HK1164986B - Magnetocaloric heat generator - Google Patents

Description

Magnetocaloric heat generator

Technical Field

The invention relates to a magnetocaloric heat generator comprising: at least two magnetocaloric elements arranged one after the other and forming at least two successive thermal stages, said magnetocaloric elements being crossed by a separate heat transfer fluid and each comprising two opposite ends; a magnetic device for subjecting each of said magnetocaloric elements to a varying magnetic field, a heating cycle and a cooling cycle being alternately generated in each of said magnetocaloric elements; a driving means of the heat transfer fluid, which drives the heat transfer fluid to alternately pass through the magnetocaloric elements in a direction towards one end and in a direction towards the opposite end and in the opposite direction towards the opposite end and in the direction towards the end, in a manner synchronized with the variation of the magnetic field.

Background

Cold magnetic technology has been known for more than twenty years and its advantages in terms of ecology and sustainable development are known. Limitations in their effective thermal power and their efficiency are also known. Since then, research in this field has been directed towards improving the performance of such generators by devising in terms of different parameters such as the magnetizing power, the performance of the magnetocaloric elements, the exchange area between the heat transfer fluid and the magnetocaloric elements, the performance of the heat exchangers, etc.

In order to increase the power of a magnetocaloric generator, it is known to add several magnetocaloric elements in the form of a hierarchical structure to the generator, so that the fluid coming out of a magnetocaloric element mixes with the fluid coming into the next magnetocaloric element, so as to achieve a heat exchange and increase the temperature gradient. In this configuration, the magnetocaloric elements in fluid communication with each other are always in the same magnetic state, i.e. both are subjected to a magnetic field, or both are external to the magnetic field, and so on.

Heat generators are known having a hierarchical structure of several thermal modules, each module comprising one or several magnetocaloric elements, and whose output thermal energy of a first thermal module is transferred to the inlet of a second thermal module and so on. Such generators have a number of disadvantages.

One of the drawbacks is the transfer of thermal energy between the inlet and the outlet of successive thermal modules. This transfer of thermal energy is obtained, for example, by mixing the heat-carrying fluids contained in the chambers located at the respective ends of the modules. However, such mixing requires movement of the fluid and necessarily increases the complexity of the generator as well as its cost.

The method for overcoming this drawback consists in using the same drive means for moving the heat transfer fluid inside the chamber concerned. However, this configuration results in inherent drawbacks related to the transfer of the heat transfer fluid between the thermal modules: channels must be made for this fluid exchange, which increases the complexity of the heat generator, is not conducive to proper mixing of the heat transfer fluid, does not allow optimal heat exchange between the output fluid of a magnetocaloric element and the input fluid of the next thermal module, and contributes to increased load losses.

In addition, the use of known stepped generators leads to additional difficulties, especially in the case of thermal modules used for operation in different temperature ranges. In fact, in the case of a hierarchical structure comprising two stages, for example, the magnetocaloric elements of one stage may operate in a negative temperature range and the magnetocaloric elements of the second stage in a positive temperature range. It is therefore necessary to use a suitable heat transfer fluid whose exchange coefficient and viscosity are optimal in both temperature ranges. However, the heat transfer fluids that are freely available on the market today do not have the best characteristics over a large temperature range, which requires a compromise and does not make the most use of the thermal capacity of the generator.

Disclosure of Invention

The object of the present invention is to overcome these drawbacks by proposing a solution to the above-mentioned problems. To this end, the magnetocaloric heat generator according to the invention is implemented so as to optimize the capacity of the hierarchical structure to generate thermal power and the heat transfer between two successive thermal modules or two successive magnetocaloric elements of the hierarchical structure.

To this end, the invention relates to a magnetocaloric generator of the type indicated above, characterized in that said magnetocaloric elements are thermally connected two by two at their successive ends by heat exchange means in contact with the heat transfer fluid flowing in said first magnetocaloric element and with the heat transfer fluid flowing in said second magnetocaloric element, respectively.

Advantageously, the heat exchange element may comprise two transfer zones thermally connected to each other forming a thermal bridge. These transfer zones can be crossed separately by the heat transfer fluid of each of said magnetocaloric elements.

Preferably, the transfer zones can be arranged adjacent to the respective ends of two successive magnetocaloric elements.

In this configuration, the transfer zone can be made of a heat-conducting material, for example aluminum or copper or an alloy thereof, and can be provided with through-passages for the heat transfer fluid. As a variant, the transfer zone can also be porous, so that the heat transfer fluid can pass through its pores.

In a first variant, the two transfer zones of the heat exchange element can be interconnected by a body made of heat-conducting material.

In a second variant, the two transfer zones of the heat exchange element can be connected to each other by at least one heat pipe (heat pipe).

The driving means of the heat transfer fluid may comprise: a central actuator in fluidic connection with successive ends of said magnetocaloric element; and two end actuators, each end actuator being mounted opposite one of the free ends of the magnetocaloric element.

In addition, to improve the heat exchange between the two heat carrying fluids, the central actuator can be made of a heat conductive material and in contact with said heat exchange means.

As a variant, the central actuator may be a double-acting piston made of thermally conductive material, and the bushing of the central actuator is made of thermally insulating material. In this case, the central actuator may constitute the heat exchanging part.

The driving means of the heat transfer fluid may also comprise: two central actuators, each central actuator being in fluidic connection with one of the successive ends of the magnetocaloric element; and two end actuators, each end actuator being in fluid connection with one of the free ends of the magnetocaloric element.

Advantageously, the moving part may be a piston selected in the group comprising a single-acting piston and a double-acting piston.

In addition, the magnetocaloric generator may comprise a magnetic arrangement enabling successive magnetocaloric elements to be located either always in two different cycles or always in the same cycle. Of course, the cycle includes a heating cycle or a cooling cycle.

Finally, in order to make effective use of the thermal capacity of each magnetocaloric element, the heat transfer fluid passing through said magnetocaloric elements may have different chemical compositions and/or thermal characteristics. Of course, this component is adapted to the optimum operating temperature of each magnetocaloric element, in particular centered on its curie temperature.

Drawings

The invention and its advantages will be better shown in the following description of several embodiments, given as a non-limiting example, with reference to the accompanying drawings, in which:

figures 1A and 1B are schematic views of a first embodiment of a heat generator according to the invention;

figures 2A and 2B are similar to figures 1A and 1B, showing a second embodiment of the heat generator according to the invention;

figures 3A and 3B are similar to figures 1A and 1B, showing a third embodiment of the heat generator according to the invention;

fig. 4A and 4B show an embodiment variant of the heat generator of fig. 1A and 1B;

fig. 5A and 5B show another embodiment.

Detailed Description

In the illustrated embodiment, identical parts or portions are written with the same reference numerals.

Each heat generator 1, 10, 20, 30, 40 comprises two magnetocaloric elements 2, 12, each comprising one magnetocaloric material. The invention is not limited to such a configuration and extends to more than two magnetocaloric elements 2, 12, each comprising one or several magnetocaloric materials. In fact, each magnetocaloric element 2, 12 can be made of several magnetocaloric materials comprising different curie temperatures and generating a great magnetocaloric effect, so that the juxtaposition of several magnetocaloric materials makes it possible to create a high temperature gradient between the hot and cold ends of the heat generator 1, 10, 20, 30, 40 and thus obtain an even higher efficiency. This configuration may also cover a wide temperature range corresponding to the operating and use range of the generator.

Each magnetocaloric element 2 and 12 comprises two opposite ends, respectively 3 and 4, and 13 and 14. The heat transfer fluid flows according to the variation of the magnetic field in the direction of one or the other of said opposite ends 3, 4 and 13, 14 of each magnetocaloric element 2, 12. A specific heat transfer fluid passes through each magnetocaloric element 2, 12. The fluid circuits of the magnetocaloric elements 2, 12 are separated so that the heat transfer fluids are never mixed.

The components of the heat transfer fluid used may be different or identical. Their composition will depend on the magnetocaloric materials used to make the magnetocaloric elements 2, 12 and on their operating temperature range. The heat transfer fluid is made to flow through said magnetocaloric materials 2, 12 in the direction of one or other of their ends 3, 4 and 13, 14, so as to implement and maintain a temperature gradient between the opposite ends 3 and 14 of the heat generators 1, 10, 20, 30, 40, said flow of heat transfer fluid being associated with a variation of said magnetic field.

In order to facilitate the heat exchange with the heat transfer fluid, the magnetocaloric materials constituting the magnetocaloric elements 2, 12 may be porous, so that their pores form channels for the passage of the fluid. They may also be in the form of solid blocks in which small or micro-channels are machined, or assembled from plates with overlapping grooves, and between which the heat-carrying fluid can flow. They may also be in the form of powders or granules, so that the gaps form fluid channels. Of course, any other embodiment allowing the heat transfer fluid to pass through said magnetocaloric materials is applicable.

The magnetic means (not shown) can be constituted by a set of permanent magnets that are relatively movable with respect to each magnetocaloric element 2, 12, by sequential energization or by any other similar means capable of generating a variation of the magnetic field.

In the heat generator 1 shown in fig. 1A and 1B, the magnetocaloric elements 2, 12 are arranged in a row and form two successive thermal stages. Both of them are always subjected to the same magnetic field variation and are either in the heating cycle or in the cooling cycle. As such, in fig. 1A, the magnetocaloric elements 2 and 12 are magnetically activated so that they heat up. The heat transfer fluid is caused to flow to the right in fig. 1A in the direction of the arrow shown. In fig. 1B, the magnetocaloric elements 2 and 12 are magnetically deactivated so that they cool. The heat transfer fluid flows to the left in fig. 1B in the direction indicated by the arrow.

The magnetocaloric elements 2 and 12 are thermally connected by a heat exchange member 5, the heat exchange member 5 being constituted by a U-shaped piece made of heat conductive material and the branch ends of which are provided with two transfer zones 22 and 23. Each transfer zone 22, 23 comprises a transverse channel 6 through which a heat transfer fluid can flow. These two transfer zones 22 and 23 are arranged in the heat generator 1 adjacent to the successive ends 4 and 13 of the two magnetocaloric elements 2, 12. These transfer zones 22 and 23 are therefore in direct contact with said magnetocaloric elements 2 and 12.

The drive means of the heat transfer fluid comprise: on the one hand, two pistons 7 arranged in a row and forming an end actuator, each piston 7 being mounted opposite a free end 3, 14 of said magnetocaloric elements 2, 12, these pistons 7 moving simultaneously in the same direction in order to transmit a reciprocating motion to two heat transfer fluids; and, on the other hand, a double-acting piston 8 forming a central actuator and located in the exchange section 5, said piston being aligned with the other two pistons 7, being in fluid connection with the successive ends 3, 14 of said magnetocaloric elements 2, 12, and moving in the same direction as the other two pistons 7. These pistons 7, 8 are controlled by any known means, such as by a control cam, a variable magnetic field, a fluid system or any other similar means.

A double-acting piston 8 is interposed between the two magnetocaloric elements 2 and 12 and therefore makes it possible to distribute the thrust required for the movement of the heat transfer fluid between the different actuators or pistons, thus better compensating for the load losses.

In addition, the double-acting piston 8 separates the volumes in which the magnetocaloric elements 2 and 12 are arranged. This configuration makes it possible to use different heat transfer fluids compatible with each type of magnetocaloric element and therefore with its operating temperature. The fact of using different fluids makes it possible to select the fluids so that their heat transfer coefficient and their viscosity are adapted to the temperature at which they vary around the temperature, and thus to make it possible to exploit to the maximum extent the thermal capacity of each magnetocaloric element 2, 12.

Thus, during the period in which the magnetocaloric elements 2 and 12 are magnetically excited (see fig. 1A), the heat-carrying fluid associated with the first magnetocaloric element 2 is carried by the piston 7 to flow in the first magnetocaloric element 2, heated and then passes through the corresponding transfer zone 22 of the heat exchange element 5 to reach the lining of the double-acting piston 8. At the same time, the heat transfer fluid associated with the second magnetocaloric element 12 flows out of the chamber of the double-acting piston 8, passes through the other transfer zone 23 of the thermal energy transfer means 5, flows in the second magnetocaloric element 12 in the direction of the piston 7, and is heated. Consequently, the thermal energy of the heat transfer fluid associated to the first magnetocaloric element 2, hereinafter referred to as first heat transfer fluid, is absorbed by the heat exchange means 5 through the transfer zone 22 and released to the heat transfer fluid associated to the second magnetocaloric element 12, hereinafter referred to as second heat transfer fluid, through the transfer zone 23. The transfer of thermal energy is achieved almost simultaneously by heat conduction between the first heat carrier fluid and the heat exchange means 5 on the one hand and between said heat exchange means 5 and the second heat carrier fluid on the other hand.

In the period of magnetic deactivation of the magnetocaloric elements 2, 12 shown in fig. 1B, the heat transfer fluid flows from right to left, while the two magnetocaloric elements 2, 12 cool. The second heat carrying fluid exchanges heat with the respective transfer zones 23 of the heat exchange means 5, while the respective heat exchange means 5 exchanges heat with the first heat carrying fluid at their respective transfer zones 22.

In this heat generator 1, the two magnetocaloric elements 2, 12 comprise different magnetocaloric materials, the curie temperature of the first magnetocaloric element 2 being lower than the curie temperature of the second magnetocaloric element 12, so that the first magnetocaloric element 2 can be effective, for example, in the negative temperature range (actif) and the second magnetocaloric element 12 in the positive temperature range. This configuration can expand the operating range of the heat generator 1.

Of course, the invention also contemplates the possibility of using magnetocaloric elements 2, 12 comprising the same magnetocaloric material.

In this way, the heat exchange means 5 connecting two successive magnetocaloric elements 2, 12 in a hierarchical structure can transfer thermal energy from one stage to the other without fluid transfer and contribute to increasing the temperature gradient from one stage to the other, with the result of contributing to increasing the temperature gradient between the cold end 3 and the hot end 14 of the heat generator 1.

In addition, the heat generator 1 comprises, at its opposite ends 3 and 14 constituted by the free ends of the magnetocaloric elements 2 and 12, exchange means 16 which allow the exchange of thermal energy with an external device or application (application). These external applications may be, for example, the air surrounding the heat generator, a device or a thermal barrier.

The exchange means 16 also comprise a transfer zone 17 made of a heat-conducting material, provided with through channels 18 for the heat transfer fluid and adjacent to the free ends 3, 14 of the magnetocaloric elements 2, 12, so that the heat transfer fluid passes through said transfer zone 17 each time it enters or exits a magnetocaloric element. The transfer zone 17 can therefore exchange thermal energy with the heat-carrying fluid at each cycle and therefore constitute a very efficient heat exchanger. In addition, the transfer zone 17 is thermally connected to the external application by a closed circuit provided with channels 19 incorporated in said exchange means 16, the heat transfer fluid associated with the external application flowing in the channels 19.

Of course, the invention is not limited to such heat exchangers, and any other suitable heat exchanger may be used.

In the heat generator 10 shown in fig. 2A and 2B, the magnetocaloric elements 2, 12 are arranged in rows one after the other and always in different heating or cooling cycles. As such, in fig. 2A, the magnetocaloric element 2 or the first magnetocaloric element 2 located on the left is magnetically deactivated, and the magnetocaloric element 12 or the second magnetocaloric element 12 located on the right is magnetically activated. In the direction of the arrows shown, the heat transfer fluid is brought to the left in the first magnetocaloric element 2 and to the right in the second magnetocaloric element 12. In fig. 2B, the magnetocaloric elements 2 and 12 are in opposite magnetic states, the heat transfer fluid being driven to the right in the first magnetocaloric element 2 and to the left in the second magnetocaloric element 12.

The heat exchange member 5 is the same as the heat exchange member shown in fig. 1A and 1B. It also allows to achieve a heat exchange between the heat transfer fluids flowing in the successive magnetocaloric elements 2 and 12. In this embodiment, the heat transfer fluid is on the one hand made to flow by two pistons 7 arranged in a row and identical to the pistons inserted in the heat generator 1 of fig. 1A and 1B, at the free ends 3 and 14 of the magnetocaloric elements 2 and 12, but at the same time moved in two opposite directions. The operation of the heat transfer fluid is also carried out at the successive ends 4 and 13 of the two magnetocaloric elements 2 and 12 by two separate single-acting pistons 9, which form the central actuator and each push the heat transfer fluid in one of the magnetocaloric elements 2 and 12.

The transfer zones 22 and 23 of the heat exchange means 5 are arranged in the heat transfer fluid path between the end 4, 13 of a magnetocaloric element 2, 12 and its single-acting piston 9 and are therefore crossed simultaneously by the heat transfer fluid at each inlet and each outlet of the magnetocaloric element 2, 12.

In the heat generator 20 shown in fig. 3A and 3B, the fluid flows in the same manner as in the heat generator 1 of fig. 1A and 1B. But its operation is different. The double-acting piston 8 is replaced by two single-acting pistons 11, 15, each of which is in fluid connection with one of the magnetocaloric elements 2, 12. Thus, when the piston 11 or 15 forming the central actuator draws in the heat transfer fluid of its corresponding magnetocaloric element 2 or 12, the other piston 15 or 11 pushes the heat transfer fluid in its corresponding magnetocaloric element 12 or 2, and vice versa.

In this configuration, the transfer zones 22 and 23 of the heat exchange means 5 are also arranged in the passage of the heat transfer fluid, adjacent to said ends 4, 13, between the ends 4, 13 of the magnetocaloric elements 2, 12 and the single-acting pistons 11, 15. Thus, the transfer zone is simultaneously crossed by the heat transfer fluid at each magnetic cycle: on the one hand, the outlet of the first heat transfer fluid in the magnetocaloric elements 2 and the inlet of the second heat transfer fluid in the magnetocaloric elements 12 (see fig. 3A), and, on the other hand, each inlet of the first heat transfer fluid in the magnetocaloric elements 2 and the outlet of the second heat transfer fluid in the magnetocaloric elements 12 (see fig. 3B).

The heat generator 30 shown in fig. 4A and 4B constitutes an embodiment variant of fig. 1A and 1B, wherein the central piston 8' is made of a heat-conducting material and its lining is formed in the heat exchange part 35. In this way, the thermal energy of the heat transfer fluid flowing in two adjacent magnetocaloric elements 2, 12 is exchanged simultaneously at the transfer zones 22 and 23 of the heat exchange means 35 and at the central piston 8'. The central piston 8' can, on the one hand, carry out a heat exchange directly between the two heat transfer fluids with which it is in contact and, on the other hand, a heat exchange with the heat exchange means 35, the heat exchange means 35 itself carrying out a heat exchange with said heat transfer fluids. This configuration makes it possible to further improve the heat exchange between the two heat transfer fluids.

In a variant of the combination, not shown and which can be combined with any of the embodiments shown in fig. 1A, 1B, 2A, 2B, 3A, 3B, 4A and 4B, the two transfer zones 22 and 23 of the exchange means 5, 35 can be connected to each other by at least one heat pipe to ensure the exchange of thermal energy between them.

Fig. 5A and 5B show an embodiment of a heat generator 40, whose structure is substantially identical to that of the heat generator 30 of fig. 4A and 4B, and in which the heat exchange means 25 are made by a central actuator located between two successive magnetocaloric elements 2, 12. The central actuator 25 is a double-acting piston made of a heat-conducting material and its bushing 27 is made of a heat-insulating material. This bush 27 has the same shape as the bush of the heat exchange means 35 of the heat generator 30 of fig. 4A and 4B, but differs in that its constituent material is a thermally insulating material and there is no transfer zone, which is replaced by two passage zones 26 for the heat carrier fluid. In this configuration, the exchange of thermal energy between the two heat transfer fluids is achieved by the central piston or by a double-acting piston 25 in contact with the two heat transfer fluids.

To further improve the exchange capacity, the central piston 8', 25 of fig. 4A, 4B, 5A, 5B may comprise vanes on its working surface in contact with the heat-carrying fluid.

In all the heat generators 1, 10, 20, 30, 40 shown, exchange elements 16 are added each time to the cold 3 and hot 14 ends of the generators. However, the invention is not limited to such a configuration and also extends to embodiments wherein only one of the cold end 3 or hot end 14 is associated with such an exchange member 16 and/or the heat exchange member 5, 35 is thermally connected to an external device or application.

In addition, the invention is not limited to heat generators comprising only two successive magnetocaloric elements 2, 12. In practice, it can be extended to more than two successive magnetocaloric elements. Each stage may comprise several adjacent magnetocaloric elements.

Finally, the invention is not limited to the use of pistons made as actuators for moving the heat-carrying fluid. Other types of actuators, such as diaphragms, are contemplated.

Possibility of industrial application

From this description it is clear that the invention achieves the intended aim, namely to propose a heat generator 1, 10, 20, 30, 40 of simple structure, in which the transfer of thermal energy between the constituent magnetocaloric elements 2, 12 of the different stages is simplified and efficiently achieved.

Such thermal energy generators 1, 10, 20, 30, 40 can be used in industrial and domestic heating, air conditioning, warming, cooling or other fields at competitive prices and with small space requirements.

The invention is not limited to the described embodiments but extends to modifications and variants that are obvious to a person skilled in the art, while remaining within the scope of protection defined by the appended claims.

Claims (14)

1. Magnetocaloric heat generator comprising: at least two magnetocaloric elements (2, 12) arranged one after the other and forming at least two successive thermal stages, said magnetocaloric elements being crossed by a separate heat transfer fluid and each comprising two opposite ends (3 and 4, 13 and 14); -a magnetic device for subjecting each of said magnetocaloric elements (2, 12) to a varying magnetic field, generating alternately a heating cycle and a cooling cycle in each of said magnetocaloric elements (2, 12); a driving means of the heat transfer fluid which drives the heat transfer fluid through the magnetocaloric elements alternately in the direction of one end and in the direction of the opposite end and vice versa, in synchronism with the variation of the magnetic field,

said magnetocaloric generator (1, 10, 20, 30, 40) being characterized in that said magnetocaloric elements (2, 12) are thermally connected two by two at their successive ends (4, 13) by means of heat exchange means (5, 35) in thermal contact with a heat transfer fluid flowing in a first of said magnetocaloric elements (2) and a heat transfer fluid flowing in a second of said magnetocaloric elements (12), respectively.

2. Magnetocaloric heat generator according to claim 1, characterized in that said heat exchange means (5, 35) comprise two transfer zones (22, 23) thermally connected to each other and crossed by the heat transfer fluid of each magnetocaloric element (2, 12), respectively.

3. Magnetocaloric heat generator according to claim 2, characterized in that the two transfer zones (22, 23) are arranged adjacent to the successive ends (4, 13) of two successive magnetocaloric elements (2, 12).

4. Magnetocaloric heat generator according to claim 2, characterized in that the two transfer zones (22, 23) are made of a heat-conducting material and are provided with through channels (6) for the heat transfer fluid.

5. Magnetocaloric heat generator according to claim 2, characterized in that the two transfer zones (22, 23) of the heat exchange means (5, 35) are interconnected by a body made of a heat conductive material.

6. Magnetocaloric heat generator according to claim 5, characterized in that the two transfer zones (22, 23) of the heat exchange means (5, 35) are interconnected by at least one heat pipe.

7. Magnetocaloric heat generator according to claim 1, characterized in that said driving means of the heat transfer fluid comprise: -one central actuator (8, 8', 25) in fluid connection with the successive ends (4, 13) of said magnetocaloric elements (2, 12); and two end actuators (7), each of which is mounted opposite one of the free ends (3, 14) of the magnetocaloric elements (2, 12).

8. Magnetocaloric heat generator according to claim 7, characterized in that the central actuator (25) is made of a heat conducting material and is in contact with the heat exchange means (5).

9. Magnetocaloric heat generator according to claim 7, characterized in that the central actuator (8') is a double-acting piston made of heat conducting material and the bushing of the central actuator is made of heat insulating material; and, the center actuator constitutes the heat exchanging member.

10. Magnetocaloric heat generator according to claim 1, characterized in that said driving means of the heat transfer fluid comprise: two central actuators (9; 11 and 15), each of which is in fluidic connection with one of the successive ends (4, 13) of the magnetocaloric elements (2, 12); and two end actuators (7), each of which is in fluid connection with one of the free ends (3, 14) of the magnetocaloric elements (2, 12).

11. Magnetocaloric heat generator according to claim 7, characterized in that the driving means of the heat transfer fluid comprise a piston selected in the group comprising single-acting pistons and double-acting pistons.

12. Magnetocaloric heat generator according to claim 10, characterized in that it comprises a magnetic arrangement enabling successive magnetocaloric elements (2, 12) to be always in two different cycles.

13. Magnetocaloric heat generator according to claim 7, characterized in that it comprises a magnetic arrangement enabling successive magnetocaloric elements (2, 12) to be always in the same cycle.

14. Magnetocaloric heat generator according to any one of the preceding claims, characterized in that the heat transfer fluids passing through the magnetocaloric elements (2, 12) have different chemical compositions and/or thermal characteristics.