Speed ​​variation detector for an electrically conductive fluid flow, comprising an electromagnetic transducer.

Abstract

Speed ​​variation detector for an electrically conductive fluid flow, comprising an electromagnetic transducer. The invention relates to a speed variation detector for an electrically conductive fluid flow, comprising: - an electromagnetic transducer (10), comprising: a metallic cylindrical tube (2) forming a core with high magnetic permeability, an electrical coil (3), called the primary coil, wound around the tube and intended to be electrically powered by direct current, or a permanent magnet arranged around the tube, at least one electrical coil (4), called the receiving coil, wound around the tube while being adjacent to the primary coil or the permanent magnet, - at least one envelope detector circuit (7) connected to the receiving coil, comprising at least one diode (8; 8.1, 8.2) and a load (9; 9.1, 9.2) in electrical series with the diode, the load being made up of a capacitor (90; 90.1, 90.2), and an electrical resistance (91; 91.1, 91.2). Figure for the abbreviation: fig.11.

Description

Title of the invention: Speed ​​variation detector for an electrically conductive fluid flow, comprising an electromagnetic transducer. technical field

[0001] The present invention relates to the field of instrumentation and measurement, and more particularly to that of transducers dedicated to local, point velocimetry of electrically conductive fluids.

[0002] The invention relates to a speed variation detector of an electrically conductive fluid comprising an electromagnetic transducer.

[0003] The invention applies generally to any electrically conductive fluid. These fluids include, for example, electrically conductive ionic solutions such as salt water, and even more so, liquid metals. Typically, these metals include, for example, sodium, potassium, lead, lithium, aluminum, copper, iron, zinc, titanium, and their alloys.

[0004] More particularly, the invention applies to measurements in dense liquid-type fluids having a density in a range of 100 kg.m3 to more than 1000 kg.m3.

[0005] The invention is particularly suitable for fluid velocity measurements where the melting temperature range is the melting temperature range of metals treated, shaped or used in liquid form, typically from about -50 °C to over 1500 °C.

[0006] One advantageous application envisaged is the measurement of velocities of heat transfer fluids, in particular of nuclear fission and fusion reactors. Previous technique

[0007] In many applications, it is necessary to know the velocity field of an electrically conductive fluid in motion.

[0008] This is the case in the metal foundry industry, where knowledge of the velocity range in foundry molds and their feeding circuits makes it possible to predict the quality of the parts produced and limit scrap. Knowledge of flow velocities allows for the control and optimization of the filling of foundry molds.

[0009] In the nuclear industry, the velocity field of the metallic heat transfer fluids used in the circuits of certain nuclear reactors is a major factor in the stress on the metallic structures in contact. Therefore, knowledge of it is essential.

[0010] This is also a major factor in the heat exchanges existing in the heat exchangers and at the level of the nuclear fuel of these reactors.

[0011] Knowledge and analysis of the velocity field in key locations of a reactor (heat exchangers, core outlet, pump, etc.) is also an indicator of proper operation and therefore, a means of increasing safety and overall the monitoring possibilities of these machines.

[0012] Scientific experiments involving liquid metals in large volumes, as well as tests carried out with a view to knowing flow distributions in exchanger manifolds, also require knowledge of the velocity field of the flows involved.

[0013] In the various flow zones mentioned, the flow conditions are three-dimensional. What also most often characterizes these flows is their temperature level, most often several hundred degrees, and the density of the fluids used, which can range from a few hundred kg.m3 to several thousand kg.m3.

[0014] Various velocimetry techniques are known and used to measure the velocity components of a flow of electrically conductive liquid.

[0015] Among these, electromagnetic techniques are particularly relevant and robust, in terms of the resistance of materials to the stresses applied to them by the environment in which the measurement is to be carried out. These techniques are all the more advantageous when dealing with a dense and chemically reactive fluid, such as liquid metals.

[0016] The operating principle of electromagnetic transducers is illustrated by the expression of Ohm's law in the moving fluid subjected to a magnetic field.

[0017] It shows that the conductivity o of the fluid leads to the development of currents (electric current density J) under the action of the displacement velocity u combined with the external magnetic field B:

[0018] [Equation 1]

[0019] X =

[0020] This occurs even in the absence of an electric field E.

[0021] The current densities Ju are the source of a magnetic field Bu. This field Bu distorts the external field B.

[0022] It is specified here that, for the sake of simplicity, the vector symbolized by the letter B, which is the magnetic flux density or magnetic induction, is referred to throughout this application as the magnetic field. It is also specified that the various formulations indicated later are written within the framework of the quasi-steady-state approximation, allowing certain quantities involved to be neglected. in Maxwell's equations, such as displacement currents.

[0023] To date, measurements of a single velocity component of a flow are commonly carried out by electromagnetic transducers, commonly referred to by the acronym DDF for "Flow Distortion Flow Meter", or the Anglo-Saxon ECFM ("Eddy Current Flow Meter") or PSFM ("Phase Shift Flow Meter").

[0024] A conventional DDF, generally designated by reference numeral 1, is shown in Figures 1, 2, and 2A: it is axisymmetric with central axis Z and typically consists of a core 2, a primary transmitting coil 3, and one or two secondary receiving coils 4, 5. The core 2 is formed of a solid rod 20 extending along the central axis Z and regularly spaced solid disks 21 along the central axis (X), the solid rod connecting the disks. The primary coil 3 and secondary coils 4, 5 are wound around the solid rod 20 between two of the solid disks 21.

[0025] An alternating electric current is imposed in the primary coil. The flow of this current creates an external magnetic field B in the immediate vicinity of the primary coil, according to the Maxwell-Ampère equation:

[0026] [Equation 2]

[0027] vx B = / / J

[0028] with:

[0029] V: differential operator

[0030] l1: magnetic permeability with ~

[0031] : magnetic permeability of vacuum

[0032] B: passes through the receiving coils.

[0033] The primary current is alternating, so that B is also alternating. In this way, B induces an electrical voltage in each of the receiving coils, according to the Maxwell-Faraday equation:

[0034] [Equation 3]

[0035] xg _ toB

[0036] with:

[0037] E: electric field.

[0038] Furthermore, B also induces the development of current densities h in the fluid, as well as in any surrounding electrical conductor subjected to this magnetic field, including the metal of the tubes. Figures 3 and 4 show the development of induced current densities under the action of the external magnetic field, in the absence of flow velocity, for a DDF, respectively with one secondary coil 4, and with two secondary coils 4, 5.

[0039] The current densities Ji in turn create a magnetic field Bi deforming the external field B. Thus, the field B is not the same depending on whether the DDF is surrounded by a fluid that conducts electricity or not.

[0040] In the absence of fluid movement, the receiving coil(s) deliver electrical voltages which are functions of the external magnetic field B and the field Bi.

[0041] In the presence of fluid movement, new current densities Ju appear and are the source of a magnetic field Bu. This new field modifies B, which is somehow blown away by the flow of conducting fluid and deforms in the direction of the flow, as illustrated in Figures 5A, 5B and 6.

[0042] The magnetic flux passing through the receiving coil(s) depends on the flow velocity.

[0043] The receiving coil(s) therefore deliver electrical voltages reflecting the influence of the magnetic fields Bt and Bu which distort the external field B.

[0044] Numerical simulations illustrate this. Figures 7A and 7B are numerical simulations of the magnetic field around a DDF respectively in the absence and in the presence of flow velocity of electrically conductive fluid.

[0045] The analysis of the electrical voltages delivered by the receiving coils makes it possible to determine the flow velocity of the fluid moving in the area of ​​action of the magnetic field B.

[0046] As shown in [Fig.8], if the single receiving coil 4 of a DDF 1 is upstream with respect to the direction of fluid flow, it experiences a decrease in magnetic flux as the velocity increases (and vice versa). The alternating voltage ej that it delivers decreases by Ae;.

[0047] The alternating voltage ej supplied by the DDF is the image of the flow velocity (with an indication of the relative direction thanks to the comparison of the amplitude of the current signal with the amplitude of the signal without velocity).

[0048] In addition to this, in the case of a DDF with two receiving coils, the downstream receiving coil experiences an increase in the flux passing through it as the fluid velocity increases. Its voltage e2 increases by Ae2.

[0049] We have IAe21= IAeJ

[0050] Generally, the two receiving coils 4, 5 of a DDF are electrically coupled in anti-series, as shown in [Fig.9].

[0051] In this way, the signal V supplied by the two-coil DDF is given by:

[0052] V=le2l-le7l

[0053] with lej: magnitude or amplitude of the voltage ex.

[0054] The signal V is proportional to the velocity component of the flow projected onto the axis of revolution of the DDF.

[0055] In practice, the DDF with two receiving coils is preferred, because the use The combined voltages delivered by these two coils double the sensitivity and eliminate the dependence of the DDF's response on irrelevant quantities such as temperature:

[0056] V = (le2l - le7l) / (le2l + le7l)

[0057] The sign of V gives the direction of the velocity without needing to compare it with the amplitude of the signal without flow velocity.

[0058] As regards the arrangement of the DDFs relative to the fluid flow, they can be internal to the flow, i.e. positioned on the axis of a tube in the middle of the flow to be characterized: [1], A DDF is thus within the fluid flow, the latter being peripheral to the DDF.

[0059] In practice, as shown in [Fig. 10], an internal DDF 1 is generally placed in the center of an annular space, delimited by two concentric tubes T1, T2, in which flows the fluid F whose velocities we seek to measure.

[0060] Other DDFs may be external to the flow. The coils and core of the external DDFs are thus arranged around the fluid flow for which velocities are to be measured.

[0061] In practice, an external DDF is placed around a tube to measure the velocity of the fluid flowing in that tube: [2].

[0062] When DDFs are used to evaluate the velocity of a fluid flowing in a tube, whether internal or external to the latter, they can only measure a velocity component which is that along the axis of the tube and therefore along their axis of axisymmetry X. Indeed, the tube guides the flow of the fluid and gives it its principal direction.

[0063] In general, signal processing from a conventional DDF or currently existing flow meters can be complex to achieve.

[0064] There is therefore a need to propose a simplified solution for measuring speed and processing the associated signal, of the flow of electrically conductive fluids, which can be dense, for a range of high speeds and / or at high temperatures, even in large volumes.

[0065] The aim of the invention is to meet at least part of this need. Description of the invention

[0066] To this end, the invention relates to a velocity variation detector for the flow of an electrically conductive fluid, comprising:

[0067] - an electromagnetic transducer, comprising:

[0068] a cylindrical metallic tube forming a core with high magnetic permeability,

[0069] an electrical coil, called the primary coil, wound around the tube and intended to be electrically powered by direct current, or a permanent magnet arranged around from the tube,

[0070] at least one electrical coil, called the receiving coil, wound around the tube while being adjacent to the primary coil or the permanent magnet, - at least one envelope detector circuit connected to the receiving coil, comprising at least one diode and a load in electrical series with the diode, the load being made up of a capacitor and an electrical resistor.

[0071] According to a first embodiment, the detector comprises a single envelope detector circuit.

[0072] Alternatively, according to a second embodiment, the detector comprises two envelope detector circuits in parallel with the receiving coil, the diode of one of the two circuits being mounted in opposite direction to the diode of the other circuit. A detector according to this mode allows for the detection of both increases and decreases in the fluid flow velocity.

[0073] Advantageously, the detector includes an electronic device connected to the envelope detector circuit(s) to detect the electrical voltage threshold(s) at the output of the capacitor(s). The electronic device is preferably a Schmitt flip-flop.

[0074] Preferably, the core has low electrical conductivity to limit the losses induced by the variable magnetic induction, namely the joule losses related to the circulation of the induced current and the hysteresis losses.

[0075] Thus, the invention essentially consists of a unidirectional fluid velocity variation detector electrically comprising an electromagnetic transducer which operates either with a primary coil powered by direct current or with a permanent magnet.

[0076] An envelope detector circuit is very simple as a device for processing the signal received by the receiving coil.

[0077] A detector according to the invention makes it possible to measure variations in the speed of a fluid whose nominal speed can be from a few millimeters per second to several meters per second.

[0078] In addition, it is suitable for measuring velocity variations of electrically conductive liquids, which are dense, typically with a density of the order of 100 to more than 10,000 kg.m3, and / or which are at high temperature, typically in the range of melting temperatures of metals processed, shaped or used in liquid form.

[0079] In conclusion, a detector according to the proposed invention overcomes the identified limitations of prior art devices and offers numerous advantages, including:

[0080] - a processing of the signals it produces, very simple compared to the de- existing bitmeters, and significantly less complex than the reconstruction algorithms required for DDFs according to the state of the art and tomographic measurement methods;

[0081] - the possibility of positioning within the flow to be characterized in the area to be studied.

[0082] Other advantages and features will become clearer upon reading the detailed description, given by way of illustration and not limitation, with reference to the following figures. Brief description of the drawings

[0083] [Fig.1] [Fig.1] is a schematic side view of a State of the Art Flow Distortion (FDD) Flowmeter with a receiving (secondary) coil.

[0084] [Fig.2] [Fig.2] is a schematic side view of a DDF according to the state of the art, at two receiving (secondary) coils.

[0085] [Fig.2A] [Fig.2A] is a longitudinal sectional view of [Fig.2].

[0086] [Fig.3] [Fig.3] reproduces [Fig.1] and illustrates the development of densities of currents induced under the action of the external magnetic field in the absence of flow velocity.

[0087] [Fig.4] [Fig.4] reproduces [Fig.2] and illustrates the development of densities of currents induced under the action of the external magnetic field in the absence of flow velocity.

[0088] [Fig. 5A], [Fig. 5B] Figures 5A and 5B reproduce [Fig. 1] and illustrate the development loppement of current densities induced under the action of the external magnetic field in the presence of a flow velocity.

[0089] [Fig.6] [Fig.6] reproduces [Fig.2] and illustrates the development of densities of currents induced under the action of the external magnetic field in the presence of a flow velocity.

[0090] [Fig.7A], [Fig.7B] Figures 7A and 7B are representations of simulations magnetic field metric around a DDF according to the state of the art, respectively in the absence and in the presence of flow velocity of electrically conductive fluid.

[0091] [Fig.8] [Fig.8] reproduces [Fig.1] and illustrates the electrical voltage across the terminals of the DDF receiving coil according to the state of the art.

[0092] [Fig.9] [Fig.9] reproduces [Fig.2] and illustrates on the one hand an electrical coupling pre the differential of the receiving coils in anti-series as well as the electrical voltages across the coil terminals the final voltage measured across the DDF terminals according to the state of the art.

[0093] [Fig. 10] [Fig. 10] is a reprographic reproduction of a DDF according to the state of the art as arranged internally in an implantation tube for the measurement of a one-dimensional velocity of a fluid F in flow.

[0094] [Fig. 11] The [Fig. 11] is a schematic side view of an electromagnetic transducer of a speed variation detector according to the invention, with a primary coil supplied with direct current and a receiving (secondary) coil.

[0095] [Fig. 12] [Fig. 12] is a schematic side view of an electromagnetic transducer of a speed variation detector according to the invention, with a permanent magnet and a receiving coil (secondary).

[0096] [Fig. 13] [Fig. 13] is a schematic view of an envelope detector circuit for a detector according to the invention.

[0097] [Fig. 14] [Fig. 14] is a schematic view of a dual detector envelope circuit for a detector according to the invention. Detailed description

[0098] Throughout this application, the terms "upstream" and "downstream" are to be understood by reference to the direction of the flow of a fluid around the transducer along the Z-axis.

[0099] Figures 1 to 10 have already been described in the preamble. They will therefore not be detailed further.

[0100] Figure

[11] shows an electromagnetic transducer 10 of a detector according to the invention, intended to measure the variation in speed of a flow of an electrically conductive fluid.

[0101] The transducer 10 is axisymmetric with central axis X and typically consists of a core with high magnetic permeability 2, an electrical transmitting coil, called primary 3, and an electrical receiving coil, called secondary 4.

[0102] The core 2 is formed of a tube extending along the central axis X.

[0103] The primary coils 3 and secondary coils 4 are wound around the tube 2.

[0104] An alternative to the transducer of [Fig. 11] is shown in [Fig. 12]: instead of a primary coil to be supplied with direct current, a permanent magnet 6 can be arranged around the core 2, adjacent to the secondary coil 4.

[0105] An envelope detector circuit 7 is connected to the terminals of the secondary coil 4. As illustrated in [Fig. 13], such a circuit 7 consists of a diode 8 connected in series with a load 9 consisting of a resistor 90 in parallel with a capacitor 91.

[0106] The envelope detector circuit 7 is connected to an electronic threshold detection device, not shown. This could be a Schmitt flip-flop, also commonly called a Schmitt trigger.

[0107] The operation of the electromagnetic transducer detector 10 and envelope detector circuit 7 is now explained.

[0108] In the event of a change in the velocity of the fluid surrounding the transducer 10, the receiving coil 4 experiences an induced electromotive force caused by the change in the magnetic flux originating either from the current-supplied primary coil 3 or from the permanent magnet 6.

[0109] The amplitude of the voltage signal ei delivered by the receiving coil 4 depends on the amplitude of the speed variation. The speed component to which the detector is sensitive is that which is parallel to the central axis (Z).

[0110] The sign of the detector signal indicates whether the speed variation is positive or negative (increase or decrease in speed).

[0111] Coil 4 therefore delivers a voltage ei, which is rectified by diode 8 and charges capacitor 91. Resistor 90 allows the capacitor to discharge gradually so as to limit, within a desired timeframe, the duration of a voltage e'b, which represents the envelope of the signal resulting from the values ​​of ei over time. These values ​​e'i are detected by the Schmitt flip-flop.

[0112] Thus, the existence of a voltage eb can be detected in a very simple way and can be temporarily stored for a duration which is a function of the capacitance of the capacitor 90 and the ohmic resistance of the resistor 91.

[0113] With a single envelope circuit 7 according to [Fig. 13], only the increase or reduction of the velocity of the fluid flowing around the transducer is obtained.

[0114] A variant of the double envelope circuit 7 is illustrated in [Fig. 14]: two envelope detector circuits 7 are here connected in electrical parallel to the receiving coil 4. Each of the two circuits consists of a diode 8.1; 8.2 connected in series with a load 9.1; 9.2 consisting of a resistor 90.1; 90.2 in parallel with a capacitor 91.1; 91.2.

[0115] Diode 8.1 of one of the two circuits is mounted in the opposite direction to diode 8.2 of the other of the two circuits.

[0116] With this double circuit 7, both an increase and a decrease in speed are detected. The voltages e'i and e''i indicate the existence of a positive variation, for example given by e'1, and a negative one, for example given by e''i. These output voltage values ​​e'be''i are each detected by a Schmitt flip-flop.

[0117] Other variants and improvements may be envisaged without departing from the scope of the invention. List of cited references

[0118] [1]: https: / / www.hzdr.de / db / Cms?pOid=55433&pNid=226

[0119] [2]: https: / / ieeexplore.ieee.org / stamp / stamp.jsp?arnumber=9768530

Claims

Demands

1. A velocity variation detector for a flow of an electrically conductive fluid, comprising: - an electromagnetic transducer (10), comprising: a metallic cylindrical tube (2) forming a core with high magnetic permeability, an electrical coil (3), called the primary coil, wound around the tube and intended to be electrically powered by direct current, or a permanent magnet arranged around the tube, at least one electrical coil (4), called the receiving coil, wound around the tube while being adjacent to the primary coil or the permanent magnet, - at least one envelope detector circuit (7) connected to the receiving coil, comprising at least one diode (8; 8.1, 8.2) and a load (9; 9.1, 9.2) in electrical series with the diode, the load being made up of a capacitor (90; 90.1, 90.2), and an electrical resistor (91; 91.1, 91.2).

2. Detector according to claim 1, comprising a single envelope detector circuit.

3. Detector according to claim 1, comprising two envelope detector circuits in parallel with the receiving coil, the diode of one of the two circuits being mounted in the opposite direction to the diode of the other of the two circuits.

4. Detector according to any one of the preceding claims, comprising an electronic device connected to the envelope detector circuit(s) for detecting the electrical voltage threshold(s) (e'i, e”i) at the output of the capacitor(s).

5. Detector according to claim 4, the electronic device being a Schmitt flip-flop.

6. Use of a detector according to any one of the preceding claims, for measuring the velocity variation of a flow of an electrically conductive fluid, such as a liquid metal from a nuclear reactor.

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