EP3111153B1 - Metal heat exchanger tube - Google Patents

Description

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

Such a heat exchanger tube is for example from EP 0 495 453 A1 known.

Evaporation occurs in many areas of refrigeration and air conditioning technology as well as in process and energy technology. Frequently, shell-and-tube heat exchangers are used in which liquids of pure substances or mixtures evaporate on the outside of the pipe, cooling a brine or water on the inside of the pipe. Such apparatuses are referred to as flooded evaporators.

By intensifying the heat transfer on the pipe outside and inside the pipe, the size of the evaporator can be greatly reduced. As a result, the production costs of such apparatuses decrease. In addition, the necessary filling quantity of refrigerant, which can account for a not inconsiderable share of the total system costs in the now predominantly used chlorine-free safety refrigerants, drops. In addition, today's conventional high-performance pipes are already about four times more efficient than smooth pipes of the same diameter.

The most powerful commercially available finned tube finned tubes have on the tube exterior a ribbed structure with a fin density of 55 to 60 fins per inch ( US 5,669,441 A ; US 5,697,430 A ; DE 197 57 526 C1 ). This corresponds to a rib pitch of about 0.45 to 0.40 mm.

Furthermore, it is known that performance-enhanced evaporation structures can be produced with the same fin pitch on the outside of the tube by introducing additional structural elements in the region of the groove bottom between the ribs.

In EP 1 223 400 B1 It is proposed to produce at the groove bottom between the ribs undercut secondary grooves which extend continuously along the primary groove. The cross section of these secondary grooves can remain constant or varied at regular intervals.

In addition are out DE 10 2008 013 929 B3 Structures known at the bottom of the groove, which are designed as local cavities, which is intensified to increase the heat transfer during evaporation of the process of bubbling. The location of the cavities in the vicinity of the primary groove bottom is favorable for the evaporation process, since the excess temperature is greatest at the bottom of the groove and therefore the highest driving temperature difference is available there for bubble formation.

Further examples of structures at the groove bottom are in EP 0 222 100 B1 . US 7,254,964 B2 or US 5,186,252 A to find. These structures have in common that the structural elements on Nutengrund have no undercut shape. These are either impressions made in the groove base or projections in the lower part of the channel. Higher protrusions are explicitly excluded in the prior art, since it would be feared that the fluid flow in the channel for heat exchange is adversely affected.

The invention has the object of developing a performance-enhanced heat exchanger tube for the evaporation of liquids on the outside of the tube.

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

The invention includes a metallic heat exchanger tube having integrally ribbed, ribbed and ribbed ribs formed on the tube exterior, the rib stem projecting substantially radially from the tube wall and a channel formed between the ribs in which spaced apart additional structures are disposed. The additional structures divide the channel between the ribs into segments. The additional structures locally reduce the flow-through cross-sectional area in the channel between two ribs by at least 60% and at least limit a fluid flow in the channel during operation.

These metallic heat exchanger tubes are used in particular for the evaporation of liquids from pure substances or mixtures on the tube outside.

Such efficient tubes can be manufactured on the basis of integrally rolled finned tubes. Integrally rolled finned tubes are understood to mean finned tubes in which the fins are formed from the wall material of a smooth tube. Typical integral ribs formed on the outside of the pipe are, for example, spirally encircling and have a fin root, rib flanks and fin tip, wherein the rib root protrudes substantially radially from the pipe wall. The number of ribs is determined by counting successive bulges in the axial direction of a tube.

Here, various methods are known with which the channels located between adjacent ribs are closed in such a way that Connections between channel and environment remain in the form of pores or slits. In particular, such substantially closed channels are created by bending or flipping the ribs, splitting and upsetting the ribs, or notching and upsetting the ribs.

The invention is based on the consideration that the rib gap is segmented by additional structures to increase the heat transfer during evaporation. The additional structures can be formed at least partially from material of the pipe wall solid from the channel bottom. In this case, the additional structures are preferably arranged at regular intervals starting from the channel base and extend transversely to the channel course, starting from a ribbed foot of a rib to the adjacent next ribbed foot. The additional structures can extend radially from the rib foot to the rib flank and beyond. In other words, the additional structures extend, starting from the channel bottom, for example, as massive material projections transversely to the primary groove and separate them, as a weir as only partially überströmbare cross-barrier, into individual segments. In this way, the primary groove is at least partially subdivided as a channel at regular intervals already starting from the channel base.

As a result, local overheating be generated in the interstices and intensified the process of bubble boiling. The formation of bubbles then takes place primarily within the segments and begins at germinal sites. Initially, small gas or vapor bubbles form at these nucleation sites. When the growing bubble reaches a certain size, it detaches from the surface. In the course of the bladder detachment, the remaining cavity in the segment is flooded with liquid again and the cycle begins again. The surface can be designed such that upon detachment of the bubble, a small bubble remains, which then serves as a germination point for a new cycle of bubble formation.

In the present invention is interrupted by the segmentation of the channel between two ribs in the circumferential direction over again and again and thus the migration of the resulting bubbles in the channel at least reduced or completely prevented. An exchange of liquid and vapor along the channel is increasingly less supported by the respective additional structure to no longer.

The particular advantage of the invention is that the exchange of liquid and steam controlled locally targeted and the flooding of the nucleation site in the segment takes place locally. Overall, the evaporator tube structures can be optimized in a targeted manner as a function of the application parameters by a targeted choice of the channel segmentation, whereby an increase of the heat transfer is achieved. Since the temperature of the rib foot is higher in the region of the groove bottom than at the rib tip, structural elements for intensifying the formation of bubbles in the groove base are also particularly effective.

In addition, it is also possible that the additional structures locally reduce the flow-through cross-sectional area in the channel between two ribs by at least 80%. Overall, by an increasing separation of individual channel sections in the channel segmentation, the evaporator tube structures can be further optimized depending on the application parameters to increase the heat transfer.

In an advantageous embodiment of the invention, the additional structures can complete the flow-through cross-sectional area in the channel between two ribs locally completely. In this way, the segments are completely closed locally for a fluid passage. The channel section lying between two segments is thus separated from the adjacent channel sections on the fluid side.

In a preferred embodiment of the invention, the channel can be completed radially outward to individual local openings. In this case, the ribs may have a substantially T-shaped or Γ-shaped cross-section, whereby the channel between the ribs is closed except for pores as local openings. Through these openings, the resulting vapor bubbles in the evaporation process can escape. The deformation of the rib tips is done with methods that can be found in the prior art.

The combination of the segments according to the invention with a channel which is closed except for pores or slots gives a structure which has a very high efficiency in the evaporation of liquids over a very wide range of operating conditions. In particular, when the heat flow density or the driving temperature difference is varied, the heat transfer coefficient of the structure reaches a consistently high level.

In an advantageous embodiment of the invention, at least one local opening per segment may be present. This minimum requirement still ensures that gas bubbles which form in a channel segment during the evaporation process can escape to the outside. The local openings are designed in size and shape so that even liquid medium can pass and flow into the channel section. Thus, to maintain the vaporization process at a local orifice, the same quantities of liquid and vapor must be transported through the orifice in mutually opposite directions. Usually liquids are used, which wet the pipe material well. Such a liquid can penetrate into the channels due to the capillary effect through each opening in the outer tube surface against an overpressure.

In a particularly preferred embodiment, the quotient of the number of local openings to the number of segments can be 1: 1 to 6: 1. Further preferred may this quotient is 1: 1 to 3: 1. The channels located between the ribs are substantially closed by material of the upper rib areas, the resulting cavities of the channel segments being connected by openings to the surrounding space. These openings can also be designed as pores, which can be designed in the same size or in two or more size classes. In a ratio in which a plurality of local openings are formed on a segment, especially pores with two size classes may be suitable. For example, following a regular, repetitive pattern, each channel is followed by a large opening along the channels. This structure creates a directional flow in the channels. Liquid is preferentially drawn through the small pores with the aid of capillary pressure and wets the channel walls, producing thin films. The vapor accumulates in the center of the channel and escapes at the lowest capillary pressure points. At the same time, the large pores must be dimensioned so that the steam can escape sufficiently quickly and the channels do not dry out. The size and frequency of the vapor pores in relation to the smaller liquid pores are then matched.

Advantageously, the first additional structures may be outwardly projecting radially outward protrusions from the channel bottom. As a result, the exchange of liquid and steam is determined locally. The segmentation of the channel over the groove base is particularly favorable for the evaporation process, since the excess temperature is greatest at the bottom of the groove and therefore there is the highest driving temperature difference for the bubble formation available.

In a preferred embodiment of the invention, the first additional structures may be formed at least from material of the channel bottom between two integrally encircling ribs. This leaves a cohesive Get a connection for a good heat exchange from the pipe wall into the respective structural elements. The segmentation of the channel from a uniform material of the channel bottom is particularly favorable for the evaporation process.

In a particularly preferred embodiment, the first additional structures formed from the channel base may have a height between 0.15 and 1 mm. This dimensioning of the additional structures is particularly well matched to the high-performance finned tubes and expresses that the structure sizes of the outer structures are preferably in the submillimeter to millimeter range.

In a further advantageous embodiment of the invention, second additional structures can be formed at least from the rib flanks of the integrally encircling ribs via lateral protrusions. This may be performed alternatively or in addition to further projections from the channel base material.

In a preferred embodiment of the invention, the second additional structures can be formed, starting at least from one rib from the fin tip, in the direction of the channel bottom. Consequently, the channel can also be tapered or completely closed by a desired amount from a combination of several complementary structural elements from below and / or from the side and / or from above. In any case, so that the channel between the ribs is divided into discrete segments.

In a further supplementary embodiment, additional structures can be introduced at least partially via additional material. Additional material may be in nature and in relation to the interaction with the fluid selected for operation from the material of the remaining heat exchanger tube differ. For example, it is also contemplated to use materials with different surface properties compared to the fluid used.

Advantageously, the additional structures may have asymmetrical shapes. The asymmetry of the structures appears here in a plane perpendicular to the tube axis cutting plane. Asymmetrical shapes, especially if a larger surface is formed, can make an additional contribution to the evaporation process. The asymmetry can be pronounced both at additional structures at the channel bottom as well as at the rib tip.

In a preferred embodiment of the invention, the additional structures can have a trapezoidal cross section in a sectional plane running perpendicular to the tube axis. Trapezoidal cross sections are in the context of integrally rolled finned tube structures technologically well controllable structural elements. Minor manufacturing-related asymmetries of the otherwise parallel bases of a trapezoid can occur here.

Advantageously, the respective reduced by cross-sectional structures, durchströmbare cross-sectional area in the channel between two ribs vary. In this way, more or less continuous areas can be created locally in the channel. For this purpose, for example, additional structures may have a different height at the channel bottom.

Embodiments of the invention will be explained in more detail with reference to the schematic drawings.

Fig. 1

schematisch eine Teilansicht eines Querschnitts eines Wärmeaustauscherrohrs mit durch Zusatzstrukturen unterteilten Segmenten,

Fig. 2

schematisch eine Teilansicht eines Querschnitts eines weiteren Wärmeaustauscherrohrs mit variierten Zusatzstrukturen im Bereich der Rippenspitze, und

Fig. 3

schematisch eine Teilansicht eines Querschnitts eines Wärmeaustauscherrohrs mit nahezu abgeschlossenen Segmenten.

Show:

Fig. 1

1 is a schematic partial view of a cross section of a heat exchanger tube with segments divided by additional structures;

Fig. 2

schematically a partial view of a cross section of another heat exchanger tube with varied additional structures in the rib tip, and

Fig. 3

schematically a partial view of a cross section of a heat exchanger tube with almost closed segments.

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

Fig. 1 schematically shows a partial view of a cross section of a heat exchanger tube 1 according to the invention divided by additional structures 7 segments 8. The integrally rolled heat exchanger tube 1 has on the outside of the tube helically encircling ribs 2, between which a primary groove is formed as a channel 6. The ribs 2 extend continuously without interruption along a helix line on the tube outside. The ribbed foot 3 projects essentially radially from the tube wall 10. The rib height H is measured on the finished heat exchanger tube 1 from the lowest point of the channel base 61, starting from the ribbed foot 3 over the rib flank 4, to the fin tip 5 of the completely shaped 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 bottom 61. These protrusions 71 are referred to as the first additional structure and formed of material of the tube wall 10 from the channel base 61. The solid projections 71 are arranged at preferably regular intervals in the channel base 61 and extend transversely to the channel profile of a fin 3 of a rib 2 for in the plane of the figure not shown above next rib foot. In this way, the primary groove is at least partially tapered as a channel 6 at regular intervals. The resulting segment 8 favors bubble nucleation in a special way. The exchange of liquid and vapor between the individual segments 8 is thereby reduced.

In addition to the formation of the projections 71 on the channel base 61, the rib tips 5 are expediently deformed as the distal region of the ribs 2 in such a way that they partly 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 deformation of the rib tips 5 is done with methods that can be found in the prior art. The primary grooves 6 in this way represent undercut grooves. The combination of the first and second additional structures 71 and 72 according to the invention results in a segment 8 in the form of a cavity which is further characterized in that it over a very wide range of operating conditions a very high performance in evaporation of liquids. The liquid evaporates within the segment 8. The resulting vapor exits the channel 6 at the local openings 9, through which liquid fluid also flows. For subsequent flow of the fluid also well wettable pipe surfaces can be of help.

Fig. 2 schematically shows a partial view of a cross section of another heat exchanger tube 1 with varied second additional structures 72 in the region of the rib tip 5. In addition to the formation of the projections 71 on the channel base 61 again the rib tips 5 are deformed as a distal portion of the ribs 2 so that they the channel 6 in Partially close the radial direction as a further second additional structure 72. The connection between the channel 6 and the environment is in the form of inclined tubes as local openings 9 designed for the escape of vapor bubbles from the channel 6 and inflow of liquid fluid into the channel 6. The primary grooves 6 in this way in turn represent undercut grooves. The second additional structure 72 is formed starting from a rib from the fin tip 5 in the direction of the channel base 61 and protrudes in the radial direction into the channel 6. As soon as a first and a second additional structure overlap one another radially, the through-flow cross-sectional area in the channel 6 between two ribs 2 reduces locally particularly effectively, thereby limiting the fluid flow in the channel 6 during operation.

Fig. 3 schematically shows a partial view of a cross section of a heat exchanger tube 1 with the additional structures 7 Fig. 2 , The second additional structures 72 protrude almost into the projections of the first additional structures 71 into the channel 6, so that almost complete segments 8 form. In this case, the quotient of the number of local openings 9 to the number of segments 8 in the preferred interval is 1: 1 to 3: 1 and is on average about 1.7: 1 to 2.3: 1. Here, all formed as tubes local openings 9 are still continuous, even if an opening 9 comes to rest on a projection 71. The resulting steam can still escape at the local openings 9 from the channel 6. Due to its surface tension, the liquid fluid can flow in the tubes 9 in a particularly efficient manner by means of capillary action.

The combination of the first and second additional structures 71 and 72 according to the invention results in a segment 8 in the form of a cavity, which is further characterized by having a very high performance in the evaporation of liquids over a very wide range of operating conditions. In particular, when the heat flow density or the driving temperature difference is varied, the heat transfer coefficient of the structure at a high level remains almost constant. The inventive Solution refers to structured pipes where the heat transfer coefficient on the outside of the pipe is increased. In order not to shift the majority of the heat transfer resistance to the inside, the heat transfer coefficient can be intensified on the inside by a suitable internal structure 11 also. The heat exchanger tubes 1 for shell-and-tube heat exchangers usually have at least one structured region and smooth end pieces and possibly smooth intermediate pieces. The smooth end or intermediate pieces limit the structured areas. So that the heat exchanger tube 1 can be easily installed in the tube bundle heat exchanger, the outer diameter of the structured areas must not be greater than the outer diameter of the smooth end and intermediate pieces.

LIST OF REFERENCE NUMBERS

1

heat exchanger tube

2

ribs

3

fin base

4

rib flank

5

Rib tip, distal regions of the ribs

6

Channel, primary groove

61

channel base

7

additional structures

71

first additional structure as overhangs at the channel bottom

72

second additional structure in the area of the rib tip

8th

segment

9

local opening, pores, tubes

10

pipe wall

11

internal structure

Claims (15)

1. Metal heat exchanger pipe (1), having integral ribs (2) which are formed on the outer side of the pipe and which have a rib base (3), rib flanks (4) and a rib tip (5), wherein the rib base (3) protrudes substantially radially from the pipe wall and there is formed between the ribs (2) a channel (6) in which there are arranged additional structures (7, 71, 72) which are spaced apart from each other and which are arranged so as to extend least partially from the channel base (61) and which extend transversely relative to the path of the channel (6),
   characterised in that

   - the additional structures (7, 71, 72) divide the channel (6) between the ribs (2) into segments (8), and

   - in that the additional structures (7, 71, 72) reduce the cross-sectional surface-area through which it is possible to flow in the channel (6) between two ribs (2) locally by at least 60% and thereby during operation at least to limit a fluid flow in the channel (6).
2. Heat exchanger pipe (1) according to claim 1, characterised in that the additional structures (7, 71, 72) reduce the cross-sectional surface-area through which it is possible to flow in the channel (6) between two ribs (2) locally by at least 80%.
3. Heat exchanger pipe (1) according to claim 2, characterised in that the additional structures (7, 71, 72) locally completely close the cross-sectional surface-area through which it is possible to flow in the channel (6) between two ribs (2).
4. Heat exchanger pipe (1) according to any one of claims 1 to 3, characterised in that the channel (6) is closed at the radially outer side with the exception of individual local openings (9).
5. Heat exchanger pipe (1) according to any one of claims 1 to 4, characterised in that at least one local opening (9) is provided per segment (8).
6. Heat exchanger pipe (1) according to any one of claims 1 to 5, characterised in that the quotient of the number of local openings (9) to the number of segments (8) is from 1:1 to 6:1.
7. Heat exchanger pipe (1) according to any one of claims 1 to 6, characterised in that first additional structures (7, 71) are radially outwardly directed protrusions extending from the channel base (61).
8. Heat exchanger pipe (1) according to any one of claims 1 to 7, characterised in that the first additional structures (7, 71) are formed at least from the material of the channel base (61) between two integrally circumferential ribs (2).
9. Heat exchanger pipe (1) according to claim 8, characterised in that the first additional structures (7, 71) which are formed from the channel base (61) have a height between 0.15 and 1 mm.
10. Heat exchanger pipe (1) according to any one of claims 1 to 7, characterised in that second additional structures (7, 72) are formed at least from the rib flanks (4) or rib tips (5) of the integrally circumferential ribs (2) by means of lateral protrusions.
11. Heat exchanger pipe (1) according to claim 10, characterised in that the second additional structures (7, 72) are formed at least from a rib extending from the rib tip (6) in the direction towards the channel base (61).
12. Heat exchanger pipe (1) according to any one of claims 1 to 11, characterised in that additional structures (7) are introduced at least partially by means of additional material.
13. Heat exchanger pipe (1) according to any one of claims 1 to 12, characterised in that the additional structures (7, 72) have asymmetrical shapes.
14. Heat exchanger pipe (1) according to any one of claims 1 to 12, characterised in that additional structures (7, 71) have a trapezoidal cross-section in a plane of section which extends perpendicularly to the pipe axis.
15. Heat exchanger pipe (1) according to any one of claims 1 to 14, characterised in that the respective cross-sectional surface-area through which it is possible to flow in the channel (6) and which is reduced by additional structures (7, 71) varies between two ribs (2).

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