WO1980001358A1

WO1980001358A1 - Method and apparatus for actuating particles

Info

Publication number: WO1980001358A1
Application number: PCT/SE1980/000003
Authority: WO
Inventors: M Olsson
Original assignee: MATSOLSSON KONSULT AB
Current assignee: MATSOLSSON KONSULT AB
Priority date: 1979-01-04
Filing date: 1980-01-04
Publication date: 1980-07-10
Anticipated expiration: 1981-07-04
Also published as: EP0029029A1; SE7900067L; SE416891B

Abstract

A method for actuating particles comprises the step of exposing the particles to a rapid reciprocating air flow generated by intense sound, preferably of a low frequency. An apparatus for working the method comprises a double resonator (10, 10A, 10B) having a sound generator (18, 18A, 18B) and two resonator compartments (15, 16) which communicate with each other through an air tunnel (17, 17A, 17B, 29, 29A, 29B). The phase shift between the compartments corresponds to a half cycle. The air tunnel is constructed to receive the particles (20, 26, 28, 32) to be actuated.

Description

METHOD AN D APPARATUS FOR ACTUATI NG PART I CL ES

The present invention relates to a method for ac¬ tuating particles, by which the particles can be removed e.g. from textiles, can be carried through one or more screens, can be mixed or can be evaporated.

1 ,4-dichlorobenzene is used for protecting textiles against attacks by moths and other insects said substance being marketed under the trade name paradichlorobenzene which will be used below in the present specification. The invention has been made i.a. to make possible to re¬ move paradichlorobenzene from easily damaged textile ma¬ terial but is not 1-imited to this specific use.

Paradichlorobenzene is a crystalline, volatile, very evil -smel 1 ing substance having the molecule weight 147.01 and in Sweden it is registered as a means of control re¬ ferred to class 3. It has been shown that it is harmful to human beings to inhale paradichlorobenzene, and the highest concentration of the substance allowed in the air at work premises has been determined to be 75 ppm. More¬ over, paradichlorobenzene penetrates into the body when contacted with the skin and, therefore, it is injurious in this respect too.

The textile collections of the Ethnographical Museum of Stockholm comprise about 45,000 items such as cos¬ tumes, textiles ,_. feather handicraft, furs, leather, and archaeological textiles, which have been stored in 120 cases each containing on an average 100 kg. In order to pro¬ tect said items against attacks by noxious insects para¬ dichlorobenzene has been sprinkled twice a year into a cover arranged at the top in each case, from the begin¬ ning of the thirties up to the end of the sixties, and the accumulated quantity of paradichlorobenzene thus supplied to the material amounts to about 3 tons.

In connection with the unpacking of the textile

OMPI items from the cases illness has occurred among the per¬ sonnel taking care of the^' unpacking, due to the contact with the paradichlorobenzene. Moreover, it has turned out that the textiles treated with paradichlorobenzene deteriorate very rapidly when exposed to light or heat, due to the fact that some fibres and dyes are broken down in a very short time. This was found to be true particularly as far as specific blue fibres in the tex- iles are concerned. Due to the dangerousness of the paradichlorobenzene there is accordingly a need of being able to remove the paradichlorobenzene from the textile collections at the unpacking without the risk of injurious affect on per¬ sonnel or material. Since the paradichlorobenzene is in- soluble in water, it is not to be thought of using water washing for the purpose. Technically, dry cleaning could be used but considering that old, fragile and in some cases irreplaceable items are concerned also dry cleaning cannot be used. Considering that the paradichlorobenzene is volatile one could air off the paradichlorobenzene by hanging the items in dark, cool premises but that method would re¬ quire a long time. When the paradichlorobenzene is eva¬ porated a local cloud of paradichlorobenzene vapour is formed around the solid particles of the paradichloroben¬ zene. The partial pressure of the vapour is increased progressively and as a consequence thereof the rate of evaporation is decreased. The energy required for the vaporization (the vaporization heat) is taken from the surrounding air and, accordingly, the temperature there¬ of will be decreased. If the air around the particles is stagnant, the evaporation rate will decrease also due to the local decrease in temperature .^■ Thus , the evaporation requires a continuous ventilation around the particles, which may be difficult to provide if the particles are

OMP well protected by the textile fibres.

Additionally, an unreasonably large space is re¬ quired and severe working environment problems are cre¬ ated by hanging the items for airing. In order to make possible to remove the paradichloro¬ benzene from the damageable textiles without the risk of personnel being injured or items being damaged, the in¬ vention provides a method of the kind initially referred to having the characteristics which appear from claim 1, 0 and an apparatus for working said method, having the characteristics which appear from claim 8.

It has been found that it has been possible to re¬ move, by application of the. invention, 96 - 99% of the paradichlorobenzene in five minutes at a sound pressure 5 level of 140 dB at the frequency 50 cps. The physical process would be the same as in airing, the sound forcing the air back and forth fifty times per second between the textile fibres while the paradichlorobenzene is be¬ ing vaporized. 0 In other words the effect could be described as a forced or accelerated airing. A ye ry good point about the method according to the invention is that the air move¬ ment produced is able to remove the paradichlorobenzene without being sufficiently intense to adversely affect 5 the textile fibres. In ye y thin, tight textiles a flutter may arise but otherwise the textiles stay unaffected by the sound, which is a prerequisite for treating fragile and damageable textiles.

The forced or accelerated airing provided by the D method according to the invention is based on the air movement of the sound. In order to obtain a good.effect the amplitude of the sound movement should be consider- ably greater than the- dimensions- of the particl es Of the substance to be vaporized. This requirement can be met 5 by using sound of a high intensity and a low frequency.

OMPI However, it is difficult to generate low frequency sound of high sound intensity and, moreover, such sound is in¬ jurious to human beings. In order to avoid that human beings are affected by the sound and the released para¬ dichlorobenzene the cleaning therefore should take place in a space which is substantially closed.

The invention is not, however, limited to the eva¬ poration of paradichlorobenzene; it can be applied in all sublimation, i.e. the evaporation of solid substances at a temperature which is lower than the fusion tempera¬ ture, and in evaporation of liquids, particularly if the liquid is present as drops or as humidity in a fibrous or particulate material which can be exposed to the sound. If the temperature of the surroundings is higher than the boiling temperature of the substance, boiling takes place and also in this case the evaporation rate will increase at exposure to sound. Thus, the invention can be applied to the drying of cloths and other textiles as well as drying of particulate material in the food and pharmaceutical industry.

Another effect of the exposure to the low frequency sound, that has been observed, is thatscent agents can be driven out from textiles. Thus, the method can be used for making cloths and rugs free from the smell of e.g. fire or tobacco smoke. The physical process is that the reciprocating air movement through the textile carries along the scent particles.

At a sound intensity which is sufficiently high the low frequency sound is able to remove also dust particles such as grits, skin fragments, ash particles, etc from cloths, furs, rugs and other textile items.

Finally, it should be mentioned that the invention can also be applied in order to screen a mixture of par¬ ticles of different sizes into two-or more fractions, and to obtain a thorough mixture of different particles,

OMP WIP e.g. in mixing -dye pigments.

In order to illustrate the invention several appli¬ cations of the proposed method will be described in more detail below references being made to the accompanying drawings which disclose diagram atically several embodi¬ ments of the apparatus according to the invention, where¬ in

FIG. 1 is a central vertical cross sectional view of an apparatus for cleaning textiles, e.g. for re- moving paradichlorobenzene, which meets the require¬ ment of protecting the personnel taking care of the cleaning, against the sound as well as the evaporated parachlorobenzjsne,

FIG. 2 is a further cross sectional view of the ap- paratus along line 11-11 in FIG. 1 ,

FIG. 3 is a central vertical cross sectional view of an apparatus for drying particulate material , FIG. 4 is a central vertical cross sectional view of an apparatus similar to that in FIG. 3 but ar- ranged for screening particulate material ,

FIG. 5. is a central vertical cross sectional view of an apparatus for the same purpose as that in FIG. 4 but including a resonator of another type, FIG. 6 is a central vertical cross sectional view of an apparatus including an open double resonator, for cleaning indefinitely largeite s, and FIG. 7 is a central vertical cross sectional view of anapparatus for the same purpose as that in FIG. 6 but having a double resonator of another type. The apparatus shown in FIGS. 1 and 2 of the drawings comprises a parallelepipedic sound box 10 with heavy, well . sound-insulated side walls 11 and a heavy, well sound- -insulated bottom 12. The sound box is open at the top where it is covered by a transparent cover 13 such as a ' glass cover, which can be opened and for that purpose can be arranged in a guide allowing the cover to be lifted some millimetres and then displaced lateraly for uncover¬ ing the interior of the: sound box at the top thereof. A gasket is mounted between the cover and the sound box to seal between the cover and the sound box when the cover is in the closed position.

In the sound box a vertical partition wall 14 is provided which divides the interior of the sound box in¬ to two compartments 15 and 16 communicating with each other through an air tunnel 17. In the embodiment shown this air tunnel is of rectangular cross sectional form. Each compartment 15 and 16, respectively, forms together with the air tunneT 17 a Helmholtz resonator, and the compartments form together a closed double resonator. An electrically driven loud-speaker 18 of the dia¬ phragm type is mounted in the partition wall 14 and for practical reasons this loud-speaker is intended to be operated with alternating current of the frequency 50 cps Therefore, the double resonator is dimensioned to have the resonance frequency 50 cps. The loud-speaker gene¬ rates a strong sound pressure in the two compartments 15 and 16 at exactly the same frequency but at a phase shift of a half cycle. The changing sound pressure forces the air back and forth in the air tunnel 17 at the frequency 50 cps. Then, the air in the two compartments operates as springs for the air movement, and in order to obtain a maximum air movement the volume of the resonator com¬ partments 15 and 16 should have a specific relationship to the sound frequency and to the cross sectional area of the air tunnel. The cross sectional form of this tunnel is of no importance as long as the prescribed cross sec¬ tional area is provided. Thus, it is possible to make_. the tunnel e.g. cylindrical instead of rectangular, as shown in the illustrative embodiment, but the rectangular form is preferred for the purpose of treating textiles. As far

OMP as the dimensioning of _.the resonator compartments and the air tunnel is concerned, common principles for double resonators can be applied.

The items to be freed from paradichlorobenzene are to be placed in the air tunnel 17 below the transparent cover 13, and for this purpose there is mounted in the air tunnel a substantially horizontal netting 19 or other permeable support. The item to be treated, indi¬ cated at 20, is placed on this netting, and during the entire treatment the item can easily be observed through the transparent cover 13. With respect to the construc¬ tion of the apparatus and also with respect to the handl¬ ing of the items it is preferred that such items can be disposed horizontally in the air tunnel 17 but it should be noted that good results are obtained also if the items are disposed in the transverse direction of the air tun¬ nel , i.e. in the transverse direction of the changing air current generated by the sound generator.

For the removal of the paradichlorobenzene evaporat- ing from the textiles when they are treated in the air tunnel 17, there should be provided in the air tunnel a slight air flow, and for this purpose an air inlet 21 to the compartment 15 and an air outlet 22 from the compart-, ment 16 are provided. The inlet 21 has a restriction 23 in order that a certain subatmospheric pressure can be main¬ tained in the sound box in relation to the surroundings such that the cover 13 is kept pressed against the sound box with the sealing gasket therebetween. A suction fan 24 is connected to the air outlet 22 which preferably comprises-a hose, an.d tfve pressure side o the. fan is con¬ nected to a suitable evacuating conduit for the removal of the air with paradichlorobenzene entrained therein, to a. pl-ace wtie.re. the—P-arad-ichl or-obenzene cannot be in¬ jurious. The air inlet 21 as well as the air outlet 22 has a

- OSMIP3I_ Λ, WIPO - cross dimension (diameter) which is substantially less than the wave-length of the sound generated in the sound box in order that the sound energy which can "leak" from the sound box through these openings shall be reduced as much as possible.

When the method according to the invention is applied by using the sound box described an intense sound is gene¬ rated by the electrically driven loud-speaker^' 18 at the frequency which substantially equals 50 cps. As a conse- quence thereof a strong sound pressure is produced in the two resonator compartments 15 and 16 while the air move¬ ment in these compartments is insignificant; as mentioned above the compartments act as springs. However, the air movement in the air tunnel 17 is considerable but the sound pressure therein is low. For these reasons a rela¬ tively thin glass panel or other transparent panel , e.g. of plastics, can be used as a cover on the sound box be¬ cause the cover will not be exposed to such a strong pressure as the side walls 11 and the bottom 12 which must be of a heavy construction. Under the influence of the sound the paradichlorobenzene present in the item 20 will be evaporated rapidly and will be removed from the item and the air tunnel 17 by means of the slight air flow passing through the tunnel. In this manner the para- dichl orobenzene is removed substantially completely in a short time without any detrimental effect on the items such as fragile and damageable textiles, to be treated. During the entire treatment the item can be observed with¬ out any risk for the personnel taking care of the cleaπ- ing, such that the treatment can be interrupted if a ten¬ dency of damage of the item should be noted.

It is practical to perform the cleaning at a fre¬ quency of about 50 cps because then the loud-speaker can be operated directly from the electrical mains when the mains voltage has been stepped down to a suitable voltage.

OM /., WIP Previous experience- from other cases wherein sound clean¬ ing has been applied, e.g. cleaning of filter fabrics by using sound, has shown that frequencies of the order of 15 - 50 cps are effective-. For practical reasons a fre- quency as high as possible should be used because the lower the frequency, the greater the difficulty. More¬ over, the dimensions of the resonator will increase in proportion to the square of the inverted value of the frequency. The sound insulation of the side walls and bottom of the sound box should be so efficient that the sound level outside the sound box does not exceed the values allowed, i.e. 70 dB (A) or 90dB (Tin).

When- dimensioning the double resonator it should be taken into account that the sound pressure is at maximum at the frequency of the loud-speaker. However, the reson¬ ance peak must not be too sharp because the acoustic con¬ ditions in the resonator are disturbed by the items 20 placed in the air tunnel 17 on the netting 19. This means that the sound pressure should not be allowed to decrease too much if the frequency or other acoustic conditions are changed slightly.

For drying particulate material it is suitable to arrange the double resonator according to FIG. 3.

In this case all walls of the sound box 10 are heavy and well sound-insulated as in the apparatus of FIGS. 1 and 2 though this has not been shown in FIG. 3. The parti¬ tion wall 14 with the electrically operated diaphragm loud-speaker 18 therein is mounted horizontally, and ac¬ cordingly the air tunnel 17 between the two compartments 15 and 16 is arranged vertically. The compartment 15 has an air inlet 21 and the compartment 16 has an air outlet 22 for circulating air through the compartments and the tunnel by means of a fan not shown.

The tunnel 17 is provided at the ends thereof with confining walls 25 for the retention of the particulate

OMPI material 26 to be dried in the tunnel , and these confin¬ ing walls are of such nature that they allow the air and sound to pass but not the material particles. In other words, they have the character of a filter. At a sound intensity which is sufficiently high the material 26 in the tunnel will be fluidized and, thus, the method according to the invention can be used in or¬ der to obtain a thorough mixture of different particles, e.g. in mixing dye pigments. If the tunnel 17 is provided with one or more screens 27 of different mesh sizes between the two outer confin¬ ing walls 25 as shown in FIG. 4 wherein the apparatus for the rest is as in F G. 3, the air movement imparted to the particles by the sound, be utilized for screening a mixture 28 of particles having different sizes, into two or more fractions. Preferably, the actuation provided by the sound is supplemented by a superimposed air current. The confining walls 25 should be of a sufficient fine mesh in order to retain all particles which can pass through the screen 27 of the finestmesh.

Also closed resonators of other types can be used as in FIG. 5 wherein the screening is performed at the center of a half-wave resonator. This resonator comprises a tube 29 having a length which substantially equals half a wave lengthof the sound generated by the diaphragm loud-speaker 18 which is mounted at one end of the tube 29 while the other end thereof is closed by an end wall 30. The material 28 whichis to bescreened is enclosed in the tube 29 which in this case has the same function as the tunnel in FIGS. 3 and 4, between the confining walls 25 arranged at each side of the screens 27. As will be realized the apparatus in FIG. 5 can be used also for drying particulate material in the manner described with reference to FIG. 3. The apparatus according to FIG. 6 is an open double

OMP resonator which can be used for removing dust particles e.g. from rugs and furs.

Each compartment 15 and 16, respectively, comprises a parallel epipedic box 10A and 10B, respectively, which can be of the- ame^' construction- as^* the box 10 in FIGS. 1 and 2, and these boxes are located in parallel with each other, tubular sockets 17A and 17B on the adjacent side walls 14A and 14B, respectively, being arranged coaxial- ly and the ends thereof, facing each other, being utual- ly spaced so that there is a gap 31 therebetween. Two loud-speakers 18A and 18B are mounted in the side walls 14A and 14B, respectively. Each box 10A and 10B, respec¬ tively, forms an open resonator.

The two loud - speakers are connected to the same ope- rating source but are directed in such a way that the sound pressure in the two resonators has a phase shift of a half cycle. The open double resonator as a consequence thereof operates in the same manner as the closed double resonator e.g. in FIG. 1. Because the sound pressure in the two resonators acts at a phase shift of exactly a half period sound "leaks" from the gap 31 between the sockets 17A and 17B to a very small extent. Accordingly, the open resonator, contrary to the closed one, can be used for cleaning indefinitely large items 32, e.g. large floor coverings, which are in¬ serted through the gap 31.

The sound emission from the loud-speakers is sub¬ stantially lower than that from the air tunnel in a Helmholtz resonator, and therefore the total sound emission to the surroundings can be kept at anacceptable level though the resonators are open.

The actuated dust particles are removed also in this case by means of an evacuating apparatus by the resonators being provided with an air inlet 21 and an air outlet 22, respectively.

OMPI The principle described above can be applied also to resonators of other types, e.g. two .quarter-wave re¬ sonators according to FIG. 7.

Each quarter-wave generator comprises a tube 29A and 29B, respectively, having substantially a quarter-wave length , which is open at one end and is provided with a loud-speaker 18A and 18B, respectively, at the other end. The tubes are arranged coaxially with the open ends facing each other and mutually spaced to form the gap 31. The tubes are provided with an air inlet 21 and an air outlet 22, respectively.

Claims

1. A method for actuating particles c h a r a c ¬ t e r i z e d in that the particles are exposed to a rapid reciprocating a r flow gene raired y^~ an fnterrs sound, preferably of a low frequency.

2. A method according to claim l c h a a c t e r- i z e d in that the sound has a frequency of the order of 15 - 50 cps.

3. A method according to claim l c h a r a c t e r - i z e d in that the sound has a frequency of about 50 cps.

4. A method according to any of claims 1 - 3 c h a r a c t e r i z e d in that the particles to be actuated are located on or in a porous material.

5. A method according to claim 4 c h a r a c t e r- i z e d in that the porous material is in sheet or web form, e.g. a textile material.

6. A method according to claim δ c h a r a c t e r - i z e d in that the material is located substantially in parallel with the direction in which the sound is ra¬ diated.

7. A method according to any of claims 1 - 3 c h a r a c t e r i z e d in that the particles are en¬ closed between sound and air permeable confining walls in a passage arranged substantially in parallel with the direction in which the sound is radiated.

8. An apparatus for actuating particles by working the method according to any of claims 1 - 7 c h a r a c - t e r i z e d by a double resonator (10, 10A, 10B) having a sound generator (18, 18A, 18B) and two resonator com¬ partments (15, 16) which communicate with each other through an air tunnel (17, 17A, 17B, 29, 29A, 29B), the phase shift between the compartments corresponding to a half cycle, and that the air tunnel is constructed to re- ceive the particles (20, 26, 28, 32) to be actuated. ^•

OMPI

^* *

9. An apparatus according to claim δ c h a r a c - t e r i z e d in that the double resonator comprises an open double resonator (10A, 10B) having a gap (31) in the air tunnel (17A, 17B, 29A, 29B) between the resonator compartments (15, 16) to receive the particles therein.

10. An apparatus according to claim 8 or 9 c h a - r a c t e r i z e d in that the sound generator compri¬ ses a diaphragm loud-speaker (18, ISA, 18B) which is mounted in a bounding wall (14, 14A, 14B) of each reso- nator compartment.

11. An apparatus according to any of claims 8 - 10 c h a r a c t e r i z e d in that openings (21, 22) are provided for passing air into one compartment (15) from the outside and for evacuating air from the other compart- ment (16).

12. An apparatus according to claim 11 c h a r a c ¬ t e r i z e d in that the cross dimension of the open¬ ings (21 , 22) is substantially smaller than the wave- -length of the sound generated by the sound generator (18, 18A, 18B).

- RE

OM