EP1312885B1 - Heat exchange tube structured on both sides and process for making same - Google Patents

Description

The invention relates to metallic, double-sided structured heat exchanger tubes, in particular finned tubes, according to the preamble of claim 1.

State of the art

Heat transfer occurs in many areas of refrigeration and air conditioning technology as well as in the Process and energy technology. For heat transfer in these areas commonly used tube bundle heat exchanger. In many applications flows Here on the tube inside a liquid, which depends on the direction of the Heat flow is cooled or heated. The heat gets to the outside of the pipe the medium is discharged or withdrawn. It is booth the technique that in Rohrbündelwärmeaustauschem instead of smooth tubes on both sides structured tubes are used. As a result, the heat transfer on the inside of the pipe and on the outside of the pipe intensified. The transferred heat flux density is increased and the heat exchanger can be made more compact. Alternatively, the heat flow density can be maintained and the driving temperature difference be lowered, resulting in a more energy-efficient heat transfer is possible.

Have structured heat exchanger tubes for tube bundle heat exchanger usually at least one structured area and smooth end pieces and possibly smooth spacers. Limit the smooth end or intermediate pieces the structured areas. So that the tube easily into the tube bundle heat exchanger can be installed, the outer diameter of the structured Areas should not be greater than the outer diameter of the smooth end and intermediate pieces.

Heat exchanger tubes are known for example from US 3,861,462, the are structured on both sides. The structure is first rolled into strip material, which is then formed into a tube and welded to the butt joint.

Other structured heat exchanger tubes are often rolled as integral Used finned tubes. Under integrally rolled finned tubes are finned Understood tubes in which the ribs of the wall material of a Smooth tube were formed and seamless (US 5,992,513, US 4,733,698). Finned tubes have on their outside ring-shaped or helical circumferential Ribs. In many cases, they have on the tube inside a variety of axially parallel or helically encircling ribs, the Improve heat transfer coefficient on the inside of the pipe (US 3,768,291). These internal ribs run with a constant cross section parallel to the tube axis or in the form of helical lines at a certain angle to the tube axis. ever higher the inner fins, the greater the improvement of the heat transfer coefficient. The production of such pipes is described for example in DE 23 03 172 described. It is important that by the disclosed there Use of a profiled rolling mandrel for producing the inner ribs the Dimensions of the inner and the outer structure of the finned tube from each other can be set independently. This allows both structures on the adapted to respective requirements and so the tube can be optimally designed.

In recent times many possibilities have been developed, depending on the application Heat transfer on the outside of integrally rolled finned tubes continues to increase increase, by the ribs on the tube outside with other structural features be provided. For example, when condensation of refrigerants on the Outside of the pipe, the heat transfer coefficient increases significantly when the rib flanks be provided with additional convex edges (US 5,775,411). at Evaporation of refrigerants on the outside of the pipe has become performance enhancing proved to be partially between the channels located between the ribs Close, so that cavities are created by the pores or slots with the Environment are connected. In particular, such are substantially closed Channels by bending or flipping the rib (US 3,696,861, US 5,054,548), by splitting and upsetting the rib (DE 2,758,526, US 4,577,381), and by notching and swaging the rib (US 4,660,630, EP 0,713,072, US 4,216,826).

The mentioned performance improvements on the outside of the tube have the consequence that the majority of the total heat transfer resistance on the tube inside is moved. This effect occurs especially at low flow rates on the inside of the pipe - ie e.g. at partial load operation - on. Around It is therefore to significantly reduce the overall heat transfer resistance necessary to further increase the heat transfer coefficient on the inside of the pipe increase. This would be by increasing the height of the inner ribs in principle possible, but due to the increasing, strong deformation of the material is technically difficult to control and also to a high weight of the structured Pipe leads. For cost reasons, this is undesirable.

Task:

The object of the invention is to provide both sides with structured heat exchanger tubes To produce increased performance internal structure, wherein the weight fraction of the Internal structure of the total weight of the pipe may not be higher than in conventional, helical internal ribs of constant cross section. The dimensions The internal and external structure of the finned tube must be independent of each other be adjustable.

Brief description of the invention:

The task is solved in a heat exchanger tube of the type mentioned, in each of which adjacent inner ribs are separated by a parallel to the inner ribs extending primary groove, according to the invention,
in that the inner ribs are crossed by secondary grooves running at a pitch angle β, measured against the pipe axis,
the secondary grooves extend at an inclination angle γ of 60-85 ° with respect to the inner ribs,
that the depth T of the secondary grooves is at least 20% of the rib height H of the inner ribs, and
the density of the intersections of inner ribs (20) and secondary grooves (22) is 90 to 250 points of intersection / cm ² .

By introducing the secondary grooves, the inner ribs now have no constant Cross section more. Following the course of the inner ribs, then changes the cross-sectional shape of the inner ribs at the locations of the secondary grooves. By the Secondary grooves arise in the pipe side flowing medium additional vortex in close to the wall, which increases the heat transfer coefficient. It is Seeing that by adding secondary grooves the weight fraction of the Internal structure on the total weight of the pipe is not increased.

The depth of the secondary grooves becomes radial from the top of the inner fin Direction measured. The depth of the secondary grooves is at least 20% of the Height of the inner ribs. If the depth of the secondary grooves is equal to the height of the Inner ribs, then arise on the inside of the tube spaced apart Structural elements similar to truncated pyramids.

Claims 2 to 10 relate to preferred embodiments of the invention Heat exchanger tube.

The invention further provides, according to claims 12 to 16, a Process for the preparation of the heat exchanger tube according to the invention.

According to the invention, to produce a heat exchanger tube structured on both sides with the proposed secondary grooves in the inner structure the Tool for forming the outer ribs in at least two spaced apart Rolled disc packages built. The internal structure is different by two profiled roll mandrels shaped. The first mandrel supports the pipe in the first forming area under the first roll disk package and forms first helical circumferential or axially parallel inner ribs, these Inner ribs initially have a constant cross-section. The second rolling mandrel supports the pipe in the second forming area under the second roll disk package larger diameter and shapes the secondary grooves according to the invention in the previously formed helical circumferential or paraxial ribs. The Depth of the secondary grooves is essentially determined by the choice of diameter set two mandrels.

Detailed description:

The invention will be explained in more detail with reference to the following exemplary embodiments:

Fig.1:

schematisch die Herstellung eines erfindungsgemäßen Wärmeaustauscherrohres mittels zweier Dome mit unterschiedlicher Orientierung der Drallwinkel;

Fig.2:

eine Teilansicht eines erfindungsgemäßen Wärmeaustauscherrohrs, bei dem sich die Sekundärnuten über die gesamte Höhe der Innenrippe ausdehnen, so dass pyramidenstumpfartige Elemente als Innenstruktur erzeugt werden. Die Ansicht ist teilweise als Schnitt dargestellt;

Fig.3:

ein Foto einer Innenstruktur, bei der sich die Sekundärnuten nur über einen Teil der Höhe der Innenrippe erstrecken;

Fig.4:

schematisch einen Schnitt durch die Innenstruktur von Fig. 3 entlang der Linie X-X von Fig. 3;

Fig.5:

ein Diagramm, das den Leistungsvorteil durch die Sekundärnuten der Innenstruktur dokumentiert;

It shows:

Fig.1:

schematically the preparation of a heat exchanger tube according to the invention by means of two domes with different orientation of the helix angle;

Figure 2:

a partial view of a heat exchanger tube according to the invention, in which the secondary grooves extend over the entire height of the inner fin, so that truncated pyramid-like elements are produced as an internal structure. The view is partially shown as a section;

3 shows:

a photograph of an internal structure in which the secondary grooves extend over only a portion of the height of the inner rib;

Figure 4:

schematically a section through the inner structure of Figure 3 along the line XX of Fig. 3.

Figure 5:

a diagram that documents the performance advantage of the secondary grooves of the internal structure;

The integrally rolled finned tube 1 according to Figures 1 and 2 has on the tube outside helically encircling ribs 3 on. The preparation of the invention Finned tube is carried out by a rolling process (see US Patent Nos. 1,865,575 /3,327,512 and DE 23 03 172) by means of the device shown in Figure 1.

A device is used which consists of n = 3 or 4 tool holders 10 consists, in each case at least two spaced-apart rolling tools 11 and 12 are integrated. (In Fig. 1, for reasons of clarity, only one tool holder 10). The axis of the tool holder 10 is simultaneously the Axle of the two associated rolling tools 11 and 12 and it extends obliquely to Tube axis. The tool holder 10 are each offset by 360 ° / n at the periphery of Finned tube arranged. The tool holder 10 are radially deliverable. you are in turn arranged in a stationary (not shown) rolling head. The rolling head is fixed in the basic framework of the rolling device. The rolling tools 11 and 12 each consist of several juxtaposed rolling disks 13 and 14, whose diameter increases in the direction of the arrow. The rolling disks 14 of the second Rolling tool 12 thus have a larger diameter than the rolling disks 13 of the first rolling tool 11.

Also part of the device are two profiled mandrels 15 and 16, with whose help the internal structure of the pipe is created. The mandrels 15 and 16 are attached to the free end of a rod 9 and rotatably mounted to each other. The Rod 9 is attached at its other end to the skeleton of the rolling device. The mandrels 15 and 16 are in the working range of the rolling tools 11 and 12 to position. The rod 9 must be at least as long as the one to be produced Finned tube 1. Prior to machining, the smooth tube 2 is used for undelivered rolling tools 11 and 12 almost completely over the mandrels 15 and 16 on the Pushed rod 9. Only the part of the smooth tube 2, the finished finned tube 1 is to form the first smooth end piece is not on the mandrels 15 and 16 pushed.

To edit the tube are arranged on the circumference, rotating Rolling tools 11 and 12 delivered to the smooth tube 2 radially and with the smooth tube 2 engaged. The smooth tube 2 is thereby rotated. Because the Axis of the rolling tools 11 and 12 is inclined to the tube axis, forming the Rolling tools 11 and 12 helically encircling ribs 3 from the Tube wall of the smooth tube 2 and push at the same time the resulting finned tube 1 corresponding to the pitch of the helical circumferential ribs 3 in FIG Arrow direction. The ribs 3 preferably run like a multi-start thread around. The distance between the centers of two adjacent ones measured along the tube axis Ribs are referred to as rib pitch p. The distance between the two Rolling tools 11 and 12 must be adapted so that the rolling disks 14 of the second rolling tool 12 engage in the grooves 4, which between the first Rolling tool 11 are shaped ribs 3a. Ideally, this distance is one integer multiple of the rib pitch p. The second rolling tool 12 then performs the further shaping of the outer ribs 3 away.

In the forming zone of the first rolling tool 11 (= first forming area) is the Supported pipe wall by a first profiled rolling mandrel 15, and in the Forming zone of the second rolling tool 12 (= second forming area) is the Tube wall supported by a second profiled rolling mandrel 16. The axes the two mandrels 15 and 16 are identical to the axis of the tube. The Mandrels 15 and 16 are profiled differently and the outer diameter of the second rolling mandrel 16 is at most as large as the outer diameter of the first Rolling mandrel 15. Typically, the outside diameter of the second rolling mandrel is 16 up to 0.8 mm smaller than the outer diameter of the first rolling mandrel 15. Das Profile of the mandrels usually consists of a variety of trapezoidal or nearly trapezoidal grooves parallel to each other on the outer surface of the Walzdorns are arranged. Located between two adjacent grooves Material of the rolling mandrel is referred to as web 19. The webs 19 have an im significant trapezoidal cross-section. The grooves are usually under a helix angle of 0 ° to 70 ° inclined to the axis of the mandrel. At the first rolling mandrel 15, this twist angle is denoted by α, and in the second rolling mandrel 16 by β.

Twist angle 0 ° corresponds to the case that the grooves are parallel to the axis of the mandrel run. If the helix angle is different from 0 °, the grooves are helical. Helical grooves can be left-handed or right-handed be oriented. FIGS. 1 and 2 show the case that the first one Rolling mandrel 15 right-hand grooves 17 and the second rolling mandrel 16 left-hand grooves 18 has. One speaks in this case of oppositely oriented grooves 17 and 18 or of different orientation of the two helix angles α and β. In this case For example, the helix angles α and β can have equal amounts. (Same goes for the case that the first rolling mandrel 15 left-handed grooves 17 and the second rolling mandrel 16th right-hand grooves 18.) However, it is also possible that both mandrels 15 and 16 have grooves 17 and 18 with the same direction. In this case However, the helix angles α and β must differ in terms of their amount. The two mandrels 15 and 16 must be rotatably mounted to each other.

Due to the radial forces of the first rolling tool 11, the material of Pipe wall pressed into the grooves 17 of the first rolling mandrel 15. This will be helically encircling internal ribs 20 on the inner surface of the finned tube 1 shaped. Between two adjacent inner ribs 20 extend primary grooves 21. According to the shape of the grooves 17 of the first rolling mandrel 15 have this Inner ribs 20 has a substantially trapezoidal cross section, the first stays constant along the inner rib. The inner ribs 20 are opposite to the Pipe axis by the same angle α (pitch angle) inclined as the grooves 17 to Axis of the first rolling mandrel 15. The pitch angle of the inner ribs 20 is thus equal to the helix angle α of the first rolling mandrel 15. The height of the inner ribs 20 is denoted by H and is usually 0.15-0.40 mm.

Due to the radial forces of the second rolling tool 12, the inner ribs 20 pressed onto the second rolling mandrel 16. Since the grooves 18 of the second rolling mandrel 16 at a different angle to the dome axis and thus at a different angle to the Tube axis run as the grooves 17 of the first rolling mandrel 15, meet the inner ribs 20 in sections on a groove 18 or a web 19 of the second rolling mandrel 16. In the sections where an inner fin 20 meets a groove 18, the Material of the inner rib 20 pressed into the groove. In the sections where one Inner rib 20 meets a web 19, the fin material is deformed and it become parallel to each other secondary grooves 22 in the inner ribs 20th imprinted. According to the shape of the webs 19 of the second rolling mandrel 16 have the secondary grooves 22 a trapezoidal cross-section. Secondary grooves 22 coming from the the same web 19 are stamped into different inner ribs 20 are to each other arranged in alignment. The pitch angle that the secondary grooves 22 with the Form pipe axis is equal to the helix angle β, the grooves 18 of the second rolling mandrel 16 with the axis of the second rolling mandrel 16 include. The angle of inclination γ, which include the secondary grooves 22 with the inner ribs 20 results in roll mandrels 15 and 16 with the same direction orientation of the grooves 17 and 18 from the difference of the helix angle α and β, with roll mandrels 15 and 16 with opposite directions Orientation of the grooves 17 and 18 from the sum of the helix angles α and β. Of the Angle γ is between 60 ° and 85 °. Angle γ smaller than 90 ° are manufacturing technology easier to control than angle γ greater than 90 ° and usually cause a smaller pressure drop as angle γ greater than 90 °.

The depth T of the secondary grooves 22 is from the top of the inner fin 20 in Measured radial direction. By suitable choice of the outside diameter of the both mandrels 15 and 16, and by a suitable choice of the outer diameter The largest rolling disks of the two rolling tools 11 and 12, the Depth T of the secondary grooves 22 are varied: the smaller the difference in outer diameter between the first rolling mandrel 15 and the second rolling mandrel 16, the greater the depth T of the secondary grooves 22. A change in the outer diameter from one of the two mandrels 15 or 16 but not only one Changing the depth T of the secondary grooves 22 result, but usually causes also a change in the height of the outer ribs 3. This effect can However, be compensated by the structure of the rolling tools 11 and 12 modified. In particular, for this purpose, the largest rolling disks 13 of the first Rolling tool 11 as the smallest rolling disks 14 of the second rolling tool 12th or the smallest rolling disks 14 of the second rolling tool 12 as the largest Rolling discs 13 of the first rolling tool 11 can be used.

In order to influence the flow of the liquid flowing in the tube clearly, should the depth T of the secondary grooves 22 at least 20% of the height H of the inner ribs 20th be. Preferably, T is at least 40% of the height H of the inner fins 20. If the depth T of the secondary grooves 22 is smaller than the height H of the inner fins 20, then is the finished shaped finned tube 1, the course of the inner ribs 20 can still be seen. This is shown in FIG. Altered along the course of the inner ribs 20 But now the cross-sectional shape of the inner ribs 20: The height of the inner ribs 20th is reduced at the locations of the secondary grooves 22 by the depth T thereof. The prime intestines 21 are continuous without interruption between the inner ribs 20. Aligned to each other Secondary grooves 22 are spaced by the primary grooves 21.

FIG. 4 shows schematically a section through the internal structure of FIG. 3 along the Line X-X of Fig. 3. The height relationships between inner ribs 20, primary grooves 21st and secondary grooves 22 are clearly visible here.

If the depth T of the secondary grooves 22 is equal to the height H of the inner fins 20, then on the finished molded finned tube 1, the course of the inner fins 20 no longer detect. The inner ribs 21 are in this case by the secondary grooves 22 in individual, spaced apart elements 23 divided. This is shown in FIG. 2. Due to the trapezoidal cross section of the initially formed inner ribs 20 and the secondary grooves 22, the spaced elements 23 have the shape of truncated pyramids.

By profiling the two mandrels 15 and 16, the density of the intersections of inner ribs 20 and secondary grooves 22 is determined. The density of the intersections is between 90 and 250 intersections per cm ² . The reference surface is the inner tube surface, which results from removing the inner structure completely from the tube.

By the secondary grooves 22, the inner structure of the finned tube 1 with additional Edges provided. Fluid flows on the inside of the tube, then arise at these edges additional vortex in the liquid, which is the heat transfer to improve the pipe wall. Usually, the pressure drop of the Pipe flowing liquid to the same extent as the heat transfer coefficient. By suitable choice of the dimensions of the internal structure, in particular of the Tilt angle γ and the depth T of the secondary grooves 22, this increase in the Pressure drop, however, be favorably influenced.

The description of the production process according to the invention shows that the multitude of tool parameters that can be selected in this method are the dimensions the outer and inner structure in a wide range of independent can be adjusted. In particular, allows the division of the rolling tool in two spaced rolling tools 11 and 12, the depth T of the secondary grooves 22 to vary without simultaneously changing the height of the outer ribs 3.

Double-sided structured finned tubes for refrigeration and air conditioning are often made of copper or copper alloys. Since in these metals the pure price of material accounts for a not inconsiderable share of the total cost of the finned tube, competition requires that the weight of the tube be minimized for a given tube diameter. The proportion by weight of the internal structure in the total weight is in today commercially available finned tubes, depending on the height of the internal structure and thus depending on the performance of 10% to 20%. By means of the secondary grooves 22 according to the invention in the inner ribs 20 of ribbed tubes structured on both sides, the performance of such tubes can be considerably increased without the weight proportion of the inner structure being increased. For finned tubes consisting of materials with a density of 7.5 to 9.5 g / cm ³ (eg copper, copper alloys or steel), the proportion by weight of such an internal structure relative to the outer envelope surface of the finned tube is usually between 500 g / m ² and 1000 g / m ² , preferably between 600 g / m ² and 900 g / m ² . In finned tubes, which consist of materials with a density of 2.5 to 3.0 g / cm ³ (ie, aluminum), the weight fraction of such an internal structure, which relates to the outer envelope surface of the finned tube, is usually between 150 g / m ² and 300 g / m ² , preferably between 180 g / m ² and 270 g / m ² . If one chooses the width of the primary grooves 21 and the secondary grooves 22 large, then a low weight of the internal structure can be realized.

5 shows a diagram which documents the performance advantage of the internal structure according to the invention. The heat transfer coefficient is plotted against the heat flow density at condensation of refrigerant R-134a on the outside of the pipe and cooling water flow on the pipe inside. The condensation temperature is 36.7 ° C, the water velocity 2.4 m / s. The two compared finned tubes have the same structure on their outer side, but differ in the internal structure, as indicated in the diagram. The prior art is represented by the tube, which is provided with a standard internal structure of height 0.35 mm. 2, the height of the truncated pyramids is approximately 0.30 mm, the density of the intersections of inner ribs 20 and secondary grooves 22 is 143 per cm ² and the angle γ is 96 °. The finned tube with internal structure with truncated pyramids has an advantage in the heat transfer coefficient of 13% to 22%. This advantage is due solely to the internal structure, since the heat transfer coefficient on the tube outside is the same for both tubes.

The use of internal ribs with secondary grooves to improve heat transfer on the inside of heat exchanger tubes is known from pipes, which only have an internal structure. For seamless pipes are such Internal structures produced by means of two differently profiled mandrels (e.g., Japanese Laid-Open Patent Publication No. 1-317637). This technique is so far only on the outside of the tube smooth tubes used. The transfer of this technique to bilaterally structured, However, integrally rolled finned tubes is due to the significantly different Production method not obvious: with tubes on the outside of the tube smooth is the required to generate the internal structure, radial force by relatively wide, arranged on the outside of the tube rollers, rollers or balls applied. The propulsion of the tube in the tube longitudinal direction is characterized by a accomplished separate drawing device. In contrast, with both sides structured, integrally rolled finned tubes both the radial force for simultaneous Forming the outer and inner structure as well as the axial force for propulsion of the tube through the rolling tool, which is made up of relatively thin discs is provided by itself. The most powerful, commercially available finned tubes are made with rolled discs whose thickness is between 0.40 mm and 0.65 mm is.

Claims (16)

1. Seamless heat-exchange pipe (1) having optionally smooth ends, at least one structured region at the outer side of the pipe and at the inner side of the pipe and optionally smooth intermediate regions, and having the following features:

   a) integral outer ribs (3) extend around the outer side of the pipe in the manner of a helix,

   b) integral inner ribs (20) extend on the inner side of the pipe in an axially parallel manner or in the manner of a helix at an angle of pitch of α = from 0 to 70° (measured relative to the pipe axis), with primary grooves (21) being formed,
   characterised in that

   c) the inner ribs (20) are crossed by secondary grooves (22) which extend at an angle of pitch β (measured relative to the pipe axis),

   d) the secondary grooves (22) extend at an angle of pitch γ of from 60 to 85° relative to the inner ribs (20),

   e) the depth T of the secondary grooves (22) comprises at least 20% of the rib height H of the inner ribs (20), and

   f) the density of the intersections of inner ribs (20) and secondary grooves (22) is from 90 to 250 intersections/cm².
2. Heat-exchange pipe according to claim 1, characterised in that the angle of pitch is γ = from 30 to 100°.
3. Heat-exchange pipe according to claim 1 or 2, characterised in that, when the inner ribs (20) and secondary grooves (22) extend in opposite directions, the angle of pitch γ is produced as the sum of the angles of pitch α and β: γ = α + β.
4. Heat-exchange pipe according to claim 1 or 2, characterised in that, when the inner ribs (20) and secondary grooves (22) extend in the same direction, the angle of pitch γ is produced as the difference between the angles of pitch α and β: γ = α - β.
5. Heat-exchange pipe according to any one or more of claims 1 to 4, characterised in that
   the depth T of the secondary grooves (22) is at least 40% of the rib height H.
6. Heat-exchange pipe according to any one or more of claims 1 to 5,
   characterised in that
   the rib height H = from 0.15 to 0.40mm.
7. Heat-exchange pipe according to any one or more of claims 1 to 6, characterised in that
   the depth T of the secondary grooves (22) corresponds to the rib height H.
8. Heat-exchange pipe according to claim 7, characterised in that the inner side of the pipe has a truncated pyramid-like structure (23).
9. Heat-exchange pipe according to any one or more of claims 1 to 8, characterised in that
   the weight proportion of the inner structure in relation to the outer covering face of the heat-exchange pipe (1) is from 500 to 1000g/m², preferably from 600 to 900g/m², and in that the density of the material used is from 7.5 to 9.5g/cm³.
10. Heat-exchange pipe according to any one or more of claims 1 to 8, characterised in that
    the weight proportion of the inner structure in relation to the outer covering face of the heat-exchange pipe (1) is from 150 to 300g/m², preferably from 180 to 270g/m², and in that the density of the material used is from 2.5 to 3.0g/cm³.
11. Method for producing a heat-exchange pipe (1), according to any one or more of claims 1 to 10, having outer ribs (3) and inner ribs (20) which extend around the outer side of the pipe in the manner of a helix and which extend on the inner side of the pipe in an axially parallel manner or in the manner of a helix and which are integral, that is to say, are formed out of the pipe wall, and which are crossed by secondary grooves (22), wherein the following method steps are carried out:

    a) at the outer side of a smooth pipe (2), outer ribs (3) which extend in the manner of a helix are formed in a first shaping region, with the rib material being obtained by material being pressed out of the pipe wall by means of a first rolling step and the ribbed pipe (1) which is produced being caused to rotate by the rolling forces and being pushed forwards in accordance with the ribs (3) which are produced in the manner of a helix, the outer ribs (3) being shaped with increasing height from the otherwise non-deformed smooth pipe (2),

    b) the pipe wall is supported in the first shaping region by means of a first rotatable and shaped roller mandrel (15) which is located in the pipe,

    c) in a second rolling step, the outer ribs (3) are formed with further increasing height in a second shaping region which is spaced apart from the first shaping region and the inner ribs (20) are provided with secondary grooves (22),

    d) the pipe wall being supported in the second shaping region by means of a second roller mandrel (16) which is located in the pipe and which is also constructed so as to be rotatable and shaped, but whose shaping is different from the shaping of the first roller mandrel (15) with regard to the magnitude or the orientation of the angle of twist.
12. Method according to claim 11, characterised in that
    the spacing of the shaping regions is substantially selected as an integer multiple of the rib pitch p.
13. Method according to claim 11 or 12, characterised in that the outer diameter of the second roller mandrel (16) is selected so as to be smaller than the outer diameter of the first roller mandrel (15).
14. Method according to any one or more of claims 11 to 13 for producing a heat-exchange pipe (1) according to claim 4,
    characterised in that
    roller mandrels (15, 16) are used having grooves (17, 18) which are directed in opposite directions.
15. Method according to any one or more of claims 11 to 13 for producing a heat-exchange pipe (1) according to claim 5,
    characterised in that
    roller mandrels (15, 16) are used having grooves (17, 18) which are directed in the same direction.
16. Method according to any one or more of claims 11 to 15,
    characterised in that
    the depth T of the secondary grooves (22) is adjusted by selecting the diameters of the roller mandrels (15, 16) and by selecting the diameters of the largest roller discs of the two roller tools (11, 12) in each case.

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