EP2795233B1 - Evaporator pipe with optimised external structure - Google Patents

Description

The invention relates to a metallic heat exchanger tube for the evaporation of liquids from pure substances or mixtures on the pipe outside according to the preamble of claim 1.

Heat transfer occurs in many technical processes, for example in refrigeration and air conditioning technology or in chemical and energy engineering. In heat exchangers, heat is transferred from one medium to another. The media are usually separated by a wall. This wall serves as a heat transfer surface and for separating the media.

In order to allow the heat transfer between the two media, the temperature of the heat-emitting medium must be higher than the temperature of the heat-absorbing medium. This temperature difference is called the driving temperature difference. The higher the driving temperature difference, the more heat can be transferred per unit of heat transfer area. On the other hand, one often strives to keep the driving temperature difference small, as this has advantages for the efficiency of the process.

It is known that the structuring of the heat transfer surface can improve heat transfer. This can be achieved that more heat can be transmitted per unit of heat transfer surface than a smooth surface. Furthermore, it is possible to reduce the driving temperature difference and thus make the process more efficient.

An often used embodiment of heat exchangers are tube bundle heat exchangers. In these apparatuses tubes are often used, which are structured both on their inside and on their outside. Structured heat exchanger tubes for shell-and-tube heat exchangers usually have at least one structured region and smooth end pieces and possibly smooth intermediate pieces. The smooth end or intermediate pieces limit the structured areas. So that the tube can be easily installed in the shell and tube heat exchanger, the outer diameter of the structured areas must not be greater than the outer diameter of the smooth end and intermediate pieces.

To increase the heat transfer during evaporation, the process of bubbling is intensified. It is known that the formation of bubbles begins at germinal sites. These germinal sites are usually small gas or steam inclusions. Such nucleation sites can already be produced by roughening the surface. When the growing bubble reaches a certain size, it detaches from the surface. If in the course of bladder detachment the germinal site is flooded by inflowing liquid, the gas or vapor inclusion can be displaced by liquid. In this case, the germinal site is inactivated. This can be avoided by a suitable design of the germinal sites. For this purpose, it is necessary that the opening of the nucleus is smaller than the cavity located below the opening.

It is state of the art to produce such designed structures based on integrally rolled finned tubes. Integrally rolled finned tubes are understood to mean finned tubes in which the fins are formed from the wall material of a smooth tube. The ribs are therefore monolithically connected to the pipe wall and can thus transfer heat optimally. Such finned tubes have a round cross section over their entire length and the outer contour of the finned tube is coaxial with the tube axis. Various methods are known with which the channels located between adjacent ribs are sealed in such a way that connections between channel and environment remain in the form of pores or slots. Since the opening of the pores or slots is smaller than the width of the channels, the channels are suitably shaped cavities that promote formation and stabilization of nucleation sites. In particular, such substantially closed channels are formed by bending or flipping the ribs (FIG. US 3,696,861 . US 5,054,548 . US 7,178,361 . US 7,254,964 ), by splitting and upsetting the ribs ( DE 27 58 526 A1 . US 4,577,381 ) and by notching and upsetting the ribs ( US 4,660,630 . EP 0 713 072 A2 . US 4,216,826 . US 5,697,430 . US 7,789,127 ) generated. In the case of structures which are produced by bending over or splitting the ribs, it is disadvantageous that even slight changes in the rib geometry caused by manufacturing tolerances or tool wear lead to a performance-reducing change in the pore structure.

The most powerful commercially available finned tube finned tubes have on the tube exterior a ribbed structure with a fin density of 55 to 60 fins per inch ( US 5,669,441 . US 5,697,430 . DE 197 57 526 C1 ). This corresponds to a rib pitch of about 0.45 to 0.40 mm. In principle, it is possible to improve the performance of such pipes by an even higher fin density or smaller fin pitch, as this increases the bubble nuclei density. A smaller rib division inevitably requires equally finer tools. Finer tools are however subjected to a higher risk of breakage and faster wear. The currently available tools enable the safe production of finned tubes with rib densities of up to 60 ribs per inch. Further, as the rib pitch decreases, the production rate of the tubes becomes smaller, and hence the manufacturing cost becomes higher. It is known that the efficiency of evaporator tubes can be increased by introducing further structures in the region of the channel bottom. In EP 1 223 400 B1 For this purpose, undercut secondary grooves are proposed. Similarly, the in US 7,789,127 proposed, additional lateral elements on the flanks of the ribs. In US 2008/0196876 A1 a finned tube is described, which is to be used both for evaporation and for the condensation of refrigerants. To intensify the evaporation, the channels between the ribs are largely closed off by pore flanks, lateral material projections on only slightly different levels except for pores. Since these material protrusions act as an almost closed barrier for the exchange of liquid and vapor, compliance with the correct pore size is a difficulty. Further lateral protrusions on the fin tip do not contribute to masking the channels, but serve to improve heat transfer upon condensation ,

The object to be compared to the prior art performance-enhanced heat exchanger tube for the evaporation of liquids on the outside of the tube with the same tube-side heat transfer and pressure drop and the same production costs are given.

The invention is represented by the features of claim 1. The other dependent claims relate to advantageous embodiments and further developments of the invention.

The invention includes a metallic heat exchanger tube for the evaporation of liquids on the tube outside with a tube axis, with a tube wall and with on the tube outside circumferential, integrally molded ribs. The ribs have a ribbed foot, rib flanks and a ribbed tip, the ribbed foot projecting substantially radially from the tube wall. Between two adjacent ribs in the axial direction is in each case a groove. On the rib flanks lateral material projections are arranged, which are formed from material of the ribs. According to the invention, at least first, second and third lateral material projections are arranged such that the grooves are largely covered by the entirety of the material projections, wherein the first, second and third lateral material projections are formed on the tube wall in the radial direction each differently spaced levels.

The present invention relates to structured tubes for use in heat exchangers in which the heat-absorbing medium vaporizes. As evaporator tube bundle heat exchangers are often used in which liquids of pure substances or mixtures evaporate on the outside of the tube and thereby cool a brine or water on the inside of the tube.

The invention is based on the consideration that in evaporator tubes performance increases can be achieved by closing the grooves between the ribs by deformation of the ribs in a suitable manner, so that an undercut structure is formed. During bladder boiling, there are small pockets of steam in the grooves at the bottom of the groove in the area of the rib foot. These steam inclusions are the germinal sites of the vapor bubbles. When the growing bubble reaches a certain size, it separates from the groove between the ribs and from the tube surface. If the germinal site is flooded with fluid in the course of bladder detachment, the germinal site is deactivated. The structure on the pipe surface must therefore be designed so that when detaching the bubble a small bubble remains, which then serves as a germination point for a new cycle of blistering.

Investigations have shown that it is advantageous for the process of blistering when the grooves are formed by lateral material projections formed on both flanks of the grooves formed on at least three levels of rib side or fin tip material spaced radially from the tube wall in the radial direction , are largely covered. Here, the material projections of at least three levels in each case contribute a significant share to the overlap of the grooves. By the extensive, almost complete covering of the grooves by means of the lateral material projections according to the invention prevents the small steam inclusions can escape during the nucleate boiling out of the grooves. Thus, the nucleation sites are better retained in the grooves than in structures known in the art. The penetration of liquid into the grooves is reduced so much that even small bubble nucleation sites are not flooded. The formed vapor is retained in the structure until the vapor bubble has reached a sufficient size to detach from the bubble site.

As a measure of the degree of overlap of the grooves visible in the radial direction of view portion of the groove base can be selected based on the outer pipe surface. Under outer tube surface is here the smooth tube surface formed with the outer tube diameter (= envelope surface) understood. Investigations show that the lower the visible part of the groove bottom, the better the evaporation performance. An extensive coverage of the grooves in the context of this invention is present when the visible in the radial direction of view portion of the groove base relative to the outer pipe surface is not more than 10%.

The size of the steam pockets, which act as bubble nucleation site, depends on the properties of the substance to be vaporized, the pressure and the local temperature conditions, in particular the overtemperature of the tube wall with respect to the evaporation temperature. So that the steam inclusions can assume a sufficient size, it is advantageous to select the distance of the lateral material projections, which are formed closest to the pipe wall, greater than half the groove width, relative to the pipe wall. The width W of the groove is measured between the rib flanks above the rib foot. These material projections are consequently arranged in the region of the rib flank above the rib foot.

The lateral material projections may be continuous or discontinuous in the tube circumferential direction. Continuously formed lateral material projections change their cross section along the pipe circumferential direction only insignificantly. Discontinuous lateral material projections substantially change their cross section along the pipe circumferential direction; they can even be interrupted in some places. It is also possible to make one part of the lateral material projections continuous and another part of the lateral material projections discontinuous.

In a preferred embodiment of the invention, the grooves can be covered so far that in the radial direction of the groove bottom is visible on at most 4% of the pipe surface. This can be achieved by a suitable dimensioning of the ribs and the lateral material protrusions. The material projections may be formed on both flanks of the groove. In particular, the width W of the grooves and the lateral extent of the material projections can be matched to one another.

Preferably, the grooves may be covered so far that at least 2% of the pipe surface is visible in the radial direction of the groove bottom. Again, material protrusions may be formed on both flanks of the groove.

A very advantageous embodiment of the invention can be realized if the grooves are so far covered, for example, by material protrusions formed on both flanks of the groove, that the groove bottom is not visible in the radial direction of view.

In a preferred embodiment of the invention, on at least one level, the lateral material projections may be discontinuous in the pipe circumferential direction. As a result, discrete openings or pores are formed in the system of lateral material projections. The transport of liquid and vapor then takes place through these openings.

In order to be able to influence the process of bubble formation in a targeted manner, it is favorable to dispose the lateral material projections of the different levels, which are discontinuously formed in the circumferential direction of the tube, in a random manner, but to position them in the circumferential direction of the tube in a predetermined manner and correlated to one another. This allows an optimal structure to be created on the entire pipe surface.

In a particularly advantageous embodiment of the invention, the lateral material projections may be formed discontinuously in the tube circumferential direction at least two levels and the lateral material projections of these levels to each other in the pipe circumferential direction at least partially offset. Due to the partially staggered arrangement of the material projections, a system of interrupted planes with passages is created. The cross-sectional areas of the passage openings are larger than visible in the radial direction of view. The resulting steam can thus leave the groove without much resistance. At the same time, liquid can not be taken directly from penetrate the environment in the groove base, since the groove bottom is largely covered by the material projections according to the invention. This effectively prevents the flooding of bladder nucleation sites and thus stabilizes the nucleation process. Thus, a structure is formed which brings the liquid supply and Dampfabtransport in a favorable manner into balance.

In a particularly advantageous embodiment, the grooves may be covered so far that in the radial direction of view of the groove bottom is visible only through openings with a maximum area of 0.007 mm ² . Due to statistical variations in the manufacturing process, individual openings may be larger than 0.007 mm ² . It will be understood by those skilled in the art that the mean area of the openings should not be greater than 0.007mm ² , with the variation in aperture size preferably being chosen to be small enough not to adversely affect the performance of the structure. In the case of discontinuously formed, regularly recurring lateral material projections, the pitch and the extension of the material projections in the circumferential direction can be adapted in order to cover the groove base accordingly. The smaller the visible part of the groove bottom in the radial direction of view, the better the evaporation performance.

Furthermore, a further advantageous embodiment may be present if, at at least one level, the lateral extension of the material projections is so large that they overlap with the lateral material projections which are formed on the opposite rib edge on at least one other level in the axial direction and that the radial distance this material projections of the pipe wall is chosen so that in the overlap region narrow passages remain between the material projections. As a result, the bladder germs are particularly effectively held in the groove. The groove bottom is in many places in multiple ways covered. The narrow passages in the overlap area ensure the exchange of liquid and vapor.

In a particularly advantageous embodiment, the ribs of an integrally rolled finned tube may be provided with notches extending from the fin tip towards the rib foot. The depth of the notch is less than the height of the ribs. At the level of the notches, material of the rib which has been radially displaced by the notches forms first lateral material projections which partially overlap the groove between two axially adjacent ribs at a first level. Between the fin tip and the level of the notches are second lateral material projections which partially overlap the groove at a second level. The portions of the fin tip that are located between two circumferentially adjacent notches are axial so that the widened portions of the fin tip form third lateral material projections that partially overlap the groove at a third level. Due to the totality of the material projections, the grooves are largely covered. The first material projections formed by notching the rib and the third material projections on the fin tip are discontinuously formed in the pipe circumferential direction. To each other, these two material projections are arranged offset. The second lateral material protrusions may be formed by substantially radially displacing rib tip material. They may be discontinuous or nearly continuous. In this embodiment, the first, second and third lateral material protrusions are circumferentially arranged in a predetermined correlation with each other. The lateral material protrusions are designed to be suitable if, viewed radially from the outside, the groove bottom is visible on less than 4% of the pipe surface. Ideally, the groove bottom is no longer visible from the outside.

Embodiments of the invention will be explained in more detail with reference to the schematic drawings.

• Fig. 1 zeigt schematisch eine Schnittansicht eines erfindungsgemäßen Rippenrohrs;
• Fig. 2 zeigt die Außenansicht eines erfindungsgemäßen Rippenrohrs mit teilweise sichtbarem Nutengrund;
• Fig. 3 zeigt eine Schnittansicht des in Fig. 2 dargestellten Rippenrohrs in der Schnittebene A-A;
• Fig. 4 zeigt eine Schnittansicht des in Fig. 2 dargestellten Rippenrohrs in der Schnittebene B-B;
• Fig. 5 zeigt eine Schnittansicht des in Fig. 2 dargestellten Rippenrohrs in der Schnittebene C-C;
• Fig. 6 zeigt eine Schnittansicht des in Fig. 2 dargestellten Rippenrohrs in der Schnittebene D-D;
• Fig. 7 zeigt die Außenansicht eines erfindungsgemäßen Rippenrohrs mit nicht sichtbarem Nutengrund;
• Fig. 8 zeigt eine Schnittansicht des in Fig. 7 dargestellten Rippenrohrs in der Schnittebene A-A;
• Fig. 9 zeigt eine Schnittansicht des in Fig. 7 dargestellten Rippenrohrs in der Schnittebene B-B;
• Fig. 10 zeigt eine Schnittansicht des in Fig. 7 dargestellten Rippenrohrs in der Schnittebene C-C;
• Fig. 11 zeigt eine Schnittansicht des in Fig. 7 dargestellten Rippenrohrs in der Schnittebene D-D.

Show:

• Fig. 1 shows schematically a sectional view of a finned tube according to the invention;
• Fig. 2 shows the external view of a finned tube according to the invention with partially visible groove bottom;
• Fig. 3 shows a sectional view of the in Fig. 2 illustrated finned tube in the sectional plane AA;
• Fig. 4 shows a sectional view of the in Fig. 2 illustrated finned tube in the sectional plane BB;
• Fig. 5 shows a sectional view of the in Fig. 2 illustrated finned tube in the sectional plane CC;
• Fig. 6 shows a sectional view of the in Fig. 2 illustrated finned tube in the sectional plane DD;
• Fig. 7 shows the outside view of a finned tube according to the invention with invisible groove bottom;
• Fig. 8 shows a sectional view of the in Fig. 7 illustrated finned tube in the sectional plane AA;
• Fig. 9 shows a sectional view of the in Fig. 7 illustrated finned tube in the sectional plane BB;
• Fig. 10 shows a sectional view of the in Fig. 7 illustrated finned tube in the sectional plane CC;
• Fig. 11 shows a sectional view of the in Fig. 7 illustrated finned tube in the sectional plane DD.

Corresponding parts are provided in all figures with the same reference numerals.

The integrally rolled finned tube 1 according to FIGS. 1 to 11 has a pipe wall 2 and on the pipe outer side 21 one or more helically encircling ribs 3. In order to keep the production costs low, the ribs 3 usually run around like a multi-start thread. The case that only a rib 3 rotates like a catchy thread makes no difference to the invention. Therefore, this case is included in the invention, even though the term 'ribs' is always used in the plural. The ribs 3 are substantially radially from the tube wall 2 from. The ribs 3 have a ribbed foot 31, rib flanks 32 and a ribbed tip 33. In the region of the ribbed foot 31, the ribs 3 have a curved contour which can be described by means of a radius of curvature. The rib foot 31 extends radially from the tube wall 2 to the point where the curved contour of the rib 3 merges into the rib flank 32. The rib flank 32 extends from the rib foot 31 to the rib tip 33. The rib height H is measured from the tube wall 2 to the rib tip 33. All ribs have the same height H. The rib height H is typically 0.5 to 0.7 mm and thus depending on the pipe diameter between 2% and 5% of the pipe diameter. The grooves 35 are at least twice as wide as the radius of curvature at the rib foot 31. The width W of the groove 35 is measured between the rib flanks 32 above the rib foot 31.

Fig. 1 shows a sectional view of a fin tube 1 according to the invention along the tube axis. On the left side of each rib 3 are located above the fin foot 31 first lateral material projections 41. On the right side of each rib 3 are second lateral material projections 42 which are spaced from the tube wall 2 further than the first material projections 41. The second material projections 42 are disposed below the rib tip 33 on the rib flank 32. Further, on the left side of each rib 3 at the level of the rib tip 33 are third lateral material projections 43. Die The third material protrusions 43 are spaced further from the tube wall 2 than the second material protrusions 42. The first material protrusions 41 and the second material protrusions 42 extend laterally over the groove 35 such that an axial overlap exists between the first 41 and second 42 material protrusions, respectively adjacent ribs 3 is formed. Since the first 41 and second 42 material projections are spaced differently far from the tube wall 2, a narrow passage 62 remains between the first 41 and second 42 material projections. The second material projections 42 and the third material projections 43 laterally extend over the groove 35 such that a Overlap between the second 42 and the third 43 material projections each adjacent ribs 3 is formed in the axial direction. Since the second 42 and third 43 material projections are spaced differently far from the tube wall 2, remains between the two material projections 42 and 43, a narrow passage 66. The in Fig. 1 shown material projections 41, 42 and 43 may be formed continuously or discontinuously in the tube circumferential direction. If they are continuously trained, the in Fig. 1 shown sectional view to find in each sectional plane in the tube circumferential direction in at most slightly changed form. In this case, the whole of the lateral material projections 41, 42 and 43, the grooves 35 between two axially adjacent ribs 3 completely covered, so that the groove bottom 36 is not visible from the outside.

Fig. 2 shows the outside view of an advantageous embodiment of a finned tube according to the invention 1. The ribs 3 extend in the FIG. 2 in the vertical direction, the tube axis runs in a horizontal direction. The ribs 3 are provided with notches 51 which extend from the rib tip 33 in the direction of rib foot. The notches 51 preferably enclose with the ribs 3 an angle of approximately 45 °. At the level of the notches 51, material of the rib 3 forms first lateral material projections 41, which form the groove 35 partially overlap between two adjacent ribs 3 in the axial direction. Between the fin tip 33 and the level of the notches 51 are second lateral material projections 42 which partially overlap the groove 35. Further, the portions 54 of the rib tip 33, which are located between two circumferentially adjacent notches 51, are spread unilaterally in the axial direction, so that the expanded portions 54 of the rib tip 33 form third lateral material projections 43 which partially overlap the groove. The first lateral material protrusions 41 formed by the notches of the rib 3 and the third lateral material protrusions 43 on the rib tip 33 are discontinuously formed in the tube circumferential direction. To each other, these material projections 41 and 43 are arranged offset. The second lateral material protrusions 42 may be formed by substantially radially displacing material of the rib tip 33. If, as in Fig. 2 shown, two adjacent in the tube circumferential direction second material projections 42 are not adjacent to each other, then they are formed discontinuously. In this embodiment, the first 41, second 42 and third 43 lateral material projections are arranged in the circumferential direction in a predetermined correlation to each other. Further, by notching the rib, material protrusions 53 are formed on the flanks of the notch 51. These material projections 53 connect the first lateral material projections 41 with the second 42 and third 43 lateral material projections. Due to the totality of all lateral material projections 41, 42 and 43 as well as the material projections 53 on the flanks of the notches 51, the grooves between two adjacent ribs 3 in the axial direction are largely covered. At the in FIG. 2 illustrated embodiment, the groove bottom 36 is visible in the radial direction of view from the outside only a few places.

Fig. 3 shows a sectional view of the in Fig. 2 illustrated finned tube 1 in the sectional plane AA. On the left side of each rib 3 are located above the rib foot 31 first lateral material projections 41, which through the notches of Rib 3 were formed. On the right side of each rib 3 are second lateral material projections 42 which are spaced further from the tube wall 2 than the first material projections 41. The second material projections 42 are arranged below the rib tip 33 on the rib flank 32. The first material projections 41 and the second material projections 42 extend laterally over the groove 35 such that an overlap in the axial direction between the first 41 and the second 42 material projections of adjacent ribs 3 is formed. Therefore, in the sectional plane AA of the groove base 36 is not visible from the outside in the radial direction of view. Since the first 41 and second 42 material projections are spaced differently far from the tube wall 2, remains between the two material projections 41 and 42, a narrow passage 62nd

Fig. 4 shows a sectional view of the in Fig. 2 represented finned tube 1 in the sectional plane BB. The cutting plane is chosen so that it lies approximately centrally in a notch 51. The displaced by the notches of the ribs 3 material on the flanks 52 of the notches 51 forms in the sectional plane BB material projections 53 which are arranged on both sides of the rib 3 Y-like. In the sectional plane BB, the material projections 53 connect the level of the notches 51 with the level of the second lateral material projections 42. The material projections 53 on the flanks 52 of the notches 51 extend over the groove 35 in such a way that, together with the second lateral material projections 42, an overlap in the axial direction between the material projections 53 adjacent ribs 3 is formed. Therefore, in the sectional plane BB of the groove base 36 is not visible from the outside in the radial direction of view.

Fig. 5 shows a sectional view of the in Fig. 2 illustrated finned tube 1 in the sectional plane CC. On the right side of each rib 3 are already in FIG. 3 The second lateral material projections 42 are visible on the left side of each rib 3. Third lateral ones are located on the rib tip 33 on the left side of each rib 3 Material projections 43, which were formed by widening the rib tip 33. The third lateral material protrusions 43 are spaced further from the tube wall 2 than the second material protrusions 42. The second material protrusions 42 and the third material protrusions 43 extend laterally over the groove 35 so as to axially overlap between the second 42 and third 43 material protrusions each adjacent ribs 3 is formed. Therefore, in the sectional plane CC of the groove base 36 is not visible in the radial direction from the outside. Since the second 42 and third 43 material projections are spaced differently far from the pipe wall 2, remains between the two material projections 42 and 43, a narrow passage 66th

Fig. 6 shows a sectional view of the in Fig. 2 illustrated finned tube 1 in the sectional plane DD. On the right side of each rib 3 are already in the Figures 3 and 5 apparent, second lateral material projections 42. On the left side of each rib 3 are located at the rib tip 33 already in FIG. 5 apparent, third lateral material projections 43, which were formed by widening the rib tip 33. The third lateral material projections 43 are spaced further from the tube wall 2 than the second material projections 42. In contrast to the sectional plane CC, the second lateral material projections 42 extend less far beyond the groove 35 in the sectional plane DD, so that no overlap in the axial direction between the second 42 and the third 43 material projections each adjacent ribs 3 is formed. Therefore, in the sectional plane DD of the groove base 36 is visible from the outside in the radial direction of view. Due to the totality of all lateral material projections 41, 42 and 43 as well as the material projections 53 on the flanks of the notches 51, the grooves 35 are largely covered between two axially adjacent ribs 3, so that in the in Fig. 2 to 6 illustrated embodiment of a finned tube according to the invention the groove bottom 36 is visible from the outside only in a few places.

Fig. 7 shows the outside view of an advantageous embodiment of a finned tube according to the invention 1. The ribs 3 extend in the FIG. 7 in the vertical direction, the tube axis runs in a horizontal direction. The ribs 3 are provided with notches 51 which extend from the rib tip 33 in the direction of rib foot. The notches 51 preferably enclose an angle of about 45 ° with the ribs. At the level of the notches 51, material of the rib 3 forms first lateral material projections 41, which partially cover the groove between two axially adjacent ribs 3. Between the rib tip 33 and the level of the notches 51 are second lateral material projections 42 which partially overlap the groove. Further, the portions 54 of the rib tip 33, which are located between two circumferentially adjacent notches 51, are spread unilaterally in the axial direction, so that the expanded portions 54 of the rib tip 33 form third lateral material projections 43 which partially overlap the groove. The first lateral material protrusions 41 formed by the notches of the rib 3 and the third lateral material protrusions 43 on the rib tip 33 are discontinuously formed in the tube circumferential direction. To each other, these material projections 41 and 43 are arranged offset. The second lateral material projections 42 may be formed by radially displacing the rib tip 33. By simultaneous, appropriate displacement of the material of the rib tip 33 in the circumferential direction, they can then be formed continuously or almost continuously in the tube circumferential direction. In this embodiment, the first 41, second 42 and third 43 lateral material projections are arranged in the circumferential direction in a predetermined correlation to each other. Further, 3 material protrusions 53 are formed on the flanks of the notch 51 by the notches of the rib. These material projections 53 connect the first lateral material projections 41 with the second 42 and third 43 lateral material projections. Through the entirety of all lateral material projections 41, 42 and 43 and the material projections 53 on the flanks of the notches 51, the grooves between two in the axial direction completely overlapping adjacent ribs 3. At the in FIG. 7 illustrated embodiment, the groove bottom is therefore not visible from the outside in the radial direction of view.

Fig. 8 shows a sectional view of the in Fig. 7 illustrated finned tube 1 in the sectional plane AA. On the left side of each rib 3 are located above the rib foot 31 first lateral material projections 41, which were formed by the notches of the rib 3. On the right side of each rib 3 are second lateral material projections 42 which are spaced further from the tube wall 2 than the first material projections 41. The second material projections 42 are arranged below the rib tip 33 on the rib flank 32. The first material projections 41 and the second material projections 42 extend laterally over the groove 35 such that an overlap in the axial direction between the first 41 and the second 42 material projections of adjacent ribs 3 is formed. Therefore, in the sectional plane AA of the groove base 36 is not visible from the outside in the radial direction of view. Since the first 41 and second 42 material projections are spaced differently far from the tube wall 2, remains between the two material projections 41 and 42, a narrow passage 62nd

Fig. 9 shows a sectional view of the in Fig. 7 represented finned tube 1 in the sectional plane BB. The cutting plane is chosen so that it lies approximately centrally in a notch 51. The displaced by the notches of the ribs 3 material on the flanks 52 of the notches 51 forms in the sectional plane BB material projections 53 which are arranged on both sides of the rib 3 Y-like. In the sectional plane BB, the material projections 53 connect the level of the notches 51 with the level of the second lateral material projections 42. The material projections 53 on the flanks 52 of the notches 51 extend over the groove 35 such that, together with the second lateral material projections 42, an overlap in the axial direction between the material projections 53rd adjacent ribs 3 is formed. Therefore, in the sectional plane BB of the groove base 36 is not visible from the outside in the radial direction of view.

Fig. 10 shows a sectional view of the in Fig. 7 illustrated finned tube 1 in the sectional plane CC. On the right side of each rib 3 are already in FIG. 8 On the left side of each rib 3 are at the rib tip 33 third lateral material projections 43, which were formed by widening the rib tip 33. The third lateral material protrusions 43 are spaced further from the tube wall 2 than the second material protrusions 42. The second material protrusions 42 and the third material protrusions 43 extend laterally over the groove 35 so as to axially overlap between the second 42 and third 43 material protrusions each adjacent ribs 3 is formed. Therefore, in the sectional plane CC of the groove base 36 is not visible in the radial direction from the outside. Since the second 42 and third 43 material projections are spaced differently far from the pipe wall 2, remains between the two material projections 42 and 43, a narrow passage 66th

Fig. 11 shows a sectional view of the in Fig. 7 illustrated finned tube 1 in the sectional plane DD. On the right side of each rib 3 are already in the FIGS. 8 and 10 apparent, second lateral material projections 42. On the left side of each rib 3 are located at the rib tip 33 already in FIG. 10 apparent, third lateral material projections 43, which were formed by widening the rib tip 33. The third lateral material protrusions 43 are spaced further from the tube wall 2 than the second material protrusions 42. In contrast to the in FIG FIG. 6 illustrated embodiment extend in the in FIG. 11 illustrated embodiment, the second material projections 42 and the third material projections 43 laterally via the groove 35, that an overlap in the axial direction between the second 42 and the third 43 material projections each adjacent ribs 3 is formed. Therefore, in the sectional plane DD of the groove base 36 is not visible from the outside in the radial direction of view. Through the entirety of all lateral material projections 41, 42 and 43 and the material projections 53 on the flanks of the notches 51, the grooves 35 are completely covered between two axially adjacent ribs 3, so that in the in Fig. 7 to 11 illustrated embodiment of a finned tube according to the invention the groove base 36 is not visible from the outside.

It has been found that it is convenient to locate the lateral material protrusions closest to the tube wall at a level which is 40% to 50% of the fin height H spaced from the tube wall. The most distant from the tube wall lateral material projections are preferably located at the level of the rib tip. So they are formed by a lateral broadening of the rib tip. According to the invention, there are further lateral material projections between these two levels, which are arranged at a level which is spaced from the tube wall by 50% to 80%, preferably 60% to 70% of the rib height H. Here, the radial distance between each two adjacent levels should be 15% to 30%, preferably 20% to 25% of the rib height H.

The lateral extension of the material projections is preferably 35% to 75% of the width W of the groove. In a particularly preferred embodiment, there are at least two arranged on opposite rib edges and at different levels of material projections, the lateral extent together is more than 100% of the groove width W. This ensures that these material projections overlap in the axial direction and at the same time remain in the overlap area narrow passages.

LIST OF REFERENCE NUMBERS

1

heat exchanger tube

2

pipe wall

21

Pipe outside

3

Rib on the tube outside

31

fin base

32

rib flank

33

fin tip

35

groove

36

groove base

41

first material advantage

42

second material projection

43

third material advantage

51

score

52

Flank of the notches

53

Material projection on the flanks of the notches

54

Area of the rib tip between the notches

62

passage

66

passage

H

fin height

W

groove width

Claims (9)

1. Metal heat exchanger tube (1) for the evaporation of liquids on the outside (21) of the tube, comprising a tube axis, a tube wall (2), and integrally formed ribs (3) that run circumferentially on the outside (21) of the tube, comprising a rib foot (31), rib flanks (32), and a rib tip (33), wherein the rib foot (31) projects substantially radially from the tube wall (2), a groove (35) is located in each case between every two ribs (3) which are adjacent to one another in the axial direction, and wherein lateral material projections are arranged at the rib flanks (32) which are formed from the material of the ribs (3), wherein at least first (41), second (42), and third (43) lateral material projections, which are arranged in such a way that the grooves (35) are largely covered by the entirety of the material projections (41, 42, 43),
   characterised in that
   the first (41), second (42), and third (43) lateral material projections are formed on levels that are in each case differently spaced apart from the tube wall (2) in the radial direction.
2. Heat exchanger tube (1) according to claim 1, characterised in that the grooves (35) are covered to an extent that a maximum of 4% of the tube surface is visible in radial viewing direction of the groove base (36).
3. Heat exchanger tube (1) according to claim 2, characterised in that the grooves (35) are covered to an extent that a maximum of 2 % of the tube surface is visible in radial viewing direction of the groove base (36).
4. Heat exchanger tube (1) according to claim 3, characterised in that the grooves (35) are covered to an extent that the groove base (36) is not visible in radial viewing direction.
5. Heat exchanger tube (1) according to any of claims 1 to 4, characterised in that at least on one level, the lateral material projections (41, 42, 43) are discontinuously formed in the circumferential direction of the tube.
6. Heat exchanger tube (1) according to claim 5, characterised in that at least on two levels, the lateral material projections (41, 42, 43) are discontinuously formed in the circumferential direction of the tube, and that at least some of the lateral material projections (41,42,43) are offset from each other in the circumferential direction of the tube.
7. Heat exchanger tube (1) according to any of claims 5 or 6, characterised in that the grooves (35) are covered to an extent that in the radial viewing direction, the groove base (36) is only visible through openings with a surface of 0.007mm² max.
8. Heat exchanger tube (1) according to any of claims 1 to 7, characterised in that at least on one level, the lateral extension of the material projections (41, 42, 43) is large enough that they overlap in the axial direction with the lateral material projections (41, 42, 43) which are formed at the opposite rib flank (32) on at least one other level, and that the radial distance of these material projections (41, 42, 43) from the tube wall (2) is selected such that narrow passageways remain in the overlapping section between the material projections (41, 42, 43).
9. Heat exchanger tube (1) according to any of claims 1 to 8, wherein the ribs (3) are provided with notches (51) extending from the rib tip (33) towards the rib foot (31), wherein the depth of the notches is lower than the height (H) of the ribs (3), on the level of the notches (51), material of the rib (3) forming first lateral material projections (41) which partly cover the groove (35) between two ribs (3) which are adjacent to one another in the axial direction on a first level, between the rib tip (33) and the level of the notches (51) there are second lateral material projections (42), which partly cover the groove (35) between two ribs (3) which are adjacent to one another in the axial direction on a second level, and the sections (54) of the rib tip (33) which are located between two notches (51) which are adjacent to one another in the circumferential direction of the tube, are broadened in the axial direction so that the broadened sections (54) of the rib tip (33) form third lateral material projections (43), which partly cover the groove (35) between two ribs (3) which are adjacent to one another in the axial direction on a third level, characterised in that the grooves (35) are mostly covered between two ribs (3) which are adjacent to one another in the axial direction by the entirety of the material projections (41, 42, 43).

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