WO2002050489A1

WO2002050489A1 - Serrated rib and heat exchanger tube provided therewith

Info

Publication number: WO2002050489A1
Application number: PCT/DE2001/004832
Authority: WO
Inventors: Georg BRÜNDERMANN
Original assignee: Bruendermann Georg
Priority date: 2000-12-21
Filing date: 2001-12-20
Publication date: 2002-06-27
Also published as: AU2002227876A1; DE10063831A1

Abstract

The invention relates to a serrated rib (2) from sheet metal to be mounted on the periphery (14) of a metal tube (1a). Said rib (2) is configured from a rib base (3) with freely protruding lug-shaped rib segments (4) facing the tube (1a) when mounted and from interstices (5) provided between the rib segments (4). The width of the rib segments (4) is defined by the distance of the adjacent interstices (5) and increases from the rib base (3) towards the free end of the rib segment (4). The thickness (d) of every rib segment (4) decreases from the rib base (3) towards the free end of the rib segment (4). The invention also relates to a heat exchanger tube that is provided with a serrated rib.

Description

Serrated rib and heat exchanger tube provided with it

The invention relates to a serrated fin made of sheet metal for attachment to the circumferential surface of a metal tube, the fin being formed from a fin base facing the tube in the attached state with tab-shaped fin segments protruding freely therefrom and gaps provided between the fin segments. The invention also relates to a heat exchanger tube which is provided with at least one serrated rib.

In principle, it is known to use smooth or serrated fins for heat exchanger tubes which project approximately perpendicularly from the circumferential surface of the tube. Compared to a heat exchanger tube with a smooth fin, the medium flowing around is swirled more strongly by a serrated fin. The swirling causes a better heat transfer between the heat exchanger tube and the medium flowing around the heat exchanger tube.

Because of the improved heat transfer, a serrated fin can be made shorter to provide the same heat transfer performance than a smooth finned fin. With the same heat transfer capacity, a heat exchanger tube with a serrated rib therefore has a lower weight than a heat exchanger tube with a smooth rib.

The well-known serrated rib is made from a sheet metal strip. The usual cross-section of the strip is rectangular _U nd for example, has a width of 19 mm and a thickness of 1 mm. The sheet metal strip is cut with shear cuts approximately perpendicular to one of the narrow sides. The individual rib segments result from the incisions. The sheared narrow sides of each rib segment are aligned parallel to each other. The material cohesion is removed locally without removing material. The length of the shear cuts is usually about 2/3 to 3/4 of the width of the sheet metal strip. The part of the sheet metal strip which has not been cut forms the fin base, which must be integrally connected to the tube in order to obtain a heat exchanger tube.

To connect the rib to the tube, the beginning of the sheet metal strip is attached to the base of the rib on the circumferential surface of the tube and selectively connected to it with a material fit. The tube is then set in rotation relative to the sheet metal strip while the sheet metal strip is guided tangentially to the tube by means of a device. The straight sheet metal strip is bent by the rotation of the tube, so that the fin foot conforms to the circumferential surface of the tube. The fin base is welded to the circumferential surface of the tube. Due to the deformation of the sheet metal strip, the shear surfaces of adjacent rib segments, which are initially still closely spaced apart, are spread apart, so that the wedge-shaped gaps arise between the rib segments.

The well-known serrated rib and the heat exchanger tube provided with it form a good compromise between, on the one hand, the good heat transfer based on the turbulence and, on the other hand, the increase in flow resistance which is induced by the turbulence of the medium flowing around.

The invention has for its object to develop a serrated rib so that the heat transfer is further improved while maintaining the advantages of the known serrated rib.

According to the invention, the object is achieved in that the width of each rib segment, which is defined by the spacing of the adjacent gaps, increases from the rib base to the free end of the rib segment, and that the thickness of each rib segment element decreases from the rib base to the free end of the rib segment.

This simple measure increases the effective surface for the heat transfer for a fin with the same material expenditure. In a specific embodiment of a serrated fin, which is made from a sheet metal strip with a rectangular cross section 19 mm x 1 mm, 280 fins per meter of heat exchanger tube can be provided. With an outer diameter of the tube of, for example, 38 mm, the serrated fin according to the prior art has a heat transfer area of 1.80 m ² . On the same tube, 280 serrated fins according to the proposed construction result in a heat transfer area of 2.04 m ² . This corresponds to an increase in the heat transfer area of about 13% for the same material expenditure for the fin.

For a large heat exchanger, which previously required 1000 heat exchanger tubes with conventionally serrated fins for its required heat transfer capacity, only 870 heat exchanger tubes are required when using the serrated rib according to the invention. This means a significant advantage due to lower material costs and manufacturing costs. In addition, the lower weight and smaller size simplify and reduce the cost of transporting and storing heat exchanger tubes or heat exchangers.

The tab-shaped sheet of each rib segment advantageously has approximately the shape of a trapezoid. The trapezoid is the most favorable geometry for the rib segments spread apart from one another in order to spread a rib segment into the adjacent wedge-shaped gaps. The area of the wedge-shaped gap is reduced by the trapezoidal shape of the rib segments. This will narrow the wedge-shaped gap.

The longitudinal section of the rib segments is simply wedge-shaped shaped because this simple geometry is easy to manufacture and easy to calculate.

The surface of the rib segments is expediently smooth in order to keep flow losses low.

From a fluidic point of view as well as for the production, it is advantageous if the surface of each rib segment has a structure which is produced by a rolling or a drawing process. This is because these manufacturing processes result in a surface smoothness that is favorable for heat transfer and because the manufacturing processes specified are easy to carry out.

A further benefit is seen when the deepest point of each gap, which reaches the base of the rib, has a rounded shape with little notch. This shape prevents the crack from progressing from the gap into the fin base during the relatively strong shaping and nestling of the fin base onto the peripheral surface of the tube.

A7 On the rib base of the serrated rib there is preferably a web which extends transversely to the rib and has a contact surface for the peripheral surface of a metal tube. The contact surface of the web is intended to be welded to the pipe surface of a heat exchanger pipe.

The web can be provided with a curvature which points in the direction of a freely projecting rib segment.

The rib with the web can have an L-shaped cross section, the L-leg projecting freely on the web forming the rib. Two U-legs are preferably attached to the web, so that the web and ribs have a U-shaped cross section, the U-legs projecting freely on the web forming ribs.

The distance between two U-legs of adjacent turns of the helically wound rib preferably corresponds to the leg distance that the U-shaped cross section has.

A weld seam consisting of an additional material is preferably made narrower than the width of the web.

On a simple heat exchanger tube with a serrated rib according to the invention, at least one rib is integrally connected to the peripheral surface of the tube along an annular line. Several ring-shaped ribs can be easily pre-produced and cohesively connected with the in a subsequent step using a soldering or welding process

Connect pipe.

An alternative construction of a heat exchanger tube provides that at least one rib is connected to the peripheral surface of the tube in a helical manner or along a helical line. For reasons of heat transfer and from a manufacturing point of view, it can be advantageous to arrange several ribs in the manner of the threads of a multi-start thread on the circumferential surface of the tube, in which case each rib has to be looped around the circumferential surface of the tube with a larger pitch angle than with one catchy tube with a rib wrapped around it.

The invention is illustrated by way of example below in a drawing and described in detail with reference to individual figures. Show it: 1 is a sectional view of a heat exchanger tube with a serrated fin according to the prior art,

2 shows a detail of three rib segments of the serrated rib according to FIG. 1,

3 shows the side view of a narrow side of the serrated rib according to FIG. 2,

4 is a sectional view of a heat exchanger tube with a serrated rib according to the invention,

5 shows a detail of three rib segments of the serrated rib according to FIG. 4,

6 shows the side view of the narrow side of a rib segment according to FIG. 5,

7 is a side view of a serrated rib with a web and an L-shaped cross section,

Fig. 8 is a side view of a serrated rib with a web and a U-shaped cross section.

the prior art is shown in FIGS. 1 to 3 for ease of understanding. The same technical features are provided with the same reference numerals both in the prior art figures and in the figures for the exemplary embodiment described.

Fig. 1 shows a sectional view through a heat exchanger tube 1 according to the prior art. The hatching shows the wall thickness of a metal tube la, the outer diameter of which is 38 mm. On the peripheral surface 1b of the tube ia is a serrated rib 2 made from a sheet metal strip welded to the narrow side of her rib foot 3 and protrudes perpendicularly from the peripheral surface 1b. The serrated rib 2 is made from a straight, elongated sheet metal strip which was initially provided with shear cuts at regular intervals. The shear cuts have divided the sheet into rib segments 4. The sheet metal strip has then been bent by bending in such a way that it clings to the circumferential surface of the tube 1 a. As a result of the reshaping, the rib segments 4 have been spread apart and the wedge-shaped gaps 5 have arisen between the rib segments 4. The opposite shear surfaces 4a and 4b of a rib segment 4 are, as can best be seen in FIG. 2, parallel to one another. The thickness d of the rib segment 4 which can be seen in FIG. 3 is constant and corresponds to the thickness of the sheet metal strip.

The serrated rib according to the invention is illustrated in Figures 4 to 6. Fig. 4 shows the cross section of a heat exchanger tube 1, which is provided with the serrated rib 2 according to the invention. It is very easy to see that the wedge-shaped gaps 5 between the individual rib segments 4 are narrower than in the prior art rib segments 4 according to FIG. 1. The comparison between FIGS. 2 and 5 shows that the wedge angle of the gap 5 has more than halved in the serrated rib 2 according to the invention. It should be noted that a rib segment 4 according to FIG. 5 has the same amount of material as a rib segment 4 according to FIG. 2.

The shape and width of a rib segment shown in FIG. 5 comes about because the amount of material of the rib segment 4 is distributed differently than in the case of the rib segment 4 according to the prior art shown in FIG. 2. It can be seen in FIG. 6 that the thickness d of the rib segment 4 decreases continuously from the rib base 3 to the free end of the rib segment 4. By DIE _se design and with this embodiment DAR provided proportions, the effective heat transfer surface of the serrated rib 2 according to the invention increases by approximately 13% compared to the serrated rib 2 of the prior art according to FIGS. 1 to 3.

5 has approximately the shape of a trapezoid, the opposite narrow shear surfaces 4a and 4b of the rib segments 4 forming the oblique sides of the trapezoid.

According to the exemplary embodiment, 280 individual annular serrated fins 2 are arranged at a regular distance from one another on a meter tube length of the heat exchanger tube 1. Alternatively, a one-piece serrated rib 2 can be welded along a screw line on the circumferential surface of the tube, the sum of the same length and thus the same heat transfer surface as is achieved with 280 ring-shaped individual ribs.

It has been found that, in the case of a ring-shaped attachment of a plurality of ribs 2 as well as a one-piece helical attachment of a serrated rib 2, there is no appreciable increase in the flow resistance for the medium flowing around in comparison with the prior art. The new design is a very satisfactory compromise between increased heat transfer performance and induced flow resistance.

The longitudinal section or the profile according to FIG. Β shows that a rib segment 4 is wedge-shaped and has a blunt wedge end 4c. The material thinned towards the free end of the rib segment 4 has been redistributed into the rib segment width. The surface of the rib segments 4 is smooth. In this way, frictional losses due to the friction of the flow _a of the surface of the rib segments 4 n kept low. The deepest point of each gap 5 reaching the fin 3 has a low-notch rounded shape 5a, which prevents the shear cut from progressing into the fin 3 while the sheet metal strip is being formed.

FIGS. 7 and 8 show embodiments of a serrated rib, the rib base 3 of which has a web 6 pointing transversely to the rib. 7, the rib-web cross section is L-shaped. 8, a U-shaped rib-web cross-section is provided.

In both cases, the web 6 has a contact surface βa, with which it rests in the connected state on the circumferential surface of a metal tube. The bearing surface βa of the web 6 is the part which is welded to the pipe surface of a heat exchanger pipe.

8, the web 6 is provided with a curvature 7 which points in the direction of the freely projecting rib segment 4. The curvature 7 of the web 6 is thus directed upwards from the tube surface of a heat exchanger tube. In the assembled state, a cavity 8 is created between the curvature 7 and the pipe surface. Welding processes are used to produce a heat exchanger pipe. A filler metal is fed in the form of a welding wire. The cavity 8 simplifies the guiding of the weld seam or the welding wire. The weld seam is limited and guided on the side. The cavity 8 serves to prevent the weld seam from breaking out. In addition, the amount of the filler metal required is limited by the volume of the cavity 8. The filler metal does not come out or only slightly beyond the width of the web 6.

Of course, the cavity can also be dispensed with become. The straight web, which is then formed without curvature, is shown in dashed lines in FIG. 8.

The distance between two of the two U-legs according to FIG. 8 in the wound state of the serrated rib is such that the rib segments 4 of adjacent turns have a distance from each other which corresponds to the leg distance that the U-legs have on the common web.

The bearing surface 6a of the web 6 is provided with a profile (not shown) which is designed in the form of fine longitudinal ribs. The profiling improves the weldability of the rib via electric arc welding processes. The longitudinal ribs are rolled during the manufacturing process in a rolling device by means of special rollers.

Serrated rib and heat exchanger tube provided with it

LIST OF REFERENCE NUMBERS

1 heat exchanger tube la metal tube

1b peripheral surface

2 serrated rib

3 ribbed feet

3a narrow side

4 rib segment

4a shear area

4b shear area

4c blunt wedge end

5 gap

5a rounded shape

6 bridge

6a contact surface

7 curvature

8 cavity α wedge angle d thickness

Claims

Serrated rib and heat exchanger tube provided with it

1. Serrated rib (2) made of sheet metal for attachment to the circumferential surface (lb) of a metal tube (la), the

Rib (2) is formed from a rib base (3) facing the tube (la) in the attached state with tab-shaped rib segments (4) projecting freely therefrom and gaps (5) provided between the rib segments (4), characterized in that the width of each Rib segment (4), which is defined by the distance of the adjacent gaps (5), increases from the rib base (3) to the free end of the rib segment (4), and that the thickness (d) of each rib segment (4) from that Rib foot (3) decreases towards the free end of the rib segment (4).

2. Jagged rib according to claim 1, so that each rib segment (4) has approximately the shape of a trapezoid.

3. Jagged rib according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the longitudinal section of the rib segments (4) is wedge-shaped.

4. Jagged rib according to one of claims 1 to 3, d a - d u r c h g e k e n n z e i c h n e t that the surface of the rib segments (4) is smooth.

A serrated fin according to claim 3, wherein the surface of each fin segment (4) has a structure made by a rolling or drawing process.

6. Jagged rib according to one of claims 1 to 4, since - characterized in that the deepest point of each gap (5), which reaches the fin base (3), has a rounded shape with little notch.

7. Jagged rib according to one of claims 1 to 6, characterized in that on the rib base (3) a crosswise to the rib web (6) is provided, and that the web is a bearing surface (6a) for the peripheral surface (1b) of a metal Rohres (la) has.

8. Jagged rib according to claim 7, so that the web is provided with a curvature (7) which points in the direction of a freely projecting rib segment (4).

9. jagged rib according to claim 7 or 8, d a d u r c h g e k e n n z e i c h n e t that the rib with the web has an L-shaped curved cross section, wherein the L-leg protruding freely on the web forms the rib.

10. Jagged rib according to claim 7 or 8, d a d u r c h g e k e n n z e i c h n e t that two U-legs are attached to the web, so that the web and ribs have a U-shaped curved cross-section, the U-legs projecting freely on the web form ribs.

11. Jagged rib according to claim 10, so that the distance between two U-legs (7) of adjacent turns of the helically wound rib corresponds to the leg distance that the U-shaped cross-section has.

12. Jagged rib according to one of claims 7 to 12, characterized in that a weld made of filler material is made narrower is than the width of the web.

13. Heat exchanger tube (1) with at least one serrated rib (2) according to one of claims 1 to 6, dadurchge - indicates that at least one rib (2) integrally connected along an annular line with the peripheral surface (lb) of the tube (la) is.

14. Heat exchanger tube with at least one serrated rib according to one of claims 1 to 6, d a d u r c h g e k e n n z e i c h n e t that at least one rib (2) along a screw line is firmly connected to the peripheral surface (lb) of the tube (la).