US3124442A

US3124442A - Method and apparatus for manufacturing an aerosol

Info

Publication number: US3124442A
Authority: US
Publication date: 1964-03-10
Anticipated expiration: 1981-03-10

Description

T. A. RICH March 10, 1964 METHOD AND APPARATUS FOR MANUFACTURING AN AEROSOL Filed Jan. 17, 1962 [VJ entor 7%e0o0re A. F/a/J fly 4 4 W 6545 A'forvvey from higher altitudes.

United States Patent 3,124,442 METHOD AND APPARATUS FOR MANUFAC- TG AN AEROSQL Theodore A. Rich, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Jan. 17, 1962, Ser. No. 166,794 (Ilairns. ((11. 62-419) releasing the pressure to vaporize the liquid to obtain an aerosol in a fine spray form. Another conventional method consists of storing solid particles in a pressurized container and releasing the pressure to obtain an aerosol of the solid particles. A limitation'in either of these conventional methods is that the particles which com prise the aerosol are not available as discrete particles before they are dispersed in the air. In the liquid spray method there is no separation of the liquid particles, While inthe solid particle method, there is separation but the problem of coagulation of the particles exists. This inability to obtain discrete particles before dispersal as an aerosol is a limiting factor in determining the size of the particles which are obtained in the aerosol. Thus aerosol particles produced by the liquid spray method are small in size when the pressure is first released, at which time the pressure is high, and become larger in size :as the pressure decreases with time. Moreover, the minimum size of an aerosol produced by a spray is limited. Theparticles of an aerosol produced by the solid particle method are likewise irregular in size due to the problem of coagulation of the individual particles while stored within the container.' Further, the inability to store discrete particles before dispersal as an aerosol,

prevents obtaining an aerosol composed of particles of known uniform size when this is desired.

Within recent years the science of measuring particles has grown in importance but no recognized laboratory standard for particle size measurement'exists since no means has been available to store particles of known uniform size without coagulation during the storage period: .Another area-in which aerosols are important is in crop dusting from an airplane; Conventional crop dusting requires a low flying airplane for proper dispersal of the aerosol over the area to be treated. The release of an aerosol at high altitudes allows. it to be carried by the wind and there is little control on the area treated This need for a low flying airplane can become a problem if there are obstacles of considerable height on the ground, in the path of the airplane, and

can also have a possible harmful side'eifeot of frightening animals located within close proximity of the crop dusting. Therefore, a need exists tonconduc-t crop dusting Further, in areas such as the field of medicine, it may be desired to store particles, both animate and inanimate, in: such a manner as to prevent any interaction between the particles, or between the particles and the surrounding environment. Finally, the

study of particles is also important in developing filters such as for air conditioning equipment.

Therefore, one of the principal objects of this invention is to develop a new and i-mproved'aerosol which can be stored as discrete particles and will not coagulate over the period of time during storage.

Another object of this invention is to develop a new 3,124,442 Patented Mar. 10, 1964 and improved aerosol in which the particles are of uniform size.

Another object of this invention is to develop a new and improved aerosol that can be dispersed from a considerable altitude.

Still another object of this invention is to develop a i new and improved method and apparatus for producing encapsulated particles are stored by maintaining them at a low temperature during the storage period to forestall sublimation of the sheath, and thereby prevent coagulation since the particles are finitely separated from each other. Exposing the encapsulated particles to ambient temperature sublimates the solid sheath and causes the particles to become airborne. The method and apparatus for encapsulating the panticles employs a means in which the particles and gaseous carbon dioxide are mixed in a cold air stream to solidify the carbon dioxide about the particle. 'The encapsulated particles can be dispersed into the air immediately after they are formed, or they may be collected as amass having the general appearance of a flufiy mass of snow, then formed into the general shape of a snowball and stored at a low temperat-ure until the aerosol is to be dispersed at which time the snowball is released to the atmosphere.

The features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself together with turther objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings.

FIGURE 1 illustrates an apparatus for encapsulating and collecting aerosol particles.

FIGURE 2 illustrates a modification of the apparatus of FIGURE 1.

Referring particularly to the apparatus illustrated in FIGURE 1, there is shown a container designated by numeral 1, filled with solid carbon dioxide and maintained at ambient temperature. Due to the ambient temperature, the solid carbon dioxide sublimates and flows into the conduit means 2 in gaseous form. The conduit means may be a glass tubing. The gaseous carbon dioxide then passes through a filter 3 of conventional design to remove any contaminants which may have been present in the solid carbon dioxide. The filtered gaseous carbon dioxide then continues on its path through the conduit into the particle chamber 4; wherein are located the particles to be encapsulated. A pump 5 agitates the particles within the chamber 4to mix the particles with the incoming carbon dioxide, thereby causing a particle laden gaseous carbon dioxide stream to flow through conduit 6. Air at ambient conditions is pumped into conduit 7 by means of pump 8. The air passes through a dryer 9 of conventional design to remove any moisture in the air which could subsequently condense and freeze while passing through a cooling chamber and thereby clog the conduit. The dry air next passes through a filter it) of conventional design to remove any contaminants which might have been present in the ambient air and then passes into conduit 11. Conduits 6, 7 and 11 may be made of glass tubing. A first cooling chamber which 'terial such as expanded plastic.

is designated as a whole by the numeral 12, is comprised of a container 15, divided into two sections 13 and 14. The container may be made of metal or wood or a like material, and is lined with a thermal insulation ma- The body of the thermally insulated container 15, is enclosed by a cover 16. Conduits 6 and 11 carrying the gaseous carbon dioxideparticle mixture and filtered dry air, are joined to cooling tubes 17 and 18 respectively. The cooling tubes may comprise spiral copper tubing to obtain high heat transfer. Within the cooling chamber 12, the space in each section 13 and 14, surrounding the cooling tubes 17 and 18, contains a cooling medium to cool the gases and particles flowing through the cooling tubes. Thus solid carbon dioxide is contained within space 13 to lower the temperature of the gaseous carbon dioxide-particle mixture, and liquid nitrogen is contained within space 14 to lower the temperature of the filtered dry air. The outlets of cooling tubes 17 and 18 converge at junction 19, wherein the cold airupon striking the cooled carbon dioxide-particle mixture, causes the carbon dioxide to solidify about each of the particles, thereby encapsulating them. The outlet from junction 19 to chamber 20 may be a copper conduit 21 of constant cross-section as shown, or an expansion orifice, the latter resulting in a further reduction in temperature of the encapsulated particles which may be necessary under some conditions. The encapsulated particles, having a general appearance of miniature snow flakes, are drawn into a second cooling chamber 20 which may be a flanged cylinder of glass, sealed at its upper end in any conventional manner to the first cooling chamber 12 by means of the flanged section 22, and open at its lower end 23 to permit a vacuum pump 24 to draw a small vacuum thereby pulling the encapsulated particles from the junction 19 at which they were produced. A metal screen 25 having a layer of synthetic fur on its upper side encloses the lower end of second cooling chamber 20. The encapsulated particles are preferably deposited on the synthetic fur rather than the bare metal screen since there is less heat transfer with the fur, therefore, immediate melting of the snow flakes is avoided when the snow laden fur screen is removed to the ambient air. The snow flakes may be deposited to any desired depth on the fur. A flanged cylindrical'glass container 26 encloses cooling chamber 20, and the lower half of the space between the two

cylindrical surfaces

20 and 26 is filled with solid carbon dioxide 27, which is maintained at a slightly reduced pressure by the action of the vacuum pump 24 to obtain a lower temperature and thereby maintain the carbon dioxide which encapsulates the particles in a solid state. Flange 28 of container 26 is sealed to the bottom of cooling chamber 12 in the same manner as flange 22. Alternatively, flange 22 may extend outwardly to the region of flange 28 and there be sealed to both flange 28 and the bottom of chamber 12. A perfect seal is not required at the joint between the bottom of chamber 12 and the

flanges

22 and 28 since the purpose of this seal is merely to permit the snow flakes to be maintained at a temperature low enough to prevent sublimation of the carbon dioxide while stored on the fur. However, a gasket may be used at this joint if the temperature cannot be maintained sufliciently low in chamber 20 due to considerable air leaks at the joint. A cylindrical glass wall 29, concentric with the wall of container 26, is joined to the outer surface of container 26, at its upper and lower end. This glass wall 29 may extend up to the flange 28 and down to the bottom of container 26, even surrounding the bottom if necessary. The space 30 between

walls

26 and 29, is maintained at a vacuum thereby acting as a thermal insulation. snow flakes on the fur screen 25 can be viewed through the

glass walls

20, 26, 29 and when an appropriate amount is produced, the flakes may be removed by removing screen 25, The screen 25 may be removed by The production of 4- any of several methods. The bottom of container 26 may be made removable to permit access to screen 25, or the seal at flange 28 may be opened. Vacuum pump 24 is not intended to create an appreciable vacuum within

containers

20 and 26, but merely to aid in the flow of the gaseous carbon dioxide particles and air through the conduits and to draw off the produced encapsulated particles from junction 19 to prevent clogging at that point, and also to slightly lower the temperature of the solid carbon dioxide in region 27 to insure that the particles remain encapsulated while forming a flulfy snow mass on the fur screen. After the snow laden fur screen is removed from chamber 20, the fiufiiy mass of snow may be pressed into a generally snowball shape. The encapsulated particles in snowball form can be stored for considerable lengths of time with the asurance that the particles will not coagulate as long as the snowball is stored at a temperature below K. in the case of carbon dioxide encapsulated particles. Thus, if particles of known uniform size are available in particle chamber 4, they can be stored in a snowball form and transported to any location which has a need for particles of known size. Particles of size down to 5 10 cm. radius may be encapsulated by the method described herein.

The encapsulated particles are released as an aerosol of individual particles by exposing the snowball to the ambient atmosphere. If the snowball is released from a considerable altitude, as for crop dusting, the snowball will fall rapidly to the ground and dispersal can take place at a selected target. The dispersal from the snowball may be made in a variety of ways. Explosive scattering of the snowball into small pieces can be done by a powder charge or even by the pressure built up by the subliming solid carbon dioxide. Self dispersal requires a container with a small outlet through which the gaseous carbon dioxide streams with an appreciable velocity that carries the aerosol to the outer air and minimizes the diffusion of water vapor into the container. Self dispersal Without a container is difficult to obtain, since water vapor in the air condenses on the surface of the snowball as it is falling, and the surface tension restrains the aerosol particles, thereby preventing their escape.

The apparatus in FIGURE 1 therefore produces encapsulated particles by mixing gaseous carbon dioxide and the particles in one flow path of the system, introducing filtered dry air into a second flow path of the system, separately cooling each flow path and then mixing the output of both flow paths whereby the cold dry air causes the carbon dioxide to solidify and encapsulate the particles. FIGURE 2 illustrates a modified apparatus for producing encapsulated particles. In this arrangement filtered dry air is mixed with the particles, the mixture is subsequently cooled by liquid nitrogen and finally the cold particles traveling in the cold air stream are mixed with gaseous carbon dioxide and thereby encapsulated.

Referring particularly to FIGURE 2, wherein the numerals identical to those used in FIGURE 1 represent identical components, filtered dry air is pumped into conduit 11, the pump, dryer, and filter not being shown,

' but being similar to those indicated in FIGURE 1, and

this filtered dry air enters particle chamber 4. The particles to be encapsulated are located in particle chamber 4, and are agitated by blades 31 which are rotated by motor 32. The particle-air mixture then enters conduit 33 and exists into cooling chamber 34. Liquid nitrogen in container 35 is caused to drip into the cooling chamber in the region of the conduit 33 outlet, thereby cooling the particle laden airstream flowing therefrom. Thermal insulation 36 of the type disclosed in FIGURE 1 surrounds the cooling chamber 34 and liquid nitrogen container 35. Solid carbon dioxide located in container 1 is caused to sublime due to being maintained at ambient temperature and the gaseous carbon dioxide flows into conduit 2, through filter 3 and into the coolingchamber 34 wherein it is mixed with the cold particle laden airstream thereby causing the carbon dioxide to solidify about the particles, and encapsulate them. The encapsulated particles, appearing as miniature snow flakes, are drawn into a second cooling chamber 20, maintained at a low temperature by solid carbon dioxide 27, and are deposited on fur screen 25 with the aid of vacuum pump 24 in the same manner as disclosed for the apparatus in FIGURE 1. Storage of the 'encapsulted particles in the form of a snowball, and its subsequent release to the atmospherefor particle dispersal as an aerosol is performed in the same manner as disclosed in the description of FIGURE 1. Flow meters 37 and '38, located in the air and gaseous carbon dioxide conduits, respectively, are useful in determining the amount of encapsulated particles produced. Flow meters could likewise be employed in the conduits 6 and 11 of FIGURE 1 to indicate the volume of flow therein. All of the conduits and chambers in which there is a gas flow, air or carbon dioxide, are preferably cylindrical in shape with a minimum of sharp bends in the conduits to aid in the gas flow and prevent collection of any matter on the sides which would decrease the efiiciency of the system and could eventually block the flow. The conduits may be made of materials other than glass, the only requirement being that the conduit material does not react with the gas or particle flow. Copper is indicated as a preferred material in parts of the system Where high heat transfer is desired. The apparatus illustrated may also be employed to store liquid particles by forming a snowfall of carbon dioxide and spraying it with liquid droplets as it grows. At ambient temperature the carbon dioxide sublimates and disseminates the frozen droplets.

Having described a new aerosol and a new method and apparatus of producing the aerosol in accordance with the invention, it is believed obvious that other modifications and variations of the invention are possible in light of the above teachings. For example, pumps may be placed in all of the flow paths and controlled to regulate the resultant production of the aerosol. Furthermore, cooling means other than liquid nitrogen may be employed. Also, the encapsulating material is not limited to carbon dioxide, but may be any material characterized by its capacity to sublime, an example being camphor. It is obvious that different temperatures would be required if difiterent encapsulating materials are employed. Finally, the carbon dioxide need not'be initially in the container 1 in a solid state, but may be available as a gas stored in a tank. It is therefore to be understood that changes may be made in particular embodiments of the invention described which are within the full intended scope of the invention as defined by the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A method for producing an aerosol comprising the steps of encapsulating particles of size assmall as 5 X centimeter radius with a sheath of solid material which is characterized by its capacity to sublime, and exposing the encapsulated particles to ambient temperature when the aerosol particles are to be released.

2. A method for making particles airborne comprising the steps of encapsulating aerosol particles of size as small as 5X10- centimeter radius with a sheath of solid material which is characterized by its capacity to sublime, and exposing the encapsulated particles to ambient temperature when the aerosol particles are to be released thereby sublimating the solid sheath and causing the particles to become airborne.

3. A method for preventing coagulation of aerosol particles While storing an aerosol comprising the steps of encapsulating individual particles of size as small as 5 10' centimeter radius with a sheath of solid material which is characterized by its capacity to sublime,

collecting the encapsulated particles in a container maintained at a low temperature to prevent sublimation of the solid material, and maintaining the encapsulated particles at the low temperature during the period of storage.

4. A method of'manufacturing an aerosol to be stored comprising the steps of introducing gaseous carbon dioxide into a flow path of a system, admitting a filtered dry air stream into another fiow path of the system, introducing aerosol particles of size as small as 5 1O centimeter radius into oneof the flow paths, mixing the gasous carbon dioxide, dry air, and particles, and cooling the mixture to solidify the carbon dioxide on the particles to form a sheath enclosing the particles.

5. A method of manufacturing an aerosol comprising the steps of introducing gaseous carbon dioxide into a flow path of a system, mixing the gaseous carbon dioxide with aerosol particles of size as small as 5 l0" centimeter radius under controlled conditions, admitting a filtered dry air stream into another flow path of the system, separately cooling the flow paths of particle laden carbon dioxide and air, and mixing the output of both flow paths to solidify the carbon dioxide about the particles thereby encapsulating them.

6. A method for storing an aerosol comprising the steps of introducing gaseous carbon dioxide into a fiow path of a system, admitting filtered dry air into another flow path of the systems, suspending aerosol particles of size as small as 5 l0- centimeter radius in the dry air under controlled conditions, cooling the particles and dry air, mixing the gaseous carbon dioxide and cooled particles and dry air to solidify the carbon dioxide on the particles, thereby encapsulating them, and maintaining the encapsulated particles at a low temperature to prevent coagulation during the storage period.

7. A method of dispersing an aerosol comprising the steps of encapsulating aerosol particles of size as small as 5X 10- centimeter radius with a sheath of solid carbon dioxide, collecting the encapsulated particles in a container maintained at low temperature to prevent sublimation of the carbon dioxide, forming the collected encapsulated particles into a generally snowball shape, and exposing the snowball to atmospheric conditions to permit a dispersal of the aerosol particles as the carbon dioxide sublimated.

8. Apparatus for producing an aerosol comprising, means for releasing a flow of material characterized by its capacity to sublime into a first conduit means in gaseous form, means for introducing a flow of filtered dry air into a second conduit means, means for suspending aerosol particles of size as small as 5X 10" centimeter radius in one of the gas flows, means for cooling at least one of said gas flows, and a common outlet means for mixing said gaseous material, filtered dry air, and aerosol particles in a cold atmosphere, thereby encapsulating said particles with said solid material within said air stream.

9. Apparatus for producing a carbon dioxide aerosol comprising, a container means for releasing carbon dioxide in a gaseous form into a first conduit means, a chamber under controlled flow pump conditions for suspending particles of size as small as S lO-' centimeter radius in the gaseous carbon dioxide flow, means for introducing an ambient air stream into a second conduit means under controlled flow pump conditions, said air stream being dried and filtered in said second conduit means, a cooling chamber container one section for receiving said first conduit means with the gaseous carbon dioxide and suspended particles therein and a second section for receiving said second conduit means with the filtered dry air stream therein, an outlet means in said cooling chamber maintained at a cold temperature and being connected to the outlets of both of said conduit means to mix the cooled carbon dioxide, particles and air to eifect encapsulation of the particles by solidified carbon dioxide, and a second cooling chamber immediately adja- 7 cent to said outlet means for capturing and storing said encapsulated particles without coagulation.

10. Apparatus for manufacturing an aerosol that is to be stored for a time before dispersal comprising, means for introducing a filtered and dried air flow in a first conduit means, a chamber for agitating particles to cause said particles to become suspended in said air flow, means for releasing carbon dioxide in a gaseous form into a second conduit means, means for mixing the particles and carbon dioxide within the air flow, a first cooling means to solidify the carbon dioxide about the particles thereby Y encapsulating them Within said air flow, a second cooling means adjacent said first cooling means, said second cooling means preventing sublimation of the carbon dioxide While said encapsulated particles are being collected, and means for collecting said encapsulated particles.

References Cited in the file of this patent UNITED STATES PATENTS 1,970,437 Snitkin Aug. 14, 1934 2,570,074 Rupp Oct. 2, 1951 2,601,298 Keith June 24, 1952 2,696,718 Garbo Dec. 14, 1954 2,702,091 Smith Feb. 15, 1955 2,966,037 Gifford Dec. 27, 1960

Claims

1. A METHOD FOR PRODUCING AN AEROSOL COMPRISING THE STEPS OF ENCAPSULATING PARTICLES OF SIZE AS SMALL AS 5 X 10**-7 CENTIMETER RADIUS WITH A SHEATH OF SOLID MATERIAL WHICH IS CHARACTERIZED BY ITS CAPACITY TO SUBLIME, AND EXPOSING THE ENCAPSULATED PARTICLES TO AMBIENT TEMPERATURE WHEN THE AEROSOL PARTICLES ARE TO BE RELEASED.