WO2005054737A1

WO2005054737A1 - Fluid conduit with improved flow

Info

Publication number: WO2005054737A1
Application number: PCT/US2004/039889
Authority: WO
Inventors: Tony Bougebrayel; Victor Rasanow
Original assignee: Swagelok Company
Priority date: 2003-11-29
Filing date: 2004-11-29
Publication date: 2005-06-16

Abstract

A fluid conduit (10) with improved flow characteristics by use of a new flow passage geometry concept. In one embodiment, the fluid conduit (10) has a flow passage with a cross-section that transitions from a circular area at the inlet portion (12), to a non-circular area at a transition portion (30), and to a circular area at the outlet portion (20).

Description

FLUID CONDUIT WITH IMPROVED FLOW

Related Application This application claims the benefit of United States provisional patent application serial no. 60/481,720 for FLUID CONDUIT WITH IMPROVED FLOW filed November 29, 2003, the entire disclosure of which is fully incorporated herein by reference.

Technical Field The present invention relates generally to a fluid conduit with improved flow characteristics. In particular, the present invention relates to a fluid conduit with improved flow characteristics by use of a new flow passage geometry concept.

Background of the Invention Fluid conduits, such as pipe and tube fittings are in common use. Often, these conduits are used to change the direction of fluid flow. One typical type of fluid conduit used to change flow direction is a 90 degree elbow fitting characterized by a body that defines a flow passage having a circular cross-section and a 90 degree corner. A typical elbow fitting, shown in Fig. 1, has a sharp corner formed at the juncture or transition of two intersecting passages with circular cross-sections that extend transverse to each other. The sharp 90- degree angle at the corner creates a flow resistance that inhibits fluid flow. Flow resistance in the typical elbow fitting results from, among others factors, the smaller cross-sectional area of the flow passage at the bend, fluid flow momentum loss due to the sharp change in direction of flow, and flow separation zones which can cause cavitation as well as particles to collect in the flow passage. Elbow fittings are also known that form a more gradual corner between two cylindrical passages, as shown in Fig. 1 A. These fittings, however, require a larger bend radius and have a flow passage that remains a circular cross-section throughout the length of the fitting. Hydroforming is a known metal forming process in which a metal tube is formed into a desired shape with the use of hydraulic pressure applied to the inner surface of the metal tube. The metal tube is placed in a die cavity and filled with a hydraulic fluid under pressure to expand the tube in relation to the shape and geometry of the die cavity. Summary of the Invention In accordance with one aspect of the invention, a fluid conduit has improved flow characteristics by use of a new flow passage geometry concept, hi accordance with this aspect of the invention, the flow passage is defined by having a fluid inlet portion, a fluid outlet portion and a transition portion which fluidly couples the inlet and the outlet portion to form a flow passage therethrough. In one embodiment, the flow passage has a cross-section that transitions from a circular area at the inlet portion, to an elliptical area at the transition portion, and to a circular area at the outlet portion. In another embodiment, the transition portion provides a smooth continuous, inner surface. The present invention also relates to a method of forming a tube fitting having a circular cross-section and a non-circular cross-section, by use of a hydroforming process.

Brief Description of the Drawings The foregoing features of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, in which: Fig. 1 illustrates a prior art elbow fitting; Fig. 1A illustrates a prior art sweep elbow fitting; Fig. 2 is a perspective view of a fluid conduit in accordance with a first embodiment of the present invention; Fig. 3 is a transverse sectional view of the fluid conduit of Fig. 2, taken generally along line 3-3 of Fig. 2; Fig. 4 is a longitudinal sectional view of the fluid conduit of Fig. 2, taken generally along line 4-4 of Fig. 2; Fig. 5 is a flow chart illustrating the steps in one process of forming a fluid conduit in accordance with the present invention; Fig. 6-7 are longitudinal sectional views of the steps in a second process of forming a fluid conduit in accordance with the present invention Fig. 8 is a longitudinal sectional view of a fluid conduit in accordance with a second embodiment of the invention. Detailed Description of the Invention The present invention relates generally to a fluid conduit with improved flow characteristics. In particular, the present invention relates to a fluid conduit with a fluid flow passage having a geometry that improves fluid flow. While the invention is described with particular reference to an exemplary elbow conduit, such description is for explanation purposes and should not be construed as a limitation on the use of the present invention. While various aspects of the invention are described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects may be realized in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sub- combinations are intended to be within the scope of the present invention. Still further, while various alternative embodiments as to the various aspects and features of the invention, such as alternative materials, structures, configurations, methods, devices, and so on may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the aspects, concepts or features of the invention into additional embodiments within the scope of the present invention even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the invention may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present invention however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated. Those skilled in the art will readily appreciate that the invention may be realized using a variety of materials including metal or plastic. Any number of different types of metal materials may be used for the fluid conduit including but not limited to 316, 316L, 304, 304L, any austenitic or ferritic stainless steel, any duplex stainless steel, any nickel alloy such as HASTALLOY, INCONEL or MONEL, any precipitation hardened stainless steel such as 17- 4PH for example, brass, copper alloys, any carbon or low alloy steel such as 1018 steel for example, and any leaded, re-phosphorized or re-sulphurized steel such as 12L14 steel for example. Figs. 2-4 illustrate a fluid conduit 10 in accordance with a first embodiment of the invention. The conduit 10 has a fluid inlet portion 12 with a substantially circular cross- sectional geometry. The inlet portion 12 includes a wall 14 with an inner surface 16 defining an inlet passage 18. The conduit 10, also has a fluid outlet portion 20 with a substantially circular cross-sectional geometry. The outlet portion 20 includes a wall 22 with an inner surface 24 defining an outlet passage 16. The inlet and outlet passages 18 and 26 are cylindrical and have the same diameter, designated D3 in the drawings. It should be understood that the invention is also applicable to a conduit 10 having an inlet passage 18 and an outlet passage 26 with different diameters from one another. The diameter D3 may be in the range of about one quarter inch to about two inches, however, other diameters, larger or smaller, may be used. The conduit 10 includes a transition portion 30 that provides fluid communication between the inlet portion 12 with the outlet portion 20. The transition portion 30 of the conduit 10 includes a wall 32 having an inner surface 34 defining a transition passage 36. The transition portion 30 fluidly couples the inlet portion 12 with the outlet portion 20 in such a manner that the inlet passage 18, the outlet passage 26, and the transition passage 36 fonn a fluid flow passage 38 within the conduit 10. The inner surface 34 of the wall 32 of the transition portion 30 is preferably, but not necessarily, smooth, that is, is substantially free of ridges or corrugations or edges of the type that that can be formed when an elbow fitting is made by certain processes, for example, as in the prior art shown in Fig. 1. The conduit 10 thus may be made by processes that produce a smooth inner wall surface 34 for improved fluid flow. In some applications, however, fluid flow can be improved by the geometry of the flow path, whether the interior surfaces are smooth or not and regardless of the process used to form the conduit. Suitable processes include hydro forming of a metal tube or pipe, or machining the conduit 10 from a block of metal, among others. In the embodiment of Figs. 2-4, the conduit 10 is hydro formed. In the embodiment of Fig. 8, as described below, the conduit 10 is machined from a block of metal. The embodiment in Figs. 2-4 illustrates the outlet portion 20 of the conduit 10 transverse to the inlet portion 12. hi particular, the outlet portion 20 extends at about a ninety degree angle to the inlet portion 12 of the conduit 10 and is fluidly coupled to the inlet portion 12 by a curved transition portion 30. As a result, fluid flowing through the fluid flow passage 38 of the conduit 10 makes about a ninety degree turn as it travels from the inlet passage 18 through the transition passage 36 to the outlet passage 26. Thus, the included angle 0 between the inlet passage 18 and the outlet passage 26 is about 90 degrees. It should be understood that the included angle 0 may be greater than 90 degrees or less than 90 degrees, in the range of from near zero degrees to near 180 degrees. Unlike the inlet portion 12 and the outlet portion 20, the transition portion 30 of the conduit 10 does not have a circular cross-section. Instead, the transition portion 30 has a non- circular configuration along its length. In the embodiment illustrated in Figs. 2-4, the conduit 10 has an elliptical cross-section at a location along the transition portion 30 that generally bisects the included angle 0 between the inlet portion 12 and outlet portion 20. The transition portion 30 of a conduit 10 in accordance with the invention may, alternatively, have any one of several other non-circular cross-sectional configurations. For example, an oval cross-section can be provided. The elliptical cross section in the transition portion 30 has a first diameter or major diameter Dl, as measured along the major axis of the elliptical cross-section, and a second diameter or minor diameter D2, as measured along the minor axis of the elliptical cross- section. The first diameter Dl of the transition portion 30 is preferably greater than the diameter D3 of the inlet and outlet passages 18 and 26. Conversely, the second diameter D2 of the transition portion 30 is preferably less than the diameter D3 of the inlet and outlet passages 18 and 26. As a result, the transition portion 30 of the conduit 10 has a shape that, compared to the shape of the inlet and outlet portions 12 and 20, is wider in a first direction (Dl) transverse to the direction of the fluid flow, and narrower in a second direction (D2) transverse to the direction of the fluid flow and normal to the first transverse direction. The transition passage 36 does not have a constant elliptical cross-section along its entire length. Instead, the cross-section of the fluid flow passage 38 gradually transitions from the circular cross-section of the inlet passage 18 to the elliptical cross-section of the transition passage 36, and to the circular cross section of the outlet passage 26. The gradual transition of the fluid flow passage 38 helps to maintain the fluid flow rate in the conduit 10. It is understood, however, that the transition passage 36 may maintain a constant elliptical cross-section for a portion of the length along the transition portion 30. In the embodiment in Figs. 2-4, the major axis Dl of the cross-section of the transition passage 36 gradually expands until reaching a widest point. The minor axis D2 of the cross-section of the transition passage 36 gradually contracts until reaching a nanowest point. For illustration purposes, Figs. 2-4 define the elliptical cross section at a location along transition portion 30 that bisects the included angle 0 between the inlet portion 12 and the outlet portion 20. It is understood, however, that the major axis Dl may be widest and the minor axis D2 may be narrowest at a location along the transition portion 30 other than the location that bisects the included angle 0 between the inlet portion 12 and the outlet portion 20. Thus, Dl may reach its widest position and D2 may reach its nanowest position at a location prior to or after the location that bisects the included angle 0 between the inlet portion 12 and the outlet portion 20. In addition, Dl and D2 need not be widest and narrowest, respectively, at the same location along the transition portion 30. In addition to the transition in cross-sectional shape of the transition passage 36, the cross-sectional area of the transition passage 36 can be configured to be greater than the cross-sectional area of the inlet passage 18 or the outlet passage 26. Prior art elbow fittings having a circular cross-section with a sharp 90° comer, as shown in Fig. 1, or a 90° sweep elbow fitting as shown in Fig. 1 A (as shown also in U.S. Patent No. 6,164,706) do not have larger cross-sectional areas in their respective transition passages. The greater cross-sectional area can enable the use of smaller bend radii while still maintaining the flow rate through the conduit 10. h addition, the larger flow area may result in the flow resistance in the transition portion 30 being less than the flow resistance in the inlet portion 12 or the outlet portion 20. In manufacturing of the conduit 10, the provision of the non-circular transition portion 30 can reduce localized stresses that could arise during the bending process. It should be understood that the cross-sectional area of the transition passage 36 need not be greater than the cross- sectional area of the inlet passage 18 or the outlet passage 26 in order to achieve improved flow characteristics. The smooth inner surface 34 and elliptical cross-section of the transition passage 36 of the conduit 10 results in reduced flow resistance and a smoother and more consistent flow, as compared to a fitting having a circular cross-section with a sharp 90° corner as shown in Fig. 1. In particular, as compared to the fitting in Fig. 1, the conduit 10 of the present invention exhibits less recirculation of fluid, shorter separation zones, less momentum loss, and more uniform and laminar flow. In addition, the conduit 10 reduces or prevents the formation of stagnation zones that result in collection of particles within the conduit 10. A conduit 10 in accordance with the present invention is preferably manufactured by hydro forming to form the inlet portion 12, the outlet portion 20, and the transition portion 30 as an single, integral part. Conventional hydroforming processes may be used to form the conduit 10, however, other manufacturing processes such as casting, molding, or machining may alternatively be used. The steps for hydroforming a conduit 10 in accordance with the present invention are diagrammed in Figure 5. In step 101, a die assembly is provided having a cavity with an inlet portion and an outlet portion with circular cross sectional areas and a transitioning portion with a non- circular (preferably elliptical) cross-sectional area. At step 102, a tube is inserted into the cavity in the die assembly. At step 103, pressurized fluid, such as water, fills the inside of the tube. At step 104, the pressurized fluid expands the tube from the inside to press the outer surface of the tube into engagement with the cavity of the die assembly to form a fluid conduit 10 having an inlet portion and an outlet portion that define flow passages with circular cross-sectional areas and a transition portion that defines a flow passage with a non-circular cross-sectional area. Figs. 6-7 illustrate a method of forming the fluid conduit 10 in accordance with the present invention in which pressurized fluid structurally supports a tube 50 during fonning by a die assembly 56. In Fig. 6, the tube 50 having an outer surface 52 and inner surface 54 is placed into a die assembly 56. The die assembly 56 has an upper die 58 and a lower die 60 spaced apart to allow the tube 50 to be placed between the upper and the lower die 58 and 60. A pressurized fluid, such as water, fills the inside of the tube 50 exerting a fluid pressure 62 against the inner surface 54 of the tube 50. h Fig. 7, the upper die 58 and the lower die 60 engage the outer surface 52 of the tube 50 with sufficient force to form the tube 50 into the fluid conduit 10. The fluid pressure 62 against the inner surface 54 of the tube 50 stracturally supports the tube 50 during fonning. The support by the fluid pressure 62 prevents the flow passage 38 from developing a smaller cross-sectional area at the bend due to buckling or bending of the tube 50. The fluid conduit 10 resulting from this process, has a transition portion that defines a flow passage with a non-circular cross-sectional area and an inlet portion and an outlet portion that define flow passages with circular cross-sectional areas. The cross-sectional area of the non-circular flow passage is at least equal to the cross- sectional area of the circular flow passage. It should be understood that the processes for forming the conduit 10 illustrated in Fig. 5 and in Figs. 6-7, may incorporate both expansion of the tube by the pressurized fluid and movement of all or part of the die assembly to form the tube into the conduit 10. The advantages of hydroforming may include reducing raw material requirements and faster, less expensive manufacturing when compared to machining and molding processes. The hydroforming process allows close control of the process parameters in order to control the quality of the product and to prevent damage to the parts. Using the hydroforming process to produce the conduit could potentially improve fluid flow and ease of cleaning, as well as reduce weight and cost of existing machined products. Fig. 7 illustrates a conduit 10a in accordance with a second embodiment of the invention. The conduit 10a differs from the conduit 10 in that the conduit 10a is formed by machining a block of metal 40 rather than being formed from a metal tube or a pipe like the conduit 10. The conduit 10a has a flow passage 38a that includes an inlet passage 18a, a transition passage 36a, and an outlet passage 26a. The flow passage 38a of the conduit 10a has the same configuration as the flow passage 38 of the conduit 10. Because the fitting 10a is formed from a larger piece of metal rather than being a metal tube, the several walls of the fitting 10a do not substantially follow the shape of flow passage 38a as walls 14, 22, and 32 substantially follow the shape of the flow passage 38.

Claims

Having described the invention, it is now claimed:

1. A fluid conduit, comprising: a fluid inlet portion; a fluid outlet portion; a transition portion fluidly coupling said inlet portion and said outlet portion, said inlet portion, outlet portion, and transition portion defining a flow passage with a cross-section that transitions from a circular area at the inlet portion, to an elliptical area at the transition portion, and to a circular area at the outlet portion.

2. The fluid conduit of claim 1 wherein said fluid inlet portion and said fluid outlet portion are tubular.

3. The fluid conduit of claim 1 wherein said fluid outlet portion is transverse to said fluid inlet portion.

4. The fluid conduit of claim 1 wherein said transition portion creates an included angle between said fluid inlet portion and said fluid outlet portion of about 90 degrees.

5. The fluid conduit of claim 1 wherein said elliptical cross-section has a major diameter and a minor diameter, said major diameter being greater than the diameter of said circular cross-section and said minor diameter being less than the diameter of said circular cross section.

6. The fluid conduit of claim 1 wherein said elliptical cross-section has an area greater than the cross-sectional area of said circular cross-section.

7. The fluid conduit of claim 1 wherein the diameter of said flow passage in said fluid inlet portion is equal to the diameter of said flow passage in said fluid outlet portion.

8. The fluid conduit of claim 7 wherein said diameter is in the range of about one quarter inch to about two inches.

9. A fluid conduit, comprising: a fluid inlet portion having an inner surface with a circular cross-sectional area; a fluid outlet portion having an inner surface with a circular cross-sectional area; a transition portion having an inner surface with a non-circular cross-sectional area, said transition portion fluidly coupling said inlet portion and said outlet portion, wherein said inlet portion inner surface, outlet portion inner surface, and transition portion inner surface form a flow passage; said flow passage having a smooth inner surface along the length of said transition portion inner surface.

10. The fluid conduit of claim 9 wherein said non-circular cross-sectional area is elliptical.

1 1. The fluid conduit of claim 10 wherein said non-circular cross-section has a major diameter and a minor diameter, said major diameter being greater than the diameter of said circular cross-section and said minor diameter being less than the diameter of said circular cross section.

12. The fluid conduit of claim 9 wherein said non-circular cross-sectional area is oval.

13. The fluid conduit of claim 9 wherein said non-circular cross-sectional has an area greater than the cross-sectional area of said circular cross-section.

14. The fluid conduit of claim 9 wherein said fluid inlet portion and said fluid outlet portion are tubular.

15. The fluid conduit of claim 9 wherein said fluid outlet portion is transverse to said fluid inlet portion.

16. The fluid conduit of claim 9 wherein said transition portion creates an included angle between said fluid inlet portion and said fluid outlet portion of about 90 degrees.

17. The fluid conduit of claim 9 wherein said non-circular cross-section has an area greater than the cross-sectional area of said circular cross-section.

18. The fluid conduit of claim 9 wherein the diameter of said flow passage in said fluid inlet portion is equal to the diameter of said flow passage in said fluid outlet portion.

19. The fluid conduit of claim 18 wherein said diameter is in the range of about one quarter inch to about two inches.

20. A metal elbow fitting, comprising: a fluid inlet portion; a fluid outlet portion; a curved transition portion, said transition portion joining said fluid inlet portion to said fluid outlet portion to form an integral metal hydroformed part, wherein said part forms a flow passage with smooth inner surface, said smooth inner surface gradually transitioning along said curved transition portion from a circular cross-section area to a non-circular cross-section area and to a circular cross-section area.

21. The fluid conduit of claim 20 wherein said non-circular cross-sectional area is elliptical.

22. The fluid conduit of claim 21 wherein said non-circular cross-section has a major diameter and a minor diameter, said major diameter being greater than the diameter of said circular cross-section and said minor diameter being less than the diameter of said circular cross section.

23. The fluid conduit of claim 20 wherein said non-circular cross-sectional area is oval.

24. The fluid conduit of claim 20 wherein said non-circular cross-sectional has an area greater than the cross-sectional area of said circular cross-section.

25. The fluid conduit of claim 20 wherein said fluid inlet portion and said fluid outlet portion are tubular.

26. The fluid conduit of claim 20 wherein said transition portion creates an included angle between said fluid inlet portion and said fluid outlet portion of about 90 degrees.

27. The fluid conduit of claim 20 wherein said non-circular cross-section has an area greater than the cross-sectional area of said circular cross-section.

28. The fluid conduit of claim 20 wherein the diameter of said flow passage in said fluid inlet portion is equal to the diameter of said flow passage in said fluid outlet portion.

29. The fluid conduit of claim 28 wherein said diameter is in the range of about one quarter inch to about two inches.

30. A fluid conduit, comprising: a fluid inlet portion with a first flow resistance; a fluid outlet portion with a second flow resistance; a curved transition portion with a third flow resistance, said curved transition portion fluidly coupling said inlet portion and said outlet portion to define a flow passage with a smooth inner surface, said third flow resistance being less than said first flow resistance and said second flow resistance.

31. The fluid conduit of claim 30 wherein said flow passage in said transition portion has an elliptical cross-sectional area.

32. The fluid conduit of claim 30 wherein said flow passage has a cross-section that transitions from a circular area at the inlet portion, to an elliptical area at the transition portion, and to a circular area at the outlet portion.

33. The fluid conduit of claim 30 wherein said flow passage in said transition portion has an elliptical cross-sectional area.

34. A process for forming a fluid conduit having an inlet portion and an outlet portion that define flow passages with circular cross-sectional areas and a transitioning portion that defines a flow passage with a non-circular cross-sectional area, from a tube that defines a flow passage with a circular cross-section area, said process comprising the steps of: providing a die assembly having a cavity with an inlet portion and an outlet portion with circular cross-sectional areas and a transitioning portion with a non-circular cross-sectional area; inserting a tube into said cavity in the die assembly; filling said tube with pressurized fluid; expanding said tube from the inside to press said tube into engagement with the said cavity of the die assembly to fonn a fluid conduit having an inlet portion and an outlet portion that define flow passages with circular cross-sectional areas and a transitioning portion that defines a flow passage with a non-circular cross-sectional area.

35. The process of claim 34 wherein said non-circular cross-sectional area is elliptical.

36. The process of claim 34 wherein said non-circular cross-sectional area is oval.

37. The process of claim 34 wherein said fluid outlet portion is transverse to said fluid inlet portion.

38. The process of claim 34 wherein the included angle between the inlet portion and the outlet portion is about 90 degrees.

39. The process of claim 34 wherein the included the tube is metal.

40. A process for forming a fluid conduit having an inlet portion and an outlet portion that define flow passages with circular cross-sectional areas and a transitioning portion that defines a flow passage with a non-circular cross-sectional area, from a tube that defines a flow passage with a circular cross-section area, said process comprising the steps of: placing the tube into a die assembly; filling the tube with pressurized fluid; engaging the tube with the die assembly to form a fluid conduit having an inlet portion and an outlet portion that define flow passages with circular cross-sectional areas and a transitioning portion that defines a flow passage with a non-circular cross- sectional area, wherein the pressurized fluid acting on the tube results in the cross- sectional area of the non-circular flow passage being at least equal to the cross- sectional area of the circular flow passage.

41. The process of claim 40 wherein said non-circular cross-sectional area is elliptical.

42. The process of claim 40 wherein said non-circular cross-sectional area is oval.

43. The process of claim 40 wherein said fluid outlet portion is transverse to said fluid inlet portion.

44. The process of claim 40 wherein the included angle between the inlet portion and the outlet portion is about 90 degrees.

45. The process of claim 40 wherein the included the tube is metal.