US2713510A - Coanda - Google Patents

Description

Fatented July i9, i955 tice ATMEZERS Henri Cuanta, Paris, France, assigner to Sebac Nouvelle S. A., ausanne, Switzerland, a corporation of Switzerland Application November 14, ll, Serial No. 256,255

Claims priority, application France November 18, 195i) 4 Claims. (Cl. 299-456) This invention relates to improvements in or relating to atomizers consisting of the application of the physical phenomenon described in my U. S. Patent No. 2,052,869 and hereinafter referred to as the Coanda effect for carrying along a considerable volume of gas with the matter to be spread by using a limited amount of gas compressed at a reduced pressure.

The Coanda effect is apparent when a stream of fluid emerges from any container under a certain pressure, through a slot, if one of the lips of the slot orifice is extended and recedes continuously from the direction of the axis of said slot. Under such conditions, the uid clings to the said extended lip and tends to increase its velocity, producing accordingly an underpressure and therefore a suction and an intake of gas.

In the atomization of liquids, it is known that atomization can be achieved by the removal of particles from a liquid mass by a stream of air, the separated or removed particles being subsequently projected in any desired direction.

When the mass of liquid has certain properties it may happen that, as soon as a certain quantity of liquid is atomized and owing to the presence of a zone of reduced pressure over the remaining liquid another quantity may directly be atomized.

Generally, according to the known practice, this phenomenon is achieved by use of a jet of air or steam emerging from a nozzle, the nozzle being situated either in the throat of a convergent-divergent Venturi, or in a position such that it blows over the opening through which the liquid is otered.

In each case, at the ori'lice leading up from the liquid, a relatively low pressure exists, the liquid being then carried along, entrained and reduced more or less to mists. These mists or" liquid surrounded by rapidly moving air or steam are thrown in the direction of the jet.

The speed of the gaseous jet carrying the liquid particles is a function of the pressure which prevails on it prior to its emergence from the orifice of the conveying duct.

It is possible to act on the mass of the jet, a function of the area and ot the speed of the jet, which is caused to collide violently with the much slower ow of the liquid which passes through an opening of determined size to produce such a flow, so that, under the impact, the very small mass of liquid is disintegrated and projected in more or less large and homogeneous droplets in the direction of the carrier jet.

Alternatively it is possible to act by means of the surface of contact between the carrier jet and the liquid to be driven. In this latter case a solid cylindrical carrier jet derives little benefit from its mass.

The conditions are entirely different when the cylindrical jet is hollow so that the ratio of its mass to the contact surface area with the liquid is more and more reduced. When the thickness ot' the annular him of the carrier jet is very small, the area of its contact surface with a surrounding liquid becomes extremely large, if

the conveyance of the particles of the latter is effected without impact, and said particles are very homogeneous, of greatly reduced dimension and greatly diffused in the nal jet; the output efiiciency of the operation is, on an average, very high.

Naturally this state of affairs is applicable to pulverized materials.

The present invention has for an object a system capable of acting in this manner.

lt is another object of the invention to provide an atomizer comprising a nozzle making use of the aforementioned Coanda effect, for carrying along a matter to be spread in a very divided or coinrninuted condition by means of a limited amount of a compressed gas.

The aforesaid and other objects, features and advantages of the invention will be more easily and fully understood from the illustration of one embodiment of an atomizer according to the invention, being understood that the invention is not restricted to the details of the illustrated and described embodiment but that is susceptible to modications and adaptations.

In the attached drawings:

Fig. 1 is a View, partly in section, ot an atomizer according to the invention.

Fig. 2 is an enlarged section of the upper part of Fig. 1, showing the nozzle assembly, after a rotation of 90.

lReferring rst to Fig. l, compressed air (or gas) arriving from a source, not shown, penetrates cylinder i8 through connection ia. From said cylinder 18 the compressed air reaches, through duct 17, the upper part of a container 19 in which the liquid (or powder) lo to be atoinized is enclosed and also reaches, through duct 17a, the circular gap or slot l.

The pressure maintained through pipe 17 on liquid l may be made, if desired, adjustable by means of a pressure-reducer system not shown.

If liquids of low viscosity are to be atornized, it is not necessary to maintain a pressure in the container 19, on the low viscosity liquid i6, by means of pipe 17 and said pipe may be deleted.

Liquid i6 is sucked up as explained hereinafter by vthe nozzle Il through duct 2t?, the extremity of which nearly reaches the bottom of container 19, being immersed in the liquid 16.

An opening le serves as a vent for the air, so that the functioning of lthe atomizer may be suspended when said opening is not stopped; when, on the contrary, said opening l5 is stopped, for example with the thumb of the operator, the air pursues its way through duct i751 (and duct 17) and acts as described hereinafter.

Referring now to Fig. 2 a circular gap or slot l receives air in the direction indicated by arrow 2 (or another gas) under pressure from the extremity of pipe 17u; said air, in passing through said gap l, tends to flow outwardly into the space 3. One of the lips of the orifice 4 -ot' the gap l is extended as at S; said extended lip 5 forms angle ot 25 to 50 with the direction 6 of the outlet from the gap l. Around the sharp edge '7, formed by the extended lip 5 with the lip of the orifice 4, the speed of ilow is accelerated so that reduced pressure exists along the wall d or the cylinder 8 which is the continuation of the extended lip 5. This reduced pressure causes intake of air in the direction indicated by arrow 9 through the convergent channel l0 thus increasing the mass of air carried along pipe 2 and passing through the gap without substantially reducing the speed of the eftiux.

Inside the cylinder 3 a liquid supply tube or nozzle il is mounted. In order to increase the area of the contact surface between the liquid, which arrives through nozzle 1l, with the air from cylinder 8', the extremity of the interior walls of said nozzle ll forms a divergent portion i2; the liquid arriving from il along said wall spreads out. The rapidly flowing layer of air which surrounds this divergent portion l2 portion which ends slightly in front of the extremity of cylinder 8 (in the direction of flow as represented by the arrows l3)-car ries along without impact the liquid particles arriving through said divergent portion 12 and projects said particles in the direction 13, producing a mixture ifiof liquid particles and air.

At the outlet from the divergent portion 12 exists, due to the aforementioned Coanda eiiect, a zone or reduced pressure which obliges at once the liquid to move at a speed directed in the direction of the air which is carried along (arrows 13); accordingly, the fluid in motion is merely accelerated, without a sudden change of speed from zero to the speed of the carrier ,ict as in the previous devices.

The liquid layer leaving the divergent 12 becomes very thin and the surface tension of the liquid accordingly does not usually permit said liquid layer to keep a continuous surface; the liquid layer is split, and is transformed into highly homogeneous droplets; the liquid is carried along in the condition of a mist in the final jet.

When the supply of air is cut otf, for example by opening the orilice 15 (Fig. 1), the reduced pressure zone existing at the outlet from the divergent portion l2 disappears immediately and the movement of the liquid is stopped.

It is not necessary in the apparatus, according to the invention, to use high pressures, since the high eliiciency of the nozzle system allows it to be operated at relatively low pressures,

Not only a liquid but also a pulverised matter can be spread with the described apparatus utilizing the abovementioned Coanda effect.

lf desired, a system of atomizers constituted by several sets of apparatuses, as described above, may be mounted together in order to give to the final jet the desired shape.

Although the invention has been described with reference to certain specitic embodiments thereof, it is to be distinctly understood that various modifications and adaptations of the arrangements herein disclosed may be made as may readily occur to persons skilled in the art without constituting a departure from the spirit and scope of the invention as defined in the objects and in the appended claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent, is:

l. ln an atomizcr, an inner tubular nozzle having a discharge end, means for supplying to said nozzle fluent material to be atomized, means defining an annular chamber surrounding said nozzle, Said chamber being substantially heart-shaped in axial section and having a tubular inner wall portion surrounding and spaced from said inner nozzle to deline an outer nozzle coaxial with said inner nozzle and having an inlet end and a discharge wall portion converging with said tubular inner wall portion to define a sharp annular edge at the discharge end of said outer nozzle and a substantially conical inner end, said chamber having a substantially conical outer wall portion inclined inwardly toward the inlet end of said outer nozzle and terminating in a lip spaced from Iii said inner nozzle to deiine an annular passageway open to the atmosphere, the discharge end of said inner nozzle terminating short of the discharge end of said outer nozzle, and means for supplying gas under pressure to chamber, said chamber having in its inner Wall a substantially conical annular slot defined by said lip of said conical inner Wall portion and a second lip formed by the inlet end of said outer nozzle, said slot being inclined inwardly and toward the discharge ends of said nozzles, the flow of gas through said slot from said chamber to and through said outer nozzle inducing the iniiow of air through said passageway and the inflow of fluent material from said inner nozzle.

2, An atomizer according to claim 1, in which said 'i second lip is convexly curved as viewed in axial section and progressively recedes from a straight line representing the direction of liow of said gas entering said slot.

3. in an atomizer, an inner tubular nozzle having a discharge end, means for supplying to said nozzle iiuent material to be atomized, an annular chamber surrounding said nozzle and having a tubular inner Wall portion surrounding and spaced from said inner nozzle to deiine an outer nozzle coaxial with said inner nozzle and having inlet and discharge ends open to the atmosphere, an outer wall portion joining said inner wall portion at the discharge end and an inlet end portion that extends inwardly from said outer wall portion toward the axis of said nozzles and terminates in an annular lip which surrounds and is spaced from said inner nozzle and is spaced from the inlet end of said tubular inner wall portion to provide an annular slot detined by said lip of said inlet end portion and a second lip constituted by the inlet end of said tubular inner wall portion, said slot opening from said annular chamber into the inlet end of said outer' nozzle and being inclined inwardly and toward the discharge end of said nozzles, the discharge end of the inner nozzle terminating short of the discharge end ot the outer nozzle, means for supplying gas under pressure to said chamber, the flow of said through said slot and thence through the outer nozzle inducing the inliow of air into the inlet end of the outer nozzle and the fiow of fluent material from said inner nozzle, said second lip being convexly curved as viewed in axial section and progressively receding from a straight line representing the direction of iow of said gas entering said slot.

4. An atomizer according to claim 3, in which said inlet end portion of said chamber slopes inwardly toward the axis of said nozzles and toward the discharge end ot said nozzles at an acute angle to said axis and terminates in a sharp edge.

References Cited in the iile of this patent UNITED STATES PATENTS 1,531,354 Stackpole Mar. 31, 1925 1,811,637 Ladisch June 23, 1931 1,864,647 Geer June 28, 1932 1,922,920 Aherne Aug, 15, 1933 1,935,977 Geer Nov. 21, 1933 2,052,622 Hale Sept. 1, 1936 2,351,697 Nielsen June 20, 1944 2,532,711 Goddard Dec. 5, 1950

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