Heat exchanger tube and methods for producing a heat exchanger tube

Abstract

A heat exchanger tube with a tube axis, a tube wall, a tube outside and a tube inside. Continuously running, axially parallel or helically circling inner ribs are formed out of the tube wall on the tube inside, each inner rib having two rib flanks and a rib tip. A continuously extending groove is formed between adjacent inner ribs. The rib tip has at regular intervals recurring elevations which have an essentially frustopyramidal form. The inner ribs are raised in the radial direction on the contour line which is defined by the transitional edge of a rib flank to the rib tip and protuberances advancing out of the rib flank are formed in this region. Furthermore, the invention relates to a method for producing a heat exchanger tube.

Claims

1. A method for producing a heat exchanger tube, comprising the steps of: deforming the wall of a smooth tube (10) radially in a first forming region by a first rolling tool (300) encircling the outside of the smooth tube to form helically running outer ribs (4) of a first height on the outside of the smooth tube; supporting the tube wall in the first forming region with a first rolling mandrel (100) which lies inside of the tube, is mounted rotatably therein and has axially parallel or helical grooves of a depth T1 provided on its mandrel outer face and forming an inner structure on the inside of the tube wall out of material of the tube wall pressed into the grooves of the first rolling mandrel; forming outer ribs with an increased rising height on the outside of the tube wall in a second forming region spaced apart from the first forming region; supporting the tube wall in the second forming region with a second rolling mandrel (200) which lies inside the tube, is mounted rotatably therein and has axially parallel or helical grooves of a depth T2 provided on its mandrel outer face and newly forming helical, continuously running inner ribs (3) from material of the tube wall and material of the first inner structure both being pressed into the grooves of the second rolling mandrel, wherein the inner ribs formed in the second forming region are more pronounced than the inner structure formed in the first forming region and elevations (34) on the tip of the inner ribs (3) are formed from material pressed into the grooves of the first rolling mandrel (100) in the first forming region.

2. The method according to claim 1, characterized in that, by means of the inner structure formed in the first forming region, the inner surface area of the tube having this inner structure is increased by from 4-30% with respect to the inner surface area of the non-deformed smooth tube (10).

3. The method according to claim 1, characterized in that the depth T2 of the grooves of the second rolling mandrel (200) is at least 2.5 times as great as the depth T1 of the grooves of the first rolling mandrel (100).

4. The method according to claim 1, characterized in that the flank angle of the grooves of the first rolling mandrel (100) amounts at most to 120.

Description

(1) Exemplary embodiments of the invention are explained in more detail by means of the diagrammatic drawings in which:

(2) FIG. 1 shows an oblique view, emphasized by shadings, of the tube inner structure with ribs and with frustopyramidal elevations,

(3) FIG. 2 shows a diagrammatic oblique view of the tube inner structure according to FIG. 1,

(4) FIG. 3 shows a view, in the form of a detail, of a frustopyramidal elevation at the rib tip,

(5) FIG. 4 shows an oblique view, emphasized by shadings, of the tube inner structure with ribs and with asymmetric frustopyramidal elevations,

(6) FIG. 5 shows a diagrammatic oblique view of the asymmetric tube inner structure according to FIG. 4,

(7) FIG. 6 shows a view, in the form of a detail, of an asymmetric frustopyramidal elevation at the rib tip,

(8) FIG. 7 shows diagrammatically a view of the device for producing an externally ribbed heat exchanger tube with inner mandrels,

(9) FIG. 8 shows diagrammatically an oblique view of the device for producing an externally ribbed heat exchanger tube with an outer rolling tool and with inner mandrels, and

(10) FIG. 9 shows a graph of the improvement of internal heat transition as a result of the solution according to the invention.

(11) Parts corresponding to one another are given the same reference symbols in all the figures.

(12) FIG. 1 shows an oblique view, emphasized by gray shadings, of the structure of the tube inside 22 of a heat exchanger tube 1 with inner ribs 3 and with frustopyramidal elevations 34. FIG. 2 shows a diagrammatic oblique view of the tube inner structure according to FIG. 1.

(13) Continuously running, helically circling inner ribs 3 are formed on the tube inside 22, each inner rib 3 having two rib flanks 31 and a rib tip 32. A continuously extending groove 33 is formed in each case between adjacent inner ribs 3. The rib tip 32 has at regular intervals recurring elevations 34 which have an essentially frustopyramidal form. The rib flanks 31 of the inner ribs 3 are raised on the contour line defined by the transitional edge of a rib flank 31 to the rib tip 32. FIG. 3 shows a view, in the form of a detail, of a frustopyramidal elevation 34 on the rib tip 32, with protuberances 37 in the radial direction which are formed out of the rib flank 31 at the contour line in this region.

(14) In FIG. 3, two flanks 36 of the frustopyramidal elevation 34 illustrated are of concave form. These flanks 36 are also part of the rib tip 32 and have a curvature which is directed into the pyramid interior and by means of which edge structures projecting markedly on the surface area of the pyramid frustum or being sharper are formed in the shape of protuberances 37 in the radial direction. The rib tip 32 is configured in the form of a depression 35 between elevations 34. The sharp-edged structures have a beneficial effect upon the formation of vortices in order to increase the heat transmission properties.

(15) FIGS. 4 to 6 show, again, an oblique view, emphasized by gray shadings, of the structure of the tube inside 22 of a heat exchanger tube 1 with inner ribs 3 and with frustopyramidal elevations 34. FIG. 5 shows a diagrammatic oblique view of the tube inner structure according to FIG. 4. In FIGS. 4 to 6, the frustopyramidal elevations 34 are formed asymmetrically.

(16) In FIG. 6, once again, two flanks 36 of the frustopyramidal elevation 34 illustrated are of concave form. These flanks 36 are also part of the rib tip 32 and have a curvature which is directed into the pyramid interior and by means of which edge structures projecting markedly on the surface area of the pyramid frustum or being sharper are formed in the shape of protuberances 37 in the radial direction. As a result of the asymmetry, sharp-edged structures appropriately adapted to the flow conditions inside the tube and conducive to the formation of vortices are formed by the protuberances 37 in the radial direction.

(17) FIG. 7 shows a view of a device for producing an externally ribbed heat exchanger tube 1 with two rolling mandrels 100 and 200. FIG. 8 shows an oblique view of the device for producing an externally ribbed heat exchanger tube with an outer rolling tool and with inner mandrels, corresponding to FIG. 7. In the method for producing a heat exchanger tube 1 according to the invention, helically running outer ribs 4 are formed on the outside of a smooth tube 10 in a first forming region, in that the rib material is obtained through the displacement of material out of the tube wall 2 by means of a rolling tool 300, constructed from rolling disks 301, in a first rolling step. The ribbed tube obtained is set in rotation by the rolling forces and is pushed forward correspondingly to the helical outer ribs 4 obtained. The tube wall 2 is supported in the first forming region by a first rolling mandrel 100 which lies in the tube and which is mounted rotatably and has axially parallel or helical grooves of the first depth on its mandrel outer face 101, a relatively low pronounced inner structure being formed by material of the tube wall 2 being pressed into the grooves of the first rolling mandrel 100.

(18) In a second rolling step, the outer ribs 4 are formed with further-rising height on the tube outside 21 in a second forming region spaced apart from the first forming region, and the tube wall 2 is supported in the second forming region by a second rolling mandrel 200 which lies in the tube and which is likewise mounted rotatably and has helical grooves of the second depth on its mandrel outer face 201, helical, continuously running inner ribs 3 being newly formed on the tube inside 22, in that material of the tube wall 2 and material of the inner structure formed in the first rolling step are pressed into the grooves of the second rolling mandrel 200. The inner ribs formed in the second forming region are markedly more pronounced than the inner structure which was formed in the first forming region. The elevations 34 on the tip of these inner ribs 3 are formed from material which was pressed into the grooves of the first rolling mandrel 100 in the first forming region.

(19) FIG. 9 shows a graph which documents the advantage of the inner structure according to the invention in terms of performance. Using the example of tubes with an inside diameter of 16 mm, the improvement in internal heat transfer is illustrated in relation to a smooth tube as a function of the velocity of the water flowing in the tube. The mean temperature of the water in this case amounts to 9 C. The graph illustrates both the performance behavior of a tube according to the prior art and the performance behavior of a tube having an inner structure according to the invention. Structures according to the instructions of the prior art from publication U.S. Pat. No. 5,992,513 are implemented in the reference tube. It can be seen that the inner structure according to the invention has significant increases in performance, as compared with the tube according to the prior art, for water velocities lower than 2 m/s. The advantage amounts to approximately 40% in the case of water velocities lower than 1 m/s.

LIST OF REFERENCE SYMBOLS

(20) 1 Heat exchanger tube 2 Tube wall 21 Tube outside 22 Tube inside 3 Inner ribs 31 Rib flanks 32 Rib tip 33 Groove 34 Elevations 35 Depression 36 Flanks of an elevation 37 Protuberances 4 Outer ribs 10 Smooth tube 100 First rolling mandrel 101 Mandrel outer face of the first rolling mandrel 200 Second rolling mandrel 201 Mandrel outer face of the second rolling mandrel 300 Rolling tool 301 Rolling disks A Tube axis