US3214846A

US3214846A - Sonic generator

Info

Publication number: US3214846A
Application number: US230094A
Authority: US
Inventors: Robert S Soloff
Original assignee: Branson Ultrasonics Corp
Current assignee: Branson Ultrasonics Corp
Priority date: 1962-10-12
Filing date: 1962-10-12
Publication date: 1965-11-02
Anticipated expiration: 1982-11-02

Description

Nov. 2, 1965 R. s. SOLOFF 3,214,846

SONIC GENERATOR Filed Oct. 12, 1962 2 Sheets-Sheet 1 INVENTOR.

ROBERT S. SOLOFF Nov. 2, 1965 R. s. SOLOFF 3,214,846

SONIC GENERATOR Filed Oct. 12, 1962 2 Sheets-Sheet 2 RELATIVE ENERGY PERCENTAGE INVENTOR. ROBERT S. SOLOFF ATTORNEY United States Patent 3,214,846 SONIC GENERATOR Robert S. Soloti, Brooklyn, N.Y., assignor, by mesne assignments, to Branson Instruments, Incorporated, Stamford, Conn., a corporation of Delaware Filed Oct. 12, 1962, Ser. No. 230,094 2 Claims. (Cl. 34-142) This invention relates to a sonic dryer and to a sonic generator producing intense sonic vibrations from a compressed gas whistle without a concomitant blast of compressed gas.

It has been proposed to accelerate the drying of finely divided solids by passing them through a dryer of conventional design, at one end of which is a high powered whistle operated by compressed gas, usually compressed air. The resulting sonic vibrations in the dryer accelerate the drying of the solid particles. However, a serious problem has arisen. In order to produce intense sonic vibrations a very large volume of compressed air is necessary and this produces a blast of air along with the sonic vibrations. The blast has seriously interfered with proper drying and has sometimes blown out solid particles which has produced a serious dust hazard. As a result the theoretically attractive concept of sonic drying has achieved but little practical utility.

The present invention has for its heart a compressed air or gas whistle which produces intense sonic vibrations without any accompanying blast of air. The large volumes of air escape substantially at right angles without interfering with the production of the sonic vibrations. When this generator is mounted in a conventional dryer the intense sonic vibrations are imparted to the air in the dryer which moves slowly and the blast of air pro ducing the sonic vibrations escapes at right angles to the generator and does not enter the dryer. There is thus obtained the intense sonic vibrations without any air blast and the dryer can be operated with a gentle stream of warmed air for optimum drying. The full effect of the sonic vibrations is retained without any of the drawbacks encountered previously as a result of the air blast.

Reference has been made to sonic vibrations. For best drying purposes normally this is a high frequency sound, for example of the order of 10,000 cycles. The invention is, however, in no sense limited to the particular frequency of sonic vibrations used. They may be higher or lower, and even extend into the ultrasonic region. However, as will be pointed out, the frequency of the sound is connected in a critical manner with other dimensions of the generator and so, while various sound frequencies may be used, once a sound frequency is chosen it will have to be maintained unless the generator is readjusted or rebuilt to different dimensions.

The invention will be described in greater detail in connection with the drawings in which:

FIG. 1 is a section through a dryer;

FIG. 2 is a detailed section on an enlarged scale of the sonic generator, and

FIG. 3 is a graph of variation of sonic intensity with generator element dimensions.

The dryer, which is conventional in form, is shown with a rotatable drum 1 provided with vanes for lifting and dropping particulate matter through the atmosphere in the dryer. The drum of the dryer is turned by gears 3 from a driving source (not shown). At one end is a feed hopper 4 which feeds wet or damp particulate solids into one end of the dryer. This is surrounded with an air introducing annulus 6 through which warm air is introduced at relatively slow speeds. At the other end of the dryer there is an outlet chute through which introduced air escapes and also the dried solids particles.

Patented Nov. 2, 1965 In this end of the drum there is the entrance pipe 7 of the sonic generator which is shown in detail in FIG. 2. The entrance pipe 7 is attached to the dryer by means of the flange 8 and bolts 9.

Turning now to FIG. 2 the entrance pipe 7 is connected to a block of metal 10 through pins 16. The block 10 has a hollowed tapered portion 11 in which is located centrally a spindle 15 on which is mounted a cup shaped resonating cavity 14. The fastening is made permanently by the pin 18. A connection to a source of high pressure compressed air 12 is also fastened to the block 10. The spindle 15 forms with the hollowed portion 11 a nozzle 13 through which the compressed air escapes at supersonic speeds. This blast strikes the resonator 14. The blast of air produces intense sonic vibrations and passes out along the sloping end of the reflecting surface 17, through the space between the tube 7 and the block 10. The violent sonic vibrations traverse the tube 7 through relatively stagnant air with no sub stantial portion of the air blast which generates the sound flowing through the tube 7. The sonic vibrations, largely in the form of standing waves, continue through the relatively gently moving air in the dryer, accomplishing the effect of increased drying, which is the purpose of all sonic dryers.

The dimensions of the tube 7 are quite critical for optimum efiicieney. This tube may be considered acoustically as an open organ pipe, and the sonic vibrations set up a standing wave phenomenon within the tube. Ordinarily, the greatest intensity of energy is produced a half wave length from the sonic generator, and so one would expect that for maximum efficiency the tube 7 should be a half wave length long for the particular sonic frequency employed. It has been found that this is exactly what should not be done. For maximum efficiency the tube should be two half wave lengths long. This is directly contrary to ordinary acoustic experience, but it is observed with complete regularity and is a characteristic of the sonic generator of the present invention.

FIG. 3 shows three points corresponding to three tube lengths, in the form of a bar graph, one being a single half wave length, as shown on the abscissa, the second being the preferred two half wave lengths, and the third, three half wave lengths. In an ordinary organ pipe, acoustic theory specifies that maximum sound energy is produced at a length of half a wave length, falling off for successive half wave lengths in an exponential manner. FIG. 3 shows that maximum intensity is obtained with a tube length of two wave lengths, the theoretically best length of a single half wave length being 2 db down, or about 63%, and even the third half Wave length is only down 1 db, and so is considerably stronger than the theoretically preferable single half wave length tube. The reasons for this anomalous behavior of the sonic generator of the present invention have not been rigorously established and so the invention is in no sense intended to be limited to any particular theory as to why ordinary acoustic practice does not hold in the present invention. Needless to say, the length of the tube 7 is adjusted to be two half wave lengths long for the particular frequency to be used. This frequency can be determined by air pressure and location of the resonator 14 and should be accurately fixed. The particular frequency chosen is of much less significance than the accurate dimensioning of the tube 7 for the frequency used.

While the sonic generator of the present invention finds its greatest practical field of utility in sonic dryers it is of course not limited to this use and may be employed anywhere where it is important to generate intense sonic vibrations without an accompanying blast of gas. It should be noted that in the present invention the blast of air is ejected at an angle to the tube 7. It is essential that there be baflling means which prevent this blast from moving forward and mixing with the sonic vibrations at the end of the tube 7. In the case of the dryer the end wall of the dryer forms its bafile.

The invention was illustrated in connection with a dryer which represents a substantially incloscd space. Standing waves are therefore set up and so no special directing means need be attached to the tube. When the invention is used with or in relatively unconfined spaces directing elements such as horns are advantageously attached to the tube. The horn shapes are well known and are therefore not illustrated in the drawings. Cones and exponential horns are among the most common shapes. They all act as baflles, but when maximum coupling to unconfined air is desired exponential horns exhibit somewhat greater efiiciency. Due to the high frequencies the difierence in coupling between cones and exponential horns is not very great as it is at lower frequencies.

The phenomenon is quite diflerent from that of a toroidal acoustic reflector which has been proposed and which leads a blast of air around and backward by reason of the shape of its surface. With such a reflector no tube analogous to the tube 7 is used. The present invention is strictly limited to the combination of such a tube of definite length with a sonic generator of the, resonating cavity type.

I claim:

1. A sonic generator comprising,

(a) a nozzle adapted to carry gas under pressure at supersonic velocities,

(b) a sonic cavity resonator axially aligned with said nozzle, and spaced therefrom to produce sonic vibrations of a predetermined wavelength,

(0) a reflecting element surrounding the nozzle and,

(d) an open ended resonant tube surrounding the cavity and connected to the reflector to provide a peripheral escape slot for air blast, said tube having a length approximately equal to two half wave lengths of the sonic vibrations. v

2. A sonic dryer comprising in combination (a) a drum,

(b) means for rotating the drum slowly, and means carried by the drum for distributing finely particulate material through the atmosphere in the drum,

(c) means for introducing particulate material to be dried in one end of the drum, means for maintaining a slow movement of atmosphere through the drum, and

(d) a sonic generator according to claim 1, the tuned tube thereof protruding into one end of the drum, said drum end being sealed against air blast from the sonic generator.

References Cited by the Examiner UNITED STATES PATENTS 1,245,517 11/17 Scuterud 84410 2,344,7 5 4 3/44 Vang.

2,413,420 12/46 Stephanofl.

2,576,297 11/51 Horsl'ey et al. 34-4 3,064,619 11/62 Fortman 116l3 WILLIAM F. O DEA, Primary Examiner. NORMAN YUDKOFF, Examiner.

Claims

1. A SONIC GENERATOR COMPRISING, (A) A NOZZLE ADAPTED TO CARRY GAS UNDER PRESSURE AT SUPERSONIC VELOCITIES, (B) A SONIC CAVITY RESONATOR AXIALLY ALIGNED WITH SAID NOZZLE, AND SPACED THEREFROM TO PRODUCE SONIC VIBRATIONS OF A PREDETERMINED WAVELENGTH, (C) A REFLECTING ELEMENT SURROUNDING THE NOZZLE AND,