GB2180776A

GB2180776A - Method for producing suspension in air of ultra-fine mist particles

Info

Publication number: GB2180776A
Application number: GB08622410A
Authority: GB
Inventors: Masahiko Izumi
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-09-21
Filing date: 1986-09-17
Publication date: 1987-04-08
Also published as: IT1196617B; SE8603728L; CH669834A5; BR8604462A; CN1004860B; AU6250586A; CA1265435A; DK426086D0; IN168582B; GB8622410D0; IT8648442A0; SE8603728D0; DK426086A; CN86106342A; FR2587628A1; NL8602323A; GB2180776B; AU577203B2; JPH0577466B2; JPS6268515A

Abstract

The interior of a room is cleaned by supplying thereto mist-carrying air suspending therein, per cubic foot, more than 2,000,000, preferably, more than 5,000,000, and more preferably, more than 10,000,000 ultra-fine moisture particles or micro- droplets of 0.5 microns or smaller in particle size, produced by passing air through an atomizer (1) in which a great number of ultra-fine mist particles or micro-droplets are produced by injecting water at a gage pressure of 0.3-5.5 kg/cm<2>, preferably, of 0.5-2.5 kg/cm<2> from a water injection pipe (2) with a large number of nozzles (3) of a diameter of 0.2-8 mm, preferably, of 0.5-3 mm against a side wall located at a distance of 10-150 cm from the injection nozzles (3). <IMAGE>

Description

SPECIFICATION Method for producing suspension in air of ultra-fine mist particles BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a method for producing a suspension in air of ultra-fine mist particles or micro-droplets of water, suspending per cubic foot more than 2,000,000, preferably, more than 5,000,000, and more preferably, more than 10,000,000 finely atomized mist particles or micro-droplets, and a method for cleaning the interior of a room by the use of such a suspension of ultra-fine mist particles.

Description of the Prior Art Clean air free of dusts and microbes is needed in hospitals, pharmaceutical plants, food manufactories, refrigerative food storage rooms, laboratories, experiment rooms and the like. In this connection, it has been the conventional practice to send in clean air through an air filter or to provide an air curtain at the entrance of a room. Nevertheless, difficulties are encountered in obtaining clean air of satisfactory quality by these measures even in combination with an air shower room.

Therefore, at the present moment, it is considered almost impossible to supply ultra-clean air or gas on an industrial scale in LSI and VLSl manufacturing plants, biopharmaceutical manufacturing plants, surgical operating rooms, precision machinery-washing plants, sterilized food manufacturing plants, refrigerative storage rooms and the like which require a severer contol to preclude intrusion of not only bacteria and viruses but also dusts particles of a size smaller than 0.5 microns.

Under these circumstances, the present invention contemplates to reply to the strong demand for a method for establishing a high degree of cleanness in refrigerative storage rooms, operating rooms, manufacturing plants or the like in various industrial fields.

As a result of an intensive study on the adsorptive air cleaning phenomenon of the moisture particles which are suspended in air, it has been found that, in addition to fine dust particles in air, even bacteria, mold fungi, spores and viruses can be removed by adsorption on mist particles by the use of air which contains more finely atomized moisture particles or micro-droplets substantially smaller than 0.5 microns at a rate of more than 2,000,000 particles, preferably, at a rate of more than 5,000,000 particles, more preferably, at a rate of more than 10,000,000 particles per cubic foot.Unexpectedly, it has also been found that a gaseous atmosphere suspending therein such finely atomized microdroplets can manifest the cleaning effect without wetting an object or article in the atmosphere despite the existence of moisture particles as long as they are in the form of ultrafine micro-droplets. A further study revealed that an ordinary gas can be highly cleaned into an ultra-clean state by passing the gas through a gaseous atmosphere suspending ultra-fine mist particles or micro-droplets, permitting to apply such highly cleaned gas directly to a room, a particular space or any other place needing supply of such an ultraclean gas.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a method of producing air suspending ultra-fine mist particles or microdroplets, which essentially comprises the steps of: injecting water in an atomizing chamber under pressure of 0.3-5.5 kg/cm2, preferably, under pressure of 0.5-2.5 kg/cm? from a water injection pipe with a large number of nozzles having a diameter of 0.2-8 mm, preferably, a diameter of 0.5-3 mm, bombarding the injected water against a wall located at a distance of 10-150 cm from the nozzles to produce ultra-fine mist particles or micro-droplets; and passing air through the atomizing chamber to entrain therein per cubic foot more than 2,000,000, preferably, more than 5,000,000, and more preferably, more than 10,000,000 ultra-fine micro-droplets of 0.5 microns or smaller in particle size, and a method of cleaning the interior of a room by circulating the mist suspending air thereinto.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Figure 1 is a diagrammatic longitudinal section of an atomizer embodying the present invention; Figure 2 is a diagrammatic cross-sectional view of a middle portion of the atomizer shown in Fig. 1; Figure 3 is a diagrammatic sectional view of a cyclone for removing moisture particles; Figure 4 is a view similar to Fig. 1 but showing another embodiment of the atomizer according to the invention; Figure 5 is a diagrammatic cross-sectional view of an upper portion of the atomizer of Fig. 4; Figure 6 is a diagrammatic cross-sectional view of a middle portion of the atomizer of Fig. 4; Figure 7 is a diagrammatic view of a cleaning system as applied to an actual semiconductor manufacturing plant; Figure 8 is a diagrammatic sectional view of a heat-exchanger to be connected posterior to the atomizer; and Figure 9 is a diagrammatic cross-sectional view of an upper portion of the heat-exchanger.

DESCRIPTION OF PREFERRED EMBODIMENTS According to the present invention, the atomizer is provided with a water injection pipe which contains, for example, 30 to- 1500 nozzles of a diameter of 0.2-8 mm, preferably, of a diameter of 0.5-3 mm. Water is fed to the injection pipe under high pressure and injected through the nozzles under pressure of 0.3-5.5 kg/cm2, preferably, under pressure of 0.5-2.5 kg/cm2 (gage pressure), spurting water through each nozzle at a rate of 1-3 I/min. The injected water is bombarded against a wall which is located at a distance of 10-150 cm from the nozzles, and atomized into ultra-fine micro-droplets, while air is fed into the atomizer at a velocity of 15-50 m/sec and at a rate of 3-300 m/min to entrain therein, per cubic foot, more than 2,000,000, preferably, more than 5,000,000, more preferably, more than 10,000,000 ultrafine micro-droplets of a diameter smaller than 0.5 microns.

Now, the method of the present invention is described more specifically with reference to the drawings which illustrates examples of the apparatus suitable for carrying out the method of the invention.

Referring first to Fig. 1, there is illustrated an atomizer of the most fundamental form which is necessary for carrying out the present invention. The atomizer 1 is provided with water injection pipes 2 which are extended on and along the opposing inner wall surfaces of its atomizing chamber and each provided with a multitude of nozzles 3, preferably, in staggered positions relative to the nozzles of the opposing injection pipe. More specifically, each water injection pipe is provided with 30 to 1500 nozzles of a diameter of 0.2-8 mm, -preferably, of 0.5-3 mm to inject water under pressure of 0.3-5.5 kg/cm2, preferably, under pressure of 0.5-2.5 kg/cm2 (gage pressure) toward the opposing inner wall surface which is located at a distance of 10-150 cm from the nozzles.

The injected water is bonbarded against the opposing inner wall surface and atomized into ultra-fine micro-droplets, so that the atomizer 1 is filled with such ultra-fine moisture particles. On the other hand, air is blown into the atomizer 1 at a velocity of 15-50 m/sec and at a flow rate of 3-3000 m3/min through an air inlet 4 to entrain therein, per cubic foot, more than 2,000,000, preferably more than 5,000,000, more preferably, more than 10,000,000 ultra-fine micro-droplets before it leaves the atomizing chamber through an air outlet 5. In order to remove objectionably large droplets which may also be entrained, the air from the air outlet 5 is fed into a cyclone 6 through its tangential inlet 7. The air from the cyclone, which contains the ultrafine mist particles, is circulated to a room or rooms which need cleaning, and then returned to the atomizer for recirculation.

Figs. 4 through 9 illustrate another embodiment of the atomizer, which is provided with a temperature control for producing the suspension of ultra-fine micro-droplets or mist particles more efficiently.

In this case, the atomizer 40 has an evaporation pipe 47 of a refrigerator arranged spirally on and along the inner surface of its cylindrical atomizing chamber 41. The evaporation pipe 47 may be located in a slightly or completely offset position relative to water injection nozzle 45. The injection nozzles 45 are arranged such that water from the respective nozzles is sprayed perpendicularly against the opposing portions of the evaporation pipe 47.

The water injection pipe 44 is provided with 30 to 1500 nozzles of a diameter of 0.2-8 mm, preferably, of 0.5-3 mm to inject water under pressure of 0.3-5.5 kg/cm2, preferably, under pressure of 0.5-2.5 kg/cm2 and at a flow rate of 1 to 3 I/min through each nozzle.

The nozzles are located at a distance of 10-150 cm from the opposing wall surface.

The atomizer is provided with a filter 48, a water tank 49 and a pump 50 in series to its conical bottom portion 51. Accordingly, cold water is circulated in the direction of arrow B, namely, successively through water circulating pipe 46, injection pipe 44, cylindrical portion 41 of the atomizer, conical portion 51, filter 48, water tank 49 and pump 50 in that order.

A refrigerant, in particular, a high-temperature refrigerant (of 1"C to - 50C) is circulated through the evaporation pipe 47 in the direction of arrow C. Air is fed into the atomizer through an air inlet 42 in the direction of arrow A, and it is cooled while picking up the micro-droplets to form the aimed mist-carrying air, which is discharged through an outlet pipe 43 to serve for an intended purpose.As water is injected from the nozzles 45 in the water injection pipe 44 under pressure of 0.3-5.5 kg/cm2, preferably, under pressure of 0.5-2.5 kg/cm2 (gage pressure) and bombarded against the evaporation pipe 47 of the refrigerator and/or the side wall of the cylindrical atomizing chamber 41 which is located at a distance of 10-150 cm from the nozzles (E), it is atomized into ultra-fine micro-droplets and cooled (the water streams bombarded against the evaporation pipe 47 being sumultaneously cooled by heat exchange with the refrigerant flowing through the pipe 47). Air is passed through such an atmosphere, at a velocity of 15-50 m/sec and at a flow rate of 3-300" m3/min as indicated by arrow A.

While entraining therein the ultra-fine mist particles, the air itself is cooled by heat exchange with the cooled micro-droplets, forming mistcarrying air containing per cubic foot more than 2,000,000, preferably, more than 5,000,000, more preferably, more than 10,000,000 micro-droplets of a particle size of 0.5 microns or smaller. In this instance, droplets substantially larger than 0.5 microns in particle size are separated by the centrifugal action resulting from the air circulation. If necessary, such droplets may be removed by the use of a cyclone.

Referring to Fig. 7, there is diagrammatically illustrated a complete system which is actually applicable to a 64-kilobit RAM manufacturing plant. As described hereinbefore, the air entraining or suspending the ultra-fine mist particles, which are produced in the atomizer 40, is fed into the cyclone 50 as indicated by arrow A to remove large droplets. Namely, the air coming out of the atomizer 40 is introduced into the cyclone 50 in a tangential direction through an inlet which is provided in its side wall, removing excessive or large droplets while the air is whirled in the cyclone to prepared a suspension in air of ultra-fine mist particles more than 90% of which are smaller than 0.5 microns in particle size. The mist suspending air is discharged through an outlet pipe at the center of the cyclone 50.

The micro-droplet suspending air from the cyclone is passed through a pipe P with a filter F to remove droplets which are substantially larger than 0.5 microns, and sent to an air-shower room 60 and then to an adjacent ultra-clean room 70 to clean the workers in that room. Concurrently, part of the mist suspending air is directly sent to the ultra-clean room 70 for supplying thereto clean air free of dust and for washing silicon substrates to be used for the production of LSls. The air used in the ultra-clean room 70 is discharged through a pipe P and fan F for return to the atomizer 40, thereafter repeating the abovedescribed cycle of operation. It has been confirmed that, according to this method, the air in the ultra-clean room can be maintained in an extremely clean state with less than one particle of dust of 0.5 microns or larger in a space of one cubic foot.In view of the fact that several tens thousand of dust particles are usually suspended in a cubic foot of air in an ordinary manufacturing plant, it will be understood that the method of the present invention has an excellent effect.

The micro-droplet suspending air may be passed through a heat exchanger 100 as illustrated in Figs. 8 and 9, which is located downstream of the cyclone 50, thereby to raise the temperature of the air to an optimum level. The heat exchanger 100 is arranged in the manner as follows. Its barrel 101 is centrally provided with a vertical air discharge pipe 105 which communicates at its upper end with a pipe 105' which is provided outside the barrel 101. Accordingly, the air from an air inlet pipe 104 is whirled within the barrel 101 as it flows downward, and then enters the air discharge pipe 105 through is lower end and climbs up in the arrowed direction. The vessel 101 is interiorly provided with an outer pipe 106 and an inner pipe 107 the lower ends of which are communicated with a pump 108 which is located beneath the vessel 101.Warm or cold water is passed through these pipes and discharged from upper outlet ends 109 and 110. In upper and lower portions, the vessel 101 is provided with a large number of water injection nozzles 11 lea and 11 1b in a washing water pipe 111 at positions over or beneath the vertical rows of the helics of the pipes 106 and 107 to spurt washing water toward the pipes 106 and 107, the inner surfaces of the vessel 101 and the outer surfaces of the air discharge pipe 105. Provided beneath a cone portion 102 is a discharge pipe 112' to discharge therethrough the washing water as well as the drain resulting from the gas cooling.

Accordingly, the air entering the vessel 101 through the air inlet 104 is stripped of dust or the like by its cyclonic effect, and heated or cooled by the pipes 106 and 107 to an optimum temperature. The air of the optimum temperature is sent out through the air discharge pipe 105. The separated dust or impurities are washed away with water which is supplied through the washing water pipe 111 and injected through the nozzles 111 a, 111 b and so forth.

The air which has been treated in this manner suspends therein a large number of ultrafine micro-droplets mostly smaller than 0.5 microns, so that it can be suitably used for a purgatory treatment of a room or cleaning various objects or articles.

The ultra-fine micro-droplets with a particle size smaller than 0.5 microns, which are used in the method of the present invention, are extremely low in surface tension, so that they easily adhere to dust particles floating in the air and cohere into larger particles of conspicuously increased weights which can be easily sweeped away with blasts. In particular, owing to the use of ultra-fine micro-droplets, the method of the present invention can remove not only extremely fine dust particles but also bacteria and viruses, so that it has a prominent effect in cleaning a room both physically and biologically. For the removal of viruses, it has been the conventional practice to resort to an air filter or the like, which is however incapable of sufficiently filtering out viruses as small as 0.5 to 0.01 micron.

Namely, one is less susceptible to catching a cold in a room purged by the method of the present invention, and therefore the invention is particularly suitable for application to hospitals, pharmacies, laboratories, maternity hospitals and the like.

Further, the method of the present invention, with a distinctive feature pf excluding bacteria, is also suitable for appiication to a food manufacturing plant for washing food or production facilities or to a food store or supermarket or the like for thawing frozen meat, keeping salad, vegetables, fresh fish, fresh meat and the like. Particularly, the method of the invention makes easy the pro duction of uncooked ham, which has thus far been restricted by the possibilities of infestation of bacteria and the like.

Claims

1. A method for producing a suspension in air of ultra-fine micro-droplets of water, said method comprising atomizing water into ultrafine micro-droplets by injecting same in an atomizing chamber at a gage pressure of 0.3-5.5 kg/cm2 by the use of a water injecting pipe with a large number of nozzles of a diameter of 0.2-8 mm against a side wall located at a distance of 10-150 cm from said nozzles, and passing air through said atomizing chamber to entrain therein per cubic foot more than 2,000,000 ultra-fine micro-droplets of 0.5 microns or smaller in particle size.

2. A method according to claim 1, wherein the water injection occurs at a gage pressure of 0.5-2.5 kg/cm2.

3. A method according to claim 1 or 2, wherein the diameter of the nozzles is 0.5-3 mm.

4. A method according to any preceding claim, wherein more than 5,000,000 of the ultra-fine micro-droplets are entrained per cubic foot in said atomizing chamber.

5. A method according to claim 4, wherein more than 10,000,000 of the ultra-fine microdroplets are entrained per cubic foot in said atomizing chamber.

6. A method of producing a suspension in air of ultra-fine micro-droplets of water, substantially as hereinbefore described, with reference to the accompanying drawings.

7. A method of cleaning the interior of a room by sending thereinto the suspension in air of ultra-fine micro-droplets obtained by the method of any preceding claim.