RU2555517C2 - Large-bore electromagnetic flow meter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: electromagnetic flow meter for liquid metals features cylindrical tube out of non-magnetic material, two measuring electrodes welded to external tube surface, inductor with induction coil and magnetic conductor with two pole plates connected by a bracket, where the pole plates are positioned at one tube side so that axis of each pole plate passes through channel centre perpendicularly to the channel axis at an angle under 180° to the other plate axis, while measuring electrodes are positioned opposite in the line passing through the tube channel centre, induction coil is mounted on the bracket so that a line connecting measuring electrodes coincides with the coil symmetry axis. Four additional electrodes at coordinates ±0.538R and ±0.906R, where R is the channel radius, are positioned along the tube generatrix passing at equal distance between inductor poles inside an angle under 180° against crossing point of generatrix with the coil symmetry axis.

EFFECT: flow meter indication independent of magnetic Reynolds number.

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Description

The invention relates to instrumentation, in particular to electromagnetic flowmeters designed to measure the flow of liquid metals.

Known electromagnetic flowmeters of liquid metals, the principle of which is based on the law of electromagnetic induction [1]. The electromagnetic flowmeter has a stainless steel pipe without an insulating coating on the inner surface, measuring electrodes welded to the outer surface of the pipe wall, and an inductor that creates a magnetic field in the working area of the pipe channel. The inductor may consist of a magnetic circuit and permanent magnets or be an electromagnet, i.e. consisting of a magnetic circuit and an induction coil located on it, fed by electric current.

To measure the flow of liquid metals in large pipes, an inductor is used that creates a magnetic field in the local part of the channel, which simplifies the design of the inductor and the flowmeter as a whole [2]. The magnetor lead has two pole plates connected by a bracket, and the pole plates are located on one side of the pipe so that the axes of each pole plate pass through the center of the channel perpendicular to the channel axis and form an angle of less than 180 ° to each other, and the measuring electrodes are diametrically opposite on the line passing through the center of the pipe channel. The induction coil is located on the bracket so that the line connecting the electrodes is the axis of symmetry of the coil.

The disadvantage of this flow meter is the nonlinearity of the dependence of the readings on the volumetric flow rate of the liquid metal. The non-linearity of the flowmeter characteristic is caused by circulating currents in the liquid metal, which at high flow rates form secondary magnetic fields that distort the magnetic field of the excitation generated by the induction coil. The magnitude of the induced (secondary) magnetic field can be characterized by a magnetic Reynolds number (Re _m )

$${\mathrm{Re}}_m=Lv\sigma \mu ;(\mathrm{one})$$

where L is the characteristic linear size, v is the flow velocity, σ is the electrical conductivity of the measured medium, μ is the magnetic permeability of the measured medium. In this case, the characteristic linear size L is understood as the distance between the centers of the pole plates of the inductor, which roughly characterizes the dimensions of the local magnetic field in the flowmeter channel.

If the magnetic Reynolds number reaches values greater than unity (Re _m > 1), then the magnetic field in the flowmeter channel undergoes noticeable changes caused by induced circulation currents in the measured medium, which reduce the sensitivity of the flowmeter to the flow rate of liquid metal. Since the magnetic Reynolds number depends on the flow velocity, there is no magnetic field distortion at low flow rates and gradually increases with increasing flow rate, thus a nonlinear dependence of the readings on the flow rate occurs.

The flowmeter described in the patent [2] is the closest prototype of the present invention.

The aim of the invention is the creation of a liquid metal flow meter in a large-diameter pipe with a linear dependence of the readings on the flow, i.e. insensitive to magnetic Reynolds number.

The proposed electromagnetic liquid metal flow meter differs from that described in [2] in that four additional electrodes with the following coordinates relative to the point of intersection of the forming pipe with the symmetry line of the induction coil are located along the generatrix pipe inside an angle less than 180 °: ± 0.538R and ± 0.906R, where R is the channel radius.

The flowmeter measuring device sequentially measures the potential difference between one measuring electrode remote from the inductor and each of the five other electrodes located on the pipe near the inductor. Then, the measured potential differences are summarized programmatically, taking into account the weight coefficients inherent in the applied Gaussian integration method over five points, and the dependence of the resulting sum on the flow is constructed. In this case, a linear characteristic of the flow meter readings from the volume flow is achieved, regardless of the magnetic Reynolds number.

The essence of the invention is as follows. A secondary magnetic field induced in a liquid metal is formed only at the edges of a portion of the working magnetic field distributed in the channel of the device. Moreover, if at the inlet along the flow it weakens the initial magnetic field, then at the outlet it amplifies it to the same extent. As a result of the addition of the initial and secondary magnetic fields, the resulting field did not change its integral value, but it turns out to be biased in the direction of motion of the liquid metal with slightly deformed front edges. The magnitude of the displacement of the magnetic field and the deformation of the edges are greater, the greater the magnetic Reynolds number. The displacement of the magnetic field of the excitation naturally causes a similar displacement of the induced electric field on the outer surface of the pipe. If we summarize the signals taken from several points located on an extended section of the pipe that captures the boundary zones, the total value of the signals is linearly related to the flow rate and, therefore, insensitive to the magnetic Reynolds number. The measuring electrode, located on the opposite side of the pipe from the inductor, is relatively far from the magnetic field of the excitation, therefore, it has practically zero electric potential, i.e. little dependent on the value of the flow rate and Re _m , while on the generatrix of the pipe, where five electrodes are located, the electric field substantially depends on the volumetric flow rate and the magnetic Reynolds number. The distance between these five electrodes is made taking into account the application of the Gaussian integration method over five points [3]. This arrangement of electrodes allows for the highest accuracy of signal integration with a minimum number of electrodes.

Figure 1 shows a design diagram of the proposed electromagnetic liquid metal flow meter.

The electromagnetic liquid metal flow meter consists of a pipe 1 made of stainless steel, a bipolar magnetic circuit consisting of a bracket 2 and two pole plates 3. An induction coil 4 is located on the central part of the bracket 2. The pole plates 3 of the magnetic circuit are mounted on one side of the pipe so that their axes pass through the center of the channel perpendicular to the axis of the channel and form an angle α between themselves of less than 180 °. Electrodes are welded to the pipe, moreover, one electrode 5 is located at the intersection with the line of symmetry 7 of the generating pipe, is removed from the induction coil, and five electrodes 6 are located on the generating pipe near the induction coil 4.

An electromagnetic liquid metal flow meter operates as follows. An electric current is supplied to the induction coil, as a result of which a local magnetic field is created in the pipe channel between the pole plates of the inductor. When a liquid metal moves along a pipe channel in a liquid metal crossing a magnetic field, an electric field is excited, which causes circulation currents to appear in the liquid metal and the pipe wall in contact with it. As a result of the flow of currents along the pipe wall, an electric field is created, which serves as a measure of the volumetric flow rate of liquid metal. The measuring device of the flow meter sequentially measures the potential difference between one measuring electrode 5 located remotely from the inductor and each of the five other electrodes 6 located near the inductor. Then, the measured potential differences are summed up taking into account their weight coefficients, which correspond to the Gaussian integration method over five points [3], and the dependence of the obtained sum on the flow is constructed. In this case, a linear dependence of the readings on the volumetric flow rate is achieved, regardless of the magnetic Reynolds number.

The technical result that can be obtained by carrying out the invention is to improve the accuracy of the metrological characteristics of the flow meter.

SOURCES OF INFORMATION

1. Kremlin P.P. Multiphase flow measurement. Publishing House "Engineering", Leningrad, 1982, 214 p.

2. Patent RU No. 2474791, Bull. No 4, 2013

3. G. Korn, T. Korn, Handbook of Mathematics, Moscow "Science", 1984, 832.

Claims (1)

An electromagnetic liquid metal flow meter having a cylindrical pipe made of non-magnetic material, two measuring electrodes welded to the outer surface of the pipe, an inductor having an induction coil and a magnetic circuit having two pole plates connected by a bracket, the pole plates being on one side of the pipe in this way that the axes of each pole plate pass through the center of the channel perpendicular to the axis of the channel and form an angle of less than 180 ° with each other, and the measuring electrodes are of diameter It is opposite on the line passing through the center of the pipe channel, the induction coil is located on the bracket so that the line connecting the measuring electrodes is the axis of symmetry of the coil, characterized in that along the generatrix of the pipe at an equal distance between the poles of the inductor inside an angle smaller 180 °, relative to the point of intersection of the generatrix with the line of symmetry of the coil, there are an additional four electrodes with the following coordinates: ± 0.538R and ± 0.906R, where R is the radius of the channel.