The present invention refers to a method for producing an active magnetic regenerator made of magneto caloric material, and to a magnetic regenerator produced by said method.

Active magnetic regenerators made of magneto caloric material are generally known and are formed either based on bulk structures, such as bulk powder or beads for instance, or based on ordered structures, such as flat plates for instance. Said bulk active magnetic regenerators have rather low efficiency due to relatively high pressure lost of the fluid flowing through.

An embodiment of an active magnetic regenerator which is more acceptable from the energy point of view provides for usage of flat plates comprising as large surface as possible to transfer heat. Thus, several methods for producing such structures has prevailed. So for instance, one of such methods provides inserting said plates into carriers made for the particular end, said carriers provide for a spacing between plates of magneto caloric material. Said carriers of magneto caloric plates occupy space in a magnetic field which should be otherwise occupied by magneto caloric material, therefore, the efficiency of such structure is less acceptable to exploit. In addition, such a method does not guarantee a sufficient stiffness of the active magnetic regenerator where during operation both the magnetic force and pressure force work upon. Said method also does not allow for the arbitrary small spacing between the plates.

Further know such method provides production of said plates of magneto caloric material by means of cutting, resulting in a spacing between the magneto caloric material. On one hand said method is low priced due to relatively high amount of scrap material, and on the other it does not provides for a small enough spacing between said plates that would enable a better heat transfer.

Yet another known method provides an adhesive bonding of the magneto caloric material and spacers which provides for a spacing between said plates of magneto caloric material. Said adhesive bonding is rather unreliable since it does not enables a uniform spacing between plates which represents the ultimate requirement for the efficient operation of the active magnetic regenerator. Here, a rather substantial possibility exists for the part of the adhesive to fill up the spacing between the plates. The adhesive itself occupies a certain space between the spacers and the magneto caloric material thus, lowering the amount of the magneto caloric material to be exploited. Additionally, the adhesive in time becomes susceptible to fluid for heat transfer which flows over the active magnetic regenerator.

It is the object of the present invention to create a method for producing an active magnetic regenerator which remedy drawbacks of known solutions. Further object of the invention is to create an active magnetic regenerator produced by said method. he object as set above is solved by characteristics disclosed in claim 1. Details of the invention are disclosed in sub-claims. According to the invention it is provided for to produce at least one spacer on a plate made of at least one kind of a magneto caloric material, and afterwards a plurality of said plates made of a magneto caloric material and formed with at least one spacer is stacked upon each other in order to create a stack. Said stack of the plurality of plates made of a magneto caloric material and formed with at least one spacer is then mutually connected into an active magnetic regenerator by means of a positive material joint.

The invention is further described in detail by way of non-limiting preferred embodiment, and with a reference to the accompanying drawings, where Fig. 1 shows a three dimensional view of a plate of an active magnetic regenerator according to the invention,

Fig. 2 shows a three dimensional view of an active magnetic regenerator of Fig. 1, Fig. 3 shows a cross-sectional view of a plate of an active magnetic regenerator of Fig. 1 in a vertical plane III,

Fig. 4 shows a second embodiment of a plate of an active magnetic regenerator of Fig. 1, Fig. 5 shows a cross-sectional view of a plate of an active magnetic regenerator of Fig. 2 in a vertical plane V.

An active magnetic regenerator according to the invention comprises a plurality of plates 1 stacked upon each other, said plates being made of magneto caloric material, preferably of such a magneto caloric material which comprises as good magneto caloric properties as possible at the ambient temperature, such as gadolinium (Gd) and compounds thereof, lanthanum (La) and compounds thereof, manganese (Mn) and compounds thereof, and similar. When viewed in the direction of the fluid flow through the regenerator, said plate 1 can be formed of a same magneto caloric material, i.e. of only one kind of a magneto caloric material, or it may be formed of different materials and in different combinations thereof.

Said plate 1 is formed at the two opposite sides, preferably in the marginal area, with at least one spacer 2 placed on and pressed against said plate 1. Said plate 1 and each said spacer 2 are mutually connected by means of plurality of point welds 3 preferably made by means of a pulsed laser welding. In the present embodiment, said plate 1 comprises a thickness d = 0,25 mm whereas said spacer 2 comprises a thickness t = 0,1 mm. According to the present invention an embodiment is possible where said spacers 2 are formed in a single piece integral with said plate 1 of magneto caloric material such as by means of casting, sintering, cold and/or hot forming of the plate 1 and similar.

The active magnetic regenerator according to the invention is created in a manner to stack upon each other a plurality of said plates 1 of magneto caloric material to obtain a stack 4, said plates being formed with a pair of spacers 2 in a manner as described above. Said spacers 2 are located only at the sides of plates 1 facing each other. Mutual connection of said stack 4 is achieved by means of a positive material joint, such as by means of welding and/or adhesion bonding of said plates 1, for instance. In the present embodiment, the connection of said stack 4 of plates 1 is achieved by means of a plurality of linear welds 5 preferably made by means of a pulsed laser welding.

It has been demonstrated, according to the present invention, that preferred thickness d of said plate 1 in relation to the thickness t of said spacer 2 lies in the range of between approximately 100 : 1 to approximately 1 : 10, preferably in the range of between approximately 10 : 1 to approximately 1 : 1.

Thermal characteristics of the active magnetic regenerator according to the invention are strongly dependent on the geometry of the plates 1 and the spacers 2, in particular on the thickness thereof. Thus, it has been demonstrated that the characteristics of the heat transfer are better for about 50 % when the thickness t of said spacers 2 amounts to approximately half the thickness d of each plate 1, comparing to the case when the thickness t of said spacers 2 equals the thickness d of said plates 1. Nevertheless, when selecting said thickness d, t the care must be exercised in order for the spacing and, respectively, the thickness t of the spacer 2 between the two neighbouring plates 1 is not decreased excessively since, as a result, the pressure drop of the fluid is increased.

Said pulsed laser welding with the present embodiment is selected in a manner that the pulse strength increases linearly from approximately 30 % of the maximum laser power to 100 % of the maximum laser power. Particularly, such pulsed laser welding is suitable for welding of thin plates thus, preventing the spacer 2 to be remelted to quickly. The highest power of said pulse for a linear weld 5 has been selected in the range of about 0,5 kW whereas the highest power of said pulse for a point weld 3 has been selected in the range of about 0,8 kW. Higher power of said pulse is required in order to produce the point weld 3, since each spacer 2 is to be remelted over the entire thickness t thereof. The duration time of the laser pulse has been selected in the range of approximately 3 ms. Pulsing laser beam and, respectively, the molten pool created by said beam comprises a diameter of between 0,6 mm in 0,8 mm. The temperature distribution inside pulse comprises a form of a Gaussian distribution where the highest temperature amounts to over 5.000 °C.

It is provided for according to the present invention that said plates 1 are of the form to feature active magneto caloric condition already from the very beginning of said method, and afterwards they are provided with said spacers 2, assembled into said stack 4 and mutually connected by means of a positive material joint. It is possible however, particularly in cases when certain materials featuring active magneto caloric condition are not suitable for welding and, respectively, not capable of being welded, that firstly said plates 1 are supplied with said spacers 2, assembled into said stack 4 and mutually connected by means of a positive material joint, and afterwards they are treated to receive appropriate magneto caloric features.

Obviously, different welding parameters may be used which depend both on used materials as well as on the thickness thereof, and different combinations of materials, without departing from the spirit and scope of the invention.