid in the insulation pipe wall of standard gauge electromagnetic flowmeter The cross-sectional area is different, the volume of liquid and air in the insulating tube wall is different, and the equivalent relative permittivity of the liquid and air mixture in the insulating tube wall is different, so the capacitance value between the two electrode plates changes, thus establishing an electrode The relationship between the capacitance value between the plates and the liquid level height in the insulating pipe wall, and then calculate the liquid level height of the liquid in the pipe through the capacitance value.

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