EP3465056B1 - Heat exchanger tube - Google Patents

Description

The present invention relates to a heat exchanger tube according to the preamble of claim 1.

Heat transfer occurs in many areas of refrigeration and air conditioning technology as well as in process and energy technology. Shell and tube heat exchangers are often used for heat transfer in these areas. In many applications, a liquid flows on the inside of the pipe, which is cooled or heated depending on the direction of the heat flow. The heat is given off to the medium on the outside of the pipe or withdrawn from it.

It is generally known that structured tubes are used in tube bundle heat exchangers instead of plain tubes. The heat transfer is improved by the structures. This increases the heat flow density and the heat exchanger can be made more compact. Alternatively, the heat flux density can be maintained and the driving temperature difference lowered, allowing for more energy-efficient heat transfer.

Heat exchanger tubes structured on one or both sides for tube bundle heat exchangers usually have at least one structured area as well as smooth end pieces and possibly smooth intermediate pieces. The smooth end or intermediate pieces delimit the structured areas. In order for the tube to be easily installed in the tube bundle heat exchanger, the outer diameter of the structured areas should not be larger than the outer diameter of the smooth end and intermediate pieces.

Integrally rolled finned tubes are often used as structured heat exchanger tubes. Integrally rolled finned tubes are understood to mean finned tubes in which the fins were formed from the material of the wall of a plain tube. In many cases, finned tubes have a large number of axially parallel or helically circumferential ribs on the inside of the tube, which increase the inner surface and improve the heat transfer coefficient on the inside of the tube. On the outside, the finned tubes have annular or helical fins running all the way around.

In the past, many options have been developed to further increase the heat transfer on the outside of integrally rolled finned tubes, depending on the application, by providing the fins on the outside of the tube with additional structural features. As for example from the pamphlet U.S. 5,775,411 It is known that when refrigerants condense on the outside of the tube, the heat transfer coefficient increases significantly if the fin flanks are provided with additional convex edges. When refrigerants evaporate on the outside of the tube, it has proven to improve performance if the channels located between the ribs are partially closed, resulting in cavities that are connected to the environment by pores or slits. As is already known from numerous publications, such essentially closed channels are formed by bending or folding over the rib ( U.S. 3,696,861 , U.S. 5,054,548 ), by splitting and upsetting the rib ( DE 2 758 526 C2 , U.S. 4,577,381 ) and by notching and upsetting the rib ( U.S. 4,660,630 , EP 0 713 072 B1 , U.S. 4,216,826 ) generated.

The above-mentioned performance improvements on the outside of the tube mean that the majority of the overall heat transfer resistance is shifted to the inside of the tube. This effect occurs in particular at low flow velocities on the inside of the pipe, such as during part-load operation. In order to significantly reduce the overall heat transfer resistance, it is necessary to reduce the heat transfer coefficient on the inside of the tube to increase further.

In order to increase the heat transfer on the inside of the tube, the axially parallel or helically circumferential inner ribs can be provided with grooves, as described in the publication DE 101 56 374 C1 and DE 10 2006 008 083 B4 is described. It is important here that the dimensions of the inner and outer structure of the finned tube can be set independently of one another by the use of profiled rolling mandrels disclosed there for producing the inner ribs and grooves. As a result, the structures on the outside and inside can be adapted to the respective requirements and the tube can be designed in this way.

The pamphlets U.S. 2005/0145377 A1 and WO03104735A1 disclose improved heat transfer surfaces that facilitate heat transfer from one side of the surface to the other. Described herein is another method of improving heat transfer surfaces by using a tool to cut the inner surface of a tube. The tool has at least one tip with a cutting edge and a lifting edge. Protrusions are formed by cutting the inner surface of a heat exchanger tube and raising the cut surface. Boiling surfaces produced in this way have a multiplicity of primary grooves, projections and secondary grooves, for example to form boiling cavities.

Furthermore, from the pamphlet U.S. 3,776,018 A a tube having a longitudinal axis and internal ribs extending obliquely to the axis and indented to form a plurality of fins on the ribs. Also a method of making such a tube from a round inner fin tube blank by partially flattening the blank to press opposing ones together Scoring and then expanding the partially flattened blank by internal fluid pressure is described.

Against this background, the object of the present invention is to further develop the internal and external structures of heat exchanger tubes of the aforementioned type in such a way that a further increase in performance is achieved compared to tubes that are already known.

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

In this case, the structured area can in principle be formed on the outside of the tube or the inside of the tube. However, it is preferred to arrange the rib sections according to the invention inside the pipe. The structures described can be used for both evaporator and condenser tubes.

Protrusion height is conveniently defined as the dimension of a protrusion in the radial direction. The height of the projection is then, in the radial direction, the distance starting from the pipe wall to the point of the projection which is furthest away from the pipe wall.

The cutting depth, also known as the notch depth, is the distance measured in the radial direction from the original tip of the rib to the deepest point of the notch. In other words: the notch depth is the difference between the original rib height and the remaining rib height at the deepest point of a notch.

The invention is based on the consideration that the rib sections can in principle be formed on the outside of the tube or the inside of the tube. However, it is preferred to arrange the rib sections according to the invention inside the pipe. The structures described can be used for both evaporator and condenser tubes.

The rib sections according to the invention are particularly suitable for internal structures. Here, the inner surface of the tube is enlarged with a plurality of projections divided into rib portions. As a result, the heat transfer resistance on the pipe side is reduced considerably and the heat transfer coefficient is increased. The projections create additional Pathways for fluid flow within the tube, thereby increasing the turbulence of the heat transfer medium flowing within the tube. This measure reduces the boundary layer built up from the fluid near the inner surface of the tube.

Compared to smooth surfaces, the projections provide a multiple of additional surface area for additional heat exchange. Tests show that the performance of tubes with the specially designed fin sections of this invention is significantly increased.

The process-side structuring of the heat exchanger tube according to the invention can be produced using a tool which in the DE 603 17 506 T2 is already described. The disclosure of this publication DE 603 17 506 T2 is fully included in the available documents. As a result, the projection height and the distance can be made variable and individually adapted to the requirements, for example the viscosity of the liquid or the flow rate.

The tool used has a cutting edge for cutting through the ribs on the inner surface of the tube to create rib segments and a lifting edge for raising the rib segments to form the projections. In this way, the protrusions are formed without removing metal from the inner surface of the tube. The protrusions on the inner surface of the tube may be formed in the same or different processing as the formation of the ribs.

The structuring of the axis-parallel or helically circumferential ribs running continuously from the tube wall with the primary grooves extending continuously between adjacent ribs can be done with the DE 101 56 374 C1 described procedural measures are produced.

The solution according to the invention, in which the ribs are divided into rib sections, which are divided into a plurality of projections with a projection height, causes the projections to deviate from the regulated order. This in turn results in optimized heat transfer with the lowest possible pressure loss, since the fluid boundary layer, which is a hindrance to good heat transfer, is interrupted by additionally generated turbulence. An interruption caused by the division of the projections also leads to an increase in turbulence and to an exchange of fluid over the course of the primary rib, which also causes an interruption in the boundary layer. In this case, the structured area can in principle be formed on the outside of the tube or the inside of the tube. However, it is preferred to arrange the rib sections according to the invention inside the pipe. The structures described can be used for both evaporator and condenser tubes.

A homogeneous arrangement of the projections can only partially achieve this targeted interruption of the boundary layer. The shapes, heights and arrangement of the distances can be adjusted and optimized by adjusting the cutting blades or cutting geometries and by individually adapted primary rib shapes and geometries. In order to optimize the fluid flow, the shape of the projections can be individually adjusted and the boundary layer can thus be broken efficiently. These optimizations for the turbulent or laminar flow form are realized by different projection heights.

In a preferred embodiment of the invention, the rib sections of the ribs can be formed from the ribs of secondary grooves running at a pitch angle β, measured against the longitudinal axis of the pipe.

Here, the secondary grooves can run at a pitch angle of at least 10° and at most 80° relative to the inner ribs. The depth of the secondary grooves can vary and be at least 20% of the original rib height of the inner ribs. By incorporating the secondary grooves, the inner ribs no longer have a constant cross-section. If one follows the course of the inner ribs, then the cross-sectional shape of the inner ribs changes at the locations of the secondary grooves. The secondary grooves create additional vortices in the medium flowing on the pipe side and axial passage points in the area close to the wall, which further increases the heat transfer coefficient.

When the depth of the secondary grooves is equal to the height of the original internal ribs, spaced rib sections are formed on the inside of the tube as structural elements resembling truncated pyramids. A targeted adjustment is possible by applying secondary grooves, since the projections are formed only in the area in which the primary rib is still formed.

According to the invention, the projections have alternately changing cutting depths due to a rib.

With such a design, the height of the individual projections can be specifically adjusted and varied in relation to one another in order to dip into the different boundary layers of the flow up to the flow core, particularly in the case of laminar flow, through different rib heights and dissipate the heat to the tube wall. In this case, the cutting or notching depth can also extend through the entire original rib into the core wall.

A changing notch or cutting depth is also synonymous with the fact that the deepest point of the notch alternates and consequently changes the distance to the pipe wall. Equivalent to this is also that the respective deepest point of the Notches - here referred to as the notch base - alternate at a distance from the longitudinal axis of the pipe over successive notches in the direction of the ribs.

In this case, the indentations that are adjacent at least by a projection can vary in the indentation depth by at least 10%. More preferably, the variation in notch depth can be at least 20% or even 50%.

In an advantageous embodiment of the invention, at least one projection can project from the main alignment along the course of the ribs over the primary groove. This brings with it the advantage that the boundary layer formed in the space between the ribs is interrupted by this projection projecting into the primary groove, which results in improved heat transfer.

In an advantageous embodiment of the invention, the rib sections of the ribs can be elongated along the course of the ribs. Here, the ribs are divided into rib portions divided into a sufficient plurality of projections with a projection height. For example, a rib section comprises at least 3, preferably at least 4, projections. The rib sections can be spaced apart from one another, as a result of which passage points for the fluid are formed. This in turn results in optimized heat transfer with the lowest possible pressure loss, since the fluid boundary layer, which is a hindrance to good heat transfer, is interrupted by additionally generated turbulence. An interruption also leads to an increase in turbulence and to an exchange of fluid over the course of the primary rib, which also causes an interruption in the boundary layer.

Advantageously, a plurality of projections can have a surface parallel to the longitudinal axis of the tube at the point furthest away from the tube wall.

In a preferred embodiment of the invention, the projections in Projection height, shape and orientation vary with each other in order to adjust the height of the individual projections in a targeted manner and to vary them in relation to one another in order to immerse themselves in the different boundary layers of the flow up to the flow core and dissipate the heat to the pipe wall, especially in the case of laminar flow through different rib heights.

In a particularly preferred embodiment, a projection can have a pointed tip on the side facing away from the tube wall. This leads to optimized projection tip condensation in condenser tubes using two-phase fluids.

In a further advantageous embodiment of the invention, a projection can have a curved tip on the side facing away from the pipe wall, the local radius of curvature of which, starting from the pipe wall, is reduced with increasing distance. The advantage of this is that the condensate that forms at the tip of a projection is transported more quickly to the base of the ribs due to the convex curvature, thus optimizing the heat transfer during condensation. During the phase change, here in particular during the liquefaction, the main focus is on the liquefaction of the vapor and the discharge of the condensate away from the tip towards the bottom of the fins. A convexly curved projection forms an ideal basis for effective heat transfer. The base of the projection protrudes essentially radially from the tube wall.

In an advantageous embodiment of the invention, the projections can have a different shape and/or height from the beginning of the pipe along the longitudinal axis of the pipe to the opposite end of the pipe. The advantage of this is a targeted adjustment of the heat transfer from the beginning of the pipe to the end of the pipe.

Advantageously, the tips of at least two projections along touching or crossing each other along the course of the ribs; which is particularly advantageous in reversible operation during the phase change, since the projections for the liquefaction protrude far out of the condensate and form a kind of cavity for the evaporation.

In a preferred embodiment of the invention, the tips of at least two projections can touch or cross one another across the primary groove. This is particularly advantageous in reversible operation during the phase change, since the projections for the liquefaction protrude far out of the condensate and form a kind of cavity for the evaporation.

In a particularly preferred embodiment, at least one of the projections can be deformed in such a way that its tip touches the inside of the pipe or the outside of the pipe. This is advantageous in particular in reversible operation during the phase change, since the projections form a kind of cavity for the liquefaction for the evaporation and thus bubble nuclei.

Advantageously, the projections can be formed from ribs, with at least one of the ribs varying from one another in at least one of the characteristics of rib height, rib spacing, rib tip, rib spacing, rib opening angle and twist.

Exemplary embodiments of the invention are explained in more detail with reference to the schematic drawings.

Fig. 1

schematisch eine Schrägansicht eines Rohrausschnitts mit der erfindungsgemäßen Struktur auf der Rohrinnenseite;

Fig. 2

schematisch eine weitere Schrägansicht eines Rohrausschnitts mit der erfindungsgemäßen Innenstruktur mit Sekundärnut;

Fig. 3

schematisch einen Rippenabschnitt mit unterschiedlicher Kerbtiefe;

Fig. 4

schematisch einen Rippenabschnitt mit einem über die Primärnut kragenden Strukturelement;

Fig. 5

schematisch einen Rippenabschnitt mit einem in Rippenrichtung an der Spitze gekrümmten Vorsprung;

Fig. 6

schematisch einen Rippenabschnitt mit einem Vorsprung mit einer parallelen Fläche an der von der Rohrwand entferntesten Stelle;

Fig. 7

schematisch einen Rippenabschnitt mit zwei sich entlang dem Rippenverlauf sich gegenseitig berührenden Vorsprüngen;

Fig. 8

schematisch einen Rippenabschnitt mit zwei sich entlang dem Rippenverlauf sich gegenseitig überkreuzenden Vorsprüngen;

Fig. 9

schematisch einen Rippenabschnitt mit zwei sich über die Primärnut hinweg gegenseitig berührenden Vorsprüngen; und

Fig. 10

schematisch einen Rippenabschnitt mit zwei sich über die Primärnut hinweg gegenseitig überkreuzenden Vorsprüngen.

Show in it:

1

schematically an oblique view of a pipe section with the structure according to the invention on the inside of the pipe;

2

schematically another oblique view of a pipe section with the inner structure according to the invention with a secondary groove;

3

schematically a rib section with different notch depth;

4

schematically a rib section with a structural element projecting over the primary groove;

figure 5

schematically shows a rib section with a projection curved at the tip in the rib direction;

6

schematically a rib section with a projection with a parallel face at the farthest point from the tube wall;

7

schematically a rib section with two mutually touching projections along the course of the ribs;

8

schematically a rib section with two mutually crossing projections along the course of the ribs;

9

schematically a rib section with two mutually touching projections across the primary groove; and

10

schematically shows a rib section with two mutually crossing projections across the primary groove.

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

1 shows schematically an oblique view of a tube section of the heat exchanger tube 1 with the structure according to the invention on the tube inside 22. The heat exchanger tube 1 has a tube wall 2, a tube outside 21 and a tube inside 22 shaped. The longitudinal axis A of the tube runs at a certain angle relative to the ribs. Continuously extending primary grooves 4 are formed between each adjacent ribs 3 .

The ribs 3 are divided along the course of the ribs into periodically repeating rib sections 31 which are divided into a large number of projections 6 .

The protrusions 6 are formed by cutting the ribs 3 with a cutting depth across the rib run to form rib segments and raising the rib segments with a main orientation along the rib run between primary grooves 4 .

In 1 the rib portions 31 of the ribs 3 are elongated along the course of the ribs. In this case, a rib section 31 is delimited by an uncut portion of a rib 3 from the following one. The original height of the primary rib 3 can also be partially preserved there.

2 shows a further oblique view of a tube section of the heat exchanger tube 1 with the structure according to the invention on the tube inside 22 with a secondary groove 5. The ribs 3 are in turn divided along the course of the ribs into periodically repeating rib sections 31, which are divided into a large number of projections 6.

In 2 the rib sections 31 of the ribs 3 are in turn elongated along the course of the ribs. A rib section 31 is delimited from the following one by a secondary groove 5 running at a pitch angle β, measured against the longitudinal axis A of the pipe. The secondary groove 5 can have a small notch depth or, as in the exemplary embodiment shown, come close to the primary groove with a large notch depth.

3 1 shows schematically a rib section 31 with different cutting or notching depths t ₁ , t ₂ , t ₃ . The terms cutting depth and _{notch depth} represent the same _terminology within the scope of the invention. Dashed is indicated in the 3 the original formed helical circumferential rib 3. From this, the projections 6 are by cutting the rib 3 with a Cutting depth t ₁ , t ₂ , t ₃ transverse to the rib path to form rib segments and shaped by raising the rib segments with a major orientation along the rib path. The different cutting depths t ₁ , t ₂ , t ₃ are consequently dimensioned based on the indentation depth of the original rib in the radial direction.

The projection height h is in 2 is plotted as the dimension of a protrusion in the radial direction. The height h of the projection is then, in the radial direction, the distance starting from the pipe wall to the point of the projection which is furthest away from the pipe wall.

The notch depth t ₁ , t ₂ , t ₃ is the distance measured in the radial direction, starting from the original rib tip to the deepest point of the notch. In other words: the notch depth is the difference between the original rib height and the remaining rib height at the deepest point of a notch.

4 shows schematically a rib section 31 with a structural element 6 protruding over the primary groove 4. This is a projection 6 which extends from the main alignment with the tip 62 along the course of the rib over the primary groove 4. The further the projection is formed, the more the boundary layer of the fluid formed in the space between the ribs is disturbed, which results in improved heat transfer.

figure 5 shows schematically a rib section 31 with a projection 6 curved in the direction of the ribs at the tip 62. The projection 6 has a changing course of curvature at the curved tip 62. The local radius of curvature decreases with increasing distance from the pipe wall. In other words: the radius of curvature decreases towards the tip 62 along the line indicated by the points P1, P2, P3. This has the advantage that the condensate that forms at the tip 62 in the case of two-phase fluids is transported more quickly to the base of the ribs due to the increasing convex curvature.

This optimizes the heat transfer during liquefaction.

6 shows schematically a fin section 31 with a projection 6 with a parallel surface 61 at the point furthest from the tube wall in the area of the tip 62.

7 FIG. 1 schematically shows a rib section 31 with two projections 6 touching one another along the course of the rib. FIG 8 schematically a rib section 31 with two along the course of the ribs mutually crossing projections 6. Also 9 FIG. 12 shows schematically a rib section 31 with two projections touching each other across the primary groove 4. FIG. 10 shows schematically a rib section 31 with two mutually crossing projections 6 over the primary groove 4.

At the in the Figures 7 to 10 The structural elements shown are advantageous, especially in reversible operation with two-phase fluids, that they form a kind of cavity for evaporation. The cavities of this special type form the exit points for bubble nuclei of an evaporating fluid.

Reference List

1

heat exchanger tube

2

pipe wall

21

pipe exterior

22

pipe inside

3

rib

31

rib section

4

primary groove

5

secondary groove

6

head Start

61

parallel surface

62

Top

A

longitudinal axis of the pipe

β

pitch angle

t1

first cutting depth

t2

second cutting depth

t3

third cutting depth

H

protrusion height

Claims (13)

1. Heat transfer pipe (1) having a longitudinal pipe axis (A), a pipe wall (2), an outer pipe side (21) and an inner pipe side (22), wherein

   - continually extending, axially parallel or helically circumferential ribs (3) are formed from the pipe wall (2) at the outer pipe side (21) and/or inner pipe side (22),

   - continuously extending primary grooves (4) are formed in each case between adjacent ribs (3),

   wherein the ribs (3) are subdivided along the rib extent into periodically repeating rib portions (31) which are separated into a large number of projections (6) with a projection height (h), wherein the projections (6) are formed by cutting the ribs (3) at a cutting depth (t₁, t₂, t₃) transversely relative to the rib extent in order to form rib segments and by raising the rib segments with a main orientation along the rib extent between primary grooves (4), characterised in that the projections (6) have alternately changing cutting depths (t₁, t₂, t₃) through a rib (3).
2. Heat transfer pipe (1) according to claim 1, characterised in that the rib portions (31) of the ribs (3) are formed from the ribs (3) by secondary grooves (5) which extend at an angle of inclination β measured with respect to the longitudinal pipe axis (A).
3. Heat transfer pipe (1) according to claim 1 or 2, characterised in that at least one projection (6) protrudes from the main orientation along the rib extent over the primary groove (4).
4. Heat transfer pipe (1) according to claim 2 or 3, characterised in that the rib portions (31) of the ribs (3) are constructed to be elongate along the rib extent.
5. Heat transfer pipe (1) according to any one of claims 1 to 4, characterised in that a plurality of projections (6) have at the location furthest away from the pipe wall (2) a face (61) which is parallel with the longitudinal pipe axis (A).
6. Heat transfer pipe (1) according to any one of claims 1 to 5, characterised in that the projections (6) vary relative to each other in terms of projection height (h), shape and orientation.
7. Heat transfer pipe (1) according to any one of claims 1 to 6, characterised in that a projection (6) has an acutely tapering tip (62) at the side facing away from the pipe wall (2) .
8. Heat transfer pipe (1) according to any one of claims 1 to 7, characterised in that a projection (6) at the side facing away from the pipe wall (2) has a curved tip (62) whose local radius of curvature is reduced with increasing spacing from the pipe wall (2).
9. Heat transfer pipe (1) according to any one of claims 1 to 8, characterised in that the projections (6) have a different shape and/or height from a pipe beginning along the longitudinal pipe axis (A) towards the opposing pipe end.
10. Heat transfer pipe (1) according to either claim 7 or claim 8, characterised in that the tips (62) of at least two projections (6) touch or intersect each other along the rib extent.
11. Heat transfer pipe (1) according to either claim 7 or claim 8, characterised in that the tips (62) of at least two projections (6) touch or intersect each other over the primary groove (4).
12. Heat transfer pipe (1) according to either claim 7 or claim 8, characterised in that at least one of the projections (6) is formed in such a manner that the tip (62) thereof touches the inner pipe side (22) or the outer pipe side.
13. Heat transfer pipe (1) according to any one of claims 1 to 12, characterised in that the projections (6) are formed from ribs (3), wherein at least one of the ribs (3) varies relative to the others in terms of at least one of the features rib height, rib spacing, rib tip, intermediate rib space, rib opening angle and torsion.

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