EP0782885A1 - High efficiency spray device particularly for producing water microdroplets - Google Patents

Abstract

The water micro-drop spray has a first water filled vat (1a) and second water filled vat (1b) separated by a central transducer (5). The transducer has two faces flush with the water one for each vat section. The piezoelectric transducer transmits waves in both water sections, and each water vat has an open section (4a,4b) opposite the transducer faces.

Description

The present invention relates to a high efficiency spray device, in particular water in the form of micro-droplets.

It is known to use devices for micro-spraying water to humidify the ambient air.

Such devices are thus known comprising a piezoelectric ceramic transducer excited by a high frequency electrical signal which emits ultrasonic waves in a small tank filled with water.

The waves propagate in the water in a nonlinear way and there is an accumulation of static pressure towards the surface of the water, from where the appearance of a jet of liquid called "acoustic fountain", which is surrounded by a mist of micro-droplets.

An air current created in the vicinity of the water jet then evacuates the micro-droplets to the outside of the device, into the ambient air.

In such a device, the energy supplied by the transducer is used only partially to generate the microdroplets because the face of the transducer which is not in contact with water emits waves which are absorbed by the support of the transducer and also in the tank by multi-reflection and are lost.

In addition, the internal losses in the transducer and the saturation phenomena of the emission level due to the high stresses and the rise in temperature of the transducer limit the acoustic efficiency of the latter.

The present invention aims to provide a spraying device which has a high yield, in particular eliminating the above-mentioned problem.

The present invention relates to a device for spraying liquid, comprising a first elongated tank closed at one of its ends by a first free face of a piezoelectric transducer capable of emitting waves in a liquid filling the tank and open to its end opposite to the piezoelectric transducer, characterized in that the piezoelectric transducer has a second free face, opposite to its first free face, and that a second elongated tank is disposed, relative to the piezoelectric transducer, symmetrically with the first tank, the second tank being closed at one of its ends by said second free face of the piezoelectric transducer, which is thus able to also emit waves in a liquid filling the second tank, this second tank being open at its end opposite the piezoelectric transducer.

It is understood that the fact of completely immersing the piezoelectric transducer in the two liquids contained in the two tanks allows a great diffusion of heat from the transducer towards the liquids, which limits the rise in temperature of the transducer and therefore improves its operation. Furthermore, the presence of liquid on both sides of the piezoelectric transducer symmetrizes the mechanical stresses in the transducer and improves the transfer of acoustic energy to the surrounding liquids. The combination of the thermal effects and the acoustic effects mentioned above makes it possible to improve the electroacoustic efficiency of the transducer and therefore to generate greater acoustic power in liquids for the same electrical input power.

Thus, the device according to the invention has a high yield since it makes it possible to generate a lot more droplets than if it had only one tank.

In a preferred embodiment of the invention, the two tanks are able to be completely filled with liquid.

In another preferred embodiment, the waves emitted by the piezoelectric transducer in each tank are concentrated in the vicinity of the opening of each tank, the cross section of each tank having a gradual narrowing in the direction of the opening of the tank.

In a particular embodiment, the part of each tank having a narrowing of section has a shape of paraboloid of revolution whose focal point is located in the vicinity of the corresponding opening.

Thanks to this narrowing of the cross section, the liquid contained in each tank is not very sensitive to the accelerations of the medium in which the device according to the invention is installed.

By way of example, the device according to the invention can be installed in an automobile, a boat or an airplane.

In a preferred embodiment of the invention, the walls of each tank are made of a hard material, capable of reflecting waves, and are shaped so as to concentrate the waves in the vicinity of the central part of the opening of the tank.

Thus, the walls of each tank fulfill at least two distinct functions, namely a limitation of the risk of liquid overflowing outside the tank on the one hand, and a concentration of waves in the vicinity of the central part of the opening of the tank on the other hand.

In a particular embodiment of the invention, each tank comprises, in the vicinity of its opening, heating means, for example electrical resistances, making it possible to raise the temperature of the liquid just before it is sprayed.

In a variant of this embodiment, part of the acoustic energy supplied by the waves is converted into heat, preferably in the vicinity only of the opening of each tank, otherwise in the entire wall of each tank, thanks to the presence of an acoustically absorbent material such as a polymer.

For this purpose, it is possible, for example, to use the laminating polyester sold by the company SOLOPLAST.

The polymer may be found only in the vicinity of the opening of the tank, or may constitute the whole of the tank, in which case the reflection of the waves may be less good but sufficient to obtain the concentration of the waves in the vicinity of the opening, while the view walls heat all of the liquid in it.

Advantageously, the device according to the invention is provided with ventilation means to create an air circulation in the vicinity of the surface of the liquid contained in each tank.

In a preferred embodiment of the invention, the device comprises a collection container in which the tanks are placed, a pump being connected on the one hand to the collection container, on the other hand to each tank, and being capable of permanently circulate the liquid between each tank from which it overflows and the collection container where it is collected, a liquid reservoir, also connected to the pump, making it possible to keep constant the quantity of liquid circulating in the device by compensating for the consumption of liquid necessary for the production of droplets.

Thus, the instability of the liquid level at the opening of each tank, which could result from unforeseeable overflows due to strong accelerations undergone by the device, is for the most part compensated by the fact that, the liquid constantly and forcibly overflowing at the opening of each tank, even strong accelerations can only cause a slight fluctuation in the quantity of liquid overflowing, without appreciably modifying the level of the liquid at the opening of each tank.

In addition, not only is such a device not very sensitive to accelerations, but in addition, by its symmetry and thanks to the use of forced circulation of liquid, it is not very sensitive to variations in inclination and can operate in any position.

Advantageously, the flow rate of the pump is high enough to generate a jet of liquid at the opening of each tank, independently of the acoustic fountain which results from the sole action of ultrasonic waves.

In this way, the energy of the waves can be mobilized mainly for spraying the liquid, the formation of acoustic fountains being facilitated by the fact that the liquid jets are already created by the pump.

To further increase the effectiveness of the spraying, it is preferable, according to the invention, to choose the diameter of the opening of each tank, close to that of the acoustic fountain which would be naturally formed by waves in the absence of pump, so as to best superimpose the water jet formed by the pump and the acoustic fountain generated by the waves.

In a preferred embodiment, a deflector is provided in the extension of the opening of each tank, to retain the large drops of liquid which are thus recovered in the collection container, while the air flow generated by the means ventilation system evacuates micro-droplets to the outside of the device.

• la figure 1 est une vue schématique en élévation et en coupe d'un mode de réalisation du dispositif selon l'invention,
• les figures 2 à 4 sont des vues en perspective de variantes de formes d'ouverture d'une cuve du dispositif de la figure 1, et
• la figure 5 est une vue en coupe selon V-V de la figure 2.

In order to better understand the invention, we will now describe an embodiment given by way of non-limiting example with reference to the accompanying drawing in which:

• FIG. 1 is a schematic view in elevation and in section of an embodiment of the device according to the invention,
• FIGS. 2 to 4 are perspective views of alternative forms of opening of a tank of the device in FIG. 1, and
• FIG. 5 is a sectional view along VV of FIG. 2.

The device shown in the drawing comprises two elongated tanks 1 a, 1 b, revolution which each comprise a base cylindrical 2 a , 2 b and an upper part 3 a , 3 b whose section narrows in the direction of an opening 4 a , 4 b .

Each opening may be circular, as shown in Figure 2 or scalloped as shown in Figure 3, or even provided with a central waveguide which closes its central part and leaves only an annular passage free, as shown in Figure 4.

Each tank 1 a , 1 b is intended to be completely filled with water.

A piezoelectric transducer 5 constituted by a disc-shaped ceramic is placed between the two tanks 1 a , 1 b , opposite their respective openings 4 a , 4 b .

The transducer 5, which has two opposite free faces 5 a , 5 b each constituting the bottom of a tank 1 a , 1 b , is capable of emitting ultrasonic waves in the water contained in each tank, in the direction of the corresponding opening 4 a , 4 b .

The walls of each tank are made, for example, of stainless steel which is a material hard enough to reflect waves by absorbing minimal energy.

The converging shape of the walls of each tank is determined so as to concentrate the waves in the central part of the corresponding opening.

The tanks 1 a , 1 b are housed inside a closed container 6 which constitutes a collection container within the meaning of the invention.

Inside this collection container 6 is arranged a fan 7, driven by a motor not shown.

Outside the collection container 6, there is a water tank 8 in which is housed a pump 9 connected on the one hand to each tank 1 a , 1 b via a first conduit 10, d on the other hand to the collection container 6 by means of a second conduit 11, two openings 41 a , 41 b of which open opposite the open ends of each tank and two other openings 41 c of which open in the vicinity of the transducer 5.

The fan 7 is housed in a common compartment 12 of the collection container 6. This compartment 12 is delimited by an external wall 13 of the collection container 6 and by a sealed internal partition 14 which leaves two passages 15 free to compartments 16 a and 16 b each containing a tank.

An air current is thus created in each compartment 16 a , 16 b , between several deflectors 17 which convey the air to an opening 18 a , 18 b from which the air and the water droplets escape. formed above the openings of each tank, as indicated by the arrows 19.

The end part of each tank 1 a , 1 b is enclosed in a spherical cap-shaped deflector 20 a , 20 b with an axis substantially perpendicular to the longitudinal axis of each tank, and whose concavity is opposite to the direction displacement of the air stream.

Each cap 20 a, 20 b is secured to the outer wall of the vessel 1 as a seal 21a, 21b.

In the vicinity of the opening 4 a , 4 b of each tank, electrical resistors 22 are provided which are inserted into the thickness of the wall of each tank and allow the water to be heated before being sprayed.

The heating power is calculated so as to heat only the periphery of the jet to limit the electrical power required.

Heating can also be obtained by taking part of the acoustic waves to heat the end of the tank, for example with a polymeric material which heats up by absorbing the waves. Preferably, this sandwich material is placed between two metal walls to protect it from direct attack by waves.

In Figure 5, there is shown the part having a narrowing of section of a metal tank 1 b which has a thickness of a polymer 25 in a recess made on its inner face, in the vicinity of its opening 4 b .

The polymer is covered with a thin metallic layer 24 of a few hundred micrometers which is intended to protect said polymer from direct attack by waves.

In operation, the waves are partially absorbed by the polymer which heats up and thus raises the temperature of the water.

This heating, by acting on the surface tension of the water and on its saturated vapor pressure, creates a compromise on its parameters favorable to spraying and further increases the yield of the device.

We know from experience that if the liquid temperature rises from 20 ° C to 40 ° C, the volume of vaporized liquid doubles.

We will now explain the operation of the spray device shown in the drawing.

To facilitate the explanation, it is considered that the orientation of the device is vertical, as shown in FIG. 1.

Each tank is filled with water.

The pump 9 discharges water through the conduit 10, so that a first jet of water gushes at the opening of the tank 1b and a second jet of water flows at the opening from tank 1 a .

Depending on the shape of the openings 4 a and 4 b , three examples of which are shown in FIGS. 2 to 4, water jets of circular section are obtained, in the form of a daisy or a ring.

Because the generation of droplets occurs on the surface of the water jet, the shapes of openings in Figures 3 and 4 give rise to larger surface water jets and therefore increase the production of droplets compared to the simple form of Figure 2.

In other words, since the circumference of the water jets is increased with the openings in FIGS. 3 and 4, and since the mist is generated from the surface of the water jets, which is proportional to the circumference of these jets, the amount of mist obtained with the openings of Figures 3 and 4 is increased.

Of course, the shape of the openings 4 a and 4 b is not limited to those shown in the drawing.

The water is recovered by the collection container 6 and recirculated by the pump 9, via the conduit 11.

The ceramic 5 emits waves in the two tanks, waves which progress in the water along planes perpendicular to the longitudinal axis of the tank.

The converging shape of the walls of each tank 1 a , 1 b concentrates the waves substantially in the central part of the corresponding opening 2 2 a , 2 b .

This concentration of wave energy in the vicinity of the water surface propagates inside the jet, which allows the formation of a mist of micro-droplets surrounding each jet of water.

These micro-droplets, in a preferred mode, have a diameter of less than 5 micrometers. They are carried outwards by the air current created by the fan 7.

Other, heavier drops form and are recovered by the spherical caps 20 a , 20 b and fall by gravity to the bottom of the collection container 6 to be recirculated by the pump 9, in the same way as the non-sprayed water from water jets.

The diameter of the openings 4 a , 4 b is chosen so that the waves are concentrated in the vicinity of the opening in each tank.

Thus, the energy of the waves, which is not used to form the acoustic fountains, is mainly used to spray the water.

In other words, the spraying efficiency is increased because on the one hand the wave energy is used mainly for spraying water, the water jets being already formed by the pump, on the other hand, the use of a jet assisted by an external pump allows a better adjustment of the operating parameters of the device, which makes it possible to achieve an optimal operation in which the jet exceeds in length the jet which would be created by the sole sound pressure due to waves.

Thus, the spray surface is further increased from which the water droplets can form.

In addition, as already explained, the two faces 5 a and 5 b of the transducer 5 are used for spraying, which makes it possible to significantly increase the production of water droplets compared to a device which would comprise only one tank.

Thanks to the different deflectors, it is possible to operate the device described in all the positions which may result from a pivoting of this device around an axis 23, perpendicular to the longitudinal axis of the tanks and included in the plane of the drawing. .

The water tank 8 allows the pump 9 to keep the amount of water circulating in the device constant, by compensating for the volume of water discharged to the outside by micro-spraying.

It is clear that this device, whose overall dimensions are of the order of 4 cm in diameter and 10 cm long, can be easily installed in a vehicle.

The fact that it is able to function properly while being inclined allows easy use in all kinds of vehicles.

For example, the device according to the invention can be installed in the passenger compartment of an automobile with its longitudinal axis inclined by 10 degrees relative to the horizontal, which gives it bulk. vertical of approximately 5.7 cm which allows it to be housed in the passenger compartment ceiling, for example.

The device according to the invention can also be carried on an airplane or on a boat where the conditions of stability are, a priori, not very good.

In the building industry, solutions in which the jets are vertical can be very useful for generating very large volumes of droplets from a small footprint.

In particular, because of the gravity, the water jet leaving the lower opening is straight and extends to the bottom of the lower compartment. Therefore, the humidification volume is increased since the surface of the water jet is increased.

It is understood that the embodiment which has just been described has no limiting character, and that it can receive any desirable modifications without departing from the scope of the invention.

Claims (11)

Liquid spraying device comprising a first elongated tank (1 a ) closed at one of its ends by a first free face (5 a ) of a piezoelectric transducer (5) capable of emitting waves in a liquid filling the tank and open at its end (4a) opposite the piezo-electric transducer (5), characterized in that the piezoelectric transducer comprises a second free face (5b) opposite its first free face (5b), and that second elongated tank (1 b ) is arranged symmetrically with the first tank (1 a ) relative to the piezoelectric transducer (5), the second tank being closed at one of its ends by said second free face (5 b ) of the transducer piezoelectric (5), which is thus able to also emit waves in a liquid filling the second tank (1 b ), this second tank (1 b ) being open at its opposite end (4 b ) to the piezoelectric transducer. Device according to claim 1, characterized in that the two tanks (1 a , 1 b ) are able to be completely filled with liquid. Device according to claim 2, characterized in that the waves emitted by the piezoelectric transducer (5) in each tank (1 a , 1 b ) are concentrated in the vicinity of the opening (4 a , 4 b ) of each tank, the cross section of each tank (1 a , 1 b ) having a progressive narrowing (3 a , 3 b ) in the direction of the opening of the tank. Device according to claim 3, characterized in that the tanks have, in their part having a progressive narrowing (3 a , 3 b ), a form of paraboloid of revolution whose focal point is located in the vicinity of the corresponding opening. Device according to any one of Claims 1 to 4, characterized in that each tank (1 a , 1 b ) comprises, near its opening (4 a , 4 b ), heating means (22) allowing '' raise the temperature of the liquid just before spraying. Device according to claim 5, characterized in that the heating means consist of a thickness of material absorbing the acoustic energy of the waves (24), provided in the vicinity of the opening of each tank. Device according to any one of Claims 1 to 6, characterized in that it comprises ventilation means (7) to create an air circulation in the vicinity of the surface of the liquid contained in each tank (1 a , 1 b ). Device according to any one of Claims 1 to 7, characterized in that the walls of each tank (1 a , 1 b ) are made of a hard material capable of reflecting waves and are shaped so as to concentrate the waves in a point located in the vicinity of the central part of the opening (4 a , 4 b ) of each tank (1 a , 1 b ). Device according to any one of claims 1 to 8, characterized in that it comprises a collection container (4) in which are placed tanks (1 a , 1 b ), a pump being connected on the one hand to the collection container (6), on the other hand to each tank (1 a , 1 b ) and being capable of circulating the liquid permanently between the tanks (1 a , 1 b ) from where it overflows and the container of collection (6) where it is collected, a liquid reservoir also being connected to the pump (9) to keep the amount of liquid circulating in the device constant. Device according to any one of Claims 1 to 9, characterized in that each opening (4 a , 4 b ) of the tanks (1 a , 1 b ) has a diameter close to that of the acoustic fountain which would naturally be formed by waves in the absence of a pump (9). Device according to any one of Claims 1 to 10, characterized in that deflectors, for example in the form of spherical caps (20 a , 20 b ) are provided in the extension of the opening (4 a , 4 b ) of each tank (1 a , 1 b ) to retain the large drops of liquid which are thus collected in the collection container (6).

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