WO2010054949A1

WO2010054949A1 - Device and method for guiding a liquid flow, and printer, vehicle, heat exchanger and manifold using this guide device

Info

Publication number: WO2010054949A1
Application number: PCT/EP2009/064474
Authority: WO
Inventors: Christophe Ybert; Cyril Duez; Lyderic Bocquet; Christophe Clanet
Original assignee: Université Lyon 1 Claude Bernard; Centre National De La Recherche Scientifique
Priority date: 2008-11-17
Filing date: 2009-11-02
Publication date: 2010-05-20
Also published as: FR2938612A1

Abstract

This guide device comprises: - a wall (20) such as to have a wettability that is modifiable from a value θ₁ to a value θ₂ in response to a control signal and this wall being shaped in such a way that the liquid flows along this wall: - for a distance d₁ in the direction of flow before detaching from the wall when the wettability has the value θ₁, and - for a distance d₂ in the direction of flow before detaching from the wall when the wettability has the value θ₂, and - a control unit (30) suitable for generating a control signal to modify the wettability of the wall from the value θ₁ to the value θ₂.

Description

DEVICE AND METHOD FOR GUIDING LIQUID FLOW, PRINTER, VEHICLE, THERMAL EXCHANGER AND COLLECTOR USING THE GUIDE DEVICE

The invention relates to a device and a method for guiding a liquid flow. The invention also relates to a printer, a vehicle, a heat exchanger and a liquid collector implementing this guiding device. There are numerous devices for guiding a liquid flow comprising a wall along which the liquid flows before detaching it. Once the liquid has come off the wall, it flows into an external environment. This external medium is either a gaseous medium or a liquid medium, in the latter case the liquid medium is immiscible with the liquid that flows.

The flow can take the form of a film of liquid flowing along the wall before detaching under the effect of its weight, it is called in this case a "film flow". Flow can also occur in a pipe. In the latter case, the flow can occupy the entire cross section of the pipe before being ejected through an orifice.

A flow is characterized by a non-zero flow. These flows are therefore also characterized by a non-zero Weber number. Weber's number is defined by the following formula: We = (px U ² xa) / γ where:

- We are Weber's number,

p is the density of the liquid expressed in kg / m ³ ,

- U is a characteristic speed of the liquid flow in m / s,

a is a characteristic length of the flow in meters, and Y is the surface tension between the external medium and the liquid expressed in J / m ² .

For example, U is the average speed of the flow. The length a is, for example, the thickness of the film when the flow is a film flow. When the liquid flow takes the shape of the pipe, the length a is, for example, the inner diameter of this pipe.

Here, the flows to which we are interested are preferably flows which generally correspond to a Weber number greater than 0.1, 1 or 10. Preferably, these flows also correspond to a Weber number of less than 1000, 500, 100 or 50. Indeed, it is in these ranges of Weber numbers that the guiding device described subsequently produces the most perceptible effects. It has already been observed that the liquid seems to "stick" to the wall before detaching it, for example, under the effect of the force of gravity and the force of inertia. This phenomenon is known as the "teapot effect". However, the distance traveled in the direction of flow before the liquid comes off the wall is difficult to control. Thus, there is no simple device for guiding a liquid flow along a wall using the teapot effect.

The invention aims to remedy this lack by proposing a simple device for guiding a liquid flow along a wall using the teapot effect.

It therefore relates to a device for guiding a liquid flow in which the wall is arranged to have a modifiable wettability of a forward contact angle value θi at a contact angle value Q ₂ to the advance in response to a control signal and this wall being shaped so that the liquid flows along this wall:

a distance di in the direction of flow before detaching from the wall when the wettability has the value θi, and

- over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ , and - the device comprises a control unit able to generate the control signal to modify the wettability of the wall of the value θi at the value Q ₂ so as to vary the distance traveled by the liquid along the wall

The above device controls the wettability of the wall to vary the distance traveled by the flow before detaching from the wall. The wettability of a wall is a simple physical property to control so that the device as a whole is simple to perform. In addition, it allows a guiding liquid that flows without having to mechanically move a room. This device is based on the discovery that the teapot effect can be controlled by adjusting the wettability of the wall along which the liquid flows. The teapot effect is the phenomenon that can be observed when you gently pour tea into a cup. In this situation, it often happens that the tea, instead of falling into the cup, flows along a lower wall of the spout of the teapot and falls next to the cup. This phenomenon may appear surprising because in this situation, the flow along the lower wall of the spout is against the force of gravity. Indeed, if only the force of gravity was exerted on the liquid, one could expect that the liquid is detached from the teapot at the end of the spout. Now, instead, the liquid seems to stick to the wall lower spout. Thus, the attraction exerted by this lower wall on the liquid that flows is greater than the force of gravity.

A first explanation of this phenomenon has been given in the following article: - J. B. Keller, "Teapot effect", Journal of Applied Physics, Volume 28, No. 2, August 1957.

Classically, the teapot effect is explained as resulting from a pressure difference between the pressure exerted on the external face of the liquid exposed to the external environment and the pressure exerted on the inner face of the liquid in contact with the spout wall. Indeed, the liquid flows faster inside the trajectory than outside. Its pressure is therefore lower according to the Bernouilli principle.

This article also explains that the teapot effect is not due to surface tension or adhesion of the liquid to the surface. These explanations have been continually repeated since then. For example, one can refer to the following literature:

- Jearl Walker, "Carnival of Physics", paragraph 4.116: "Sticky Beer", page 109 and page 222, Dunod edition, Paris 1997, ISBN 210-03479-0, - Jearl Walker, magazine "For science", December 1984, pages 117 to

122

- F. Guechi and H. Mekiof, "Effect of surface tension on two dimensional free surface flow", Journal of Engineering and Applied Science, pages 350 to 353, 2007. In particular, the article by Jearl Walker explains very clearly that the solution to prevent the teapot effect from appearing is to play on the geometry of the spout. By cons, play on the adhesion of liquid on the wall (see the example of the wall coated with margarine) does not prevent the appearance of the teapot effect. Or the adhesion of a liquid on a wall depends on its wettability.

Thus, until now, nobody had perceived the role of the wettability of the wall in the teapot effect. Therefore, the ability to control the teapot effect by playing on this parameter to create a device for guiding a liquid flow had until now remained unsuspected. The advanced contact angle is a method of measuring the wettability of a wall. For example, the advanced contact angle and its method of measurement are described in the following book:

Pierre-Gilles de Gennes, Françoise Brochard-Wyard, David Quere, "Drops, bubbles, pearls and waves", Publisher: Belin, 2005, ISBN 2-7011-4055-2, Chapter 3 .. The embodiments of this guiding device may comprise one or more of the following features: the wall is equipped with an electrode and a layer of electrically insulating material the electrode of the liquid, and the control unit is suitable generating, as a control signal, a potential difference between this electrode and the liquid; the wall is made of a material having a wettability that varies with the temperature, and the control unit is adapted to vary, as a control signal, the wall temperature to change its wettability;

B the wall is made of a material having a wettability that varies as a function of the power of an electromagnetic radiation in a predetermined range of wavelengths, and the control unit is able to vary, as a signal of controlling, the power of the electromagnetic radiation, to which the wall is exposed, in the predetermined range of wavelengths to modify the wettability of the wall;

B the value θi is greater than 130 ° or the value Q ₂ is less than 5 °. The invention also relates to an ink jet printer comprising:

a wall forming at least a portion of the lips of an orifice through which ink is projected towards a printing medium, this wall being arranged to have an modifiable wettability of a value θi d advancing contact angle at an advancing contact angle Q ₂ in response to a control signal and this wall being shaped so that the ink flows along the wall :

- over a distance di in the direction of flow before detaching from the wall when the wettability has the value θi, and - over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ , and

a control unit capable of generating a control signal for modifying the wettability of the wall of the value θi at the value Q ₂ so as to vary the distance traveled by the ink along the wall. The invention also relates to a vehicle equipped with a rainwater guiding device comprising:

a wall arranged to have an modifiable wettability of an advancing contact angle value θi at an advancing contact angle value Q ₂ in response to a control signal and this wall being shaped from so that the rain water flows along this wall: a distance di in the direction of flow before detaching from the wall when the wettability has the value θi, and

- over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ , and - a control unit able to generate a control signal to modify the wettability of the wall of the value θi at the value Q ₂ so as to vary the distance traveled by the rainwater along the wall

The invention also relates to a heat exchanger comprising a coolant and a wall along which the heat transfer liquid flows. The wall is arranged to have an modifiable wettability of an advancing contact angle value θi at an advancing contact angle value Q ₂ in response to a control signal and this wall being shaped from in such a way that the coolant flows along this wall: - over a distance di in the direction of flow before detaching from the wall when the wettability has the value θi, and

- over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ .

The heat exchanger comprises a control unit capable of generating a control signal for modifying the wettability of the wall of the value θi at the value Q ₂ so as to vary the distance traveled by the heat transfer liquid along the wall.

The invention also relates to a liquid collector comprising:

a wall along which the liquid flows, and a liquid collection orifice disposed with respect to the wall so as to be traversed by the liquid when the latter flows along the wall for a distance d ₂ and so as not to be traversed by the liquid when it flows along the wall by a distance di, The wall is arranged to have a modifiable wettability of a value θi contact angle to advancing to an advancing contact angle value Q ₂ in response to a control signal and this wall being shaped so that the liquid flows along the wall:

- on the distance di in the direction of flow before detaching from the wall when the wettability has the value θi, and - on the distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ .

The collector comprises a control unit capable of generating a control signal for modifying the wettability of the wall of the value θi at the value Q ₂ so as to vary the distance traveled by the liquid along the wall. The subject of the invention is also a method for guiding a liquid flow along a wall having an modifiable wettability of an advancing contact angle value θi to a contact angle value Q _2. in advance in response to a control signal and this wall being shaped so that the liquid flows along this wall:

- over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ , the method comprises generating the control signal to modify the wettability of the wall so as to vary the distance traveled by the liquid along this wall

The subject of the invention is also another device for guiding a liquid flow comprising: the liquid forming the liquid flow, this liquid having a physicochemical property capable of varying between a value Pi and a value P ₂ ,

a wall along which the liquid flows.

The wall is arranged to have a wettability with respect to this liquid equal to: - the value θi of advancing contact angle when the physicochemical property of the liquid has the value Pi, and

at a contact angle value Q ₂ when the physicochemical property of the liquid has the value P ₂ ,

This wall is also shaped so that the liquid flows along this wall:

- over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ . Embodiments of this other device for guiding a liquid flow may include the following feature:

the physicochemical property of the liquid likely to vary is a concentration of constituents present in this liquid and the wall has an affinity with these constituents causing the modification of the wettability of the wall as a function of the concentration of these constituents in the liquid;

the physico-chemical property of the liquid is the pH or the temperature. Finally, the subject of the invention is also a device for measuring wettability comprising:

- a wall along which flows a liquid whose wettability vis-à-vis the wall must be measured, a sensor of a physical quantity representative of the distance traveled by the liquid along said wall before detaching it, this physical quantity representing a measurement of the wettability of the face with respect to the liquid. The invention will be better understood on reading the description which follows, given solely by way of nonlimiting example and with reference to the drawings in which:

FIGS. 1a and 1b are illustrations of a fluid collector in two different states; FIG. 2 is a flowchart of a method for guiding a liquid flow implemented in the collector of FIGS. and 1b,

FIGS. 3 to 5 are schematic and partial illustrations of an ink jet printer,

FIG. 6 is a schematic illustration of a vehicle equipped with a device for guiding rainwater,

FIG. 7 is a schematic illustration of a heat exchanger, and

- Figures 8, 9 and 10 are schematic illustrations of different embodiments of a liquid collector.

In these figures, the same references are used to designate the same elements.

In the remainder of this description, the features and functions well known to those skilled in the art are not described in detail.

Figures 1a and 1b show a fluid manifold 2 capable of switching between an ejection position (shown in Figure 1) and a runoff position (shown in Figure 2). The collector 2 comprises:

a port 4 for supplying liquid,

a device 6 for guiding the liquid flow, and

an orifice 8 for collecting the liquid which flows when the collector 2 is in its runoff position. For example, the orifice 8 corresponds to the inlet mouth of a pipe or a container 10.

The orifice 4 is the outlet mouth of a pipe 12 arranged vertically. This pipe 12 brings a liquid 14 which falls vertically along an axis of symmetry 16. The device 6 comprises a wall 20 for guiding the flow of the liquid 14. This wall 20 is arranged with respect to the orifice 4 of so that the liquid 14 flows along this wall. Here, the wall 20 is located below the orifice 4 on the axis of symmetry 16.

The wall 20 is shaped so that the liquid 14 flows along this wall before detaching. Typically, the wall 20 forms a rounded edge around which the liquid flow can rotate. The liquid 14 flows along the wall 20 for a distance d before detaching from the wall 20 in an ejection direction F. This direction F makes an angle β with the vertical. In the ejection position, the angle β and the distance d are functions of one another. Here, the shorter the distance d, the closer the angle β is to 90 °. Moreover, all things being equal, the angle β between this direction F and the vertical varies as a function of the wettability of the wall 20. The angle β also varies as a function of the flow velocity of the fluid 8. regardless of the flow velocity of the fluid 8, the angle β depends on the wettability of the wall 20. More precisely, it has been established that the angle β can be estimated by means of a relationship of the following form:

Cot β = A [2 (1 + cosθ)] ^1/2 We- ¹ ' ² (1) where:

- β is the angle between the direction F and the vertical, - A is a constant function of the geometry of the edge, θ is the contact angle at the advance, and

- We is the Weber number for this flow.

For example, the constant A is determined experimentally.

Note that for very fast flow rates, that is to say corresponding to a Weber number greater than 500, the angle β tends to 90 ° regardless of the wettability because the number of Weber is very large . Thus, when the flow velocity is very fast, the variations of the angle β and therefore of the distance d as a function of the wettability of the material used to make the wall 20 are less and less noticeable to the naked eye. Therefore, preferably, the guiding device is implemented for flows having a Weber number greater than or equal to 0.1, 1 or 10 and less than or equal to 1000 or 500. In even more preferred embodiments. the flow has a Weber number greater than or equal to 10 and / or less than or equal to 100 or 50. The relation (1) also shows that the angle β is a function of the geometry of the edge. Here, so that the flow difference between the ejection position and the runoff position is particularly visible, the radius of curvature of the wall 20 is chosen strictly greater than 10 μm or 30 μm and, even more preferred at 500 m or 1 mm. Many choices are possible for the exact shape of the wall 20. Here, the exact shape of the wall 20 is determined experimentally. For example, this form is determined so that when the wettability of the wall has a value θ ₂ then the liquid flows along this wall by a predetermined distance d ₂ . Here, Figure 1b, represents the distance d ₂ in a particular case where it corresponds to a complete bypass of the wall 20 simultaneously by two opposite sides before the flows on each of the sides meet for for example, the wall 20 has a circular vertical section whose center is placed on the axis 16. The outer diameter of this vertical section is greater than 5mm.

The wall 20 is made of a material whose wettability varies in response to an electrical signal. For this purpose we use the principle of electrowetting. This principle and detailed information for its implementation are described in the following article:

F. Mugele, J-C Baret, "Electrowetting: from basics to applications", Journal of

Physics: Condensed! Matter 17, R705-R774. Here, the wall 20 comprises an electrode 22 completely covered with a layer 24 of electrically insulating material. The layer 24 electrically isolates the electrode 20 from the liquid 14.

The material chosen to produce the layer 24 is naturally non-wetting. It is considered that a material is naturally non-wetting if in the absence of electrical stress, it has a low wettability corresponding to a value θi contact angle advance with the liquid strictly greater than 90 °. The material used for layer 24 is determined experimentally. Here, it is chosen: so that the liquid 14 flows along the wall 20 over a predetermined distance d1 before detaching it when the wettability of the wall is equal to the value θi, and so that its wettability is adjustable to Q ₂ when a potential difference is applied.

Preferably, the material chosen here naturally has wetting characteristics corresponding to an advancing contact angle of greater than 100 ° or 120 °. In an even more preferred embodiment, the material naturally has a very low wettability, that is to say a wettability corresponding to an advancing contact angle greater than 130 °.

Many materials suitable for the production of the layer 24 are cited in the article by F. Mugele. For example, the insulating material of the layer 24 is selected from the group consisting of amorphous fluoropolymer, polyethylene, polytetrafluoroethylene (PTFE).

The electrode 22 is made of an electrically conductive material whose conductivity is at least ten times greater than that of the material used for the layer 24. For example, the electrode 22 is made of metal.

The wettability of the wall 20 thus produced has a wettability which varies as a function of the potential difference between the electrode 22 and the liquid 14.

To vary this potential difference, the device 6 also comprises another electrode 28 in contact with the liquid 14. Typically, the electrode 28 electrically connects the liquid 14 to ground. The liquid 14 is here a conductive liquid, that is to say a liquid whose conductivity is at least ten times greater than that of the material used to make the layer 24. For example, the liquid 14 is non-water demineralized. Finally, the device 6 comprises a control unit 30 able to vary the wettability of the wall 20 in response to a control signal. For this purpose, the unit 30 is electrically connected to the electrodes 22 and 28. It comprises a controllable voltage source 32 able to vary the potential difference between the electrodes 22 and 28.

The unit 30 thus makes it possible to vary the wettability of the wall 20 from the value θi of the contact angle to the advance to the value Q ₂ of contact angle at the advance. The values θi and Q ₂ depend on the nature of the liquid 14, the material chosen to produce the layer 24 as well as the potential difference applied by the unit 30. However, whatever the difference between the values θi and Q ₂ , there is a difference between the distances di and d ₂ defined as follows:

di is the distance, in the direction of flow, through which the liquid 14 passes along the wall 20 before detaching it when the wettability has the value θi;

d ₂ is the distance, in the direction of flow, through which the liquid 14 passes along the wall 20 before detaching it when the wettability has the value Q ₂ .

The distances di and d ₂ are measured under the same conditions with the exception of the difference in wettability of the wall 20.

In general, the larger the difference between the values θ i and θ _{2, the} greater the difference between the distances di and d ₂ is large.

The distances di and d ₂ depend on the shape of the wall 20 but also on the values θ i and θ ₂ .

Here, in order to obtain significantly different flows between the ejection position and the runoff position, the material used to make the layer 22 and the potential difference applied by the unit 30 are chosen so that the difference between the values θ i and θ ₂ is greater than 20 ° and preferably greater than 30 °. The values θ i and θ ₂ correspond respectively to the ejection and runoff positions.

The orifice 8 is disposed below the wall 20 to collect the fluid 14 in the runoff position. On the contrary, in the ejection position, the fluid 14 passes next to the orifice 8.

The operation of the collector 2 will now be described with reference to the method of FIG.

During a step 36, the liquid 14 is continuously discharged onto the wall 20 from the orifice 4. Thus, the liquid flows continuously along the wall 20. In parallel, during a step 37, the unit 30 applies no potential difference between the electrodes 22 and 28. The wettability of the wall 20 therefore has the value θi and the collector 2 is in its ejection position. . In this position, as long as the value θi of the wettability is maintained, the liquid flows along the wall 20 over the distance d1 before detaching it in the direction F under the effect of the force of inertia and force of gravity. The liquid 14 therefore falls next to the orifice 8 and is not collected in the container 10.

Then, during a step 38, the unit 30 applies a potential difference between the electrodes 22 and 28. The wettability of the wall 20 thus passes to the value Q ₂ . In response, the collector 2 passes into its runoff position. In this position, as long as the Q ₂ value of the wettability is maintained, the liquid flows over the distance d ₂ before detaching from the wall under the effect of gravity. The distance d ₂ is much longer than the distance di. Thus, in this position, the liquid passes through the orifice 8 to be collected in the container 10.

Steps 37 and 38 are repeated alternately. Indeed, the variation of wettability by eletromouillage is reversible.

This difference in the flow of fluid 14 between the ejection position and the runoff position is explained by the modification of the wettability of the wall 20.

Thus, in this embodiment, the device 6 acts as a flow switch. In the ejection position, the fluid 14 does not cross the orifice 8 while in the runoff position, the orifice 8 is traversed by the fluid 14. Figures 3 to 5 show a printer 40 capable of projecting a jet or a drop of ink on a print medium 42.

To simplify the illustration, only a portion of a printing nozzle 44 of the printer 40 has been shown in FIGS. 3 to 5.

This nozzle 44 comprises a multitude of orifices through which are projected drops or jets of ink. To simplify the illustration, only an orifice 46 has been shown in FIGS.

The lips of this orifice 46 are formed by an upper wall 48 and a lower wall 50.

In a manner similar to that described with reference to FIGS. 1a and 1b, the shape of these walls 48 and 50 is chosen so that the ink 52: flows along a distance d 1 along the wall 48 or 50 when the wettability of the wall 48 or 50 has a value θi of advancing contact angle, and flows, under the same conditions, over a longer distance d ₂ when the wettability has a value θ ₂ from contact angle to advanced. For example, the wettability of the walls 48 and 50 is modified by electrowetting. For this purpose, each of the walls 48 and 50 comprises an electrode 54 covered with a layer 56 of insulating material. The layer 56 is directly in contact with the ink 52. The material of the layer 56 is chosen in a manner similar to that described for the layer 24.

The electrode 54 of the wall 48 is connected to a control unit 60 while the electrode 54 of the wall 50 is connected to a control unit 62. The control units 60 and 62 are controllable voltage generators. An electrode 64 connected to a reference potential such that the mass is also introduced into a channel bringing the ink 52 to the orifice 46.

The control units 60 and 62 make it possible to vary the wettability, respectively, of the walls 48 and 50 between values θ i and θ ₂ .

As illustrated in FIG. 3, when the wettability of the walls 48 and 50 are set to a value θi of low wettability, the ink 52 is projected towards the printing support 42 in a collinear ejection direction with an axis 66 horizontal. The axis 66 is also an axis of symmetry of the orifice 46. Under these conditions, the transverse diameter of the ejected drop, in a plane perpendicular to the direction of ejection, is low. If the wettability of the wall 48 is maintained at the value θi while the wettability of the wall 50 is increased by lowering the value Q ₂ , then the ink 52 flows longer on the wall 50 than on the wall 48. The ink 52 thus remains longer in contact with the wall 50 than with the wall 48. Under these conditions, the direction of ejection of the ink 52 towards the support 42, represented by an axis 68 in FIG. , forming a non-zero angle with the axis 66. Thus, by acting on the wettability of the walls 48 and 50, it is possible to incline more or less the direction of ejection of the ink with respect to the axis 66 For example, this is used to aim a printing point on the support 42 which is not strictly opposite the orifice 46. Thus, without it being necessary to move the nozzle printing, it becomes possible to make several printing points on the support 42 juxtaposed or overlapping from of one and the same ink projection port.

FIG. 5 represents another possible mode of guiding the ink 52. In this guiding mode, the wettability of the walls 48 and 50 are both set to the value Q ₂ . Under these conditions, the distances d ₂ traversed by the ink along the walls 48 and 50 are equal and longer than in the case of FIG. 3. This makes it possible to obtain an ink jet 52 whose transverse diameter is more flared than in the case of Figure 3. Thus, the diameter of the dots printed on the support 42 is adjusted by adjusting the wettability of the walls 48 and 50. Here, the liquid is detached from the wall 48 or 50 mainly under the effect of the inertial force and not under the effect of gravity. On the other hand, the force of inertia as the force of gravity is directly related to the mass of the liquid. Figure 6 shows a vehicle 70 such as a motor vehicle equipped with a device 72 for guiding rainwater. The device 72 comprises a wall 74 forming a rounded edge. For example, this ridge is located above the rear windshield of the vehicle 70. This wall 74 is shaped so that the rainwater that flows on the roof of the vehicle in a direction 76 flows along the wall 74 over a distance di when the wettability of the wall 74 has the value θi and a distance d ₂ when the wettability of the wall 74 has the value θ ₂ . The distance di is less than the distance d ₂ .

The device 72 also comprises a control unit 78 able to vary the wettability of the wall 74 between the values θ i and θ ₂ . For example, for this purpose, electrowetting is used. Thus, the wall 74 is formed of an electrode 80 covered with a layer 82 of insulating material. For example, the layer 82 is made of the same material as the layer 24.

The roof 83 of the vehicle 70, which forms a conductive electrode, is electrically connected to the unit 78 as well as to the electrode 80. Under these conditions, when the control unit applies a potential difference between the roof 83 and the electrode 80, the wettability of the wall 74 is modified. If the wettability takes the value θi, the rain that flows along the roof in the direction 76 is ejected from the vehicle in a direction 84. Here, the wall 74 is made in such a way that the ejection direction 84 prevents the rain water run off along the rear windshield of the vehicle 70. Conversely, when the control unit adjusts the potential difference so that the wettability of the wall 74 is equal to the value θ ₂ , then the water flowing along the roof of the vehicle streamed along the wall 74 and is directed on the rear windshield as shown by the arrow 86.

This guiding device therefore allows for example to rinse, from time to time, the rear windshield.

FIG. 7 represents a heat exchanger 90. This heat exchanger is equipped with a pipe 94 provided with an orifice 96 which discharges a coolant 98 along a vertical axis 100.

A piece 102 to be cooled or heated is arranged along the axis 100 so as to be inside the flow of the liquid 98. By way of illustration, this piece 102 comprises several fins which extend in a direction perpendicular to the flow direction of the fluid 98. For example, the part 102 has four fins 104 to 107. Here, these fins extend substantially in a horizontal direction. The end of each fin is formed of a wall 110 shaped so that the liquid 98 flows along this wall for a distance di when the wettability of this wall has the value θi and a distance d ₂ when the wettability of this wall has the value Q ₂ . The distance di is shorter than the distance d ₂ .

The variation of the wettability of this wall 110 is obtained by electrowetting. Each wall 110 is made as described opposite the wall 20. Thus, each wall 110 comprises an electrode 111 covered by a layer of insulating material 111b. Each wall 110 is connected to a control unit 112. This control unit 112 is also connected to an electrode 114 whose one end is immersed in the liquid 98. The control unit 112 is able to apply a potential difference between the electrodes 111a and 114 so as to vary the wettability of the value θi to the value Q ₂ and vice versa.

In FIG. 7, to the left of the axis 100, the shape of the fluid flow 98 along the fins 104 to 107 is illustrated in the case where the wettability has the value θi. Conversely, to the right of the axis 100, the shape of the flow of the liquid 98 along the fins 104 to 107 is illustrated in the case where the wettability of the wall 110 has the value Q ₂ . The contact surface between the part 102 and the coolant 98 is greatly reduced when the wettability of the wall 110 has the value θi. Thus, by adjusting the value of the wettability of the wall 110, it is possible to adjust the contact surface between the piece 102 and the liquid 98 and thus to adjust the amount of heat exchanged between the piece 102 and the liquid 98.

FIG. 8 represents a collector 120 of a liquid 122. This collector 120 directs, alternately, the liquid 122 either inside a container 124 or outside this container 124. For this purpose, the liquid 122 flows along a wall 126. This wall is shaped so that when the wettability of the wall has a value θi, the liquid 122 is ejected from the wall in a direction 128 as represented by the flow The shape of the wall 126 is also chosen so that when the wettability of this wall has a value Q ₂ , then the liquid 122 is either ejected with a different direction or it flows along this wall to detach at a point 132. In Figure 8, the wall 126 is shaped so that the liquid 122 flows to the point 132 when the wettability has the value Q ₂ . The container 124 is located below this point 132 so as to collect the liquid.

Here, the wall 126 is made of a material whose wettability can be changed from the value θi to the value Q ₂ in response to exposure to electromagnetic radiation. For example, this electromagnetic radiation is light and more specifically UV radiation (Ultra-Violet). Such materials whose wettability can be modified in response to exposure to electromagnetic radiation are described in the following publications:

- Hongli Ge, Guojie Wange, Yaning He, Wang Xiaogong, Yanlin Song, Lei Jiang and Daoben Zhu, "Photoswitched Wettability on Inverse Opal Modified by a Self Assembled Azobenzene Monolayer", ChemPhysChem 7, p575-578, 2006.

- Sho Katoka, Marc A. Anderson, "Capillarity between two TiO2 thin-films: evaluating photo-activated wetting", Thin Solid Films 446 (2004) 232-237.

- Kunihiro Ichimura, Sang Keun Oh, Masaru Nakagawa, "Light-Driven Motion of

Liquids on a Photoresponsive Surface ", Sience, 288, June 2, 2000. A control unit 134 irradiates the wall 126 with radiation.

UV to modify its wettability. Here, the unit 134 is disposed opposite the wall 126 on the side where the liquid 122. flows. In this embodiment, the liquid 122 is a liquid transparent to the radiation generated by the unit 134. For example, the liquid 122 is water. The operation of this collector is similar to that described with reference to FIGS. 1a and 1b except that the wettability variation is obtained thanks to a variation in the power of the electromagnetic waves emitted by the unit 134 for a given wavelength. Such a device can be practical when the use of electric current is prohibited in the liquid collector.

FIG. 9 represents a collector 140 of a liquid 142. For example, this collector 140 is identical to the collector 120, except that the wall 126 is replaced by a wall 144 and the control unit 134 is replaced. by a control unit 146 connected to a heating electrode 148.

Here, the wall 144 is made of a material whose wettability varies as a function of temperature. For example, this material is the material known as P-nipam. More information on such materials can be found in the following publications: - L. Huber, Ronald P. Manginell, Michael A. Samara, Byung-ll Kim,

Bruce C. Bunker, "Progammed adsorption and release of proteins in a microfluidic deice", Science, vol. 301, July 18, 2003.

Guillaume Paumier, Jan Sudor, Anne-Marie Gue, Françoise Vinet, Meng Li, Yves J. Chabal, Alain Esteve, Mehdi Djafari-Rouani, "Nanoscale actuation of electrokinetic flows on thermoreversible surfaces",

Electrophoresis 2008, 1245-1252.

In order to vary the wettability of the wall 144, the electrode 148 is disposed near the wall 144 and the unit 146 makes it possible to control and adjust the temperature of the wall 144 to vary its wettability. The operation of the collector 140 is identical to that of the collector 120 except that the wettability variation of the wall 144 is obtained by means of a variation in temperature.

Figure 10 shows a manifold 150 of a liquid 152. This manifold 150 is identical to the manifold 140 except that the electrode 148 and the control unit 146 are omitted.

Here, the variation of wettability of the wall 154 is caused by a variation of a physicochemical property of the liquid 152. Here, the physicochemical property of the liquid 152 which varies is its temperature. Thus, this collector 150 makes it possible to automatically discriminate a cold liquid from a hotter liquid to be collected in the receptacle 124.

A sensor 154 capable of measuring the angle β that the ejection direction 128 makes with the vertical is provided. This angle β is representative of the distance traveled by the liquid 152 along the wall 144 before detaching it. For example, the sensor 154 is a camera associated with an image processing processor.

The combination of the collector 150 and the sensor 154 forms a device for measuring the wettability of the wall 144 with respect to the liquid 152. Indeed, as described with regard to the relation (1), the angle β is function of the angle θ of contact with the advance. This relation between the angles β and θ is, for example, determined experimentally or from physical equations of the system. Thus, the measurement of the angle β makes it possible to determine the wettability. In addition, here, since the wettability depends on the temperature of the liquid 152, by measuring the wettability, a measurement of the temperature of the liquid 152 is also obtained. Many other embodiments are possible. For example, the runoff position may be replaced by a position of ejection of the liquid in a direction of ejection different from that obtained in the other ejection position. The guidance then consists in varying the direction of ejection.

To implement the principle of electrowetting as shown in Figures 1a and 1b, it is not necessary for the liquid to be contacted with an electrode. For embodiments in which the liquid is not contacted with an electrode, it is possible to refer to section 6 of the following article:

F. Mugele, J-C Baret, "Electrowetting: from basics to applications," Journal of Physics: Condensed! Matter 17, R705-R774.

It is also possible to modify the wettability of a wall by electrowetting without it being composed of an electrode covered with a layer of insulating material. In this case, the wall is made of a polarizable material. Alternatively, the wall whose wettability varies can be achieved by using a material whose wettability varies depending on the pH of the liquid flowing on the wall. Such a material is described in the following publication: J. Lindquvist, D. Nystrom, E. Osmark, P. Antoni, A. Carlmark, M. Johansson, A. Hults and E. Malmstrm, "Intelligent Dual Responsive Cellulose Surfaces via Surface ATRP ", Biomarcromolecules 2008, 9, 2139-2145. For example, the wall 144 of the embodiment of FIG. 10 is replaced by such a wall whose wettability varies as a function of the pH. The collector thus produced is then able to discriminate liquids according to their pH.

When a sensor of the angle β or the distance d is associated with a collector, such as the collector 150, they together form a device for measuring the wettability of the wall vis-à-vis the liquid. This wettability varies according to at least one parameter. Thus, this set also forms a device for measuring this parameter. For example, if a sensor, such as the sensor 154 is associated with the device 2, then this sensor can measure the voltage applied between the electrodes 22 and 28. The parameter that varies can also be a physicochemical property of the liquid. In this case, the sensor makes it possible to measure this physicochemical property of the liquid. There are many walls whose wettability varies depending on a physico-chemical property of the liquid flowing over it. For example, the wall may be made of a material that has affinity with components of the liquid. This affinity between the wall and these constituents modifies the wettability of the wall. Typically, the modification of the wettability of the wall is a function of the concentration in the liquid of these constituents. Thus, when such a wall is used in place of the wall 144, the sensor 154 then makes it possible to measure this physico-chemical property such as the concentration of these constituents in the liquid. As an illustration of such an embodiment, the wall 144 is replaced by a wall whose wettability varies depending on the pH. In this embodiment, the wall then has an affinity with the H + ions contained in the liquid. The sensor 154 then makes it possible to measure this pH.

By measurement, we also mean the detection of a physicochemical property. The sensor 154 may be omitted if it is simply desired to guide the liquid 152 according to its physico-chemical properties for example. The container 124 may be omitted.

The guiding device 72 is also applicable to other vehicles such as aircraft and in particular on aircraft wings. Indeed, in certain circumstances, it is interesting to run the water along these wings to, for example, increase the weight of the aircraft. Conversely, in other circumstances, it is more interesting to detach as quickly as possible this water from the wall of the wings of the aircraft. For example, this makes it possible to lighten the weight of the aircraft at takeoff.

What has been described here does not apply only to film flows. As shown in the example described with reference to Figures 3 to 5, this also applies to walls forming the opening lips opening pipes or pipes. Neither is it necessary for the liquid to flow under the force of gravity or from top to bottom.

In a variant, the variation of the wettability of the wall is not reversible. It is not necessary for the flow of the liquid to be continuous. For example, alternatively, it may be a trickle flow.

Many liquids can be guided using the guiding devices described herein. For example, the liquid may be paint, oil, solvent, fuel, molten glass, molten metal, galvanizing bath, molten plastic, beverage, milk, compote, fruit juice, cream, jam, liquid chocolate, liquid honey, fish juice, dough such as bakery pasta. It can also be powder in liquid form as well as biological fluid such as blood.

The fluid guiding device described here finds many other applications besides printers, vehicles, fluid collectors and heat exchangers.

Claims

1. Device for guiding a liquid flow comprising a wall (20; 48; 50; 74; 110; 126; 144) along which the liquid flows, characterized in that the wall is arranged to have an modifiable wettability a forward contact angle value θi to a forward contact angle value Q ₂ in response to a control signal and said wall being shaped so that the liquid flows along this wall:

- over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ , and

the device comprises a control unit (30; 60; 62; 78; 112; 134; 146) for generating the control signal for modifying the wettability of the wall of the value θi at the value Q ₂ so as to vary the distance traveled by the liquid along the wall.

2. Device according to claim 1, wherein the wall is equipped with an electrode (22; 54; 80; 111a) and a layer (24; 56; 82; 111b) of electrically insulating material. liquid, and the control unit (30; 60; 62; 78; 112) is adapted to generate, as control signal, a potential difference between this electrode and the liquid.

3. Device according to claim 1, wherein the wall (144) is made of a material having a wettability that varies as a function of temperature, and the control unit (146) is able to vary, as a signal. of control, the temperature of the wall to modify its wettability.

4. Device according to claim 1, wherein the wall (126) is made of a material having a wettability which varies according to the power of an electromagnetic radiation in a predetermined range of wavelengths, and the unit ( 134) is adapted to vary, as a control signal, the power of the electromagnetic radiation, to which the wall is exposed, in the predetermined range of wavelengths to modify the wettability of the wall.

5. Device according to any one of the preceding claims, wherein the value θi is greater than 130 ° or the value Q ₂ is less than 5 °.

6. Device according to any one of the preceding claims, wherein the radius of curvature of the wall is strictly greater than 10 microns.

7. An ink jet printer, characterized in that the printer comprises: a wall (48, 50) forming at least a portion of the lips of an orifice through which ink is projected towards the of a printing medium, this wall being arranged to have a modifiable wettability of an advancing contact angle value θi to a contact angle value Q ₂ in response to a signal control and this wall being shaped so that the ink flows along this wall:

- over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ , and - a control unit (60, 62) capable of generating a control signal to modify the wettability of the wall of the value θi to the value Q ₂ so as to vary the distance traveled by the ink along the wall.

8. Vehicle equipped with a device (72) for guiding rainwater, characterized in that this device comprises:

a wall (74) arranged to have a modifiable wettability of an advancing contact angle value θi to a contact angle value Q ₂ in advance in response to a control signal and this wall being shaped so that the rainwater flows along the wall: - over a distance di in the direction of flow before detaching from the wall when the wettability has the value θi, and

a control unit (78) capable of generating a control signal for modifying the wettability of the wall from the value θi to the value Q ₂ so as to vary the distance traveled by the rainwater along the wall; .

9. Heat exchanger comprising: a coolant (98), and - a wall (1 10) along which the heat transfer liquid flows, characterized in that the wall (1 10) is arranged to have a modifiable wettability of an advancing contact angle value θi to an advancing contact angle value Q ₂ in response to a control signal and said wall being shaped such that the heat transfer liquid flows. along this wall: a distance di in the direction of flow before detaching from the wall when the wettability has the value θi, and

- over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ , and - the heat exchanger comprises a control unit (112) capable of generating a control signal to modify the wettability of the wall of the value θi to the value Q ₂ so as to vary the distance traveled by the heat transfer liquid along the wall.

10. Liquid collector comprising:

a wall (20; 126; 144) along which the liquid flows, and

a liquid collecting orifice (8) arranged with respect to the wall so as to be traversed by the liquid when the latter flows along the wall for a distance d ₂ and so as not to be traversed by the liquid when the latter flows along the wall over a distance di, characterized in that the wall is arranged to have a modifiable wettability of a value θi of advancing contact angle to a value Q ₂ of advancing contact angle in response to a control signal and this wall being shaped so that the liquid flows along this wall: - on the distance di in the direction of the flow before detaching from the wall when the wettability has the value θi, and

- over the distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ , and

the collector comprises a control unit (30; 134; 146) capable of generating a control signal for modifying the wettability of the wall of the value θi at the value θ ₂ so as to vary the distance traveled by the liquid on the along the wall.

11. A method for guiding a liquid flow along a wall having an modifiable wettability of an advancing contact angle value θi at an advancing contact angle value θ ₂ θ ₂ to a control signal and this wall being shaped so that the liquid flows along this wall:

a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ , characterized in that the method comprises generating (37, 38) the control signal to modify the wettability of the wall so as to vary the distance traveled by the liquid along this wall.

12. Device for guiding a liquid flow, this device comprising:

the liquid (152) forming the liquid flow, this liquid having a physicochemical property capable of varying between a value Pi and a value P ₂ ; a wall (144) along which the liquid flows, characterized in that the wall is arranged to have a wettability with respect to this equal liquid:

at the value θi of advancing contact angle when the physicochemical property of the liquid has the value Pi, and at a value Q ₂ of advancing contact angle when the physicochemical property of the liquid has the value P ₂ , this wall being shaped so that the liquid flows along this wall:

- over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value θ ₂ .

13. Device according to claim 12, wherein the physicochemical property of the liquid that can vary is a concentration of constituents present in this liquid and the wall has an affinity with these constituents causing the modification of the wettability of the wall as a function of the concentration of these constituents in the liquid.

The device of claim 12, wherein the physicochemical property of the liquid is pH or temperature.

15. Device for measuring wettability, characterized in that the measuring device comprises: a wall (144) along which a liquid whose wettability vis-à-vis the wall is to be measured is measured, this wall; being shaped so that the liquid flows along this wall:

- over a distance di in the direction of flow before detaching from the wall when the wettability has the value θi, and - over a distance d ₂ in the direction of flow before detaching from the wall when the wettability has the value Q ₂ ,

a sensor (154) of a physical quantity representative of the distance traveled by the liquid along said wall before detaching it, this physical quantity representing a measurement of the wettability of the wall with respect to the liquid.