Electrolysis device comprising a transducer configured to generate an ultrasonic wave

Abstract

The present invention relates to an electrolysis device (1) comprising a circuit (16) configured to circulate a liquid through the device, a plate (3) oriented perpendicular to an axis (X) and partially arranged within the circuit, the plate comprising two opposing principal faces (5, 7), the device being configured to carry out an oxidation or reduction reaction of the liquid against the plate, and a transducer (9) located against the plate outside the circuit where the two principal faces are flat, the transducer (9) being configured to generate an ultrasonic wave (10) in the plate, one of the two faces of the plate comprising an oblique portion (12) located within the circuit (16), the oblique portion (12) corresponding to a deviation towards the other of the two faces as it travels along the plate from the transducer to the oblique portion, the oblique portion having a non-zero projection onto the axis (X). Figure for the abstract: Figure 1

Description

Title of the invention: Electrolysis device comprising a transducer configured to generate an ultrasonic wave.

[0001] The invention relates to an electrolysis device, in particular a water electrolysis device for the industrial-scale production of green hydrogen. PRIOR TECHNOLOGY

[0002] The production of green hydrogen and other gases has become a major challenge for our society. Research on this subject focuses primarily on finding the best approach to produce these gases using so-called renewable energy (solar, wind, etc.) in order to reduce the carbon footprint emitted by human activity. Current electrolyzers exhibit significant inefficiency when the available energy is insufficient to operate the electrolyzer at its nominal efficiency. Unfortunately, solar and wind energy are intermittent, which forces green hydrogen producers to partially shut down their electrolyzers when they are operating at less than 50% of their nominal efficiency.

[0003] Water sonolysis devices can produce hydrogen and, more generally, both powerful reducing and oxidizing agents. Sonolysis also allows for secondary oxidation and reduction reactions. The use of ultrasound can then be employed to treat low levels of organic contamination in water. The OH- radicals produced by water sonolysis are capable of attacking virtually all organic compounds (including halocarbons, pesticides, and nitro-aromatics) and, through a series of reactions, completely oxidizing them. Sonolysis devices also exhibit significant inefficiency when available energy, particularly solar or wind power, is insufficient to operate the device at its nominal efficiency.

[0004] There is therefore a need for an electrolysis device with extended operating ranges, particularly when powered by an intermittent energy source. EXPOSED

[0005] One aim of the present presentation is to propose an electrolysis device whose operating ranges are extended compared to the prior art.

[0006] The goal is achieved by means of an electrolysis device comprising a circuit configured to circulate a liquid through the device, a plate oriented perpendicular to an axis and arranged partly in the circuit, the plate comprising two opposing principal faces, the device being configured to carry out against the plate an oxidation or reduction reaction of the liquid, and a transducer situated against the plate outside the circuit where the two principal faces are flat, the transducer being configured to generate in the plate an ultrasonic wave, one of the two faces of the plate comprising an oblique portion situated in the circuit, the oblique portion corresponding to a deviation towards the other of the two faces by traversing the plate from the transducer to the oblique portion, the oblique portion having a non-zero projection on the axis.

[0007] Such a device is advantageously and optionally complemented by the following various features, taken alone or in combination:

[0008] - a seal placed against the plate, the seal being configured to ensure the sealing of the circuit,

[0009] the joint being located between the transducer and the oblique portion;

[0010] - the circuit comprises a first cavity and a second cavity separated from each other by the other by the plate, the seal being a first seal configured to ensure the sealing of the first cavity, the device comprising a second seal placed against the plate and separated from the first seal by the plate, the second seal being configured to ensure the sealing of the second cavity, the device being configured to carry out an oxidation reaction along the plate in the first cavity and a reduction reaction along the plate in the second cavity;

[0011] - the plate is centered on the axis, the oblique portion is located in a radial direction of the plate between the transducer and the axis, the face opposite the face including the oblique portion is flat and a length of the oblique portion along the radial direction is greater than a wavelength of the ultrasonic wave in the material of the plate;

[0012] - the plate is centered on the axis, the oblique portion is located in a radial direction of the plate between the transducer and the axis, each face includes an oblique portion facing each other, the oblique portions define a deformation of the plate, each face approaches the other face along the deformation traversed in the radial direction from the transducer to the axis and a length of the deformation in the radial direction is greater than a wavelength of ultrasonic ground in the material of the plate;

[0013] - the plate is centered on the axis, the oblique portion is located in a radial direction of the plate between the transducer and the axis, a plate thickness measured along the axis is constant, the plate includes a deformation including the oblique portion such that the plate is flat outside the deformation, a length of the deformation along the radial direction is greater than or equal to twice the thickness and less than or equal to ten times the thickness and a height of the deformation along the axis is greater than or equal to two times the thickness;

[0014] - the plate is centered on the axis, the joint, the oblique portion and the transducer presenting an annular shape centered on the axis;

[0015] - the plate is centered on the axis, the joint and the oblique portion having a annular shape centered on the axis, the transducer being a first transducer, the device comprising a group of transducers including the first transducer, the transducers being in contact with the plate and distributed angularly in a periodic manner around the axis;

[0016] - a control unit configured to control each transducer with a signal associated with the transducer, the control unit being configured to modify an amplitude and phase of a signal associated with a transducer independently of another signal associated with another transducer;

[0017] - the plate is a first plate, the device comprising a set of plates including the first plate, the plates being centered on the axis and arranged perpendicular to the axis, the axis being oriented in one direction, the device comprising for each plate a first cavity and a second cavity situated on either side of the plate such that the first cavity, the plate, and the second cavity are ordered along the direction of the axis, the device being configured to carry out an oxidation reaction along the plate in the first cavity and a reduction reaction along the plate in the second cavity; and

[0018] - for each plate, a group of transducers in contact with the plate and distributed angularly around the axis, a first group of transducers in contact with a first plate having the same angular gap between two neighboring transducers as a second group of transducers in contact with a second plate adjacent to the first plate, an angular position of the transducers of the first group having an offset with respect to an angular position of the transducers of the second group, so that a projection of a transducer of the first group along the axis does not cover a projection of a transducer of the second group along the axis.

[0019] The presentation also relates to an electrolysis process comprising the following steps:

[0020] - putting a liquid into circulation in a circuit,

[0021] - generation outside the circuit of an ultrasonic wave in an arranged plate at least partially within the circuit, the plate being oriented perpendicular to an axis, the plate comprising two opposing principal faces, the two principal faces being flat outside the circuit,

[0022] - propagation of the ultrasonic wave generated in the plate so as to enter the circuit,

[0023] - deviation of the ultrasonic wave against an oblique portion of one of the faces of the plate, the oblique portion being located in the circuit, the oblique portion corresponding to a deviation towards the other of the two faces while traversing the plate from the transducer to the oblique portion, the oblique portion presenting a non-zero projection onto the axis, and

[0024] - carrying out an oxidation or reduction reaction of the liquid against the plate.

[0025] Such a method is advantageously and optionally complemented by the following various features taken alone or in combination:

[0026] - the generated ultrasonic wave is an oscillation of a measured plate thickness along the axis, the oscillation corresponds to symmetrical deformations of the principal faces with respect to a plane orthogonal to the axis passing through a center of the plate;

[0027] - a step of measuring the temperature of the liquid in the circuit, the step of ultrasonic wave generation comprising a decrease in the power of the generated ultrasonic wave when the measured temperature rises above an intermediate temperature and preferably a zeroing of the power when the measured temperature exceeds a threshold temperature higher than the intermediate temperature, and / or a renewable energy supply step for the electrolysis process and a renewable energy level measurement step, the ultrasonic wave generation step comprising a decrease in the power of the generated ultrasonic wave when the measured level rises above an intermediate level and preferably a zeroing of the power when the measured level exceeds a threshold level higher than the intermediate level; and

[0028] - the ultrasonic wave is a first ultrasonic wave generated at a first point of the plate, the method further comprising a repetition of the steps of generating outside the circuit an ultrasonic wave, of propagating the ultrasonic wave in the plate so as to enter the circuit and of deflecting the ultrasonic wave against an oblique portion of one of the faces of the plate to generate a second ultrasonic wave at a second point of the plate distinct from the first point, the method comprising setting a phase shift between the first ultrasonic wave and the second ultrasonic wave. DESCRIPTION OF THE FIGURES

[0029] Other features and advantages will become apparent from the following description, which is purely illustrative and not limiting, and should be read in conjunction with the accompanying drawings on which:

[0030] [Fig.1] and [Fig.2] are schematic representations of an electrolysis device;

[0031] [Fig.3] is a schematic representation of a plate of the electrolysis device,

[0032] [Fig.4]

[0033] [Fig.5]

[0034] [Fig.6]

[0035] [Fig.7]

[0036] Figures 4 to 7 are schematic cross-sections of the plate,

[0037] [Fig.8] is another schematic representation of the plate;

[0038] [Fig. 9] is a schematic representation of an electrolysis process; and

[0039] [Fig. 10] is a set of curves illustrating the amplitude of out-of-plane movement of a plate according to three plate configurations. DETAILED DESCRIPTION OF THE INVENTION

[0040] In relation to [Fig. 1], an electrolysis device 1 extends around a longitudinal axis X. The electrolysis device 1 includes a circuit 16 configured to circulate a liquid through the device 1. The liquid is intended to be electrolyzed in the device 1, and more specifically in a body 2 of the device 1.

[0041] The circuit 16 includes a liquid inlet 17 which allows the liquid to be conveyed into the body 2, and two electrolysis product outlets 19 and 21 which allow the electrolysis products to be extracted from the body 2.

[0042] The body 2 of the device 1 comprises a plate 3 which is oriented perpendicularly to the X-axis. The plate 3 can be centered on the X-axis. The plate comprises two opposing principal faces 5 and 7. One of the principal faces 5 is a first end of the plate 3 in an axial direction defined by the X-axis, and the other principal face 7 is a second end of the plate 3 in the axial direction. In other words, the plate 3 has a thickness measured along the X-axis, the thickness being measured from one principal face 5 to the other principal face 7.

[0043] The main faces 5 and 7 are essentially parallel to each other and orthogonal to the X axis. However, the plate exhibits a deformation 34, 38 in which at least one of the faces is not orthogonal to the X axis.

[0044] Plate 3 may have a circular or square shape when projected along the X-axis. The plate may also be oval, rectangular, rhombic, or more generally polygonal, etc.

[0045] The plate 3 comprises one or more external faces 8 which are parallel to the X axis and which join one main face 5 to the other main face 7.

[0046] The plate is arranged partly within the circuit 16, which means that a first part of the plate is an internal wall of the circuit 16 and is intended to enter into The first part of the plate is the wet part of the plate. It is advantageously located in the center of the plate. The second part of the plate is outside the circuit 16, meaning it cannot come into contact with the liquid when it is circulated through the circuit. This second part is the dry part of the plate. It is advantageously located on the outer edge of the plate.

[0047] The circuit's seal can be ensured, in particular, by one or more seals 24 that separate the inside of the circuit from the outside of the circuit. The plate can be in contact with one of these seals 24, and on one side of the seal is the dry part of the plate and on the other side is the wet part of the plate.

[0048] The plate includes a conductive coating at the level of at least one of the two main faces 5 and 7 so that the electrolysis device 1 is configured to carry out against the plate an oxidation reaction or a reduction reaction.

[0049] With reference to [Fig. 1], the device 1 can, for example, be configured to carry out a reduction reaction against the main face 5 of the plate 3. In this situation, the device 1 includes an oxidation electrode 30 which is located opposite the main face 5 inside the circuit 16. In other words, the circuit 16 defines within the body 2 of the device 1 a chamber 20, 18 into which the liquid can flow, the chamber 20, 18 separating on the one hand the main face 5 and on the other hand the oxidation electrode 30. The chamber 20, 18 is fluidically connected to the liquid inlet 17 of the circuit 16.

[0050] The device 1 includes an electrical system 50 configured to electrically energize the oxidation electrode 30 and the conductive coating of the main face 5. The oxidation electrode is brought to an electrical potential higher relative to the electrical potential of the main face 5.

[0051] The device 1 may include a membrane 22 that separates the chamber 20, 18 into a reduction cavity 18 located on the main face side 5, in which the reduction reaction is carried out, and an oxidation cavity 20 located on the oxidation electrode side 30, in which the oxidation reaction is carried out. The membrane 22 allows, for example, the separation of the gaseous products of the electrolysis reaction. In the case of water electrolysis, the oxygen produced by the oxidation reaction is generated in the oxidation cavity 20, and the hydrogen produced by the reduction reaction is generated in the reduction cavity 18. The membrane keeps the hydrogen and oxygen extracted from the body 2 of the device 1 separated by the electrolysis product outlets 19 and 21. The reduction cavity 18 is, for example, in fluidic communication with the outlet 19, and the oxidation cavity 20 is, for example, in fluidic communication with the outlet 21.The exit. 19 is then the outlet of the oxidation products and outlet 21 the outlet of the reduction products.

[0052] Since these gases tend to move vertically upwards, that is, away from the ground, it is advantageous to place: - the fluidic connections of outlets 19 and 21 at the top of chamber 18, 20, that is to say, at a position in the chamber which is intended to be at the top of the chamber when the device is in operation, and - The fluidic connection of the inlet 17 at the bottom of the chamber 18,20, that is to say at a position of the chamber which is intended to be at the bottom of the chamber when the device is operated.

[0053] The plate 3 can be a bipolar plate, that is to say that each of the two main faces 5 and 7 includes a conductive covering insulated from each other so that the electrolysis device 1 can carry out an oxidation reaction along one of the main faces 5 and a reduction reaction along the other of the main faces 7.

[0054] The plate 3 may include on each of its main faces a circulation channel configured to better circulate the liquid and gases along each face.

[0055] In this case, for example, the plate separates two chambers 18,20 in a sealed manner and in a first chamber the main plate 5 allows the oxidation reaction to be carried out in the oxidation cavity 18 of the first chamber and in a second chamber the main plate 7 allows the reduction reaction to be carried out in the reduction cavity 20 of the second chamber.

[0056] In addition to the previously mentioned oxidation electrode 30, the device may include a second bipolar plate or a reduction electrode 28 opposite the main face 7 of the first bipolar plate inside the circuit 16. In other words, the circuit 16 defines within the body 2 of the device 1 a second chamber 20, 18 into which the liquid can flow, the chamber 20, 18 separating on the one hand the main face 7 of the first bipolar plate and on the other hand the second bipolar plate or the reduction electrode 28. This second chamber 20, 18 is fluidically connected to the liquid inlet 17 of the circuit 16. This second chamber may also include a membrane 22 and fluidic connections to the liquid outlets 19 and 21.

[0057] When the device comprises a set of plates including the first plate, the plates are advantageously centered on the axis and arranged perpendicular to the axis, the axis being oriented in one direction, the device comprising for each plate a first cavity and a second cavity located on either side of the plate such that the first cavity, the plate and the second cavity are ordered according to The device is configured to carry out an oxidation reaction along the plate in the first cavity and a reduction reaction along the plate in the second cavity. The device includes, on either side of the plate assembly, an oxidation electrode 28 and a reduction electrode 30, such that the oxidation electrode 28, the plate assembly, and the reduction electrode are arranged along the axis.

[0058] The oxidation electrode 28 and the reduction electrode 30 constitute the ends of the circuit 16 in the body 2 of the device 1 along the direction of the X axis.

[0059] The plate(s) of the electrolysis device may be of the alkaline electrolyzer, PEM or AEM type.

[0060] The device includes, for each plate, a transducer 9 placed against the plate and configured to generate in the plate an ultrasonic wave 10 propagating along a propagation direction 14 orthogonal to the X axis.

[0061] The transducer 9 can be a piezoelectric pellet or a Langevin type transducer, "Tonpilz" or even a shear wave generator.

[0062] Pellet-type transducers can be used to generate low-frequency or high-frequency ultrasonic waves using their own resonances. These resonances can be used to reduce energy consumption. For example, the planar resonances of a piezoelectric pellet depend on the width of the piezoelectric element according to the following table.

[0063] [Tables 1] Piezo width Planar resonance 2mm 750kHz 5mm 300kHz 10mm 150kHz 20mm 75kHz 30mm 50kHz 40mm 38kHz 50mm 30kHz

[0064] According to another example, the thickness resonances of a piezoelectric pellet depend on the thickness of the piezoelectric element according to the following table.

[0065] [Tables2] Piezoelectric thickness Resonance thickness 5 mm 0.41 MHz 2 mm 1.03 MHz 1mm 2.06MHz 0.7mm 2.95MHz 0.5mm 4.15MHz 0.3mm 6.92MHz 0.2mm 10.40MHz

[0066] This is equivalent for Langevin or Tonpilz transducers, but mass can modify the resonance frequency

[0067] The ultrasonic wave advantageously has a frequency greater than or equal to 20 kHz and less than or equal to 100 kHz if it is desired to generate primarily physical effects. Alternatively, the frequency is advantageously greater than or equal to 150 kHz and less than or equal to 4 MHz if it is desired to generate primarily chemical effects. The ultrasonic wave may also have two or more frequencies selected from the ranges mentioned above.

[0068] The transducer 9 is configured to generate an ultrasonic wave 10 which propagates, at least initially, in a direction of propagation which is globally parallel to the plate, the direction of propagation 14 and the plate 3 both being orthogonal to the X axis.

[0069] The transducer 9 is located outside the circuit, i.e. it is configured so as not to be in contact with the liquid when the latter is put into circulation in the circuit 16. The transducer 9 is placed against the dry part of the plate 3.

[0070] When the dry part of the plate 3 corresponds to the outer part of the plate, the transducer can generate an ultrasonic wave which propagates towards the center of the plate, i.e. towards the inside of the circuit 16. When the plate has a circular shape, the propagation direction 14 is oriented in a radial direction towards the center of the plate.

[0071] According to a first option illustrated in figures 4 and 7, the transducer is placed against one of the main faces 5 or 7.

[0072] According to a second option illustrated in [Fig.5], the transducer is a first transducer 9A placed against a first main face 7 and the device includes a second transducer 9B placed against the second main face 5. The transducers 9A and 9B are arranged opposite each other, i.e., a projection of the first transducer 9A along the X axis covers a projection of the second transducer 9B.

[0073] According to a third option illustrated in [Fig.6], the transducer is placed against an outer face 8 of the plate 3.

[0074] The transducer is notably configured to generate an ultrasonic wave 10 which is an oscillation of a plate thickness measured along the axis, the oscillation corresponding to deformations of the two principal faces, the deformations being symmetrical with respect to a plane orthogonal to the axis passing through a center of the plate. This is called a symmetrical wave.

[0075] One of the two main faces 5 and 7 of the plate includes an oblique portion 12 which is located in the circuit, that is to say, it is placed in the wet part of the plate 3 and it can be in contact with the liquid when the latter is put into circulation in the circuit 16.

[0076] The main faces 5 and 7 are essentially flat and orthogonal to the X axis. However, the plate exhibits a deformation in which at least one of the faces is not orthogonal to the axis.

[0077] At least one of the principal faces, a first principal face, has an oblique portion 12. Tracing this first principal face from the transducer 9 to the oblique portion, the first principal face is initially flat and parallel to the second principal face. Then, in the oblique portion, the first principal face is deflected towards the interior of the plate, or in other words, towards the second plate. The oblique portion has a non-zero projection onto the X-axis, which means that in the oblique portion, the first principal face is not orthogonal to the X-axis.

[0078] After the oblique part, the deformation of the plate ends and the main faces 5 and 7 are again flat and orthogonal to the X axis.

[0079] The oblique portion 12 is oblique with respect to a direction orthogonal to the axis and going from the transducer towards the oblique portion. This means that the oblique portion 12 defines a plane and that the direction orthogonal to the axis and going from the transducer towards the oblique portion is neither parallel to nor orthogonal to this plane.

[0080] The angle between the oblique portion and the direction orthogonal to the axis and going from the transducer to the oblique portion is typically [value missing]. It is greater than or equal to 1° and less than or equal to 25° depending on the wavelength of the ultrasonic wave.

[0081] Advantageously, the plate is centered on the X-axis, the wet part is at the center of the plate, and the X-axis passes through the wet part. The dry part is on the outer radial portion of the plate and surrounds the wet part. The oblique portion 12 is located in the wet part between the center of the plate and the transducer 9, which is itself located in the dry part.

[0082] The two main faces are parallel to each other and orthogonal to the X axis radially outside the oblique portion 12 and radially inside the oblique portion 12.

[0083] The oblique portion 12 is oblique with respect to the radial direction passing through the transducer.

[0084] Preferably, the oblique portion 12 is defined by a component directed along a local circumferential direction and a component located in a radial plane which is oblique with respect to the X axis.

[0085] Different embodiments of the plate deformation are illustrated in Figures 4, 5, 6, and 7. Plate 3 is shown in cross-section along a radial direction AA' as illustrated in [Fig. 3]. Plate 3 is centered on the X-axis, and the oblique portion 12 is located on the radial direction AA' of plate 3 between the transducer 9 and the X-axis. In each embodiment, the main face 7, which includes the oblique portion 12, is radially flat outside the oblique portion 12 and radially flat inside the oblique portion 12.

[0086] The oblique portion 12 defines an inner portion of the plate located between the oblique portion 12 and the X-axis and an outer portion located radially outside the oblique portion 12 with respect to the X-axis. Preferably, for each mode, the oblique portion is located as far outside the plate 3 as possible. In other words, the oblique portion is located as far away from the X-axis as possible, or the inner portion is sized as large as possible. Advantageously, the oblique portion is located at a distance of a few centimeters to a few tens of centimeters (up to 50 cm) from the X-axis. This corresponds to an inner portion with a diameter of a few centimeters to a few tens of centimeters (up to 1 m).

[0087] A first embodiment of the plate deformation is illustrated in [Fig. 4]. The main face 5, opposite the face 7 which comprises the oblique portion, is flat from the outer radial end of the plate 3 to the center of the plate 3 through which the X-axis passes. The length 36 of the oblique portion 12 along the radial direction AA' is greater than one wavelength of the ultrasonic wave in the plate material. The wavelength is typically greater than or equal to 1 mm and less than or equal to 50 mm. The wavelength is, for example, 10 mm, 20 mm, 30 mm, or 40 mm.

[0088] The main face 5 is flat at the oblique portion 12 of the main face 7, so that the plate 3 has a bevel. The thickness of the plate 3, measured along the X-axis, decreases as one travels along the plate from the outer radial end of the plate 3 to the center of the plate 3 through which the X-axis passes. This decrease can be linear as a function of the distance traveled from the outer radial end of the plate 3 to the center of the plate 3. In this case, the oblique portion has a straight shape in a cutting plane passing through the X-axis. Alternatively, this decrease can be non-linear and correspond in the cutting plane to a curvature. for example exponential, elliptic or sinusoidal. The outer thickness denoted E of plate 3 is greater than the inner thickness denoted e of plate 3. The ratio E / e is typically greater than or equal to 4 and less than or equal to 10. The inner thickness e is typically 500 pm or 300 pm.

[0089] A second embodiment of the plate deformation is illustrated in Figures 5 and 6. The main face 5, opposite the face 7 which includes the oblique portion denoted here as 12A, also includes an oblique portion denoted as 12B. The two oblique portions 12A and 12B are included in the deformation 38 of the plate.

[0090] In the oblique part 12B, the main face 5 is deflected towards the inside of the plate or in other words towards the second plate when the main face 5 of the transducer 9 is traversed towards the X axis, that is to say along the radial direction AA' traversed in the direction of the X axis.

[0091] Each main face 5, 7 approaches the other face 7,5 along deformation 38 of the plate traversed along the radial direction AA' of the transducer 9 to the X axis.

[0092] The length 40 of the deformation 38 along the radial direction AA' is greater than one wavelength of the ultrasonic wave in the plate material. The wavelength is typically greater than or equal to 2 mm and less than or equal to 50 mm. The wavelength is, for example, 10 mm, 20 mm, 30 mm, or 40 mm.

[0093] The main face 5 is flat at the oblique portion 12 of the main face 7, so that the plate 3 has a bevel. The thickness of the plate 3 measured along the X-axis decreases as one travels along the plate from the outer radial end of the plate 3 to the center of the plate 3 through which the X-axis passes. The outer thickness, denoted E, of the plate 3 is greater than the inner thickness, denoted e, of the plate 3. The ratio E / e is typically greater than or equal to 4 and less than or equal to 10. The inner thickness e is typically 500 µm or 300 µm.

[0094] A third embodiment of the plate deformation is illustrated in [Fig. 7]. The thickness 42 of the plate 3 is constant, particularly along the entire length of the plate traversed in the radial direction AA'. The plate is generally flat, with principal faces that are in the same axial position measured along the X-axis, except at the deformation 34. The deformation 34 comprises the oblique portion 12 of the principal face 7; the oblique portion 12 changes the axial position of the principal face 7. The deformation 34 includes another oblique portion of the principal face 7 that returns the face 7 to its initial axial position. Similarly, the other principal face 5 also comprises two oblique portions parallel to the oblique portions of the principal face 7. The deformation 34 corresponds to a bump or notch in the plate 3.

[0095] The advantage of such a notch lies in the simplicity of manufacturing the plate, which is favorable for mass production. In thin sheet metal, the notch can easily be made by "cold forming" or stamping.

[0096] The notch must be perpendicular to the incident wave

[0097] The length 44 of the deformation 34 along the radial direction AA' is greater than or equal to twice the thickness 42 of the plate 3 and less than or equal to ten times the thickness 42. The length 44 may be less than or equal to three times the thickness 42.

[0098] The height 46 of the deformation 34 measured along the X axis is greater than or equal to twice the thickness 42.

[0099] The main face 5 is flat at the oblique portion 12 of the main face 7, so that the plate 3 has a bevel. The thickness of the plate 3 measured along the X-axis decreases as one travels along the plate from the outer radial end of the plate 3 to the center of the plate 3 through which the X-axis passes. The outer thickness, denoted E, of the plate 3 is greater than the inner thickness, denoted e, of the plate 3. The ratio E / e is typically greater than or equal to 4 and less than or equal to 10. The inner thickness e is typically 500 µm or 300 µm.

[0100] The most commonly used electrolyzers are dry cell electrolyzers, which use compactly arranged electrode plates and separators (membranes) placed between two plates, containing the electrolyte in a small space. Unlike wet cell electrolyzers, which immerse the electrodes in a reservoir of electrolyte solution, dry cell electrolyzers can be fitted with a mesh, lattice, or grid. This addition improves the flow of the liquid and the evacuation of gases. In particular, it prevents excessive gas buildup on the electrodes.

[0101] In a "zero-gap" configuration, flow channels are added to the electrodes. A flow channel is a raised feature on the main surface that improves the flow of liquid and gases along the plate. A "zero-gap" configuration occurs when the electrodes are in direct contact with the membrane to reduce the electrical resistance of the stack, i.e., the electrical resistance of the stack of electrode plates. A (flexible) mesh between the electrodes and the membrane can also be added in the "zero-gap" configuration to protect the electrodes from short circuits.

[0102] The device 1 in a "dry cell" or "dry cell" electrolyzer configuration can also be equipped with a mesh or grid to better guide the liquid and gases. In this configuration, and when the plate has a decrease of its thickness as you approach the center of the plate as previously described, then the space between two adjacent plates which is due to the oblique portions can be filled with material such as mesh, wire mesh or lattice.

[0103] It should be noted that each plate 3 may include on one of its main faces a circulation channel.

[0104] For each plate, the electrodes of the plate can for example be made of stainless steel or nickel.

[0105] The transducer 9 is located against the plate 3 outside the circuit 16, and the oblique portion 12 of the plate 3 is located within the circuit 16. As illustrated in Figures 3 to 8, a gasket 24 can be provided, pressed against the plate 3, which is located between the transducer 9 and the oblique portion 12. The gasket 24 separates the inside of the circuit 16, where the oblique portion 12 is located, from the outside of the circuit 16, where the transducer 9 is located.

[0106] Preferably for each mode, the oblique portion is located as close as possible to the joint. In this way, the inner portion of the plate is sized as large as possible. Advantageously, the oblique joint is located at a distance of a few centimeters to a few tens of centimeters (up to 50 cm) from the X-axis. This allows the oblique portion to also be placed at a distance of a few centimeters to a few tens of centimeters (up to 50 cm) from the X-axis.

[0107] With reference to [Fig. 1], and when the plate 3 is a bipolar plate and the electrolysis device 1 is configured to carry out an oxidation reaction along one of the main faces 5 and a reduction reaction along the other of the main faces 7, the main face 5, which is the site of the reduction reaction, opens onto a first cavity 18 of the circuit 16, and the main face 7, which is the site of the oxidation reaction, opens onto a second cavity 20 of the circuit 16. The device 1 includes a first seal 24 placed against the plate 3 and configured to seal the first cavity 18, and a second seal 26 placed against the plate 3 and configured to seal the second cavity 20. The first cavity 18 and the second cavity 20 are separated by the plate 3, as are the first seal 24 and the second seal 26.

[0108] When the plate 3 is centered on the X-axis, the seal 24, the oblique portion 12, and the transducer 9 can have an annular shape centered on the X-axis. This situation is shown in [Fig. 3]. The oblique portion 12 corresponds to a first ring centered on the X-axis and located inside a second ring corresponding to the annular seal 24. The annular seal 24 is itself inside a third ring corresponding to the annular transducer 9.

[0109] When the transducer is annular, it creates a circularly symmetric ultrasonic wave in the plate. The maximum out-of-plane oscillation is then located at the center of the plate, corresponding to the center of the transducer.

[0110] Alternatively, and particularly when the plate is larger, the joint 24 and the oblique portion 12 can be provided to have an annular shape centered on the X axis and the transducer 9 is actually a group of transducers 9 in contact with the plate and distributed angularly in a periodic manner around the axis. This situation is schematically represented in [Fig. 8].

[0111] Indeed, for larger sizes of the plate 3 and the device 1, it is possible to use larger oblique annular portions and annular joints, but it is more complicated to use larger transducers. A group of transducers 9 is then used in contact with the plate 3 and distributed angularly in a periodic manner around the axis. For example, if the plate is in contact with n transducers, where n is an integer greater than or equal to two, two adjacent transducers can be separated angularly by an angle a = (360° / n) centered on the X-axis.

[0112] When the device 1 comprises a group of transducers 9 in contact with the plate 3, the device advantageously includes a control unit 48 configured to control each transducer 9 with a signal associated with the transducer, the control unit being configured to modify the amplitude and phase of a signal associated with one transducer independently of another signal associated with another transducer. Such a control unit 48 makes it possible to control each transducer with an individual control signal. In this way, it is possible to control two transducers in contact with the same plate with out-of-phase signals. This makes it possible to adjust the position within the plate of the maximum out-of-plane oscillation. The maximum can be placed outside the center of the plate.

[0113] This allows, for example, the generation of bubbles at the bottom of the plate. Their upward movement generates an upward current in the liquid, thus improving the performance of the reaction.

[0114] It is possible to use time reversal techniques or space-time inverse filtering to determine the phase shift and amplitude to be sent to each transducer to create a maximum of out-of-plane oscillation at a precise location on the board.

[0115] When the device 1 comprises a plurality of plates, each can be in contact with a group of transducers.

[0116] For two adjacent plates, it is possible to choose to place the n transducers at the same angular positions around the X axis.

[0117] Different angular positions can also be chosen, particularly if the chosen transducers are thick or have a large footprint. This can notably be the case for "Tonpilz" type transducers.

[0118] In this case, for a first group of n transducers in contact with a first plate and a second group of n transducers in contact with a second plate, an offset is introduced between the angular position of the transducers in the first group and the angular position of the second group. This offset is sufficient to ensure that a transducer in the first group does not come into contact with a transducer in the second group. It can also be ensured that a projection of a transducer in the first group along the axis does not overlap a projection of a transducer in the second group along the axis.

[0119] The angular offset can, for example, be equal to an angle of a / 2 = (360° / 2n) centered on the X-axis. In this case, if a third group of n transducers is added to the device in contact with a third plate, the third plate being adjacent to the second plate, and the second plate being located between the first and third plates, then the angular position of the transducers in the first group and the angular position of the third group do not exhibit any offset. In other words, using an offset of a / 2 = (360° / 2n), we obtain an angular offset between the plates that is periodic with a period of 2 plates.

[0120] More generally the angular shift can for example be equal to an angle of a / p=(360° / p*n) centered on the X axis, where p is an integer greater than or equal to 3. In this case, we obtain an angular shift between the plates which is periodic with period p plates.

[0121] With reference to [Fig. 2], which schematically illustrates an exploded view of the electrolysis device, the device 1 may comprise a plurality of plates stacked along the X-axis between a reduction electrode 28 and an oxidation electrode 30. Some plates 3 have an oblique wall 12, but the device 1 may also comprise a plate 4 that does not have an oblique wall. Two plates are separated by a joint 24, 26, and there is also a joint between a first plate and the reduction electrode 28 and a last plate and the oxidation electrode. Finally, the device 1 comprises, for each plate having an oblique wall, a transducer 9 that is attached to the plate.

[0122] The entire plate assembly is held tightly between the reducing electrode 28 and the oxidizing electrode 30. Referring to Figures 3 and 8, the plates may include orifices 32 passing through the plate along the X-axis in the dry portion of the plate. Similarly, the reducing electrode 28 and the oxidizing electrode 30 may include this type of orifice. The device 1 may include fastening rods configured to pass through the orifices so as to fix transversely along the X axis a stack of plates and reduction electrodes 28 and oxidation electrode 30. The device 1 may also include clamping parts which allow a constraint to be exerted along the X axis to keep the set of plates clamped between the reduction electrode 28 and the oxidation electrode 30.

[0123] The device 1 may also include a temperature sensor 52 configured to determine a temperature of the liquid.

[0124] Device 1 can be powered by electrical energy, in particular by renewable electrical energy. Since this electrical energy is often intermittent, Device 1 may advantageously include a renewable energy level sensor 54 configured to determine the flow of renewable energy received and intended to operate Device 1.

[0125] The electrolysis device 1 as just described allows an electrolysis process P to be implemented. The steps of this process are described in relation to [Fig.9].

[0126] In a first SI step, the electrolysis device is supplied with electrical energy. Optionally, the device can be supplied with renewable electrical energy.

[0127] During a second step S2, a liquid to be electrolyzed is circulated in the circuit 16 of the device 1. The liquid can in particular be pre-loaded into a reservoir of the device 1.

[0128] During an optional step S3, a temperature of the liquid in the circuit 16 is measured. The sensor 52 can be used for this purpose.

[0129] During an optional step S4, a level of renewable energy received by device 1 is measured. Sensor 54 can be used for this purpose.

[0130] During a step S5, an ultrasonic wave is generated outside the circuit 16 in the plate 3, which is at least partially arranged within the circuit 16. The plate is oriented perpendicular to an axis and comprises two opposing principal faces. As shown in [Fig. 4], the transducer 9, positioned against the plate 3, can generate the ultrasonic wave. The ultrasonic wave propagates within the plate along a propagation direction 14 towards the circuit 16.

[0131] For example, if the transducer 9 is located in a dry area radially outside the plate 3 and the wet area is located radially inside the plate 3, the plate being centered on the X axis, then the propagation direction 14 is radial towards the center of the plate, i.e. radial towards the X axis.

[0132] In particular, the ultrasonic wave is symmetrical. That is to say, it is an oscillation of the plate thickness measured along the X-axis; each principal face oscillates so that locally the faces move away from or towards the central plane of the plate, which is orthogonal to the X-axis, in the same way. Each surface produces a bump or a hollow of the same amplitude and in the same place on the plate.

[0133] It is possible to generate such a symmetrical wave with the different transducer configurations that have been presented previously.

[0134] In the case of a single transducer 9 in contact with a main face, as illustrated in figures 4 and 7, a shear wave generator or a piezo pellet can be used in particular according to a planar resonance.

[0135] In the case of two transducers plated against opposite principal faces as illustrated in [Fig.5], the transducers can be driven with signals in phase so that they deform uniformly at the same frequency to favor the symmetrical mode.

[0136] In the case of a transducer attached to the edge 8 of the plate or the outer face 8 of the plate, a piezoelectric ceramic or a "Tonpilz" type transducer can be used. This configuration is preferable if very high frequencies are desired. It should be noted that a piezoelectric ceramic vibrates primarily within its thickness in this configuration.

[0137] During a sixth step S6, the ultrasonic Fonde propagates and enters the circuit. As illustrated in [Fig. 4], Fonde propagates through the plate towards the center and passes through the joints 24 and 26, thus entering the interior of the circuit. It should be noted that a symmetrical Fonde corresponds to a relatively small amplitude of out-of-plane movement of the plate, i.e., movement along the X-axis. The area of ​​the plate in contact with the joints corresponds to the plate's mechanical holding zone. It is at this point on the plate that the force holding the plate stack is exerted. A relatively small out-of-plane movement of the plate limits the mechanical stress on the joints and preserves the mechanical stability and sealing of the device.

[0138] In a seventh step S7, the ultrasonic waveform is deflected against the oblique portion 12 of one of the main faces of the plate. The oblique portion 12 is located inside the circuit 16. As described previously, the oblique portion 12 corresponds to an inward deflection of the plate 3 as it travels across the plate from the transducer to the oblique portion. This oblique portion 12 intersects the propagation direction 14, as illustrated in reference 13 of [Fig. 4]. This allows for a reflection of the ultrasonic waveform inside the plate, i.e., a deflection of the ultrasonic waveform that no longer propagates in a radial direction oriented towards the center. Advantageously, this deflection effect can be improved by providing that the length 36 of the oblique portion 12 is greater than or equal to one wavelength in the material, or to each of the wavelengths in the material when there are more, of Ultrasonic Foundation.

[0139] As illustrated in [Fig. 4], this deflection changes the direction of wave propagation and creates an axial component, i.e., along the X-axis, of the wave propagation direction. The ultrasonic wave bounces many times inside the plate alternately against each of the main faces of the plate while propagating towards the center of the plate 3.

[0140] The symmetrical waves propagating in the plate upstream of the oblique portion 12 are transformed into asymmetrical waves corresponding to much larger out-of-plane movements of the plate.

[0141] This wave propagation mode corresponds to a significant increase in the amplitude of the out-of-plane movement of the plate. In particular, in the case of an annular transducer or a plurality of transducers distributed angularly around the X-axis, there is an addition of different radial contributions which creates a maximum amplitude at the center of the plate.

[0142] This propagation of ultrasonic waves generates, in particular, acoustic cavitation along the plate in the circuit 16, once the oblique portion 12 has been passed. The acoustic cavitation occurs within the inner portion of the plate. This cavitation corresponds to the nucleation (or generation), then the growth, and finally the implosion of microbubbles. An acoustic flow phenomenon is also produced. This accelerates, or at least assists, the generation of gases produced during the oxidation or reduction reaction.

[0143] Each cavitation bubble can behave as a local "hot spot" corresponding to significant increases in temperature and pressure (above 5000 °C and 2000 atm) which triggers several chemical reactions.

[0144] As mentioned previously, it is advantageous to place the oblique portion as far out as possible on the plate 3 to define the largest possible inner portion. This allows for a large surface area where cavitation occurs. This surface can be chosen to be sufficiently large to obtain the desired acoustic cavitation effect.

[0145] During an eighth step S8, an oxidation or reduction reaction of the liquid is carried out against the plate.

[0146] By generating an ultrasonic wave with the transducer, the cavitation phenomenon in the liquid promotes the oxidation or reduction reaction. This expands the operating ranges of the electrolysis device. It should be noted that the presented device avoids placing the transducer in the wet zone of the plate, thus simplifying the transducer's power supply configuration and improving its reliability.

[0147] In relation to [Fig. 10], the amplitude of out-of-plane movement of a plate has been represented according to three different configurations of the plate.

[0148] In each of the three configurations, the plate is a bipolar plate with a wet zone diameter of 200 mm and a central thickness of 300 µm. The transducer's excitation voltage is 100 volts, and it generates symmetrical waves. It should be noted that similar results can be obtained with other geometric or electrical values, and in particular with larger dimensions.

[0149] In a first configuration corresponding to curve 56, the plate has a bevel according to the first embodiment of the deformation as illustrated in [Fig.4]. The bevel extends over a radial length of 30 mm.

[0150] In a second configuration corresponding to curve 58, the plate has a bevel according to the first embodiment of the deformation as illustrated in [Fig.4]. The bevel extends over a radial length of 10 mm.

[0151] In a third configuration corresponding to curve 60, the plate is flat and has no bevel or deformation.

[0152] Each curve corresponds to the amplitude of the out-of-plane movement of the plate measured at the center of the plate as a function of the generated ultrasonic frequency.

[0153] The amplitude of the movement reaches more than 5 microns for a radial length of the bevel of 10 mm at a frequency close to 60 kHz. The amplitude of the movement reaches more than one micron for a radial length of the bevel of 30 mm at a frequency close to 50 kHz. These amplitudes are sufficient to produce the cavitation phenomenon. The amplitude of the movement remains zero in the case of a flat plate without a bevel or deformation.

[0154] This [Fig. 10] illustrates the fact that it is not possible to obtain, without deformation of the plate, an ultrasonic wave that is generated outside the circuit both without damaging the joint (i.e., with a symmetrical wave at the joint) and further inside the circuit, which produces a cavitation phenomenon. [Fig. 10] also shows that a radial bevel length of 10 mm is more effective at producing cavitation than a radial bevel length of 30 mm.

[0155] As an option to the process P described above, it is possible to modulate the ultrasonic wave generation step in two different and possibly cumulative ways.

[0156] On the one hand, the power of the generated ultrasonic wave can be reduced when the measured temperature rises above an intermediate temperature. In addition to, or instead of, this reduction, the power of the ultrasonic wave can be reduced to zero, meaning that the ultrasonic wave is not generated at all, when the measured temperature is above a threshold temperature that is higher than the intermediate temperature.

[0157] It is known that electrolysis is less efficient when the liquid temperature is relatively low. Therefore, assisting the electrolysis reaction by generating ultrasonic waves becomes more useful as the liquid temperature decreases. Conversely, as the liquid temperature increases, assisting the electrolysis reaction by generating ultrasonic waves becomes less useful. It is therefore possible to reduce the ultrasonic wave energy or even eliminate it beyond predetermined thresholds.

[0158] On the other hand, the power of the generated ultrasonic wave can be reduced when the renewable energy level increases beyond an intermediate level. In addition to or instead of this reduction, the power of the ultrasonic wave can be reduced to zero, i.e., there will be no generation of ultrasonic waves, when the measured renewable energy level is above a threshold energy level higher than the intermediate energy level.

[0159] It is known that an electrolyzer requires a minimum supply voltage to operate safely, and in particular without risk of explosion. This is why current electrolyzers only operate at 50% of their nominal efficiency. This is a disadvantage when the power supply is renewable, for example solar or wind, and therefore intermittent. Assisting the electrolysis reaction with ultrasonic wave generation can allow the electrolyzer to operate safely at lower supply voltages. The lower the supply energy, the more beneficial ultrasonic wave generation is for assisting the electrolysis reaction. Conversely, the higher the supply energy, the less beneficial ultrasonic wave generation is for assisting the electrolysis reaction.It is then possible to reduce the energy of the ultrasonic wave or even cancel this energy beyond predetermined level thresholds. The goal is to maximize hydrogen production with a minimum of energy input.

[0160] When the device 1 includes a group of transducers in contact with the plate, it is possible to adjust the phase shift between the transducer control signals as previously mentioned. In this case, the method may include, in addition to generating a first ultrasonic wave, generating a second ultrasonic wave at another point on the plate and adjusting the phase shift between the first and second ultrasonic waves.

Claims

Demands

1. Electrolysis device (1) comprising a circuit (16) configured to circulate a liquid through the device, a plate (3) oriented perpendicular to an axis (X) and arranged partly in the circuit, the plate comprising two opposing principal faces (5,7), the device being configured to carry out an oxidation or reduction reaction of the liquid against the plate, and a transducer (9) located against the plate outside the circuit where the two principal faces are planar, the transducer (9) being configured to generate in the plate an ultrasonic wave (10), one of the two faces of the plate comprising an oblique portion (12) located in the circuit (16), the oblique portion (12) corresponding to a deviation towards the other of the two faces by traversing the plate from the transducer to the oblique portion, the oblique portion having a non-zero projection onto the axis (X).

2. Electrolysis device according to claim 1 comprising a seal (24, 26) placed against the plate (3), the seal (24, 26) being configured to ensure the sealing of the circuit (16), the seal (24, 26) being located between the transducer (9) and the oblique portion (12).

3. Device according to claim 2 in which the circuit comprises a first cavity (18) and a second cavity (20) separated from each other by the plate (3), the seal being a first seal (24) configured to ensure the sealing of the first cavity (18), the device comprising a second seal (26) placed against the plate (3) and separated from the first seal (24) by the plate, the second seal (26) being configured to ensure the sealing of the second cavity (20), the device being configured to carry out an oxidation reaction along the plate in the first cavity (18) and a reduction reaction along the plate in the second cavity (20).

4. A device according to any one of claims 1 to 3 wherein the plate is centered on the axis (X), the oblique portion (12) is located on a radial direction (AA') of the plate (3) between the transducer (9) and the axis (X), the face opposite the face comprising the oblique portion is planar, and a length (36) of the oblique portion (12) along the radial direction (AA') is greater than one wavelength of the ultrasonic wave in the plate material.

5. A device according to any one of claims 1 to 3, wherein the plate is centered on the axis (X), the oblique portion (12) is located on a radial direction (AA') of the plate (3) between the transducer (9) and the axis (X), each face comprises an oblique portion (12A, 12B) facing each other, the oblique portions define a deformation (38) of the plate (3), each face approaches the other face along the deformation (38) traversed in the radial direction (AA') from the transducer (9) to the axis (X) and a length (40) of the deformation (38) in the radial direction (AA') is greater than a wavelength of the ultrasonic wave in the material of the plate.

6. Device according to any one of claims 1 to 3 wherein the plate is centered on the axis (X), the oblique portion (12) is located on a radial direction (AA') of the plate (3) between the transducer (9) and the axis (X), a thickness (42) of the plate measured along the axis (X) is constant, the plate includes a deformation (34) including the oblique portion (12) such that the plate is flat outside the deformation (34), a length (44) of the deformation along the radial direction (AA') is greater than or equal to twice the thickness (42) and less than or equal to ten times the thickness (42) and a height (46) of the deformation along the axis is greater than or equal to twice the thickness (42).

7. Device according to any one of claims 1 to 6 wherein the plate is centered on the axis, the joint, the oblique portion and the transducer having an annular shape centered on the axis.

8. Device according to any one of claims 1 to 6 wherein the plate is centered on the axis, the joint and the oblique portion having an annular shape centered on the axis, the transducer being a first transducer, the device comprising a group of transducers including the first transducer, the transducers being in contact with the plate and distributed angularly in a periodic manner around the axis.

9. A device according to claim 8 comprising a control unit (48) configured to control each transducer (9) with a signal associated with the transducer, the control unit being configured to modify the amplitude and phase of a signal associated with a transducer independently of another signal associated with another transducer.

10. A device according to any one of claims 1 to 9 wherein the plate is a first plate, the device comprising an assembly of plates including the first plate, the plates being centered on the axis and arranged perpendicular to the axis, the axis being oriented in one direction, the device comprising for each plate a first cavity and a second cavity situated on either side of the plate such that the first cavity, the plate and the second cavity are ordered along the direction of the axis, the device being configured to carry out an oxidation reaction along the plate in the first cavity and a reduction reaction along the plate in the second cavity.

11. Device according to claims 8 and 10 comprising, for each plate, a group of transducers in contact with the plate and distributed angularly around the axis, a first group of transducers in contact with a first plate having the same angular spacing between two neighboring transducers as a second group of transducers in contact with a second plate adjacent to the first plate, an angular position of the transducers of the first group having an offset with respect to an angular position of the transducers of the second group, such that a projection of a transducer of the first group along the axis does not cover a projection of a transducer of the second group along the axis.

12. A process (P) of electrolysis comprising the following steps: (S2) Circulating a liquid in a circuit, (S5) Generating an ultrasonic wave outside the circuit in a plate arranged at least partially in the circuit, the plate being oriented perpendicular to an axis, the plate comprising two opposing principal faces, the two principal faces being planar outside the circuit, (S6) Propagating the ultrasonic wave generated in the plate so as to enter the circuit, (S7) Deflecting the ultrasonic wave against an oblique portion of one of the faces of the plate, the oblique portion (12) being located in the circuit (16), the oblique portion (12) corresponding to a deflection towards the other of the two faces by traversing the plate from the transducer to the oblique portion, the oblique portion having a non-zero projection on the (X) axis, and (S8) Carrying out against the plate an oxidation or reduction reaction of the liquid.

13. A method according to claim 12 wherein the generated ultrasonic wave is an oscillation of a plate thickness measured along the axis, the oscillation corresponding to symmetrical deformations of the principal faces with respect to a plane orthogonal to the axis passing through a center of the plate.

14. A method according to any one of claims 12 and 13 comprising: - a step (S3) of measuring the temperature of the liquid in the circuit, the ultrasonic wave generation step comprising a decrease in the generated ultrasonic power when the measured temperature increases beyond an intermediate temperature and preferably a zeroing of the power when the measured temperature is above a threshold temperature above the intermediate temperature, and / or - a step (S1) of supplying renewable energy to the electrolysis process and a step (S4) of measuring a renewable energy level, the ultrasonic wave generation step comprising a decrease in the generated ultrasonic power when the measured level increases beyond an intermediate level and preferably a zeroing of the power when the measured level is above a threshold level above the intermediate level.

15. A method according to any one of claims 12 to 14 wherein the ultrasonic wave is a first ultrasonic wave generated at a first point on the plate, the method further comprising a repetition of steps (S5) (S6) and (S7) to generate a second ultrasonic wave at a second point on the plate distinct from the first point, the method comprising setting a phase shift between the first ultrasonic wave and the second ultrasonic wave.

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