Metal Heat Exchanger Tubes

Abstract

Develop a highly efficient heat exchanger tube that evaporates liquid on the outside of the tube. [Solution] The present invention relates to a metal heat exchanger tube (1) having integral fins (2) molded on the outside of the tube, the fin bases (3), fin sides (4), and fin tips (5), the fin bases (3) projecting radially from the tube wall (10), and the fins (2) defining flow passages (6) having flow passage bottoms (61) within which spaced-apart additional structures (7, 71, 72) are disposed, dividing the flow passages (6) between the fins (2) into segments (8). The additional structures (7, 71, 72) locally reduce the cross-sectional area available for flow through the flow passages (6) between two fins (2), thereby restricting fluid flow within the flow passages (6) at least during operation. The first additional structures (7, 71) are protrusions (71) extending radially outward from the channel bottom (61) and defined by end faces (713) located radially between the channel bottom (61) and the fin tip (5), thereby limiting the radial extent of the protrusions (71). A cavity (72) is arranged as a second additional structure (7, 72) facing radially outward at the location of the protrusions (71), and is formed from the material of the fin side portion (4) and the end faces (713) located radially outward of the protrusions (71). The cavities 72 are radially disposed between the end faces 713 and the fin tips 5, respectively, and are formed so that the cavities 72 extend radially above the flow channel bottom 61 of the flow channel 6 and around the radial extent of the protrusions 71 to the sides of the fin side portions 4. The cavities 72 are open in the axial direction.

Description

[Technical field]

[0001] The present invention relates to a metallic heat exchanger tube according to the preamble of claim 1. [Background technology]

[0002] Evaporation occurs in many areas of cooling and air conditioning technology as well as in process and energy technology. Often, tube bundle heat exchangers are used, in which the liquid of a pure substance or mixture evaporates on the outside of the tubes, while salt water or water is cooled on the inside of the tubes.

[0003] By enhancing the heat transfer on the outside and inside of the tubes, the size of the evaporator can be significantly reduced. This reduces the manufacturing costs of such equipment. Moreover, it reduces the required refrigerant volume, which may have become a significant proportion of the total equipment costs with the chlorine-free safe refrigerants that have been mainly used up until now. Moreover, the high-efficiency tubes that are common today are already about four times more efficient than smooth tubes of the same diameter.

[0004] The most efficient commercially available fin tubes for flooded evaporators have a fin structure with a fin density of 55 to 60 fins per inch on the outside of the tube (see U.S. Pat. No. 5,399,411, U.S. Pat. No. 5,499,421, U.S. Pat. No. 5,523,633). This corresponds to a fin pitch of approximately 0.45 to 0.40 mm. It is further known that an evaporator structure with the same fin pitch can be created on the outside of the tube with increased efficiency by inserting additional structural members between the fins in the groove bottom area.

[0005] In US Pat. No. 5,399,436 it is proposed to create undercut secondary grooves at the bottom of the grooves between the fins which run continuously along the primary grooves, the cross section of which may remain constant or vary at regular intervals.

[0006] Furthermore, from US Pat. No. 5,399,513 a structure of the groove bottom formed as a local cavity is known, which intensifies the process of nucleate boiling in order to improve the heat transfer during evaporation. The location of the cavity near the primary groove bottom is favorable for the evaporation process, since at the groove bottom the temperature overrise is greatest and therefore the largest driving temperature difference is available there for bubble formation.

[0007] Further examples of groove bottom structures can be found in US Pat. No. 5,399,623, US Pat. No. 5,499,667, US Pat. No. 5,523,366 or US Pat. No. 5,523,366. These structures have in common that the structural elements of the groove bottom do not have an undercut shape. Here, recesses in the groove bottom or protrusions in the lower region of the channel are concerned. Relatively high protrusions are explicitly excluded in the prior art, since they would block the fluid flow in the channel to the detriment of the heat exchange.

[0008] Another solution is disclosed in the patent application WO 2005 / 023363, which has a relatively high structure starting from the bottom of the groove. This structure is a protrusion in the flow channel, which causes a division into segments. By dividing the flow channel into segments between two fins, the flow channel is blocked many times in the circumferential direction, so that the generated gas bubbles and the movement of the heat exchange fluid in the flow channel are at least reduced or completely prevented. The exchange of liquid and vapor along the flow channel is further reduced or is no longer promoted by each additional structure. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Pat. No. 5,669,441 [Patent Document 2] U.S. Patent No. 5,697,430 [Patent Document 3] German Patent No. 19757526 [Patent Document 4] European Patent No. 1223400 [Patent Document 5] German Patent No. 102008013929 [Patent Document 6] European Patent No. 0222100 [Patent Document 7] U.S. Patent No. 7,254,964 [Patent Document 8] U.S. Patent No. 5,186,252 [Patent Document 9] European Patent No. 3111153 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention is based on the problem of developing a highly efficient heat exchanger tube that evaporates liquid on the outside of the tube. [Means for solving the problem]

[0011] The invention is set forth by the features of claim 1. The other dependent claims relate to preferred configurations and developments of the invention.

[0012] The invention encompasses a metal heat exchanger tube with integral fins formed on the outside of the tube, the fin base protruding radially from the tube wall, the fins forming a passage with a passage bottom, in which spaced apart additional structures are arranged, the additional structures dividing the passage between the fins into segments, the additional structures locally reducing the cross-sectional area through which the passage between two fins can pass, at least thereby restricting the fluid flow in the passage during operation. A first additional structure is a protrusion starting from the passage bottom and directed radially outward, which is defined by a terminal surface between the passage bottom and the fin tip, respectively, in the radial direction, thereby limiting the radial extent of the protrusion. A cavity is arranged radially outward at the location of the protrusion as a second additional structure, which is formed from the material of the fin side and the terminal surface arranged radially outward of the protrusion. The cavities are disposed radially between the end faces and the fin tips, respectively, such that the cavities are formed to the sides of the fin flanks about the radial extent of the protrusions above the flow channel bottom of the flow channel. The cavities are open in the axial direction.

[0013] The metallic heat exchanger tubes are used in particular for evaporating liquids consisting of pure substances or mixtures on the outside of the tubes.

[0014] Such efficient tubes can be produced using rolled plates on the basis of integrally rolled fin tubes. An integrally rolled fin tube is understood to mean a finned tube in which the fins are formed from the wall material of a smooth tube. A typical integral fin formed on the outside of the tube has a fin base, a fin side and a fin tip, for example in a spiral manner, the fin base protruding approximately radially from the tube wall. The number of fins is determined by counting the ridges that are successive in the axial direction of the tube. The structure according to the invention is produced by a rolled plate with an acute angle, which preforms and protrudes the material from the fin side, and a rolled plate with teeth that follows in the process technology, which processes both the wall material of the channel bottom and the preformed material of the fin side to form the cavities. The structure according to the invention can be produced, so to speak, only by a rolled plate with teeth, which processes both the wall material of the channel bottom and the material from the fin side to form the cavities.

[0015] Various methods are known here for closing the channels between adjacent fins in such a way that the connection of the channels with the surroundings remains in the form of holes or slits, in particular such nearly closed channels are produced by turning or folding the fins back, by splitting and upsetting the fins or by notching and upsetting the fins.

[0016] The invention starts from the consideration that the spaces between the fins are divided into segments by additional structures to improve the heat transfer during evaporation. This leads to localized overheating in these spaces, enhancing the process of nucleate boiling. The bubble formation then occurs primarily inside the segments, starting at nucleation sites. At these nucleation sites, small bubbles of gas or steam are first formed. When the expanding bubbles reach a certain size, they detach from the surface. As the bubbles detach, the remaining voids in the segments fill up again with liquid, and the cycle begins anew. The small bubbles left behind during the detachment of the bubbles may then form a surface that can be used as nucleation sites for a new bubble formation cycle.

[0017] In order to further form bubbles inside the segment, according to the solution according to the invention, there are further bubble nucleation sites in the region of the first additional structure in the form of a protrusion facing radially outward. This bubble nucleation site is placed as a cavity facing radially outward on the protrusion. In the gap formed by the cavity, bubble nuclei are advantageously formed, which contribute to the formation of bubbles in the segment. The protrusions can extend axially between the respective fin bases of the adjacent fins over the entire channel bottom or over only a part of the channel bottom. They are, so to speak, barriers extending between the two fins, starting from the channel bottom, which extend radially outward and at least partially close the channel in the circumferential direction. The protrusions spaced apart from one another and continuing into the channel and the cavities formed radially outward as additional structures can each have different heights and shapes.

[0018] In other words, the cavity, which is placed on the preferably solid protrusion of the channel bottom structure, is molded from the material of the fin side part and forms a flowing transition to both sides of the protrusion below it in approximately the radial direction. The cavity is formed in a cave-like manner from the side and the top surface which terminates in the direction of the fin tip, from the protrusion end surface arranged radially outward, and from the surface part of the fin side part which defines it on the back side. In the cavity, these side and top surfaces are boundary surfaces which extend approximately in the longitudinal axis direction of the tube, for example, in this axial direction approximately to the center of the channel. The protrusion end surface arranged radially outward can extend over the entire width of the channel. The cavity has an opening for releasing bubble nuclei in the axial direction. The bubble nuclei can leave there and contribute to bubble formation in two circumferentially adjacent segments. As long as the gas nuclei formed from the gaseous fluid at the location of this gas nucleation site arranged on the protrusion do not predominate and, so to speak, do not prevent the passage, the liquid fluid between the adjacent segments can also be exchanged there. In other words, as long as the gas nuclei do not block the connection site of the adjacent segments, the liquid fluid can also reach the adjacent segment. The protrusion on which the cavity rests is therefore a threshold for the passage of the fluid.

[0019] In this case, the side of the cavity may be longer in the axial direction toward the adjacent fin than the top surface. This creates a cavity opening that is obliquely disposed relative to the longitudinal axis of the tube, which relatively easily releases the bubble nuclei into the adjacent segment where the bubbles expand. In this case, the front contour of the side and top surface forming the cavity opening may be configured to be arcuate or irregular. Even in this preferred embodiment, the cavity is open approximately in the axial direction, even if it is disposed to a certain extent obliquely.

[0020] In the present invention, by dividing the flow passage between the two fins into segments in this way, this passage is blocked many times in the circumferential direction, so that the movement of the generated gas bubbles in the passage is at least reduced or even completely prevented, and the exchange of liquid and vapor along the passage is further reduced or no longer promoted by each additional structure.

[0021] A particular advantage of the present invention is that the liquid-vapor exchange is well controlled locally and the filling of bubble nucleation sites within the segments is localized. Overall, by properly selecting the segmentation of the flow passages, the evaporator tube structure can be effectively optimized according to the operating parameters, whereby an improvement in heat transfer is achieved. Furthermore, structural elements that enhance bubble formation at the groove bottom are particularly effective, since in the groove bottom area the temperature at the fin base is higher than at the fin tip.

[0022] Furthermore, it is advantageous that the additional structure locally reduces the cross-sectional area through which the flow can pass in the flow passage between the two fins. Overall, the segmentation of the flow passages increases the separation of the respective flow passage sections, which allows the evaporator tube structure to be further optimized depending on the application parameters in order to further improve the heat transfer.

[0023] In a preferred embodiment of the invention, the protrusions and cavities may locally reduce the cross-sectional area available for flow in the flow channel between two fins by at least 30%. In this way, the segment is locally sufficiently restricted for fluid passage. The channel section between two segments is therefore sufficiently or as far as possible isolated on the fluid side from the adjacent channel section.

[0024] Advantageously, the protrusions and cavities may locally reduce the cross-sectional area available for flow in the flow passage between two fins by 40 to 70%, the section of the flow passage between two segments forming a significant threshold on the fluid side with respect to the adjacent section of the flow passage.

[0025] In an advantageous embodiment of the invention, the flow passages may be closed radially outwardly up to the respective local openings. The fins may then have an approximately T- or Γ-shaped cross section, whereby the flow passages between the fins are closed up to the holes as local openings. Through these openings, the steam bubbles produced during the evaporation process can escape. The deformation of the fin tips is carried out in a manner available from the prior art.

[0026] In this regard, the fin tips may be axially folded and even shaped to some extent towards the bottom of the channel. The channel may thus be tapered or completely closed to the desired extent from below and laterally and / or from above by a combination of complementary structural members, in any case such that the channel between the fins is divided into discontinuous segments.

[0027] The combination of the segments according to the invention with the channels closed up to holes or slits results in a structure with a very high efficiency in the evaporation of the liquid over a very wide range of operating conditions, in particular the heat transfer coefficient of the structure remains constant and reaches a high level even when the heat flux or the driving temperature difference changes.

[0028] In a preferred embodiment of the invention, there may be at least one local opening per segment. This minimum condition further ensures that any gas bubbles that may form in a channel segment during the evaporation process can escape to the outside. The local openings are designed in terms of size and shape to allow the liquid medium to pass through and flow into the channel section. Therefore, to be able to support the evaporation process at the local openings, equal amounts of liquid and vapor must be transported through said openings in opposite directions. Usually, a liquid is used that wets the tube material well. Due to the capillary effect, such a liquid can enter the channel through each opening in the outer tube surface, even against an overpressure.

[0029] Furthermore, the ratio of the number of local openings to the number of segments may be between 1:1 and 6:1. More advantageously, this ratio may be between 1:1 and 3:1. The channels between the fins are substantially closed by the material of the upper fin area, and the resulting voids of the channel segments are connected to the surrounding space by openings. These openings may also be formed as holes of the same size or of two or more sizes. In the case of a number of local openings on one segment, holes with two sizes may be particularly suitable. Each small opening is followed, for example, by a large opening along the channel according to a regularly repeated pattern. This structure results in a directional flow in the channel. The liquid is advantageously taken up through the small holes with the help of capillary pressure and wets the channel walls, whereby a thin film is created. The vapor collects in the center of the channel and escapes there due to the smallest capillary pressure. At the same time, the dimensions of the large holes must be determined in such a way that the vapor can escape fast enough and the channel does not dry out. The size and number of the vapor holes relative to the relatively small liquid holes are then adjusted to one another.

[0030] In an advantageous embodiment of the invention, the protrusion as the first additional structure may be molded at least from the material of the channel bottom between two integrally circumferential fins, so that a material-bonded connection for good heat exchange from the tube wall to the respective structural element remains. Moreover, the protrusion may also consist of the material of the fin side. Dividing the channel into segments from a single material of the channel bottom is particularly advantageous for the evaporation process.

[0031] In a particularly advantageous embodiment, the protrusion as the first additional structure may have a height of 0.15 to 1 mm, the dimensioning of this additional structure being particularly well adapted to high-efficiency fin tubes, which represent structural sizes of the external structure advantageously in the sub-millimeter to millimeter range.

[0032] Preferably, the protrusions may have an asymmetric shape. The asymmetry of the structure is manifested here in a cut surface extending perpendicular to the longitudinal axis of the tube. The asymmetric shape may further contribute to the evaporation process, especially if a relatively large surface is formed. The asymmetry may be formed both in the additional structure at the bottom of the channel and also in the fin tips.

[0033] In an advantageous embodiment of the invention, the protrusions may have a trapezoidal cross section in a cut plane perpendicular to the tube longitudinal axis. The trapezoidal cross section is a structural element that is technically well controllable for integrally rolled fin tube structures. Slight manufacturing-induced asymmetries of the normally parallel trapezoidal bases may appear here.

[0034] Preferably, at the location of the protrusion, two opposing cavities may be formed in the direction of the tube longitudinal axis. In both cavities, the openings releasing the bubble nuclei are therefore directly opposite each other in the axial direction. The bubble nuclei can leave there and contribute to the bubble formation in both adjacent segments in the circumferential direction. The protrusion on which both cavities rest is therefore a threshold for the passage of the fluid. Here, cavity openings that are obliquely placed with respect to the tube longitudinal axis can prove to be particularly suitable, which release the bubble nuclei relatively easily into the adjacent segment where the bubbles expand. [Brief description of the drawings]

[0035] [Figure 1] 1 shows a schematic partial cross-sectional view of a heat exchanger tube having segments separated by additional structures. [Diagram 2] 1A and 1B are schematic perspective views of a portion of the external structure of a heat exchanger tube having folded fin tips; [Diagram 3] 1 shows a detailed view of the cavity at the location of the protrusion diagrammatically. [Figure 4] 1 shows a schematic perspective view of a portion of the external structure of a heat exchanger tube having two cavities facing each other at the location of a protrusion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Exemplary embodiments of the invention will now be described in more detail with the aid of schematic drawings, in which corresponding parts are provided with the same reference numerals in all figures.

[0037] 1 shows a schematic partial cross-sectional view of a heat exchanger tube 1 according to the invention with segments 8 separated by additional structures 7. The integrally rolled heat exchanger tube 1 has fins 2 which run helically around the outside of the tube with primary grooves as channels 6 between them. The fins 2 run continuously along a helix on the outside of the tube. The fin bases 3 protrude approximately radially from the tube wall 10. The fin height H is measured in the finished heat exchanger tube 1 from the deepest point of the channel bottom 61 to the fin tip 5 of the fully formed fin tube.

[0038] A heat exchanger tube 1 is proposed in which additional structures 7 in the form of radially outwardly directed protrusions 71 are arranged in the region of the channel bottom 61, which protrusions 71 are each defined in the radial direction by a terminal surface 713 between the channel bottom 61 and the fin tip 5. These protrusions 71 are called first additional structures and are formed from the material of the tube wall 10 from the channel bottom 61. The protrusions 71 are advantageously arranged at regular intervals on the channel bottom 61 and extend transversely to the extension of the channel from the fin base 3 of the fin 2 at least partially or completely towards the next fin base beyond, which is not shown in the drawing. At the location of the protrusions 71, cavities 72 are arranged as second additional structures 7, facing radially outwardly, which cavities 72 are formed from the material of the fin side 4 and from the terminal surfaces 713 arranged radially outward of the protrusions 71. The cavities 72 are arranged radially between the end faces 713 and the fin tips 5, respectively, so that the cavities 72 are formed around the radial extent of the projections 71 above the channel bottoms 61 of the channels 6, laterally of the fin flanks 4. The cavities 72 are open in the axial direction. The primary grooves as channels 6 are thus at least partially tapered at regular intervals. The resulting segments 8, together with the cavities 72, are particularly favorable for bubble nucleation. The exchange of liquid and vapor between the respective segments 8 is at least reduced.

[0039] In order to form the protrusions 71 with the cavities 72 on the radially outer side at the channel bottom 61, the fin tips 5 as the end regions of the fins 2 are advantageously further deformed in such a way that the fins 2 radially partially close the channels 6 at the axially folded fin tips 51. In order to allow the steam bubbles to escape from the channels 6, the connections of the channels 6 with the surroundings are made in the form of holes 9 as local openings. The deformation of the fin tips 5 is carried out by means of a rolling technique available from the prior art. The primary grooves 6 are thus undercut grooves. By combining the protrusions 71 and the cavities 72 as additional structures 7, segments 8 in the form of voids are obtained, which furthermore are distinguished by a very high efficiency in the evaporation of the liquid over a very wide range of operating conditions. The liquid evaporates inside the segments 8 supported by the cavities 72 as additional nucleation sites. The resulting steam leaves the channels 6 at the local openings 9 through which the liquid fluid also flows. For the flow of the fluid, a well-wettable tube surface may also be of help.

[0040] The solution according to the invention concerns a structured tube with an increased heat transfer coefficient on the outside of the tube. In order not to transfer most of the thermal resistance to the inside, the heat transfer coefficient on the inside can be further enhanced by a suitable internal structure 11. Heat exchanger tubes 1 for tube bundle heat exchangers usually have at least one structured area as well as smooth end pieces and possibly smooth intermediate pieces. These smooth end pieces or intermediate pieces define the structured area. In order to be able to mount the heat exchanger tube 1 in the tube bundle heat exchanger without any problems, the outer diameter of the structured area must not be larger than the outer diameter of the smooth end pieces and intermediate pieces.

[0041] FIG. 2 shows a schematic perspective view of a part of the external structure of a heat exchanger tube 1 with a folded fin tip 51. For a better illustration, only the structural elements of the external structure that are most important for understanding are shown. In order to form a protrusion 71 with a radially outer cavity 72 at the channel bottom 61, the fin tip 5 as the end region of the fin 2 is again deformed so that the fin 2 radially partially closes the channel 6 at the axially folded fin tip 51. The connection of the channel 6 with the surroundings is made as a local opening 9 for the escape of steam bubbles from the channel 6 and for the inflow of liquid fluid into the channel 6. The primary groove 6 is thus again an undercut groove. The axially folded fin tip 51 is formed from the fin 2 and extends axially beyond the channel 6. The transition area from the fin side 4 to the folded fin tip 51 can be recognized in the figure by a small plateau-like structure along the extension of the fin. The additional structure 7 reduces the cross-sectional area available for flow in the flow passage 6 between the two fins 2 locally in a particularly effective manner, so that the fluid flow in the flow passage 6 is restricted during operation.

[0042] FIG. 3 shows a schematic detailed view of the cavity 72 at the location of the protrusion 71. The cavity 72, which rests radially on the preferably solid protrusion 71, is produced from the material of the fin side 4 by a toothed rolling plate which processes both the wall material at the channel bottom 61 and the material at the fin side 4. Although the protrusion 71 and the cavity 72 are formed from different areas of the tube wall, the cavity 72 may mainly form a radially flowing transition to the two side surfaces 711 of the protrusion 71 below it. In this case, the protrusion 71 only extends over a portion of the channel bottom 61 and ends in the tube axial direction with a front surface 712. The cavity 72 is formed cavernously from the side surfaces 721 and the top surface 722, as well as from the end surface 713 of the protrusion 71 arranged radially outward, and from the surface part of the fin side surface (hidden by the side surface 721 in FIG. 3) that defines it on the rear side. The side surface 721, the top surface 722 and the end surface 713 of the protrusion 71 are the boundary surfaces of the cavity 72, which extend approximately in the direction of the longitudinal tube axis A, for example almost to the center of the flow path in this axial direction. Here, the end surface 713 of the protrusion 71 may extend further in the direction of the longitudinal tube axis A or over the entire width of the flow path between the opposing fins. The cavity 72 has an opening 723 for releasing bubble nuclei mainly in the axial direction of the tube. The bubble nuclei can leave therefrom and contribute to bubble formation in the two circumferentially adjacent segments 8. The protrusion 71 on which the cavity 72 rests is therefore a threshold for the passage of the fluid.

[0043] 3, the side surface 721 of the cavity 72 is longer in the axial direction toward the adjacent fin than the top surface 722. This results in an opening 723 of the cavity 72 that is obliquely oriented relative to the tube longitudinal axis A and relatively easily releases bubble nuclei into the adjacent segment 8 where the bubbles expand. Nevertheless, this results in the cavity 72 being open in approximately the axial direction A even when the opening 723 is slightly oblique.

[0044] FIG. 4 shows a schematic perspective view of a part of the external structure of a heat exchanger tube 1 with two cavities 72 facing each other at the location of the protrusion 71 and the folded fin tip 51. For a better explanation, only the structural parts of the external structure that are most important for understanding are shown. In order to form the protrusion 71 with the radially outer cavity 72 at the channel bottom 61, the fin tip 5 as the end region of the fin 2 is also modified in such a way that the fin 2 radially partially closes the channel 6 at the axially folded fin tip 51. The connection of the channel 6 with the surroundings is made as a local opening 9 for the escape of steam bubbles from the channel 6 and for the inflow of liquid fluid into the channel 6. The protrusion 71 and the cavity 72 as additional structure 7 reduce the cross-sectional area available for flow in the channel 6 between the two fins 2 locally and particularly effectively, so that the fluid flow in the channel 6 is restricted during operation.

[0045] In this case, the protrusion 71 extends in the direction of the tube longitudinal axis A over the entire flow width between adjacent fins 2. At the location of the protrusion 71, two opposing cavities 72 are formed facing radially outward. In both cavities 72, the openings for releasing the bubble nuclei are consequently directly opposite each other in the axial direction A. The bubble nuclei can leave therefrom and contribute to bubble formation in the two circumferentially adjacent segments. The protrusion 71 on which both cavities 72 rest is therefore a threshold for the passage of the fluid. Here, it can be seen that an opening of the cavity 72 that is somewhat obliquely placed with respect to the tube longitudinal axis A is particularly suitable, which relatively easily releases the bubble nuclei into the adjacent segment where the bubbles expand. [Explanation of symbols]

[0046] 1 Heat Exchanger Tube 2 Fins 3 Fin base 4 Fin side 5 Fin tip, fin end region 51 Axial bent fin tip 6 Flow path, primary groove 61 Bottom of channel 7 Additional structures 71 Protrusion as the first additional structure at the bottom of the channel 711 Side of protrusion 712 Front of protrusion 713 End surface of protrusion 72 Cavity as a second additional structure 721 Side of the cavity 722 Top surface of the cavity 723 Opening of cavity 8 Segments 9 Local opening, hole 10 Tube wall 11 Internal structure A Tube vertical axis H Fin Height

Claims

1. A metal heat exchanger tube having integral fins molded on the outside of the tube, the fin bases projecting radially from a tube wall, channels between the fins having channel bottoms, and spaced apart additional structures disposed within the channels; the additional structure divides the flow passage between the fins into recessed segments and locally reduces the cross-sectional area available for flow through the flow passage between two of the fins, thereby at least restricting fluid flow in the flow passage during operation; the additional structure includes a first additional structure and a second additional structure; the first additional structure is a protrusion extending radially outwardly from the flow channel bottom, the protrusion being defined by a terminal surface located radially between the flow channel bottom and the fin tip, the terminal surface limiting the radial extent of the protrusion; a cavity located radially at the protrusion is arranged as the second additional structure, the second additional structure being formed from material of the fin side portion and the end surface located radially outward of the protrusion; The cavity is radially disposed between the end face and the fin tip, and is formed to be located laterally of the fin side portion around a radial extent of the protrusion above the flow channel bottom of the flow channel, and is axially open to the protrusion. A metallic heat exchanger tube.

2. The protrusions and cavities locally reduce the cross-sectional area available for flow in the flow passage between two of the fins by at least 30%.

2. A heat exchanger tube according to claim 1 .

3. The protrusions and cavities locally reduce the cross-sectional area available for flow in the flow passage between two of the fins by 40 to 70%.

3. A heat exchanger tube according to claim 1 or 2, characterized in that

4. The flow passage is partially closed in the radial direction by the fin tips and opens radially outwardly by local openings formed between the fin tips. A heat exchanger tube according to any one of claims 1 to 3, characterized in that

5. There is at least one said local opening for each said segment.

5. A heat exchanger tube according to claim 4.

6. The protrusion is molded from the material of the channel bottom between two integrally circumferential fins. A heat exchanger tube according to any one of claims 1 to 5.

7. The protrusions have a height of 0.15 to 1 mm.

7. A heat exchanger tube according to claim 6.

8. The protrusion has a trapezoidal cross section when cut perpendicular to the longitudinal axis of the tube. A heat exchanger tube according to any one of claims 1 to 7.

9. At the location of the protrusion, two of the cavities facing each other in the direction of the tube longitudinal axis are formed. A heat exchanger tube according to any one of claims 1 to 8.

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