AU2011288328A1

AU2011288328A1 - Thermal generator containing magnetocaloric material

Info

Publication number: AU2011288328A1
Application number: AU2011288328A
Authority: AU
Inventors: Jean-Claude Heitzler; Christian Muller
Original assignee: Cooltech Applications SAS
Current assignee: Cooltech Applications SAS
Priority date: 2010-08-09
Filing date: 2011-08-03
Publication date: 2013-02-07
Anticipated expiration: 2031-08-03
Also published as: MX2013001519A; WO2012020183A1; WO2012020183A8; KR101771772B1; RU2013108442A; EP2603747A1; AU2011288328B2; CN103097834B; CA2805988A1; EP2603747B1; ES2536795T3; JP2013533456A; CN103097834A; BR112013002573A2; PL2603747T3; KR20130107272A; JP5822170B2; RU2573421C2

Abstract

The present invention relates to a thermal generator (100) with at least one thermal module (110) comprising at least two magnetocaloric elements (111, 112). The thermal generator (100) is characterized in that it comprises at least two magnetic assemblies (131, 132) each subjecting at least one magnetocaloric element (111, 112) of said thermal module (110) to an alternation of magnetic phases and in that it comprises a means for insulating the magnetic assemblies (131, 132) from one another, forming thermally insulated cells (141, 142) comprising a magnetic assembly (131, 132) and the associated magnetocaloric elements (111, 112) thereof.

Description

1 THERMAL GENERATOR CONTAINING MAGNETOCALORIC MATERIAL Technical scope: 5 The present invention relates to a thermal generator with at least one thermal module comprising at least two magnetocaloric elements. Prior technique: 10 Magnetic refrigeration technology at ambient temperature has been known for more than twenty years and the advantages it provides in terms of ecology and sustainable development are widely acknowledged. Its limits in terms of its useful calorific output and its efficiency are also well known. Consequently, all the research undertaken in this field tends to improve the performances of such a generator, by adjusting the various 15 parameters, such as the magnetization power, the performances of the magnetocaloric materials, the heat exchange surface between the heat transfer fluid and the magnetocaloric materials, the performances of the heat exchangers, etc. The choice of the magnetocaloric materials is determining and influences directly the 20 performances of a magnetocaloric thermal generator. The magnetocaloric effect reaches its maximum in the neighborhood of the Curie temperature of the magnetocaloric materials. In order to operate a magnetocaloric thermal generator in a wide temperature range, it is known to associate several magnetocaloric materials having different Curie temperatures. 25 So, many magnetocaloric thermal generators make use of the magnetocaloric effect of several magnetocaloric elements by circulating a heat transfer fluid along or through said magnetocaloric materials, in two opposite directions, according to the magnetic field increase phases and to the magnetic field decrease phases the magnetocaloric 30 materials are subjected to. When starting up such a thermal generator, the circulation of the fluid allows obtaining a temperature gradient between the opposite ends of the 2 magnetocaloric material. Obtaining this temperature gradient depends on various factors such as the initial temperature, the flow of the heat transfer fluid, the intensity of the magnetocaloric effect, the Curie temperature and the length of the magnetocaloric materials. The closer the initial temperature and the Curie temperature of the 5 magnetocaloric material, the faster a temperature gradient will be achieved from which the generator will be able to operate and to produce or exchange thermal energy with an external circuit. Now, the initial temperature of the heat transfer fluid and of the magnetocaloric materials is not controlled and is equal to the temperature outside the generator. It may for example lie within a very wide temperature range, for example 10 between - 20 and + 60'C. This implies that reaching the temperature gradient, that is to say the operational phase of a magnetocaloric thermal generator, may take a long time. Furthermore, the fact of working on a large temperature range implies that the magnetic system, which is generally made of an assembly of permanent magnets, is subjected to 15 an important temperature variation. The magnetocaloric materials are generally arranged in the air gap of the magnetic system and thus lead by thermal convection to a temperature change in the magnetic system. To that purpose, figures 1A and 1B illustrate a thermal generator comprising a magnetic system made of two magnets M1 and M2 forming an air gap G in which two magnetocaloric materials MC 1 and MC2 are 20 moving. Almost the whole volume of the air gap is filled alternately by a magnetocaloric material MCI or MC2. When one of said magnetocaloric materials MCI and MC2 is located inside of the air gap, there is a minimum space between magnets Ml, M2 and said magnetocaloric material MCI, MC2, in order to increase the thermal power. The first magnetocaloric material MCI has a Curie temperature of 0 0 C 25 and an operating or transition zone reaching from -10'C to +10'C and the second magnetocaloric material MC2 has a Curie temperature of 20'C and an operating or transition zone reaching from +10'C to +30'C. Figure 1A represents a first phase of the cycle, in which the first magnetocaloric material MCI is subjected to an increasing magnetic field and the second magnetocaloric material MC2 30 is subjected to a decreasing magnetic field, and figure lB represents the second phase of the cycle, in which the first magnetocaloric material MCI is subjected to a decreasing 3 magnetic field and the second magnetocaloric material MC2 is subjected to an increasing magnetic field. The magnets undergo a thermal amplitude of 40'C (from 10 C to +30 C). With their thermal inertia, the magnets adversely affect the temperature gradient in the magnetocaloric materials MCI and MC2: they carry out thermal 5 exchanges with said magnetocaloric materials MCl and MC2, which reduces the temperature gradient of the magnetocaloric materials. From this results that the performance of a magnetocaloric thermal generator, which is linked to this temperature gradient, is reduced. 10 Description of the invention: The present invention aims to overcome the above-mentioned disadvantages by offering a thermal generator with an improved thermal efficiency. 15 To this purpose, the thermal generator according to the invention is characterized: - in that it includes at least two magnetic assemblies, each magnetic assembly subjecting at least one magnetocaloric element of said thermal module to an alternation of magnetic phases, and - in that it comprises a means for isolating the magnetic assemblies from each 20 other, forming thermally insulated cells comprising a magnetic assembly and the associated magnetocaloric elements thereof. Said at least two magnetocaloric elements can preferably have different Curie temperatures and be in fluidic communication with each other at their ends or end 25 sections according to their increasing Curie temperature. Said thermal module can have a temperature gradient corresponding to the temperature difference between the cold end or cold end section of the magnetocaloric element having the lowest Curie temperature and the hot end or hot end section of the magnetocaloric element having the highest Curie temperature. Said at least two magnetocaloric elements can preferably 30 cover the temperature gradient of the thermal module so that two magnetocaloric elements in fluidic communication with each other have a close temperature, and said at 4 least two magnetocaloric elements can also be subjected alternately each to an increase and to a decrease of the magnetic field while being in contact with a heat transfer fluid whose direction of flow changes from one end or end section to the other end or end section of said magnetocaloric elements at each magnetic phase change. 5 The magnetocaloric elements are intended to be in thermal contact with the heat transfer fluid that circulates from their cold end towards their hot end during a first phase of the magnetic cycle, which corresponds to a phase in which the magnetocaloric materials or elements are subjected to an increase of their temperature (for the described 10 magnetocaloric elements, the magnetic field increase phase), and from their hot end towards their cold end during a second phase of the magnetic cycle, in which the magnetocaloric materials or elements are subjected to a decrease of their temperature (for the described magnetocaloric elements, the magnetic field decrease phase). For the materials having a reverse magnetocaloric effect, an increase of the magnetic field leads 15 to a decrease of their temperature and a decrease of the magnetic field leads to an increase of their temperature. The thermal contact between the heat transfer fluid and the magnetocaloric elements can be achieved with a heat transfer fluid passing along or through magnetocaloric materials. To that purpose, the magnetocaloric elements can be made of one or several magnetocaloric materials and can be permeable to the heat 20 transfer fluid. They can also comprise fluid circulation passages extending between the two ends of the magnetocaloric materials. These passages can be created by the porosity of the magnetocaloric materials, or by channels machined or obtained with a set of plates out of magnetocaloric material. 25 The heat transfer fluid is preferably a liquid. To that purpose, it is for example possible to use pure water or water with an antifreeze product, a glycolated product or a brine. In addition, and according to the invention, the ends of the magnetocaloric elements that are in fluidic communication have close temperatures, that is to say that the temperature 30 difference between the two connected ends is low, and that these two ends have preferably the same temperature.

5 A magnetic phase corresponds to an increase or to a decrease of the magnetic field. Thus, a magnetic cycle undergone by a magnetocaloric element corresponds to an increase and a decrease of the magnetic field in said magnetocaloric element and leads 5 to a corresponding increase and decrease (or the contrary) of the temperature of said magnetocaloric element. The magnetic assemblies can include a combination of permanent magnets, as illustrated, or electromagnets. In the case of using permanent magnets, the magnetic 10 phase change can be achieved, for example, by a relative movement between the magnetic assemblies and the corresponding magnetocaloric elements. Of course, other possibilities allowing to vary the magnetic field are not excluded from the present invention. 15 According to the invention, for said thermal module, a magnetic assembly can be assigned to a magnetocaloric element. This thermal generator can also comprise at least two thermal modules and at least one common magnetic assembly can subject the magnetocaloric elements of at least two 20 thermal modules to alternating magnetic phases. The insulation means can be made of a layer of at least one thermally insulating material arranged around each magnetic assembly and the associated magnetocaloric elements thereof. 25 The insulation means can also be fastened to the magnetic assemblies. According to the invention, said thermally insulated cells can be sealed enclosures. 30 So, said thermally insulated cells can be under vacuum.

6 Said thermally insulated cells can also be filled with a gas or a mix of different gases with low thermal conductivity. This gas may for example be argon or krypton. In a first variant, the pressure of the gas contained in said thermally insulated cells can 5 be equal to the atmospheric pressure. In another variant, the gas contained in said thermally insulated cells can be under pressure. 10 Furthermore, a layer of thermally insulating material can be arranged between each magnetic assembly and the associated magnetocaloric elements thereof. Brief description of the drawings: 15 The present invention and its advantages will be better revealed in the following description of embodiments given as non limiting examples, in reference to the drawings in appendix, in which: - figures 1A and 1B are schematic representations of a thermal generator according to the prior art, respectively in two successive magnetic phases, 20 - figures 2A and 2B are schematic representations of a thermal module comprising two magnetocaloric elements of a generator according to a first embodiment of the invention, respectively in two successive magnetic phases, - figures 3A and 3B are schematic representations of a thermal module of a generator according to a second embodiment of the invention, in two successive 25 magnetic phases, - figures 4A and 4B are schematic front views of the generator of figures 3A and 3B, and - figures 5A and 5B are schematic views of two thermal modules of a generator according to a third embodiment of the invention, in two successive magnetic phases. 30 Illustrations of the invention: 7 In the illustrated embodiments, identical parts have the same numerical references. Figures 2A and 2B represent schematically a thermal module 110 of a thermal generator 5 100 according to a first embodiment of the present invention. This thermal module 110 comprises two magnetocaloric elements 111 and 112. The cold end C1I of thermal module 110 corresponds to the end located on the left side of figures 2A and 2B of first magnetocaloric element 111 and the hot end H 11 of thermal module 110 corresponds to the end located on the right side of figures 2A and 2B of second magnetocaloric element 10 112. Each magnetocaloric element 111 and 112 is subjected to a magnetic cycle carried out by a corresponding magnetic assembly 131, 132. During the first alternation (see fig. 2A), the heat transfer fluid F circulates from cold end C1i of magnetocaloric element 111, which is subjected to an increase of the magnetic field, towards the other end of this magnetocaloric element 111 (its hot end) and from hot end H11 of 15 magnetocaloric element 112, which is subjected to a decrease of the magnetic field, towards the other end of this magnetocaloric element 112 (its cold end) and, during the second alternation, the direction of circulation is reversed. Each magnetic assembly 131, 132 is made of two permanent magnets arranged opposite 20 to each other. This allows achieving a thermal insulation between the two magnetic assemblies 131, 132 with the associated magnetocaloric materials 111 and 112 thereof by creating thermally insulated cells 141 and 142. The thermal insulation is made out of a layer of a very highly insulating material arranged around the magnetic assemblies 131, 132. In this example, the movement of the magnetic assembly leads to a change of 25 the magnetic field. The magnetocaloric elements III and 112 have the same characteristics as the magnetocaloric elements MCl and MC2 described in relation with the generator according to the prior art represented in figures 1A and 1B. However, the thermal 30 generator 100 of the invention has an increased efficiency, since the thermal impact of the inactive mass of magnets 131, 132 is reduced thanks to the presence of two 8 thermally insulated cells 141 and 142. So, in cells 141 and 142, the temperature gradient undergone by magnetic assemblies 131 and 132 amounts to twenty degrees (respectively between -10 0 C and +10 0 C and between +10 0 C and +30'C), while it was forty degrees in the generator according to the prior art. So, the temperature difference 5 between magnetocaloric materials 111 and 112 and their corresponding magnetic assemblies 131, 132 is also reduced, so that the efficiency of the thermal generator is increased. Figures 3A and 3B represent schematically a thermal module 210 of a thermal generator 10 200 according to a second embodiment of the present invention. This example suits particularly for the rotary thermal generators 200 in which the magnetic assemblies 231, 232, 233 are mounted on a shaft that rotates around a longitudinal axis 5 of generator 200. Figures 4A and 4B represent a simplified front view of this thermal generator 200 showing more specifically a part of magnetic assembly 231 in the positions 15 corresponding respectively to the positions of figures 3A and 3B. These figures 4A and 4B show the interaction between the magnetic assemblies 231 and a magnetocaloric element 211, 1211, 2211, 3211, 4211, 5211, 6211 and 7211 of the eight thermal modules 210, 1210, 2210, 3210, 4210, 5210, 6210 and 7210 of this 20 thermal generator 200. Each magnetic assembly 231, 232, 233 is made of two groups of four permanent magnets arranged opposite to each other and forming a magnetic air gap 6 in which the magnetocaloric materials of the corresponding thermal modules are positioned. These permanent magnets are regularly spaced around longitudinal axis 5 of magnetocaloric thermal generator 200, so that they create four radial magnetic sectors 25 separated by four radial non-magnetic sectors (see in particular figures 4A and 4B). So, the rotation of shaft or axis 5 drives the magnetic assemblies 231, 232, 233, which subject the corresponding magnetocaloric elements to a variation of the magnetic field and thus to an increase and a decrease of their temperature according to their magnetic phase. 30 9 The thermal module 210 comprises three magnetocaloric elements 211, 212 and 213 connected by a heat transfer fluid that circulates through said magnetocaloric elements 211, 212, 213. In this example, the magnetocaloric material 211 located on the left in figures 3A and 3B has the lowest Curie temperature and is able to generate a 5 temperature gradient from -10 0 C to 0 0 C between its cold and hot ends. It is in fluidic contact with magnetocaloric material 212 located in the centre of thermal module 210, which is able to generate a temperature gradient from 0 0 C to +10 0 C between its cold and hot ends. Finally, the third magnetocaloric material 213, which has the highest Curie temperature, is connected with the second magnetocaloric material 212 and is 10 able to generate a temperature gradient from +10 C to +20'C. This embodiment includes eight thermal modules 210, 1210, 2210, 3210, 4210, 5210, 6210 and 7210, whereas the magnetocaloric materials are arranged radially around the shaft, so that, when a magnetocaloric material is inside the air gap of the magnetic 15 assembly (that is to say between two permanent magnets), the two adjacent magnetocaloric materials are outside the air gap, and conversely. Such a configuration allows optimizing the volume of thermal generator 200 by using continuously the magnetic field created by magnetic assemblies 231, 232, 233. To that purpose, figures 3A, 3B and 4A, 4B represent two successive magnetic phases undergone by the 20 magnetocaloric materials. In this second embodiment, the magnetic assemblies 231, 232, 233 are insulated by layers of a high insulation performance foam placed on said magnetic assemblies 231, 232, 233 (for the longitudinal insulation) and around thermal generator 200 (for the 25 radial insulation), so that twenty-four thermally insulated cells are created (only cells 241, 242 and 243 are represented). In these conditions, in each insulated cell 241, 242, 243, the temperature difference between the magnetocaloric material 211, 212, 213 and the corresponding magnetic assembly 231, 232, 233 is low and does not affect the temperature gradient of the magnetocaloric materials. In other words, the magnetic 30 assemblies 231, 232, 233 of the corresponding magnetocaloric materials 211, 212, 213 are divided into sections and form thermally insulated individual cells 241, 242, 243, 10 which can perform thermal exchange only with the fluid that circulates through all these cells. The thermal insulation is made out of a layer of a thermally insulating material such as a high insulation performance foam. This layer can also be applied on another component or a frame inside of thermal generator 200 to create these thermally 5 insulated cells. Although this second embodiment describes a configuration with three magnetic assemblies and eight thermal modules, the invention is not restricted to this number of magnetic assemblies and magnetocaloric materials. Other configurations are possible 10 and may depend on the application that is to be connected to the magnetocaloric thermal generator, on the volume available for the magnetocaloric thermal generator, etc. The displacement of the heat transfer fluid in two opposite directions is achieved by a piston 2 associated with each thermal module 210, but any other suitable device may 15 also be used. The piston 2 moves the heat transfer fluid towards hot end H21 of thermal module 210 during the heating up of the corresponding magnetocaloric materials (fig. 3A) and towards cold end C21 of thermal module 210 during the cooling down of the corresponding magnetocaloric materials (fig. 3B). 20 So, in figure 3A, thermal module 210 undergoes a temperature increase because the magnetocaloric materials 211, 212, 213 are located in air gap 6 of the corresponding magnetocaloric sets 231, 232, 233 and the heat transfer fluid is moved from cold end C21 of magnetocaloric material 211, which has the lowest Curie temperature of thermal module 210, towards hot end H21 of magnetocaloric material 213, which has the 25 highest Curie temperature. In figure 3B, thermal module 210 undergoes a temperature decrease because the magnetocaloric materials 211, 212, 213 are outside the air gap of the magnetic assemblies 231, 232, 233 and the heat transfer fluid is moved from hot end H21 of magnetocaloric material 213, which has the highest Curie temperature of thermal module 210, towards cold end C21 of magnetocaloric material 211, which has 30 the lowest Curie temperature. This alternation in the directions of circulation of the fluid allows obtaining and maintaining a temperature gradient in heat module 210.

11 According to the invention, the fact of dividing thermally the magnetic assemblies 231, 232, 233 and of assigning one or several magnetocaloric materials able to operate over a limited temperature range shows two main advantages. On the one hand, when starting 5 the thermal generator, the magnetocaloric materials 211, 212, 213 keep their temperature between two magnetic phases and the global temperature gradient in thermal module 210 is reached faster. The thermal insulation allows taking advantage of the thermal inertia of the magnetocaloric materials 211, 212, 213. On the other hand, the efficiency of thermal generator 200 is increased, since the temperature gradient 10 undergone by every pair of magnets 231, 232, 233 is limited, and thus the magnets have less thermal influence on the temperature gradient of the corresponding magnetocaloric material 211, 212, 213 and no energy is used to reach again the maximum temperature gradient in said magnetocaloric material. The thermal insulation also allows taking advantage of the thermal inertia of magnetic assemblies 231, 232, 233. 15 It is furthermore possible to realize insulated cells 241, 242, 243 in the form of sealed enclosures and to place them under vacuum or to fill them with a gas with low thermal conductivity such as argon or krypton, for example, or with a mix of these gases. This gas has preferably a pressure equal to atmospheric pressure. It may also be pressurized. 20 Sealing systems with stuffing boxes can be used to ensure the tightness of the enclosures while still allowing connections (electrical, mechanical, etc.) with the outside of the enclosures. The insulated cells according to the invention are particularly realizable in the 25 configurations such as those described, since the direction of circulation of the fluid in the magnetocaloric elements is perpendicular to the direction of variation of the magnetic field. The same advantages as those described previously in relation with the first 30 embodiment also apply to this second embodiment.

12 Figures 5A and 5B represent a thermal generator 300 according to an embodiment variant of generator 100 of figures 2A and 2B. It proposes to insert a thermally insulating material 151, 152 between the magnetic assemblies 131, 132 and their corresponding magnetocaloric elements 111, 112. In figures 5A and 5B, this insulating 5 material 151, 152 is a foam layer placed on the magnetocaloric elements 111, 112. The insulating material can also be an aerogel-type material. However, the invention is not linked to this type of configuration, since the foam can also be applied on the magnetic assemblies 131, 132, for example. This preferred configuration allows reducing even more the thermal effect of the magnetic assemblies on the magnetocaloric elements 111, 10 112. Possibilities for industrial application: This thermal generator 100, 200, 300 finds an application in any technical area requiring 15 heating, tempering, cooling or air-conditioning. The present invention is not restricted to the examples of embodiment described, but extends to any modification or variant which is obvious to a person skilled in the art while remaining within the scope of the protection defined in the attached claims. 20

Claims

1. Thermal generator (100, 200, 300) with at least one thermal module (110, 210) comprising at least two magnetocaloric elements (111, 112, 211, 212, 213), thermal 5 generator (100, 200, 300) characterized: - in that it comprises at least two magnetic assemblies (131, 132, 231, 232, 233), each magnetic assembly (131, 132, 231, 232, 233) subjecting at least one magnetocaloric element (111, 112, 211, 212, 213) of said thermal module (110, 210) to an alternation of magnetic phases, and 10 - in that it comprises a means for isolating the magnetic assemblies (131, 132, 231, 232, 233) from each other, forming thermally insulated cells (141, 142, 241, 242, 243) comprising a magnetic assembly (131, 132, 231, 232, 233) and the associated magnetocaloric elements (111, 112, 211, 212, 213) thereof. 15

2. Thermal generator according to claim 1, characterized in that for said thermal module (110, 210) a magnetic assembly (131, 132, 231, 232, 233) is assigned to a magnetocaloric element (111, 112, 211, 212, 213).

3. Thermal generator according to claim 1 or 2, characterized in that it comprises at 20 least two thermal modules (210, 1210, 2210, 3210, 4210, 5210, 6210, 7210) and in that at least one common magnetic assembly (231, 232, 233) subjects the magnetocaloric elements of at least two thermal modules (210, 1210, 2210, 3210, 4210, 5210, 6210, 7210) to alternating magnetic phases. 25

4. Thermal generator according to any of the previous claims, characterized in that the insulation means is made of a layer of at least one thermally insulating material arranged around each magnetic assembly (131, 132, 231, 232, 233) and its associated magnetocaloric elements (111, 112, 211, 212, 213). 30

5. Thermal generator according to any of the previous claims, characterized in that the insulation means is fastened to the magnetic assemblies. 14

6. Thermal generator according to any of the previous claims, characterized in that said thermally insulated cells (141, 142, 241, 242, 243) are sealed enclosures. 5

7. Thermal generator according to claim 6, characterized in that said thermally insulated cells (141, 142, 241, 242, 243) are under vacuum.

8. Thermal generator according to claim 6, characterized in that said thermally insulated cells (141, 142, 241, 242, 243) are filled with a gas or a mix of gases with low thermal 10 conductivity.

9. Thermal generator according to claim 8, characterized in that the pressure of the gas contained in said thermally insulated cells (141, 142, 241, 242, 243) is equal to the atmospheric pressure. 15

10. Thermal generator according to claim 8, characterized in that the gas contained in said thermally insulated cells (141, 142, 241, 242, 243) is under pressure.

11. Thermal generator according to any of the previous claims, characterized in that a 20 layer of thermally insulating material (151, 152) is arranged between each magnetic assembly (131, 132) and the associated magnetocaloric elements (111, 112) thereof. 25