Device for measuring the median radius of bubbles in a foamed plaster blend

Abstract

The present invention relates to a method for determining a median radius R 0 of a collection of bubbles in a foamed medium, which liquid is suitable for being cured and to form, after curing, a solid construction material or a solid polymer foam, the method comprising the steps of conveying the foamed medium into a cavity, transmitting an ultrasound pulse into the cavity, detecting the pulse, measuring a component chosen from an amplitude of the detected pulse and a phase of the pulse, and subsequently determining the median radius Ro of the bubbles in the foamed medium in the cavity on the basis of the determined component.

Description

Device for measuring the median radius of bubbles in a foamed plaster mix FIELD OF THE INVENTION

[0001] The present invention relates to the manufacture of a mix, more particularly a foamed plaster mix. In particular, it relates to a method for determining the median radius of the bubbles in a foamed plaster mix, and a device for implementing such a method. STATE OF THE ART

[0002] Plaster production is energy-intensive, and it is desirable to reduce the energy required for this process. To this end, it is known to increase the volume fraction of air in plaster by introducing air into a plaster batch in the form of bubbles. Thus, it is possible to reduce the amount of water used to produce a predetermined volume of plaster, and thus reduce the total energy used to produce the batch.

[0003] However, since plaster is an opaque material, it is impossible to optically control the median radius of the bubbles formed inside the mixture in a non-destructive manner. However, it is necessary to control this median radius of the bubbles: in fact, this radius controls the mechanical characteristics of the plaster after the mixture has set.

[0004] For this purpose, it is known to measure the median radius of air bubbles in a plaster mix or in a plaster that has already set by X-ray tomography. However, this method is complex, expensive and does not allow for online measurements.

[0005] An aim of the invention is to propose a solution for simplifying a measurement of a median radius of a set of bubbles formed in a liquid medium with regard to a measurement implemented by X-ray tomography.

[0006] This object is achieved within the scope of the present invention by means of a method for determining a median radius R0 of a set of bubbles included in a liquid foamed medium adapted to be cured and to form, after curing, a solid material for construction or a solid polymer foam, the foamed medium having a liquid phase and a gaseous phase formed by the set of bubbles, and having a predetermined gaseous volume fraction φ of between 0.05 and 0.8 inclusive, the method comprising the steps of: a) transporting the foamed medium into a cavity, b) emitting an ultrasonic wave pulse towards the cavity by an ultrasonic wave pulse transmitter, c) detecting the pulse by an ultrasonic wave pulse detector, d) determining, from the pulse detected during step c) and a reference pulse,of at least one element chosen from a transmissionT of the pulse through the cavity and a reflectionR of the pulse on a surface delimiting the cavity,e) determination of the median radiusR0 of the set of bubbles from the element(s) determined during step d) and the predetermined gas volume fraction φ.,

[0007] The present invention is advantageously completed by the following characteristics, taken individually or in any of their technically possible combinations: - the foamed medium is non-transparent, - a predetermined gas volume fraction φ is in particular between 0.1 and 0.8 inclusive, preferably between 0.15 and 0.7, preferably between 0.15 and 0.5, - the cavity has a width l, and the emitter and the detector are arranged on either side of the width l of the cavity so that the pulse propagates in the foamed medium along the width l of the cavity, and, during step d), the transmission T of the pulse through the cavity is determined, the method is suitable for determining a maximum median radius R 0max predetermined from the set of bubbles, and, in step b), the pulse is emitted at an emission frequency f t strictly greater than a permissible propagation frequency pp equal to , c0 being the velocity of the pulse in the liquid phase of the foamed medium, - the cavity has a widthl, and in which the emitter and the detector are arranged on either side of the widthl of the cavity so that the pulse propagates in the foamed medium along the widthl of the cavity, and in which, during step d), the transmissionT of the pulse through the cavity is determined, the method being adapted to determine a median radius R0 of the set of bubbles less than a maximum median radius R 0max of the predetermined set of bubbles, wherein, in step b), the pulse is emitted at an emission frequency f t strictly greater than a permissible propagation frequency pp equal to , c0 being the speed of the pulse in the liquid phase of the foamed medium, - the cavity has a widthl, the emitter and the detector are arranged on either side of the widthl of the cavity so that the pulse propagates in the foamed medium along the widthl of the cavity, during step d), the transmissionT of the pulse through the cavity is determined, the method is suitable for determining a maximum median radiusR 0max predetermined from the set of bubbles, and, in step b), the pulse is emitted at an emission frequency f t strictly lower than a sensitivity limit frequencyf ls between 4. and 10. , and preferably between 4. and 6. ,

[0008] - the cavity has a widthl, the emitter and the detector are arranged on either side of the widthl of the cavity so that the pulse propagates in the foamed medium along the widthl of the cavity, during step d), the transmissionT of the pulse through the cavity is determined, the method being adapted to determine a median radius R0 of the set of bubbles less than a maximum median radius R 0max of the predetermined set of bubbles, and, in step b), the pulse is emitted at an emission frequency f t strictly lower than a sensitivity limit frequencyf ls between 4. and 10. , and preferably between 4. and 6. ,- the method is devoid of a step in which a pulse having a frequency lower than the permissible propagation frequency pp is emitted, - the emission frequencyf tis between 0.4 MHz and 56 MHz,- the cavity has a width l, and the emitter and the detector are arranged on either side of the width l of the cavity so that the pulse propagates in the foamed medium along the width l of the cavity, during step d), the transmission T of the pulse through the cavity is determined, the width l being less than 5 mm, in particular 2 mm, and more preferably 0.8 mm,- during step e), the median radius R0 is determined from the gas volume fraction φ, the component and the width l,- during step e), the median radius R0 is determined from an attenuation factor α representative of the attenuation of the amplitude of the pulse in the foamed medium along the width l,- during step a), a flow of the foamed medium is entrained in a channel comprising the cavity, and step b) of emission and step c) of detection are implemented during the flow,- the foamed medium comprises at least one element chosen from a foam and a mix, preferably at least one element chosen from a plaster mix, a cement mix, a lime mix, a mortar mix, a polyurethane foam and a polyisocyanurate foam,- during step b), the pulse has a duration of between 0.03 µs and 10 µs,- during step d), the component is determined from the start of the pulse up to a predetermined duration, the predetermined duration being preferably less than 5 µs,- the cavity has a widthl, and the emitter and the detector are arranged on either side of the widthl of the cavity so that the pulse propagates along the widthl of the cavity and in which the pulse is a longitudinal ultrasonic wave pulse,- the cavity has a widthl,and the emitter and the detector are arranged on either side of the width of the cavity so that the pulse propagates in the foamed medium along the width of the cavity, in step d), the transmissionT of the pulse through the cavity is determined, and, in step e), a modulus of a complex transmission is determined, of the pulse through the cavity at least from the transmissionT and we determine the median radiusR0 from the ratio defined by:

[0009]

[0010] A being a distance between 20 µm and 500 µm and in particular between 100 µm and 150 µm, B being a dimensionless number between 0.1 and 1 and in particular between 0.2 and 0.6, and g1 being a function having as variables the width expressed in mm, the gas volume fraction φ and the modulus of the complex transmission , the function g1 is equal to

[0011]

[0012] E being a constant value preferably between 0.01 mm and 0.5 mm,

[0013] - step e) of determining the median radius R0 of the set of bubbles is implemented without resorting to the resonance frequency of the set of bubbles,- in which the pulse is emitted at an emission frequency f t between 0.4 MHz and 56 MHz.

[0014] Another aspect of the invention is a device for determining a median radius R0 of a set of bubbles included in a liquid foamed medium adapted to be cured and to form, after curing, a solid material for construction or a solid polymer foam, the foamed medium having a liquid phase and a gaseous phase formed by the set of bubbles, and having a predetermined gaseous volume fraction φ of between 0.05 and 0.8 inclusive, the device comprising: - a cavity adapted to receive the foamed medium, - an ultrasonic wave pulse emitter arranged to emit an ultrasonic wave towards the cavity, - an ultrasonic wave pulse detector arranged to detect an ultrasonic wave pulse and, - a control unit configured to: determine, from a pulse detected by the detector and a reference pulse,at least one element chosen from a transmissionT of the pulse through the cavity and a reflectionR of the pulse on a surface delimiting the cavity, and to determine the median radiusR0 of the set of bubbles from the determined element(s) and the predetermined gas volume fraction φ.,

[0015] Advantageously, the cavity has a width l, the transmitter and the receiver are arranged on either side of the width l of the cavity so that the pulse propagates through the width l of the cavity, and the width l is preferably less than 5 mm, in particular 2 mm, and more preferably 0.8 mm.

[0016] Advantageously, the device comprises a channel adapted for the flow of the foamed medium, the channel comprising the cavity.

[0017] Advantageously, the device is configured to measure a maximum median radius R 0maxpredetermined length of the bubble assembly, the transmitter comprising a first transducer extending along a lengthL in a direction perpendicular to a direction of emission of the pulse by the transmitter, the lengthL being greater than 30.R 0max and preferably at 50.R 0max . DESCRIPTION OF FIGURES

[0018] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0019] - schematically illustrates a method according to one embodiment of the invention,

[0020] - schematically illustrates a device according to one embodiment of the invention,

[0021] - illustrates a variation of an attenuation of an ultrasonic wave pulse transmitted through a cavity of a device, as a function of the frequency of the pulse,

[0022] - illustrates a variation of the real part of the natural logarithm of the transmission of an impulse through a cavity filled with a foamed medium comprising bubbles, as a function of the median radius of the bubbles,

[0023] - illustrates a device according to an embodiment of the invention adapted to allow a flow of the liquid medium in the cavity,

[0024] - illustrates a calibration of a device according to an embodiment of the invention.

[0025] Throughout the figures, similar elements have identical references. DEFINITIONS

[0026] “Non-transparent” means a foamed medium, arranged in a cavity of a predetermined geometry, having a blur factor greater than 1%, in particular greater than 5% and preferably greater than 10%.

[0027] The term "blur factor" refers to the ratio between the intensity of a light beam scattered by passing through the medium (diffuse fraction) at an angle greater than 2.5° and the intensity of a light beam transmitted through the medium. The blur factor can be measured using spectroscopy techniques. Integrating the intensity over the entire visible range (from 380 nm to 780 nm) allows the normal transmission to be determined. L and diffuse transmissionT d . Such a measurement can also be obtained by using a Hazemeter.

[0028] The median radius R0 of a set of bubbles is the median radius R0 determined from a distribution of rays, the distribution being formed by the radii of each bubble in the set of bubbles.

[0029] TransmissionT of a pulse is understood to mean a quantity determined from a pulse detected after propagation of the pulse through a predetermined quantity of a foamed medium in a cavity and from a reference pulse. ReflectionR of a pulse is understood to mean a quantity determined from a pulse detected after reflection of the pulse on a surface delimiting the cavity and from a reference pulse.

[0030] Preferably, "complex transmission T" of a pulse transmitted through a predetermined quantity of a foamed medium in a cavity is understood to mean the ratio between the complex Fourier transform, at frequency f temission, of the pulse transmitted through a cavity, for a cavity filled with the foamed medium, and between the Fourier transform at frequency f t , for a water-filled cavity. The transmissionT and / or reflectionR of a pulse can be determined at 25°C.

[0031] In a system formed by a cavity of width l, formed by a first material, and comprising the medium to be measured, the transmission Tcomplex of a pulse can be the quantity defined by the formula described in the following equation (1):

[0032] (1)

[0033] in whichZ is the acoustic impedance of the measured medium,Z p is the acoustic impedance of the first material,Z0is the impedance of the water in the cavity,kis the wave number for a pulse propagation in the measured medium andk0is the wave number for a pulse propagation in the liquid phase of the measured medium.

[0034] The term "attenuation α" of a pulse propagating through a cavity of width is understood to mean the linear attenuation defined by . Preferably, the attenuation is measured for a pulse propagating in the cavity filled with a bubble-free liquid medium identical to the medium of the liquid phase of the foamed medium.

[0035] A "solid construction material" means any solid material suitable for the implementation of a construction project. A solid construction material can be plaster, mortar, lime, cement, concrete and / or coating. DETAILED DESCRIPTION OF THE INVENTION

[0036] General principle of determining a median radius R0 of a set of bubbles 1

[0037] With reference to and to, one aspect of the invention is a method 100 for determining a median radius R0 of a set of bubbles 1 included in a liquid foamed medium 2 adapted to be cured and to form, after curing, a solid material for construction or a solid polymer foam. The foamed medium 2 may be a non-transparent medium, and in particular an opaque medium.

[0038] The foamed medium 2 has a liquid phase and a gaseous phase formed by the set of bubbles. The foamed medium 2 has a predetermined gas volume fraction φ of between 0.05 and 0.8 inclusive. It is possible to predetermine the gas volume fraction φ by mixing a predetermined volume of bubble-free liquid and a predetermined volume of gas. The predetermined gas volume fraction φ can be confirmed or determined by weighing the foamed medium following the introduction of the gas into the liquid.

[0039] The method 100 comprises a step 101 of transporting the foamed medium 2 into a cavity 3. The cavity 3 is filled with the foamed medium 2. It is possible to take a sample of the foamed medium 2 and pour it into a cavity 3 so as to fill the cavity 3.

[0040] The method 100 comprises a step 102 of transmitting an ultrasonic wave pulse to the cavity 3 by an ultrasonic wave pulse transmitter 4. The ultrasonic wave pulse can then be transmitted by the cavity 3 or reflected by the cavity 3.

[0041] The method 100 comprises a step 103 of detecting the pulse by an ultrasonic wave pulse detector 5.

[0042] The method 100 comprises a step 104 of determining, from the pulse detected during step 103 and a reference pulse, at least one element chosen from a transmissionT of the pulse through the cavity 3 and a reflectionR of the pulse on a surface delimiting the cavity 3.

[0043] Following the step 104 of determining at least one element, the method 100 comprises a step 105 of determining the median radius R0 of the set of bubbles 1 from the element(s) determined during step 104 and the predetermined gas volume fraction φ.

[0044] Thus, a transmission of the pulse through the cavity 3 or a reflection of the pulse on the cavity 3 makes it possible to solicit the bubbles of the foamed medium 2, each of the bubbles acting as a local acoustic diffuser. The detected pulse includes the contributions of each of the local diffusers formed by the bubbles, and the detection of the transmitted or reflected pulse makes it possible to determine the median radius R0 in the volume fraction range between 0.05 and 0.8. The measurement of the median radius of the bubbles is then simplified with respect to a measurement implemented by X-ray tomography.

[0045] Transmission frequency f T of the impulse

[0046] The method 100 can be adapted to determine a maximum median radius R 0max predetermined of the set of bubbles. In other words, the method 100 can be adapted to determine a median radius R0 of the set of bubbles less than a maximum median radius R 0maxof the predetermined set of bubbles. The cavity 3 may have a width l. The emitter 4 and the detector 5 may be arranged on either side of the width l of the cavity 3 so that the pulse propagates in the foamed medium 2 along the width l of the cavity 3. This configuration allows detection of the pulse by transmission of the pulse. With reference to FIG. 3, during the emission step 102, the pulse may be emitted at an emission frequency f t strictly greater than a permissible propagation frequency pp . The frequency pp is equal to ,c0 being the speed of the pulse in the liquid phase of the foamed medium 2, notably without bubbles. Thus, it is possible to transmit the pulse by propagation through the cavity. Indeed, for frequencies f t lower than the permissible propagation frequency pp, the transmission of the pulse is due to an evanescent regime in cavity 3. In the evanescent regime, the attenuation is very high compared to the attenuation in the propagation regime, which makes it impossible to detect the pulse. For this reason, the frequency f t may be higher than the frequencyf pp .

[0047] The method 100 can be adapted to determine a maximum median radius less than 700 µm, in particular equal to 250 µm. For a maximum median radius R 0max equal to 250 µm and a gas volume fraction φ equal to 0.05, the permissible propagation frequency pp is equal to 0.4 MHz. The transmission frequency t may be greater than 0.4 MHz, in particular when the foamed medium 2 is a mix, in particular greater than 1 MHz and preferably greater than 4 MHz.

[0048] The method 100 can be adapted to determine a minimum median radius R 0min greater than 20 µm.

[0049] Illustrates the attenuation α of a pulse transmitted through the cavity 3 comprising a foamed medium 2 having a gas volume fraction φ equal to 0.35 and the bubbles having a median radius R0 equal to 75 µm.

[0050] With reference to Figure 4, the method 100 may be adapted to determine a maximum median radius R 0max predetermined of the bubble set 1. In the emission step 102, the pulse can be emitted at an emission frequency f t strictly lower than a sensitivity limit frequencyf ls between 4. and 10. and preferably between 4. and 6. . Thus, it is possible to increase the sensitivity of the determination of the median radius R0 when the median radius R0 tends towards R 0max . Indeed, the sensitivity of the detection of the median ray R0 is significantly higher for f t less than f ls that pourf t greater than fls.

[0051] The sensitivity limit frequencyf ls may be between 2.5 MHz and 140 MHz and preferably between 3 MHz and 10 MHz.

[0052] The method 100 may be devoid of a frequency sweep. t . Indeed, a detection of the pulse at a single frequency t can be used to determine the median radius R0. The emitted pulse can have a frequency spectrum centered on the emission frequency f t . The method 100 may be devoid of a step in which a pulse having a frequency lower than the permissible propagation frequency pp is emitted. Thus, the determination of the resonance frequency of the bubbles of a foamed medium can be avoided to determine the median radius R0, which makes it possible to accelerate and simplify the determination of the median radius R0 with regard to a process in which the acquisition of a frequency spectrum covering the resonance frequency of the foamed medium would be necessary.

[0053] Determination of the median radius R0 from the element

[0054] The cavity 3 may have a width l, and the emitter 4 and the detector 5 may be arranged on either side of the width l of the cavity 3 so that the pulse propagates in the foamed medium 2 along the width l of the cavity. In step d), the transmission T of the pulse through the cavity 3 may be determined. In the determination step 105, the median radius R0 may be determined from the gas volume fraction φ, the component and the width l.

[0055] Preferably, the median radius R0 can be determined by evaluating a radius determination function g dr having as variables the gas volume fraction φ, the width l, and the complex transmission T. The function for determining the radius g dr can have as variable the module|T|of the complex transmission.

[0056] The known independent scattering approximation model (ISA, described in Sheng P., 2006, Introduction to wave scattering, localization and mesoscopic phenomena, Vol. 88, Springer Science & Business Media) does not allow to determine the median radius R0 for a gas volume fraction φ greater than 2%.

[0057] To this end, the inventors developed a phenomenological model from data comprising pairs associating the complex transmission T with the median radius R0.

[0058] With reference to the, one can determine the median radius R0 from a predetermined function by a fit defined from a set of series of elements, each series of elements comprising at least one median radius R 0i predetermined and a complex transmission associated with the median radius R0. Each series may also include a gas volume fraction φ associated with the median radius R 0i , and / or a width associated with the median radius R 0i . The median rayR 0i predetermined can be obtained by different types of known measurements, such as optical measurement or X-ray tomography measurement.

[0059] The median radius R0 can be determined from the formula defined in equation 2 below:

[0060] (2)

[0061] in whichA is a distance between 20 µm and 500 µm and in particular between 100 µm and 150 µm,B is a dimensionless number between 0.1 and 1 and in particular between 0.2 and 0.6, andg1 is a function having as variables the width expressed in mm, the gas volume fraction φ and the modulus of the complex transmission .

[0062] The function g1 can be defined as described in the following equation 3:

[0063] (3)

[0064] in whichE is a constant value homogeneous at a distance, and preferably between 0.01 mm and 0.5 mm, and in particular between 0.070 mm and 0.090 mm.

[0065] The method 100 can be adapted to measure a median radius R0 between 20 µm and 120 µm, A being equal to 120 µm, B being equal to 0.5 and E being equal to 0.072 mm. Curve (a) of illustrates the variation of |T| for a model including these parameters.

[0066] The method 100 can be adapted to measure a median radius R0 between 50 µm and 200 µm, A being equal to 110 µm, B being equal to 0.25 and E being equal to 0.072 mm. Curve (b) of illustrates the variation of ln|T| for a model including these parameters.

[0067] The determination of the median radius R0 can be implemented from an attenuation factor α representative of the linear attenuation of the amplitude of the pulse in the foamed medium 2. The phenomenological model developed can take into account the attenuation α of the pulse during its propagation in the cavity 3 filled with a liquid medium without bubbles and identical to the liquid medium the liquid phase of the foamed medium. Each series used for the determination of the function predetermined by an adjustment can include the attenuation α. ​​The median radius R0 can be determined from the formula defined in the following equation 4:

[0068] (4)

[0069] The function g2 can be defined by the following equation 5:

[0070] (5)

[0071] Architecture of device 6 for determining the median radius R0

[0072] With reference to the, another aspect of the invention is a device 6 for determining the median radius R0 of the set of bubbles 1 included in the foamed medium 2. The device 6 is adapted to implement the method 100.

[0073] Foamed medium 2

[0074] The foamed medium 2 is liquid and suitable for being cured and for forming, after curing, a solid material for construction or a solid polymer foam. The foamed medium 2 may be non-transparent, and preferably opaque. Indeed, the method 100 makes it possible to determine the median radius R0 of the set of bubbles 1 without it being necessary to use the optical transmission properties of the foamed medium 2.

[0075] The predetermined gas volume fraction φ of the foamed medium 2 is between 0.05 and 0.8 inclusive, in particular between 0.1 and 0.8 inclusive and preferably between 0.3 and 0.8. Indeed, the method 100 makes it possible to measure media having very high predetermined gas volume fractions φ compared to the state of the art.

[0076] The foamed medium 2 may comprise a cement mix, a plaster mix, a lime mix or a mortar mix. Thus, it is possible to control the median radius R0 of the bubbles 1 introduced into a mix so as to lighten the material formed by the solidified mix without degrading the mechanical performance of this material.

[0077] Foamed medium 2 can be produced by mixing water in a proportion of 3 / 7 and plaster in a proportion of 4 / 7 in a mechanical mixer (e.g. a blender of the registered trademark Tefal, model BL305801), adjusting the volume of water and plaster relative to the total volume of the mixer so that the gas fraction is between 0.05 and 0.8.

[0078] The foamed medium 2 may comprise a polyurethane foam and a polyisocyanurate foam.

[0079] Cavity 3

[0080] The device 6 comprises a cavity 3 adapted to receive the foamed medium 2. The cavity 3 may have a width l. The width l may be measured according to the direction of propagation of the pulse.

[0081] The transmitter 4 and the receiver 5 may be arranged on either side of the width 1 of the cavity 3, so that the pulse propagates across the width 1 of the cavity 3, preferably in the foamed medium 2. The transmitter 4 may comprise a first transducer 11. The receiver 5 may comprise a second transducer 12. The first transducer 11 may be arranged to emit a pulse towards the second transducer 12.

[0082] The width l may be less than 5 mm, in particular less than 2 mm, and preferably less than 0.8 mm. Thus, it is possible to determine the median radius R0 by acquiring a signal representative of a ballistic part of the transmitted pulse. Indeed, for widths l greater than 5 mm, the signal acquired by the detector 5 is mainly representative of the superposition of several diffusion paths in the foamed medium 2, which is driven by a gas volume fraction of between 0.05 and 0.8. This part of the transmitted signal can be called "coda". Due to a width l less than 5 mm, it is possible to acquire a part of the transmitted signal devoid of coda. This part is also called "ballistic part of the signal". Only the ballistic part of the signal can make it possible to determine the median radius R0.

[0083] 4 ultrasonic wave pulse transmitter

[0084] The device 6 comprises an ultrasonic wave pulse transmitter 4 arranged to emit an ultrasonic wave towards the cavity 3.

[0085] The emitter 4 may be configured to emit a longitudinal ultrasonic wave pulse and / or a transverse ultrasonic wave pulse. During the step 101 of emitting a pulse, when the ultrasonic wave pulse is longitudinal, the method 100 may comprise a step 103 of detecting the pulse propagated through the cavity 3. The detector 5 may then be arranged on the side opposite the emitter 4 relative to the cavity 3. When the ultrasonic wave pulse is transverse, the method 100 may comprise a step 103 of detecting the pulse reflected by the cavity 3. The detector 5 may then be arranged on the same side as the emitter 4 relative to the cavity 3.

[0086] The transmitter 4 may comprise a voltage generator 10. The first transducer 11 may be an immersion transducer. The first transducer 11 may be focused at infinity. The first transducer 11 may be, for example, a transducer of the V308-SU model of the registered trademark Olympus.

[0087] The device 6 may be configured to measure a maximum median radius R 0max predetermined length of the bubble set and the first transducer 11 may extend along a lengthL in a direction perpendicular to a direction of emission of the pulse by the transmitter 4. The lengthL may be greater than 30.R 0max and preferably greater than 50.R 0max.Ainsi, il est possible d’augmenter la proportion de la partie balistique de l’impulsion détectée et de réduire la proportion de lacodade l’impulsion détectée. En effet, une longueurLélevée du premier transducteur 11 au regard du rayon maximalR0maxdes bulles permet de moyenner des signaux chacun entraîné par une diffusion individuelle sur une bulle. Le rayon médian maximumR0maxprédéterminé peut être égal à 300 µm et la longueurLpeut être supérieure à 9 mm et de préférence supérieure 15 mm.

[0088] The voltage generator 10 may be a high-voltage electrical pulse generator, configured to emit an electrical pulse having an amplitude greater than 50 V, in particular greater than 100 V and preferably greater than 400 V. The voltage generator 10 may be configured to emit an electrical pulse having a negative average voltage, so that the voltage of the electrical pulse is always negative. Thus, it is possible to counterbalance the attenuation of the amplitude of the pulse caused by transmission by the cavity 3 or a reflection on the cavity 3, and thus to allow the detection of the pulse by the detector 5. The voltage generator 10 may be configured to emit an electrical pulse having a duration of between 0.03 µs and 10 µs. The voltage generator 10 may be a generator of the DPR300 model of the registered trademark JSR Ultrasonics.

[0089] Ultrasonic wave pulse detector 5The device 6 comprises an ultrasonic wave pulse detector 5 arranged to detect an ultrasonic wave pulse. The detector 5 may comprise a second transducer 12.

[0090] The emitter 4 and the detector 5 may be arranged on either side of the width of the cavity 3 so that the pulse propagates in the foamed medium 2 along the width of the cavity 3. This configuration corresponds to a measurement of the pulse in transmission through the cavity 3. The first transducer 11 and the second transducer 12 may be identical. The second transducer 12 may be a transducer of the model V308-SU of the registered trademark Olympus. The second transducer 12 may extend along a length L in a direction perpendicular to a direction of emission of the pulse by the emitter 4. The length L may be at least greater than 30.R 0max and preferably at 50.R0max.Ainsi, il est possible d’augmenter la proportion de partie balistique de l’impulsion détectée et de réduire la proportion de lacodade l’impulsion détectée.

[0091] The emitter 4 and the detector 5 may be arranged on the same side of the cavity 3, so that the pulse is reflected by the cavity 3. This configuration corresponds to a measurement of the pulse in reflection on the cavity 3. During a measurement in reflection, the pulse does not propagate in the cavity 3, but the foamed medium 2 of the cavity 3 causes a modification of the signal reflected towards the detector 5. In this configuration, the first transducer 11 and the second transducer 12 may be the same transducer. The transducer may be directly connected to the control unit 7.

[0092] The detector 5 may also comprise an array of second transducers 12. Thus, it is possible to image the pulse propagated through the cavity 3. The array of second transducers may be a linear array in which the second transducers are arranged in a direction perpendicular to the width 1.

[0093] Control unit 7

[0094] The device 6 comprises a control unit 7 configured to acquire at least one component chosen from an amplitude of the pulse detected by the detector 5 and a phase of the pulse detected by the detector 5.

[0095] The control unit 7 is configured to determine, from a pulse detected by the detector 5 and a reference pulse, at least one element chosen from a transmission T of the pulse through the cavity 3 and a reflection R of the pulse on a surface delimiting the cavity 3. The control unit 7 can also be configured to determine the modulus of the complex transmission |T|.

[0096] The control unit 7 is configured to determine the median radius R0 of the set of bubbles 1 from the determined element(s) and the predetermined gas volume fraction φ. For this purpose, the control unit 7 may be configured to calculate the median radius R0 from the model previously described. The control unit 7 may comprise at least one processor and at least one memory, making it possible to implement the calculation of the component and / or the median radius R0. The memory may comprise data representative of the reference pulse(s).

[0097] The control unit 7 may be connected to the detector 5, in particular to the second transducer 12 of the detector 5. The control unit 7 may be configured to control the voltage generator 10 of the transmitter 4. The control unit 7 may comprise a multiplexer for acquiring a signal associated with a pulse from the first transducer 11 and / or the second transducer 12.

[0098] In determining step 104, the element may be determined from a signal representative of the start of the pulse up to a predetermined duration of the pulse. The predetermined duration may be less than 2.(1 / f t ) and preferably less than (1 / f t). Thus, it is possible to avoid taking into account possible echoes of the pulse when determining the component. The control unit 7 can be configured to determine the median radius R0 from the component determined only from the start of the pulse to the predetermined duration.

[0099] Flow of foamed medium 2

[0100] With reference to the, the device 6 may comprise a channel 8 adapted for a flow of the foamed medium 2. The channel 8 comprises the cavity 3. The channel 8 may have a thinning along the main flow direction of the channel 8, a thinned portion of the channel forming the cavity 3.

[0101] During the transport 101 of the foamed medium 2 into the cavity 3, a flow of the foamed medium 2 can be driven into the channel 8. Thus, it is possible to control the median bubble radius R0 of a foamed medium 2 during its production by diverting a sample of this foamed medium 2 to the channel 8. The flow of the foamed medium 2 can be driven by a flow generator 9.

[0102] The flow of the foamed medium 2 can be sequential. The flow is then distinct from the emission step 102, detection step 103.

[0103] The flow of the foamed medium 2 can be continuous. The emission 102 and the detection 103 are then implemented during the flow. Thus, it is possible to average the effect of the bubbles on the diffusion of the pulse(s), which makes it possible to increase the accuracy of the determination of the median radius R0.

[0104] Device Calibration 6

[0105] With reference to the, the device 6 can be calibrated from measurements of median radius r RX implemented by X-ray tomography. Illustrates a calibration curve determined from the median radius measurements implemented by X-ray tomography and from the determination of the associated median radii for the same liquid media 2. The median radii are determined using the model described by the formulas of equations (2) and (3) previously described.

Claims

A method for determining a median radius R0 of a set of bubbles (1) included in a liquid foamed medium (2) suitable for being cured and for forming, after curing, a solid material for construction or a solid polymer foam, the foamed medium having a liquid phase and a gaseous phase formed by the set of bubbles, and having a predetermined gaseous volume fraction φ of between 0.05 and 0.8 inclusive, the method comprising the steps of: a) transporting the foamed medium (2) into a cavity (3), b) emitting an ultrasonic wave pulse to the cavity (3) by an ultrasonic wave pulse transmitter (4), c) detecting the pulse by an ultrasonic wave pulse detector (5), d) determining, from the pulse detected during step c) and a reference pulse, at least one element chosen from a transmission T of the pulse through the cavity (3) and a reflectionR of the impulse on a surface delimiting the cavity (3),e) determination of the median radius R0 of the set of bubbles (1) from the element(s) determined during step d) and the predetermined gas volume fraction φ., Method according to claim 1, wherein the cavity (3) has a width l, and wherein the emitter (4) and the detector (5) are arranged on either side of the width l of the cavity (3) so that the pulse propagates in the foamed medium (2) along the width l of the cavity (3), and wherein, during step d), the transmission T of the pulse through the cavity (3) is determined, the method being adapted to determine a maximum median radius R 0max predetermined of the set of bubbles (1), in which, in step b), the pulse is emitted at an emission frequency f t strictly greater than a permissible propagation frequency pp equal to , being the velocity of the impulse in the liquid phase of the foamed medium (2). Method according to claim 2, wherein the cavity (3) has a width l, and wherein the emitter (4) and the detector (5) are arranged on either side of the width l of the cavity (3) so that the pulse propagates in the foamed medium (2) along the width l of the cavity (3), and wherein, during step d), the transmission T of the pulse through the cavity (3) is determined, the method being adapted to determine a maximum median radius R 0max predetermined of the set of bubbles (1), in which, in step b), the pulse is emitted at an emission frequency f t strictly lower than a sensitivity limit frequencyf ls between 4. and 10. , and preferably between 4. and 6. . A method according to claim 2 or 3, without a step in which a pulse having a frequency lower than the permissible propagation frequency f pp is issued. Method according to one of claims 2 to 4, in which the transmission frequency f t is between 0.4 MHz and 56 MHz. Method according to one of claims 1 to 5, in which the cavity (3) has a width l, and in which the emitter (4) and the detector (5) are arranged on either side of the width l of the cavity (3) so that the pulse propagates in the foamed medium (2) along the width l of the cavity (3), and in which, during step d), the transmission T of the pulse through the cavity (3) is determined, the width l being less than 5 mm, in particular 2 mm, and more preferably 0.8 mm. Method according to claim 6, in which, during step e), the median radius R0 is determined from the gas volume fraction φ, the component and the width l. Method according to claim 7, in which, during step e), the median radius R0 is determined from an attenuation factor α representative of the attenuation of the amplitude of the pulse in the foamed medium (2) along the width l. Method according to one of claims 1 to 8, in which during step a), a flow of the foamed medium (2) is entrained in a channel (8) comprising the cavity (3), and preferably in which step b) of emission and step c) of detection are implemented during the flow. Method according to one of claims 1 to 9, in which the foamed medium (2) comprises at least one element chosen from a foam and a mix, preferably at least one element chosen from a plaster mix, a cement mix, a lime mix, a mortar mix, a polyurethane foam and a polyisocyanurate foam. Method according to one of claims 1 to 10, in which, during step b), the pulse has a duration of between 0.03 µs and 10 µs. Method according to one of claims 1 to 11, in which, during step d), the component is determined from the start of the pulse up to a predetermined duration, the predetermined duration preferably being less than 5 µs. Method according to one of claims 1 to 12, wherein the cavity (3) has a width l, and wherein the emitter (4) and the detector (5) are arranged on either side of the width l of the cavity (3) so that the pulse propagates along the width l of the cavity (3) and wherein the pulse is a longitudinal ultrasonic wave pulse. Method according to one of claims 1 to 13, in which step e) of determining the median radius R0 of the set of bubbles (1) is implemented without using the resonance frequency of the set of bubbles. The method of claim 14, wherein the pulse is transmitted at a transmission frequency f t between 0.4 MHz and 56 MHz. Method according to one of claims 1 to 15, wherein the cavity (3) has a width l, and the emitter (4) and the detector (5) are arranged on either side of the width l of the cavity (3) so that the pulse propagates in the foamed medium along the width l of the cavity (3), and wherein during step d), the transmission T of the pulse through the cavity is determined, and, during step e), a modulus of a complex transmission of the pulse through the cavity is determined at least from the transmission T and the median radius R0 is determined from the ratio defined by: A being a distance between 20 µm and 500 µm, B being a dimensionless number between 0.1 and 1, and g1 being a function having as variables the width expressed in mm, the gas volume fraction φ and the modulus of the complex transmission, the function g1 is equal to Being a constant value. Device (6) for determining a median radius R0 of a set of bubbles (1) included in a liquid foamed medium (2) adapted to be hardened and to form after hardening a solid material for construction or a solid polymer foam, the foamed medium having a liquid phase and a gaseous phase formed by the set of bubbles, and having a predetermined gaseous volume fraction φ of between 0.05 and 0.8 inclusive, the device (6) comprising: - a cavity (3) adapted to receive the foamed medium (2), - an ultrasonic wave pulse emitter (4) arranged to emit an ultrasonic wave towards the cavity (3), - an ultrasonic wave pulse detector (5) arranged to detect an ultrasonic wave pulse and, - a control unit (7) configured to: determine, from a pulse detected by the detector (5) and a reference pulse,at least one element chosen from a transmissionT of the pulse through the cavity (3) and a reflectionR of the pulse on a surface delimiting the cavity (3), and to determine the median radiusR0 of the set of bubbles (1) from the determined element(s) and the predetermined gas volume fraction φ., Device (6) according to claim 17, in which the cavity (3) has a width l, the transmitter (4) and the receiver (5) being arranged on either side of the width l of the cavity (3) so that the pulse propagates through the width l of the cavity (3), the width l being preferably less than 5 mm, in particular 2 mm, and more preferably 0.8 mm. Device (6) according to claim 17 or 18, comprising a channel (8) adapted for the flow of the foamed medium (2), the channel (8) comprising the cavity (3). Device (6) according to one of claims 17 to 19, configured to measure a maximum median radius R 0max predetermined of the set of bubbles, the transmitter (4) comprising a first transducer (11) extending along a lengthL in a direction perpendicular to a direction of emission of the pulse by the transmitter (4), the lengthL being greater than 30.R 0max and preferably at 50.R 0max.

21. Device according to one of claims 17 to 20, in which the control unit is configured to determine the median radius R0 of the set of bubbles (1) from the determined element(s) and the predetermined gas volume fraction φ without using a resonance frequency of the set of bubbles, the pulse being emitted at an emission frequency f t between 0.4 MHz and 56 MHz. Device according to one of claims 17 to 21, wherein the cavity (3) has a width l, and the emitter (4) and the detector (5) are arranged on either side of the width l of the cavity (3) so that the pulse propagates in the foamed medium along the width l of the cavity (3), and wherein the control unit is configured to determine the transmission T of the pulse through the cavity, determine a modulus of a complex transmission of the pulse through the cavity at least from the transmission T and determine the median radius R0 from the ratio defined by: A being a distance between 20 µm and 500 µm, B being a dimensionless number between 0.1 and 1, and g1 being a function having as variables the width expressed in mm, the gas volume fraction φ and the modulus of the complex transmission, the function g1 is equal to Being a constant value.

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