EP0733871A1 - Heat transfer tube for a heat exchanger - Google Patents

Abstract

The pipe (1) has a smooth outer surface (2) and a structured inner surface (3) having parallel ribs (7) running at an angle ( alpha ) of 90 degrees to the longitudinal axis (6) of the exchange pipe. The ribs have sloping flanges (8) and form channels (13) and cross running troughs (14). The middle longitudinal plane of the troughs runs at 90 degrees to the longitudinal axis of the exchange pipe. The troughs have a sine curve formed shape in their longitudinal cross-section and are formed with a micro roughness (16) upper surface (8,10,11) and have rounded ribbed (7) heads. The oppositely lying, neighbouring ribs of the flanges are connected to the channel soles (12) by rounded transitions (11).

Description

The invention relates to an exchanger tube for a heat exchanger according to the features in the preamble of claim 1.

Such an exchanger tube is part of the prior art through US Pat. No. 5,332,034. Both the ribs and the channels laterally delimited by the ribs each have a trapezoidal cross section. The cross-sectional volume of the ribs is approximately half the size of the cross-sectional volume of the channels.

The troughs formed in the ribs are produced by rolling. The material deformed from the ribs bulges into the channels at the front of the troughs. The bottoms of the troughs are at a distance from the canal bases.

The known exchanger tube is produced by first producing the structure of the subsequent inner surface on one side on a metal strip in a two-stage rolling process, then forming the metal strip into a slot tube with an internal surface structure and then welding the slot edges.

The two-stage rolling of the inner surface structure leads to high manufacturing costs. Several roller embossing tools are required, which affect the economy. The troughs of the ribs are created by rolling over an initially existing volume fraction of the ribs that were formed in the first rolling step. This former volume share of the ribs is only distributed in the immediate vicinity. However, a noteworthy reduction in the meter weight cannot be achieved.

Furthermore, due to the flatness of the top sides and the flanks of the ribs in practical use, it is possible to form condensate films which are difficult to tear open and which delay condensation, so that barrier layers with heat-insulating properties are formed. Only a few edges are available as vapor bubble nuclei for evaporation.

Based on the prior art, the invention is based on the object of creating an exchanger tube with an inner surface structure in which, on the one hand, the advantages of an equally good evaporation or condensation performance combined with a reduced fin weight are combined and, on the other hand, a one-step embossing process is used to produce the exchanger tube can.

This object is achieved according to the invention in the features listed in the characterizing part of claim 1.

The core of the invention is formed by such an internal, rough surface structure, which has only rounded transitions and avoids sharp edges. Consequently, the rough surface structure can be produced in a particularly advantageous manner by roller embossing in a single step. This considerably reduces the expenditure on equipment.

Furthermore, with regard to the intensification of the heat transfer between the fluid flowing in the exchanger tube and the coarse surface structure, it is now advantageous that the surfaces of the ribs up to the channel soles are additionally provided with a targeted micro-roughness. This is particularly noticeable in the condensation and evaporation of refrigerants if the exchanger tube is integrated into a corresponding heat exchanger. The cross-sectional volume of the ribs has been reduced in favor of increasing the number of ribs. This makes it possible to enlarge the heat-exchanging surface structure and thus to improve the heat transfer. In this context, very slim ribs and thus narrow channels can also be created. The ribs rounded at the head have the particular advantage that when a heat exchanger tube is drawn into fins of a heat exchanger, in particular by widening by means of a tool moved through the heat exchanger tube, the head portions of the ribs are only insignificantly flattened, so that the formation of condensate films that are difficult to tear open is also effective is opposed. Nevertheless, the large number of projections, edges, tips and depressions which are advantageous for effective evaporation can be provided as vapor bubble nuclei by the micro-roughness due to the large fin surfaces, without the need for larger amounts of material.

If necessary, the surfaces of the fins can also be provided with a coarse structure corresponding to the inner structure of the exchanger tubes and / or with a micro-roughness.

The invention is applied to exchanger tubes made of metal, but especially of copper or copper alloys. Such exchanger tubes can have, for example, a round or oval cross section. Round exchanger tubes preferably have an outside diameter of approximately 6 mm to 20 mm.

Basically, it is conceivable according to the invention that the central longitudinal planes of the troughs run parallel to one another, but are offset in the longitudinal direction of the ribs.

In contrast, the embodiment according to claim 2 provides that the central longitudinal planes of the troughs of adjacent ribs run in alignment.

The micro-roughness of the fin surfaces can be achieved in various ways. For example, a diffuse roughening by blasted corundum is conceivable. Notching of the rib surfaces in the form of linear micro-grooves is also conceivable (claim 3). These micro grooves then preferably extend parallel to one another. However, their longitudinal direction deviates from the longitudinal direction of the ribs.

The micro-roughness can moreover be formed according to claim 4 by intersecting micro-grooves which deviate from the longitudinal direction of the ribs.

Instead of continuous micro grooves, punctual depressions can also be provided. These can also be arranged in a line or cross shape at a distance one behind the other.

The microroughness can also be generated in various ways. A preferred variant is seen in the features of claim 5. Here, the micro-roughness of the fin surfaces is produced by irradiation with hard particles, such as corundum, or by texturing using laser beams. It is possible to either process the starting material (sheet metal strip) already provided with the surface structure accordingly or to provide an embossing roller itself with the desired negative micro-roughness.

Profiling the embossing roller by spark eroding is also possible.

Internal investigations have shown that to achieve an equally good condensation and evaporation performance according to claim 6, it is advantageous if the depth of the micro roughness is 0.075 mm or less.

According to claim 7, the flank angle of the ribs can be 5 ° to 60 °, but preferably 10 ° to 40 °. In this way, a very slim rib contour can be produced.

The course of the ribs relative to the longitudinal axis of the exchanger tube takes place according to the features of claim 8 at an angle of 1 ° to 89 °, preferably 20 ° to 55 °.

Furthermore, it makes sense within the scope of the invention if the angle enclosed between the longitudinal direction of the ribs and the central longitudinal planes of the troughs is 90 ° and smaller.

According to claim 10, it is advantageous if the distance between two adjacent ribs is 0.10 mm to 2.0 mm, preferably 0.26 mm to 0.6 mm.

Depending on the tube diameter, the height of the fins is appropriately between 0.03 mm and 1.0 mm, preferably 0.05 mm to 0.35 mm.

Furthermore, it is advantageous according to the invention if, according to claim 12, the distance between two adjacent troughs of a rib is 0.2 mm to 4.0 mm, preferably 0.3 mm to 1.0 mm.

The bottoms of the troughs and the channel soles do not have to lie on one level. The minimum distance between the trough floors and the channel soles should then be at least 0.01 mm.

According to the features of claim 14, it is also conceivable that the trough floors and the channel soles lie in the same plane.

Figur 1

in der Perspektive einen Längenabschnitt eines Austauscherrohrs;

Figur 2

in der Draufsicht einen Längenabschnitt eines strukturierten Blechbands;

Figur 3

in der Perspektive den Ausschnitt III der Figur 2;

Figur 4

in vergrößerter Darstellung einen vertikalen Querschnitt entlang der Linie IV-IV der Figur 2;

Figur 5

einen vertikalen Längsschnitt entlang der Linie V-V der Figur 4 und die

Figuren 6 und 7

anhand von Diagrammen einen Leistungsvergleich an Wärmeaustauschern in Koaxialbauweise mit verschiedenen Rohrausführungen.

The invention is explained in more detail below on the basis of exemplary embodiments illustrated in the drawings. Show it:

Figure 1

in perspective a length section of an exchanger tube;

Figure 2

in plan view a length section of a structured sheet metal strip;

Figure 3

in perspective the section III of Figure 2;

Figure 4

in an enlarged view a vertical cross section along the line IV-IV of Figure 2;

Figure 5

a vertical longitudinal section along the line VV of Figure 4 and

Figures 6 and 7

Based on diagrams, a performance comparison of heat exchangers in coaxial design with different pipe designs.

1 in FIG. 1 denotes a longitudinal section of a longitudinally welded exchanger tube for an otherwise not shown heat exchanger for the condensation and evaporation of refrigerants.

The exchanger tube 1, which is circular in outer and inner cross section, has a smooth outer surface 2 and a structured inner surface 3. To fix the exchanger tube 1 in a fin of a heat exchanger, which may be penetrated by several mutually parallel exchanger tubes 1, the exchanger tube 1 is placed in one of its own Outside diameter adapted opening inserted in the lamella and fixed by widening in the opening. For this purpose, an appropriately designed expansion tool, not shown, is moved through the exchanger tube 1.

In the exemplary embodiment, the exchanger tube 1 has an outer diameter D of 9.52 mm.

The exchanger tube 1 is produced from a sheet metal strip made of copper, which is flat on both sides and not shown. The sheet metal strip is subjected to a single-stage roller stamping process, one side of the sheet metal strip 4 remaining smooth (the later outer surface 2 of the exchanger tube 1) and the other side with a structured surface (the later inner side 3 of the exchanger tube 1) as shown in FIGS. 2 and 3 ) is provided. Only the edge regions 5 of the sheet metal strip 4 (FIG. 2) used for welding remain unstructured. After the roll embossing, the sheet metal strip 4 is formed into a slotted tube and then welded along the longitudinal seam and divided into lengths.

The structure of the inner surface 3 of the exchanger tube 1 is subsequently explained in more detail with reference to FIGS. 2 to 5.

It comprises at an angle α of 45 ° to the longitudinal axis 6 of the exchanger tube 1 parallel ribs 7 (Figures 2 and 3) with inclined flanks 8 (Figures 3 and 4). Of the Flank angle β of the ribs 7 is 20 ° in the exemplary embodiment and the distance A between two adjacent ribs 7 is 0.35 mm (FIGS. 2 and 4). Its height H is 0.30 mm (Figure 4). The base section 9 connecting the ribs 7 in the foot region has a thickness D1 of 0.30 mm (FIG. 5).

It can also be seen from FIGS. 3 and 4 that both the head regions 10 of the ribs 7 and the transitions 11 from the flanks 8 to the channel soles 12 are rounded. The cross-sectional volume of the ribs 7 is smaller than the cross-sectional volume of the channels 13 between the ribs 7.

As particularly illustrated in FIGS. 3 and 5, each rib 7 is provided with a sinusoidal ridge shape when viewed in longitudinal section. Because of this sinusoidal wave crest of the ribs 7 in their longitudinal directions LR, transverse troughs 14 are formed in the ribs 7. As FIG. 2 shows in this connection, troughs 14 of adjacent ribs 7 are arranged one behind the other at an angle γ of 45 ° to the longitudinal axis 6 of the exchanger tube 1. The angle δ enclosed between the longitudinal direction LR of the ribs 7 and the central longitudinal planes MLE of the troughs 14 is 90 °. The distance A1 between two troughs 14 adjacent in the longitudinal direction of a rib 7 is 0.50 mm (FIGS. 2 and 5) and the distance A2 of the trough bottoms 15 from the channel soles 12 is 0.01 mm. The troughs 14 have a depth T1 of 0.25 mm (FIGS. 4 and 5).

As can be seen in FIG. 5 in a deliberately exaggerated representation based on the wave crest of the ribs 7, the surfaces 8, 10, 11 of the ribs 7, ie the head regions 10, the flanks 8 and the transitions 11 from the flanks 8 to the channel soles 12, but possibly also the channel soles 12, provided with a micro-roughness 16, the depth T of which is 0.005 mm.

In the exemplary embodiment, the microroughness 16 is produced directly during the roll embossing. For this purpose, the embossing roller has been provided with a negative diffuse surface structure by means of irradiation with corundum, which then ensures the generation of the surface structure on the later inner surface 3 of the exchanger tube 1.

Due to the structured inner surface 3, the exchanger tube 1 illustrated in FIG. 1 has a significantly better heat transfer coefficient k '(W / mK) compared not only to an exchanger tube with a smooth inner surface, but also to an internally grooved exchanger tube.

This fact can be seen from the diagrams according to FIGS. 6 and 7 drawn up on the basis of comparative investigations without additional explanations (FIG. 6 —condensation, FIG. 7 — evaporation).

List of reference symbols

1 -

Exchanger tube

2 -

outer surface v. 1

3 -

inner surface v. 1

4 -

Metal strip

5 -

Marginal areas v. 4th

6 -

Longitudinal axis v. 1

7 -

Ribs

8th -

Flanks v. 7

9 -

Base section v. 4th

10 -

Head areas v. 7

11 -

Transitions v. 8 on 12

12 -

Channel soles

13 -

channels

14 -

Hopper

15 -

Trough floors

16 -

Micro roughness

A -

Distance between two adjacent ribs 7

A1 -

Distance between two adjacent MLE on a rib 7

A2 -

Distance from 12 to 15

D -

Outer diameter of 1

D1 -

Thickness v. 9

H -

Height of 7

LR -

Longitudinal direction v. 7

MLE-

Middle longitudinal planes of directly adjacent troughs 14 on different ribs 7

T -

Depth of 16

T1 -

Depth of 14

α -

Angle between 6 u. 7

β -

Flank angle v. 7

γ -

Angle between 6 u. MLE

δ -

Angle between LR and MLE

Claims (15)

1. Exchanger tube for a heat exchanger, which has a smooth outer surface (2) and a structured inner surface (3), which extends from an angle (α) deviating from 90 ° to the longitudinal axis (6) of the exchanger tube (1) parallel ribs (7) is formed with inclined flanks (8), channels (13) laterally delimited by the ribs (7) and transverse troughs (14) formed in the ribs (7), the central longitudinal planes (MLE) of the troughs (14) run at an angle () deviating from 90 ° to the longitudinal axis (6) of the exchanger tube (1), characterized in that the troughs (14) have a micro-roughness due to their longitudinally sinusoidal design of the surfaces (8, 10, 11) (16) and ribs (7) rounded on the head side, the opposite flanks (8) of adjacent ribs (7) being connected to the channel soles (12) by rounded transitions (11). 2. Exchanger tube according to claim 1, characterized in that the central longitudinal planes (MLE) of the troughs (14) of adjacent ribs (7) run in alignment. 3. Exchanger tube according to claim 1 or 2, characterized in that the micro-roughness (16) of the fin surfaces (8, 10, 11) is formed by mutually parallel, from the longitudinal direction (LR) of the ribs (7) deviating micro-grooves. 4. Exchanger tube according to claim 1 or 2, characterized in that the micro-roughness (16) of the fin surfaces (8, 10, 11) is formed by cross-cutting, from the longitudinal direction (LR) of the ribs (7) deviating micro-grooves. 5. Exchanger tube according to one of claims 1 to 4, characterized in that the micro-roughness (16) is produced by particle beams or by means of laser beams. 6. Exchanger tube according to one of claims 1 to 5, characterized in that the depth (T) of the microroughness (16) is dimensioned 0.075 mm or less. 7. Exchanger tube according to one of claims 1 to 6, characterized in that the flank angle (β) of the ribs (7) is 5 ° to 60 °, preferably 10 ° to 40 °. 8. Exchanger tube according to one of claims 1 to 7, characterized in that the longitudinal direction (LR) of the ribs (7) at an angle (α) of 1 ° to 89 °, preferably 20 ° to 55 °, to the longitudinal axis (6) of the exchanger tube (1). 9. Exchanger tube according to one of claims 1 to 8, characterized in that between the longitudinal direction (LR) of the ribs (7) and the central longitudinal planes (MLE) of the troughs (14) included angle (δ) is 90 ° and smaller. 10. Exchanger tube according to one of claims 1 to 9, characterized in that the distance (A) between two adjacent ribs (7) is 0.10 mm to 2.0 mm, preferably 0.26 mm to 0.6 mm. 10. Exchanger tube according to one of claims 1 to 9, characterized in that the distance (A) between two adjacent ribs (7) is 0.10 mm to 2.0 mm, preferably 0.26 mm to 0.6 mm. 11. Exchanger tube according to one of claims 1 to 10, characterized in that the height (H) of the ribs (7) is 0.03 mm to 1.0 mm, preferably 0.05 mm to 0.35 mm. 12. Exchanger tube according to one of claims 1 to 11, characterized in that the distance (A1) between two adjacent troughs (14) of a rib (7) 0.2 mm to 4.0 mm, preferably 0.3 mm to 1.0 mm. 13. Exchanger tube according to one of claims 1 to 12, characterized in that the trough bottoms (15) are arranged at a distance (A2) from the channel soles (12). 14. Exchanger tube according to one of claims 1 to 12, characterized in that the trough bottoms (15) are arranged in the same plane as the channel soles (12).

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