From Big Medical Encyclopedia

AEROSOL DEVICES — devices for transfer of substances in a condition of aerosols. And. at. were widely adopted in various areas. They enter in quality, an element many technological processes, are used in devices of chemical, food, building industry, in devices for fuel burning in piston engines and turbines of internal combustion, in jets and fire chambers. In medicine and veterinary science And. at. apply to disinfection and disinsection, aerogenic vaccination, inhalation and outside chemotherapy (see. Aerosoltherapy ). In crop production and forestry And. at. apply to fight against harmful insects and causative agents of diseases. And. at. found application in military science for creation of smoke screens. And. at. widely apply in the course of use of many products of household chemicals and perfumery and cosmetic products.

And. at. are used on the earth (figurative, hinged, self-propelled), and also in air (mounted by airplanes or helicopters).

Transfer of substance in a condition of an aerosol (see. Aerosols ) it can be carried out only at the time of use of drug since, unlike emulsions and suspensions, the aerosol cannot be prepared in advance. Spraying of solids goes to two stages: in the beginning substances are exposed to crushing, and then spraying. The mechanism of spraying of liquids in all cases is that under the influence of hydraulic pressure, centrifugal or aerodynamic force liquid is extended in narrow streams (threads) or films, to-rye then break up to drops under the influence of surface tension forces.

The main element of any device for receiving dispergatsionny aerosols is the nozzle. In mechanical nozzles and centrifugal sprayers the fluid jet is split up under the influence of the centrifugal forces arising at rotation of a stream or the sprayer. In hydraulic nozzles spraying is reached at the expense of friction forces arising on an interface liquid — gas as a result of the high relative speed of gas and liquid. For movement of a stream concerning air use various ways. The first way — liquid follows with high speed in a motionless gaseous fluid; for spraying its motive energy is used. On the second way the liquid following with a small speed in a moving gas flow is crushed at the expense of its motive energy.

Devices for generation of aero disperse systems are called aerosol generators. They share: 1) on the devices creating aerosols by method of dispersion due to crushing (spraying) of rather large volumes liquid or solids on particles of the small sizes; 2) devices for creation of aerosols by a condensation method when the colloido-dispersion phase arises from molekulyarnodispersny (gaseous).

The generators used for receiving dispergatsionny aerosols can be divided into three groups: mechanical, pneumatic and ultrasonic. Carry centrifugal sprayers and sprayers of direct action to mechanical generators. The principle of operation of centrifugal sprayers is that raspylivayemy liquid twists in the channel or in the vortex camera and then through a nozzle is thrown out a gaseous fluid. At the same time the fluid jet breaks up to particles, forming an aerosol. Pressure of liquid before a nozzle makes from 6 to 60 kg/cm 2 .

Sprayers of direct action are based on emission from a nozzle of not twirled stream of raspylivayemy liquid with high peripheral speed. Pressure at the same time can reach the size of 1000 kg/cm2. Mechanical sprayers have considerable productivity, demand high pressures on the sawn liquid and are, as a rule, a little suitable for use in the medical aerosol equipment, and to a thicket are used in the disinfection equipment (see below the section Aerosol devices for disinfection and disinsection).

Fig. 1. Schematic diagram of the centrifugal generator: 1 — a circular nozzle; 2 — a disintegrator (shooters specify the direction of the movement of raspylivayemy liquid in a cone; shooters in a snivel — an exit of an aerosol; an arrow at the top of the drawing — rotation of a cone).

Operation of the centrifugal generator (fig. 1) is based that raspylivayemy liquid climbs walls of the soaking-up cone set in rotary motion by the electric motor or an air turbine and goes on disks. Under the influence of centrifugal force the liquid film breaks from disks and fine aerosol particles and larger drops are formed. At hit of the particles and drops moving by inertia on plates of a disintegrator there is a further crushing of drops, and the largest, settled on plates of a disintegrator and walls, flow down back in a tank for raspylivayemy liquid. With increase in speed of rotation of disks the speed of fluid movement on escaping of a nozzle increases, productivity of the sprayer increases and there is a reduction of average radius of the generated particles.

The greatest distribution was gained by pneumatic generators (sprayers), in to-rykh sawing is carried out by a gas jet (steam). At the same time ejector sprayers are, as a rule, used. Pressure of gas before a nozzle from 0,5 to 2,0 kg/cm 2 .

Fig. 2. Schematic diagram of the pneumatic generator: 7 — an air jet; 2 — a separator; 3 — a liquid nozzle; 4 — raspylivayemy liquid (the direct arrow specifies the movement of compressed gas; curved shooters — an exit of an aerosol).

The elementary pneumatic generator (fig. 2) works as follows. Compressed air, oxygen or water vapor comes to an air jet and leaves it with high speed. It is resulted by depression and raspylivayemy liquid climbs a liquid nozzle, gets to a gaseous fluid, pulses and breaks up to drops. The particles which are formed at disintegration move by inertia and get on a separator. Coarse particles partially break into smaller, and are partially besieged and flow down back, mixing up with raspylivayemy liquid.

Fig. 3. Schematic diagram of the electroaerosol generator: 1 — an air jet; 2 — a liquid nozzle; 3 — raspylivayemy liquid; 4 — the ball serving as a separator. On an air jet positive electric potential moves (+), on a liquid nozzle negative electric potential moves (—); in the drawing at the left — a tube for an exit of a negative aerosol. Fig. 4. Schematic diagram of the supersonic aerosol generator: 1 — the spraying chamber; 2 — the valve for reduction of excessive pressure in the spraying chamber; 3 — a tube for supply of medicinal substance; 4 — a vessel for medicinal liquid with a sound-transmitting bottom; 5 — terminals for connection of the generator of electric fluctuations of ultrasonic frequency; 6 — the special plate generating ultrasonic fluctuations (piezoelectric transducer); 7 — water for carrying out ultrasonic fluctuations to a vessel with medicinal substance; 8 — a point of the greatest intensity of ultrasonic fluctuations (focus) where the aerosol is formed of medicinal liquid; 9 — an aerosol; 10 — a mouthpiece; 11 — the valve for air delivery which mixes up with the inhaled aerosol.

Kind of the pneumatic generator is the electroaerosol generator (fig. 3). Compressed gas comes to an air jet, and raspylivayemy liquid podsasyvatsya through a liquid nozzle. The ball can serve as a separator. On an air jet positive potential, and on a liquid nozzle and a separator — negative potential moves. The fluid jet following from a nozzle breaks up to particles, to-rye owing to electrostatic induction get a negative charge (if to change poles of electrodes, then particles will gain positive charge). This method of electrization of particles electrostatic induction is the most widespread in the medical aerosol equipment.

Pneumatic centrifugal (vortex) sprayers are used to receiving an aerosol with a solid dispersed phase. Air or oxygen comes via the channel executed in the case to the spraying chamber, in a cut there is previously crushed sawn powder. At an exit of a gas stream the whirlwind is formed of the channel directed on a tangent to the cylindrical camera, to-ry breaks from the surface of powder of a particle and takes out it through outlet opening. Thus there is a «superficial» raspylivaniye of powder, level to-rogo is below an input of gas in the camera. In process of ablation of particles consolidation of a layer of powder and formation of well streamline profile happens a turbulent flow of gas, ablation of particles decreases and then stops. At increase in speed of an air flow the raspylivaniye renews. In nek-ry cases apply the method of a raspylivaniye of powder consisting in blowing off of gas through its layer.

Generation of an aerosol at an ultrasonic method is carried out by energy of the ultrasonic fluctuations with a frequency from 0,8 to 2,5 MHz focused on the surface of the sawn liquid. The top of the fountainlet which is formed under pressure of these fluctuations breaks up to aerosol particles, to-rye a gas flow are taken out from the spraying chamber.

Supersonic generators (fig. 4) possess high in comparison with pneumatic productivity, and the aerosol generated with their help has a narrow range of the sizes. At the same time with increase in frequency of fluctuations the average radius of particles decreases. Productivity of the generator is regulated by intensity (amplitude) of ultrasonic fluctuations.

Fig. 5. Hydraulic sprayer automax.: 1 — a tank; 2 — the handle of the pump; 3 — a cover of an opening for filling of solution; 4 — a nozzle; 5 — a hose; 6 — a bar; 7 — zaplechny belts.
Fig. 6. Motor sprayer of MRZh-2 liquids: 1 — capacity for gasoline; 2 — a frame; 3 — the engine; 4 — the pump; 5 — a comb for connection of hoses with tips sprayers; 6 — the manometer.

Aerosol devices for disinfection and disinsection. The abundance and a variety of objects and conditions of disinfection and disinsection do not allow to be limited to one type of the device for creation of aerosols. Treat hydraulic sprayers hydropanel (see), automax. (fig. 5), dezinfal, the motor sprayer of liquids — MRZh-2 (fig. 6), applied in practice of medical disinfection and disinsection. Necessary pressure for ejection of liquid from a tank in the hydropanel, an avtomaksa and the dezinfal is created by means of manual piston pumps, in the device MRZh-2 — by means of the gear pump.

Fig. 7. Hand sprayer of ZhR-6 liquids: 1 — the pump; 2 — a siphon pipe; 3 — capacity for solution.

Pneumatic sprayers are presented by hand sprayers of ZhR-6 liquids (fig. 7) and the powders PR-1, the sprayer of low pressure RND-1, the opylivatel who is a part of the combined KDU disinfection installation. The specified devices create the aerosols containing coarse particles and giving the chance to receive considerable concentration of disinfecting drugs on surfaces.

For receiving the high-disperse, rather long not settling aerosols usually use condensation methods. Condensation aerosols are formed at volume condensation of supersaturated steams. The principle of operation of the corresponding devices consists in administration of solution of a disinfectant or insecticide in a flow of the hot gas moving with high speed. Gas turbines, internal combustion engines, turbojet and jets can be a source of hot gases for evaporation of solutions of drugs.

Fig. 8. Schematic diagram of the aerosol AG-UD-2 generator: 1 — a tank with combustible (gasoline); 2 — a tank with raspylivayemy liquid; 3 — a nozzle in which the gas stream breaks the liquid arriving from a tank (2) to a condition of an aerosol; 4 — the combustion chamber of fuel for receiving a high gas stream (it is specified by shooters); 5 — the pump airsupercharger.

In medical disinfection and disinsection use thermomechanical generators to formation of high-disperse fogs. Formation of fogs in this case represents set of processes of mechanical spraying, full or partial evaporation of the formed drops and steam condensation after escaping of a nozzle in rather cold air. An example of this kind of devices is the aerosol generator of AG-UD-2 (fig. 8).

Recently compressorless, motorless thermomechanical aerosol generators of the pulsing type gained distribution; the device «Micron» and a figurative aerosol generator can be their example. Thermomechanical generators have rather big productivity that allows to apply them to processing of considerable volumes and areas. However allocation of products of fuel combustion causes an opportunity to use these devices in rooms only in absence of people and at respect for necessary precautions.

Aerosol (smoke) checkers are in certain cases applied to receiving high-disperse aerosols of insecticides. The principle of their action consists in use of warmth of exothermic reactions of pyrotechnic mix for sublimation of chemical, to-ry at the subsequent mixing with air forms a condensation aerosol. The aerosol checker represents the metal or cardboard cylinder supplied with a diaphragm and a cover. Ignition of a checker is made by means of ignition adaptation. During the receiving aerosols by means of checkers there is no need for the use of solvents because powdery reagents are mixed in checkers with the insecticide making up to 60% of mix. So, in the pesticidal checkers used for disinsection as actively active ingredient apply gamma isomer of hexachlorocyclohexane.

Rather recently for receiving insecticidal aerosols low-temperature checkers are offered, in to-rykh exothermic decomposition of reagents it is used for formation of water vapor and other carrier gases of an insecticide. In the course of work of checkers of this kind due to the lack of processes of burning rise in temperature is much less, than in pyrotechnic checkers. A large amount of water vapor and gases provides evaporation of an insecticide and its mixing with free air. Aerosol checkers are effective hl. obr. in fight against the flying insects; their use is reasonable in the nature and in non-residential premises.

Finely dispersed aerosols of insecticides with particles less than 10 microns in size can be received as a result of explosion of an aerosol bomb — a tight container from brittle material, in Krom there is a sprayed solid matter and carbonic acid under pressure from 3 to 20 at. For the prevention of aggregation of finely dispersed particles apply protective coating on their surface, napr, diethylene glycol of mono-laurate in number of 0,1 — 5% (on weight).

Fig. 9. Schematic diagram of an aerosol can: 1 — a protective cap; 2 — the sawing head; 3 — a cup of the valve; 4 — the case; 5 — shank bore of a cylinder with saturated steam of raspylivayemy liquid; 6 — a siphon pipe; 7 — the liquid which is subject to spraying in mix with propellant.

One of eurysynusic methods of receiving aerosols is use of superheated liquid. The corresponding devices carry the name of aerosol cans, aerosol packages or packagings under pressure. The aerosol can combines in itself the raspylitelny device and an energy source; it consists of the bottletight vessel (more often than metal) supplied with a siphon pipe and the device for regulation of an exit of drug (fig. 9). The release of an aerosol in the atmosphere happens through a diaphragm in the sawing head (during the pressing the last the valve opens) at the expense of pressure of the saturated steam which is in a cylinder over liquid, edges after escaping of a cylinder becomes superheated and as a result of rough boiling up breaks up in air to small drops. Then propellant evaporates, and chemical forms an aerosol of a dispergatsionny origin.

Thus, important feature of a method of dispersion by means of superheated liquid is an opportunity to receive aerosols with the set degree of dispersion, regulation a cut can be carried out by one of the next three ways: by a variation of the sizes of outlet opening; due to change of pressure of a saturated steam of the evacuating liquid and by means of a variable ratio between amount of chemical and the evacuating liquid. In the course of dispersion of chemicals by means of superheated liquid high-disperse aerosols with particles can be received, the sizes to-rykh are usually characteristic of condensation aerosols.

Use of an aerosol can is profitable for individual use when for disinfection or disinsection in small rooms it is necessary to create is rather long not settling aerosols, or for a uniform covering of the surfaces limited on the area a thin coat of drug. Aerosol cans — absolutely self-contained small-size periodically operating units — can be used in any conditions that gives the chance to recruit the population in anti-epidemic actions.

See also Disinfection devices .

Bibliography: Vitman L. A., Katsnel-s about B.'s N of and P and l e e in I. I. Sawing of liquid nozzles, M. — L., 1962; Fuchs N. A. Mechanics of aerosols, M., 1955; C etlinv.m. Aerosol cans, M., 1970, bibliogr.; C e t of l and N V. M. and Vilkovich V. A. Physical and chemical factors of disinfection, M., 1969; Eknadiosyants O. K. Spraying of liquids in the ultrasonic fountain, the Ultrasonic equipment, No. 1, page 8, 1966, bibliogr.; I r N y 10th V. S. Mechanization of veterinary and sanitary works, M., 1965.

V. I. Vashkov, V. M. Tsetlin; S. A. Glukhov (medical tekhn.).