CA1082094A - Atomizing device - Google Patents

Abstract

ATOMIZING DEVICE

ABSTRACT OF THE DISCLOSURE
The atomizing device of the present invention, compris-ing a cylindrical swirl chamber provided with a nozzle, and a pipe running coaxially through the chamber and the nozzle to extend into the zone of material atomization, said device being provided, according to the invention with a second chamber which is essentially an acoustic resonator, the outlet end of said pipe entering the interior of the second chamber which adjoins the nozzle. The second chamber is desirably a quarter-wave acoustic resonator. The present invention has most utility when applied in those industries where quality atomization and/or mixture-formation of various materials is involved, which may be the case in chemical engineering industry.

Description

" ~0~3Z094 This invention relates to heat-power engineering and has particular reference to atomizing device; the invention finds appiication in those industries where quality atomization and/or mixture-formation of various materials is involved, which may be the case in firing systems, diverse chemical-engineering apparatus and the like.
One prior-art atomizing device (cf., e.g. British Patent No. 1,210,699 Cl.B2F~comprises a cylindrical swirl chamber with a cylindrical nozzle maintained coaxially thereto, said nozzle having a length much greater than its diameter. A small chamfer-like widening of the nozzle is provided at the nozzle exit. A pipe feeding the material to be atomized runs through the swirl chamber and the nozzle respectively, the outlet pipe ena having a plurality of through holes which may be situated only within said chamf~er, while the outside end face of the pipe outlet end is fiush with the nozzle exit end.
An atomizing gas is fed into the cylindrical swirl chamber tangentially to the surface thereof, with the result that said gas is given a rotary motion. While passing length-wise along the axis of the device the atomizing gas passes intothe nozzle and from thence into the adjacent space of a corres-ponding apparatus. When the a~omizing gas passes from the swirl chamber into the nozzle, its degree of swirling -'

-2 : - - - , - - - - : , :
.

1~)8Z094 is greatly increased due to the nozzle diameter being much less than the swirl chamber diameter, to such an extent that acoustic oscillations are set up in the nozzle. Upon feeding the material being atomized inside the chamfer of the nozzle end, said oscillations promote its finer atomization and further, after the mixture has left the nozzle, to higher-quality rnixture forming.
However, only in a specific particular embodiment of the device and at given particular rates of flow of the atomizing gas, when the size of the device is selected within an optimum ratio, a maximum power of acoustic oscillations emitted is attained which cannot be provided in the device under consideration owing to some particular feature of gasodynamic phenomena proceed-ing therein. Furthermore, provision of the pipe outlet end flush with the nozzle exit end adversely affects aerodynamic conditions of the gas flow through the nozz~e annular ~ap which results in further losses of energy given to the material being atomized to make said material pass through said annular gap, and reduces the amount of the energy of acoustic oscillations generated in the nozzle.
It is therefore a general object of the present invention to obviate the disadvantages mentioned above.
It is a specific object of the present invention to provide such a construction of an atomizing device that would ~ ' ' - " -1C)82094 enable one to considerably increase the power of the generated acoustic oscillations of the flow of atomizing gas.
Said object is accomplished due to the fact that an atomizing device, comprising a cylindrical swirl chamber, wherein rotation of the flow of an atomizing gas occurs, said swirl chamber having a nozzle to provide a higher degree of swirling resulting in generation of acoustic oscillations, and a pipe coaxially running through the chamber and the nozzle into the zone of atomizing of the material fed therethrough, according to the invention is provided with a second chamber which i5 a reson-ator of acoustic oscillations corresponding to those of a swirled flow of the atomizing gas, said chamber with its inlet hole adjoining the nozzle end, while the outlet pipe end extends substantially outwards of the nozzle to enter through the inlet hole inside said second chamber, wherein atomization of the feed material occurs.
Such an embodiment of the construction of the present atomizing device enables one to considerably increase the power of the generated acoustic oscillations of the flow of atomizing gas.
The second chamber is desirably a quarter-wave acoustic resonator.
The above~eature provides for o~timum conditionsof am~lifvinq~ --the acoustic oscillations of the respective harmonics.

, The second chamber is suitably a cylinder whose diameter is a few times that of the nozzle.
This enables one to bring hydrodynamic and acoustic characteristics of the second chamber in accord with those of the nozzle, wherein acoustic oscillations are generated.
The length of the second chamber is suitably equal to or greater than the diameter thereof.
This makes it possible to attain a simultaneous maximum concentration of acoustic energy in one direction and maximum ampiification thereof.
In addition, the outlet pipe end suitably has a plural-ity of through holes and/or be provided with a spray spout.
This is conducive to a higher-quality atomization of the material discharged from the pipe and better mixture forming, accordingly.
In what follows the present invention is illustrated in some specific embodiments thereof given with reference to the accompanying drawings, wherein:
FIG. 1 is a schematic longitudinal sectionalview of an atomizing device, according to one embodiment of the invention;
FIG. 2 is a schemat~~c cross-sectional view of the swirl chamber in a specific embodiment of the present invention featuring a tangentia~ feed of the atomizing gas, according to the invention; and ~.

~ 30 .

.

~ ' ; : ` ' ' .

FIG. 3 is a schematic view of a part of the second chamber along with the outlet end of the pipe coaxially running through the swirl chamber and the nozzle, in the case where the outlet pipe end is provided with a spray spout, according to the invention.
Reference to the accompanying drawings, the atomizing device comprises a cylindrical swirl chamber 1 (FIG. 1) adapted to cause the flow of an atomizing gas to rotate, said chamber having a nozzle 2 adapted to enhance the degree of swirling said gas resulting in the generation of acoustic oscillations.
A second chamber 3 adjoins the nozzle 2, for the oscillations generated in the nozzle 2 to amplify. A pipe 4 is arranged concentrically with the swirl chamber 1, the nozzle 2 and the second chamber 3, said pipe being adaoted for the material being atomized to feed to the point of its admission to the second chamber 3.
An inside surface 5 of the swirl chamber 1 is cylindri-cal-shaped so as to provide optimum conditions for causing rotation of the flow of the atomizing gas. The shape of the surface 5 of the swirl chamber 1 may be arbitrary to suit additional re-quirements imposed upon the device. The swirl chamber 1 communi-cates with the nozzle 2 through an opening 6. The places of transition from the swirl chamber 1 to the nozzle 2 are desirably rounded off to reduce hydrodynamic losses. The transition from the inside cylindrical surface 5 ' of the swirl chamber ~ to the nozzle 2 ma~ be made curviline-ar with a view to reducing hydrodynamic losses and improving the hydrodynamic flow conditions of the swirled flow of the atomizing gas. ~he nozzle 2 has an end 7.
~ ~ An inside surface 8 of the nozzle 2 is cylindrical-sha-

3~ i ped and is coaxial ~e the swirl chamber 1. ~ength ~1 of the ~ozzle 2 must be e~ual to about 0.7 to 5.0 of height ~2 f the swirl chamber 1. With said dimensional requirements satis-fied an optimum acoustical coupling between the interior spa-ces of tha swirl chamber 1 and the nozzle 2 is achieved. In addition, with the abovesaid length ~1 of the nozzle 2 a stable s~irled flow of the atomizing gas is established ~hich promotes the generation of stable acoustic oscillations. The diameter D2 of the ~ozzle 2 is selected to be i~ a strict relationship with the diameters I1 of the swirl chamber 1 ~nd the diameter D3 of the inlet tangential sleeve 9 whenever a tangential (with respeot to the inside cylindrical surface 5) admission of the atomizing gas is effected through the tangential sleeve 9 (~IG. 2). ~his relationship is termed the geometrical characteristic o~ a~ atomizing device and -proves to be a dimensionless quantit~ expressed in a mathema-tical ~unctiou A = ~
ris where A is the geometricsl characteristic of the atomi-zing device;

.. . ~ .

,.. .
. - :
- ~ ~
- .
- ' ' ' `` ~08Z094 R is the radius of the swirl chamber 1, (R = Dl );

rn is the radius of the nozzle 2 (rn= D2 );

riS is the cross-sectional radius of the inlet sleeve 9 (r = D
lS 2 The numerical value of the geometrical characteristic A is selected so as to obtain optimum operating conditions there-of. It is established experimentally that when generating acoustic oscillations at a frequency of, say, 3.0 to 6.0 kHz, the geometrical characteristic A of the atomizing device should be within about 27 to 32 to obtain a maximum power of said oscillations. ;
An inside surface 10 of the second chamber 3 is similar-ly shaped as a cylinder to obtain its optimum hydrodynamic characteristics. A surface 11 of the second chamber 3 (as shown in FIG. 1~ is shaped as a parabola, though it may be shaped as a plane or cone. The second chamber 3 has an inlet hole 12.
The second chamber 3 is adapted for amplifying the acoustic oscillations generated in the nozzle 2, using the resonation principle. The second chamber 3 is thus, in effect, - a resonator, and its being connected, through the inlet hole 12 thereof, to the end 7 of the nozzle 2 results in an abrupt amplification of the acoustic oscillations (by about 25 to 30 per cent). This owes its onset to the presen-.. ....

- -- , ~ . : .

ce o~ a resonance o~ the natural Dscillation ~requency of the cavity of the second chambar 3 and the frequency of one of the harmonics of acoustic oscillations emi'~ted i~ the nozzle 2. In this respect the dimensions of the second cham-ber 3 are to be selected so as to gain a specific acoustic oscillation harmo~ic emitted by the nozzle 2. Thus, the se-cond chamber 3 is essentially a third acoustic cavity a~ter the swirl chamber 1 and the nozzle 2. At a de~inite rate of ~low of the atomizing gas and an invariable spatial dimen-sions of the device, the base ~requenc~of the emitted acous-tic oscillations prove B to be definite. Accordingly, the di-mensions o~ the second chamber 3 are strictly definite. ~he length ~3 of the second chamber 3 o~ the acoustic resonator is calculated b~ the known ~ormula f = a where f is the resonant frequency of acou6tic oscilla-tions; -a is the sound velocity in the swirled outflow of the atomizing gas;
L3 is the length of the second chamber 3 which is a resonant ¢avity of acoustic oscillations.
~ he diameter D4 of the second chamber 3 is to be selec-ted to suit the desired angle of flare of the spray at the e~it o~ the nozzle 2 and proceedi~g ~rom the axial velocity _9_ .

.. : . -.
, . .' - ~ ~ . ` - -. . . ... .. . . . . . .
~ .. .. . . . . . .

o~ the swirled ~low of gas, i.e., the flow rate thereof At s~all angles of ~lare the diameter D4 of the second cham-ber ~ is small, and vice versa.
Nlaximum amplification of acoustic oscillations by the --second chamber 3 occurs when the ratio between the diameter D4 thereo~ and the diameter D2 of the nozzle 2 equals approxi mately 1.2 to 4.5.
Inasmuch as the second chamber 3 is an acoustic resona-~or it must meet all requirements i~posed upon resonant acous~
tic cavities. ~hus, e.g., its length L3 may be divisible by one-~ourth of the wavelength of acoustic oscillations of the swirled ~low of the atomizing gas, i.e., the second cham-~ber 3 may serve as a quarter-wave reso~ator. In additio~, it must satisfy the following prerequisite: its length ~3 must ~-be equal to or in excess of the diameter D4 thereof. The admission end of the pipe 4 is communicated with a pipe 14 feedi~g the material to be atomized thereto through a hole 13. A sur~ace 15 of the pipe 4 is cylindrical throughout its entire length. ~he pipes 4 and 14 are in~erco~nected through a bushing 16 servi~g for a conce~tric arrangement of the pipe 4 inside the swirl chamber 1, the nozzle 2 and th~
second chamber ~. Apart ~rom that, an outside sur~ace 17 o~
the bushing 16 is prov~ded with helical grooves 18 for the atomizing gas to ~eed ~rom a pipe 19 into the swirl chamber 1, -~ ., ., ., . . . , - , , , ~; . . .

. .. . .... .. . - . .. .. .... .. .. . .
. , ., . - . . .. . . . - . -: - . . . . - , . . .
.: . . .- - - . - ... . ..
. . . - .
- . - ,- . - . . .
.

at the same time rotating the ~low of gas with a view to ef-fecting a tan~entional admission of said atomizing gas into the swirl chamber 1.
The outlet portion of the pipe 4 is closed at the exit end thereof by a blank plug 20 ~hich is taper-shaped in the given particular embodiment of the device, said blank plug 20 having a number o~ holes 21 for the material to be atomi-zed to discharge. ~he cylindrical surface 15 of the outlet portion o~ the pipe 4 also has a number o~ through holes 22 for the atomized material to discharge. The discharge holes 22 may be arranged in several rows. Apart from the discharge holes 21 and 22 the outlet portio~ o~ the pipe 4 may be provi ded with a spray spout 23 as illustrated in ~IG. 3 with an outlet cone 24 ~eaturing a flare angle o~ about 20 to 160 and a helical insert 25 for the atomized material to rotate.
Variation of the distance ~4 from the axis of the holes 22 to the e~it section of the second chamber 3 changes the quality of atomization and operational reliability o~ the device a~d mixture-~ormation. ~he best operating conditions of the ~evice as a ~hole is attained when the outside diameter ~5 of the pipe 4 equals 0.30 to 0.85 of the inside diameter D2 of the nozzle 2.
~ he material to be atomized is ~ed in the direction indi cated by the arro~ A to get i~to the pipe 14, said pipe ~4 having the diameter D6 large enough to reduce its hydrody~a--'11-!V `

:,~.. . . ,,,, .. , . . ., ,'' :

''' ',' . '' '~'.' ''- ' ' '. ', ' :' ': ' - : ' ' . - :

', ' " .,'- :

.

mic resistance. ~rom the pipe 14 the material passes into the pipe 4 through the holc 13 to flow along said pipe to the discharge holes 2~ and 22 through which it is fed into the second chamber 3 in a number of fine streams. ~Jhen the materi al being atomized flows out from the d~charge holes 21 and 22 it becomes preatomized in the flow o~ atomizing gas due to said flow expanding while passing through the second chamber 3. ~he atomizing gas is fed in the direction indicated by the arrows B to the pipe 19 having a diameter D7 large enough to reduce hydrodynamic losses therein. ~rom the pipe 19 the atomizing gas gets into the helical grooves 18, wherein it is i~parted rotation and is then admitted tangentially to the swirl chamber ~. It is in the swirl chamber 1 ~hat the ~low conditions of t~e atomizing gas becomes stabilized. ~rom the swirl chamber 1 the rotated flow of the atomizing gas is di-rected to the ~ozzle 2, where its rotational velocity is gre-atly increased to such an amount that acoustic oscillations set up in the nozzle 2. Said oscillations owe their origin to an intexaction of the swirled flow of the atomizing gas flowing ou-t from th~ nozzle 2 and the back flow of the surrou nding atmosphere getting into the nozzle 2, i.e., to a ver~
high rarefaction established at the exit of the nozzle 2. It shall b~ noted that a rarefaction, though o~ much less extent has been provided in the swirl chamber 1 as well. ~hen the acoustically e~cited flow of the atomiziug gas is fed from .` - '.

.:

. . . . , . - .

:- - . , . ~ . :
. . , ~ . .
. . . - .. . . .
. , . . - .
. : . - .
: . ' ' ~08Z094 the nozzle 2 to the second chamber 3, wherein the natural oscillation f~equency equals that of acoustic oscillations of the swirled ~low of t~e atomizing gas. It is in said chamber that the ~low ~f the atomizing gas is turned to get forced against the inside surface thereof, thus ~lowi~g around said surface while moving about the axis of the second chamber 3 and lengthwise said axis. Thus, the provision of the abovemen tioned gasdynamic phenomena makes it possible to amplify the acoustic oscillations of the rotating flow of the atomizing gas due to the presence of t~e followi~g effects. ~irst, am-plification of acoustic oscillations occurs in the second chamber 3 due to a resonance between the frequency o~ acous-tic oscillations of the swirled flow of the atomizing gas and the frequency of the natural oscillatio~s of the second cham-ber 3. Secondly9 the conditions of reflection and interferen-ce of acoustic waves provided in the second chamber 3 enable said waves to be amplified and, moreover,, concentrated in a single direction. Furthermore, amplification of acoustic oscillations is affected by the interaction of the swirled flow o~ the atomizing gas flowing out ~rom the second chamber 3 with the ~low of the atmosphere surrounding the atomizing de~ice, maki~g its wa~ into the second chamber 3.
- ~he flow of the atomizi~g gas fiwirled i~side the second chamber 3 with the amplfied acoustic oscillations therei~

- -. : - - .. .. -- ~ - ~, - - -. - ~ , . ~, . -' ' ' ' :' ' . :'' ,~

-::

:: . . :

ac~s upon the streams of the material being atomized flowin~
out from the discharge holes 21 and 22 of the outlet portion of the pipe 4 to atomize said streams. The atomizing effect is intensified also due to the fact that t~e rotating acous-tically excited flow of the atomizing gas acts upon the streams o~ the material being handled just at the instance said streams are no longer a solid medium but are i~ fact a stream of separate particles, i.e.~ lurther disintegration thereo~ takes place. This i8 conduced by the spatial dimensi-ons o~ the second chamber 3 which enable one to provide the distance long enough ~or th~ streams of the material to preat omize when said streams pass from the holes 22 to the surface 10 of the second chamber 3. Provision of a definite and long enough distance ~4 between the streams flowing out ~rom the holes 21 and 22, and the e~it section o~ the second chamber 3 establishes a condition for a quality preliminary mixture formation ~eaturing high ~ineness ratio of the particles thereo~ a~d their evan spread across the spray area. All this what is just needed for utilization o~ the gi~en atomi-zing device i~ those process appsratus where quality disper-sion and mi~ture ~ormation is required. -It i8 a quality dispersing and mixture forming that is necessary, say, i~ ~uel combustion process occurring in bur-ner de~ices. ~here~ore, the given atomizing de~ice may be .

~.................................. . . . . .
' ~. . ' ~- .
.
... . . . .
, : :
. . . - ,.

108;~094 applied in diverse burner devices, preferably in those fired by liquid or gaseous fuels.
In such devices fuel and oxidant are fed into the ~iring chamb~r as a preliminary prepared mixture, as preliminary mixi~g proves to be one of the most e~ficien~ ways of inten-sifying the combustion process.
~ he herein-proposed atomizing device, according to the invention is advantageous i~ that acoustic energy concentra-ted along the axis thereo~ makes it possible not only define a quality mixture ~ormation but also establish a mLxture spray discharged from the device, of the required shape.
Moreover, a secondary air stream flowing around the device from out~ide, co~tributes to more efficient combustion due to formation of fuel mixtures required for a complete ~uel combustion, and providi~g an additio~al combustion front Apart from that effect, the secondary air stream additi-onally cools the atomizing device of the present i~vention, whereby the device is applicable i~ high-temperature and cor-rosive conditions of Yiring systems, such as those of chemi-cal engineering apparatus.

-'15 -- . .. - ... . ., . . - . -~ - . . . : .
.
.

--:

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An atomizing device, comprising: a cylindrical swirl chamber, means in said swirl chamber for imparting rotation to the flow of an atomizing gas, said swirl chamber being provided with a nozzle adapted for enhancing the degree of swirling of said gas flow so as to generate acoustic oscillations; a second chamber comprising a resonator of acoustic oscillations corres-ponding to acoustic oscillations of said swirled flow of atomizing gas, said chamber adjoining said nozzle; and a pipe arranged coaxially in said chambers and said nozzle and adapted to feed the material being atomized into said second chamber.

2. An atomizing device as claimed in claim 1, wherein said second chamber comprises a quarter-wave acoustic resonator.

3. An atomizing device as claimed in claim 1, wherein said second chamber is a cylinder whose diameter is a few times that of said nozzle.

4. An atomizing device as claimed in claim 1, wherein the length of said second chamber is equal to or greater than the diameter thereof.

5. An atomizing device as claimed in claim 1, 2 or 3 wherein the outlet end of said pipe has a plurality of discharge holes.

6. An atomizing device as claimed in claim 1, 2 or 3 wherein the outlet end of said pipe is provided with a spray spout.