EP2996786A2

EP2996786A2 - Device for forced drainage of a multiphase fluid

Info

Publication number: EP2996786A2
Application number: EP14729425.0A
Authority: EP
Inventors: Vincent MIRALLES; Isabelle CANTAT; Bertrand SELVA; Julien MARCHALOT; Marie-Caroline Jullien
Original assignee: Fonds ESPCI Georges Charpak
Current assignee: Ecole Superieure de Physique et Chimie Industrielles de Ville Paris
Priority date: 2013-05-13
Filing date: 2014-05-13
Publication date: 2016-03-23
Also published as: WO2014184490A2; WO2014184490A3; US20160082365A1; FR3005426A1

Abstract

The invention relates to a device (100) for configuring a multiphase fluid consisting of at least two immiscible phases on either side of separation surfaces, which comprises: a chamber (110) containing a multiphase fluid, a means (155) for generating a temperature gradient along the chamber in order to vary the surface tension of the separation surfaces along the chamber and to cause at least one of the phases of the multiphase fluid to move, and a means for extracting the multiphase system. In some embodiments, the means (155) for generating a temperature gradient comprises at least one electrical resistor formed on the surface of the chamber in order to provide a variable heat density along the wall of the chamber (110).

Description

DEVICE FOR FORCED DRAINAGE OF MULTIPHASIC FLUID

TECHNICAL FIELD OF THE INVENTION

The present invention provides a device for forced drainage of multiphase fluids. It applies in particular to the field of industrial foams, bullous liquids, and emulsions.

STATE OF THE ART

The multiphase fluids consist of at least two immiscible phases on both sides of separation surfaces. Multiphase fluids include, in particular, foams, bullous liquids and emulsions. As for foams, they are involved in many industrial processes, whether in liquid form, shampoo, beer, or in solid form, such as metal foams or chocolate foams. These materials have been studied and characterized for a long time.

Structured foams are of great interest in different fields, for example:

- metal foams, for their high mechanical strength,

catalysts, for their high surface area to volume ratio or

- phononic materials, for their ability to absorb sounds.

One of the major difficulties in the manufacture of these materials is the control of the evolution of the foam before solidification. Conversely, other applications require the destabilization of foams produced during industrial processes, such as wastewater treatment.

The evolution of the foam depends on three phenomena:

drainage due to gravity, which leads to a gradient of the liquid fraction (the proportion of liquid being higher in the lower part of the foam),

- The diffusion of gas through the liquid films leading to a decrease in the total number of bubbles and an increase in their dimensions and the coalescence, that is to say, the meeting, of neighboring bubbles.

Recent publications show that controlling this evolution is a crucial issue in many fields of application (see, for example, A.-L Fameau, A. Saint-Jalmes, F. Cousin, B. Houinsou Houssou, B. Novales, L. Navailles, F. Nallet, C. Gaillard, F. Boué, and J.-P. Douliez "Smart foams: Switching reversibility between ultrastable and unstable foams "Angew Chem., 50, 8264-8269, 201 1; DE Moulton and JA Pelesko." Reverse drainage of a magnetic soap film. " Phys. Rev. E., 81, 046320, 2010 and E. Chevallier, C. Monteux, F. Lequeux and C. Tribet. "Photofoams: remote control of foam destabilization by exposure to light using an azobenzene surfactant" Langmuir, 28, 2308-2312, 2012.

Methods for draining the liquid phase of a foam by incorporating materials into the foam, such as magnetic particles or photosensitive or thermosensitive surfactants, are known.

However, besides their cost, these materials pollute the foam and can modify certain physical, chemical, or physicochemical properties.

OBJECT OF THE INVENTION

One of the objects of the present invention concerns the possibility of controlling the drainage of the foam by applying a temperature gradient in the foam.

According to a first aspect, the present invention provides a device for configuring a multiphase fluid consisting of at least two immiscible phases on either side of separation surfaces, which comprises:

an enclosure containing a multiphase fluid,

a means for generating a temperature gradient along the enclosure for varying the surface tension of the separation surfaces along the enclosure and causing a displacement of at least one of the phases of the multiphase fluid and

a means for extracting the multiphase system.

The inventors have, in fact, discovered that the thermocapillarity forces cause drainage of a phase, for example liquid, at a relatively high speed. For example, for a foam having an initial liquid fraction of 35%, the device that is the subject of the present invention makes it possible to drain 70% of the liquid phase in less than 30 seconds.

It is noted that the multiphasic system may comprise at least one liquid phase, or at least one gaseous phase.

In the case of the applications of the invention to a monolayer of bubbles placed in a system extending essentially in two horizontal dimensions, it is also advantageous to have no gravity drainage along two adjacent bubbles, only the drainage. thermocapillary operating in this configuration. In embodiments, the temperature gradient generation means comprises at least one electrical resistance formed on the surface of the enclosure to provide a variable heat density along a wall of the enclosure.

The advantage of this means of generating a temperature gradient is to have a very short transient time.

In large-scale applications, the temperature gradient can be generated on the edges of an enclosure via different heating techniques (Joule effect, pre-heated fluids, microwaves ...). The difference lies in the transient time of establishing the temperature gradient. For example, at a scale of one meter it will take several tens of minutes for a conventional material (conductive metals such as copper).

In embodiments, the device that is the subject of the present invention comprises means for generating the multiphase fluid upstream of the enclosure.

In embodiments, the device that is the subject of the present invention comprises means for generating the multiphase fluid inside the enclosure.

In embodiments, the multiphasic fluid generating means is configured to provide foam.

In embodiments, the multiphasic fluid generating means is configured to provide a bullous liquid.

It is recalled here that a bullous liquid is a liquid in which bubbles are predominantly non-contiguous with neighboring bubbles.

In embodiments, the multiphasic fluid generating means is configured to provide an emulsion.

In embodiments, the device that is the subject of the invention comprises a means for solidifying the multiphase fluid.

In embodiments, the means for generating a temperature gradient along the enclosure to cause a displacement of at least one of the phases of the multiphasic fluid is configured to cause at least half of the enclosure to leave the enclosure. one of the phases of the multiphase fluid.

This is the case of an open chamber without upstream liquid reservoir.

In embodiments, the temperature gradient generating means along the enclosure for causing a displacement of at least one of the phases of the multiphasic fluid is configured to humidify the fluid. multiphasic, increasing the liquid fraction in the case of foams, since via an upstream liquid reservoir.

This is the case of an open chamber with a liquid reservoir upstream.

In embodiments, the means for generating a temperature gradient along the enclosure to cause a displacement of at least one of the phases of the multiphase fluid is configured to homogenize, in the enclosure, the phase distribution. multiphase fluid.

These embodiments apply to open enclosures, closed enclosures and, in particular, where at least one of the phases experiences the effect of earth's gravity, counteracting this effect by the thermocapillary effect.

This produces a continuous production line, for example standardized foam, destabilized foam or elastomer with uniformly distributed bubbles.

According to a second aspect, the present invention provides a method for configuring a multiphasic fluid consisting of at least two immiscible phases on either side of separation surfaces, which comprises:

a step of constituting a chamber filled with multiphase fluid,

a step of generating a temperature gradient along the enclosure for varying the surface tension of the separation surfaces along the enclosure and causing a displacement of at least one of the phases of the multiphase fluid and

a step of extracting the multiphase system.

The advantages, aims and particular characteristics of this method being similar to those of the device object of the present invention, they are not recalled here.

BRIEF DESCRIPTION OF THE FIGURES

Other advantages, objects and features of the invention will emerge from the description which follows of at least one particular embodiment of the device and method that are the subject of the present invention, with reference to the appended drawings, in which:

FIG. 1 represents, schematically, a particular embodiment of the device that is the subject of the present invention, FIG. 2 represents, in the form of a photograph, the path of a control particle in the device illustrated in FIG. 1, while it follows the thermocapillary flow,

FIGS. 3a and 3b show, respectively, a curve representing a temperature gradient and a curve representing a corresponding temperature profile along a longitudinal axis of an enclosure illustrated in FIG. 1;

FIGS. 4 and 5 represent, in the form of photographs, foams at the beginning and during the operation of the device which is the subject of the present invention, showing the decrease of the liquid fraction,

FIG. 6 represents, over time, the evolution of the volume fraction of the liquid phase in the device illustrated in FIG. 1;

FIG. 7 shows, over time, an evolution of the number of bubbles in the device illustrated in FIG. 1;

FIG. 8 represents, in the form of photographs, the displacement of a control particle in the device illustrated in FIG. 1, with an enclosure placed vertically,

FIG. 9 represents, in the form of a logic diagram, steps of a particular embodiment of the device illustrated in FIG. 1 and of its operation; FIG. 10 shows, schematically, a particular embodiment in a foam; in three dimensions, of the present invention,

FIG. 11 represents, schematically, a foam production line configured by implementing the present invention,

FIG. 12 represents, in the form of successions of points and interpolation curves, temporal evolutions of liquid fractions, in three configurations and

FIG. 13 represents, in the form of successions of points, a comparison of a model and experimental results. DESCRIPTION OF EXAMPLES OF EMBODIMENT OF THE INVENTION

As of now, we note that the figures are not to scale.

In general, the invention relates to the control of the drainage of multiphase fluids, for example foams, by applying a temperature gradient in this foam. Multiphasic fluids consist of least two immiscible phases on either side of separation surfaces, or interfaces. The temperature gradient causes a bubble surface tension gradient, known as the Marangoni effect.

In the description, one embodiment of the present invention is mainly applied to a foam in two dimensions, that is to say that the foam consists of a monolayer of bubbles placed between two plates whose distance which separates is at least about and preferably at least an order of magnitude smaller than the other dimensions. In addition, the thickness of the foam corresponds to the vertical axis, which reduces the effect of gravity compared to the case where one of the other dimensions is vertical. However, the present invention is not limited to two-dimensional foam applications but extends, on the contrary, to all configurations of multiphase fluids, foams, bullous liquids and emulsions liable to be subjected to a temperature gradient. and also, in some configurations, to gravity.

Below, we focus on a foam in two dimensions in micro confinement, that is to say located between two parallel plates separated by a gap of less than 100 microns, for example about 30 microns.

The two-dimensional foam study has been extensively analyzed both theoretically and experimentally since Plateau's first experiments in 1873. The advantage of studying two-dimensional foams is in particular the absence of gravity drainage if both plates forming the enclosure are positioned horizontally. On a millimeter scale or higher, the geometry of a dry foam consists of bubbles separated by films of height generally equal to the height of the gap separating the two plates. In this case, there is a general agreement between theory and experiment for the aging of foams, which is essentially governed by Von Neumann's law, related to the process of diffusion of gases through films as specified in the introduction. At a micrometric scale, Von Neumann's law is still observed with an effective diffusion coefficient about an order of magnitude smaller than on a millimetric scale.

The inventors have shown that this divergence stems from the geometry of the two-dimensional micro-foam: even if the foam has the geometry of a dry foam in the observation plane, it has a wet structure in the transverse plane (presence of a line of contact instead of a film between two adjacent bubbles).

In the remainder of the description, a system capable of forcing the drainage of the liquid phase using a thermocapillary stress is presented. This thermocapillary stress is generated by the application of a temperature gradient, preferably constant, that is to say a constant derivative of the temperature with respect to the distance traveled on a longitudinal axis of the enclosure.

In embodiments, an optimized resistance pattern provides a high temperature gradient with a linear profile. This motif is described in the following publications:

- B. Selva, J. Marchalot, M.-C. Jullien. "An optimized resistor pattern for temperature gradient control in microfluidics." Journal of Micromechanics and Microengineering, 19, 065002, 2009 and

V. Miralles, A. Huerre, F. Malloggi, M.-C. Jullien. "A review on heating and temperature control in microfluidic Systems: techniques and applications." MDPI

Diagnostics, 3, 33-67, 2013.

In the device which is the subject of the present invention, the thermocapillary forces generate a forced drainage of the liquid phase of the foams with a high velocity (millimetric velocity in a microfluidic channel): for a foam whose fraction of the initial liquid phase is 35 %, more than 70% of the liquid phase was drained in less than 30 seconds. It is therefore possible to have effective and rapid control of the liquid fraction of the foam, by the simple use of a temperature gradient.

Hereinafter, a particular embodiment of the device which is the subject of the present invention is described.

As illustrated in FIG. 1, this device 100 has two parts:

a flow focusing system 105 generating bubbles and

an enclosure 1 10 comprising a static foam 1 15 between an inlet 120 and an outlet 125.

The system 105 and the enclosure 1 10 are connected with a capillary tube 130.

The system 105 is described, for example, in the publication Ganan-Calvo AM and Gordillo JM, "Perfectly monodisperse microbubbling by capillary flow focusing", Phys. Rev. Lett., 87 2001 274501. The flux focusing system 105 has an intersection 135 through a channel 140, in which the continuous phase enters on either side of a dispersed phase inlet 145. Garstecki et al. (P. Garstecki, MJ Fuerstman, HA Stone, GM Whitesides. "Training of droplets and bubbles in a microfluidic T-junction-scaling and break-up mechanism." Lab Chip, 6, 437-446, 2006.) showed that the dispersity of the bubble sizes generated by this procedure can be controlled by different flow rates of liquids and gases.

The enclosure 1 10 manufactured, for example, by soft lithography, covers at least one wall 150, a resistor 155 manufactured, for example by lithography. The procedure for making a micro-system by soft lithography is detailed in Xia Y. and G. Whitesides, "Soft Lithography," Angew. Chem., Int. Ed., 37 1998 550.

The resistors 155 and the electrical connections 1 60 are produced by evaporation of chromium (15 nm, heating resistor) and gold (150 nm, conductive resistance) respectively on a substrate (in English "wafer") and then etched using a photoresist (Microposit S181 8, registered trademarks) following ultraviolet exposure through a mask. Engraving involves two steps: (i) the first creates a connection between the heating resistors and the current generator (in gold: high electrical conduction, with a negligible Joule effect) and (ii) the second stage involves the construction of optimized resistors in chrome.

As illustrated in FIG. 1, the resistors 155 are orthogonal to the main direction of the enclosure 1 10 represented by an arrow to the right of FIG. 1. This arrow is oriented according to the temperature gradient. It is observed that the sections of the resistors 155 are decreasing from top to bottom of FIG. Thus, heating of the resistor 155 shown at the top of Figure 1 is less than that of the next resistor and so on until the last resistor 155, shown at the bottom in Figure 1.

Gold connectors 160 are disposed at each end of each resistor 155. A current generator 165 is connected to the connectors 160.

The temperature gradient obtained with the resistors 155 is constant along the 2.5 mm length of the cavity, as illustrated in FIG. 3b. The heating resistors 155 are electrically insulated by a thin coating. For example this Thin coating is a 40 micron thick coating of Polydimethylsiloxane ("PDMS").

In the experimental embodiment, a 45-micron Hele-Shaw PDMS cell with a width of 1.5 mm and a length of 2.5 mm in the horizontal plane is then sealed to the substrate containing the heating resistors using an air or oxygen plasma, to form the enclosure 1 10.

The multiphase fluids consist of at least two immiscible fluids. In the proposed embodiment, the air bubbles generated in the flux focusing system 105 are introduced into the chamber 1 through the capillary tube 130. The continuous liquid phase is composed, for example, of deionized water (91.0% by weight), glycerol (5.68% by weight), an anionic surfactant (SDS 0.26% by weight) and titanium dioxide (3.00% by weight).

The concentration of the surfactant is therefore 9 mmol / L, which is just above the critical micelle concentration (cmc of about 8 mmol / L at 20 ° C). The surface tension of the solution with air was measured by the Wilhelmy plate method and is 30.2 mN.m ^-1 at 25 ° C. The temperature dependence dy / dT is evaluated at -2.06 10 ^"4 Nm ^{" 1} .K ^"1 with the same method described in B. Selva, J. Marchalot, M.- C. Jullien. An optimized resistor pattern for temperature gradient control in microfluidics. Journal of Micromechanics and Microengineering, 19, 065002, 2009, incorporating a thermostatic bath.

The thermostatic bath is a commercial device (for example of the trademark "Julabo") for regulating the temperature of a liquid contained in an enclosure. It consists of an enclosure, a heating resistor and a thermocouple for temperature control of the liquid contained in the enclosure. For the measurement of surface tension, the two fluids are placed in a tank, called measuring, in which the Whilelmy plate is immersed. This tank contains enclosure walls in which a liquid can circulate. A pump equipped with connections enables the thermostatic liquid to be conveyed to the chamber walls of the measuring tank, thus making it possible to thermostate the two phases contained in the measurement vessel.

When the chamber 1 10 is completely filled with bubbles, a static foam is produced in the chamber by disconnecting the capillary tube or stopping the flow of foam that it conveys. In the first case, the pressure on both the arrival and at the outlet of the chamber 1 10 is equal to the atmospheric pressure, that is to say that no pressure gradient is applied along the chamber 1 10. Moreover, there is There is no reservoir of liquid upstream of the flow initiated in the continuous phase of the foam, which causes the drying of the foam during drainage. The current generator which feeds the resistors 155 via the electrodes 160 is then turned on to apply a longitudinal temperature gradient in the chamber 1 10.

The speed of the continuous phase (here the liquid phase) in the foam to which a temperature gradient is applied has been estimated by incorporating very small particles in the foam and following their course over time. FIG. 2 represents bubbles 205 and the path 210 of such a particle, between five points 215 successively observed over time (every 200 ms). As we observe, the particle moves towards the cold zone of the chamber 1 10.

In the case of the embodiment illustrated in FIG. 1, the drainage rate of the continuous phase was measured between 0.7 to 2.6 mm. s ^"1 for temperature gradients between 2.2 and 7.0 K.mm ^{" 1} .

FIG. 3a shows a curve 255 representing the dimensionless average temperature gradient (dimensioned by the temperature gradient obtained in the stationary state) along the chamber 1 10 as a function of time. FIG. 3b shows a curve 260 representing a dimensionless temperature profile (dimensioned by the maximum temperature) as a function of the longitudinal axis of the enclosure 1 10.

FIG. 4 represents a geometry 305 of foam before energizing the resistors 155. The liquid phase is identified in clear while the bubbles constituting the foam are black. FIG. 5 shows a geometry 355 of the same foam after 60 seconds of supply of the resistors 155, with a temperature gradient of 2.2 K / mm, for a cavity of the enclosure with a length of 2.5 mm, a width of 1, 5 mm and a thickness of 28 microns.

Because there is no liquid reservoir upstream of the chamber 1 10, the continuous phase extracted from the cavity by the drainage is not regenerated. The comparison of FIGS. 4 and 5 shows that the liquid fraction decreases significantly over time. In the embodiment of FIG. 1, for a foam of FIG. 4 having an initial volume fraction of 35%, it is possible to drain more than 70% of the continuous phase in less than 30 seconds for a temperature gradient of 7.0 K / mm. FIG. 6 shows a curve 405 of temporal evolution of the normalized liquid fraction (liquid fraction at time t / initial liquid fraction). It is observed that, in the embodiment indicated, the liquid fraction decreases exponentially during the first 10 seconds.

Figure 7 shows a curve 455 of evolution of the number of bubbles in the chamber 1 10, over time for a temperature gradient of seven K / mm. It is observed that beyond 60 seconds, the number of bubbles in the cavity decreases drastically with time, which is a signature of the maturation of the foam by diffusion of gas through the films.

Work on the maturation of a foam in a Hele-Shaw cavity has already been carried out (J. Marchalot et al., EPL 83, 64006 (2008)) and show that the number of bubbles inside the cavity was inversely proportional to the time of experience. When the foam is subjected to a temperature gradient, which induces a flow of the external phase, the number of bubbles seems to decrease linearly with time. The application of a temperature gradient therefore seems to influence the ripening dynamics of the foam.

The present invention thus also has applications to the curing of foam by application of a temperature gradient.

In FIG. 7, a relatively linear average slope of decrease of the number of bubbles in the chamber is observed in particular.

The inventors have determined that a calculation in scaling laws in the case where the cavity is placed vertically shows that the tangential stress induced by the application of a temperature gradient is of the same order of magnitude as the original pressure. hydrostatic at the level of a single bubble.

The present invention can therefore be implemented so that the thermocapillary effect slows or even stops or counterbalances the gravitational force density. The present invention can thus be used to standardize the foam during its solidification, by counteracting the effect of gravity drainage or, on the contrary, to destabilize it in an accelerated manner, by reinforcing the effect of gravity drainage. FIG. 8 shows, in a cavity oriented vertically with its least heated portion at the top, the successive positions 555 of a control particle of the

m

drainage. The vector g indicates the direction of the gravity and the vector V indicates the direction of the tangential stress and therefore the pumping of liquid.

Figure 8 shows that, in a context where gravity drainage occurs, it can be countered by thermocapillary pumping.

It is observed that this particle moves vertically from bottom to top, showing that the gravity drainage can be reversed with a speed of about 1 10 μιτι / s, or even lessened or canceled for lower temperature gradients.

Figure 9 shows steps of a particular embodiment of the device object of the present invention and its operation.

During a step 605, at least one resistor 615 is formed on at least one wall and at least one electrical connection 610 for connecting the resistors to an electrical source. For example, each resistor and electrical connection is formed by lithography, in which the resistors are produced by chromium evaporation (15 nm, heating resistor) and gold electrical connections (150 nm, conductive resistance) on a substrate, then etched into using an S1818 photoresist in ultraviolet light through a mask.

The etching comprises a step 610 for creating a connection between the heating resistors and the current generator (in gold: high electrical conduction, with a negligible Joule effect) and a step 615 for building resistors optimized in chromium.

During a step 630, a current generator is connected to the connectors. During a step 600, a thin insulating coating is deposited, for example 40 microns thick PDMS on a wall intended to form the enclosure.

During a step 625, a Hele-Shaw cavity is formed in PDMS, for example at a height of 45 microns, with a width of 1.5 mm and a length of 2.5 mm, by sealing each wall carrying at least one resistance, for example using an air plasma or oxygen. We thus form the enclosure. During a step 635, the enclosure is connected to a multiphase fluid source. During a step 640, one introduces or generates multiphasic fluid in the enclosure. During a step 645, an electric current is applied through each resistor formed on a wall of the enclosure to form a temperature gradient inside the enclosure.

After a predetermined time, the multiphasic fluid is extracted during a step 650. It is noted that, during the extraction step, the residual multiphase fluid can be extracted alone, after drainage, the continuous phase alone, a combination of the two or even the liquid supplied from the outside in the multiphasic fluid, for example to moisten it (increase the liquid fraction in the case of foams), via a liquid reservoir placed upstream.

The present invention applies in particular to the control of:

- manufacture of metal foams / solids (eg polyurethane),

- manufacture of food foams,

- manufacture of silica foams,

- manufacture of cosmetics and cleaning products

- enhanced oil recovery,

- wastewater treatment and

- manufacture of phononic materials

FIG. 10 shows a particular embodiment, in a three-dimensional foam, of the device that is the subject of the present invention. This device 705 comprises a tank, here cylindrical, provided with lateral heating means 710 and a lower heating means 715, which jointly apply a vertical temperature gradient to the multiphase fluid contained in the tank. A means for generating this multiphase fluid 720 is provided in the bottom of the tank. This generation means 720 is represented here as a set of two blades applying shear to generate a multiphase fluid.

FIG. 11 shows a particular embodiment of the device that is the subject of the present invention applied to a solid foam production line or a solid containing gas inclusions. The device 755 comprises, on a conveyor 770, a device 760 and a device 765 similar to that shown in FIG. 1, on an optionally different scale. The device 760 applies a temperature gradient to the multiphasic fluid it contains to move at least one of the two phases. Once the pumping is done, the device 760 is moved by the conveyor 770 to the position of the device 765. In this position, the device 765 serves to solidify the multiphasic fluid it contains, for example by raising or lowering the temperature. At the next station, not shown, is carried out the extraction of the multiphasic residual system, here of the solidified foam or the solid containing gas inclusions, by opening the device and removing the foam.

Since the temperature gradient is a relative value, in other embodiments, the temperature gradient is maintained during the solidification of the foam. In these embodiments, the average temperature increases or decreases but the temperature gradient is maintained, which preserves the effect of thermocapillary drainage during the solidification of the foam.

FIG. 12 shows the evolution of the fraction of liquid, in%, over time for different temperature gradients, for a vertical enclosure. The triangles forming the curve 805 show that the gravity drainage can be stopped when the temperature gradient exerts an upward force, which counterbalances the gravitational force. The lozenges forming curve 810 show the effect of gravity alone, in the absence of a temperature gradient. Finally, the circles forming the curve 815 show the antagonistic effect of the gravity and the temperature gradient when the latter dominates the first, leading to a drainage from the bottom to the top.

Below is a model that can predict the evolution of the liquid fraction as a function of time. The gravity and the interfacial stress indicated by dy / dx (variation of the surface tension along the cavity) are taken into account. The exponents th and g refer, respectively, to the thermocapillary and gravitational contributions. The only adjustable parameters are a and β, which can be likened to a porosity / permeability.

The conservation of the mass is expressed by:

d (ewLO) / dt = ± (Q ^th + Q ^g )

where e is the thickness of the cavity, w is its width and L is its length. Φ is the continuous phase fraction. Q is the pumped phase flux, the indices th and g refer, respectively, to the thermocapillary and gravitational contributions.

The contributions to the velocity of the liquid in a section (yz) are expressed by:

v _x ^'th = a dxY e / η and ν _χ ^{~ 9} = - β pge ² / η

is :

Q ^th = v _x - ^th ewO and Q ^'9 = v _x ⁹ ewO Which we get Ιη (Φ / Φο) = - / 1 / t _d ^th - the tfl t

with

tj ^h = nU (ad _{x Y} e) and tj> = ηί / (β pge ² )

where η is the viscosity of the continuous phase, p is its density and Φο is the initial continuous phase fraction. v _x is the velocity projected in the longitudinal direction of the cavity, td is the characteristic drainage time; in both cases the indices th and g refer, respectively, to the thermocapillary and gravitational contributions.

We observe in Figure 13 that the model perfectly reproduces the experimental results. Whatever the experiments, the values of a and β are identical (a = 3.7 × 10 ^-3 and β = 4.7 × 10 ^-3 ). This shows the robustness of the model expressed above.

This defines a characteristic drainage time t _d :

Ιη (Φ / Φο) = - I1 / t _d ^th - t = V

The figure successively represents horizontally conducted experiments for a temperature gradient of: 1 K.mm- ¹ represented by the hollow triangles 845; 1, 2 K.mm- ¹ represented by the crosses 850; 2.2 K.mm- ¹ represented by the solid diamonds 825, 3.5 K.mm- ¹ represented by the hollow squares 820; 7 K.mm ^"1 represented by the solid circles 830. The gravity-only experiments are represented with the hollow diamonds 840 and the experiments conducted with the gravity and a temperature gradient of 7 K.mm- ¹ are represented by the hollow circles. 835.

Two tables are given below where the geometrical and physico-chemical parameters (other surfactant) have been varied. It is observed that we always find substantially the same values of a and β.

Table above: Dimensionless permeability obtained by varying the experimental parameters.

Table above: Dimensionless β-permeability obtained by varying the geometric parameters of the cell.

In each of the embodiments, it is implemented an extraction means (not shown) of the multiphasic system, which extracts either the multiphasic fluid after at least partial displacement of at least one of its phases, or a multiphasic system comprising at least one solid phase, according to the application of the present invention.

In embodiments, the means 155, 710, 715 for generating a temperature gradient along the enclosure to cause a displacement of at least one of the phases of the multiphase fluid is configured to get out of the enclosure at least half of one of the phases of the multiphase fluid. In embodiments, the means 155, 710, 715 for generating a temperature gradient along the enclosure to cause a displacement of at least one of the phases of the multiphase fluid is configured to homogenize, in the enclosure , the phase distribution of the multiphasic fluid.

In embodiments, the temperature gradient generating means along the enclosure for causing a displacement of at least one of the phases of the multiphasic fluid is configured to humidify the multiphasic fluid, increasing the liquid fraction in the case foam, since via a liquid reservoir placed upstream.

The dimensions and characteristics of the implementation device presented are not restrictive. The dimensions of the device can be adjusted according to the intended application, both for the size of the enclosure and those of the heating resistors. Similarly, the material constituting the enclosure must be adapted to the intended application according to, for example, its thermomechanical and / or chemical resistance. All the techniques making it possible to generate a temperature gradient are suitable, one can cite in particular, besides the Joule effect, the microwaves, the use of infrared, the solar storage, the induction, or the heating using a laser. In the case of Joule heating resistors, all conductive materials may be used in addition to chromium. Finally, the invention can be applied to all multiphase fluids consisting of at least two immiscible phases.

It is noted that the multiphasic fluid can be generated outside the chamber, as illustrated in FIG. 1, then introduced into the chamber, but can also be generated in the chamber, as illustrated in FIG. 10, by means mechanical, chemical or physical.

The reader will be able to refer to the known techniques of foaming in situ. According to a first example, one simply shakes an enclosure containing liquid, gas (in separate phases) and a solid object for generating the foam. According to a second example, a solid object is integrated in an enclosure filled with liquid and gas and the enclosure is rotated for the generation of foams. In industrial processes, such as for the formation of metal foams (J. Dairon, Metal foams, 2009, Technical Editions of the Foundry Industries.), There is a multitude of foaming techniques. Solid foams find a large number of applications in the industrial world. he There are various methods for making such foams. Some techniques involve molten metals whose viscosity has been adjusted. Foams can be formed from such molten metals, for example by injecting gas or foaming agents capable of releasing gas, which creates bubbles during their in-situ decomposition. An alternative method is to prepare supersaturated metal-gas systems under high pressure, and initiate bubble formation by controlling pressure or temperature. Finally, metal foams can be formed by mixing a metal powder with a foaming agent and, after compression, by foaming the whole by melting the compact mixture. The direct foaming process continuously produces a large volume of low density foam. In addition, these foams are certainly cheaper than those produced from metallic cellular materials.

There is also the possibility of foaming by bubbling (a tip is placed at one end of a chamber containing liquid and gas, through which gas is injected). In the case of glassmakers, glass foam appears "spontaneously" when the silica is melted.

The above description illustrates the implementation of the present invention on multiphase fluids made of foam. However, the present invention also applies to multiphase fluids of the "bullous liquid" type. Indeed, foams form a "compact" network of bubbles, but certain applications (or development of materials) require introducing inclusions (gas cavities) into the material. Elastomers such as those used in the manufacture of coatings may be mentioned. In this case, the present invention is applied to achieve a more uniform distribution of inclusions in the matrix by thermocapillary transport of inclusions. The difference with the case of foams is that the bubbles can move in the bullous liquid. The tangential stress produced by the device induces a flow of the external phase to the bubbles, and by conservation of the mass, the bubbles move towards the hottest part of the liquid, where the surface tension is the lowest, in other words where the interfacial energy of each bubble is the lowest. In the case where the variation of surface tension with the temperature is of sign opposite to the preceding case (lower interfacial energy in the coldest regions), the direction of migration is of opposite direction. The present invention also applies to the setting in motion in a multiphase fluid comprising a liquid in place of the gas in the two configurations mentioned either the continuous phase is set in motion (compact network of drops), or the drops are moved individually (no contact between adjacent drops).

The present invention also applies to the manufacture of materials involving drying dynamics in their manufacturing process (for example for structuring deposition of nanoparticles in menisci in the case of polymeric materials for flexible electronics) or for manufacturing new intelligent materials with a hydrodynamic response to an electrically controlled thermal action.

Note that for the generation of a temperature gradient, it is possible to implement resistors on each side of the enclosure.

In large-scale applications, the temperature gradient can be generated on the edges of the enclosure via different heating techniques (Joule effect, pre-heated fluids, microwaves ...). The difference with what is described with reference to Figures 1 to 7 lies in the transient time of establishment of the temperature gradient. For example, at a scale of one meter it will take several tens of minutes for a conventional material (conductive metals such as copper).

It is noted that the interface is set in motion by the temperature gradient relative to the center of mass of the bubble.

Claims

1. Device (100, 705, 755) for configuring a multiphasic fluid consisting of at least two immiscible phases on either side of separation surfaces, characterized in that it comprises:

an enclosure (1 10) containing a multiphasic fluid,

means (155, 710, 715) for generating a temperature gradient along the enclosure for varying the surface tension of the separation surfaces along the enclosure and causing a displacement of at least one phases of the multiphase fluid and

a means for extracting the multiphase system.

2. Device (100, 705, 755) according to claim 1, wherein the means (155, 710, 715) for generating a temperature gradient comprises at least one electrical resistance formed on the surface of the enclosure to provide a variable heat density along a wall of the enclosure (1 10).

3. Device (100, 755) according to one of claims 1 or 2, which comprises means (105) for generating the multiphase fluid upstream of the enclosure (1 10).

4. Device (705) according to one of claims 1 to 3, which comprises means (720) for generating the multiphasic fluid inside the enclosure (1 10).

5. Device (100, 705, 755) according to one of claims 3 or 4, wherein the means (105, 720) for generating the multiphase fluid is configured to provide foam.

6. Device (100, 705, 755) according to one of claims 3 or 4, wherein the means (105, 720) for generating the multiphase fluid is configured to provide a bullous liquid.

7. Device (100, 705, 755) according to one of claims 3 or 4, wherein the means (105, 720) for generating the multiphase fluid is configured to provide an emulsion.

8. Device (755) according to one of claims 1 to 7, which comprises means (765) for solidifying the multiphase fluid.

9. Device (100, 705, 755) according to one of claims 1 to 8, wherein the means (155, 710, 715) for generating a temperature gradient along the enclosure to cause a displacement of at least one of the phases of the multiphasic fluid is configured to cause the enclosure to exit at least half of one of the phases of the multiphase fluid.

10. Device according to one of claims 1 to 8, wherein the means (155, 710, 715) for generating a temperature gradient along the enclosure to cause a displacement of at least one of the phases of the multiphase fluid is configured to homogenize, in the enclosure, the phase distribution of the multiphase fluid.

1 1. Device according to one of claims 1 to 8, wherein the temperature gradient generation means along the enclosure for causing a displacement of at least one of the phases of the multiphase fluid is configured to humidify the multiphase fluid, in increasing the liquid fraction in the case of foams, since via an upstream liquid reservoir.

12. A method of configuring a multiphasic fluid consisting of at least two immiscible phases on either side of separation surfaces, characterized in that it comprises:

a step (605 to 640) of constituting a chamber filled with multiphase fluid,

a step (645) of generating a temperature gradient along the enclosure for varying the surface tension of the separation surfaces along the enclosure and causing a displacement of at least one of the phases of the fluid multiphasic and

a step (650) for extracting the multiphase system.