EP3465055B1 - 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 The heat is given off to the medium on the outside of the pipe or withdrawn from it.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. The outside diameter of the structured areas should not be larger than the outside so that the tube can be easily installed in the tube bundle heat exchanger Diameter of 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. To significantly increase the overall heat transfer resistance reduce, it is necessary to further increase the heat transfer coefficient on the inside of the tube.

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 adjusted 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 U.S. 03/104736 A1 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.

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 and the inside of the tube. However, according to the invention, the rib sections according to the invention are to be arranged 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 notch depth is the distance measured in the radial direction 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.

A changing notch depth is also synonymous with the fact that the deepest point of the notch alternates and consequently changes the distance to the pipe wall. Equally important here is that the respective deepest point of the notches, which in this context is referred to as the notch base, alternates at a distance from the longitudinal axis of the pipe over successive notches in the direction of the ribs.

The invention is based on the consideration that a different notch depth essentially results in a different height, orientation and shape of the projections relative to one another. It follows that the Projections deviate from a regulated order. This requires an optimized heat transfer with the lowest possible pressure loss in the single-phase flow, since the fluid boundary layer, which is an obstacle to good heat transfer, is interrupted by additionally generated turbulence. Compared to a uniform, homogeneous arrangement of the projections, this targeted interruption of the boundary layer has a particularly positive effect on the heat transfer coefficient. The shapes, heights and arrangement of the projections can be adjusted by setting suitable cutting knives or cutting geometries and by individually adapted rib shapes and geometries.

In the laminar flow area, on the other hand, the projections cause irregular immersion in the laminar flow core and thus optimized heat conduction from the tube wall into the laminar flow core or from the laminar flow core to the tube wall. These optimizations for the turbulent and laminar flow form are realized by the different cutting depths and orientation of the projections according to the solution according to the invention.

According to the invention, the indentations that are adjacent at least by one projection vary in the indentation depth by at least 10%.

More preferably, the variation in notch depth can be at least 20% or even 50%. This results in projections of different heights, which in turn lead to an interruption in the boundary layer and to an increase in turbulence and thus to an increase in the heat transfer coefficient.

In an advantageous embodiment of the invention, the maximum notch depth can extend as far as the pipe wall. This breaks the boundary layer and increases turbulence. This leads to a Increase in the heat transfer coefficient. Indentations that extend into the tube wall tend to be disadvantageous and can lead to an undesirable weakening of the material in the tube wall without, in return, having a significantly further positive effect on the heat transfer coefficient.

According to the invention, the indentations may be formed by cutting the inner ribs with a cutting depth transverse to the rib path to form layers of ribs and raising the layers of ribs with a main orientation along the rib path between primary grooves.

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 reference 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 fins on the inner surface of the tube to create layers of fins and a lifting edge for lifting the layers of fins 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.

In this way, the protrusion height and distance can be made variable and individually adapted to the requirements of the fluid in question, for example with regard to the viscosity of the liquid and the flow rate.

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

Advantageously, the sections of the rib are unchanged between the groups. Further positive influences on the heat transfer through the interruption of the boundary layer can be derived from this, since different divisions / groupings and alternating rib shapes increase the effect described above.

In a preferred embodiment of the invention, 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 particularly preferred embodiment, the projections can vary in projection height, shape and orientation. As a result, the individual projections can be specifically adapted to one another and varied in relation to one another in order to dip into the different boundary layers of the flow, especially in the case of laminar flow, through different rib heights, in order to dissipate the heat to the tube wall. This means that the height of the protrusion and the distance can be individually adapted to the requirements, e.g. viscosity of the fluid, flow rate, etc.

In a further advantageous embodiment of the invention, a projection can have a pointed tip on the side facing away from the tube wall. This results in optimized tip condensation for condenser tubes using two-phase fluids.

In a further advantageous embodiment of the invention, a projection on the of have a curved tip on the side facing away from the pipe wall, the local radius of curvature of which is reduced starting from the pipe wall 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 liquefaction. 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 can touch or cross one another along the course of the ribs; which is particularly advantageous in reversible operation during 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, in turn, is advantageous in reversible operation during the phase change, since the projections for the liquefaction protrude far out of the condensate and form a type of cavity for the evaporation.

In a particularly preferred embodiment, at least one of the projections be deformed in such a way that its tip touches the inside or 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 nucleation sites. This leads to increased heat transfer coefficients during the evaporation process.

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 einen Rippenabschnitt mit unterschiedlicher Kerbtiefe;

Fig. 3

schematisch einen Rippenabschnitt mit einem über die Primärnut kragenden Strukturelement;

Fig. 4

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

Fig. 5

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

Fig. 6

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

Fig. 7

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

Fig. 8

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

Fig. 9

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 a rib section with different notch depth;

3

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

4

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

figure 5

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

6

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

7

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

8

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

9

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 3 . Continuously extending primary grooves 4 are formed between each adjacent ribs 3 .

The projections 6 are arranged in groups 10 which are periodically repeated along the rib path. The projections 6 are formed by cutting the ribs 3 with a cutting depth transverse to the rib path to form layers of ribs and by raising the layers of ribs with a main orientation along the rib path between primary grooves 4 . The indentations 7 are formed in a rib 3 between the projections 6 within the group 10 with an alternating indentation depth.

2 shows schematically a rib section 31 with different cutting or notching depths t ₁ , t ₂ , t ₃ . Within the scope of the _invention , the terms _cutting depth and _notch depth represent the same terminology. Dashed is indicated in the 2 the original formed helical circumferential rib 3. From this the projections 6 are cut by cutting the rib 3 with a notch/cutting depth t ₁ , t ₂ , t ₃ transverse to the rib path to form rib layers and by raising the rib layers with a main orientation along the rib path shaped. The different notch/cutting depths t ₁ , t ₂ , t ₃ are consequently dimensioned based on the notch 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 projection height h is then in the radial direction Distance starting from the tube wall to the point of the projection that is furthest away from the tube 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.

3 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.

4 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 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.

figure 5 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.

The in the Figures 3 to 5 Rib portions 31 shown can in the respective Groups can be involved individually or in larger numbers.

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

At the in the Figures 6 to 9 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

6

head Start

61

parallel surface

62

Top

7

notches

10

group of projections

A

longitudinal axis of the pipe

t1

first cutting depth

t2

second cutting depth

t3

third cutting depth

H

protrusion height

Claims (12)

1. Heat transfer pipe (1) having a longitudinal pipe axis (A), wherein

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

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

   - the ribs (3) have at least one structured region at the inner pipe side (22),

   - the structured region has a plurality of projections (6) which protrude from the surface and which have a projection height (h),

   wherein adjacent projections (6) are separated by means of notches (7), wherein the projections (6) are arranged in groups (10) which are repeated periodically along the rib path,

   - the notches (7) are formed by cutting the inner ribs (3) with a cutting depth (t₁, t₂, t₃) transversely relative to the rib path in order to form rib layers and by raising the rib layers with a main orientation along the rib path between primary grooves (4), characterised in that

   - at least two notches (7) are formed between the projections (6) within the group (10) with a changing notch depth (t₁, t₂, t₃) in a rib (3), and

   - in that the notches (7) which are spaced apart by at least one projection (6) vary in terms of the notch depth (t₁, t₂, t₃) by at least 10%.
2. Heat transfer pipe (1) according to claim 1, characterised in that the largest notch depth (t₁, t₂, t₃) extends at a maximum as far as the pipe wall (2).
3. Heat transfer pipe (1) according to claim 1 or 2, characterised in that at least one projection (6) projects from the main orientation along the rib path over the primary groove (4).
4. Heat transfer pipe (1) according to any one of claims 1 to 3, characterised in that a part-portion (31) of the rib (3) is in an unchanged state between the groups (10).
5. Heat transfer pipe (1) according to any one of claims 1 to 4, characterised in that a plurality of projections (6) at the location furthest away from the pipe wall (2) have 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 each other or intersect along the rib path.
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 each other or intersect 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.

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