EP0782885B1 - High efficiency spray device particularly for producing water microdroplets - Google Patents

Description

The present invention relates to a spray device with high yield, especially of water in the form of micro-droplets.

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

We thus know such devices as that of FR-2 691 411-A comprising a transducer piezoelectric ceramic 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 it builds up static pressure towards the surface of water, hence the appearance of a liquid jet 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, in the ambient air.

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

In addition, the losses internal to the transducer and the phenomena of saturation of the emission level due to high stresses and elevation the transducer temperature limit the acoustic performance of this latest.

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

The subject of the present invention is a spraying device liquid, comprising a first elongated tank closed at one of its ends by a first free face of a piezoelectric transducer able to emit waves in a liquid filling the tank and open to its end opposite the piezoelectric transducer, characterized by the the piezoelectric transducer has a second free face, opposite its first free face, and that a second elongated tank is arranged, relative to the piezoelectric transducer, symmetrically to 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 to the piezoelectric transducer.

We understand that the fact of completely immersing the transducer piezoelectric in the two liquids contained in the two tanks allows a great diffusion of heat from the transducer towards liquids, which limits the temperature rise 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 surrounding liquids. The conjunction of thermal effects and effects acoustics mentioned above improves performance electroacoustic transducer and therefore generate greater sound power in liquids for the same electrical power entry.

Thus, the device according to the invention has a high efficiency since it allows to generate many more droplets than if it does not had only one tank.

In a preferred embodiment of the invention, the two tanks are suitable for being 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 with progressive narrowing towards the opening of the tank.

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

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

By way of example, the device according to the invention can be on board an automobile, boat or plane.

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 fill at least two separate functions, i.e. limiting the risk of overflowing the liquid outside the tank on the one hand, and a concentration of waves at near the central part of the tank opening on the other hand.

In a particular embodiment of the invention, each tank has, near its opening, heating means, by example of electrical resistances, allowing the temperature of the liquid just before spraying.

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

For this purpose, it is possible to use, for example, polyester from stratification marketed by the company SOLOPLAST.

The polymer can be found only in the vicinity of the opening of the tank, or constitute the entire tank, in which case the reflection of waves may be less good but sufficient to obtain the concentration waves near 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 air circulation in the vicinity of the surface of the liquid contained in each tank.

In a preferred embodiment of the invention, the device includes 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 able to circulate the liquid continuously between each tank from which it overflows and the collection container where it is collected, a liquid reservoir, also connected to the pump, allowing keep the amount of liquid circulating in the device constant 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 unpredictable overflows due to strong accelerations undergone by the device, is mainly compensated by the fact that, the liquid constantly overflowing and forced to the opening of each tank, even strong accelerations cannot cause a slight fluctuation in the amount of liquid overflowing, without appreciably changing the level of the liquid at the opening of each tank.

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

Advantageously, the pump flow is high enough to generate a jet of liquid at the opening of each tank, regardless 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 liquid, forming fountains acoustic being facilitated by the fact that the liquid jets are already created by the pump.

To further increase the effectiveness of the spray, 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 naturally formed by waves in the absence of a pump, so that best superimpose the water jet formed by the pump and the fountain acoustics generated by waves.

In a preferred embodiment, a deflector is provided in the extension of the opening of each tank, to retain large drops of liquid which are thus collected in the collection container, while the air flow generated by the ventilation means evacuates the 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 cylindrical base 2 a, 2 b and an upper portion 3 a, 3 b whose cross section tapers towards an opening 4 a , 4 b .

Each opening can be circular, as shown in Figure 2 or scalloped as shown in Figure 3, or provided with a central waveguide which closes its central part and leaves only one annular passage, 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 steel stainless material which is hard enough to reflect waves in absorbing minimal energy.

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

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 disposed 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 via 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 outer 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.

A stream of air is thus created in each compartment 16a, 16b, between a plurality of baffles 17 which carry air to an opening 18 a, 18 b which escape the air and the water droplets formed above the openings of each tank, as indicated by the arrows 19.

The end portion of each tank 1, 1b is enclosed in a baffle-shaped spherical segment 20a, 20b of axis substantially perpendicular to the longitudinal axis of each vessel, and whose concavity is opposite to the traveling direction of air flow.

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 removing part of the acoustic waves to heat the end of the tank, for example with a polymeric material that heats up by absorbing waves. So preferential, this material is sandwiched between two 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 direct aggression of the waves.

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

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 temperature of the liquid rises 20 ° C to 40 ° C, the volume of vaporized liquid doubles.

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

To facilitate the explanation, we consider that the orientation of the device is vertical, as shown in Figure 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 production of droplets with respect to the simple form of FIG. 2.

In other words, since the circumference of the jets water is increased with the openings of Figures 3 and 4, and since fog is generated from the surface of the water jets, which is proportional to the circumference of these jets, the amount of fog 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 collected by the collection container 6 and returned to circulation by pump 9, via conduit 11.

Ceramic 5 emits waves in the two tanks, waves which progress in water in 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 spreads inside the jet, allowing formation a mist of micro-droplets surrounding each jet of water.

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

Other, heavier drops are formed and are recovered by the spherical caps 20 a , 20 b and fall by gravity to the bottom of the collected 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.

So the wave energy, which is not used to form the acoustic fountains, mainly used to spray water.

In other words, the spraying efficiency is increased by the on the one hand that wave energy is used mainly for spray the water, the water jets already being formed by the pump, otherwise On the other hand, the use of a jet assisted by an external pump allows better adjustment of the operating parameters of the device, which allows achieve optimal operation in which the jet protrudes in length the jet which would be created by the only acoustic pressure due to the waves.

Thus, the spray surface is further increased from which 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 make operate the device described in all positions that can 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, compensating for the volume of water evacuated to the outside by micro-spraying.

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

The fact that it is able to function properly by 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 inclined longitudinal axis 10 degrees from the horizontal, which gives it space vertical of about 5.7 cm which allows for example to accommodate it in the ceiling of the passenger compartment.

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

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

In particular, because of the gravity, the water jet coming out of the lower opening is straight and extends to the bottom of the compartment inferior. As a result, the humidification volume is increased since the surface area of the water jet is increased.

It is understood that the embodiment which has just been described has no limiting nature, and that it may receive all desirable modifications without departing from the scope of the appended claims.

Claims (11)

1. Device for spraying liquid comprising a first elongated tank (1a) closed at one of its extremities by a first free face (5a) of a piezo-electric transducer (5) able to transmit waves into a liquid filling the tank and open at is extremity (4a) opposite the piezo-electric transducer (5), characterised in that the piezo-electric transducer comprises a second free face (5b) opposite its first free face (5a), and in that a second elongated tank (1b) is placed symmetrically to the first tank (1a) with respect to the piezo-electric transducer (5), the second tank being closed at one of its extremities by said second free face (5b) of the piezo-electric transducer (5), which is thus able to also transmit waves into a liquid filling the second tank (1b), said second tank (1b) being open at its extremity (4b) opposite the piezo-electric transducer.
2. Device according to claim 1, characterised in that the two tanks (1a, 1b) are able to be fully filled up with liquid.
3. Device according to claim 2, characterised in that the waves transmitted by the piezo-electric transducer (5) in each tank (1a, 1b) are concentrated near the opening (4a, 4b) of each tank, the cross section of each tank (1a, 1b) having a progressive narrowing (3a, 3b) in the direction of the opening of the tank.
4. Device according to claim 3, characterised in that inside the progressive narrowing portion (3a, 3b), the tanks have a paraboloid of revolution shape whose focal point is near the corresponding opening.
5. Device according to one of claims 1 to 4, characterised in that each tank (1a, 1b) comprises close to its opening (4a, 4b) heating devices (22) for increasing the temperature of the liquid to be increased just before it is sprayed.
6. Device according to claim 5, characterised in that the heating devices are constituted by a material thickness absorbing the acoustic energy of the waves (24) provided near the opening of each tank.
7. Device according to one of claims 1 to 6, characterised in that it comprises ventilation means (7) for creating a circulation of air near the surface of the liquid contained in each tank (1a, 1b).
8. Device according to one of claims 1 to 7, characterised in that the walls of each tank (1a, 1b) are made of a hard material able to reflect the waves and are shaped so as to concentrate the waves at a point situated near the central portion of the opening (4a, 4b) of each tank (1a, 1b).
9. Device according to one of claims 1 to 8, characterised in that it comprises a collecting receptacle (4) in which the tanks (1a, 1b) are placed, a pump being firstly connected to the collecting receptacle (6), and secondly to each tank (1a, 1b) and being able to have the liquid circulate continuously between the tanks (1a, 1b) where it overflows and the collecting receptacle (6) where it is collected, a liquid tank being also connected to the pump (9) so as to keep constant the quantity of liquid circulating inside the device.
10. Device according to claims 1 to 9, characterised in that each opening (4a, 4b) of the tanks (1a, 1b) has a diameter close to that of the acoustic fountain which would be naturally formed by the waves in the absence of the pump (9).
11. Device according to one of claims 1 to 10, characterised in that deflectors in the shape of spherical caps (20a, 20b) are provided in the prolongation of the opening (4a, 4b) of each tank (1a, 1b) so as to retain the large drips of liquid which are thus recovered in the collecting receptacle (6).

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