WO2010139329A2

WO2010139329A2 - Heat exchanger arrangement and stirling refrigerator

Info

Publication number: WO2010139329A2
Application number: PCT/DK2010/000087
Authority: WO
Inventors: Stig Kildegaard Andersen; Klaus Reinwand; Snorri Jonsson
Original assignee: Danfoss Compressors Gmbh
Priority date: 2009-06-05
Filing date: 2010-06-01
Publication date: 2010-12-09
Also published as: WO2010139329A3; DE102009024080A1

Abstract

The invention concerns a heat exchanger arrangement (1) with a housing that comprises a pipe-shaped wall (2) and a plurality of flow channels (3) inside the housing. With a simple manufacturing, it is endeavoured to achieve a good heat transition between a fluid in the flow channels and the outside of the housing. For this purpose, the flow channels (3) are formed between segments (4), which are stacked and resting upon one another in the circumferential direction, the segments (4) being held together by the pipe-shaped wall (2).

Description

Heat exchanger arrangement and Stirling refrigerator

The invention concerns a heat exchanger arrangement with a housing that comprises a pipe-shaped wall and a plurality of flow channels inside the housing.

Further, the invention concerns a Stirling refrigerator with a displacer unit comprising a housing with a compression chamber and an expansion chamber, a regenerator being arranged between the compression chamber and the expansion chamber, the housing having a pipe-shaped wall.

A heat exchanger arrangement as mentioned in the introduction is known from, for example, EP 1 208 343 B1. Here, the flow channels are formed between ra- dially extending fins, which are formed in that a thin copper strip is bent to a wave shape. This heat exchanger arrangement is applied in a Stirling refrigerator.

With machines using compression and expansion of gases to transport heat from one area to another, the design of a heat exchanger arrangement has a certain importance in connection with the efficiency of the machine. In the ideal case, the designer has a high degree of freedom when designing flow channels in the heat exchanger, that is, he can freely select the flow length, the flow cross-section, the hydraulic cross-section and the heat transition between indi- vidual components of the heat exchanger arrangement and the heat source and the heat sink. In the real case, the designer, however, has to observe certain limitations, some of which are predetermined by the possibility of manufacturing and the manufacturing cost.

Heat exchangers are known in many different embodiments. Thus, for example DE 33 10 002 A1 shows a rotating heat exchanger with a radially internal wall and a radially external wall, a plurality of flow channels being formed between said walls, all flow channels having a constant hydraulic diameter of less than 5 mm. The flow channels are formed by wave-shaped, triangular or rectangular plates that are arranged between the radial walls.

DE 10 2007 044 980 A1 , DE 27 47 846 A1 and WO 2007/125118 A1 show heat exchangers with two pipe elements, of which one is inserted into the other. Between the pipe elements radially extending ribs and steps are formed to extend from the pipe walls. For this purpose, extruded aluminium profiles can be used. The hydraulic diameter is stated to be 4 to 13 mm.

US 7 243 498 B1 shows a heat exchanger arrangement in which the flow channels are formed by fins bent in a wave shape and formed between rings. The fins can further comprise radially extending slots.

The invention is based on the task of using simple manufacturing methods to provide a good heat transition between a fluid in the flow channels and the outside of the housing.

With a heat exchanger arrangement as mentioned in the introduction, this task is solved in that the flow channels are formed between segments, which are stacked and resting upon one another in the circumferential direction, the segments being held together by the pipe-shaped wall.

With this embodiment, a good heat transition from a fluid that flows through the flow channels and the outside of the housing is achieved. On the one side, this occurs in that the segments have a good contact with the pipe-shaped wall. They rest on the pipe-shaped wall from the inside with a certain prestress. On the other side, it can be ensured that heat conduction by the segments is available across the whole radial extension of the segments. No matter at which radial position the fluid contacts the segment in question, the heat carried along by the fluid is at least partly transferred to the segment and then flows through the segment to the pipe-shaped wall and from there to the outside, so that the heat can be discharged in a good manner. Of course, the same also applies, when the heat from the outside must be transmitted to the fluid flowing through the flow channels. Preferably, the segments have a wedge-shaped cross-section. If the angle of the wedge is chosen correctly, the individual segments can rest flat on each other. At least at the radial outer edge, this results in a circumferential massive ring that ensures a high mechanical stability.

Preferably, the flow channels are formed by embossings extending axially over the length of the segments. Thus, the embossings form some kind of grooves. The segments can then be made of a band material, meaning that embossing and stamping processes can be performed at very accurate tolerances.

Preferably, radially outside and/or radially inside the embossing, the segments comprise a bearing area with which they rest on an adjacent segment. With this embodiment, two massive annular rings are then provided on the circumfer- ence, the outer ring resting from the inside on the wall of the pipe. This ensures an excellent heat transition. At the same time, a high mechanical stability occurs, as, in a manner of speaking, the segments are supported extensively on each other and only the areas of the embossings are excluded by the support, as they form the flow channels.

Preferably, in the radial direction at least two embossings are provided. Thus, the segments can additionally be supported on each other between the radial outer end and the radial inner end, which would further improve the stability. Further, the separating step between the two embossings can increase the heat transition surface between the fluid flowing through the flow channels and the segment, if; for example, its height is larger than half its width.

Preferably, at a thickest part in the circumferential direction, the segments have a thickness in the range from 200 to 500 μm. Thus, the individual segments are relatively thin. Accordingly, they can be made of a relatively thin band material by means of embossing and stamping processes.

Preferably, the embossings have a depth in the range from 50 to 100 μm. If, for example, the thickness of the segments at the thickest place is 200 μm, the depth of the embossing is approximately 60 μm. Generally, it can be ensured that the depth of the embossing amounts to approximately 1/3 to 1/2 of the thickness of the segments.

Preferably, the segments have a radial extension in the range from 3 to 15 mm. Thus, sufficiently large flow channels can be made.

Preferably, an inner pipe is located at the radial inside of the segments. The inner pipe can be used to support the segments mechanically. It can also be used to form a pressure resistant wall towards the radial inside.

Preferably, each segment has a through wall extending radially from the inside towards the outside. Thus, a good heat flow is permitted, that is, the distance from the radial inside to the radial outside is kept as short as possible.

Preferably, the segments are connected to each other in the circumferential direction. This is a way of simplifying the manufacturing. When the segments are not connected to each other, they can be assembled to a ring and pressed under pressure into the pipe-shaped wall of the housing. However, they can also be connected to each other before the insertion into the pipe-shaped wall, for example by gluing or soldering. Also a pure form-fit connection, for example a groove joint, can be provided.

With a Stirling refrigerator as mentioned in the introduction, the task is solved in that the compression chamber and/or the expansion chamber comprises an arrangement of segments, flow channels being formed between said segments, the segments being stacked and resting on each other in the circumferential direction, the segments being held together by the pipe-shaped wall. The heat that occurs during compression of a gas, thus heating the gas, can then easily be discharged radially outwards, when the gas flows through the flow channels.

In the other case, after the expansion the gas can absorb heat that is supplied via the heat exchanger from the outside. For both purposes the heat exchanger arrangement is well suited. Preferably, the segments are formed as described above.

In an advantageous embodiment, it is provided that the arrangement of segments is adjacent to the regenerator. In this case, the gas firstly flows through the heat exchanger and then immediately after through the regenerator, or vice versa.

Preferably, the flow channels in common have a hydraulic diameter that corresponds to the hydraulic diameter of the regenerator. Thus, the flow resistances are balanced to each other, so that a relatively undisturbed flow of the gas is possible. Due to the relatively flat embodiment of the flow channels, the hydraulic diameter of each individual flow channel corresponds to approximately twice the embossing depth.

In the following, the invention is described on the basis of a preferred embodiment in connection with the drawings, showing:

Fig. 1 a schematic section through a heat exchanger arrangement,

Fig. 2 a segment, and

Fig. 3 a displacer unit of a Stirling refrigerator.

Fig. 1 shows a schematic view of a heat exchanger arrangement 1 with a hous- ing that comprises a pipe-shaped wall 2, here forming an outer wall, and a plurality of flow channels 3 inside the housing through which a fluid, in particular a gas, can flow. In this connection heat contained in the gas shall be discharged to the outside, or the fluid must absorb heat from the outside.

For this purpose, the flow channels between adjacent segments 4 are formed, one being shown in detail in Fig. 2. In the circumferential direction, the segments are stacked and rest on each other, the segments being held together by the wall 2. Preferably, the wall 2 has a circular cross-section. The segments 4 rest with a certain stress on the inside of the wall 2, so that a good heat transi- tion between the segments 4 and the wall 2 occurs. Further, the wall 2 ensures that a certain contact pressure exists between the individual segments, so that the segments are pressed together accordingly.

The segments 4 are, as appears from Fig. 2, made with a wedge-shaped cross- section. One side (in Fig. 2 the upper side) comprises two embossings 5, 6 that form the flow channels 3. When the segments 4 are stacked in the circumferential direction, each of these embossings 5, 6 is then covered by a rear side 7 of the adjacent segment, so that the flow channels 3 occur. The embossings 5, 6 form groove-like recesses.

At the radial outer edge, each segment has a bearing area 8. At the radial inner end, each segment has a bearing area 9. The two embossings 5, 6 are separated from each other by a step 10 that forms an additional bearing area, on which the adjacent segment 4 bears. The rear side 7 is formed on a through wall 11 extending radially from the inside to the outside.

As mentioned above, the segment 4 is made with a wedge shape, that is, its radial outer side is thicker than its radial inner side. Radially outwards, the seg- ment 4 has a thickness d in the range from 200 to 500 μm, for example 350 μm. Here, the segment 4 can be made with very small tolerances from band material by means of embossing and punching processes. During the embossing, not only the embossings 5, 6 can be formed, but also the wedge shape can be made.

The embossings 5, 6 have a depth in the range from 50 to 100 μm. In the present case, the embossings 5, 6 have a depth of approximately 60 μm, that is, approximately one third of the thickness d.

The segment 4 has a length, that is, an extension in the axial direction that is adapted to the desired heat transition. The segment 4 has a width, that is, an extension in the radial direction that is also adapted to the desired application purpose. In the present case, the heat exchanger arrangement 1 is to be in- serted in a displacer unit 12 (Fig. 3) of a Stirling refrigerator that is not shown in detail. Here, the segment 4 has a radial extension of approximately 6 mm.

The required number of segments 4 is stacked in an annular shape and then pressed into the pipe-shaped wall 2. The pipe-shaped wall 2 then holds the segments 4 together with the desired stress. On the radial inside, an additional pipe 13 can be provided. This is not absolutely necessary for the stack of segments 4, but during operation it may increase the pressure on the outer wall.

In order to simplify the mounting, the stack of segments 4 can be pre- manufactured as a ring member, for example in that the individual segments 4 are connected to one another before insertion into the pipe-shaped wall 2. The methods of connection reach from gluing or soldering to a pure form-fit connection, for example by means of a groove-joint. Also sintering would be a possibil- ity.

The segments 4 are made of a material with good heat conduction properties, for example copper or aluminium. In the positions, in which the bearing areas 8, 9 bear on the adjacent segments 4, an annular, circumferential, massive ring occurs. With the radial outer ring 14, the stack of segments 4 rests on the inside of the pipe-shaped wall 2 with a certain pressure, so that here a good heat transition is ensured.

Fig. 3 shows a strictly schematic view of a displacer unit 12 of a Stirling refrig- erator that is not shown in detail. The displacer unit 12 comprises a piston 16 that is movable in a cylinder formed by the pipe 13. The displacer unit 12 comprises an expansion chamber 17 and a compression chamber 18. A regenerator 19 is arranged between the expansion chamber 17 and the compression chamber 18.

In the expansion chamber 17 is arranged a first heat exchanger arrangement 1a immediately adjacent to the regenerator 19. In the compression chamber 18 is arranged a second heat exchanger arrangement 1b, also immediately adjacent to the regenerator 19. The hydraulic diameter of the two heat exchangers 1a, 1b substantially corresponds to the hydraulic diameter of the regenerator 19.

The plurality of flow channels 3 result in a large heat transition surface towards the segments 4, a good conduction in the radial direction through the wall 11 of the segments 4 and a good heat transition into the pipe-shaped wall 2 because of the intensive contact on the entire area of the inside of the pipe-shaped wall 2.

The manufacturing is relatively simple, as the shape of the individual segments 4 can manufactured with very accurate tolerances from a band material by means of embossing and punching processes.

Claims

Patent Claims

1. Heat exchanger arrangement with a housing that comprises a pipe- shaped wall and a plurality of flow channels inside the housing, characterised in that the flow channels (3) are formed between segments (4), which are stacked and resting upon one another in the circumferential direction, the segments (4) being held together by the pipe-shaped wall (2).

2. Heat exchanger arrangement according to claim 1 , characterised in that the segments (4) have a wedge-shaped cross-section.

3. Heat exchanger arrangement according to claim 1 or 2, characterised in that the flow channels (3) are formed by embossings (5, 6) extending axi- ally over the length of the segments (4).

4. Heat exchanger arrangement according to claim 3, characterised in that radially outside and/or radially inside the embossing (5, 6), the segments (4) comprise a bearing area (8, 9) with which they rest on an adjacent segment (4).

5. Heat exchanger arrangement according to claim 3 or 4, characterised in that in the radial direction at least two embossings (5, 6) are provided.

6. Heat exchanger arrangement according to one of the claims 3 to 5, characterised in that at a thickest part in the circumferential direction, the segments (4) have a thickness (d) in the range from 200 to 500 μm.

7. Heat exchanger arrangement according to claim 6, characterised in that the embossings have a depth in the range from 50 to 100 μm.

8. Heat exchanger arrangement according to one of the claims 1 to 7, characterised in that the segments (4) have a radial extension in the range from 3 to 15 mm.

9. Heat exchanger arrangement according to one of the claims 1 to 8, characterised in that an inner pipe (13) is located at the radial inside of the segments (4).

10. Heat exchanger arrangement according to one of the claims 1 to 9, characterised in that each segment (4) has a through wall (11) extending radially from the inside towards the outside.

11. Heat exchanger arrangement according to one of the claims 1 to 10, characterised in that the segments (4) are connected to each other in the circumferential direction.

12. Stirling refrigerator with a displacer unit comprising a housing with a compression chamber and an expansion chamber, a regenerator being located between the compression chamber and the expansion chamber, the housing comprising a pipe-shaped wall, characterised in that the compression chamber (17) and/or the expansion chamber (18) comprises an arrangement of segments (4), flow channels (3) being formed between said segments (4), the segments (4) being stacked and resting on each other in the circumferential direction, the segments (4) being held together by the pipe-shaped wall (2).

13. Stirling refrigerator according to claim 12, characterised in that the seg- ments (4) are formed as described in claims 2 to 11.

14. Stirling refrigerator according to claim 12 or 13, characterised in that the arrangement of segments (4) is adjacent to the regenerator (19).

15. Stirling refrigerator according to claim 14, characterised in that the flow channels (3) in common have a hydraulic diameter that corresponds to the hydraulic diameter of the regenerator (19).