Metal heat exchanger tube

Abstract

A metal heat exchanger tube has integral ribs formed on the outside of the tube. The ribs have a rib base, rib flanks, and a rib tip. The rib base protrudes substantially radially from the tube wall. A channel is formed between the ribs, in which channel additional structures spaced apart from each other are arranged. The additional structures divide the channel between the ribs into segments. The additional structures reduce the cross-sectional area in the channel between two ribs through which flow is possible by at least 60% locally and, at least thereby, limit a fluid flow in the channel during operation.

Claims

1. A metal heat exchanger tube comprising: a tube wall; a plurality of integrally encircling fins formed on the outside of the tube, wherein each fin has a fin foot, fin flanks and a fin tip, and the fin foot protrudes radially from the tube wall, and a channel formed between two adjacent fins, wherein the channel has a throughflow cross-sectional area perpendicular to the course of the channel, and spaced-apart additional structures arranged in portions of the channel, a first total throughflow cross-sectional area A1 being the minimum total throughflow cross-section area measured perpendicular to the course of the channel in the portions of the channel where the additional structures are arranged; a second total throughflow cross-sectional area A2 being the maximum total throughflow cross-section area measured perpendicular to the course of the channel in the portions of the channel where the additional structures are not arranged; wherein the additional structures divide the channel into segments, and wherein a reduction of the first total throughflow cross-sectional area A1 relative to the second total throughflow cross-sectional area A2 is at least 60% of the second total throughflow cross-sectional area A2.

2. The heat exchanger tube as claimed in claim 1, wherein the additional structures reduce the throughflow cross-sectional area in the portions of the channel in which they are arranged by at least 80% as compared to the portions of the channel in which they are not arranged.

3. The heat exchanger tube as claimed in claim 2, wherein the additional structures completely close the throughflow cross-sectional area in the portions of the channel in which they are arranged.

4. The heat exchanger tube as claimed in claim 1, wherein the channel is closed radially outward except for individual openings.

5. The heat exchanger tube as claimed in claim 1, wherein there is at least one individual opening per segment.

6. The heat exchanger tube as claimed in claim 5, wherein the quotient of the number of individual openings to the number of segments is 1:1 to 6:1.

7. The heat exchanger tube as claimed in claim 1, wherein the additional structures comprise first additional structures that are radially outwardly directed projections emerging from a base of the channel.

8. The heat exchanger tube as claimed in claim 7, wherein the first additional structures are formed at least partially from material of the tube wall from the channel base.

9. The heat exchanger tube as claimed in claim 8, wherein the first additional structures formed from the channel base have a height of between 0.15 and 1 mm.

10. The heat exchanger tube as claimed in claim 7, wherein the additional structures comprise second additional structures that are formed at least from the fin flanks or fin tips of the integrally encircling fins via lateral projections.

11. The heat exchanger tube as claimed in claim 10, wherein the second additional structures are formed at least from one fin emerging from the fin tip in the direction toward the channel base.

12. The heat exchanger tube as claimed in claim 1, wherein additional structures are at least partially provided via additional material.

13. The heat exchanger tube as claimed in claim 1, wherein the additional structures have asymmetric shapes.

14. The heat exchanger tube as claimed in claim 1, wherein additional structures have a trapezoidal cross section in a section plane running perpendicularly to the tube axis.

15. The heat exchanger tube as claimed in claim 1, wherein the respective throughflow cross-sectional area in the channel between two fins that is reduced by additional structures varies.

16. A metal heat exchanger tube comprising: a tube wall; a plurality of integrally encircling fins formed on the outside of the tube, wherein each fin has a fin foot, fin flanks and a fin tip, and the fin foot protrudes radially from the tube wall, and a channel formed between two adjacent fins, wherein the channel has a through flow cross-sectional area perpendicular to the course of the channel, and spaced-apart additional structures arranged in portions of the channel, a first total throughflow cross-sectional area A1 being the minimum total throughflow cross-section area measured perpendicular to the course of the channel in the portions of the channel where the additional structures are arranged; a second total throughflow cross-sectional area A2 being the maximum total throughflow cross-section area measured perpendicular to the course of the channel in the portions of the channel where the additional structures are not arranged; wherein the additional structures divide the channel into segments, wherein a reduction of the first total throughflow cross-sectional area A1 relative to the second total throughflow cross-sectional area A2 is at least 60% of the second total throughflow cross-sectional area A2.

17. A metal heat exchanger tube comprising: a tube wall; a plurality of integrally encircling fins formed on the outside of the tube, wherein each fin has a fin foot, fin flanks and a fin tip, and the fin foot protrudes radially from the tube wall, and a channel formed between two adjacent fins, wherein the channel has a throughflow cross-sectional area perpendicular to the course of the channel, and spaced-apart additional structures arranged in portions of the channel, wherein the additional structures divide the channel into segments, wherein first ones of the additional structures project from a base of the channel and second ones of the additional structures extend radially from the fin tip such that when the second ones of the additional structures lie above the first additional structures as viewed radially there is a reduction in the throughflow cross-sectional area in the channel between two adjacent fins in order to limit fluid flow in the channel by at least 60%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are explained in more detail with reference to the schematic drawings, in which:

(2) FIG. 1 shows schematically a partial view of a cross section of a heat exchanger tube with segments subdivided by additional structures,

(3) FIG. 2 shows schematically a partial view of a cross section of a further heat exchanger tube with varied additional structures in the region of the fin tip, and

(4) FIG. 3 shows schematically a partial view of a cross section of a heat exchanger tube with virtually closed segments.

DETAILED DESCRIPTION OF THE INVENTION

(5) Mutually corresponding parts are provided with the same reference signs in all of the figures.

(6) FIG. 1 shows schematically a partial view of a cross-section of a heat exchanger tube 1 according to the invention with segments 8 subdivided by additional structures 7. The integrally rolled heat exchanger tube 1 has helically encircling fins 2 on the outside of the tube, between which a primary groove is formed as the channel 6. The fins 2 extend continuously without interruption along a helix line on the outside of the tube. The fin foot 3 protrudes substantially radially from the tube wall 10. On the finished heat exchanger tube 1, the fin height H is measured, starting from the lowest point of the channel base 61, from the fin foot 3 beyond the fin flank 4 to the fin tip 5 of the completely formed finned tube. A heat exchanger tube 1 is proposed in which an additional structure 7 in the form of solid projections 71 is arranged in the region of the channel base 61. Said projections 71 are referred to as a first additional structure and are formed from the channel base 61 from the material of the tube wall 10. The solid projections 71 are arranged at preferably regular intervals in the channel base 61 and extend transversely to the course of the channel from a fin foot 3 of a fin 2 to the next fin foot lying thereabove (not illustrated in the figure plane). In this manner, the primary groove as channel 6 is at least partially tapered at regular intervals. The resulting segment 8 promotes formation of bubble nuclei in a particular manner. The exchange of liquid and vapor between the individual segments 8 is thereby reduced.

(7) In addition to the formation of the projections 71 on the channel base 61, the fin tips 5 as the distal region of the fins 2 are expediently deformed in such a manner that they partially close the channel 6 in the radial direction as a further second additional structure 72. The connection between the channel 6 and the environment is configured in the form of pores 9 as local openings so that vapor bubbles can escape from the channel 6. The fin tips 5 are deformed by methods which can be gathered from the prior art. The primary grooves 6 thereby constitute undercut grooves. By means of the combination of the first and second additional structures 71 and 72 according to the invention, a segment 8 is obtained in the form of a cavity which is furthermore distinguished in that it has a very high efficiency for the evaporation of liquids over a very wide range of operating conditions. The liquid evaporates within the segment 8. The resulting vapor emerges from the channel 6 at the local openings 9, through which liquid fluid also flows. Readily wettable tube surfaces may also be an aid for the flowing-in of the fluid.

(8) FIG. 2 shows schematically a partial view of a cross-section of a further heat exchanger tube 1 with varied second additional structures 72 in the region of the fin tip 5. In addition to the formation of the projections 71 at the channel base 61, the fin tips 5 as the distal region of the fins 2 are in turn deformed in such a manner that they partially close the channel 6 in the radial direction as a further second additional structure 72. The connection between the channel 6 and the environment is configured as local openings 9 in the form of obliquely running tubes for the escape of vapor bubbles from the channel 6 and the flow of liquid fluid into the channel 6. In this manner, the primary grooves 6 constitute in turn undercut grooves. The second additional structure 72 is formed from a fin starting from the fin tip 5 in the direction toward the channel base 61 and thus projects into the channel 6 in the radial direction. As soon as a first and a second additional structure lie one above the other, as viewed radially, the throughflow cross-sectional area in the channel 6 between two fins 2 is reduced particularly effectively locally in order thereby to limit the fluid flow in the channel 6 during operation.

(9) FIG. 3 shows schematically a partial view of a cross-section of a heat exchanger tube 1 with the additional structures 7 from FIG. 2. The second additional structures 72 project into the channel 6 virtually as far as the projections of the first additional structures 71, and therefore virtually closed segments 8 are formed. In this case, the quotient of the number of local openings 9 to the number of segments 8 lies within the preferred range of 1:1 to 3:1 and in the section is approximately 1.7:1 to 2.3:1. All of the local openings 9 designed as tubes are still permeable here, even if an opening 9 comes to lie above a projection 71. The resulting vapor can still emerge from the channel 6 at the local openings 9. The liquid fluid, because of its surface tension, can flow particularly efficiently in the tubes 9 by means of capillary action.

(10) By means of the combination of the first and second additional structures 71 and 72 according to the invention, a segment 8 is obtained in the form of a cavity which is furthermore distinguished in that it has a very high efficiency for the evaporation of liquids over a very wide range of operating conditions. In particular, the coefficient of heat transfer of the structure remains virtually constant at a high level in the event of variation of the heat flow density or the driving temperature difference. The solution according to the invention relates to structured tubes in which the coefficient of heat transfer is increased on the outside of the tube. In order not to shift the main portion of the heat throughput resistance to the inside, the coefficient of heat transfer can be additionally intensified on the inside by means of a suitable internal structuring 11. The heat exchanger tubes 1 for tubular heat exchangers customarily have at least one structured region and smooth end pieces and possibly smooth intermediate pieces. The smooth end pieces and/or intermediate pieces bound the structured regions. So that the heat exchanger tube 1 can be easily installed in the tubular heat exchanger, the outer diameter of the structured regions should not be larger than the outer diameter of the smooth end and intermediate pieces.

LIST OF REFERENCE SIGNS

(11) 1 heat exchanger tube 2 fins 3 fin foot 4 fin flank 5 fin tip, distal regions of the fins 6 channel, primary groove 61 channel base 7 additional structures 71 first additional structure in the form of projections on the channel base 72 second additional structure in the region of the fin tip 8 segment 9 local opening, pores, tubes 10 tube wall 11 internal structure