EP1113237B1 - Heat exchange tube structured on both sides and process for making same - Google Patents

Description

The invention relates to smooth-ended heat exchanger tubes, at least one region structured on the outside and inside of the tube, the outside diameter of the structured region being no greater than the outside diameter of the blunt ends.

This type of pipe is commonly referred to as "double-sided structured pipes".

Heat exchanger tubes of the type mentioned are commonly used in shell and tube heat exchangers (see Figure 1, Source: TEMA, Standards of Tubular Exchanger Manufacturers Association, New York, 1968). These heat exchangers are characterized by a number of parallel tubes 30 which are fixedly connected at their ends to the tubesheets 31. Depending on the use condition and length, the tubes are supported by means of support plates 32. These support plates 32 also serve to direct the shell-side fluid flow in certain directions. In tubes 30, e.g. Water or a mixture of water and glycol, wherein the tube-side flowing medium is heated or cooled.

To increase the heat transfer performance of such heat exchangers, finned or structured tubes are used instead of smooth ones. Here, it is intended to increase the area available for heat transfer and to further exploit effects of surface tension. In FIG. 2 schematically shows a structured heat exchanger tube 30. It has a plurality of structured regions 2 delimited by smooth, unstructured ends 1a and smooth unstructured intermediate pieces 1b. At the smooth ends 1a, the tube 30 is usually connected by a Einwalzvorgang fixed to the tube plates 31. At the smooth intermediate pieces 1b, the tube 30 is located in the holes of the support plates 32. Thus, the tube inserted into the tubesheets 31 and support plates 32 and can be tightly connected to the tube plates 31 and 32 in the holes of the support plates not too much game, the outer diameter of the structured areas 2 must not be greater than the outer diameter of the smooth areas 1a and 1b. On the other hand, the inner diameter of the tube 30 in the structured region 2 should be as large as possible in order to keep the pressure drop of the tube-side flowing medium low. For a given type of structure, the outer and inner diameters of the tube 30 in the structured region 2 are related to one another, so that the outer diameter of the tube 30 in the structured region 2 should be as large as possible. Consequently, it is expedient to choose the outer diameter in the structured region 2 almost equal to the outer diameter of the smooth tube regions 1a and 1b.

To reduce the material costs of such pipes, the meter weight (= pipe weight per unit length) of the pipes must be reduced for a given pipe diameter. Since the minimum wall thickness is limited by safety requirements, a reduction in the weight per meter can only be achieved by reducing the weight of the structure. Increasing the heat transfer area by structuring while minimizing the structural weight requires a very fine, filigree structure.

The use of double-structured pipes is prior art in some parts of the industry (e.g., chillers). Many of these tubes are based on finned tubes with the rib tips modified by notches and fillets. Usually, such tubes are produced with a rolling process: rolling disks with a certain profile shape are constructed with increasing diameter on one or more tool shafts. These tool shafts are arranged uniformly around the circumference of the pipe to be machined. If the obliquely set, rotating whale waves delivered to the smooth tube, then penetrate the rotating discs in the tube wall, put the tube in rotation, push it according to their inclination in the axial direction and form helical ribs out of the tube wall. This process is similar to a thread rolling process. Examples of this technology are shown in US-2,868,046, US-3,327,512, US-3,383,893, US-3,481,394.

During the rolling process, the tube is supported by a mandrel lying in the tube, which absorbs the radial forces. To produce an internal structure, profiled mandrels with helical grooves are used (DE 23 03 172 C2). Since the inner structure of the tube is determined by the profile shape of the mandrel, it can be formed largely independently of the geometry of the outer ribbing. This makes it possible to optimally adapt the outer and inner structures independently of each other to the application purpose. The mandrel must rotate at a certain speed to unscrew itself from the internal structure itself. This creates high friction forces between the mandrel and tube that must be applied by the rolling discs to effect the axial advancement of the tube. A considerable proportion of these frictional forces is directed parallel to the tube axis 33 and thus also almost parallel to the axis of the rolling discs.

It is known that for certain applications (e.g., refrigerant evaporator and condenser) it is advantageous to use structures with small fin pitches to achieve an increase in heat transfer performance. In the past, fin pitches of 1.35 mm (19 ribs per inch) were used. Today, finned tubes with rib pitches of about 0.40 mm are commercially available (US 5,697,430 and DE-197 57 526). EP 0 701 100 A1 shows that the trend is even more finely divided (0.25 mm).

Finer rib divisions require thinner rolling disks, which, with the same bending stress load, entails an increased risk of breakage and greater susceptibility to wear of the tool. Tool life is becoming increasingly critical, and frequent production interruptions due to tool change are the result. Furthermore, the production speed of the rolling machines decreases with decreasing rib pitch. At the same time, due to global competition, production costs are becoming a key factor in the economic success of the production of structured pipes.

From the document CN 1230672 A, a heat exchanger tube is known, which has structured areas in the form of recesses on the outside of the pipe and the inside of the pipe, which run on the outside of the pipe with a trapezoidal cross-section helically at an angle of inclination. Ribs also run helically on the inside of the tube, measured against the tube axis.

The invention is therefore based on the object to produce a finely structured tube which has both on the outside and on the inside a large increase in surface area and has a low structural weight. The geometries of the outer and inner structures should be adaptable independently of each other. The pipe must be made at high speed, with simple tools and little tool wear. Smooth spacers should be produced without additional effort.

The object is achieved by heat pipes structured on both sides, which have recesses on the outside and ribs on the inside, through a heat exchanger tube with the features of claim 1.

The claims 2 to 7 relate to advantageous areas for dimensions of the wells or an advantageous cross-sectional shape of the inner ribs.

The invention further relates to a method according to claim 13 for the preparation of the heat exchanger tubes according to the invention.

The structuring tools used are adjusted to produce non-aligned, spaced wells.

By using additional tools, the depressions can be modified so that secondary structures are created on the flanks or bottom of the depressions or on the webs between the depressions. Depending on the application, these secondary structures can significantly increase the thermal performance of pipes. This is essentially done by exploiting surface tension effects.

For condenser tubes, it is beneficial to produce structures having convex edges and substantially circumferentially extending channels. These channels allow the drainage of condensate, which arises on the pipe itself or on the overlying pipes of the tube bundle (claims 8 to 11, 14/15).

For pipes used in flooded evaporators or spray evaporators, it is advantageous to create undercut structures by partially closing the top portions of the recesses. This is according to the invention achieved by additional smoothing tools, which are arranged behind the actual structuring tool on the tool shaft (claims 12/16).

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

Figur 3

ein Wärmeaustauscherrohr 1 mit einem glatten Ende 1a, einem Übergangsbereich, in dem die äußere Struktur beginnt, und einem strukturierten Bereich 2, wobei die Vertiefungen 3 als kontinuierliche, fluchtende Nuten geformt sind;

Figur 4

eine detaillierte Ansicht einer einzelnen Vertiefung 3, wobei der Flankenwinkel δ der Vertiefung 3 relativ zur Symmetriefläche der Vertiefung 3 gemessen wird;

Figur 5

einen Schnitt durch die Vertiefung 3 senkrecht zur Längsrichtung der Vertiefung 3;

Figur 6

das auf einer Werkzeugwelle 14 montierte Rollprofilwerkzeug 10 zur Erzeugung der in Figur 3 gezeigten Außenstruktur;

Figur 7

schematisch den Strukturierungsprozeß;

Figur 8

schematisch ein Rohrstück mit einem glatten Ende 1a, einem Übergangsbereich, in dem die äußere Struktur beginnt, und einem strukturierten Bereich 2, wobei die Vertiefungen 7 beabstandet sind, so daß sie einzelne, nicht fluchtende Vertiefungen 7 bilden;

Figur 9

eine vergrößerte Ansicht von sechs beabstandeten, nicht-fluchtenden Vertiefungen 7;

Figur 10

eine Detailansicht einer Vertiefung 3 mit sekundären Nuten 8 in den Stegen 20, wobei die sekundären Nuten 8 quer zu den primär geformten Vertiefungen 3 angeordnet sind;

Figur 11

eine Gesamtansicht des Werkzeugaufbaus zur Herstellung der Außenstruktur, die in Figur 10 dargestellt ist;

Figur 12

eine Detailansicht eines strukturierten Rohres 1, bei dem die Enden 9 der Stege 20 eingeglättet wurden, um hohlraumartige Kanäle unter der Außenoberfläche zu erzeugen;

Figur 13

eine Gesamtansicht des Werkzeugaufbaus zur Herstellung der Außenstruktur, die in Figur 12 gezeigt ist.

It shows

FIG. 3

a heat exchanger tube 1 having a smooth end 1a, a transition region in which the outer structure begins, and a structured region 2, the depressions 3 being formed as continuous, aligned grooves;

FIG. 4

a detailed view of a single recess 3, wherein the flank angle δ of the recess 3 is measured relative to the symmetry surface of the recess 3;

FIG. 5

a section through the recess 3 perpendicular to the longitudinal direction of the recess 3;

FIG. 6

the roll profile die 10 mounted on a tool shaft 14 for producing the external structure shown in FIG. 3;

FIG. 7

schematically the structuring process;

FIG. 8

schematically a tube piece with a smooth end 1a, a transition region in which the outer structure begins, and a structured region 2, wherein the recesses 7 are spaced so that they form individual, non-aligned recesses 7;

FIG. 9

an enlarged view of six spaced, non-aligned recesses 7;

FIG. 10

a detail view of a recess 3 with secondary grooves 8 in the webs 20, wherein the secondary grooves 8 are arranged transversely to the primary-shaped recesses 3;

FIG. 11

an overall view of the tool structure for producing the outer structure, which is shown in Figure 10;

FIG. 12

a detailed view of a structured tube 1, in which the ends 9 of the webs 20 have been smoothed to produce cavity-like channels under the outer surface;

FIG. 13

an overall view of the tool structure for producing the outer structure, which is shown in Figure 12.

A one-piece, metallic heat exchanger tube 1 according to FIG. 3 has smooth ends 1a and at least one structured region 2 on the tube outer and inner side (a smooth end 1a and possibly smooth intermediate regions 1b are not shown). The structure 2 consists of aligned, continuous recesses 3, which run helically around the tube 1. The beginnings 6 of the recesses 3 are on lines which are inclined by the skew angle α relative to the tube circumferential direction. The recesses 3 were formed in the tube outer side by pressing one or more rotating roll profile tools 10 into the tube wall 4 and the thus displaced material of the tube wall 4 is pressed radially inwardly. As a result, the inner diameter of the tube 1 decreases. The continuously continuous recesses 3 are formed by successive rows of finite elongated, mutually aligned individual recesses, which are formed by the Rollprofilwerkzeugen 10. The outer diameter of the tube 1 may not in the structured region 2 larger than in the smooth areas (ends 1a, intermediate areas 1b).

The pipe 1 shown in Fig. 3 has to improve the pipe-side heat transfer on its inner side in addition helically circumferential, trapezoidal ribs 5, which were also formed from the material of the pipe wall 4. The helix angle e of the ribs 5 is measured against the tube axis 33 and is usually between 10 ° and 50 °. The height H of the ribs 5 can be up to 0.60 mm. Larger rib heights are difficult to control in terms of production engineering. With such an internal structure, an area increase of up to 100% compared to an internally smooth tube is achieved. Regardless of the nature of the internal structure is generally an area increase of at least 20% compared to an internally smooth tube for a significant increase in the tube-side heat transfer required.

Fig. 4 shows a detailed view of a single continuous recess 3. The recesses 3 have a substantially trapezoidal cross-section. The unprocessed portions 20 between the recesses 3 are called webs. The outside pipe diameter, measured via these webs 20, is usually almost equal to the outside diameter of the smooth areas 1a, 1b. The bottom of the recess 3 may have a square, round, curved or other shape. This shape is determined by the shape of the elevations 13 of the roll profile tool 10. The shape can be optimized to the effect that the forming process similar to the rolling movement of form-optimized gears runs. The flank angle 5 of the recess 3, as shown in Fig. 4, measured against the symmetry surface of the recess 3.

FIG. 5 shows a sectional view of the depressions 3 perpendicular to the longitudinal direction of the depression 3. The dimensions the recesses 3 should be chosen so that the largest possible outer surfaces is achieved. In particular, the flank angle δ should be as small as possible, the depth T of the recesses 3 and the number of recesses 3 on the circumference should be as large as possible. A depth T of 0.4 mm to 1.5 mm is achievable. The preferred range for the flank angle δ is between 7 ° and 25 °. The pitch P of the recesses 3 is measured perpendicular to the surface of symmetry and is preferably 0.25 mm to 2.2 mm. The width W of the recesses 3 is measured at half the depth T. The width W is 60% to 80% of the pitch P. Consequently, the volume of the recesses 3 is greater than the volume of the webs 20, which causes a low structural weight.

Fig. 6 shows a representation of a roll profile tool 10, which is mounted on a tool shaft 14 and designed for the production of aligned, continuous grooves. The roll profile tool 10 has on its periphery a number of regular, trapezoidal elevations 13 similar to a gear. The elevations 13 extend helically with a twist angle β measured against the axis of the tool 10. In order to keep the tool wear in the front processing zone of the tool 10 low, it is advantageous to provide the roll profile tool 10 partially with a cone 11. Furthermore, it may be favorable to supplement the structured cone 11 of the roll profile tool 10 by a smooth conical region. The cylindrical part 12 of the roll profile tool 10 has the thickness s. Usually, the production machines have three or four tool shafts 14, which, like an equilateral triangle, are arranged uniformly around the tube circumference. During the machining process, the tool shafts 14 are inclined relative to the tube axis 33. The inclination angle α is inherently equal to the angle α, which the lines on which the beginnings 6 of the recesses 3 are located, with the circumferential direction of the tube include, as shown in FIG. 3 can be seen.

The patterning process is shown schematically in FIG. Pipe and roll profile tool 10 are hereby shown in longitudinal section. As a starting tube, a smooth tube 1 'by the rotating rolling profile tool 10 is set in rotation and advanced according to the inclination of the tool in the axial direction. The direction of movement of the tube in the axial direction is indicated by an arrow. When the smooth tube 1 'enters the forming zone below the rolling profile tool 10, depressions 3 are formed on the outside of the tube and the inside diameter is reduced. The material of the tube wall 4 is pressed onto the inner, structured mandrel 15. The mandrel 15 is rotatably mounted to accommodate the rotation of the tube. In the structured region 2, the remaining wall thickness of the tube 1 (measured between outer and inner structure) is necessarily smaller than the wall thickness of the smooth tube 1 ', since both the inner and outer structures are formed from the wall material of the smooth tube 1'.

It must be ensured that the individual depressions formed by each roll profile tool 10 are arranged in alignment with each other in order to produce continuously continuous depressions 3 by successive stringing of finally extended single depressions. This is achieved by the skew angle α on the pitch P of the wells 3, the number n _{R of} the wells 3 on the tube circumference, the core diameter D _{core of} the tube 1 (measured at the bottom of the wells 3) and the helix angle β of the roll profile tool 10 according to the The following equation is tuned: $$\alpha =\arccos \left(\frac{P\cdot n_R}{\pi \cdot D_{\mathrm{core}}}\right)-\beta$$

Furthermore, the thickness s of the cylindrical part 12 of the roll profile tool 10 must have the following minimum dimension so that the depressions 3 continue without interruption: $$s\ge \frac{1}{m}\cdot \pi \cdot D_{\mathrm{core}}\cdot \sin \left(\alpha \right)$$

In this case, m is the number of whale rolls 14 arranged around the tube.

The pitch angle γ of the recesses 3 is measured against the tube axis 33 and is equal to the sum of the skew angle α and the helix angle β of the roll profile tool, as shown in Fig. 3. γ lies in the range between 0 ° and 70 °.

In order to maximize the speed of the patterning process, it is favorable to choose the skew angle α of the tool 10 as large as possible. To the above equation G1. 1, the swirl angle β of the roll profile tool 10 can be adapted for a given structural geometry. In practice, when using the described method skew angle α between 5 ° and 15 ° can be achieved. Larger skew angles would allow even higher production speeds. Structured tubes, which are produced in accordance with US Pat. No. 5,697,430 or DE-197 57 526 according to the conventional ribbing method, typically require a skew angle α between 1 in the case of a rib pitch of approximately 0.4 mm, depending on the number of tool shafts 14 used and depending on the tube diameter , 5 ° and 2.5 °. This shows the advantage of the production method according to the invention with respect to production speed.

Smooth intermediate regions 1b can optionally be produced by bringing the roll profile tools 10 out of engagement with the smooth tube 1 '(cf., for example, DE-A 1.452.247).

FIG. 8 shows schematically a representation of a tube 1 structured according to the invention with spaced-apart, non-aligned depressions 7. The depressions 7 have the length L. The transition region between the smooth end 1a and the structured region 2 is shown. The depressions 7 are arranged in separated rows, which run helically around the tube 1. Such a series is called a "track". Each roller profile tool 10 arranged around the tube 1 forms its own track. To maximize surface gain, adjacent tracks should be as close as possible.

The spaced depressions 7 shown in FIG. 8 are formed by using a roll profile die 10 without conical portion 11. The roll profile tool 10 consists only of a cylindrical part 12 of thickness s. The finite length L of the spaced depressions 7 depends on the thickness s of the roll profile tool 10 and the twist angle β of the elevations 13 on the roll profile tool 10 as follows: $$L=s/\cos \beta$$

wobei m die Anzahl der um das Rohr 1 angeordneten Werkzeugwellen 14 und D_core der Kerndurchmesser des Rohres 1 ist. Falls der Schrägstellungswinkel α aus konstruktiven Gründen nach oben beschränkt ist, wird die maximale Dicke des Rollprofilwerkzeugs 10 durch folgende Gleichung bestimmt: $$s<\frac{1}{m}\cdot \pi \cdot D_{\mathrm{core}}\cdot \sin \left(\alpha \right)$$

In order to prevent the tracks of the individual roll profile tools 10 from overlapping, the skew angle α must be selected appropriately: $$\alpha >\arcsin \left(\frac{s\cdot m}{D_{\mathrm{core}}\cdot \pi }\right)$$

where m is the number of arranged around the tube 1 tool shafts 14 and D _{core of} the core diameter of the tube 1. If the skew angle α is limited upwardly for design reasons, the maximum thickness of the roll profile tool 10 is determined by the following equation: $$s<\frac{1}{m}\cdot \pi \cdot D_{\mathrm{core}}\cdot \sin \left(\alpha \right)$$

9 shows an enlarged view of the spaced, non-aligned depressions 7 of FIG. 8. Adjacent depressions 7 of a track are separated by webs 20. A thin pipe section 21 between adjacent tracks remains undeformed. Measured over the undeformed sections 21 and webs 20, the tube 1 has almost the same outer diameter as the smooth areas 1a, 1b. The recesses 7 have a substantially trapezoidal cross-section. The bottom of the recess 7 may have a polygonal, round, curved or other shape. This shape is determined by the shape of the elevations 13 of the roll profile tool 10.

The sectional view of the spaced recesses 7 is identical to the sectional view of the aligned, continuous recesses 3, which is shown in Fig. 5. For the geometric dimensions of the recesses 7, the same applies in the case of the spaced depressions 7 as in the case of the aligned, continuous depressions 3. In particular, the relationships which have been mentioned in connection with FIG. 5 apply. This results in both cases similar favorable properties of the tube 1 in terms of surface gain and structural weight.

The transfer performance of the heat exchanger tube 1 according to the invention can be further increased by taking advantage of surface tension effects. It is known that in Condenser tubes Convex edges to dilute the condensate film. The density of the convex edges is considerably increased by secondary grooves 8 which are impressed substantially transversely to the primary-shaped depressions 3, 7. Such a modified structure is shown enlarged in FIG. The displaced by the impressing of the secondary grooves 8 material of the web 20 forms projections 22 which are arranged substantially transversely to the primary-shaped recesses 3, 7. The edges 23 of these projections 22 constitute part of the desired additional convex edges. The tool structure associated with the structure of Fig. 10 is shown in Fig. 11 and consists of a primary roller tread tool 10 and a secondary pulley 16 spaced from each other Tool shafts 14 are arranged. The secondary notching disc 16 has on its periphery a number of regular elevations 17 similar to a gear. The elevations 17 extend helically with a helix angle β 'measured against the axis of the notch disk 16. The depth E of the secondary grooves 8 should be 20% to 80% of the depth T of the primary depressions 3, 7, accordingly, the diameter of the notch disk 16 is smaller The pitch should be K = 0.25 to 2.2 mm. The angle φ which the primary recesses 3, 7 enclose with the secondary grooves 8 is determined by the helix angle β of the elevations 12 of the roll profile tool 10 and the helix angle β 'of the elevations 17 of the notch disc 16. φ can be between 20 ° and 160 °.

It is an inherent advantage of the invention that the main reshaping step, in which - as shown in Fig. 7 - the primary outer structure and the inner structure are formed simultaneously, can be performed by a relatively coarse roll profile die 10. The secondary structure, which is usually much finer than the primary, is not formed from the tube wall 4, but only from the ridges 20. This means that the amount of material to be formed in the fine-structuring step is much lower than in conventional manufacturing processes in which fine-fin fins are formed directly from the solid tube wall with fine tools. This has a favorable effect on the service life of the tool.

A modified structure is obtained when the secondary grooves 8 are produced by means of a number of thin rolling disks (not shown) of constant diameter, the rolling disks being constructed as a package instead of the secondary notching disk 16 after the rolling profile tool 10 on the tool shaft 14. In this case, the direction of the secondary grooves 8 is parallel to the perpendicular to the axis of the tool shaft 14. Since the skew angle α is about 10 °, these secondary grooves 8 are thus inclined only by this relatively small angular amount from the perpendicular to the tube axis 33. In a horizontal pipe arrangement, such secondary grooves 8 have the advantage that from above dripping condensate is discharged well down in almost vertical channels.

It is known that the process of nucleate boiling can be significantly intensified when undercut, cavernous structures are formed on the pipe surface. These caverns or tunnels are connected by openings or pores with the surrounding fluid ("undercut" in this context means that the opening of the caverns is smaller than the underlying cavity). The essential part of the evaporation takes place in these caverns or tunnels. Liquid penetrates through the pores into the cavities. The generated steam escapes through the pores.

Undercut caverns or tunnels are produced according to the invention by partially closing the upper region of the depressions 3, 7. The underlying under the outer surface Cavities are then connected through openings or pores to the surrounding fluid.

Fig. 12 shows an enlarged view of a section of a structured tube 1, in which the ends 9 of adjacent, provided with secondary grooves 8 webs 20 have been smoothed. The flattened ends 9 form a partially closed cover over the recess 3. In this way, a system of lying below the outer tube surface cavities, which are connected to the environment through narrow openings 24 generated. It is advantageous to use a finer pitch for the secondary grooves 8 than for the primary wells. Fig. 13 shows a tool structure for producing such structures. A cylindrical smoothing disk 18 of constant diameter is arranged on the tool shaft 14 behind the notching disk 16. The diameter of the smoothing disk 18 is smaller than the diameter of the rolling profile tool 10.

Similar structures are obtained by partially closing non-aligned, spaced wells 7.

The closing of the recesses 3, 7 causes a reduction of the outer pipe diameter. However, this can be controlled by controlling the primary patterning step so that not all pipe exterior displaced material on the inside of the pipe may be needed to form the internal structure. For this purpose, a roll profile tool 10 with large displacement and a profiled mandrel 15 is used with narrow grooves. Furthermore, the diameter of the mandrel must be selected appropriately. The webs 20 between the recesses 3, 7 are then shaped outward in the radial direction, which results in the meantime compared to the smooth tube 1 'a larger pipe diameter in this pipe region. Subsequently, the secondary grooves 8 are formed and the resulting ends 9 of the webs 20 are smoothed to partially close the recesses 3, 7. If the process parameters are chosen as shown, then the final outer diameter in the structured region 2 may be less than or equal to the outer diameter at the unworked, smooth ends 1a.

The preceding sections demonstrate the great flexibility of the proposed technique to produce heat transfer enhancing structures on pipe surfaces. The method can be applied to both seamless drawn tubes and welded tubes made from molded metal strips. However, the proposed tubes and methods are always based on the patterning of tubes and not of ribbons.

Numerical example:

According to the described method, double-sided structured copper tubes 1 with a core diameter D _core of 17.80 mm were produced. The outer structure consists of 36 aligned, continuous recesses 3. The roll profile tool 10 was based on the following geometric data: Flank angle δ: 10 ° Helix angle β: 57 ° Division P: 0.67 mm Wide W: 0.40 mm

The skew angle α of the rolling waves 14 had to be set to 7.5 °. Accordingly, the pitch angle γ of the grooves is 64.5 °. The depth T of the recesses 3 is 0.7 mm. The inner structure consists of 41 trapezoidal ribs 5, which rotate at a helix angle e of 45 ° helically. The height H of the inner ribs 5 is 0.35 mm. The secondary grooves 8 were made with a package of 0.35 mm pitch discs. The tube structure thus produced shows good heat transfer properties when liquefied refrigerant R-134a on the outside and cooling water flow on the tube inside. Depending on the physical properties of the fluid, the pitch K of the secondary grooves 8 should be between 0.25 mm and 2.2 mm.

Claims (16)

1. Heat-exchange pipe (1) having at least one structured region (2) at the outer side of the pipe and at the inner side of the pipe, and having the following features:

   a) at the outer side of the pipe, recesses (7) which are mutually spaced-apart and which have a substantially trapezoidal cross-section are inclined at an angle of pitch γ = from 0° to 70° relative to the pipe axis (33);

   b) the pitch P of the recesses (7) is P = from 0.25 to 2.2 mm, measured perpendicularly relative to the plane of symmetry thereof;

   c) the width W of the recesses (7) is W = from 0.6P to 0.8P, measured at half of the depth T of the recesses (7);

   d) the angle δ of the side wall of the recesses (7) is δ = from 7° to 25°, measured relative to the plane of symmetry thereof;

   e) ribs (5) having a height H = from 0.15 to 0.60 mm extend around the inner side of the pipe in the manner of a helix at an angle of pitch ε = from 10° to 50°, measured relative to the pipe axis (33),

   
   characterised in that the at least one structured region (2) is arranged between smooth ends (1a) of the heat-exchange pipe (1), the outer diameter of the structured region (2) not being greater than the outer diameter of the smooth ends (1a), and in that the recesses (7) at the outer side of the pipe have a length L of a maximum of 10% of the pipe circumference.
2. Heat-exchange pipe according to claim 1, characterised in that
   smooth intermediate regions (1b) are arranged at least at two structured regions (2), the outer diameter of the structured region (2) not being greater than the outer diameter of the smooth intermediate regions (1b).
3. Heat-exchange pipe according to claim 1 or 2,
   characterised in that
   the length L of the spaced-apart recesses (7) is L = from 1 to 4mm.
4. Heat-exchange pipe according to claim 1, 2 or 3,
   characterised in that
   the depth T of the recesses (3, 7) is T = from 0.4 to 1.5mm.
5. Heat-exchange pipe according to any one or more of claims 1 to 4, characterised in that
   the angle of pitch γ of the recesses (3, 7) is γ = from 15° to 60°.
6. Heat-exchange pipe according to any one or more of claims 1 to 5, characterised in that
   the angle δ of the side wall of the recesses (3, 7) is δ = from 9° to 15°.
7. Heat-exchange pipe according to any one or more of claims 1 to 6, characterised in that
   the ribs (5) at the inner side of the pipe have a substantially trapezoidal cross-section.
8. Heat-exchange pipe according to any one or more of claims 1 to 7, characterised in that
   secondary grooves (8) extend at the outer side of the pipe transversely relative to the recesses (3, 7) at a notch angle ϕ = from 20° to 160°.
9. Heat-exchange pipe according to claim 8, characterised in that
   the notch angle is ϕ = from 30° to 150°.
10. Heat-exchange pipe according to claim 8 or 9,
    characterised in that
    the depth E of the secondary grooves (8) is E = from 0.2 T to 0.8 T of the depth of the recesses (3, 7).
11. Heat-exchange pipe according to any one or more of claims 8 to 10, characterised in that
    the pitch K of the secondary grooves (8) is K = from 0.25 to 2.2mm.
12. Heat-exchange pipe according to any one or more of claims 8 to 11, characterised in that
    the ends (9) of the webs (20) located between the recesses (3, 7) are smoothed.
13. Method for producing a heat-exchange pipe according to
    any one or more of claims 1 to 7, wherein the following method steps are carried out:

    a) recesses (7) which are mutually spaced-apart and which are inclined relative to the pipe axis (33) are formed at the outer side of a smooth pipe (1') by material of the pipe wall (4) being pressed radially inwards by means of toothed-wheel-like roller shaping tools (10), with ribs (5) which extend at the inner side of the pipe in the manner of a helix being formed,

    b) the roller shaping tools (10) being arranged around the pipe circumference,

    c) cylindrical roller shaping tools (10) being used whose trapezoidal projections (13) extend in the manner of a helix at an angle of twist β relative to the tool axis,

    d) the tool shafts (14) of the roller shaping tools (10) being positioned in an inclined manner at an angle of inclination α relative to the pipe axis (33),

    e) the thickness s of the cylindrical roller shaping tools (10) being selected according to the following equation: $$s<\frac{1}{m}\cdot \pi \cdot D_{\mathrm{core}}\cdot \sin \left(\alpha \right)$$

    

    with:

    m = number of tool shafts (14) arranged around the pipe (1') D_core = core diameter of the pipe (1) measured at the base of the recesses (7),

    f) the roller shaping tools (10) which have been caused to rotate being brought into engagement with the smooth pipe (1') in a shaping zone, whereby the pipe (1') also rotates and is pushed forwards in an axial direction in accordance with the inclined position of the roller shaping tools (10), and

    g) the pipe wall (4) being supported in the shaping zone by means of a rotatable shaped mandrel (15) which is located in the pipe (1').
14. Method according to claim 13 for producing a heat-exchange pipe (1) according to any one or more of claims 8 to 11, characterised in that
    the ends (9) of the webs (20) which are located between the recesses (3, 7) are pressed in locally by means of a toothed-wheel-like notched disc (16).
15. Method according to claim 13 for producing a heat-exchange pipe (1) according to any one or more of claims 8 to 11, characterised in that
    the ends (9) of the webs (20) which are located between the recesses (3, 7) are pressed in locally by means of roller discs.
16. Method according to claim 14 or 15 for producing a heat-exchange pipe (1) according to claim 12, characterised in that
    the ends (9) of the webs (20) are deformed by means of radial pressure using a smoothing disc (18).

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