US2552970A - Sonic generator - Google Patents

Description

May 15 1951 c. B. HoRsLEY ET Al. 2,552,970

SONIC GENERATOR Original Filed F'eb. 24, 1949 @ardore mwy,

y www #/M Patented May l, 1945.1

SONIC GENERATOR Caperton B. Horsley, Westwood, and Gordon C. Seavey, Arlington, Mass., assignors to Sonic Research Corporation, Boston, Mass., a corporation of Massachusetts Continuation of abandoned application Serial No.

78,064, February 24, 1949.

This application ctober 22, 1949, Serial N0. 122,934

3 Claims. (Cl. 259-1) This invention relates to improvements in equipment for producing periodic variations in pressure and/or acceleration in various forms of matter in ways that are both desirable and not readily carried out by means of other available agencies. As a matter of convenience, equipment for producing such variations will herein- One desirable embodiment of the invention isY exemplified by sonic generator mechanisms which are designed for the treatment of certain liquids and hydrosols, although here it should be understood that the invention is not confined in its application to'these or any other particular form of matter. As illustrative of specific instances ofV treating liquids, known to be desirable, there mayV be noted the deflocculation of paper pulp bres, the sterilization of milk, the preparation of emulsions, and various other procedures.

Y It is to be noted thatsuch processes as those referred to may be carried out on a commercial scale only if sufcient acoustic power is available as would be provided by a sonic generator, wherein, for example, a mechanically driven piston is used to impart energy to the treated material. This is to be preferred to the use of a magneto-strictive or piezo-electric driving unit operating at a relatively low power output, as in various types of sonic generators heretofore proposed. With a piston type generator, however, there remains the need for suitable means to reduce loads on the bearings of the drive mechanism and also means for improving the distribution of acoustic energy throughout the body of treated material. Y

It is, therefore, a general object of the invention to improve apparatus for sonic treatment of uids, and to devise sound generator mechanisms having a sufiiciently low cost per Unit of acoustic power produced to make feasible the treatment of commercial quantities of materials.

It is a more specific object of the invention to devise a means for treating a body of material with effectively constant values of alternating pressure variation throughout the extent of a treating chamber or effectively constant values of alternating variation in acceleration throughout the extent of the treating chamber.

It is a further object of the invention to indicate a relationship of parts which will permit of sonic treatment with a piston type generator at low values of bearing load on the drive mechanism, irrespective of the specific lengths of the treating chamber.

The sonic generator of the invention overcomes the bearing load difculty by means of a novel arrangement and proportioning of operating parts in a piston type generator and by balancing certain forces which are set up in the generator. Essentially the generator of the invention includes a treating chamber, a piston mounted at one end of the chamber, and driving means for reciprocating the piston at some ydesired frequency of vibration.

We have discovered that for a generator structure of this character there may be built up dimensional, mass, and force relationships of an optimum character from'the standpoint of reducing operating stresses on the driving mechanism. This discovery is based upon a recognition of the fact that any system composed of solids and fluids, in which there are not excessive losses causedby internal friction, may be set into mechanical resonance at certain frequencies.

It is known in the art that one specic device utilizing this general principle has been constructed in the form of a lpiston type generator for treating liquids wherein the accompanying treating chamber consists of a tube with its axial dimension equal to a multiple of one-quarter of the wavelength of sound in the liquid being treated. In such a device the load on the bearings of the drive mechanism will be effectively cancelled out by the compensating forces exerted by the liquid on the face of the piston.

In the subject invention, however, we have devised means for treating material at a desired frequency with a piston type sonic generator whose treatment chamber` may, for convenience, be considerably less than one-quarter wavelength in its long dimension. Furthermore, the embodiments of the invention presented'operate to distribute the effects of pressure or acceleration sensibly uniformly throughout the body of the material being treated, which distribution cannot occur in the quarter wavelength chamber previously proposed in the art.

These and other objectives and novel features of the invention will be more fully understood andlappreciated from the following description of two preferred embodiments selected for purposes of illustration and shown in the accompanying drawings in which:

Fig. 1 is a cross-sectional view of a piston type sound generator of the invention for the sensibly equal distribution of pressure variation throughout a body of treated material;

Fig. 2 is a cross-sectional view of another form of sound generator of the piston type devised especially for the sensibly equal distribution of variations in acceleration throughout the treated material; and

Fig. 3 is a graph illustrating pressure and displacement variation curves in a one-.quarter wavelength segment of a standing wave at 200 cycles per second, neglecting losses.

In the structure shown in Fig. l, numeral IU denotes a tube or cylinder having a closed end I2. At the opposite end of the cylinder is slidably received a piston I4, provided with a sealing member or members IS in contact with the inner peripheral surface of the cylinder I to prevent escape of liquid in the cylinder. The cylinder in effect constitutes a treating chamber in which the liquid material may be subjected to a desired sound intensity at some selected frequency. The piston If! is reciprocated by means of a driving mechanism which includes a rod 2) secured to the piston I4 and slidably supported in a bearing 22. A link 24 is connected at one end of the rod by a pin 26. The other end of the link is engaged about a crankshaft 28 which may be actuated in any conventional manner. A housing 30 encloses the structure described.

The embodiment shown in Fig. 2, designed for the production of variations primarily in acceleration, diiers from the device of Fig. 1 in that the end of the treating chamber is closed with a exible diaphragm member 32, and the piston is supported in spaced relationship to the housing by means of spring members 34.

The embodiments noted constitute simple means of generating sound in a fluid body. It has been noted above that in devices heretofore employed in the art, it was proposed to reduce bearing loads on the driving mechanism by constructing a treating chamber in the form of a tube whose axial dimension is some integral multiple of one-quarter of the wavelength of sound in the uid to be treated. This imposes a limitation on the convenience of construction, in that the minimum length of chamber for which this scheme is eective may still prove to be cumbersome. For example, the wavelength of sound in water at a frequency of 200 C. P. S., which is desirable for some types of treatment, is 24 feet; thus the minimum allowable length of chamber for treatment at this frequency is one-quarter wavelength, or 6 feet.

Furthermore, if one considers the pattern of alternating pressure distribution in the one-quarter wavelength chamber, one nds that it varies from a minimum at the piston end to a maximum at the closed end. We have illustrated one such condition in Fig. 3, wherein the solid lines show values of pressure variation in pounds per square inch in a one-quarter Wavelength segment of a standing wave, at 200 C. P. S. in water at a sound intensity of 1,600 watts per square centimeter in a free field.

Thus, if the axial dimension of chamber IIl of Fig. l were one-quarter wavelength, there would be in the chamber the non-uniform distribution of pressure variation shown by the solid lines of Fig. 3. Also, and conversely, there would be in the chamber I I! the concomitant non-uniform distribution of displacement of treated material shown by the dotted curves, arising from the previously mentioned acceleration effect in the sound eld.

We have found, however, that it is desirable in some types of sonic treatment to maintain sensibly uniform values of pressure variation throughout the body of treated material, or in the course of treatment for other purposes to maintain a sensibly constant variation in acceleration or displacement throughout the treated material. By so doing, it is possible to produce the desired type of sonic treatment with greater efficiency and to utilize the entire treating chamber with maximum effectiveness. In still other types of treatment it may be suicient to maintain these variations above a certain predetermined minimum value throughout the chamber.

As noted above, these desirable objectives are achieved by taking advantage of resonant phenomena and constructing the apparatus described with specific dimensional relationships. Thus, in the operation of our invention, to produce pressure variations which are above a given minimum throughout the chamber, we may choose the weight of piston I6 and the length of the treating chamber I8 with reference to the physical and elastic constants of the treated material, so that the system of piston plus liquid is in resonance, at the predetermined operating frequency, even though the chamber length is not some multiple of a quarter wavelength. In this case the pressure variations throughout the chamber will be above the desired minimum value.

If this minimum value is high enough to cause the appearance of cavitation in the liquid with a resultant decrease in the eciency of sonic treatment, the mean pressure of the entire system may be increased through the addition or pressurizing means 3|, as shown in Fig. 1, to such a point that cavitation is no longer a limiting factor.

The pattern of pressure variation in the invention according to Fig. 1 may be more readily visualized with reference to the solid line curves of Fig. 3, wherein there are plotted for convenience the maximum and minimum values of oscillatory pressure in a quarter wavelength of a standing Wave pattern under the conditions specified above, namely at 200 C. P. S. in water at a sound intensity of 1,600 watts per square centimeter in a free eld.

Suppose that for a given application it were found desirable to maintain pressure variation of plus or minus 950 p. s. i. throughout the treated material. Then that portion of the one-quarter Wavelength pattern to the right of the line PP' would be ineffective in bringing about the desired result. Consequently, in accordance with the invention We choose our chamber of a length XY, and we choose our piston I6 of such a weight that it resonates with the fluid in the treating chamber to produce that pattern of pressure variation shown in the segment o f the one-quarter Wavelength pattern bouned by the lines XX and PP. In effect, the massive piston member of this embodiment replaces the fluid in the region PP-YY. Since the shorter uid column represents a stiier spring, the system-fluid plus piston-is made resonant at the chosen operating frequency (200 C. P. S.) by increasing the weight or the piston. The stroke of the crankshaft is also shortened, since with the shorter fluid column, the same pressure variation will be obtained with less movement of the piston.

In other applications it Will be desirable to maintain constant variations in acceleration or displacement, as previously mentioned. In this case, the crankshaft stroke indicated for Fig. 1 is maintained and the piston weight is not increased beyond the point required for structural rigidity. The chamber length is changed to that of Fig. 2 but a diaphragm 32 is provided at the end of the chamber so that this end is movable instead of stationary, and a system of springs 34 is added to make this system resonant at 200 C. P. S.

In operation of this latter embodiment, the chamber is chosen of such a length that the desired minimum valve of acceleration or displacement is maintained throughout the body of treated material. Thus, if it were determined that a value of plus or minus .145 of displacement were necessary for the desired treatment, the chamber length would be made equal to the distance AY. Then the elastic constants of the springs 34 would be so chosen that the system-piston plus fluid--would resonate at the chosen operating frequency of 200 C. P. S. In effect, addition of the spring elements 34 of this embodiment acts as a substitute for the compensating forces of the fluid of the region XX-AA.

It should be noted that in operation of the embodiment illustrated in Fig. 2, for the production of variations in acceleration in a body of gaseous fluid, the elastic constants of the spring members 34 may be chosen without reference to the elastic properties of the gaseous fluid where such properties wouldr contribute only a negligible amount of compensating force acting on the piston member.

In conclusion, it is pointed out that if the system composed of the fluid being treated, the piston, and the sliding rod, is resonant so that the natural frequency at which it oscillates back and forth is the same as the frequency at which it is to be driven, then the only load on the connecting pin bearing will be that required to keep the system in oscillation, and the only load on the crankshaft bearing will be the comparatively small inertia load of the connecting link, a portion of which may also be balanced out as just an addition to the piston weight, plus that required to keep the system in oscillation. If the system is not in resonance, peak loads on these bearings will be so high that in many cases it will not be feasible to construct sonic treating systems of thistype of commercially feasible size for operation at frequencies of 100 cycles or higher. Itshould be observed that advantage may be taken of the principles outlined herein at frequencies as low as cycles per second.

This application'is a continuation of abandoned application Ser. No. 78,064, filed February 24, 1949, entitled Sonic Generator.

Having thus described our invention and described in detail illustrative embodiments thereof, we claim as new and desire to secure by Letters Patent:

1. In an oscillating device for treating fluid with primarily only one of two components of quency, the mass and elastic properties of said piston assembly and container being so chosen as to constitute with the fluid a resonant system at the desired operating frequency thereby reducing bearing loads on said driving means, and the distance between the face of the piston and the end wall opposite thereto being substantially less than one-quarter wave length of sound in the fluid at such frequency, whereby said fluid will be subjected primarily only to the desired vibratory component.

2. In an oscillating device for treating fluid with primarily only the pressure variations component of tivo components of vibratory forces comprising pressure variations and acceleration variations, the combination comprising a container providingr a treating chamber adapted to be filled with the fluid to be treated, said container having an end wall and side walls, a piston assembly including a piston forming the other end wall of the container and facing said rst named end wall, and driving means associated with said assembly for vibrating said piston against the fluid at a desired frequency, the mass of said piston being so chosen as to constitute with the fluid a resonant system at the desired frequency for reducing bearing loads on said driving means, and the distance between the face of the piston and the end wall opposite thereto being substantially less than one-quarter wave length of sound in the uid at such frequency, whereby said fluid will be subjected primarily only to the pressure variations vibratory component.

3. In an oscillating device for treating fluid with primarily only the acceleration variations component of two components of vibratory forces comprising pressure variations and acceleration variations, the combination comprising a container providing a treating chamber adapted to be lled with the fluid to be treated, said container having an end wall and side walls, said end wall comprising a iieXible diaphragm, a piston assembly including a piston forming the other end wall of the container and facing said diaphragm, spring means constituting part of said assembly connected between said piston and container for tending to position the former in a constant location when at rest, and driving means for vibrating said piston against the uid at a desired frequency, the mass and elastic properties of said piston, diaphragm and spring means being so chosen as to constitute with the fluid a resonant system at the desired frequency for reducing bearing loads on said driving means, and the distance between the face of the piston and said diaphragm being substantially less than one-quarter wave length of sound in the iiuid at such frequency, whereby said fluid will be subjected primarily only to the acceleration variations component.

CAPERTON B. HORSLEzY. GORDON C. SEAVEY.

REFERENCES CITED The following references are of record in the flle of this patent:V

UNITED STATES PATENTS Number Name Date 2,015,217 Denian Sept. 24, 1935 2,090,496 Wynn Aug. 17, 1937 2,138,052 Williams Nov. 29, 1938 2,138,839 Chambers Dec. 6, 1938

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