WO2010139325A2

WO2010139325A2 - Stirling cooling arrangement

Info

Publication number: WO2010139325A2
Application number: PCT/DK2010/000083
Authority: WO
Inventors: Poul Erik Hansen; Jan Thomsen; Snorri Jonsson; Ana Mari Tataru Kjaer; Klaus Reinwand
Original assignee: Danfoss Compressors Gmbh
Priority date: 2009-06-05
Filing date: 2010-06-01
Publication date: 2010-12-09
Also published as: DE102009023973A1; WO2010139325A3

Abstract

The invention concerns a Stirling cooling arrangement (1) with a driving unit (2) that generates periodically changing gas pressures, and a displacer unit (4) connected to the driving unit (2) and comprising a displacer (15) that is movable in a displacer housing (6) along a displacer axis (16). It is endeavoured to achieve a good efficiency. For this purpose, the displacer (15) comprises a body (20) of a plastic material that is provided with a metal ring (22), whose outer diameter is larger than the outer diameter of the body (20).

Description

Stirling cooling arrangement

The invention concerns a Stirling cooling arrangement with a driving unit that generates periodically changing gas pressures, and a displacer unit connected to the driving unit and comprising a displacer that is movable in a displacer housing along a displacer axis.

Such a Stirling cooling arrangement is, for example, known from EP 1 348 918 A1. Here, the driving arrangement is a piston pump with a piston moving a cylinder. The displacer is arranged in an extension of the cylinder.

A Stirling cooling arrangement works in accordance with the Stirling principle and therefore has a relatively good relation between the generated cooling ca- pacity and the mass. A Stirling cooling arrangement is therefore well suited for mobile applications, for example a portable cooling box. As, however, with a mobile application, also the energy supply has to be carried along, a good efficiency is important. A good efficiency is also desired with stationary applications.

The invention is based on the task of ensuring a good efficiency of a Stirling cooling arrangement.

With a Stirling cooling arrangement as mentioned in the introduction, this task is solved in that the displacer comprises a body of a plastic material that is provided with a metal ring, whose outer diameter is larger than the outer diameter of the plastic material.

This will combine the advantages of a metal displacer, that is, increased stability and good running properties, with the advantages of a plastic material, namely small mass and easy manufacturing. As the metal ring has a large diameter than the body, the metal ring serves the purpose of guiding the displacer in the displacer housing. As a metal ring can be made with a relatively high accuracy, it may be ensured that an expansion chamber that is delimited by the displacer can be sealed in a good manner by the displacer. Further, a metal ring has the advantage that it usually conducts heat better than a plastic material. Thus, the metal ring can be used to discharge heat that appears in the displacer.

Preferably, a cylinder of a plastic material is arranged in the displacer housing, the displacer moving in said cylinder. The metal ring interacts with this cylinder. A material pairing of metal and plastic material can be chosen so that here only a relatively small friction occurs. Accordingly, also only little friction heat will be generated. The friction heat corresponds to a part of the driving performance that cannot be used to generate cooling. So, the lower the friction heat, the better the efficiency.

Preferably, the metal ring is located in the area of an axial end of the displacer. Then the heat that has to be discharged through the metal ring can be dis- charged from the corresponding end.

Preferably, the displacer comprises a front wall, and the metal ring connects the front wall and the body to each other. Mainly with regard to the manufacturing, this embodiment has advantages. The body can be provided with a hollow, as it is open from one side before mounting of the front wall. The metal ring then gets a second function, namely the connection of body and front wall.

It is preferred that the metal ring is made in one piece with the front wall. This causes that also the front wall is made of a metal. As, during operation, the front wall is exposed to a gas pressure, it is more loadable if made of a metal.

Preferably, the front wall is supported on an oppositely arranged bottom wall of the body by means of a spring. The spring then ensures that the displacer remains stressed in the axial direction, that is, in the direction of the displacer axis. On the other side, the spring permits small deformations during operation, so that the displacer can be deformed without damage, for example when pressure peaks occur. Preferably, a guiding pipe extends from the bottom wall, a guiding element connected to the displacer housing being arranged in said guiding pipe, the spring - being supported on the bottom wall via the guiding pipe. When the displacer is guided on the guiding element by means of the guiding pipe, the mass of the guiding element does not have to be moved along. Still, however, it is possible to provide differently dimensioned pressure application surfaces on both sides of the displacer. The guiding pipe then assumes the additional task of passing on the force of the spring from the front wall to the bottom wall.

Preferably, the spring generates radially directed forces. The displacer is then also stressed in the radial direction, so that it can rest on its running surface with a sufficient tightness.

Preferably, the body surrounds a hollow, and a volume inside the guiding pipe on the side of the guiding element that is not fixed to the displacer housing is connected to the hollow. During a movement of the displacer in relation to the guiding element, the volume delimited by the guiding element in the guiding pipe decreases and increases. This volume change causes pressure changes inside the displacer. As, however, a relatively large buffer is provided by the hollow, these pressure changes can be kept small. Thus, it can be achieved that, if required, the body can still expand somewhat in the radial direction. However, this expansion can be kept so small that it does not reach the diameter of the metal ring. Thus, it is prevented that a frictional contact occurs between the body and the running surface.

In a preferred embodiment, it is provided that the displacer comprises a front wall insert and the body is located between the metal ring and the front wall insert. The front wall is arranged at the front wall insert. The front wall insert and the metal ring are two separate elements. The body is arranged between the metal ring and the front wall insert. Accordingly, the metal ring can be used to fix the front wall insert in the body by clamping the body to the front wall insert. Firstly, this gives a stable connection, and secondly also a sufficient sealing of the hollow inside the displacer. Preferably, at least two metal rings are arranged in the body at an axial distance in relation to one another. With two metal rings, the guiding can be improved. The risk that the displacer tilts is kept small.

Preferably, the body is made as an injection moulded part. The body can thus be manufactured in an inexpensive way and still have a high accuracy.

Preferably, the body has substantially the same heat expansion coefficient as the metal ring. Thus, during operation, when the body and the metal ring are heated, unfavourable heat tensions between the metal ring and the body are avoided.

Preferably, the metal ring is made of steel. Steel has a sufficient rigidity and sufficient heat conductivity.

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

Fig. 1 a schematic sectional view through a Stirling cooling arrangement,

Fig. 2 a sectional view of a modified displacer unit, and

Fig. 3 a sectional view of another displacer unit.

A Stirling cooling arrangement 1 comprises a driving unit 2, in the present case a piston pump. The driving unit 2 has two pistons, not shown in detail, being movable in counterphase along a piston axis 3 (in Fig. 1 perpendicularly to the drawing plane). The movement of the pistons generates periodically changing gas pressures.

A displacer unit 4 is connected to the driving unit 2 via a pipe 5. The driving unit 2, the displacer unit 4 and the pipe 5 are enclosed in a gas-tight manner, so that a gas contained in the driving unit 2 and the displacer unit 4 can be prestressed to an increased pressure, for example in the range from 20 to 30 bar. The displacer unit 4 comprises a displacer housing 6 that is led through an isolating plate 7. The displacer housing 6 extends with both ends from the isolating plate 7. The end of the displacer housing 6 facing the driving unit 2 is also called the "hot side". The other end of the displacer housing 6 is called the "cold side". On the cold side a heat exchanger 8 and on the hot side a heat exchanger 9 are mounted on the displacer housing 6. Each heat exchanger 8, 9 is provided with a ventilator 10, 11, by means of which an air flow through the heat exchangers 8, 9 can be generated.

In the displacer housing 6 that can be made of metal, a cylinder 12 is arranged that is made of a plastic material. The cylinder 12 is connected to the displacer housing 6 via a foot 13 that has several openings 14, through which the gas can enter.

Inside the cylinder 12 a displacer 15 is arranged. The displacer 15 is movable along a displacer axis 16.

At one end, the displacer 15 is connected to a resonance spring 17. The con- nection occurs via a tubular rivet 18 that is inserted in a bottom wall 19 of the displacer 15. The bottom wall forms a part of a body 20 of the displacer 15, said body 20 being made of a plastic material.

At the end facing away from the bottom wall 19, the displacer 15 has a front wall 21 that is made in one piece with a metal ring 22. The metal ring 22 and the front wall 21 are made of steel. The metal ring 22 has an outer diameter that is slightly larger than the outer diameter of the body 20, so that in the area of the body 20 a gap 23 occurs between the body 20 and the cylinder 12. This gap 23 is shown excessively large in Fig. 1. If shown to scale, it would practically not be visible.

The plastic material of the body 20 has substantially the same heat expansion coefficient as the metal of the metal ring 22. Substantially means that deviations of ±20% are possible. From the bottom wall 19, a guiding pipe 24 extends in the direction of the front wall 21. In the guiding pipe is arranged a guiding element 25 that fills the inner cross-section of the guiding pipe 24. The guiding element 25 is fixed on a spring wire 26 that is led through the tubular rivet 18 and connected to the displacer housing 6.

By means of a spring 27 the front wall 21 rests on the end face of the guiding pipe 24. In this connection, the spring 27 has on the one side a force effect that is directed in parallel to the displacer axis 16, on the other side, however, also a force effect that is directed radially to the displacer axis 16. Thus, the displacer 15 is held stressed in the axial direction. At the same time, however, the metal ring 22 is also stressed in the radial direction.

The guiding element 25 subdivides the inside of the guiding pipe 24 into two sections. As the guiding pipe 24 is open at the end face, the section adjacent to the front wall 21 is connected to a hollow 28 that fills practically the whole inside of the displacer 15. Thus, the hollow 28 forms a buffer volume for gas that is displaced from the inside of the guiding pipe 24 during a movement of the dis- placer 15 to the left (in relation of the view in Fig. 1). Thus, it is possible to keep a pressure increase in the hollow 28 so small that the body 20 of the displacer 15 is not so far expanded that it gets in touch with the cylinder 12, when the pressure inside the displacer 15 increases.

At the bottom wall 19, the guiding pipe 24 recesses an area that is not available as pressure application surface. Accordingly, the pressure application surface at the front wall 21 is larger than the one at the bottom wall 19. With this dimensioning it can be achieved that the pistons in the driving unit 2 and the displacer 15 move towards each other with a mutual phase displacement of approxi- mately 90°.

Between the cylinder 12 and the displacer housing 6, extending from the hot side, a heat exchanger 29, a regenerator 30 and a further heat exchanger 31 are arranged. Together with the displacer housing 6, the front wall 21 delimits an expansion chamber 32.

The Stirling cooling arrangement works according to the Stirling process. The Stirling process is a thermodynamic cyclic process that consists of two isothermal and two isochoric state changes of a gas.

The gas supplied by the driving unit 2 is transported through the regenerator 30 that absorbs heat from the gas. The volume of the gas remains constant and the temperature decreases (first isochoric state change). The gas, now colder, on the "cold side" of the displacer housing 6 absorbs heat from the outside, the heat exchanger 9 supporting this process. The volume of the gas in the expansion chamber 32 increases at constant temperature (first isothermal state change). This displaces the displacer 15 to the left. This is possible, as the pressure application surface at the end face 21 is larger than at the bottom wall 19.

When the pressure supplied from the driving unit 2 sinks, the displacer 15 is moved back by the force of the resonance spring 17. The gas flows through the regenerator 30 and absorbs the heat stored here. The temperature increases at constant volume (second isochoric state change). The gas that is now on the hot side, discharges heat to the environment at constant temperature and decreasing volume (second isothermal state change).

Frictional heat that may occur during this process between the displacer 15 and the cylinder 12 can be discharged to the outside via the metal ring 22 and the front wall 21 , so that the displacer 15 is not exposed to an excessive temperature increase. Thus, the displacer 15 can be guided in the cylinder 12 with little friction, so that energy losses remain small, which results in a good efficiency.

Fig. 2 shows a modified embodiment of the displacer unit, the same elements having the same reference numbers. In the embodiment according to Fig. 1 , the metal ring 22 is fixed on the circumference of the body 20. In the embodiment according to Fig. 2, the metal ring 22 is connected to the guiding pipe 23 via the front wall 21. For this purpose, the front wall 21 comprises an inwardly extending projection 33 that engages the guiding pipe 24 at its end face end. The projection 33 has several openings 34, so that the inside of the guiding pipe 24 can be connected to the hollow 28 between the guiding element 25 and the front wall 21.

In this embodiment, a spring is not provided.

Fig. 3 shows a further embodiment of a displacer unit that is also doing without a spring. Same and corresponding parts have the same reference numbers as in Figs. 1 and 2.

The front wall 21 is formed at a front wall insert 35 that is inserted in the body 20. The metal ring 22 is located at an axial position of the body 20, in which it also engages around the front wall insert 35. Accordingly, the body 20 is clamped between the metal ring 22 and the front wall insert 35. Here, these clamping forces may be relatively small. Still, however, the metal ring 22 en- sures that the body 20 rests tightly on the front wall insert 35, so that the hollow 28 is tightly closed.

A second metal ring 36 is located at the end of the body facing away from the front wall 21. Thus, the body 20 is guided in the cylinder 12 at two positions, which have a relatively large axial distance to one another. Accordingly, stabilisation means inside the body 20 can be avoided.

In the bottom wall 19 a pipe 37 is inserted, through which the displacer 15 is connected to the resonance spring 17. For this purpose, these parts can be connected to the pipe 37 by means of two screws 38, 39.

Claims

Patent Claims

1. Stirling cooling arrangement with a driving unit that generates periodically changing gas pressures, and a displacer unit connected to the driving unit and comprising a displacer that is movable in a displacer housing along a displacer axis, characterised in that the displacer (15) comprises a body (20) of a plastic material that is provided with a metal ring (22), whose outer diameter is larger than the outer diameter of the body (20).

2. Cooling arrangement according to claim 1 , characterised in that a cylinder (12) of a plastic material is arranged in the displacer housing (6), the displacer (15) moving in said cylinder (12).

3. Cooling arrangement according to claim 1 or 2, characterised in that the metal ring (22) is located in the area of an axial end of the displacer (15).

4. Cooling arrangement according to one of the claims 1 to 3, characterised in that the displacer (15) comprises a front wall (21), the metal ring (22) connecting the front wall (21) and the body (20) to each other.

5. Cooling arrangement according to claim 4, characterised in that the metal ring (22) is made in one piece with the front wall (21).

6. Cooling arrangement according to claim 4 or 5, characterised in that the front wall (21) is supported on an oppositely arranged bottom wall (19) of the body (20) by means of a spring (27).

7. Cooling arrangement according to claim 6, characterised in that a guiding pipe (24) extends from the bottom wall (19), a guiding element (25) connected to the displacer housing (6) being arranged in said guiding pipe (24), the spring (27) being supported on the bottom wall (19) via the guiding pipe (24).

8. Cooling arrangement according to claim 6 or 7, characterised in that the spring (27) generates radially directed forces.

9. Cooling arrangement according to one of the claims 6 to 9, characterised in that the body (20) surrounds a hollow (28), and a volume inside the guiding pipe (24) on the side of the guiding element (25) that is not fixed to the displacer housing (6) is connected to the hollow (28).

10. Cooling arrangement according to one of the claims 1 to 9, characterised in that the displacer (15) comprises a front wall insert (35) and the body (20) is located between the metal ring (22) and the front wall insert (35).

11. Cooling arrangement according to one of the claims 1 to 10, character- ised in that at least two metal rings (22, 36) are arranged in the body (20) at an axial distance in relation to one another.

12. Cooling arrangement according to one of the claims 1 to 11 , characterised in that the body (20) is made as an injection moulded part.

13. Cooling arrangement according to one of the claims 1 to 12, characterised in that the body (20) has substantially the same heat expansion coefficient as the metal ring (22).

14. Cooling arrangement according to one of the claims 1 to 13, characterised in that the metal ring (22) is made of steel.