US20050045315A1

US20050045315A1 - Concentric tube heat exchanger and end seal therefor

Info

Publication number: US20050045315A1
Application number: US10/652,768
Authority: US
Inventors: James Seager; Allan So; Alan Brown; Darryl Watson
Original assignee: Individual
Current assignee: Dana Canada Corp
Priority date: 2003-08-29
Filing date: 2003-08-29
Publication date: 2005-03-03
Also published as: CA2439023A1; CA2439023C

Abstract

A concentric tube heat exchanger comprises an outer tube and a concentric inner tube, with an annular passageway between the tubes. The ends of the annular passageway are sealed by sealing members having axially extending inner and outer walls which are connected to one another and which are sealed to the respective outer and inner tubes. The sealing member walls are preferably connected by an integrally formed connecting wall. The walls of the sealing member are preferably resilient and diverge so as to form a friction fit with the tubes during assembly of the heat exchanger. The heat exchanger further comprises a turbulizer which comprises a plurality of rows of corrugations defining axially extending flow passages. Preferably, the corrugations have a top land width greater than a bottom land width so that the side walls of the corrugation are radially arranged in the annular passageway. Adjacent corrugations in each row are preferably offset relative to one another by an amount of from about 30 percent to about 40 percent.

Description

FIELD OF THE INVENTION

This invention relates to concentric tube heat exchangers, and more particularly to seals for closing an annular passageway between the inner and outer tubes of such heat exchangers.

BACKGROUND OF THE INVENTION

Concentric tube heat exchangers are commonly employed as transmission and transaxle oil coolers and are mounted in the coolant tank or manifold of a vehicle radiator. These heat exchangers include a cylindrical outer tube, a cylindrical inner tube and a turbulizer placed in an annular passageway between the inner and outer tubes. Oil is admitted to the annular passageway via an inlet port located at one end of the tube for passage through the turbulizer. The oil is cooled and exits via an outlet port located near the other end of the outer tube.
Numerous arrangements are known in the prior art for sealing the ends of the annular passageway. These include deformation of the inner and/or outer tubes, for example as shown in U.S. Pat. No. 3,001,767 (Straubing), U.S. Pat. No. 5,732,769 (Staffa) and U.S. Pat. No. 5,950,716 (Appelquist et al.); or by use of annular seals as described in U.S. Pat. Nos. 3,323,586 and 3,339,260 (Burne et al.)
The suitability of prior art end sealing methods can be affected by the type of material from which the heat exchanger is made. For example, in aluminum concentric tube heat exchangers, it has proven difficult to seal the annular passageway by deformation of the tubes. This has led some manufacturers to seal the annular passageway with machined aluminum end blocks, which significantly increase the weight and cost of the heat exchanger.
Accordingly, there is a need for improved methods for sealing the annular passageway in a concentric tube heat exchanger which will provide economical and reliable sealing in a variety of materials.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a concentric tube heat exchanger having a first end and a second end. The heat exchanger comprises an outer tube and an inner tube. The inner tube is received inside the outer tube and concentric therewith, wherein an annular passageway is formed between the inner and outer tubes. The heat exchanger further comprises first and second annular sealing members received inside the annular passageway between the inner and outer tubes. The first sealing member is positioned proximate the first end of the heat exchanger and the second sealing member is positioned proximate the second end of the heat exchanger. Each of the sealing members comprises an outer wall and an inner wall which are connected to one another, each of the walls having first and second axially-spaced ends, the outer wall being sealed to the outer tube and the inner wall being sealed to the inner tube,. thereby sealing the ends of the tubes.
The concentric tube heat exchanger according to the invention further comprises a turbulizer received in the annular passageway between the tubes. The turbulizer comprises a plurality of corrugations defining a plurality of axially extending flow passages extending parallel to the tubes. Each of the corrugations comprises a top land, a bottom land and a pair of side surfaces connecting the top and bottom lands, the top land being in heat exchange contact with the outer tube and the bottom land being in heat exchange contact with the inner tube. The convolutions are arranged in axially extending rows with the convolutions in each row being connected to one another and with an offset being provided between adjacent convolutions in each row. The offset has a width which is from about 30 percent to about 40 percent of a width of the top land or the bottom land.
In another aspect, the present invention provides a sealing member for sealing opposite ends of an annular passageway extending along an axis between inner and outer tubes of a concentric tube heat exchanger. The sealing member comprises an outer wall and an inner wall. The outer wall has first and second axially-spaced ends and a generally axially-extending portion between its ends for sealing to the outer tube. The inner wall has first and second axially-spaced ends, is connected to the outer wall and is spaced radially inwardly of the outer wall. The inner wall has a generally axially-extending portion between its ends for sealing to the inner tube. The generally axially-extending portions of the walls diverge from one another along said axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
FIG. 1 is a perspective view of a preferred heat exchanger according to the invention, prior to insertion of the sealing members;
FIG. 2 is a cross section through one of the sealing members along line II-II in FIG. 1;
FIGS. 3A to 3D are cross sections through alternate preferred sealing members according to the invention;
FIG. 4 is a cross section in an axial plane through one end of the heat exchanger of FIG. 1, after insertion of the sealing members;
FIG. 5 is a close-up of area A in FIG. 4;
FIG. 6 is a cross-section along line VI-VI of FIG. 1;
FIG. 7 is a front view of a portion of a turbulizer sheet according to the invention; and
FIG. 8 is a top plan view of a portion of the turbulizer sheet of FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a preferred concentric tube heat exchanger 10 according to the invention. Heat exchanger 10 comprises an outer cylindrical tube 12 and an inner cylindrical tube 14, the inner tube 14 being received in the outer tube 12 and concentric therewith, with an annular passageway 16 being formed between the outer and inner tubes 12, 14 and extending through substantially the entire length of the heat exchanger 10.
Heat exchanger 10 further comprises an inlet port 18 located adjacent its first end 20 and an outlet port 22 (FIG. 6) located adjacent its second end 24. Both the inlet and outlet ports 18, 22 comprise perforations formed in the outer tube 12 through which a fluid to be cooled, such as oil, is allowed to enter and exit the annular passageway 16. The heat exchanger 10 further comprises an inlet fitting 26 and an outlet fitting 28 which are mounted to the outer surface of the outer tube 12 in communication with the inlet and outlet ports 18, 22 respectively. To assist in mounting and sealing the fittings 26, 28 to outer tube 12, the areas surrounding inlet and outlet ports 18, 22 are preferably flattened, as shown in FIG. 6. Sealed connections are formed between fittings 26, 28 and the outer surface of tube 12, for example by brazing.
Not shown in FIG. 1, but described in detail below, is a turbulizer 30 which is received in the annular passageway 16 and extends through the annular passageway 16 between the inlet and outlet ports 18, 22.
Lastly, the heat exchanger 10 comprises a pair of annular sealing members 32 for sealing the ends of the annular passageway 16. In FIG. 1, the heat exchanger 10 is shown in a partially disassembled state with the sealing members 32 separated from the tubes 12, 14. FIG. 4 illustrates the first end of heat exchanger 10 in its assembled state with a sealing member 32 received in the annular passageway 16 and brazed to both the outer and inner tubes 12, 14.
As shown in FIG. 4, sealing member 32 is received inside the annular passageway 16 between the outer and inner tubes 12, 14. The sealing member 32 is located proximate the first end 20 of heat exchanger 10 and, more particularly, is located between the inlet port 18 and the first end 20 of the heat exchanger 10. The sealing member 32 is sealingly connected to both the inner surface of the outer tube 12 and the outer surface of the inner tube 14, preferably by brazing, with braze fillets 34 and 36 being formed between the sealing member 32 and the outer tube 12, and braze fillets 38 and 40 being formed between the sealing member 32 and the inner tube 14. The braze fillets 34, 36, 38 and 40 are shown only in the close-up of FIG. 5. It will be appreciated that the second end 24 of heat exchanger 10 is preferably sealed in an identical manner with the other sealing member 32 illustrated in FIG. 1.
The preferred sealing members 32 shown in the drawings each comprise an outer wall 42 and an inner wall 48, with the inner wall 48 being spaced radially inwardly of the outer wall 42, and preferably concentric therewith. The outer wall 42 has a first end 46 and a second end 44, the ends 44, 46 being axially spaced from one another, with at least a portion of the outer wall extending generally along the axis. Similarly, the inner wall has a first end 52 and a second end 50, the ends 50, 52 being axially spaced from one another, with at least a portion of the outer wall extending generally along the axis. In the sealing members 32 shown in the drawings, the entire outer and inner walls 42 and 46 extend along the axis, with the inner wall 48 abutting the outer surface of inner tube 14 and sealed thereto, and with the outer wall 42 abutting the inner surface of outer tube 12 and sealed thereto. However, it will be appreciated that this is not necessary that the entire outer and inner walls 42, 48 extend generally axially. Rather, it will be appreciated that only portions of walls 42, 46 are required to extend axially, sufficient to form seals with the outer and inner tubes 12, 14, respectively.
The sealing members 32 illustrated in the drawings are of generally U-shaped cross section, with the first end 46 of the outer wall 42 being connected to the first end 52 of the inner wall 48 by a radially extending connecting portion 54 which seals the radial space between the walls 42, 48. The second ends 44, 50 of the walls 42, 48 are distal to the connecting portion. Preferably, the connecting portion 54 is integrally formed with the walls 42, 48.
As shown in FIG. 2, the outer and inner walls 42, 48 of the sealing member are not necessarily parallel to one another. Rather it is preferred that the walls 42, 48, or the generally axially extending portions thereof, diverge from one another along the axis. Preferably, the walls 42, 48 diverge from one another from the connecting portion 54 toward the second ends 44, 50 such that a radial distance measured between the walls 42, 48 at the connecting portion 54 is less than a radial distance measured between the second ends 44, 50 of walls 42, 48. Furthermore, the material from which the walls 42, 48 are formed is preferably sufficiently resilient such that, when the sealing members 32 are inserted into the annular passageway with the connecting portions 54 spaced inwardly of the ends 20, 24 by a greater distance than the second ends 44, 50 of walls 42, 48 (as shown in FIG. 4), the second ends 44, 50 become compressed so that the sealing member walls 42, 48 frictionally engage the respective tubes 12, 14, thereby retaining the sealing members 32 during the assembly process. The angle at which the walls 42, 48 diverge is sufficient for easy insertion of the sealing members 32 into the annular passageway 16 with a friction fit, while ensuring substantially complete contact between the walls 42, 48 and the tubes 12, 14 after the inner tube is expanded during the manufacturing process, thus ensuring leak-proof braze joints. The inventors have found that these objects can be achieved by forming sealing members with at least one, and preferably both, side walls 42, 48 diverging from the axis by an angle θ of from about 1 to about 2 degrees, more preferably about 1.5 degrees.
As shown in FIG. 4, the sealing member 32 is preferably spaced inwardly from the end 20 of the heat exchanger 10, for at least two reasons. Firstly, it will be noted from FIG. 4 that the turbulizer 30 does not extend past the inlet port 18 and, in fact, is prevented from doing so by a collar 56 of inlet fitting 26, the collar 56 projecting into the annular passageway 16 through the inlet port 18 and acting as a stop for the turbulizer 30. Thus, the turbulizer 30 does not provide support for the portion of annular passageway 16 extending from the inlet port 18 to the first end 20 of the heat exchanger 10. To minimize the unsupported area of annular passageway 16 and thereby avoid narrowing of the annular passageway 16 in the area surrounding inlet port 18, the sealing member 32 is located inwardly of the end 20 of heat exchanger 10, between the inlet port 18 and the end 20. Secondly, locating the sealing member inward of the end 20 ensures that there is sufficient area for formation of braze fillets 34 between the top 44 of outer wall 42 and the inner surface of outer tube 12, and between the top 50 of inner tube 14 and the outer surface of inner tube 14. The formation of continuous braze fillets about the entire circumference of each sealing member ensures robust, leak proof joints at the ends 20, 24 of the heat exchanger.
As shown in FIG. 2, the connecting portion 54 of the sealing member is preferably flat and extends radially between the outer and inner walls 42, 48 of the sealing member 32. FIG. 3A illustrates an alternate preferred form of sealing member 58 having outer and inner walls 60, 62 diverging from the axis by an angle θ and connected at their bottoms by a rounded connecting portion 64. It will also be appreciated that numerous alternate constructions of sealing members are possible without departing from the present invention. For example, as shown in FIG. 3B, a sealing member 132 may be of generally H-shaped cross section, with the connecting member 154 extending radially between the sealing member walls 142, 148 intermediate the first ends 146, 152 and the second ends 144, 150. Alternatively, FIG. 3C shows a sealing member 232 which is of generally V-shaped cross section, and in which a V-shaped connecting member 254 extends between sealing member walls 242, 248, which extend generally axially. FIG. 3D shows a sealing member 332 which is of modified U-shaped construction, having a somewhat indented connecting portion 354 extending between the outer and inner walls 342, 348.
In a particularly preferred embodiment of the present invention, all the components of heat exchanger 10 are formed from aluminum or alloys thereof, and are preferably formed from brazeable aluminum alloys. In particular, the tubes 12, 14 are preferably of welded and drawn construction and comprise an aluminum alloy core layer clad on at least one side with an aluminum brazing alloy. More preferably, the inner surface of the outer tube 12 and the outer surface of the inner tube 14, i.e. the “oil-side” surfaces, are clad with a brazing alloy, while the opposite surfaces of these tubes, i.e. the “water-side” surfaces, are clad with an alloy containing an amount of zinc for sacrificial corrosion protection. Where the oil-side surfaces of tubes 12, 14 are clad with a brazing alloy, it will be appreciated that neither the turbulizer 30 nor the sealing members 32 require a cladding of brazing alloy. It will be appreciated that alternate arrangements are possible, for example, the turbulizer 30 and sealing members 32 may be clad with brazing alloy, and the tubes 12, 14 may be unclad. Alternatively, all these components may be clad with a brazing alloy. In yet another alternative, the heat exchanger 10 may be comprised of non-clad aluminum members, and the filler metal for brazing may be provided by means of a brazing paste or preform, and brazing can be accomplished by either flux or fluxless brazing by suitable selection of the braze system and materials. Similarly, a brazing paste or preform can be used to join the fittings 26, 28 to the corrosion resistant clad water-side surface of the outer tube 12.
It will be appreciated that the sealing members 32 may be installed with the second ends 44, 50 of walls 42, 48 facing the inlet or outlet port 18, 22. However, for manufacturing purposes, it is preferred that the sealing members 32 are received in the annular passageway with the second ends 44, 50 of walls 42, 48 facing the ends 20, 24 of heat exchanger 10, as shown in the drawings.
The heat exchanger 10 is preferably by assembled by inserting the inner tube 14 and the turbulizer 30 into the outer tube 12, inserting the sealing members 32 into the opposite ends 20 and 22, expanding the inner tube so that both the outer and inner tubes 12, 14 are in intimate heat exchange contact with the turbulizer 30, applying the fittings to the outer tube, and then brazing the assembly in a brazing oven.
A preferred form of turbulizer 30 is now described below with reference to FIGS. 7 and 8. Turbulizer 30 is of generally the same construction as the turbulizer described in U.S. Pat. No. Re. 35,890 (So), which is incorporated herein by reference in its entirety. In particular, prior to insertion into the annular passageway 16, the turbulizer 30 is in the form of a sheet having a plurality of convolutions 74 which define a plurality of flow passages. The flow passages extend axially (parallel to arrow A in FIG. 8) once the turbulizer 30 is rolled up and inserted into the annular passageway 16. Each of the convolutions 74 has a height H (FIG. 7), a length L (FIG. 8), a rectangular top land 76 having width W_T(FIGS. 7 and 8), a rectangular bottom land 78 having a width W_B, and a pair of side surfaces 80 extending between the top and bottom lands 76, 78. In a particularly preferred embodiment of the present invention, the convolutions 74 have a height of about 3 mm and a length of at least about 1.6 mm. It will be appreciated that all width dimensions described herein are measured perpendicular to the axial direction.
The top lands 76 of the convolutions 74 are arranged in axially extending rows, as seen in FIG. 8, which shows a single row 82 of convolutions 74. The top lands 76 of the convolutions 74 in each row 82 are connected to one another along their front and rear edges at areas 84 (FIG. 8) and are offset relative to one another, with the width of the offset being W_O(FIG. 8). It will be appreciated that a bottom plan view of the turbulizer 30 has an appearance which is substantially the same as that shown in FIG. 8.
The features of turbulizer 30 described above are also present in the turbulizer described in the above-mentioned So patent. The turbulizer 30 according to the invention differs from the So turbulizer in several important respects, which are now discussed below.
Firstly, the turbulizer 30 according to the invention has a preferred offset W_Owhich is significantly less than that of the So turbulizer, thereby maximizing the width of the area 84 along which the convolutions 84 are connected with one another. In the So turbulizer, the width of offset is about 50 percent of the width of the top and bottom lands, whereas the offset in the turbulizer 30 according to the invention is about 30 to 40 percent (i.e. W_O/W_Tor W_B=0.30-0.40), preferably about 31 to about 36 percent. The inventors have found that decreasing the offset of the convolutions 74 helps to ensure formability of the turbulizer 30 from metals such as aluminum, while providing high heat transfer and low pressure drop.
Secondly, the turbulizer 30 according to the invention is formed with the top land width W_Twhich is greater than the bottom land with W_B, and with the side surfaces 80 of each convolution 74 sloping away from one another from the top land 76 to the bottom land 78. Thus, when the turbulizer sheet 30 is rolled up and inserted into the annular passageway 16 with the bottom lands 78 in heat exchange contact with the inner tube 14 and the top lands 76 in heat exchange contact with the outer tube 12, the side surfaces 80 are extend substantially radially between the outer tube 12 and inner tube 14, producing axial flow passages of substantially constant cross-sectional area. This helps to maximize heat transfer and minimize pressure drop.
In a particularly preferred embodiment of the invention, the side surfaces are sloped at about 5° from vertical, the top land width W_Tis about 1.1 mm, the bottom land width W_Bis about 1.0 mm, the centers of rows 82 are spaced about 2.1 mm apart, and the offset with W_Ois about 0.35 mm. In a turbulizer having these dimensions, the offset expressed as a percentage of the top land width is about 31 percent and the offset expressed as a percentage of the bottom land width is about 36 percent.
The above-mentioned features of the turbulizer according to the invention, for example the top and bottom lands of different width, the radially extending side surfaces, and the decreased offset, ensure optimum fit-up of the turbulizer during assembly, thereby maximizing metal-to-metal contact between the turbulizer and the tubes, which ensures brazeability and optimum heat transfer.
Although the invention has been described in connection with certain preferred embodiments, it is not intended to be limited thereto. Rather, the invention includes all embodiments which may fall within the scope of the following claims.

Claims

1. A concentric tube heat exchanger having a first end and a second end, the heat exchanger comprising:

(a) an outer tube;

(b) an inner tube received inside the outer tube and concentric therewith, wherein an annular passageway is formed between the inner and outer tubes;

(c) first and second annular sealing members received inside the annular passageway between the inner and outer tubes, the first sealing member being positioned proximate the first end of the heat exchanger and the second sealing member being positioned proximate the second end of the heat exchanger, each of the sealing members comprising an outer wall and an inner wall which are connected to one another, each of the walls having first and second axially-spaced ends, the outer wall being sealed to the outer tube and the inner wall being sealed to the inner tube, thereby sealing the ends of the tubes.

2. The concentric tube heat exchanger of claim 1, wherein each of the sealing member walls has an axially-extending portion between its first and second end.

3. The concentric tube heat exchanger of claim 1, wherein the inner and outer walls of the sealing members are connected through a connecting portion which seals a radial space between the sealing member walls.

4. The concentric tube heat exchanger of claim 3; wherein the sealing members are generally U-shaped, with the first ends of the sealing member walls being connected to the connecting portion and the second ends of the sealing member walls being distal to the connecting portion.

5. The concentric tube heat exchanger of claim 1, wherein the sealing members are spaced inward from the ends of the heat exchanger, such that the second ends of the sealing member walls are proximate to, and spaced inwardly from, the ends of the heat exchanger.

6. The concentric tube heat exchanger of claim 5, wherein the sealing members are brazed to the tubes such that fillets of filler metal are formed between the tubes and the ends of the sealing member walls, and wherein the sealing members are spaced inwardly from the ends of the heat exchanger by a distance sufficient that the fillets between the second ends of the sealing member walls and the tubes are located inwardly of the ends of the heat exchanger.

7. The concentric tube heat exchanger of claim 3, wherein the connecting portion is rounded.

8. The concentric tube heat exchanger of claim 3, wherein the connecting portion is flat.

9. The concentric tube heat exchanger of claim 1, wherein the tubes and the sealing members are comprised of aluminum.

10. The concentric tube heat exchanger of claim 9, wherein the tubes are provided with a cladding comprised of a brazing alloy, at least on surfaces which are joined to the sealing members.

11. The concentric tube heat exchanger of claim 10, wherein the sealing members are provided with a cladding comprised of a brazing alloy, at least one surfaces which are joined to the tubes.

12. The concentric tube heat exchanger of claim 1, further comprising a turbulizer received in the annular passageway, the turbulizer comprising a plurality of corrugations defining a plurality of axially extending flow passages extending parallel to the tubes, each of the corrugations comprising a top land, a bottom land and a pair of side surfaces connecting the top and bottom lands, the top land being in heat exchange contact with the outer tube and the bottom land being in heat exchange contact with the inner tube;

wherein the convolutions are arranged in axially extending rows with the convolutions in each row being connected to one another and with an offset being provided between adjacent convolutions in each row, the offset having a width which is from about 30 percent to about 40 percent of a width of the top land or the bottom land.

13. The concentric tube heat exchanger of claim 12, wherein the width of the offset is from about 31 percent to about 36 percent of the top land width or the bottom land width.

14. The concentric tube heat exchanger of claim 13, wherein the width of the offset is about 31 percent of the top land width.

15. The concentric tube heat exchanger of claim 13, wherein the width of the offset is about 36 percent of the bottom land width.

16. The concentric tube heat exchanger of claim 13, wherein the top land width is greater than the bottom land width and wherein the side surfaces extend radially between the inner and outer tubes.

17. The concentric tube heat exchanger of claim 13, wherein the tubes and the turbulizer are comprised of aluminum with the top land being brazed to the outer tube and the bottom land being brazed to the inner tube.

18. A sealing member for sealing opposite ends of an annular passageway extending along an axis between inner and outer tubes of a concentric tube heat exchanger, the sealing member comprising:

an outer wall having first and second axially-spaced ends and having a generally axially-extending portion between its ends for sealing to the outer tube; and

an inner wall having first and second axially-spaced ends, the inner wall being connected to the outer wall and being spaced radially inwardly of the outer wall, the inner wall having a generally axially-extending portion between its ends for sealing to the inner tube;

wherein the generally axially-extending portions of the walls diverge from one another along said axis.

19. The sealing member of claim 18, wherein the inner and outer walls are connected through a connecting portion, the second ends of the sealing member walls are axially spaced from the connecting portion, the generally axially-extending portions of the sealing member walls extend between the connecting portion and the second end, and wherein the generally axially-extending portions diverge from said connecting portion to the second ends of the sealing member walls.

20. The sealing member of claim 18, wherein the generally axially-extending portions of the walls are resilient, and wherein the generally axially-extending portions diverge from one another at an angle such that, during assembly, the sealing members are slidably received in the annular passageway with the outer wall frictionally engaging the outer tube and the inner wall frictionally engaging the inner tube, and such that the generally axially-extending portions of the sealing member walls are in substantial engagement with the inner and outer tubes.

21. The sealing member of claim 18, wherein the generally axially-extending portion of at least one of the sealing member walls diverges from the axis by an angle of from about 1 to about 2 degrees.