FR2781698A1 - Aerosol generator for spraying liquid comprising a turbine aerosol generator - Google Patents

Abstract

The generator comprises a turbine (11) that generates an aerosol action to spray a supply liquid (16) aided by a rotating element (12). The air and fluid supply are controlled to adjust the operating pressure of the aerosol.

Description

AEROSOL GENERATOR OPERATING IN A WIDE RANGE

PRESSURES AND TEMPERATURES

  Field of the Invention The invention relates to an aerosol generator by mechanical spraying of a liquid using a rotary element preferably driven by an air bearing turbine, at an adjustable speed of rotation. This aerosol production technique allows operation in a wide range

  range of pressures and temperatures.

  In general, the invention applies to many types of aerosols which can be used in various fields; in particular, it finds applications in the fields of agriculture,

  microelectronics, nuclear, medical, etc.

  STATE OF THE ART There are currently many types of aerosol generators, used depending on the applications to be implemented. In fact, the needs in terms of operating conditions (temperature, pressure, gas flow, etc.) and characteristics of the aerosols to be produced (median diameter, standard deviation of the particle size distribution, mass flow, etc.) differ very widely. from an application domain to

another.

  The demand for aerosol production devices usable in several fields of application is therefore very high. An aerosol production device (or aerosol generator) making it possible to obtain an aerosol having the characteristics given below can meet this demand: median diameter of the dry solute residue varying between 0.5 and 5 μm, deviation -type of particle size distribution as low as possible (less than 1.6) and mass production flow

greater than 10 mg / h.

  A generator producing such aerosols can be used, in particular, in an atmosphere representative of that prevailing in the confinement enclosure of a nuclear reactor. In this case, the aerosol generator must be able to operate under the following operating conditions: * absolute pressure between 1 and 7 bar, * temperature varying from 20 to 160 C; and * high relative humidity (i.e.

up to 95%).

  Such operating conditions require, moreover, a relatively simple aerosol generator implementation with, in particular, little

  in situ adjustments and high reliability.

  Devices for spraying a liquid solution by an ultrasonic wave fountain or by centrifugal forces have been proposed to meet these needs. Such devices are described in the following documents: "Study of the controlled fragmentation of liquid jets from a rotating disc and realization of a generator of mono dispersed droplets", CHICHEPORTICHE JM Doctoral thesis of Pierre and Marie University Curie, 1993; "Aerosol generators calibrated" PLUS "(Ultrasonic Liquid Spraying), CHARUAU J., Radiation protection, vol. 26, n 2, p. 405-409, 1991; Generators with ultrasonic fountain are difficult to implement for conditions operating conditions different from the ambient conditions and therefore for the operating conditions mentioned above These difficulties of implementation are described by DUCRET D., ROBLOT D. and VENDEL J. in "Production of aerosols in pressure and in temperature", day 11 'Studies on aerosols, COFERA, Paris, 1995. As for devices for spraying a liquid solution by centrifugal forces generated by the rotation of a disc, their use, for aerosols' of small dimensions, is linked to the technological capacity to obtain high speeds of rotation. High speeds of rotation can be obtained by using an air bearing turbine associated with a capillary wave generator ci Such a device produces, with a high mass flow rate, monodispersed drops whose diameters are between 100 and 1000 μm, as described in the article by CHICHEPORTICHE JM and CHANAL PY, entitled "Study of the controlled fragmentation of liquid jets generated from a spinning-disk and realization of a monodispersed droplets generator ", Journal of Aerosol Science,

flight. 25, supplement 1, 1994.

  This device therefore does not make it possible to produce droplets of solutions having a diameter less than 100 μm. However, aerosols whose diameter of dry solute residue is between 0.5 and 5 im can only be obtained from droplets of solutions having a diameter less than im. In addition, the operation of this device at a high temperature is too delicate to envisage industrial manufacture. DESCRIPTION OF THE INVENTION The object of the invention is precisely to remedy the drawbacks of the techniques described above. To this end, it provides an aerosol generator by spraying a liquid solution by centrifugal forces generated by the rotation of a circular element, conventionally called a rotating disc, making it possible to obtain droplets of approximately 20 μm and operating in a wide range of

pressures and temperatures.

  More specifically, the invention relates to an aerosol generator by spraying a liquid using a rotary element, the drive of which is preferably provided by an air bearing turbine. This aerosol generator comprises a channel for supplying the liquid to be sprayed passing axially, right through, the drive device of the rotary element, and provided with an end capable of projecting the liquid out of the channel,

  around which the rotary element is positioned.

  According to the invention, the air circulation in the turbine is preferably carried out by an air intake circuit and an exhaust circuit

  adjustable in pressure independently of each other.

  Advantageously, the air intake circuit in the turbine comprises a pressure reducer ensuring an adjustment of the air supply pressure to regulate the speed of rotation of the rotary element and / or the air exhaust circuit of the turbine comprises a micrometric valve associated with a pressure gauge to adjust the operating pressure of the turbine to the conditions of use, thus ensuring a good supply of the air bearings therefore a

stabilized rotation.

  According to one embodiment of the invention, the aerosol generator comprises an electromagnetic tachometer connected to the turbine for

  measure the speed of rotation of the rotary element.

  The air intake circuit may include a main intake channel for supplying air to the turbine rotor blades and at least two secondary intake channels for supplying air

the turbine bearings.

  According to one embodiment of the invention, the rotary element has an angled edge

  lively and a central conical recess.

  The aerosol generator of the invention can be installed in a spray enclosure supplied with drive air by an aeraulic circuit ensuring the heating and the adjustment of the flow rate.

  air entrainment of the droplets produced.

Brief description of the figures

  - Figure 1 schematically shows the aerosol generator of the invention located in a spray enclosure; and - Figure 2 shows the aerosol generator of the invention with its circuit

air circulation.

  Detailed description of embodiments of

  the invention In FIG. 1, the aerosol generator according to the invention is shown diagrammatically, installed in a spray enclosure, which constitutes an application

particular of the invention.

  In this figure 1, reference has been made to 1 the spray enclosure, 10 the aerosol generator and 2 the droplets produced by this

  generator in the spray enclosure.

  This spraying enclosure 1 comprises an air drive circuit 20 for introducing compressed air into the enclosure 1 and an air diffuser 3 which ensures the diffusion of this compressed air and which allows, in particular, the transport droplets 2 off

of the enclosure through the opening 4.

  The aerosol generator of the invention, referenced 10, comprises a drive device traversed, right through, by a supply channel

  13 around which a rotary element 12 is positioned.

  As will be described in more detail below, the rotary element 12 is a mechanical support of substantially conical shape which ensures, by rotational movements, the transformation of the received liquid into fine droplets. This rotary element will be called, in

  all description, "rotating disc".

  Preferably, the drive device of the rotary element is an air bearing turbine 11. It is this type of drive device which is shown in the appended figures and described below. The axis of rotation of the rotary disc 12 is a hollow cylinder, so that a supply channel 13 can be inserted therein allowing the circulation of the liquid solution to be sprayed 16 from the outside of the turbine to to the disc

rotary 12.

  The size of the droplets formed by the rotating disc varies depending, in particular, on the

disc rotation speed 12.

  This rotation of the rotary disc 12 is ensured by an air circulation in the turbine / disc assembly, and, more specifically, by the circulation of compressed air on the blades of the turbine rotor and in the air bearings of the turbine,

  described more precisely later.

  More specifically, the air circulation in the turbine consists of an air intake circuit

  and an air exhaust circuit 18.

  The role of the air intake circuit (or supply circuit) 15 is, on the one hand, to inject compressed air onto the blades of the turbine rotor and, on the other hand, to supply the air bearings of the turbine. A regulator 15a and a pressure gauge 15b placed at the start of the intake circuit 15 make it possible to modify the air supply pressure in the turbine and thus to adjust the speed of rotation of the disc. The exhaust circuit 18 evacuates the air from the turbine. Means 18a and 18b for adjusting the exhaust pressure make it possible to adjust the operating pressure of the turbine to the operating conditions. In the application of FIG. 1, where the aerosol generator is inserted in a spraying enclosure, an aeraulic circuit 20 can be associated with the enclosure 1. This aeraulic circuit 20 is designed to fulfill two concomitant functions: drying spray droplets and entrainment

aerosol.

  This air circuit can include a pressure reducer 21 which makes it possible to adapt the drive pressure as a function of the operating conditions of the aerosol generator, as well as a control valve 22 for adjusting the air flow rate, itself measured by a rotameter, referenced 23. The temperature of the drive air can then be regulated between 20 and 200 C by an electric heater 24, equipped with a PID regulator (proportional-integral-derivative)

  which allows adaptation to operating conditions.

  The adjustment of the air flow results from an optimization between the drying of the droplets and the quantity of carrier air. Depending on the operating conditions, this

  flow rate is between 0.5 and 5 m3 / hour.

  In Figure 2, there is shown so

  more precise the aerosol generator of the invention.

  The references in this figure 2 which are identical to those in figure 1 represent

identical items.

  The aerosol generator 10 comprises a turbine 11 axially traversed, right through, by the feed channel 13 which is inserted in the axis of rotation of the disc which is a hollow cyclinder, the feed channel being provided side outlet ports. Thus, the liquid to be sprayed 16 is brought directly to the center of the rotary disc 12, which ensures a uniform distribution of the liquid on the disc 12 and therefore good homogeneity of the spraying. This direct supply of the liquid 16 to the center of the disc 12 also makes it possible to avoid cluttering the upper part of the plane of the disc, hence reducing the losses by impaction of the droplets formed. In addition, it is necessary to ensure a constant constant flow for a range of values between 0.1 and 70 ml per minute, a stable liquid flow being necessary to induce the formation of a liquid film on the disc, this who

  reduces the size dispersion of the aerosols produced.

  In addition, this liquid injection system has the advantage of not requiring any positioning adjustment, therefore greater ease of use. The rotary disc 12 is linked to the turbine by means of an extension of the axis of rotation, under the disc. This extension is fixed on

  the turbine by a biconical clamp device.

  The supply channel 13 is linked to the turbine-disc assembly by a fixing device, referenced 9, which also ensures centering.

  of the channel with respect to the axis of rotation of the disc.

  The disc 12 is rotated by means of the rotor 8 and the air bearings 11a and 11b of the turbine 11, these operating by virtue of a circulation of compressed air. This consists of an air intake circuit 15 and a circuit

air exhaust 18.

  The air intake circuit 15 comprises, in the turbine 11, a main channel 19a which supplies the blades of the rotor 8 of the turbine and two secondary channels 19b and 19c which supply the bearings lla

and llb of the turbine.

  The compressed air necessary for the operation of the turbine 11 is therefore injected by the intake circuit 15 into the main channel 19a which opens onto the blades of the turbine rotor; the air is exhausted

  then through the exhaust circuit 18.

  The secondary channels 19b and 19c of the intake circuit (or supply circuit) supply the air bearings 11a and 11b, these counteracting the axial and radial forces of the rotor. This air circuit thus ensures a good supply of the air bearings of the turbine and therefore a reliable rotation whatever the operating pressure. The compressed air intake circuit also includes a regulator 15a, possibly associated with a pressure gauge 15b, making it possible to adjust the

  air inlet pressure in the turbine.

  The air exhaust circuit 18 includes a pressure gauge 18b associated with a micrometric valve 18a for adjusting the air outlet pressure of the

turbine.

  This set of pressure adjustments 15a and 18a / 18b makes it possible to adjust the speed of rotation of the disc 12 and thus to modify the size of the

aerosol droplets.

  In particular, to maintain a sufficient supply of air bearings, whatever the operating pressure of the turbine, the pressure of the exhaust circuit 18 is adjusted via the micrometric valve 18a and the pressure gauge 18b, to a value at least equal to that of

operating pressure.

  In other words, the speed of rotation of the disc 12 is controlled by adjusting a pressure difference between the intake and the exhaust of the air circuit of the turbine. For uses of this pressure generator, the exhaust pressure is fixed at a value at least equal to the operating pressure. Then the intake pressure is

  adjusted to obtain the desired rotation speed.

  The speed of rotation of the disc 12 is measured by means of an electromagnetic tachometer formed by a winding 14 and a signal analysis circuit 17; the operation of this electromagnetic tachometer is as follows: the current induced by the rotation of the ferromagnetic rotor, previously placed in the presence of a magnetic field, is amplified, by an amplifier 17b which receives as input the voltage from the winding 14 and a voltage supply 17a from 0 - 12 volts; the amplified current is then displayed on an oscilloscope 17d to verify the absence of parasites and the stability of the sinusoidal signal. A frequency meter 17c makes it possible to measure the frequency of the signal coming from the amplifier 17b; this is, in fact, directly equal to the

disc rotation speed 12.

  The speed of rotation of the disc 12 can thus be adjusted between 1000 and 6000 revolutions per second with good stability (+ or - 10 revolutions / sec) and this, whatever the pressure varying from 0 to 10 bars and for a temperature of operating from 20 to C. The rotation disk 12 of the device is, in fact, simply a mechanical support ensuring the transfer of centrifugal energy from the turbine to the liquid to be sprayed. Given the high rotational speeds necessary for the formation of fine droplets, the disc must be of small diameter; this diameter can be approximately 8 mm. In addition, a good balance of the masses around the axis of rotation is

necessary.

  According to one embodiment of the invention, this rotation disc 12 is made of stainless steel, by machining in the mass, with a central recess of conical shape favoring the centering and the distribution of the liquid on the whole of the disc and a sharp angle edge promoting ligament formation; the advantages relating to this ligament formation are described by J.M. CHICHEPORTICHE in the article entitled "Study of the controlled fragmentation of liquid jets from a spinning disc and production of a mono droplet generator

  dispersed ", already cited above.

  The geometry of the tachometer 14/17, as well as the geometry and the connections of the air intake and exhaust circuits according to the invention are optimized, on the one hand, to limit the size of the device and, d on the other hand, to avoid the presence of obstacles above the horizontal plane of the turbine in order to reduce the risks of impact of the

droplets produced.

  This aerosol generator of the invention can be used in studies related to nuclear reactors where the operating conditions are delicate (absolute pressure from 1 to 7 bar, temperature from 20 to 160 C and high water vapor rate) , or for particle tracing which consists in determining the behavior of aerosols in confined or ventilated spaces, or in laser velocimetry techniques by particle imaging which make it possible to study complex fluid flows, or in tests of water treatment system

  industrial gaseous effluents, produced in situ.

  The invention is not limited to the embodiment described above; it covers all variants and, in particular, the use of drive devices for the rotary element, other

  than the air bearing turbines previously described.

Claims (10)

  1. Aerosol generator by spraying a liquid using a rotary element (12), characterized in that it comprises a channel (13) for supplying the liquid to be sprayed (16) passing axially, right through, the drive device of the rotary element, and provided with an end capable of projecting the liquid out of the channel,   around which the rotary element is positioned.   2. Aerosol generator according to claim 1, characterized in that the drive device of the rotary element is a turbine air bearings (11).   3. Aerosol generator according to claim 2, characterized in that the air circulation in the turbine is achieved by an air intake circuit (15) and an air exhaust circuit (18), independently adjustable in pressure the other.   4. Aerosol generator according to claim 3, characterized in that the air intake circuit comprises a pressure reducer (15a) ensuring an adjustment of the air supply pressure of the turbine to adjust the rotation speed of the rotating element.   5. Aerosol generator according to claim 3 or 4, characterized in that the air exhaust circuit (18) comprises means capable of   adjust the turbine operating pressure.   6. Aerosol generator according to claim 5, characterized in that said means capable of adjusting the operating pressure of the turbine consist of a micrometric valve (18a) associated with a pressure gauge (18b).   7. Aerosol generator according to one   any one of claims 1 to 6, characterized in that   that it includes an electromagnetic tachometer (14, 17) connected to the turbine to measure the speed of rotation of the rotary element.   8. Aerosol generator according to one   any of claims 3 to 7, characterized in that   that the air intake circuit (15) comprises a main intake channel (19a) for supplying air to the rotor blades of the turbine and at least two secondary intake channels (19b, 19c) for supplying air the turbine bearings.   9. Aerosol generator according to one   any one of claims 1 to 8, characterized in that   that the rotary element (12) has a sharp angle edge   and a central recess of conical shape.   10. Device for spraying a liquid, characterized in that it comprises a generator   aerosols according to any one of claims   1 to 9 installed in a spray enclosure (1) supplied with air to drive the droplets by an aeraulic circuit (20) ensuring the heating and   regulation of the flow of this drive air.