EP0437155B1 - Method for spraying a liquid solution by ultrasound, and droplet diffuser for this method - Google Patents

Abstract

The invention relates to a method for atomising a liquid solution by ultrasound as well as a micro-droplet diffuser for the vaporisation of a liquid solution intended especially for forming a spray of disinfecting substances for aseptisation of medical premises. According to the invention, the ultrasound (3) is generated within a bath (1) of the liquid solution to be vaporised and the ultrasonic waves (3) are focused in order that they concentrate in a zone (4) of the surface of the bath (1). Thus, a fountain (5) is created in which micro-bubbles (7) burst in order to create a spray (6) of atomised liquid. <IMAGE>

Description

The invention relates to a method of micro-spraying a liquid solution by ultrasound as well as to a micro-droplet diffuser for vaporizing a liquid solution, intended for example in the medical environment for emission vapors of disinfectants, for asepsis of premises, instruments or others.

Although the invention has been specially developed in the context of the decontamination of surgical rooms, it could perfectly extend to applications in which it is necessary to produce a calibrated micro-spraying of a liquid solution with a relatively large production. .

Currently, the production of liquid micro-droplets, for example of a disinfectant, can be obtained according to three different principles.

The first usable apparatus comprises a propeller system, the propeller of which is surrounded by baffles and comprises a perforated hub, through which the solution to be sprayed is injected. For this purpose, the hub has lateral orifices through which the liquid escapes in droplets. Due to the strong centrifugal force prevailing at this level, the droplets are ejected radially with a large live force.

In addition, at the periphery of the propeller is placed a static grid on which the droplets are sprayed in a mist then entrained by the main ventilation. The non-sprayed liquid part is collected in the bottom of the device where a pump re-injects the liquid into the propeller hub.

The advantage of this device is its simplicity, however care must be taken for its proper functioning to regularly clean it. Its use is to be avoided in a dusty atmosphere and, its faults are unfortunately numerous.

First of all, the spraying is also poorly controlled, large droplets are entrained by ventilation and there are supersaturation phenomena which result in liquid condensation in the environment close to the device. In the case of a disinfectant product, this means high consumption for non-homogeneous asepsis.

The second spraying technique employs the nozzle principle, in which the liquid to be sprayed is injected under pressure then, at the rear of the nozzle, a compressed air outlet nozzle is placed which allows the emitted droplets to be entrained.

This type of installation has a better efficiency than that described above but requires a pump and a compressor which greatly increases the cost of the installation. In addition, the control of micro-spraying is not guaranteed and one can encounter phenomena of supersaturation.

The purpose of a diffuser being to vaporize a liquid, it is important that, in the technique illustrated, the spraying results in obtaining droplets of the smallest possible dimension. Indeed, in this case, the ratio between the surface and the mass is optimum and the vaporization is easy since it suffices to supply the droplet with a very small amount of heat to result in its total vaporization.

There is also a recent ultrasound technique used to vaporize liquids. For this, ultrasonic waves are generated in the liquid to vaporize bath which, on the surface of the liquid, due to the sudden variation in impedance creates a small spray of central water accompanied by the production of drops which , in combination with cavitation phenomena within the same liquid, creates a surface fog.

The micro-droplets which form this mist can be entrained by an air current in which the micro-droplets evaporate. This principle of micro-spraying offers great advantages, particularly in terms of the powers involved and the dimensions of micro-droplets formed.

Document GB-A-1,069,048 discloses a method of micro-spraying a liquid solution by ultrasound capable of forming a mist of medicinal products such as for medical inhalation, according to which ultrasound is generated at within a bath of liquid solution and the ultrasonic waves are focused on the surface of a bath in the form of a vertical "geyser".

Also known from the Patent document Abstract of Japan, Vol. 6, No. 15 of January 28, 1982 a device equipped with a vibration element for vaporizing a solution by vibration of ultrasonic waves, which includes a waveguide in the form of a funnel turned over in order to focus the ultrasonic waves.

However, at present, these devices are unsuitable for disinfecting premises because they know significant limits in terms of the flow rates generated, which today are around 0.5 liters per hour, whereas such disinfection would require flow rates of the order of 2 liters per hour. In addition, there is no control over the size of the microdroplets formed and it is necessary to deplore a large dispersion at this level.

The main object of the present invention is to present a method of micro-spraying a liquid solution by ultrasound which offers the advantages of being able to deliver a high flow rate compatible with the capacities required for disinfecting the premises and with which there is has a mastery of the dimension of micro-droplets.

We find the advantages of an autonomous device, of modest dimensions, with however a better output and a total absence of risk of oversaturation of the environment. Consequently, the diffuser of the present invention is perfectly compatible with medical applications for disinfecting premises where it is very efficient, in particular in terms of performance.

Other objects and advantages of the present invention will appear during the description which follows which is however given only for information.

According to the invention, the method of micro-spraying a liquid solution by ultrasound, intended in particular to form a mist of disinfectant products, for sanitizing medical or other premises, according to which ultrasound is generated within 'a bath of liquid solution and the said ultrasonic waves are focused on the surface of the bath, is characterized in that the beam of ultrasonic waves is directed with an oblique incidence relative to the surface of the solution liquid to form a homogeneous fountain in an arc.

The micro-droplet diffuser for the vaporization of a liquid solution, intended in particular for the emission of vapor from disinfectant products, and designed for implementing the method according to the invention, comprising a device for producing micro-droplets by ultrasound, which is placed in an air circulation vein to entrain and diffuse the microdroplets, and comprising means for generating ultrasound within the liquid solution and for focusing on the surface of the solution liquid ultrasound, these means being in the form of a transducer, is characterized in that said transducer is placed in the liquid solution according to an arrangement such that the beam of ultrasonic waves is emitted with an incidence oblique to the surface of the liquid solution in order to obtain a homogeneous fountain in an arc.

In an alternative embodiment, the micro-droplet diffuser for vaporizing a liquid solution, intended in particular for the emission of vapor from disinfectant products and designed for carrying out the process of the invention, comprising a device for production of micro-droplets by ultrasound which is placed in an air circulation vein to entrain and diffuse the micro-droplets and which comprises means for focusing on the surface of the liquid solution the ultrasound delivered by a transducer within the liquid solution, is characterized in that the means for focusing the ultrasound concentrate and direct the ultrasound delivered by said transducer to the surface of the liquid solution with an oblique incidence relative to the surface of the liquid solution to form a homogeneous fountain in an arc.

• la figure 1 schématise le principe de fonctionnement du procédé de micro-pulvérisation par ultra-sons selon l'invention,
• la figure 2 représente un premier moyen destiné à focaliser les ondes ultra-sonores à la surface du liquide,
• la figure 3 illustre un mode avantageux de réalisation de la focalisation des ondes ultra-sonores à la surface du liquide,
• la figure 4 représente en vue de coupe les différents éléments composant le diffusion selon la présente invention,
• la figure 5 représente en vue de coupe le transducteur,
• la figure 6 montre le diagramme de rayonnement d'un transducteur apodisé.

The invention will be better understood on reading the following description accompanied by attached drawings, among which:

• FIG. 1 diagrams the operating principle of the ultrasonic micro-spraying method according to the invention,
• FIG. 2 represents a first means intended to focus the ultrasonic waves on the surface of the liquid,
• FIG. 3 illustrates an advantageous embodiment of the focusing of the ultrasonic waves on the surface of the liquid,
• FIG. 4 represents in section view the various elements making up the diffusion according to the present invention,
• FIG. 5 represents a section view of the transducer,
• Figure 6 shows the radiation diagram of an apodized transducer.

The present invention relates to a micro-spraying process of a liquid solution by ultrasound as well as a micro-droplet diffuser for the vaporization of a liquid solution allowing the implementation of said process. It will find its application in particular in the medical environment for the disinfection of premises by diffusion of a disinfectant product.

Nowadays, asepsis of surgical premises by air is widely used. To do this, a suitable chemical is sprayed into the atmosphere of the room using a diffuser. Currently, two types of diffusers are mainly used, which are characterized according to their principle of spraying the liquid solution, namely with a fan or a nozzle, as mentioned above.

Furthermore, the technique of spraying a liquid by ultrasound is known, used in low-power humidifiers according to which ultrasonic waves are maintained in a liquid bath. The waves on the surface cause a small spray of central water accompanied by the production of drops which, in combination with micro-bubbles created by cavitation generate a fog.

In the case of disinfection of medical premises by spraying with a liquid solution, it is imperative to be able to dispense at least two liters per hour of disinfectant product. Furthermore, to avoid any phenomenon of air supersaturation, it is preferable to limit the size of the liquid micro-droplets to 0.3 microns. Beyond this, the atmosphere cannot absorb the liquid element in gaseous form within a reasonable time and there is a risk of condensation or non-vaporization.

It is with these objectives of capacity and control of micro-spraying, in particular at the level of the homogeneity of the droplets generated that the present invention has been developed.

For the application of the micro-spraying method of the invention, as shown diagrammatically in FIG. 1, there is the bath 1 of liquid solution intended to be micro-sprayed, as well as a source 2 of ultrasound. The frequency used for ultrasound emissions is not imposed; however the range is from 0.5 megahertz to 5 megahertz is recommended.

Up to now, we have been exploiting the source of ultra-sounds in a “wild” way, that is to say that we are content to direct the waves towards the surface without more precision.

According to the method of the present invention, the ultrasonic waves 3 are focused on the surface 4 of the bath 1. Under these conditions, it is now believed that micro-bubbles are created by cavitation which burst on the surface of the liquid and which will generate a significant production of micro-droplets and that it has a reduced size, less than 0.3 microns.

According to the present invention, it is recommended to focus the ultrasonic waves 3 on the surface 4 of the bath with an oblique incidence relative to the level to form a homogeneous fountain 5 in the form of an arc of a circle, as illustrated in FIG. FIG. 1. Thus, there is creation of a fountain 5 which extends along the surface of the liquid and there is a formation of a mist 6 or aerosol all along the fountain 5.

The fountain 5 forms a jet of cylindrical liquid which flows regularly. In general, for a given power, the regularity of flow of the fountain 5 is optimum.

Thanks to the inclination of the fountain 5, the micro-bubbles 7, created inside the fountain 5, explode on the surface and form the aerosol 6. Thanks to the focusing in a zone 4 of the surface of the liquid , the acoustic waves propagate in the jet of the fountain 5 under high power, hence the creation of numerous micro-bubbles 7.

Care must be taken to ensure the homogeneity of the micro-droplets that form the aerosol 6 and in this regard, it is necessary to have a large surface area for the fountain 5 so that the micro-bubbles can freely emerge throughout the course of the liquid jet. Compared to an almost vertical fountain, the inclined fountain of the invention has an upper surface for a given energy and flow rate.

The power of ultrasound generally ranges from about 1 to 3 watts. For each power, the fountain has an ideal conformation that must be sought.

As an indication, it is desirable to have a sufficient fountain length as long as possible of the order of 1 to 10 cm for a central elevation above the liquid level with a jet diameter of three to five millimeters.

If the diameter of the fountain is too small, there is an increase in projections detrimental to the size of the micro-droplets.

As far as possible, secondary radiation is avoided which constitutes energy losses and can disturb the proper functioning of the production of calibrated micro-droplets. This is why a directional source 2 is used which in particular does not have secondary radiation lobes.

There are several principles for focusing the ultrasonic waves on the surface of the bath. The example in FIG. 2 shows the use of a source 2 whose profile concentrates the radiated waves 3 towards a point 4 of the liquid surface. In practice, the use of a transducer 2, the surface of which has been hollowed out in a concave profile in order to direct the waves towards a focal point, gives certain results, but not fully satisfactory.

Admittedly, a greater mist was created, but the presence of large unwanted droplets was recorded. This lack of homogeneity in the particles formed is detrimental to the complete vaporization of the aerosol produced.

On the other hand, better results have been obtained using a source 2, as illustrated in FIG. 3, the radiation of which is focused by reflection on an appropriate geometric surface 8. The geometric profile of the surface can be determined by applying the laws of reflection of waves on a surface.

FIG. 4 represents a diffuser 9 of micro-droplets for the vaporization of a liquid solution 10 authorizing an implementation of the method described above.

The diffuser 9 comprises a device 11 for producing micro-droplets by ultrasound, placed in a vein 12 for air circulation, for entraining and diffusing into the atmosphere the micro-droplets produced. In the example chosen, the circulation of air in the stream 12 is ensured by means of a motorized propeller 13.

The device 11 for producing micro-droplets firstly comprises a source 14 of ultrasound immersed in the bath 10 of solution to be vaporized and means 15 for concentrating the ultrasounds 16 on the surface 17 of the liquid solution 10.

According to the invention, the means for focusing the ultrasonic radiation are in the form of a reflection surface 18 of ultrasound with a geometric profile suitable for concentrating the radiation at a point 17 of the liquid level 10.

One can for example use a metal mirror of parabolic shape, made of a metallic material such as very hard stainless steel and perfectly polished and homogeneous.

In the example chosen, the reflecting surface 18 is formed directly by the wall of the container containing the liquid solution to be vaporized. This container has at its upper part an opening through which the micro-droplets of mist are entrained by the circulation of air set in motion by the fan 13.

It is important to work with a constant liquid level 10 so that the setting of the focal area 17 is always perfectly adjusted. In this sense, an overflow hole and a filling pump are used to keep the liquid solution always at the same level.

Figure 5 shows in detail the embodiment of the source of ultrasound 14. This is only an exemplary embodiment and other implementations could of course be adopted.

The transducer used is a pellet 19 of piezoelectric material such as aged ceramic. The front face of the patch 19 rests on a metal cup 20, for example made of stainless steel which has an electrical connection terminal. The tablet 19 and the cup 20 are placed in a housing 22 preferably made of an elastic or rubberized material.

A second cup 23 rests on the back of the pad 19 by means of lugs 24 which provide electrical contact. The cup 23 also includes an electrical connection lug 25. The welds must be avoided and the pellet is cooled on the liquid side.

By adjusting the thickness of the patch 19, the resonant frequency of the ultrasound source is adjusted. The diameter of the pellet should preferably remain of reduced size, in particular of around twenty millimeters for a frequency of two megahertz, this to limit the appearance of lobes of secondary radiation.

Of course, the use of several sources in parallel with ultrasound can perfectly be envisaged.

FIG. 6 represents the desired radiation diagram for a source of ultrasound in the context of the present invention. The patch of the transducer comprises two metallized surfaces 26 and 27 respectively of different surfaces. With such an asymmetry, the radiation lobe 28 is unique, the traditional secondary lobes are completely eliminated. The use of an apodized tablet 19 is recommended.

In the case of disinfection of premises, the spraying of approximately two liters per hour of liquid solution is considered using a fan of approximately one thousand cubic meters per hour of flow and several independent sources of ultrasound and essentially of different frequencies.

This would make it possible to use a disinfectant solution with micro-droplets of different sizes and to improve the effectiveness of the product.

Other embodiments of the present invention as described in the claims within the reach of ordinary skill in the art could also be envisaged without departing from the scope thereof.

Claims (9)

1. Process for micro-spraying a liquid solution using ultrasounds, intended, in particular, to form a spray of disinfecting produits, for asepticizing medical or other premises, according to which ultrasounds (3) are generated in a bath (1) of liquid solution (10) and the said ultrasonic waves (3) are focussed at the surface of the bath (1), characterized in that the beam of ultrasonic waves (3) is directed at an oblique angle of incidence in relation to the surface of the liquid solution (1, 10) to form a homogeneous arc-shaped fountain.
2. Process for micro-spraying a liquid solution using ultrasounds according to claim 1, characterized in that the ultrasonic waves (3) emitted by a transducer (2) are focussed by reflection from a geometrical surface (8) appropriate for directing the beam of ultrasonic waves (3) at the said oblique angle of incidence in accordance with the laws governing the reflections of waves from a surface.
3. Process for micro-spraying a liquid solution using ultrasounds according to claim 2, characterized in that the power and/or the frequency of the ultrasonic waves (3) is adjusted in order to obtain a fountain (5) with a length of approximately one to ten centimetres and a diameter of three to five millimetres.
4. Micro-droplet diffuser for the vaporization of a liquid solution (10), intended, in particular, for the emission of a vapour of disinfecting products, and designed for implementing the process according to claim 1, including a device (11) for producing micro-droplets using ultrasounds, which is placed in an air circulation stream (12) for entraining and diffusing the micro-droplets, and which includes means for generating ultrasounds (3) in the liquid solution (10) and for focussing the said ultrasounds at the surface of the said liquid solution, these means taking the form of a transducer (14), characterized in that the said transducer (14) is arranged in the liquid solution (10) in such a way that the beam of ultrasonic waves (3) is emitted at an angle of incidence oblique in relation to the surface of the liquid solution (10) with a view to obtaining a homogeneous arc-shaped fountain (5).
5. Micro-droplet diffuser for the vaporization of a liquid solution (10), intended, in particular, for the emission of a vapour of disinfecting products, and designed for implementing the process according to claim 1, including a device (11) for producing micro-droplets using ultrasounds, which is placed in an air circulation stream (12) for entraining and diffusing the micro-droplets, and which includes means (15) for focussing at the surface of the liquid solution the ultrasounds (3) output by a transducer (14) within the liquid solution (10), characterized in that the means (15) for focussing the ultrasounds (3) direct the ultrasounds output by the said transducer (14) to the surface (17) of the liquid solution (10), and concentrate them thereat, at an angle of incidence oblique in relation to the surface of the liquid solution (10) to form a homogeneous, arc-shaped fountain.
6. Micro-droplet diffuser according to claim 5, characterized by the fact that the means for directing and concentrating the ultrasounds (3) take the form of a a surface (15) for reflecting the ultrasounds (16) having a suitable geometrical profile for directing the said beam of ultrasonic waves at the said oblique angle of incidence according to the laws governing the reflection of the waves from a surface.
7. Micro-droplet diffuser according to claim 6, characterized by the fact that the reflecting surface (15) is formed by the wall of the recipient containing the liquid solution (10) to be vaporized.
8. Micro-droplet diffuser according to claim 7, characterized by the fact that the reflecting surface is formed by a perfectly polished and very homogeneous parabola shaped metallic mirror.
9. Micro-droplet diffuser according to either of claims 4 or 5, characterized by the fact that the transducer (14) is apodized.

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