US2514797A - Heat exchanger - Google Patents

Description

July 11, 1950 R. s. ROBINSON HEAT EXCHANGER 3 Sheets-Sheet 1 Filed Jan. 24, 1946 FIG.

INVENTOR. R. S. ROBINSON HIS ATTORNEY July 11, 1950 R. s. ROBINSON HEAT EXCHANGER Filed Jan. 24. 1946 3 Shets-Sheet 2 INVENTOR.

.R. S. ROBINSON HIS ATTORNEY ly 11, 1950 R. s. RbBmsON 7 2,514,797

V HEAT EXCHANGER Filed Jan. 24, 1946 3 Sheets-Sheet 3 INVENTOR.

\ R. s. ROBINSON HIS ATTORNEY Patented July 11, 1950 HEAT EXCHANGER Richard S. Robinson, Gloucester, Mass., assignor,

by mesne assignments, to Raytheon Manufacturing Company, a corporation of Delaware Application January 24, 1946, Serial No. 643,167

- 3 Claims. (or 257-73) The present inventionrelates to methods and apparatus for producing heat transfer and more particularly to heat exchangers, evaporators and similar apparatus.

It is an object of the present invention to provide a method and apparatus to increase the overall heat transfer coefficient in heat exchange apparatus.

In the operation of equipment involving the transfer of heat from one fluid to another through a metal or other wall, the major resistance to the ficw of heat has been found to be due, not to'the wall, but to surface films of the materials on the two sides of the wall. In order to obtain maximum heat transfer emciency, considerable effortsare made in the design of the apparatus to minimize film formation and its effects. In tubes, the velocity of the medium is carefully adjusted to provide the proper balance of the magnitude of heat transfer per unit length with respect to the efficiency of heat transfer. Shells or jackets are somewhat more of a problem and often contain baifies to break up the flow and thereby disturb the film. However, none of these arrangements is fully satisfactory. Failure to obtain a sufiiciently high heat transfer coemcient tends to shorten the life of the equipment from local overheating or to damage the product. It also slows down the overall process rate and increases the necessary amount of circulating medium, thereby increasing pumping costs. The

present invention provides a means for overcoming these difiiculties.

According to the present invention sonic or supersonic compressional wave vibrations are ap plied to either the circulating or the processed medium. The vibrations are thus transmitted in part to both media. In this way, waves impinging on one side of the wall through which the heat is transferred destroy the surface films on that side and, being transmitted in part through the wall, also destroy the films on the other side. In cases where water is one of the media there is the further advantage of tending to prevent scale formation whereby a permanent high heat transfer c'oeilicient is obtained.

A further understanding of the invention and the objects to be obtained will best be understood from the following description taken in connection with the accompanying drawings, in which Fig. 1 is a partially cut-away perspective view of a heat exchanger with helical tubes and means for applying compressional wave energy;

Fig. 2 shows a modification of the invention as applied to a simplified tube and shell heat exchanger; Fig. 3 is a further modification of the invention showing its applicationto a jacketed mixer or reactor; Fig. 4 is a view in elevation and partiallyin section of a further modification of the invention applied to an agitated vacuum pan evaporator or crystallizer; and Fig. 5 is a modification of Fig. 4.

Referring now to Fig. 1, the heat exchanger is provided with a plurality of helical tubes I which are connected in parallel. Material to be heated or cooled is passed through these tubes. The tubes are enclosed in a casing having two walls 2 and 3 joined by a cylindrical flanged member i. A heating or cooling medium is circulated around the tubes l inside the casing. The material to be treated may enter the coils I through an aperture 5 and be taken out through an aperture 5 while the heating or cooling medium may enter the casing through an aperture 7 and be removed through an aperture 8 in the wall 2 of the casing. Heat exchangers of this type are well known in the art.

In accordance with my invention, however, compressional wave energy is introduced in some suitable manner into the heating or cooling medium surrounding the tubes i. For this purpose I prefer to construct one of the walls of the casing of the heat exchanger, say the wall 3, in the form of a vibratable diaphragm as shown in Fig. 1. A suitable vibrating mechanism may then be provided on the outside of the diaphragm wall 3. In the arrangement shown this may include a laminated magnetic armature 9' mounted on the diaphragm 3. Separated from the armature by a suitable air gap is an electromagnet 9 provided with a winding I0 and mounted on a fixed member H which may be shaped with a flange H to provide an enclosure for the electromagnet structure. The flange ll may for example be bolted to the diaphragm member 3 by means of the bolts I2. In order to provide for the" cooling of the electromagnet structure, another chamber l3 may be formed in back of the member H by means of a member It as shown. A cooling medium may then be circulated through the chamber l3. vThe magnet 9, by means of the winding It, may be energized with alternating current of the desired frequency thereby producing vibration of the armature 9 and the diaphragm wall 3. The latter is preferably tuned to have a suit.-

able natural frequency with relation to the frequency of the exciting current.

Compressional wave energy is thereby transferred to the medium surrounding the coils I and serves to break up or prevent the formation 3 of surface films on the outside of the tube I. Some of the vibrational energy passes through the tubes and into the liquid being treated within the tubes. Here the energy also serves to break up or prevent the formation of films on the inside of the tubes A greatly improved heat transfer coefficient is thus obtained.

My invention may be applied to other forms of heat exchangers including evaporators, crystallizers and the like. By way of example, I have illustrated various other arrangements.

In Fig. 2 a conventional type of shell and tube heat exchanger is illustrated as modified in accordance with my invention. This device comprises an outer cylindrical shell l5 having entrance and exit apertures I6 and I1 usually for the heating or cooling medium. Through the interior of the shell l5 passes a tube l8 which is usually arranged in the form of a plurality of longitudinal tube sections coupled at the ends by U-shaped tube members. The material to be processed is usually pumped through the tube H3. The shell I5 is closed at the ends by head members l9 and 20, one or both of which may be constructed in the form of vibrating diaphragms. A vibratable structure I9 similar to that shown in Fig. 1 is shown in section at the left end of the shell in Fig. 2. The right end of the shell may be similarly constructed if desired. By means of vibrations of the diaphragms l9 and/or 20, compressional waves are introduced into the medium within the shell surrounding the tubes |8, thereby breaking up surface films on the outside of the tubes. Some of the sound energy will pass through the tube |8'to the inside of the tube and there likewise thoroughly break up the surface films.

Another arrangement is shown in Fig. 3, which represents a jacketed mixer or reactor. This comprises an inner container 2|, provided with an outer shell or jacket 22. Material to be treated is placed within the container 2| which may be closed by acover 23. If desired an agitator 24 may be introduced into the container 2| through the cover as shown.

Heating or cooling medium is introduced into the jacket space and thus surrounds the container 2|. To break up or prevent the formation of surface films inside and outside the container 2|, a vibratable diaphragm 25, for example like the diaphragms 3 and I9 operated by a vibrator (not shown) in the casing 26 may be provided at the bottom of the jacket 22, so that vibrations are transferred directly to the heating or cooling medium and thence in part, through the container wall 2|, to the medium being processed within the container.

Another arrangement is illustrated in Fig. 4 which represents an agitated vacuum pan evaporator or crystallizer. Here the material to be treated is contained within a chamber 30 which is surrounded by a jacket 3| through which steam or cooling water may be introduced at various points through the jacket wall. Openings 3| cut into the jacket wall at one or more places may be provided with vibratable diaphragms such as 32 and 33 as illustrated in the figure. These diaphragms may be vibrated by vibrators (not shown) in casings 34 and 35. The vibrations are thus transmitted directly to the heating or cooling medium within the jacket. Some of the vibrating energy passes through the wall 30 of the inner chamber into the ma erial being processed. Surface films on both sides of the chamber wall 30 are thereby broken up or prevented from forming whereby improved heat transfer efiiclency is obtained. In arrangements of this kind an agitator 36 is usually provided, as well as baiiies 31 and 33, within the chamber 30. In this type of equipment, particularly where steam is the medium within the jacket, it is frequently preferable to introduce the vibrations directly into the processed material rather than to the medium within the jacket. For this purpose a portion of the chamber 30 may be cut away. the edges being properly sealed, and the vibrating diaphragm may be mounted directly in the wall of the inner chamber. This modification is illustrated in Fig. 5. Here the wall 30 of the inner chamber is provided with an aperture 41 whose 'edges may be thickened as at 38. A diaphragm 39 vibrated by the vibrator 40 may then be bolted to the thickened portion 38. The outer wall of the jacket 3| must, of course, for this construction, be cut away in a suflicient area to permit of the installation of the vibrating equipment. In this case the vibrations pass through the processed material and thence outward through the chamber wall 30 and into the jacket chamber. As in the other modifications, the surface films on both inside and outside of the chamber 30 are thereby broken up, similarly producing a high heat transfer efficiency.

In carrying out my invention, any frequency of vibration may be used, the choice depending somewhat upon the kind of material being processed. I prefer, however, to use a low sonic frequency, say of the order of cycles, whereby a considerable compressional wave energy of large amplitude can readily be obtained.

Having now described my invention, I claim:

1. Heat exchanger apparatus comprising coiled tubular means having fluid inlet and outlet means and its convolutions all lying in a first plane, a chamber surrounding said tubular means, said chamber having a vibratable diaphragm as one wall thereof, said diaphragm lying in a second plane parallel to said first plane and means attached to said diaphragm for imparting vibratory energy thereto. I

2. Heat exchanger apparatus comprising tubular means coiled in a flat spiral and having fiuid inlet and outlet means, a chamber surrounding said tubular means having one wall in the form of a vibratable plane diaphragm parallel to said fiat spiral and means attached to said diaphragm for imparting vibratory energy thereto.

3. Heat exchanger apparatus as claimed in claim 1 wherein the area ofthe plane of the diaphragm is substantially coextensive with the area of said first plane. j

RICHARD ROBINSON.

REFERENCES CITED The following references are ofv record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,138,051 Williams Nov. 29, 1938 2,163,649 Weaver June 27, 1939 2,351,163 Thomas June 13, 1944 FOREIGN PATENTS Number Country Date 532,144 Great Britain Jan. 17, 1941

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