Finned heat exchange tube and process for forming same

Abstract

A finned heat exchange tube includes a metal cylindrical central tube having an outer surface and a metal fin helically disposed on and in thermally conductive contact with the outer surface of the tube. The cross-section of the fin is trapezoidal in shape, with a longer and a shorter base, the longer base being in contact with the outer surface of the tube. Alternatively, the fin can have a cross-section substantially rectangular in shape, having rounded comers and sides of longer and shorter dimensions perpendicular to one another, a side of the shorter dimension being in contact with the outer surface of the tube. A process for forming a heat exchanger tube comprises helically winding and securing a metal fin on an outer surface of a metal cylindrical central tube. The fin, which is in thermally conductive contact with the central tube, has a cross-section that can be trapezoidal or substantially rectangular in shape.

Description

FIELD OF THE INVENTION

[0002] The present invention relates to a heat exchange device and, more particularly, to a finned heat exchange tube and to a process for its fabrication.

BACKGROUND OF THE INVENTION

[0003] Heat exchange devices that include a fin helically wound around a cylindrical tube are well known in the art. Typically, the fin and the tube are each formed of metal, and their interface must be efficiently heat-conductive to ensure optimal heat transfer.

[0004] U.S. Pat. No. 2,152,331 to Shoemaker discloses a tubular body to which is attached a helically wound fin flanked on either side by heat-conductive metal stabilizing strands that can be fastened by solder to the fin and tube, each of which is preferably formed from copper.

[0005] U.S. Pat. No. 4,960,170 to Carter is directed to a heat exchanger having a tube on which is helically wrapped, in a side by side relationship, a thin fin made from a material of a higher coefficient of expansion than that of the tube and a wire from a material of the same or a smaller coefficient of expansion than that of the tube.

[0006] In addition to devices formed by winding a fin around a tube, as described in the Shoemaker and Carter patents, “low fin” heat exchangers, in which the fins are formed by machining a heavy walled tube, are commercially available. In such devices, the fin and central tube are necessarily made of the same metal.

[0007] There is a continuing need for readily manufacturable heat exchange tubes, particularly of small diameter and with a low fin that can, if desired, be constructed of a material different from that of the tube. This need is met by the present invention.

SUMMARY OF THE INVENTION

[0008] The present invention is directed to a finned heat exchange tube that comprises a metal cylindrical central tube having an outer surface and a metal fin helically disposed on and in thermally conductive contact with the outer surface of the tube. The fin has a cross-section of trapezoidal shape that comprises a longer base and a shorter base, with the longer base being in contact with the tube outer surface. Alternatively, the fin can have a cross-section substantially rectangular in shape, having rounded corners and sides of longer and shorter dimensions perpendicular to one another, a side of the shorter dimension being in contact with the outer surface of the tube.

[0009] The invention is further directed to a process for forming a heat exchanger tube that comprises helically winding and securing a metal fin on an outer surface of a metal cylindrical central tube. The fin, which is in thermally conductive contact with the central tube, has a cross-section of trapezoidal shape that comprises a longer base and a shorter base, the longer base being in contact with the tube outer surface, or alternatively, a substantially rectangular cross-section with rounded corners and sides of longer and shorter dimensions perpendicular to one another, a side of the shorter dimension being in contact with the outer surface of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a perspective view of the finned heat exchange tube of the present invention.

[0011] FIGS. 2 and 3 are, respectively, side and end views of the finned heat exchange tube.

[0012] FIG. 4 is a cross-sectional view of the heat exchange tube along line A-A of FIG.3.

[0013] FIG. 5 is a detailed view of portion B of FIG. 4 that depicts the trapezoidal cross-section of the fin.

[0014] FIG. 6 is a cross-sectional view of an alternative embodiment of the heat exchange tube wherein the fin has a substantially rectangular cross-section.

[0015] FIG. 7 is a detailed view of portion C of FIG. 6 that depicts the substantially rectangular cross-section of the fin The drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0016] FIGS. 1, 2, and 3 are various views of a finned heat exchange tube 10 in accordance with the present invention. Tube 10 comprises a metal cylindrical central tube 11 and a metal fin 12 that is helically disposed on an outer surface 13 of tube 11. Tube 11 and fin 12 can be formed from the same metal or from different metals. For example, depending on the nature of the fluid flowing through tube 10, it might be desirable to make it from stainless steel, while constructing fin 11 from copper for improved thermal conductivity. Tube 11 preferably is formed from copper, copper-nickel alloy, or stainless steel; fin 12 preferably is made of copper or aluminum. It is important that the interface 14 between tube surface 13 and fin 12 be efficiently heat-conductive to ensure optimal heat transfer. To achieve good thermal conductivity at interface 14, fin 12 can be attached to tube surface 13 by, depending on the metals employed and the intended use of heat exchange tube 10, adhering means such as solder or polymeric adhesive. Solder alternatives comprising polymeric adhesive pastes are available from, for example, Emerson & Cuming Co., Billerica Mass.

[0017] Although the length and diameter of tube 10 and the dimensions and pitch of helically wound fin 12 can be varied over a considerable range, the present invention is particularly advantageous in applications where small diameter heat exchange tubes with low fins are desired, for example, for cooling a fluid such as oil. Referring to FIG. 2, central tube 11 has an outside diameter D of, preferably, up to and including about one inch, more preferably, about ¼ inch, and fin 12 has a height H of, preferably, up to and including about {fraction (3/16)} inch, more preferably, about {fraction (1/16)} inch.

[0018] FIG. 4 is a cross-sectional view of heat exchange tube 10 along line A-A of FIG. 3. FIG. 5, a detailed view of portion B of FIG. 4, depicts the trapezoidal cross-section of fin 12.

[0019] As shown in FIG. 5, the trapezoidal cross-section of fin 12 has a longer base B1 and a shorter base B2, the longer base B1 being in contact with tube outer surface 13. This trapezoidal configuration of fin 12, which can be achieved by, for example, subjecting a wire of round cross-section to shaping by suitable roll dies, provides increased contact between fin 12 and tube outer surface 13, thereby improving heat transfer performance.

[0020] FIG. 6 is a cross-sectional view of an alternative embodiment of the invention, a heat exchange tube 20 comprising a metal central tube 11 and a metal fin 21 helically disposed on tube 11. As shown in FIG. 7, a detailed view of portion C of FIG. 6, the cross-section of fin 21 is substantially rectangular in shape, with rounded corners and sides of longer and shorter dimensions perpendicular to one another, a side of the shorter dimension being in contact with an outer surface 13 of tube 11. The cross-sectional shape of fin 21 can be achieved by, for example, using a roll die to flatten a wire of round cross-section. Apart from the cross-sectional shape of fin 21, the characteristics of heat exchange tube 20, including its process of formation and mode of operation, are similar to those of heat exchange tube 10.

[0021] The invention has been described in detail for the purpose of illustration, but it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the following claims.

Claims

1. A finned heat exchange tube comprising: a metal cylindrical central tube having an outer surface; and a metal fin helically disposed on and in thermally conductive contact with said outer surface of said central tube, said fin having a cross-section selected from the group consisting of: a trapezoidal shape comprising a longer base and a shorter base, said longer base being in contact with said outer surface of said central tube; and a substantially rectangular shape having rounded comers and sides of longer and shorter dimensions perpendicular to one another, a side of said shorter dimension being in contact with said outer surface of said tube.

2. The heat exchange tube of claim 1 wherein said fin cross-section has said trapezoidal shape.

3. The heat exchange tube of claim 1 wherein said fin cross-section has said substantially rectangular shape.

4. The heat exchange tube of claim 1 wherein said central tube and said metal fins are formed from the same metal.

5. The heat exchange tube of claim 1 wherein said central tube and said metal fins are formed from different metals.

6. The heat exchange tube of claim 1 wherein said central tube is formed from a metal selected from the group consisting of copper, copper-nickel alloy, and stainless steel.

7. The heat exchange tube of claim 1 wherein said fin is formed from a metal selected from the group consisting of copper and aluminum.

8. The heat exchanger tube of claim 1 wherein said central tube has an outside diameter of up to and including about 1 inch.

9. The heat exchanger tube of claim 8 wherein said central tube has an outside diameter of about ¼ inch.

10. The heat exchanger tube of claim 1 wherein said fin has a height of up to and including about {fraction (3/16)} inch.

11. The heat exchanger tube of claim 10 wherein said fin has a height of about {fraction (1/16)} inch.

12. The heat exchanger tube of claim 1 wherein said fin is connected to said outer surface of said central tube by adhering means.

13. The heat exchanger tube of claim 12 wherein said adhering means is selected from the group consisting of solder and polymeric adhesive.

14. A process for forming a heat exchanger tube, said process comprising: helically winding and securing a metal fin on an outer surface of a metal cylindrical central tube, said fin being in thermally conductive contact with said outer surface of said central tube and having a cross-section selected from the group consisting of: a trapezoidal shape comprising a longer base and a shorter base, said longer base being in contact with said outer surface of said central tube; and a substantially rectangular shape having rounded comers and sides of longer and shorter dimensions perpendicular to one another, a side of said shorter dimension being in contact with said outer surface of said tube.

15. The process of claim 14 wherein said fin cross-section has said trapezoidal shape.

16. The process of claim 14 wherein said fin cross-section has said substantially rectangular shape.

17. The process of claim 14 wherein said central tube and said metal fins are formed from the same metal or from different metals.

18. The process of claim 14 wherein said central tube is formed from a metal selected from the group consisting of copper, copper-nickel alloy, and stainless steel, and said fin is formed from a metal selected from the group consisting of copper and aluminum.

19. The process of claim 14 wherein said central tube has an outside diameter of up to and including about one inch, and said fin has a height of up to and including about {fraction (3/16)} inch.

20. The process of claim 19 wherein said central tube has an outside diameter of about ¼ inch, and said fin has a height of about {fraction (1/16)} inch.

21. The process of claim 14 wherein said fin is connected to said outer surface of said central tube by adhering means selected from the group consisting of solder and polymeric adhesive.

22. A finned heat exchange tube comprising: a metal cylindrical central tube having an outer surface, said tube being formed from copper or stainless steel and having an outside diameter of about ¼ inch.; and a metal fin helically disposed on and in thermally conductive contact with said outer surface of said central tube, said fin being formed from copper and having a height of about {fraction (1/16)} inch, said fin further having a cross-section selected from the group consisting of: a trapezoidal shape comprising a longer base and a shorter base, said longer base being in contact with said outer surface of said central tube; and a substantially rectangular shape having rounded comers and sides of longer and shorter dimensions perpendicular to one another, a side of said shorter dimension being in contact with said outer surface of said tube.