NL2007434C2

NL2007434C2 - Thermo-acoustic system.

Info

Publication number: NL2007434C2
Application number: NL2007434A
Authority: NL
Inventors: Hassan Tijani Moulay El; Symen Spoelstra
Original assignee: Stichting Energie
Priority date: 2011-09-16
Filing date: 2011-09-16
Publication date: 2013-03-19

Description

Thermo-acoustic system

TECHNICAL FIELD

The invention relates to a thermo-acoustic system, comprising a tube, the tube 5 comprising a regenerator unit, the regenerator unit comprising a first side and a second side, which in use have different temperatures, the regenerator unit being positioned at a location with an acoustic impedance, the tube comprising a feedback circuit to provide a feedback path between the first and second side of the regenerator unit.

10 STATE OF THE ART

Thermo-acoustic systems are known from the prior art. These systems can be used as a heat engine in which acoustic power is generated using heat as input, or can be used as a heat pump/cooler in which acoustic power is used to pump heat from a lower temperature heat source to a higher temperature heat sink, or used as a 15 combination of heat engine and heat pump/cooler. An example of a thermo-acoustic system is schematically shown in Fig. la.

The thermo-acoustic system as shown in Fig. la comprises a resonance system, which in general comprises a driver 10 and a stack 20.

Fig. la schematically depicts an example of such a thermo-acoustic system, 20 comprising a tube 1 having a driver formed by an acoustic device 10 (piston, loudspeaker) on one end of the tube 2 and a load formed by a stack 20 close to the other end of the tube 3, the other end of the tube 3 being a closed end. The tube 1 is filled with a suitable compressible medium, such as air or helium.

The stack 20 may have a first side 21, relatively close to the end of the tube 3, 25 and a second side 22, facing the driver 10 . In use, the first side 21 may have a different temperature than the second side 22. The thermo-acoustic system is usually operated at an acoustic frequency, where the tube 1 has a length L which is chosen such that a resonant system is provided and a standing acoustic wave is generated in the tube 1. By creating a standing acoustic wave in a tube 1, acoustic resonance of the first order can 30 be established, with provides an efficient acoustic system.

However, it is noted that the example shown in Fig. la is just an example and other thermo-acoustic systems are known, for instance wherein mechanical resonance is used instead of acoustic resonance.

2

According to the example shown in Fig. la, a standing wave can be generated in the tube 1, having a dynamic pressure P and velocity profile V as shown in Fig. lb. Fig. lb further shows the acoustic impedance (Z) associated with the standing acoustic wave, which is defined as the ratio of the amplitude of the local dynamic pressure P to 5 the amplitude of the local velocity V: Z = P/V. Fig. la thus is referred to as a standing wave thermo-acoustic system, wherein the dynamic pressure and velocity have a phase difference of approximately 90°.

The efficiency of thermo-acoustic systems using standing waves is however not very high, e.g. 20%. Standing wave systems are intrinsically irreversible because of the 10 imperfect thermal contact between the working gas and the stack.

US 4, 114, 380 describes that it is more efficient to use travelling waves. A thermo-acoustic system is provided wherein a regenerator unit is positioned in a tube 1, the tube forming a circuit, allowing travelling waves to travel through the circuit. The 15 small passages in the regenerator unit 20 ensure a good thermal contact between the compressible medium and the regenerator matrix (isothermal). An example of such a thermo-acoustic system is provided in Fig. 2a.

In travelling waves, the dynamic pressure P and the velocity V are in phase with each other. The dynamic pressure and velocity of travelling waves are phased 20 differently than for standing waves, as the dynamic pressure and velocity of a travelling wave are in phase and thus have their fluid movements timed to occur between the compression and expansion phases.

As heat exchange with the regenerator structure now also occurs during movement of the compressible medium-element, a more efficient heat transfer can be 25 established.

Because of the fact that the phase difference is zero between P and V, the impedance is uniform throughout the tube. So, when P is high, V is high as well, and accordingly, the viscous losses are high.

30 US 4, 355, 517 describes an improvement of US 4, 114, 380 in which the advantages of travelling and standing acoustic waves are combined. US 4, 355, 517 comprises a thermo-acoustic system different from Fig. la and Fig. 2a. A regenerator unit 20 is provided in the tube 1, the tube 1 now further comprising a feedback circuit 4 3 around regenerator 20 unit. Examples of such thermo-acoustic systems are provided in Fig.’s 2b and 2c.

The acoustic circuit formed by the circuit from Fig. 2b ensures travelling wave conditions in the regenerator unit 20 while the placement of the circuit at the pressure 5 antinode of Fig. lb (pressure antinode referring to the pressure maximum (at the closed end)) superimposes the standing wave pressure to the travelling wave (increase of P) without increasing the velocity. This will lead to a high impedance, low compressible medium velocities and hence less viscous losses in the regenerator and hence a high performance.

10

It will be understood that for a given application there is an optimal position for the regenerator unit 20 . The optimal position depends on the local conditions, i.e. the dynamic pressure amplitude is preferably relatively high and the velocity is preferably relatively low. In other words, the acoustic impedance Z, which is defined as Z = P/V, 15 is preferably relatively high. Thus, depending on the given application of the thermoacoustic system, there is a specific preferred position for the regenerator 20. Fig. 2c shows an alternative to Fig. 2b. Again, a feedback circuit 4 is provided, but now by providing a regenerator unit 20 in the tube 1 that does not fill the complete cross sectional area of the tube 1, but leaves a passage between the regenerator unit 20 and 20 the wall of the tube 1, thereby creating a feedback circuit 4. This configuration is also referred to as a coaxial configuration.

For some applications it is required to provide more than one regenerator unit 20 in the tube 1.

25 Fig. 2d shows a thermo-acoustic system comprising two regenerator units 20 positioned at different positions along the longitudinal axis of the tube 1. This is however not an optimal situation, as the second regenerator unit 20 is at a position that is less optimal than the first regenerator unit 20 with respect to the standing acoustic wave. In other words, the acoustic impedance Z can’t be the same for the two 30 regenerator units 20, so at least one of the two regenerator units 20 has a less optimal acoustic impedance. The added regenerator unit 20 is thus less efficient, as it suffers from more viscous losses in the regenerator unit 20. Summarizing, when more than one regenerator unit 20 is provided, only one of the regenerator units 20 can be positioned 4 in an optimal position, such that the other regenerator units 20 will function in a sub-optimal way.

SHORT DESCRIPTION

5 It is an object of the invention to provide a thermo-acoustic system comprising more than one regenerator unit, where all regenerator units can be used in a more efficient way.

So, according to an aspect of the invention there is provided a thermo-acoustic system comprising a tube, the tube comprising a regenerator unit, the regenerator unit 10 comprising a first side and a second side, which in use have different temperatures, the regenerator unit being positioned at a location with an acoustic impedance, the tube comprising a feedback circuit to provide a feedback path between the first and second side of the regenerator unit, wherein the feedback circuit comprises a second regenerator unit comprising a first and a second side, the second regenerator unit being 15 positioned at a second location within the feedback circuit having an acoustic impedance substantially identical to the acoustic impedance of the first regenerator unit. This makes it possible to provide a thermo-acoustic system with more than one regenerator unit, wherein each regenerator unit has an optimal acoustic impedance. The term substantially similar is used here to indicate that the acoustic impedances do not 20 differ more than 20% with respect to each other, preferably not more than 10%.

According to an embodiment the regenerator units functions as a heat pump or cooler and the thermo-acoustic system further comprises an acoustic source positioned on a first end of the tube and the regenerator units are positioned at an opposite end of the tube, the tube having a length L from the first end to the second end being arranged 25 to comprise a standing acoustic wave generated by the acoustic source. Such a thermoacoustic system can be used as a heat pump or cooler. The acoustic source may be a driver selected from the group: speaker, linear motor, piezo electrical element, piston-compressor and thermo-acoustic engine.

According to an embodiment the driver is an acoustic device positioned on a first 30 end of the tube, and the regenerator unit is positioned in the vicinity of the other end of the tube, the tube having a length L from the first end to the second end being arranged to comprise a standing acoustic wave generated by the regenerator unit.

5

According to an embodiment the regenerator units function as an engine, and the thermo-acoustic system further comprises an acoustic load positioned on a first end of the tube and the regenerator units are positioned at an opposite end of the tube, the tube having a length L from the first end to the second end being arranged to comprise a 5 standing acoustic wave generated by the regenerator units. Such a thermo-acoustic system can be used as an engine. The acoustic load is selected from the group: linear generator, thermo-acoustic heat pump, thermo-acoustic cooler.According to an embodiment the regenerator unit is used as a heat pump or a cooler.

According to an embodiment at least one of the regenerator units (20) function as 10 heat pump or cooler and at least one of the regenerator units (20) function as an engine.

According to an embodiment the acoustic impedance associated with the standing acoustic wave is defined as the ratio of the amplitude of the local dynamic pressure to the amplitude of the local gas velocity: Z = P/V.

15 According to an embodiment the tube has a longitudinal axis, and the regenerator units are located at a similar location with respect to the longitudinal axis of the tube.

According to an embodiment the tube has a longitudinal axis, and the regenerator units are located at a similar location with respect to an end of the tube.

According to an embodiment the geometry of the tube and/or the geometry of the 20 feedback circuit is tuned to make the acoustic impedance Z equal for the regenerator units.

According to an embodiment the feedback circuit is created by positioning a divider along a predetermined portion of a longitudinal axis of the tube.

According to an embodiment the feedback circuit comprises one or more further 25 regenerator units, each comprising a first side and a second side, the one or further regenerator unit each being positioned at a location with a substantial identical acoustic impedance as the first regenerator units.

SHORT DESCRIPTION OF THE DRAWINGS

30 Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: 6

Figures la, lb schematically depict a thermo-acoustic system according to the prior art,

Figures 2a, 2b, 2c and 2d schematically depict further thermo-acoustic systems according to the prior art, 5 - Figures 3a and 3b schematically depict a thermo-acoustic system according to an embodiment,

Figures 4a and 4b schematically depict a thermo-acoustic system according to a further embodiment, and

Figure 5 schematically depicts a thermo-acoustic system according to an 10 embodiment.

DETAILED DESCRIPTION

In general, the embodiments provided here relate to a resonant thermo-acoustic system comprising an acoustic source or acoustic load 10 and a regenerator unit 20.

15 However, also embodiments without such an acoustic source or load will be provided.

An embodiment will now be described with reference to Fig.’s 3a - 3b, wherein an acoustic source 10 is provided and the thermo-acoustic system functions as a heat pump or cooler.

20 The acoustic source 10 generates acoustic energy (acoustic wave) which is used by the regenerator unit 20. The regenerator unit 20, which may function as a cooler or a heat pump consumes acoustic energy generated by the acoustic source 10 to generate cooling, heating.

The term regenerator unit 20 is used in this text to refer to a combination of a 25 regenerator and heat exchangers on either side.

The acoustic source 10 can for example be a speaker, linear motor, piezo electrical element, piston-compressor and thermo-acoustic engine. In case the driver 10 is a thermo-acoustic engine, it may comprise one or more regenerator units.

30 The resonance of the thermo-acoustic system can be realized by a resonator, such as an acoustic resonator or a mechanical resonator.

7

It will be understood that in embodiments and examples provided in this text the regenerator unit 20 comprises a first side 21 which is usually denoted as the side with the relatively high temperature, i.e. higher than the temperature of the second side 22. This may however also be the other way around.

5 For instance, in case the thermo-acoustic system is used as a heat pump/cooler , the first side 21 may have the relatively high temperature, while the second side 22 may have a relatively low temperature.

Alternatively, in case the thermo-acoustic system is used as a engine, the first side 21 may have a relatively low temperature, e.g. ambient temperature, while the 10 second side 22 may have a relatively high temperature.

Fig. 3a schematically depicts a thermo-acoustic system, comprising a tube 1, the tube 1 comprising an acoustic source 10 and a regenerator unit 20 . The regenerator unit 20 comprises a first side 21 and a second side 22, which in use have different temperatures. The acoustic source 10 being arranged to generate an acoustic wave in 15 the tube 1. The regenerator unit 20 being positioned at a location with an acoustic impedance Z. The tube 1 comprises a feedback circuit 4 to provide a feedback path between the first and second side 21, 22. The feedback circuit 4 comprises a second regenerator unit 20 comprising a first and a second side 21, 22. The first and second regenerator units 20 may have their opposite sides 21,22 facing each other via the 20 feedback circuit 4, in case both regenerator units 20 function as engine or as heat pump.

In case a combination of an engine and a heat pump is used, the first and second regenerator units 20 may have similar sides 21, 22 facing each other via the feedback circuit 4 (not shown).

The second regenerator unit 20 is positioned at a second location within the 25 circuit 4 having an acoustic impedance Z substantially identical to the acoustic impedance Z of the first regenerator unit 20.

This embodiment provides the advantage that it allows using two regenerator units 20 which both can be positioned at a location with an optimal acoustic impedance Z.

30 According to an embodiment, the acoustic source is an acoustic device 10 positioned on a first end 2 of the tube 1, and the regenerator unit 20 is positioned in the vicinity of the other end 3 of the tube 1, the tube 1 having a length L such that a resonant system is provided, i.e. a standing acoustic wave is generated by the acoustic 8 source 10, as will be understood by a skilled person. The length L of the tube 1 may for instance be influenced by the shape and dimensions of the tube 1.

Alternatively, the acoustic source 10 is a thermo-acoustic engine driving a massspring system. In this case the tube 1 may have an arbitrary length, so the acoustic 5 source 10 may be positioned close to the regenerator unit 20. According to a further alternative, the acoustic source 10 may be formed by one or more thermo-acoustic engines.

in general, the dimensions of the tube may be chosen such that a standing acoustic wave may be generated in the tube 1.

10 The regenerator unit 20 may function as one of a heat pump or a cooler.

The acoustic impedance Z associated with the acoustic wave is defined as the ratio of the amplitude of the local dynamic pressure P to the amplitude of the local gas velocity V, i.e. Z = PA7.

In order to position the regenerator units 20 at a location with a substantial 15 identical acoustic impedance, the regenerator units 20 may be located at a similar and symmetrical location with respect to a longitudinal axis LA of the tube 1. This longitudinal axis LA is indicated in Fig. 3a. Also, the regenerator units 20 may be located at a similar location with respect to an end 3 of the tube 1.

This is an easy way to ensure that each regenerator unit 20 has a substantially 20 identical acoustic impedance Z. According to the example above two regenerator units 20 are provided, but from further examples provided below, it will be apparent that this may also apply for the third, fourth,... etc. regenerator unit 20 .

According to a further embodiment, the geometry of the tube 1 and/or the geometry of the feedback circuit 4 is tuned to make the acoustic impedance Z 25 substantially equal for the regenerator units 20. Tuning the geometry can be done by changing the length, width and/or shape of the tube 1 and/or the feedback circuit 4.

By reference to Fig 3a, the tuning of the impedance of each of the regenerator units 20 can be achieved by adjusting the resistance of the regenerator units and/or by adjusting the length and/or the diameter of the flow paths that make up the feedback 30 circuit 4. Increasing the resistance of the regenerator units 20 and thereby the impedance can for example be done by increasing the length of the regenerator unit 20, decreasing the diameter of the regenerator unit 20, decreasing the hydraulic radius or porosity of the regenerator unit 20. The hydraulic radius of the regenerator units 20 is 9 defined as volume available for flow divided by the wetted area. The wetted area is the interface area between the working medium and the regenerator material.

Shifting the regenerator units 20 towards the end of the tube 3 will lead to an increase of the impedance of both regenerator units 20. Since a single change of 5 diameter or length of one of the flow paths, that make up feedback circuit 4, leads to changes in impedance of all regenerator units 20, the system can be optimized in an integral way. This can be done by using computer codes describing thermoacoustic theory, like DeltaEC. This tool enables the optimal setting for all diameter, lengths en regenerator characteristics. The optimization can be done in such a way that the 10 impedances should preferably lie between 15 and 25.

Feedback circuit

The feedback circuit 4 can be created in many ways, one of which is shown in Fig.’s 3a and 3b.

15 According to the embodiment shown, the feedback circuit 4 is created by providing a divider 25 along a predetermined portion of a longitudinal axis of the tube 1. The divider 25 divides the tube 1 into two separate parts along a predetermined length of the tube 1 at the position of the regenerator units 20

Fig. 3b, showing a cross sectional view of the thermo-acoustic system, shows that 20 the divider 25 may comprise a substantial cylindrical body part 26 with two partition plates 27 protruding at opposite sides of the cylindrical body part 26. The divider 25 divides the tube 1 in different parts, thereby creating a feedback circuit 4.

It will be understood that the divider 25 may have any other suitable shape creating a feedback circuit 4. For instance, the divider 25 may also be formed by a 25 single partition plate 27 positioned along the predetermined length between the inner walls of the tube 1 creating a feedback circuit 4.

The divider 25 extends along a predetermined part of the tube 1, extending at opposite sides of the regenerator units 20. However, the divider 25 does not extend towards the closed end of the tube 3, i.e. the divider creates a passage along the closed 30 end of the tube 1 from the first to the second load 20.

According to a further embodiment, the regenerator units 20 are placed between two cylindrical tubes positioned coaxially with respect to each other. The ends of the two cylindrical tubes are closed by ellipsoidal caps to provide a curved flow channel 10 for the gas. This will reduce the losses due to the sharp edges in Fig.2c and 2d. This configuration has the advantage to be also more compact than the torus configuration of Fig.2b.

Of course, many alternatives for forming a feedback circuit 4 can be conceived.

5

According to an alternative component 10 functions as an acoustic load. The acoustic load 10 may for instance be formed by a linear generator or a thermo-acoustic heat pump or cooler. The regenerator units 20 function as a thermoacoustic engine.

10 Three or more regenerators

Instead of two, more than two regenerator units 20 may be provided. An example of this is shown in Fig.’s 4a and 4b. The feedback circuit 4 may comprise one or more further regenerator units 20, each comprising a first side 21 and a second side 22, the one or further regenerator units 20 each being positioned at a location with a 15 substantially identical acoustic impedance Z as the regenerator units 20. In Fig. 4b only one of the regenerator units 20 is shown with a dashed line for reasons of clarity.

In order to achieve this, the feedback circuit 4 may be formed as a zigzag-shaped circuit to allow more than two regenerator units 20 being positioned at a substantially identical acoustic impedance Z. Preferably, the number of regenerator units 20 is even, 20 as the zigzag shaped circuit starts and ends at the same side (i.e. facing away from the end of the tube 3), the number of available positions for a regenerator unit 20 are even. As explained above, this may involve locating the two or more regenerator units 20 at a similar location along the longitudinal axis LA or at a similar distance from the end of the tube 3.

25 Fig. 4a shows a cross sectional view of the tube 1 at the location of the feedback circuit 4. Fig. 4a shows that the feedback circuit 4 may be created by providing a divider 25, similar as shown and described with reference to Fig.’s 3a and 3b. The divider 25 is shown in more detail in Fig. 4b.

The divider 25 is positioned along a predetermined portion of the longitudinal 30 axis LA of the tube 1. The divider 25 divides the tube 1 into separate parts along a predetermined length of the tube 1 at the position of the regenerator units 20. Again, the divider 25 may comprise a substantial cylindrical body part 26, now with a number of partition plates 27 protruding at different sides of the cylindrical body part 26.

11

The divider shown in Fig.’s 4a and 4b is provided with openings and further partition walls 29 creating a path through the feedback circuit 4 via all regenerator units 20 .

Of course, many alternatives for forming a feedback circuit 4 can be conceived.

5 To ensure that the acoustic impendence is substantial equal for all regenerator units 20 , the geometry of the tube 1 and/or the geometry of the feedback circuit 4 may be tuned to make the acoustic impedance Z substantially equal for the regenerator units 20. Tuning the geometry can be done by changing the length, width and/or shape of the tube 1 and/or the feedback circuit 4.

10 This embodiment with more than two regenerator units 20 may function as heat pump or cooler in combination with an acoustic source 10. Alternatively, this embodiment may function as an engine in combination with an acoustic load 10.

According to a further embodiment, the embodiment with more than two regenerator units 20 may function without acoustic source or load 10, but may 15 comprise at least one regenerator unit 20 which functions as heat pump or cooler and at least one regenerator unit 20 which functions as an engine. An example of such an embodiment is provided in Fig. 5.

Further remarks 20 From the above it is clear that the thermo-acoustic system as described may be used as heat engine in which acoustic power is generated using heat as input, but may also be used as heat pump or cooler in which acoustic power is used to pump heat from a lower temperature heat source to a higher temperature heat sink.

In addition, the thermo-acoustic system can comprise both engine regenerator 25 units and heat pump or cooler regenerator units in accordance with the described embodiments. For instance, three engine regenerator units can be combined with one heat pump or cooler regenerator unit forming a four regenerator unit system. Any combination of engines and heat pumps or coolers are possible.

A possible application would be a cascaded cool down of a hot stream through 30 several engine stages in this system.

Furthermore, it is clear that the embodiments use travelling waves as well as standing waves. The travelling wave is used for the thermo-acoustic process (seen from a thermodynamic point of view) and a standing wave to increase the impedance Z

12 (pressure) by positioning the circuit at a pressure antinode of a resonator. The thermodynamic process thus uses a travelling wave (locally) in the regenerator unit.

The thermo-acoustic cycle in the travelling wave systems is identical to a Stirling cycle, which is one of the most efficient thermodynamic cycle.

5 A travelling wave system functions as an amplifier. In a travelling wave thermoacoustic engine an acoustic wave is fed to the relatively cold side of the regenerator unit 20 which is amplified by the temperature difference over the regenerator unit 20.

At the relatively warm side more acoustic power is obtained than provided on the 10 relatively cold side. The term relatively cold and relatively warm as used in respect of the two sides of the regenerator unit 20, here refer to the relative temperature of those sides. Thus, the relatively cold side has a low temperature compared to the relatively warm side. One of the two sides 21, 22 may in use have a temperature that is equal to or close to an ambient temperature.

15 For instance, a thermo-acoustic system used as an engine, may have a (cold) first side 21 which has an ambient temperature and a (warm) second side 22 having a higher temperature. A thermo-acoustic system used as a cooler may have a (cold) first side 21 which is a lower temperature and a (warm) second side 22 which has a higher (ambient) temperature.

20 In a travelling wave thermo-acoustic system (engine or cooler), the acoustic power enters the regenerator unit 20 from the low temperature side and it is amplified in an engine by the temperature difference across the regenerator unit 20 (thus more power at hot side). But in a cooler or heat pump the acoustic power entering from the high temperature side is used to pump heat against a temperature gradient and it is 25 attenuated (less power at low temperature side).

The circuit 4 provides feedback of part of the acoustic power to keep the process going. The acoustic circuit (acoustic resistance, acoustic inertance of the feedback, .. .etc.) determines the direction of the travelling wave in the circuit.

The descriptions above are intended to be illustrative, not limiting. Thus, it will 30 be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

A thermo-acoustic system comprising a tube (1), wherein the tube (1) comprises a regenerator unit (20), wherein the regenerator unit comprises a first side (21) and a second side (22), which during operation are different have temperatures where the regenerator unit (20) is positioned at an location with an acoustic impedance (Z), the tube (1) including a feedback circuit (4) for providing a feedback path between the first and second side ( 21, 22) of the regenerator unit (20), characterized in that the feedback circuit (4) comprises a second regenerator unit (20), comprising a first and second side (21, 22), wherein the second regenerator unit (20) is positioned is at a second location within the feedback circuit (4) with an acoustic impedance (Z) that is substantially equal to the acoustic impedance (Z) of the first regenerator unit.

The thermo-acoustic system according to claim 1, wherein the regenerator units 20 function as a heat pump or cooler and the thermo-acoustic system comprises an acoustic source (10) positioned at a first end (2) of the tube (1) and the regenerator units (20) are positioned at an opposite end (3) of the tube (1), the tube (1) having a length L from the first end to the second end such that it can comprise a standing acoustic wave which is generated by the acoustic source (10).

3. Thermo-acoustic system according to claim 2, wherein the acoustic source (10) is a driver selected from the group: loudspeaker, linear motor, piezoelectric element, piston-compressor and thermo-acoustic motor.

The thermo-acoustic system according to claim 1, wherein the regenerator units function as a motor and the thermo-acoustic system comprises an acoustic load (10) positioned at a first end (2) of the tube (1) and the regenerator units (20) positioned are at an opposite end (3) of the tube (1), the tube (1) having a length L from the first end (2) to the second end (3) such that it can comprise a standing acoustic wave which is generated by the regenerator units (20).

The thermo-acoustic system according to claim 4, wherein the acoustic load (10) is selected from the group: linear generator, thermo-acoustic heat pump, thermo-acoustic cooler. 10

The thermo-acoustic system according to claim 1, wherein at least one of the regenerator units (20) functions as a heat pump or cooler and at least one of the regenerator units (20) functions as a motor.

The thermo-acoustic system according to any of claims 1 to 6, wherein the acoustic impedance (Z) associated with the standing acoustic wave is defined as the ratio between the amplitude of the local dynamic pressure (P) and the amplitude of the local gas speed (V): Z = P / V.

The thermo-acoustic system according to any of the preceding claims, wherein the tube (1) has a longitudinal axis, and the regenerator units (20) are located at a similar location with respect to the longitudinal axis of the tube (1).

9. Thermo-acoustic system according to any of the preceding claims, wherein the tube (1) has a longitudinal axis and the regenerator units are located at a comparable location with respect to an end (3) of the tube (1).

10. Thermo-acoustic system according to one of the preceding claims, wherein the geometry of the tube (1) and / or the geometry of the feedback circuit (4) is adjusted to make the acoustic impedance Z equal for the regenerator units (20). ).

The thermo-acoustic system according to any of the preceding claims, wherein the feedback circuit (4) is created by positioning a manifold (25) along a predetermined portion of a longitudinal axis of the tube (1).

A thermo-acoustic system according to any preceding claim, wherein the feedback circuit (4) comprises one or more further regenerator units (20), each regenerator unit comprising a first side (21) and a second side (22), the one or more regenerator units (20) are each positioned at a location with a substantially identical acoustic impedance (Z) as the first regenerator unit.