US3046758A - Heat exchangers - Google Patents

Description

July 31, 1962 c. A. HEUER ETAL 3,046,758

HEAT EXCHANGERS Filed Aug. 11, 1960 3 Sheets-Sheet 1 FIG. I

INVENTORS CHARLES A. HEUER 8.

ATTORNEYS y 1952 c. A. HEUER ETAL 3,046,758

I HEAT EXCHANGERS Filed Aug. 11, 1960 3 Sheets-Sheet 2 INVENTORS CHARLES A.IHEUER 8. NORVAL A KEITH M ikug ATTORNEYS July 31, 1962 c. A. HEUER ETAL 3,046,753

HEAT EXGHANGERS Filed Aug. 11, 1960 3 Sheets-Sheet 5 INVENTORS CHARLES A. HEUER 8- NORVAL. A. KEITH BY p g United States Patent 3,046,758 HEAT EXCHANGERS Charles A. Heuer and Norval A. Keith, East ,Alton, 11]., assignors to Olin Mathieson Chemical Corporation, East Alton, 111., a corporation of Virginia Filed Aug. 11, 1960, Ser. No. 49,041 2 Claims. (Cl. 62-426) This invention relates to heat exchangers and more particularly to heat exchange apparatus of improved efficiency.

In the manufacture of heat exchangers of the type employed for effecting the transfer of heat between liquid and air, it is desirable to use the minimum of metal possible to provide the area of heat exchange necessary for obtaining the desired transfer of heat from the liquid to the air. Heat exchangers of this type ordinarily comprise a tube containing a heat exchange fluid and a plu rality of fins extending radially from the tube. Since for a given amount of heat transfer from metal to air a relatively larger surface area of heat transfer is required relative to surface area required for heat transfer between liquid and the metal, such heat exchangers are made up with secondary surfaces, in the form of fins, which form substantially the larger part of the heat exchanger. For example, one method of forming such heat exchangers involves providing openings in a plurality of spaced fins, and assembling the fins on a tube which is generally bent in a serpentine configuration with the fins mounted transverse the parallel lengths of the tubing so that the fins are in spaced relationship to each other. This results in a multitude of fins disposed transverse the parallel lengths of the tubing. The fins are then secured to the tubing in various conventional manners such as by soldering, brazing or expansion of the tubes, after the fins have been assembled thereon, to

mechanically force the tubes into a friction fit against the fins. However, this is not only an expensive and time consuming operation, but in addition, since the external fins mounted on the tubing form a major portion of the heat exchanger this further increases the cost of the heat exchanger due to the additional metal required'to provide sufficient fins to obtain the desired amount of heat transfer from the fins to the air.

Accordingly, it is an object of this invention to eliminate disadvantages of the prior art.

An additional object of this invention is to provide a novel heat exchange apparatus with improved heat transfer properties. I

Another object of this invention is to provide a liquid to air heat exchanger having an improved means for providing a more efficient transfer of heat between a confined fluid in the heat exchanger and the surrounding atmosphere.

A further object of this invention is to provide a heat exchange apparatus having an improved means for in creasing its effective heat transfer without any substantial increase in the original heat transfer area of the heat exchanger.

Other objects and advantages will become more apparent from the following description and drawings in I which:

FIGURE 1 is a perspective view partly in section illustrating one embodiment of this invention;

FIGURE 2 is a perspective view illustrating an intermediate step in the preparation of a heat exchange element employed in the embodiment of FIGURE 1;

FIGURE 3 is a partial and sectional view in perspective illustrating a subsequent treatment of the element illustrated in FIGURE 2;

FIGURE 4 is a partial cross-sectional view taken along lines IV-IV of FIGURE 3;

v n 3,046,758 Patented July 31., 1962 p ice FIGURE 5 is a perspective view of another and alternate heat exchange element that may be employed in conjunction with the embodiment depicted in FIGURE 1;

FIGURE 6 is a plan view illustrating a subsequent treatment of a portion of the element illustrated in FIG- URE 5;

FIGURE 7 is a partial view in cross-section taken along lines VII-VII of FIGURE 6;

FIGURE 8 is an elevational view partly in section i1- lustrating an application of this invention;

FIGURE 9 is a perspective view of a portion of another element that may be employed in conjunction with the invention depicted in FIGURES l and 8; and

FIGURE 10 is a partial elevational view illustrating another embodiment of this invention.

Referring to the drawings, FIGURE 1 illustrates an air duct or plenum chamber 1 having a narrowing transition portion 2 provided at one end with an air impeller 3, such as any suitable motor driven fan or blower, for propelling air through the duct for discharge at an outlet 4, not shown, provided at the other end of the duct 1. Contained and suitably supported within duct 1 are two heat exchange elements 5, or any number desired, having a plurality of fins 6 struck out of the element, so as to leave openings through the element, and so that the fins having their plane disposed in a direction parallel with the direction of fluid flow through the air duct 1. In addition, the heat exchange element 5 is provided with an internal system of passageways 7' comprising a continuous passage extending in a zig-zag orserpentine fashion to form a plurality of parallel lengths 15 interconnected at alternate adjacent ends by return bends 14. These systems of passages within the elements are preferably obtained by selectively pressure welding the adjacent superimposed surfaces of two or more component sheets in accordance with the method defined in the Well known patent to Grenell, US. 2,690,002, granted on September 28, 1954.

In accordance with this aforesaid patent, a pattern of weld-inhibiting material is applied to a clean surface of a sheet of metal 8. A clean surface of a second sheet of metal 9 is superimposed on the surface of sheet 3 and the two sheets are secured together to provide relative movement and then pressure welded together, as by hot rolling, in their adjacent areas which are not separated by the weld-inhibiting material. Such pressure welding of the sheets results in reducing the thickness of the two sheets andelongating the resultant blank in the direction of rolling while the width of the blank remains substantially the same as the initial width of the sheets. Following the pressure Welding operation, the resultant blank is preferably softened as by annealing to make it more pliable, and if desired, the blank may again be cold rolled followed by another annealing operation. After softening of the blank, the unjoined portion is expanded by injecting therein a fluid pressure of suificient magnitude to permanently distend the blank in the area defined by the weld-inhibiting material so as to bulge it out of the opposite faces of the component sheets 'while forming the desired pattern of passageways 7.

To form the fins a plurality of U-shaped slits 10 are provided, by punching and the like, at spaced points through the pressure welded or web portion ll followed by bending the portions 12 of the web 11 defined within each U-shaped slit out of and transverse the plane of element 5 so that the fins project from the face of the element to leave transfer openings 13. As will ''be observed, these transfer openings 13 serve substantially no functional purpose in the heat exchanger element other than, if at all, the equalization of fluid pressures on both sides of the element. Although the plane of the fins in this embodiment has been shown to be parallel with the s eaves parallel passageway lengths 15, it is to be understood that the plane of the fins may extend transverse these parallel lengths and with the system of passageways 7 in turn having any configuration desired, provided that the planes of the fins are parallel to the direction in which the air fluid fiows through the air duct or plenum chamber 1. In operation terminal ends 16 and 17 of the system of passageways 6 are connected by suitable conduiting, not shown, into a fluid flow system comprising means for bringing a heat exchange fluid to the desired temperature which is then caused to flow by an appropriate fluid impeller, such as a pump not shown, through the system of passageways 7 in a recirculating manner in the system.

In a preferred embodiment of the invention from which surprising results were obtained, the fins formed on element are preferably obtained by providing a plurality of aligned short parallel slits 18 in the pressure welded or web portions of element 5 so as to extend between and perpendicularly to the adjacent parallel lengths of the system of passageways 7. As illustrated in FIG- URE 5, slits are provided between adjacent parallel lengths 15 to extend between them in a direction perpendicular to the direction in which the parallel lengths are aligned. To form the fins the portion of the metal between each pair of adjacent slits is rotated or twisted to the desired angle, preferably 90, to the plane of the element to form corresponding fins 19 projecting out of opposite faces of element 5 with both ends of the fins twisted into skirts or fillets integral with the remainder of the element.

Although the formation of the fins, in the embodiment of element 5 discussed, provides substantially no increase in the heat transfer surface area of element 5, it has nevertheless been found to provide surprising results and efficiency in operation in obtaining an increase in the efiective heat transfer of the element as can be readily observed from the comparative tests set forth below. For purposes of comparison a series of comparative runs were made utilizing a heat exchange apparatus substantially such as that illustrated in FIGURE 1, with each run utilizing Within the air duct or plenum chamber in one case a pair of heat exchange elements shown in FIG- URE 6 and in the other case, for comparison, employing a prior art heat exchange element. The plenum chamber was constructed of heat insulating material so as to have dimensions of 14 inches in width, 27 inches in length with the air passage having a height of 1% inches. This plenum was attached to a transition piece at one of its ends with the transition piece in turn connected to a length of 8 inch tubular ducting. A blower was installed inside the ducting to pull air through the plenum chamber over the heat exchanger and exhaust it out of the ducting.

For determining operational results of a heat exchange apparatus in accordance with this invention, two 0.060 inch gauge pressure welded plateelike elements of 1100 type aluminum alloy were provided and finned in accordanoe with the embodiment illustrated in FIGURE 6. The slits in these elements were formed by providing a plurality of 1%. inch long slits in parallel rows as illustrated in FIGURE 5 with the slits parallel to each other and 0.375 inch apart from each other. The metal between each pair of adjacent slits was rotated by twisting to an angle perpendicular to the plane of the element. For the first three comparative runs these elements were disposed within the above described plenum chamber in parallel relationship to each other and spaced /2 inch apart from each other and form the adjacent wall of the plenum chamber.

For purposes of comparison a prior art heat exchanger such as described above and of the type illustrated in US. Patent 2,477,824, formed of an aluminum tube and aluminum fins, was disposed within the air duct of another plenum chamber with its relative dimensions, conditions of operation and results indicated below under 4 the heading Prior Art Heat Exchanger. Six comparative runs were made with the results tabulated and contrasted below:

For Runs 1, 2 and 3 Prior Art Heat Heat Exchang- Comparative Dimensions Exchanger er of This Invention Height of Plenum Opening 1% inches 1% inches. Width and Length 26.5 x 14 22 x 12.75. Primary Surface Area of Heat 1121- 1.567 sq. ft 7.8 sq. ft.

changer. Secondary Surface Area of Heat 25.00 sq. ft 0.

Exchanger. Total Surface Area of Heat Ex- 26.567 sq. ft 7.8 sq. ft.

changer. Tube Sire Me inch 0 D.... 0% X 0.180).- Cross-Sectional Area of Tubes 0 050 sq. in 0.514 sq. in. Wei ht 4.85111 3.4 lbs.

RUN 1 Prior Art Heat Heat Exchanger Exchanger of This Invention Water Temperature, Degrees F 120.8 .0. 0 Air Temperature, Degrees F-.. 80.0 82.1 Log. Mean AT 26. 6 25.1 Air Flow, Cubic Feet per Hr 2, 510 2, 550 B.t.u. Heat Transfer From Water Per Sq. Ft. of Heat Transfer Area of Heat Exchange Element 39. 8 117 B.t.u. Heat Transfer From Water Per Pound of Heat Exchange Element 218 268 RUN 2 Water Temperature, Degrees F 141. 3 140. 0 Air Temperature, Degrees F 79. 9 81. 3 Log. Mean AT 40. 8 39. 3 Air Flow, Cubic Feet per Hr 2, 510 2, 550 B.t.u. Heat Transfer From Water Per Sq. Ft. of Heat Transfer Area of Heat Exchange Element 58. 5 170 B.t.u. Heat Transfer From Wat and of Heat Exchange Element 320 391 HUN 3 Water Temperature, Degrees F 160. 0 160. 8 Air Temperature, Degrees F..- 79.7 82.0 Log. Mean AT 53. 6 53. 2 Air Flow, Cubic Feet per Hr 2,510 2, 550 Btu. Heat Transfer From Water For Sq. Ft. of Heat Transfer Area of Heat Exchange Element 74. 2 231 B.t.u. Heat Transfer From Water Per Pound of Heat; Exchange Element 406 530 For Runs 4, 5 and 6 Comparative Dimensions Prior Art Heat Heat Exchanger Exchanger of This Invention Height of Plenum Opening 1". Width and Length 23 x 13%. Primary Surface Area of at; 8.85 sq. ft.

Exchanger. Secondary Surface Area of Heat 120 fins, 25.00 (570 integral fins Exchanger. sq. ft. with surface area of 641 sq. in. Total Surface Area of Heat Ex- 26.567 sq. it"--. 2.85 sq. ft.

changer. Tube Size A5 inch O.D (1% x 0.180) Cross-Sectional Area of Tubes-.. 0.050 sq. in 0.0514 sq. in. Wei ht 4.85 lbs 3.79 lbs.

RUN 4 Prior Art Heat Ex- Heat Exchanger of changer This Invention Water Temperature, Degrees 'F 120.00 121. 1 Air Temperature, Degrees F. 81.00 80.0 Log. Mean AT 19.1 22. 7 Air Flow, Cubic Feet per Hr 2, 525 2, 545 B.t.u. Heat Transfer From Water Per Sq. Ft. of Heat Transfer Area of Heat Exchange Element 42. 114. O Btu. Heat Transfer From Water Per Pound of Heat Exchange Element 230 279 RUN Water Temperature, Degrees F 140. 8 140. 0 Air Temperature, Degrees F 80. 5 79. 2 Log. Mean AT 29. 6 36. 3 Air Flow, Cubic Feet Per Hr 2, 525 2, 545 Btu. Heat Transfer From Water For Sq. Ft. of Heat Transfer Area of Heat Exchange Element 63. 4 165. 5 B.t.u. Heat Transfer From Water Per Pound of Heat Exchange Element 346 406 RUN 6 Water Temperature, Degrees F 160. 3 160.0 Air Temperature, Degrees F 80. 4 78. 6 Log. Mean AT 40. 6 48. 2 Air Flow, Cubic Feet Per Hr 2, 525 2, 545 B.t.u. Heat Transfer From Water Per Sq. Ft. of Heat Transfer Area of Heat Exchange Element 81. 7 228 B.t.u. Heat Transfer From Water Per Pound of Heat Exchange Element 447 659 First dimension refers to the width of the internal passageways parallel to and within the plane of the element, and the second dimension indicates the height to which the passages were distended.

' As can be observed from the above tests, the heat exchanger of this invention hadin each of the runs, 'respectively, 194%, 190%, 210%, 170%, 161% and 179%, greater heat transfer per square foot of heat transfer area than the corresponding prior art heat exchanger. In each case, each run shows over a 150% greater heat exchange obtained in accordance with the structure of this invention as compared to the prior art structures. Increased heat exchange per pound of heat exchanger element is also obtained in accordance with this invention as shown in each of the runs wherein, respectively, 22.9%, 22.2%, 30.6%, 21.3%, 17.4% and 25.1% greater heat transfer is obtained over corresponding tests of the prior art heat exchanger. As can be seen this greater and increased heat exchange is obtained without substantially increasing the heat transfer surface area of the unfinned element employed in fabricating the finned element. In addition, as can be observed, with theeffcctive heat transfer obtained in accordance with the embodiment of FIGURES 5 to 7 of this invention, the performances of the prior .art structures can be equaled utilizing a finned heat exchange element in accordance with this invention having a heat transfer area over 55% less than an equivalent prior art structure.

These surprising results are obtained in that the flow of air past this embodiment of the invention does more than merely wipe the heat transfer surfaces of the element. As described above with respect to the embodiment of FIGURES 5 to 7, the finsin this embodiment are formed from metal extending between adjacent parallel slits having a direction longitudinal or parallel with the direction of air flow past the element. Upon rotation or twisting of the metal, between adjacent slits, out of both faces of the element, the ends of these fins integrally connect or extend from the transverse portion of the fin into the planar portion of the element in a more or less corkscrew configuration. In this manner these end portions of the fins, or corkscrew portions, act in the form of, both, vanes and baflles causing an extreme degree of turbulence in the air flowing past and through all portions of the element. This embodiment is 6 peculiar inthat it utilizes the transfer openings formed in the port-ions of the element from which the fins are displaced. These transfer openings, although parallel with the flow of air over them, are nevertheless, utilized in aiding and increasing the turbulence of air flow and also increase contact of the air with all portions of the element.

In this respect, when this embodiment, as utilized in runs 4, 5 and 6, was compared with an unfinned element, identical to that fromwhich this finned embodiment was made, and under the same operating conditions, the results between each of the structures are greatly contrasted; In operation, the unfinned elements provided in tests corresponding to runs 4, 5 and 6, an effective B.t.u. transfer per square foot of heat transfer area, total 9.3 square feet, respectively, of. 80, 119 and Btu. per square foot of heat transfer area. Comparison of these results with the invent-ion shows that by providing fins in these panels in accordance with the embodiment of FIGURES 5 to 7, employed in runs 4, 5 and 6, an increase in heat transfer was obtained by over, respectively, 40%, 38% and 40%. As can be observed, such increase in heat transfer is obtained without increasing the heat transfer area wherein the untinned panel has substantially the same heat transfer area as the finned embodiment of FIG- URES 5 to 7, which is 9.3 square feet. 7

FIGURE 8 illustrates the application of this invention in a conventional domestic refrigerator comprised of a cabinet 20 having an access door 21 opening into a food compartment'zz defined within the inner liner and outer liner 23 and 24, with the inner liner 24 forming a portion of the inner wall of the food compartment. Intcrposed between liners 23 and 24 is a separation memher 25 defining in conjunction with inner liner 24 a line or air passage 26. To prevent transfer of heat between the refrigerated portions of the refrigerator and the atmosphere, suitable insulating material 27 is disposed between the outer liner 23 and the separating member 25 and portions of inner liner forming the inside wall of the food compartment. Suitably mounted in flue or air passage 26 are elements 5 finned in accordance with this invention and functionally connected into any conventional refrigerating system. Also mounted within the flue or air passage 26 is a fluid impeller 28, such as any of the conventional motor driven fans or blowers, for circulating air in the refrigerator through openings 29 and 30 interconnecting the iair passage 26 and the food compartment 22. The elements 5 are disposed in flue 26 so that their fins extend perpendicularly to member 25- and inner liner 24 with the plane of the fins parallel to the flow of air thr-ough flue 26.

An alternate embodiment of the heat exchangeelement is illustrated in FIGURE 9 and comprises a heat ex change element 3 1 folded over on itself to bring the spaced portions 32 and 33 into spaced relationship with each other to form an equivalent of the plurality of elements described above. As with the preceding embodiments, both portions 32 and 3 3 of heat exchange element 31 contain an interconnected system of passages 34 extending in a serpentine manner across element 31 so as to be disposed in a plurality of parallel lengths 35 interconnected to each other by return bends 36. Element .31 is provided with fins 19 which are identical to and formed in the same manner as those illustrated in FIG- URES 5 and 6. I I

In addition FIGURE 9 also illustrates, schematically, one means for circulating a heat exchange fluid, in the system of passages 34 of heat exchange element 3 1, suitable for incorporation into :any of the embodiments discussed above. As shown herein, one terminal portion 39 of the passages 34, serving as an inlet 40, may be supplied with a compressed refrigerant by means of a conduit 41 interconnected between the inlet 40 and an outlet of a conventional refrigeration condenser section 42 which, in turn, is suitably connected by conduiting 43 to a sealed motor-compressor unit 44, such as commonly employed in conventional refrigeration systems. The refrigeration circuit may be completed by connecting the outlet of the motor-compressor 44 by means of suitable in the same manner as the element of FIGURES to 7, it differs therefrom in that the portions of the pressure welded component sheets, or Web, between each pair of adjacent slits are rotated to an angle where the fins constrain the flow of air through passage 37 to flow tangentially through the transfer openings in the element and deflect at least a portion of the airto flow downwardly, after passage through the openings, in a direction countercurrent to the general flow of the air through passage 37.

Although the invention has been described with reference to specific materials, embodiments and details, var-i ous modifications and changes, within the scope of this invention, will be apparent to one skilled in the art and are contemplated to be embraced within the invention.

What is claimed is:

1. A heat exchange structure comprising a duct forming a passage for a first heat exchange fluid therethrough, at least two spaced openings in said duct, a first fluid impeller at one of said openings for moving a current of said first fluid through said duct, a plate-like heat exchange element secured in said duet, within said current, said element containing internally disposed therein a system of internal passages having their opposite walls bulged out of corresponding faces of said element and bounded by solid web portions of said element, a plurality of slits in said web portions between said passageways with the portions of said web portions between and adjacent said slits rotated to an angle with the plane of said element into fins projecting out of both said opposite faces of said element, transfer openings for said first fluid in the:

portions of said element displaced by said fins, a second fluid impeller for moving :a second heat exchange fluid in said passage, and conduit means interconnecting said second impeller to a terminal end of said passages, said element being disposed transverse said passage at an angle to the normal of the wall of said duct to form a perforate partition in said duct, and said portion of said element between each pair of adjacent slits being rotated to an angle where said fins constrain said first fluid to flow tangentially through said transfer openings-in said element and deflect at least a portion of said first fluid in a direction countercurrent to the flow of said first fluid through said duct.

2. The structure of claim 1 wherein said duct is vertically contained in a refrigerator with said openings communicating into a cooled compartment in said refrigerator wherein said first fluid is air circulated through said duct and said compartment upwardly through said duct, said element being an evaporator plate with said fins thereon disposed at an angle deflecting said first fluid downwardly in said duct after passage through said element, and said second fluid being a refrigerant within said passages,

said passages and said second fluid impeller forming part of a closed refrigerator system.

References Cited in the file of this patent UNITED STATES PATENTS

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