US2915296A - Heat exchanger - Google Patents

Description

A. F. JOHNSON 2,915,296

HEAT EXCHANGER 3 Shets-Sheet 1 Dec. 1, 1959 Filed April 7, 1955 IINVENTOR. ARTHUR F. JOHNSON 6m 21/. 2 HAMML AGENT Fig. 2

Dec. 1, 1959 F, fis N 2,915,296

I HEAT EXCHANGER 7 Filed April 7, 1955 3 Sheets-Sheet 2 I mmvrox ARTHUR F. JOHNSON Mww AGENT Dec. 1, 1959 A. F. JOHNSON 2,915,296

HEAT EXCHANGER Filed April 7, 1955 5 Sheets-Sheet 3 Fig. 1/

INVENTOR. ARTHUR F. JOHNSON YMZU(W AGENT ilnited States Patent HEAT EXCHANGER Application April 7, 1955, Serial No. 499,956

7 Claims. (Cl. 257262.22)

This invention relates generally to metal fabrications and more particularly to a novel heat exchanger.

In manufacturing liquid to air type heat exchangers it is desirable to use the least amount of metal possible to achieve the area of heat exchange surface required to transfer the heat from the liquid to the air. Heat exchangers of this type ordinarily have a tube containing the liquid to be cooled and a plurality of fins extending radially therefrom. The transfer of a given amount of heat from metal to air requires a much larger surface area than is required to transfer the same amount of heat from the liquid to the metal. Consequently, the fins ordinarily make up the larger part of the heat exchanger. The ultimate cost of the heat exchanger is thus largely dependent upon'the amount of metal required to provide suificient fins to achieve the proper heat transfer from the fins to the air.

' Therefore, an object of this invention is to provide a heat exchanger with a novel fin having improved heat transfer properties. Another object of this invention is to provide heat exchange units having fins constructed from metals or alloys which have inferior specific heat conductivity but are economically advantageous. Another object of this invention is to provide a fin for heat exchangers having an improved. means for conducting the heat from a liquidto air. Stillanother object of this invention is to provide a liquid to air heat exchanger having fins adapted to more efficiently transfer heat from a confined fluid into the surrounding air. A still further object of this invention is to provide a method for making liquid to air heat exchangers. i

Other objects will become apparent from the following detail description and the attached drawing in which- Figure 1 illustrates in a perspective view an assembly of metal sheets suitable for forming a fin for heat exchangers in accordance with an embodiment of this invention;

Figure 2 is a elevational view of the assembly of Figure 1 after welding;

Figure 3 is a cross-sectional view taken along the line A-A of Figure 2;

Figure 4 illustrates in a perspective elevational view the embodiment of Figure 2 after inflation;

Figure 5 is a fragmentary perspective view partially in section along the line BB of Figure 4 illustrating the step of filling the hollow channel of the assembly;

Figure 6 illustrates an embodiment of this invention such as can be formed from the panel of Figure 4;

Figure 7 illustrates in a perspective view an assembly of two metal sheets prepared for welding to form another embodiment of this invention;

Figure 8 illustrates an embodiment of this invention formed from an assembly like that of Figure 7;

Figure 9 is a cross-sectional view illustrating the embodiment of Figure 8;

Figure 10 is a cross-sectional view of an embodiment "ice Figure ,11 illustrates still another embodiment of the invention.

In accordance with this invention, the foregoing objects as well as others are accomplished, generally speaking, by providing a heat exchanger fin having a tubular circuit containing a fluid coolant or refrigerant extending from the heated portion of the fin to the portion in the cooling medium. The circuit or conduit is of such configuration that the fluid contained therein can circulate from a point adjacent the heated liquid to the outer edge of the fin and back either entirely in the liquid phase or in both liquid and vapor phases. The conduit may extend around the edges of the fin or it may be of such configuration that one portion thereof extends along the hotter edge of the fin and another portion extends along the colder edge with radially extending portions connecting the two together. the fin is at a greater elevation than the edge adjacent the tube containing the heated liquid in order that the confined fluid after cooling by the air or other medium in contact with the fin can return by gravity to that portion of the conduit adjacent the heated liquid. Any suitable fluid may be used but for most purposes a fluid having a boiling point less than that of the liquid to be cooled is preferred so that cooling may be accomplished at least partly by phase transitions in the fluid between the liquid and vapor phases.

of this invention formed from three sheets of metal; and

In practice, the high boiling point liquid which is to be cooled is flowed through a tube or other means having attachedithereto the fins of this invention. Ordinarily, a plurality of the fins are utilized and the upper surface of each of the fins forms an acute angle with the tube. The

conduit of each fin is only partially filled with the fluid.

As stated above, it is preferred that the refrigerant have a boiling point less than that of the liquid to be cooled in order that it will be heated above its boiling point. This sets up a circulation in the conduit and the heated and less dense fluid flows towards the outer edge of the fin whereit is cooled. The more dense, cooler fluid flows by gravity back towards the inner edge of the fin adjacent the heated liquid where it again absorbs heat and the process is repeated. Since the fluid expands with in crease in temperature, and particularly at its boiling point, it is advantageous in some embodiments to make the portions which will contain the heated fluid of greater volume than those portions containing the fluid after it has been cooled. A conduit of gradual tapering width accomplishes this purpose by locating the wider portion near the heated tube and the narrower portion along the opposite edge 'of the fin. If only one tubular portion extends radially across the fin the fluid maybe refluxed with the cooler fluid flowing back into the boiler portion of theconduit for reheating. When cooling by transition from the liquid to the vapor phase of the fluid is contemplated a waffle pattern containing multiple conduits may sometimes be advantageous.

In order better to describe and further clarify the invention the following is a detail description of embodiments thereof with reference to the accompanying drawmg:

Superposed aluminum sheets 1 and 2 having a pattern of a suitable stop Weld 3 sandwiched therebetween are illustrated in Figure 1. Each of the sheets is degreased by immersing it in an organic solvent such as naphtha or White gasoline, any oxide clinging thereto is removed by scratch brushing and a pattern of stop weld 3 is applied before the sheets are assembled. Stop weld 3 may conveniently be composed of a mixture of about 13% colloidal graphite, about 40% calcium carbonate having a granulation of about 325 mesh or less and about 47% water. The two sheets are assembled by lying one on the other in face to face relationship and are fastened The outer edge of i of the circuit through which the fluid will flow.

together by spot welding or other means in areas not covered by stop weld 3.

The resulting assembly of sheets 1 and 2 is heated in a suitable furnace to about 1000 F. in a reducing atmosphere and while at this temperature the assembly is passed through a rolling mill to reduce its thickness about 60%. Those contacting surfaces of sheets 1 and 2 not protected by stop weld 3 are thus forge .welded together. The assembly may 'be rolled later at room temperature to the final gauge. in some embodiments, of course, the cold rolling step may not be required although it has been found that a cold rolling step is advantageous when it is necessary to control the final dimensions of the assembly to close tolerances.

The unwelded portions lying within the assembly are inflated by means of fluid pressure. As illustrated in Figure 2 a hole 4 is drilled in the assembly adjacent the unwelded area and a suitable needle or similar device 33, in Figure 3, is inserted in hole 4 and compressed air is applied therethrough. A panel such as derived fromthe. assembly of Figures 1, 2 and 3 is illustrated in Figure 4. The conduit resulting from the inflation is designated generally as 5 and the surface of the panel is'designated generally as 6.

The passageway or hole 4 is also utilized in filling the conduit 5 with a fluid refrigerant. A needle or similar somewhat pointed instrument illustrated as 7 in Figure 5 is inserted through hole 4 into the conduit and the desired amount of fluid, such as, ethyl alcohol, is allowed to flow in by gravity or it may be pumped in, if desired. The needle 7 should be of such dimensions that the air "displaced by the fluid in the conduit can escape through hole 4. Conduit 5 is only partially filled with a fluid in order to compensate for expansion of the fluid when heated. When the fluid chosen undergoes phase transition from a vapor to a liquid a relatively large condensation area is needed.

After the liquid has been introduced into conduit 5, hole 4 is plugged by soldering, brazing, cold welding or other suitable processes to complete the fabrication The resulting panel is then welded, brazed or attached by any other suitable means to a tube or other container adapted to contain the heated liquid in the heat exchanger. Such a tube is illustrated as 8 in Figure 6 and has a fin such as is formed from the panel of the preceding figures. Conduit 5 in this fin is of greater dimensions in those areas which will contain the heated fluid than in the other areas of the circuit. The direction of flow of fluid in conduit 5 is illustrated with arrows in Figure 6.

It is also possible to form the heat exchanger tube and fins by a forge welding process similar to that described in the foregoing. In such a process two aluminum sheets 11 and 12 in Figure 7 are cleaned as described in conjunction with the foregoing embodiment and twopatterns of stop weld 13, similar to pattern 3 of the foregoing embodiment, are applied to the surface of one sheet. A band of stop Weld 14 is applied to one surface of one of the sheets bisecting the sheet and ex- ,tending almost throughout its length such as illustrated in Figure 7. This assembly is heated, forge welded by rolling to reduce its thickness at least 65 percent and after inflated by means of fluid pressure. The assembly 1 4 is then trimmed along its edges to remove the passageway resulting from 15 so that the passageway resulting from 14 extends entirely through to provide a tube 19 with fins 20 and 21 similar to those as illustrated in Figure 8. The integral fins 20 and 21 have'conduits 22 and 23 and are filled with fluid refrigerant substantially as described in conjunction with the foregoing embodiments. A cross-sectional view of a fin and tube arrangement of the type illustrated in Figure 8 is shown in Figure 9.

A variation in the type of design that can be made in accordance with this invention is illustrated in Figure 10. In this particular embodiment three clean sheets of aluminum are utilized and patterns of stop weld are sandwiched between each pair of contacting surfaces of the resulting assembly of three sheets. The assembly is forge welded by hot rolling to reduce the thickness of the assembly about 65 percent and the unwelded areas protected by the stop Weld are inflated by means of fluid pressure to produce a central tube 19 having fins 20 and 21. Each of the fins has two conduits, one on each side thereof. The center sheet of the assembly of three sheets forms a partitioning member between the pair of conduits lying on each side of the fin. In the embodiment shown in Figure 10 the upper conduit of fin 20 is designated as 24 while the upper conduit of fin 21 is 25. The lower conduit of fin 20 is illustrated as 26 and the lower conduit of fin 21 is designated 27. It is to be noted that the fins are bent to form an acute angle with the axis of the tube in order that gravity can be utilized for return of the cooled liquid from the outer edge of the fin to that portion of the conduit adjacent tube 19. Tube 19 in this instance is in a horizontal position.

The embodiment illustrated in Figure 11 is a circular fin extending around the tube 28 which contains the heated liquid. This fin has a plurality of conduits having a portion 31 adjacent the heated tube 28, a portion 29 adjacent the cooler edge 32 and a radially extending portion 30 connecting portions 31 and 29. Edge 32 of the fin is at a higher elevation than the edge adjacent tube 28. In operation, the liquid confined in the conduit is heated to the boiling point and moves towards portion 29. It condenses there and flows back through the radially extending portion 30 to portion 31. The dimensions of the portions 29 and 31 can, of course, be varied but the greater the size thereof the greater the heat transfer in some instances. In some embodiments the portion 29 may be of no greater length than the width of the portion 30.

In the foregoing embodiments the fins are formed from aluminum. For some purposes it might be more desirable to form the fins from copper or copper-base alloys or ferrous alloys. Indeed the invention contemplates forming the fins from any suitable metal. Although it is advantageous to form the fins from sheet metal by forge welding as described in the foregoing it is, of course, possible to use other welding methods for forming the conduits on the surface of the fins. For example, the raised portion might be stamped from a sheet of metal and thereafter brazed or otherwise fastened to the surface of the fin to form a conduit. From the practical standpoint, however, the forge welding method with subsequent inflation by fluid pressure is favored. The assembly illustrated in Figure 8 is particularly advantageous because the fins are integral with the tube and thus the heat transfer characteristics are improved over a structure where it is necessary to weld or otherwise connect the fin to the surface of the tube. A plurality of assemblies of this type can be arranged to form heat exchangers having a tube following a serpentine path with fins extending therefrom. The heat exchanger of this invention is particularly useful for making automobile radiators or other heat exchangers where it is desirable to transfer the heat from a liquid to. air.

net-mes In one application :the fins of this 'inventionfcan be attached to 'a' cylinder suitable for 'use in internalcombustion engines and it is possible to eliminate the radiator usually required for cooling such engines. Because of the improved heat trans'tercharacteristics of the fins it is possible to air cool the cylinders. In forming an assembly of cylinders and 'fins a mold can be formed by stacking aluminum fins one 'on the other with a suitable washer interposed between eachpainof fins. assembly is clamped together'and "a Cylindrical cast iron member suitable to serve as a cylinder wall is placed inside the resulting cavity. Molten aluminum 'is""th'en poured between the external wall of this cast iron cylinder and the wall formed by the alternate aluminum fin edges and washer edges. -Upon solidification, the edges of the fins are welded to the aluminum cylindrical wall and the cast iron cylinder serves as -'a liner for the cylinder.

In another application of this invention similar. to the foregoing the .fins are made of rust resistantsheet iron and the spacing washers are of the same material.

iron in a suitable mold, the outer wall of which is constituted by the fins and spacers to which the molten cast iron firmly attaches itself.

By choosing the proper fluid and gas pressure in the conduit the cylinder temperature can be held at the most eflicient temperature. In automobiles this temperature may be above 212 F. By sealing nitrogen in the circuit at 60 lbs. gage pressure with Water, boiling of the water will not occur until about 290 F. so temperature of the auto cylinder and fin would tend to stabilize at this temperature. Very pure water containing corrosion inhibitors may be used. Also chemicals such as ethylene glycol and the like may be added to prevent freezing.

As indicated hereinbe fore it is desirable that that portion of the conduit which is to contain the captive fluid after cooling should be at an elevation greater than that portion which contains the heated captive fluid. In this way the cooler fluid will more readily flow from the edge of the fin to that portion adjacent the tube containing the heated liquid. Circulation within the conduit is also brought about by boiling of the fluid in the conduit. For this reason the fluid contained in the conduit should preferably have a boiling point less than the boiling point of the liquid in the heat exchanger tube. For example, if water is to be cooled the conduit may advantageously contain ethyl alcohol or a mixture of this and water.

As an illustration of an advantage of this invention, aluminum has a specific heat of 0.2 calorie per gram per degree centigrade temperature rise while copper has a specific heat of 0.1. If it is desired to keep the boiling point of a liquid in the heat exchanger tube, such as that illustrated as 19 in Figure 8, at a temperature between that of boiling water (100 C.) and the boiling point of ethyl alcohol (about 78 C.), ethyl alcohol may be used in the conduit and each gram of alcohol boiled in the portion of the conduit adjacent tube 19 will carry away to the extremities of the fin as much heat as would be required by raising 1020 grams of aluminum 1 C. in temperature. If copper is utilized for the fin instead of aluminum 2040 grams of copper would be required for a similar increase of 1 C. Thus the heat exchanger fin having the enclosed circuitous conduit containing a fluid permits the use of a fin with much less weight to preserve the same minimum of temperature differential between heated and cooled portions of the fin.

The configuration of the conduit may be such that a turbulent gas flow between adjacent fins is introduced without impairing the principal function of the cooling liquid. In assembling several fins together to form a heat exchanger the inflated portions forming the conduit would be alternated in position in order to cause a 6 turbulence of the air as 'it' passes between thefins. It is apparent from the foregoing that the fin of this invention can be assembled to tubes with a minimum number "of brazed joints which is, of course, advantageous not only from the standpoint of manufacturing costs but also with respect to the life of the heat exchangers. Although 'ethyl alcohol or its mixtures with water are particularly well suited in the fins for cooling heated water any other suitable fluid such as methyl alcohol, glycerine, ethylene glycol, water or its mixtures with the foregoing, xylene, or the like may be utilized. The stop weld composition given in the foregoing is: particularly well suited for aluminum but other compositions such as mixtures of colloidal graphite and sodium silicate can be utilized. The amount of reduction in the forge welding process will vary depending upon the particular metal utilized but will ordinarily fall within the range of from 35% to about 65%. I

Although embodiments of the invention have been described in considerable detail in the foregoing it is to be understood that modifications can he made therein by those skilled in the art without departing from the spirit or scope of the invention except by the scope of the appended claims.

What is claimedis':

1. A heat exchanger comprising a tube having platelike fins, each of said fins comprising a web and a fluid enclosed in a sealed conduit separate from said tube extending between a pairofl'opposed spaced exterior surfaces from the heated edge of the fin to the cooler edge thereof, said conduit comprising at least three conduit portions in said fin extending in at least three directions and serially connected to each other at their ends to form a closed conduit circuit circumscribing at least one portion of said fins, and said fins having an edge in heat exchange relationship with said tube.

2. A heat exchanger comprising, in combination, a heat exchanger fluid carrying tube having fins extending outwardly substantially from the external wall of said tube, each of said fins having substantially planar surfaces forming a solid web and at least three conduit portions within said fin extending in at least three directions and serially connected to each other at their ends to form a closed conduit circuit circumscribing at least one portion of said fin, said conduit circuit extending between distended portions of said surfaces from the heated edge of the fin to the cooled edge thereof, having a portion of said conduit circuit coextensive with a portion of said tube, and a heat exchange fluid sealed within said conduit circuit.

3. A heat exchanger comprising, in combination, a tube containing a fluid at an elevated temperature and platelike longitudinal fins extending integrally from the external wall of said tube, each of said fins having substantially planar surfaces and a conduit forming a con tinuous closed circuit in close proximity and parallel to the four edges of the fin, said conduit comprising four spaced conduit portions within said fin serially connected to each other at their ends to form a closed conduit circuit for said fluid, said conduit circuit, further, containing a vaporizable and condensable fluid having a boiling point below that of the said first fluid.

4. A heat exchanger comprising, in combination, a substantially horizontal tube containing a fluid at an elevated temperature, longitudinal fins extending outwardly in heat exchange relationship from said tube and having substantially planar surfaces intersecting said tube at an angle of elevation and between said surfaces, a conduit comprising at least three conduit portions within each of said fins extending at least in three directions and serially connected to each other at their ends to form a closed conduit circuit circumscribing at least one portion of said fins, said conduit circuit containing a vaporizable fluid having a boiling point lower than the first said fluid whereby heat from the first said fluid is transferred to the second said fluid and carried by means of circulation of the second said fluid, in said conduit circuit,'t0 the external elevated edge of the fin.

5. A heat exchanger comprising, in combination, a primary heat exchanger containing a first heat exchanger fluid having at least one secondary heat exchanger ex tending outwardly in heat exchange relationship from said primary heat exchanger, said secondary heat exchanger having substantially planar surfaces forming a solid web and at least three conduit portions within said surfaces serially connected to each other at their ends to form a sealed conduit circuit circumscribing at least one portion of said web portion of said surfaces, and a body of vaporizable and condensable heat exchange fluid at least partially filling said conduit circuit.

6. As an article of manufacture, a centrally located tube having extending integrally from the external surfaces thereof a pair of opposed substantially planar fins each having a continuous sealed conduit partially filled with a fluid adapted to adsorb the heat from a heated fluid in said tube and transfer said heat to the edge of the fin remote from said tube by circulation of the fluid in said conduit, said conduit comprising at least three conduit portions in said fins extending in at least three directions and serially connected to each other at their ends to form a closed conduit circuit for said fluid circumscribing at least one portion of said fins.

7. In an internal combustion engine having a cylinder provided with fins extending in heat exchange relationship fromthe external surface, of said cylinder, the improvement which comprises a plurality of spaced fins each having an edgeioine'd in heat-exchange relationship to a wall of the cylinder, each of said fins comprising at least three conduitportions in said fin extending in at least three directions and serially connected to each other at their ends to form a closed conduit circuit extending from adjacent the cylinder Wall to the opposite edge thereof and circumscribing at least one portion of said fin, and a fluid sealed within said conduit circuit at a predetermined pressure adapted to control the boiling point of said fluid at a predetermined temperature.

References Cited in the file of this patent UNITED STATES PATENTS 1,723,659 Rosenqvist Aug. 6, 1929 1,748,518 Midgley Feb. 25, 1930 1,750,750 Gay Mar. 18, 1930 2,083,611 Marshall June 15, 1937 2,167,901 Murray Aug. 1, 1939 2,582,358 Schoellermen Jan. 15, 1952 2,626,130 Raskin Jan. 20, 1953 2,662,273 Long Dec. 15, 1953 2,690,002 Grenell Sept. 28, 1954 FOREIGN PATENTS 139,840 Australia Jan. 3, 1951

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