HK1160985B - Magnetocaloric thermal generator - Google Patents

Description

Magnetocaloric heat generator

Technical Field

The present invention relates to a heat generator comprising at least one thermal module comprising at least two adjacent magnetocaloric elements arranged for being crossed by a heat transfer fluid, a common distribution chamber associated with circulation means of the heat transfer fluid and in fluid communication with each other of said adjacent magnetocaloric elements, and two end chambers also associated with circulation means and in fluid communication with the magnetocaloric elements located at the ends, called hot and cold ends, of said thermal module, respectively; and magnetic means for subjecting each magnetocaloric element to a variable magnetic field so as to alternately generate in each magnetocaloric element a heating cycle and a cooling cycle, the flow of the heat transfer fluid through said magnetocaloric element being effected by said circulation means in synchronism with the variation of the magnetic field.

Background

Magnetic refrigeration technology has been known for more than twenty years and the ecological and sustainable advantages that this technology brings are known. Limitations in its effective thermal power and its efficiency are also known. Since then, the research carried out in this field all tends to improve the performance of such generators by adjusting different parameters such as the magnetizing power, the performance of the magnetocaloric elements, the heat exchange area between the heat transfer fluid and the magnetocaloric elements, the performance of the heat exchangers, etc.

The choice of magnetocaloric material is decisive and directly affects the performance of the magnetocaloric generator. To improve these properties, one solution is to combine several magnetocaloric materials with different curie temperatures to increase the temperature gradient between the ends of the assembly.

Heat generators are therefore known which: it comprises at least one thermal module M, as shown in fig. 1A and 1B, having magnetocaloric materials MC arranged side by side and in line, and circulating means of the heat transfer fluid, such as a piston P, for driving the heat transfer fluid in a reciprocating motion through all the magnetocaloric materials MC between a cold end F and a hot end C of the pack of magnetocaloric materials MC, on both sides of the magnetocaloric materials MC, in synchronism with the variation of the magnetic field. As shown in fig. 1A and 1B, these pistons P are located on both sides of the assembly of magnetocaloric materials MC and move alternately in one direction and then in the other direction, fig. 1A and 1B representing the pistons in their two extreme positions.

As can be seen from fig. 1A and 1B, the fluid moves either in one direction towards hot end C (see fig. 1A, with the dotted arrows representing the direction of movement of the heat transfer fluid) when the magnetocaloric materials are subjected to a heating cycle, or in the other direction towards cold end F (see fig. 1B, with the solid arrows representing the direction of movement of the heat transfer fluid) when the magnetocaloric materials are subjected to a cooling cycle.

This thermic module M has drawbacks due to the fact that: to achieve the temperature gradient, it is necessary to pass the heat transfer fluid through all the materials. The use of a plurality of magnetocaloric elements MC results in an increase in the length of material through which the heat transfer fluid has to pass. Therefore, in order not to reduce the number of cycles (one cycle is defined by one heating and one cooling of the magnetocaloric elements), it is necessary to increase the speed of the heat transfer fluid. Increasing the speed, in turn, leads to an increase in pressure, which increases the head loss and reduces the efficiency of the heat exchange between the heat transfer fluid and the magnetocaloric elements, which leads to a reduction in the thermal efficiency of the magnetocaloric generator.

It is also known that to increase the thermal power of a magnetocaloric generator, one possibility consists in increasing the number of cycles of the cycle. But this therefore causes an increase in speed and leads to the disadvantages described above.

The heat generator comprising the thermal module M as shown in fig. 1A and 1B requires a long pre-run time to reach a usable temperature gradient between the two ends due to the plurality of magnetocaloric materials used.

Disclosure of Invention

The present invention aims to overcome these drawbacks by providing a magnetocaloric heat generator which is easy to implement, and which has an improved thermal efficiency compared to known heat generators, while using the same amount or length of magnetocaloric material.

To this end, the invention relates to a heat generator of the type indicated in the introduction, characterised in that said circulation means associated with said distribution common chamber move the heat transfer fluid simultaneously through two adjacent magnetocaloric elements in different flow directions.

The magnetic means are preferably able to constantly place said adjacent magnetocaloric elements in two different cycles, and said circulation means associated with said common chamber are able to simultaneously move the heat transfer fluid through the magnetocaloric elements undergoing a heating cycle in a direction towards the hot end and through the magnetocaloric elements undergoing a cooling cycle in a direction towards the cold end of said thermal module.

Said thermal module may further comprise at least three magnetocaloric elements, said circulation means associated with said common chamber being able to move the heat transfer fluid alternately in the direction of two adjacent magnetocaloric elements and then in the opposite direction to the outlet of said adjacent thermal module, and vice versa, two circulation means of two successive distribution common chambers being able to constantly move the heat transfer fluid in the two opposite directions, and the circulation means associated with said end chamber being able to move the heat transfer fluid in the opposite direction to the direction of the common chamber adjacent to the end chamber.

The heat generator may preferably comprise an even number of magnetocaloric elements. In this way, each thermal module has as many magnetocaloric elements during the heating cycle as during the cooling cycle at any instant.

In order to increase the operating temperature range of the heat generator (for example between-25 ℃ and +65 ℃), each magnetocaloric element may have a different curie temperature, arranged in an adjacent manner with increasing curie temperatures towards the hot end of the thermal module.

In this configuration, each magnetocaloric element may further comprise a plurality of magnetocaloric materials arranged in a manner of increasing curie temperatures thereof in the direction of the hot end of the thermal module.

In a characteristic manner, the amount of heat transfer fluid moved by the circulation means associated with the end chambers may correspond to half the amount of heat transfer fluid moved by the circulation means associated with the common chamber.

The circulation means may preferably be a piston arranged in a common chamber and an end chamber, only one end of the piston acting on the heat transfer fluid. By end portion is understood a working surface or head of the piston in contact with the heat transfer fluid. Of course, various other forms of flow-through components are also contemplated.

In a first embodiment, the thermal module may have a linear structure in which the magnetocaloric elements are arranged in a straight line and the manipulation of the pistons may be achieved by means of respective control cams mounted on a rotation shaft.

In this configuration, the heat generator may be constituted by four thermal modules, the control cam may comprise lobes arranged offset by 90 ° from each other, and the thermal modules may be located radially around the shaft, so that each lobe actuates a piston of each of the four thermal modules.

In a second embodiment, the thermal module may have a linear structure in which the magnetocaloric elements are arranged in a straight line, the manipulation of the pistons may be performed by a manipulation stage that moves along the thermal module in a reciprocating translational motion, and the manipulation stage comprises guide grooves in which the respective connection of each piston is guided.

The guide groove may have a saw-tooth shape, and the piston may be disposed substantially opposite to the manipulation stage.

In addition, the heat generator may include a plurality of thermal modules arranged one above the other in a stepped configuration.

The invention also envisages that the heat generator may comprise at least two thermal modules and that the hot end chambers may be in fluid communication with each other on the one hand and the cold end chambers on the other hand.

Furthermore, the heat generator according to the invention may comprise at least two thermal modules having the same number of magnetocaloric elements, the common chambers of said thermal modules being in fluid communication with each other two by two.

Drawings

The invention and its advantages will be more clearly apparent in the following description of an embodiment given as a non-limiting example with reference to the accompanying drawings, in which:

figures 1A and 1B are schematic views of a prior art thermic module;

fig. 2A and 2B are schematic views of a thermal module made up of four magnetocaloric elements, respectively in two different states, illustrating the movement of a heat transfer fluid through these magnetocaloric elements;

fig. 3 is a perspective view of a first embodiment of a heat generator according to the invention;

figure 4 is a transparent elevation of detail a of figure 3; and

fig. 5 is a perspective view of a second embodiment of the heat generator according to the invention.

Detailed Description

In the illustrated embodiment, the same parts or the same parts carry the same reference numerals.

The heat generator 1 shown in fig. 3 and 4 is realized according to a first embodiment of the invention. It comprises two thermal modules 1' each comprising several magnetocaloric elements 2 arranged in a line. The common chamber 3 comprises a piston 4 forming a means of forced circulation of the heat transfer fluid, each time between two adjacent magnetocaloric elements 2. In addition, the thermal module 1 'also comprises two end chambers 5 and 6, located at the hot end 9 and the cold end 11 of the thermal module 1', and each also comprising a piston 7 forming a flow-through member.

Each magnetocaloric element 2 is suitable to be crossed by a heat transfer fluid driven by pistons 4, 7 and subjected to a magnetic field variation by means of magnetic means (not shown in the figures) generating alternating heating and cooling cycles. The movement of pistons 4, 7 is synchronized with the magnetic field variations so that the heat transfer fluid moves through each magnetocaloric element 2 subjected to a heating cycle in the direction of hot end 9 (dashed arrow) and so that the heat transfer fluid moves through each magnetocaloric element 2 subjected to a cooling cycle in the direction of cold end 11 (solid arrow). This movement is made possible by the arrangement of the pistons 4, 7 in the common chamber 3 and the end chambers 5, 6 and the particular distribution of the heat transfer fluid resulting therefrom. The pistons 4 in the common chamber 3 therefore each distribute the heat transfer fluid into two adjacent magnetocaloric elements 2. In fig. 3 and 4, the pistons 4, 7 are perpendicular to the alignment of the magnetocaloric elements 2, so that only one end of said pistons 4, 7 ensures the movement of the heat transfer fluid. Of course, another configuration can be considered, provided that only one end of the piston 4 in the common chamber 3 is in contact with the heat transfer fluid and ensures the movement of the heat transfer fluid into the two magnetocaloric elements 2.

The movement of the heat transfer fluid as described above allows to generate a temperature gradient between the hot end 9 and the cold end 11 of the thermal module and to maintain this temperature gradient in the exchange or extraction of thermal energy with an external circuit or application. In practice, the heat generator according to the invention is used for thermal energy exchange with one or more external circuits of use (heating, air conditioning, temperature regulation, etc.) which are connected to the latter by means of at least one end chamber 5, 6, if necessary by means of a heat exchanger.

In addition, this applies to the two illustrated embodiments, driving the heat transfer fluid from the common chamber 3 through two adjacent magnetocaloric elements 2 and simultaneously in different flow directions inside each of these two magnetocaloric elements 2, which has a number of advantages compared to known heat generators in which the fluid passes simultaneously through all magnetocaloric elements MC in a first direction from the first to the last magnetocaloric element and then through the same magnetocaloric elements MC in the opposite direction to the first direction (see fig. 1A and 1B).

A first advantage, which emerges from fig. 2A and 2B, lies in the fact that: the head losses are dispersed and reduced, the heat transfer fluid driven by the piston 7 simultaneously passes through only one magnetocaloric element 2 and the heat transfer fluid driven by the piston 4 simultaneously passes through only two magnetocaloric elements, instead of through all the magnetocaloric elements 2 constituting the thermal module 1 ', 10'. For this purpose, with reference to fig. 2A and 2B, the arrows drawn under the magnetocaloric elements 2 show the direction of movement of the heat transfer fluid, the dashed arrows corresponding to the movement towards the hot end 9 and the solid arrows representing the movement towards the cold end 11.

A second advantage appears when comparing the known system shown in fig. 1A and 1B with the system according to the invention, in which the magnetocaloric material has the same length. It can be seen that for the same speed of the heat transfer fluid passing through the magnetocaloric elements MC, 2, in the heat generators 1, 10 of the invention, the cycle frequency is multiplied by four. The thermal power of the heat generators 1, 10 is thereby increased in the same proportion.

As a schematic example, for a heat transfer fluid speed of 100mm/s (millimeters/second) and a length of 100mm for each magnetocaloric element:

the time required for all magnetocaloric elements MC to pass through the known system shown in fig. 1A and 1B is (4 × 100) ÷ 100 ═ 4s, which corresponds to a frequency of 0.25 Hz.

The time required for all the magnetocaloric elements 2 to pass through the heat generator 1, 10 according to the invention is (1 × 100) ÷ 100 ═ 1s, which corresponds to a frequency of 1 Hz.

Furthermore, it can be seen that, still by comparing the heat generator 1, 10 according to the invention with known systems, for the same cycle frequency (demagnetization and magnetization), in the heat generator 1, 10 according to the invention the speed of movement of the heat transfer fluid is divided by 4. This results in a reduction of the pressure head losses in the heat generator according to the invention, which corresponds to an extension of the heat exchange time and thus to an increase in the thermal output of the heat exchange.

As an illustrative example, for a frequency of 0.5Hz corresponding to a heating (or magnetization) period of 1 second and a cooling (or demagnetization) period of 1 second, and a length of 100mm per magnetocaloric element:

for all the magnetocaloric elements MC of the known system shown in fig. 1A and 1B to pass within 1 second, the heat transfer fluid speed needs to be (4 × 0.100) ÷ 1 ═ 0.4m/s,

whereas the velocity of the heat transfer fluid driven at each common chamber 3 is (1 × 0.100) ÷ 1 ═ 0.1m/s for all the magnetocaloric elements 2 passing through the heat generator 1, 10 according to the invention.

The magnetocaloric elements 2 are not shown in fig. 3 for the sake of simplicity. These magnetocaloric elements comprise through-going fluid channels which may be constituted by pores of porous material, micro-or microtubes machined in a solid block or assembled, for example, by several superposed plates with grooves.

Preferably, to increase the temperature gradient between hot end 9 and cold end 11, the magnetocaloric elements 2 are arranged one with respect to the other according to their increasing curie temperatures, the magnetocaloric element 2 with the highest curie temperature being arranged at hot end 9 of the thermal module 1' concerned.

In addition, each magnetocaloric element 2 can be implemented by an assembly of a plurality of different magnetocaloric materials, also arranged according to their increasing curie temperature.

As can be seen from fig. 3, the piston 4 integrated in the common chamber 3 is operated by a control cam 13 mounted on a rotating shaft 14, said cam comprising lobes 15 arranged offset by 90 ° one with respect to the other. Depending on the angle of rotation of the shaft 14, the lobes 15 push or do not push the rod of the respective piston 4, 7, which determines the direction of movement of each piston 4, 7.

Fig. 4 shows the extreme positions that the pistons 4, 7 can assume. The pistons 7 and 4, respectively located in the end chamber 5 at the cold end 11 of the element 1' and in the common chamber 3 (on the right in fig. 4), are both in their retracted position, allowing the heat transfer fluid to fill the chamber in which they are integrated. As regards the central piston 4, it is then in the fluid-pushing position in which the fluid contained in the respective common chamber 3 is pushed in the direction of the two magnetocaloric elements 2 adjacent to this common chamber 3, but in two opposite directions. The heat transfer fluid moves according to the curved arrows drawn on fig. 4.

As is clear from this figure, the amount of heat carrier fluid displaced by the piston 7 associated with the end chamber 5 corresponds to half the amount of heat carrier fluid displaced by the piston 4 in the adjacent common chamber 3.

In addition, particularly when an even number of magnetocaloric elements 2 are integrated in a thermal module, common chamber 3 forms an intermediate tank able to equalize the temperature of the heat transfer fluid and therefore to reduce the time to reach a temperature gradient between hot end 9 and cold end 11 of each thermal module 1, 10'.

The heat generator 1 of fig. 3 and 4 comprises two thermal modules 1'. However, the number is not limiting and may be smaller or larger depending on the available space and the desired thermal power. In fact, the heat generator 2 can also comprise four thermal modules 1' distributed in a star around the shaft 14 and whose pistons 4, 7 are actuated by the cam 13.

The heat generator 10 shown in fig. 5 differs from the previous ones in the actuation of the pistons 4, 7. This is achieved by means of a manipulation stage 16, which moves along the thermal module 10' in question in a reciprocating motion according to the arrow F. The console 16 comprises a serrated guide slot 17 in which a connecting piece 18 connected to the pistons 4, 7 moves.

Although the heat generator 10 shown in fig. 5 comprises two thermal modules 10 'arranged one above the other, the heat generator 10 according to the invention is not limited to the number of such thermal modules 10' nor to their arrangement in a stacked manner.

In addition, although not represented on the drawings, in a heat generator according to the invention comprising a plurality of thermal modules, it is also possible to envisage: on the one hand, the hot end chambers 5 are in fluid communication with each other; on the other hand, the cold end chambers 6 are likewise in fluid communication with each other. It is particularly conceivable for these hot end chambers 5 to coincide, forming only one and the same chamber. The same is true for the cold end chamber 6.

Such a configuration allows the different thermic modules to be thermally coupled to each other and, in particular, to facilitate heat exchange with external applications. It also enables the thermal power of the different thermal modules to be additive or cumulative.

In a supplementary variant, it is possible to envisage that the common chambers 3 of the different thermal modules of the heat generator according to the invention are in fluid communication with each other two by two. For this purpose, these thermal modules should comprise the same number of magnetocaloric elements 2.

The advantage of this configuration lies in the fact that: the temperature of the common chamber 3 is smoothed or averaged to achieve regularity of operation of the thermal module.

Possibility of industrial application:

as is clear from the present description, the present invention allows to achieve the intended aim, namely to provide a heat generator 1, 10 of simple structure and improved efficiency.

Such heat generators 1, 10 can also find application in heating, air conditioning, temperature control, cooling or other fields, both in industry and in domestic applications, at rather competitive costs and with a small space requirement.

In addition, all the parts making up the heat generator 1, 10 can be manufactured according to reproducible industrial processes.

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

Claims (15)

1. Heat generator (1, 10) comprising: at least one thermal module (1 ', 10') comprising at least two adjacent magnetocaloric elements (2) arranged for being crossed by a heat transfer fluid, a common distribution chamber (3) associated with circulation means of the heat transfer fluid and in fluid communication with said adjacent magnetocaloric elements (2) with each other, and two end chambers (5, 6) also associated with circulation means and in fluid communication with the magnetocaloric elements (2) located at the ends, called hot end (9) and cold end (11), of said thermal module (1 ', 10'), respectively; and magnetic means for subjecting each magnetocaloric element (2) to a variable magnetic field so as to alternately generate a heating cycle and a cooling cycle in each magnetocaloric element (2), the flow of the heat transfer fluid through said magnetocaloric elements (2) being achieved by said circulation means associated with the distribution common chamber and said circulation means associated with the end chambers in synchronism with the variation of the magnetic field,

the heat generator (1, 10) is characterized in that the circulation means associated with the distribution common chamber (3) move the heat transfer fluid simultaneously through the two adjacent magnetocaloric elements (2) in different flow directions.

2. Heat generator according to claim 1, characterized in that said magnetic means constantly subject said adjacent magnetocaloric elements (2) to two different cycles; and in that said circulation means associated with said distribution common chamber (3) move the heat transfer fluid simultaneously through the magnetocaloric elements (2) subjected to a heating cycle in the direction of the hot end (9) of said thermal module and through the magnetocaloric elements (2) subjected to a cooling cycle in the direction of the cold end (11) of said thermal module (1 ', 10').

3. Heat generator according to claim 1, characterized in that said thermal module (1 ', 10') comprises at least three magnetocaloric elements (2); said circulation means associated with said distribution common chamber (3) move the heat transfer fluid alternately in the direction of said two adjacent magnetocaloric elements (2) and then in the opposite direction to the outlet of the adjacent thermal module (2) and vice versa; the two circulation means of two successive distribution common chambers (3) constantly move the heat transfer fluid in two opposite directions; and in that said circulation means associated with said end chambers (5, 6) move the heat transfer fluid in a direction opposite to that of said distribution common chamber (3) adjacent to said end chambers.

4. A heat generator according to claim 3, characterized in that it comprises an even number of magnetocaloric elements (2).

5. A heat generator according to any one of the preceding claims, characterised in that said magnetocaloric elements (2) each have a different curie temperature and are arranged in an adjacent manner according to their increasing curie temperature towards the hot end (9) of said thermal module.

6. A heat generator according to claim 3 or 4, characterized in that said magnetocaloric elements (2) each comprise a plurality of magnetocaloric materials arranged with increasing Curie temperatures towards the hot end (9) of said thermal module.

7. Heat generator according to claim 1, characterised in that the amount of heat carrier fluid displaced by the flow means associated with the end chambers (5, 6) corresponds to half the amount of heat carrier fluid displaced by the flow means associated with the distribution common chamber (3).

8. Heat generator according to claim 1, characterised in that said means of circulation associated with the distribution common chamber and with the end chambers are pistons (4, 7) integrated in said distribution common chamber (3) and in said end chambers (5, 6), only one end (12) of said pistons acting on the heat transfer fluid.

9. Heat generator according to claim 8, characterized in that said thermal module has a linear structure in which said magnetocaloric elements (2) are aligned; the pistons (4, 7) are actuated by corresponding control cams (13) mounted on a rotary shaft (14).

10. The heat generator of claim 9, wherein the heat generator is comprised of four thermal modules; the control cam (13) comprises lobes (15) staggered by 90 ° from each other; and, the thermal modules are radially located around the rotational axis (14) such that each lobe (15) actuates a piston (4, 7) of each of the four thermal modules.

11. Heat generator according to claim 8, characterized in that said thermal module has a linear structure in which said magnetocaloric elements (2) are aligned; and the actuation of the pistons (4, 7) is performed by means of an actuation carriage (16) which moves along the thermal module according to a reciprocating translational motion and has a guide slot (17) in which a respective connecting element (18) of each piston (4, 7) is guided.

12. Heat generator according to claim 11, characterised in that the guide slot (17) is saw-toothed; and the pistons (4, 7) are arranged substantially opposite the console (16).

13. A heat generator according to claim 11 or 12, wherein the heat generator comprises a plurality of thermal modules arranged one above the other in a stepped configuration.

14. A heat generator according to claim 1, characterized in that it comprises at least two thermal modules (1 ', 10'); and, on the one hand, the hot end chambers are in fluid communication with each other and, on the other hand, the cold end chambers are in fluid communication with each other.

15. Heat generator according to claim 1, characterized in that it comprises at least two thermal modules (1 ', 10') having the same number of magnetocaloric elements (2); and the distribution common chamber (3) of the thermal modules (1 ', 10') is in fluid communication with each other two by two.