RU2791036C1 - Correlation method for determining the flow rate of liquid metal and electrodeless electromagnetic flowmeter of liquid metal "pif" (perm induction flowmeter) for its implementation - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: invention relates to instrumentation, in particular, to the field of flow measurement by the electromagnetic method, and can be used to measure the flow of liquid metals, including in nuclear power plants. A correlation method is proposed for determining the flow rate of liquid metal, which consists in registering magnetic field fluctuations in two measuring sections located at a known distance from each other, and measuring the time of flight of fluctuations in these measuring sections, which is used to judge the flow rate of liquid metal. With the help of inductors of a variable rotating field, made with the possibility of their inclusion both co-directionally and oppositely, in a continuous or pulsed mode, perturbations of the velocity field are generated in a plane orthogonal to the direction of the main flow, and with the help of inductors of a constant magnetic field, supplemented by measuring coils, register fluctuations of the magnetic field caused by these perturbations. To implement the above method, an electrodeless liquid metal electromagnetic flowmeter is proposed, consisting of induction coils and a magnetic circuit, and the device contains four inductors, each of which is a stacked six-section magnetic circuit, each section of which has a rectangular rod directed towards the geometric center of the magnetic circuit, with a on it with an induction coil, two of the four inductors form a generating module, the other two inductors are supplemented with measuring coils connected to the measuring device and form a recording module, all inductors are mounted on a frame consisting of studs and three-section cheeks, and the generating inductors are made with the possibility of their switching on both co-directionally and oppositely directed, in continuous or pulsed mode.

EFFECT: invention provides the possibility of installation on a pipeline as part of an industrial circuit (separability), expansion of the ranges of the permissible temperature of the measured medium and the permissible diameter of the pipe, eliminating the need for calibration.

2 cl, 5 dwg

Description

The invention relates to instrumentation, in particular, to the field of flow measurement by the electromagnetic method, and can be used to measure the flow of liquid metals, including in nuclear power plants.

The closest known analogue to the proposed method, selected as a prototype, is a correlation method for determining the flow rate of liquid metal (see USSR patent No. 1620848, publ. distance from each other, and measuring the time of flight of fluctuations of these measuring sections, which is used to judge the flow of liquid metal, while recording fluctuations of the magnetic field of thermal currents using induction coils.

In real devices with pipelines, there are always electromagnetic pickups from operating electromagnetic pumps, which significantly noise the useful signal. For reliable operation of this method, a good signal-to-noise ratio is required, which requires the presence of temperature fluctuations in the control liquid flow with an amplitude sufficient to induce significant thermal currents, and subsequent registration of their magnetic field by induction coils. This, in turn, requires the presence of strong temperature gradients in the pipeline section up to the flow meter using this method (for example, tees in which flows of different temperatures are mixed, pipe cooling sections, etc.), which can not always be done .

Also, the use of this method implies the assumption that temperature disturbances propagate with the flow velocity. This assumption works only in a certain flow range (see the article Application of the temperature correlation method to measuring the flow rate of liquid sodium in the journal Magnetohydrodynamics, volume 54, number 4, pages 547-557 by Kolesnichenko I.V., Mamykina A.D., Golbraiha E. and Pavlinova A.M., 2021). And to expand this range, additional calibration of the flowmeter using this method is required, as well as the choice of the correct location of the recording coils relative to the source of temperature fluctuations.

Thus, the disadvantages of this method are:

1. Restriction of the operability and reliability of the method by the requirement for the presence of temperature fluctuations of sufficient amplitude in the control fluid flow, and, consequently, the presence of sources of these temperature fluctuations (tees in which different-temperature flows are mixed, pipe cooling sections, etc.)

2. Indirect determination of the liquid flow rate due to the fact that the flow rate is determined by the transfer of fluctuations of the temperature field, and not the velocity

3. Limitation of control fluid flow ranges and pipeline diameters

The objectives of the invention are:

1. No special requirements for the flow of the control fluid (for example, non-isothermal).

2. Increasing the reliability of the method due to the fact that direct rather than indirect measurements of the velocity field are carried out.

3. Expansion of control fluid flow ranges and pipeline diameters.

To achieve these goals, a correlation method is proposed for determining the flow rate of liquid metal, which consists in registering magnetic field fluctuations in two measuring sections located at a known distance from each other, and measuring the time of flight of fluctuations in these measuring sections, which is used to judge the flow rate of liquid metal, while , with the help of inductors of an alternating rotating field, connected co-directionally or oppositely in a continuous or pulsed mode, they generate perturbations of the velocity field in a plane orthogonal to the direction of the main flow, and with the help of inductors of a constant magnetic field, supplemented by measuring coils, fluctuations of the magnetic field caused by these indignation.

A distinctive feature of the proposed method is that with the help of variable rotating field inductors connected co-directionally or oppositely in continuous or pulsed mode, perturbations of the velocity field are generated in a plane orthogonal to the direction of the main flow, and with the help of constant magnetic field inductors, supplemented by measuring coils , register the fluctuations of the magnetic field caused by these perturbations.

The direction of rotation of the magnetic field in generating inductors is chosen to be the same or opposite in order to expand the range of measured flow rates and improve accuracy at low flow rates. The switched on multidirectional rotating magnetic fields create small-scale velocity fluctuations of low intensity, mainly in the plane of the pipe section - at low flow rates they will be reliably fixed by registering inductors, however, at high flow rates such small-scale weak velocity fluctuations will be quickly smoothed out by the main flow. In the case of high flow rates, rotating magnetic fields should be turned on in a co-directional manner, thereby expanding the area of influence, increasing the degree of swirling of the flow, and creating large-amplitude velocity fluctuations that will be reliably recorded by recording inductors.

An electromagnetic flow meter is known (see USSR patent No. 166514, publ. 11/19/1964), containing a rectangular pipeline and two rectangular induction coils.

The flow meter works as follows. The pulse generator feeds the generating coil located above the channel in such a way that the coil axis lies in the channel section plane with pulses of a certain shape. This causes the appearance of induced currents in the controlled electrically conductive liquid, which are carried away by it at a speed equal to the speed of the controlled flow. Due to the attenuation and movement of currents in the measuring coil, located downstream in such a way that its axis is perpendicular to the plane of the channel section, an EMF is induced. The moment of transition of the EMF from the first positive value to the negative value is a measure of the flow rate of the electrically conductive fluid.

The disadvantages of this flow meter are the small range of the measured flow rate at a fixed distance between the coils, as well as the rectangular shape of the channel - the most common, for example, in the nuclear industry are round pipes.

Known vortex electromagnetic flow meter (see patent for the invention of the Russian Federation No. 2090844, publ. 20.09.1997), containing a pipeline made of non-magnetic material with a shedder body in the form of a vortex-forming rod, the axis of which is perpendicular to the axis of the pipeline, placed on the outer surface of the pipeline bipolar magnet and sensitive an element in the form of an induction coil connected to a signal processing unit.

Vortex flowmeter works as follows. The vortices generated by the bluff body, descending alternately from one and the other side of the rod, form a double Karman vortex street with a vorticity vector parallel to the longitudinal axis of the bluff body. When a vortex passes in the area of application of a magnetic field directed mainly along the axis of the pipeline, a closed electric current and, accordingly, a secondary magnetic field arises in the vortex area, the induction vector of which is directed along the axis of the induction coil. As a result, a pulsed current is induced in the coil, the frequency of which is proportional to the repetition rate of the vortices and, accordingly, to the flow rate of the liquid. The signal from the induction coil enters the processing unit, where the flow rate and flow rate are determined from the measured frequency value, and the amount of fluid that has leaked is determined from the total number of frequency periods for a fixed period of time.

The disadvantage of this flow meter is the need to introduce a bluff body into the pipeline, which is undesirable, and in the case of measuring the flow rate of a liquid metal coolant in nuclear power plants, it is unacceptable.

A time-of-flight electromagnetic flow meter for electrically conductive liquids is known (see USSR patent No. 1340296, publ. 02/07/90), containing in two measuring sections sources of a magnetic field applied to a pipeline with a pair of electrodes in each section and a device for measuring the time shift between signals.

The flow meter works as follows. When passing through the magnetic field of sensors of vortex inhomogeneities of the longitudinal type, the axis of rotation of which is co-directed with the longitudinal axis of the pipeline, electromotive forces directed along the axis of the pipeline are induced under the poles of the magnets. The voltage drop in the area between the electrodes is a useful signal. The delay time between the signals of the first and second sensors is determined using a device for measuring the time shift between the signals. The device can also operate in the marking mode, when short discrete flow marks are created using a special swirler. On the one hand, the described device is quite universal, on the other hand, it requires the presence of electrodes, despite its inductive nature. In case of non-isothermal flow, thermal currents will be generated in these electrodes, creating noise and affecting the accuracy and sensitivity of the instrument. Over time, the electrical contact will deteriorate due to the accumulation of oxides on the inner surface of the pipe, which will also reduce the accuracy and sensitivity of the device, which means that periodic calibration will be required. Also, the presence of electrodes implies the inseparability of the device and the pipe, which makes it impossible to mount the flowmeter on a pipe as part of an industrial circuit. In addition, the device in this configuration will not be able to work on pipes with a large diameter due to the difficulty of scaling its magnetic system.

The closest known analogue to the proposed device, selected as a prototype, is an electrodeless electromagnetic flowmeter (see patent for the invention of the Russian Federation 2520165, publ. 04/20/2014), consisting of a pipe, three induction coils and a magnetic circuit, in which the induction coils are made in the form of flat multilayer printed circuit boards, the magnetic circuit is a flat plate, and the coils and the magnetic circuit are located on the outer surface of the pipe, forming three parallel layers, of which the first layer, located directly on the pipe, is occupied by two coils, the ends of the boards are in contact with each other along the line of the central perimeter of the pipe , and the second and third layers form, respectively, the third coil and the magnetic circuit located symmetrically with respect to the central perimeter of the pipe.

The flow meter works as follows. When a liquid metal moves, it interacts with a magnetic field. An electric field arises in the liquid metal, which is proportional to the speed of the metal and the strength of the magnetic field, and the electric field is orthogonal both to the direction of movement of the liquid metal and to the magnetic field lines. Due to the electric field, circuits of circulating currents arise in planes in the liquid metal parallel to the planes of the turns of the induction coils. Circulating currents form a secondary magnetic field in the channel, the strength of which is proportional to the measured flow rate of the liquid metal. The disadvantages of the above device are:

1. Integrity of the device and the pipe, which makes it impossible to mount the flowmeter on a pipe as part of an industrial circuit.

2. Limited temperature range of the measured medium. Due to the fact that the device is located directly on the surface of the pipe between it, the pipe and the measured medium, thermal contact is inevitable. Printed circuit boards, depending on the selected material and soldering method, have operating temperature limits from 120 to 170 degrees Celsius. When measuring the flow of liquid metals, it becomes necessary to work at temperatures of the liquid medium up to 450 degrees Celsius, which excludes the possibility of using a flow meter of this (attached) type.

3. Limited range of pipe diameters. The device, due to the specifics of its design, measures the flow velocity of the medium in the near-wall region, into which the magnetic field of the generating coil penetrates sufficiently. Therefore, firstly, the device requires calibration due to the need to take into account the shape of the flow profile, and, secondly, it cannot be used to measure flow in pipes of large diameters with the required accuracy for the same reasons.

4. The need to calibrate the device.

The objectives of the present invention are

1. Possibility of installation on a pipeline as part of an industrial circuit (separability).

2. Expansion of the ranges of the permissible temperature of the measured medium and the permissible diameter of the pipe.

3. Getting rid of the need for calibration.

To achieve these goals, an electrodeless electromagnetic flowmeter is proposed, consisting of induction coils and a magnetic circuit, containing four inductors, each of which is a stacked six-section magnetic circuit, each section of which has a rectangular rod directed towards the geometric center of the magnetic circuit, with an induction coil put on it , two of the four inductors are supplemented with measuring coils put on the rod and connected to the measuring device, while all the inductors are mounted on a frame consisting of studs and three-section cheeks.

A distinctive feature of the proposed device is that it contains four inductors, each of which is a stacked six-section magnetic circuit, each section of which has a rectangular rod directed towards the geometric center of the magnetic circuit, with an induction coil put on it, two of the four inductors are supplemented with measuring coils put on a rod and connected to a measuring device, while all inductors are mounted on a frame consisting of studs and three-section cheeks.

The proposed correlation method for determining the flow rate of liquid metal and an electrodeless electromagnetic liquid metal flow meter for its implementation are illustrated in Fig. 1, fig. 2, which shows a diagram of the construction of an electromagnetic flowmeter of liquid metal in the section and Fig. 3, which shows a photo of the device (without a pipe).

The diagram shows pipe 1, on which a flow meter is put on, consisting of four inductors, each of which consists of a magnetic circuit 2 and induction coils 3, put on the rods of the magnetic circuit 2.

The magnetic core 2 is assembled from six identical sections and is stackable.

Two of the four inductors make up the induction generator of vorticity of the rotating field (generating module).

The other two inductors are supplemented with measuring coils 4 and form a recording module. This module is connected to a measurement device (not shown in the figure).

The recording modules are separated by a distance greater than the distance between the generating modules. This distance is selected based on the maximum flow rate for the flow meter provided for by the technical specifications. This is necessary to ensure a sufficient time for the passage of perturbations from one recording module to another.

The generating and recording modules are rigidly mounted on a frame consisting of studs 6 and cheeks 5. Cheeks 5 are also made up of three sectors. With the help of cheeks 5, alignment relative to the pipeline can be performed, however, there is no rigid connection with the channel.

The proposed method is carried out as follows.

A rotating magnetic field is created in each inductor of the generating module by connecting the induction coils 3 to a three-phase power supply. Running in a circle in a plane orthogonal to the direction of the main flow of the control fluid, the magnetic field carries with it the working medium in the area between the rods of the magnetic cores 2, twisting it.

The direction of rotation in the inductors of the generating module can be both co-directional and opposite, and is selected based on the operating conditions, namely the pipe diameter and flow rate. The created vorticity of the flow moves at the speed of the flow of the working medium and passes sequentially through the inductors of the recording module, changes the constant magnetic field created by their coils 3, causing a response in the measuring coils 4. The signal from the coils 4 enters the measuring module (not shown in the figure), where at With the help of correlation analysis, the time of flight of the vorticity from one to the other inductor of the recording module is calculated. Knowing the distances between them, it is possible to calculate the volumetric flow rate of the working medium. The resulting flow rate does not depend on the electrical conductivity or the temperature of the medium.

The device can also operate in a marking mode, in which the generating module operates in a pulsed mode, and the measuring module measures the time of flight of the vorticity from the generating module to the recording module using signals from coils 4.

The flow meter uses a method for generating velocity pulsations, which consists in applying electromagnetic forces created in the local area of the channel with the help of rotating magnetic field inductors. Registration of such pulsations is also carried out with the help of an electromagnetic system that implements the method of electromagnetic correlations (IEC).

In FIG. Figure 4 shows an example of a computational diagram of the evolution of the profile of the liquid metal axial velocity component along the channel axis for the MEC technique. A numerical study of the IEC showed that there are modes of generation of pulsation, realized by an electromagnetic inductor, in which the burst of speed practically does not lose its intensity along the flow.

In FIG. 5 shows an example of a calculated correlation function for the best mode of implementing the IEC methodology. With a good location of the electromagnetic sensors for registering the speed pulsation, a high degree of correlation is achieved when restoring the speed values.

The calculations were carried out within the framework of a mathematical model based on the equations of magnetohydrodynamics. Regimes were considered in which the magnetic Reynolds number is less than unity, which means that the process of magnetic field transfer by the flow can be ignored and the non-inductive approximation can be used. Therefore, the problems of electrodynamics and hydrodynamics were studied separately.

Electrodynamic studies of the mathematical model based on Maxwell's equations were carried out in the Ansys Emag application using the finite element method.

The hydrodynamic studies of a mathematical model based on the Navier-Stokes equations using the LES semi-empirical turbulence model were carried out in the Ansys Fluent application using the finite volume method. The analysis of pulsation correlations and the transfer of data from the electrodynamic computational grid to the hydrodynamic one were carried out in the Matlab application. The origin of coordinates is located on the axis of the cylindrical channel and is associated with the position of the center of the generating module. The OZ axis is directed along the channel, while the OX and OY axes lie in a plane orthogonal to the OZ axis and form the right triple of vectors.

In these studies in the generating module, the direction of the rotating magnetic fields was opposite: one rotated clockwise, the other counterclockwise, relative to the channel axis. The generating module operates in a pulse mode, and the pulse time and the time between pulses are the subject of ongoing scientific research. For a given flow rate, there are intervals of the best values of these two times, at which the greatest degree of correlation is achieved in the measuring module. The intensity of electromagnetic forces is also the subject of research. For each liquid metal, it will be different for the same value of current on the windings that feed the generating model.

For the graphs presented as an example, the current on the supply windings is 1 A, the pulse duration is 1 s, and the period between them is 10 s. Isothermal processes were studied in a wide range of liquid metal consumption (from 1 to 10 cubic meters per hour). It was found that each flow rate corresponds to a set of parameters that provides the best conditions for measurement. For the presented graphs, the consumption of gallium alloy at room temperature is 5.65 cubic meters. at one o'clock.

The best position of the sensors is also the subject of research. The degree of correlation of two pulsating signals generated by the velocity field in fixed localized areas of the sensors was studied. It was found that for each set of operating parameters of the flow meter: liquid metal flow rate, its electrical conductivity, pulse duration time, period between pulses, there correspond two values of the position of the sensors that provide the best conditions for measurement with a high degree of correlation. For the presented graphs, the best distance from the first sensor to the generating module is 0.3 m, and the distance between the sensors is 0.1 m.

Claims (2)

1. A correlation method for determining the flow rate of liquid metal, which consists in registering magnetic field fluctuations in two measuring sections located at a known distance from each other, and measuring the time of flight of fluctuations in these measuring sections, which is used to judge the flow rate of liquid metal, characterized in that when with the help of inductors of a variable rotating field, made with the possibility of their inclusion both co-directionally and oppositely, in a continuous or pulsed mode, perturbations of the velocity field are generated in a plane orthogonal to the direction of the main flow, and with the help of inductors of a constant magnetic field, supplemented by measuring coils, they register magnetic field fluctuations caused by these perturbations. 2. Electrodeless liquid metal electromagnetic flowmeter, consisting of induction coils and a magnetic circuit, characterized in that the device contains four inductors, each of which is a stacked six-section magnetic circuit, each section of which has a rectangular rod directed towards the geometric center of the magnetic circuit, with a on it with an induction coil, two of the four inductors form a generating module, the other two inductors are supplemented with measuring coils connected to the measurement device and form a recording module, all inductors are mounted on a frame consisting of studs and three-section cheeks, and the generating inductors are made with the possibility of their inclusions both co-directionally and oppositely directed, in continuous or pulsed mode.

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