Use of rotating magnetic shielding system for a magnetic cooling device

Abstract

A magnetocaloric regenerator unit comprising (A) at least one magnetocaloric material unit having a higher temperature hot side and a lower temperature cold side during operation, wherein the magnetocaloric material unit contains at least one magnetocaloric material, (B) at least one magnetic unit for producing a magnetic field over the magnetocaloric material contained in the magnetocaloric material unit, (C) at least one magnetic shielding comprising at least one window wherein the at least one magnetic shielding is mounted flexible to allow movement of the magnetic shielding between at least one first position and at least one second position thereby insulating the magnetocaloric material contained in the magnetocaloric material unit from the magnetic field when the magnetic shielding is in a first position and allowing the magnetic field to act on the magnetocaloric material through the at least one window when the magnetic shielding is in a second position.

Claims

1. A magnetocaloric regenerator unit, comprising: (A) at least one magnetocaloric material unit having a higher temperature hot side and a lower temperature cold side during operation, wherein the magnetocaloric material unit contains at least one magnetocaloric material, (B) at least one magnetic unit for producing a magnetic field over the magnetocaloric material contained in the magnetocaloric material unit, (C) at least one magnetic shielding comprising at least one window wherein the at least one magnetic shielding is mounted flexible to allow movement of the magnetic shielding between at least one first position and at least one second position thereby insulating the magnetocaloric material contained in the magnetocaloric material unit from the magnetic field when the magnetic shielding is in a first position and allowing the magnetic field to act on the magnetocaloric material through the at least one window when the magnetic shielding is in a second position, wherein (D) the magnetic shielding comprises at least one soft magnetic material selected from pure iron; iron-silicon alloys; iron-cobalt alloys; nickel alloys comprising nickel and at least one element selected from iron, copper, cobalt, molybdenum, chromium and manganese like permalloy, supermalloy and mu-metal; amorphous nickel-iron based alloys and amorphous cobalt-based alloys, and wherein (E) the magnetic shielding comprises at least one layer of a first soft magnetic material and at least one layer of a second soft magnetic material achieving a saturation level at a higher value of the magnetic field than the first soft magnetic material.

2. The magnetocaloric regenerator unit according to claim 1, wherein the at least one magnetocaloric material unit contains at least 2 up to 100 different magnetocaloric materials with different Curie temperatures, which are arranged in succession by descending Curie temperature.

3. The magnetocaloric regenerator unit according to claim 2, wherein the difference in the Curie temperatures of adjacent magnetocaloric materials is 0.5 to 6° K.

4. The magnetocaloric regenerator unit according to claim 1, wherein the magnetic field produced by the magnetic unit is in the range of from 0.5 to 2.5 T.

5. The magnetocaloric regenerator unit according to claim 1, herein the magnetic shielding reduces the magnetic field produced by the magnetic unit by at least 90% when the magnetic shielding is in a first position.

6. The magnetocaloric regenerator unit according to claim 1, wherein the magnetic shielding is mounted flexible to allow rotational or lateral movement of the magnetic shielding.

7. The magnetocaloric regenerator unit according to claim 1 wherein the magnetic shielding has essentially the form of a hollow body.

8. The magnetocaloric regenerator unit according to claim 1, wherein the magnetic shielding comprises at least two windows for allowing the magnetic field produced by the magnetic unit to act on the magnetocaloric material if the magnetic shielding is in a second position.

9. The magnetocaloric regenerator unit according to claim 1, wherein the area of the at least one window is larger than the area taken by the magnetocaloric material contained within the magnetocaloric material unit when the magnetic shielding is in a second position and it is looked along the magnetic field lines of the magnetic field acting on the magnetocaloric material produced by the magnetic unit.

10. The magnetocaloric regenerator unit according to claim 1 wherein the magnetic shielding has essentially the form of a hollow cylinder with at least two windows on opposing sides in the lateral area of the hollow cylinder; wherein the magnetocaloric material is arranged within the hollow cylinder; and wherein the magnetic shielding together with the magnetocaloric material is arranged within the magnetic field produced by the magnetic unit.

11. The magnetocaloric regenerator unit according to claim 1, wherein the magnetocaloric regenerator unit comprises two magnetic shieldings having essentially the form of hollow cylinders of different radii and each hollow cylinder having at least one window in the lateral area of the hollow cylinder; wherein the two hollow cylinders are arranged in parallel one within the other, one pole of the magnetic unit is arranged within the hollow cylinder with the smaller radius, the other pole of the magnetic unit is arranged outside the hollow cylinder with the larger radius; and wherein the magnetocaloric material being arranged within the space between the two hollow cylinders.

12. A process of operating a magnetocaloric device containing at least one magnetocaloric material, said process comprising: producing a varying magnetic field used to exploit the magnetocaloric effect by moving at least one magnetic shielding comprising at least one window between at least one first position and at least one second position thereby insulating the magnetocaloric material contained in the magnetocaloric material unit from the magnetic field when the magnetic shielding is in a first position and allowing the magnetic field to act on the magnetocaloric material through the at least one window when the magnetic shielding is in a second position, wherein the magnetic shielding comprises at least one soft magnetic material selected from pure iron; iron-silicon alloys; iron-cobalt alloys; nickel alloys comprising nickel and at least one element selected from iron, copper, cobalt, molybdenum, chromium and manganese like permalloy, supermalloy and mu-metal; amorphous nickel-iron-based alloys and amorphous cobalt-based alloys, and wherein the magnetic shielding comprises at least one layer of a first soft magnetic material and at least one layer of a second soft magnetic material achieving a saturation level at a higher value of the magnetic field than the first soft magnetic material.

13. A refrigeration system, a climate control unit, or a heat pump, respectively comprising a magnetocaloric regenerator unit according to claim 1.

Description

(1) FIG. 1a to c show an inventive magnetocaloric regenerator unit comprising a magnetic unit having a positive pole (11a) and a negative pole (11b). A magnetic shielding (13) in form of a hollow cylinder with spherical base area comprising two rectangular windows (13a) and (13b) on opposing sides in the lateral area of the hollow cylinder is arranged vertical in respect to the magnetic field generated by the magnetic poles. A magnetocaloric unit (12) containing seven different magnetocaloric materials (1) to (7) is arranged within the magnetic shielding in form of the hollow cylinder (13). The different magnetocaloric materials (1) to (7) are arranged vertical to the magnetic field lines generated by the two magnetic poles (11a) and (11b). In this special embodiment the magnetocaloric materials are arranged at the rotational axis of the magnetic shielding.

(2) FIG. 1a displays a topview of this embodiment. FIG. 1b shows a lateral view of the inventive magnetocaloric regenerator unit, wherein the magnetic shielding is a first position, i.e. the 7 different magnetocaloric materials (1) to (7) contained in the magnetocaloric unit (12) are insulated by the magnetic shielding (13) from the magnetic field. FIG. 1c shows a lateral view of the inventive magnetocaloric regenerator unit, wherein the magnetic shielding is a second position, i.e. the magnetic field generated between the magnetic poles (11a) and (11b) acts through the two windows (13a) and (13b) in the magnetic shielding (13) on magnetocaloric materials (1) to (7) contained in the magnetocaloric unit (12). In this embodiment of the present invention the magnetocaloric shielding can take two first positions and two second positions, which are attained by successive rotation of the magnetic shielding (13) about 90° about the rotational axis of the magnetic shielding. This embodiment is an especially simple construction which has the advantage that due to the fixed positions of the windows no problems occur due to divergent rotational movement etc. Another advantage is that a high frequency of the variation of the magnetic field is achieved by concurrent low angular frequency of the rotating magnetic shielding when the magnetic shielding has 2 or more windows, since the number of variations of the magnetic field per round increases with the number of windows.

(3) According to another embodiment of the inventive magnetocaloric regenerator unit the magnetocaloric regenerator unit comprises two magnetic shieldings having essentially the form of hollow cylinders of different radii and each hollow cylinder having at least one window in the lateral area of the hollow cylinder; wherein the two hollow cylinders are arranged in parallel one within the other, one pole of the magnetic unit is arranged within the hollow cylinder with the smaller radius, the other pole of the magnetic unit is arranged outside the hollow cylinder with the larger radius; and wherein the magnetocaloric material being arranged within the space between the two hollow cylinders. One example of this embodiment comprising two magnetic shieldings with one window is shown in FIGS. 2a and b, another example of this embodiment comprising two magnetic shieldings with three windows is shown in FIGS. 3a and b.

(4) FIGS. 2a and 3a show topviews of two examples of the above described embodiment of the invention. Two magnetic shieldings in form of hollow cylinders having one (FIG. 2a) or three rectangular windows (FIG. 3a) in the lateral area of the hollow cylinders with different radii are provided, the hollow cylinder having the smaller radius (24) is arranged in parallel within the hollow cylinder with the larger radius (23). The two poles (21a, 21b) of the magnetic unit are arranged such, that the first pole (21a) is paced within the hollow cylinder with the smaller radius (24) and the second pole (21b) of the magnet is arranged outside the hollow cylinder with the larger radius (23). The magnetocaloric unit (12a) (FIG. 2a) or the three magnetocaloric material units (12a), (12b) and (12c) (FIG. 3a), respectively, are arranged within the space between the two hollow cylinders (23) and (24). Each magnetocaloric unit (12a), (12b) and (12c) contains 7 different magnetocaloric materials (1) to (7) with different Curie temperatures. The hollow cylinders (23) and (24) are arranged vertical in respect to the magnetic field lines generated by the two magnet poles (21a) and (21b).

(5) FIGS. 2b and 3b each show a lateral view of inventive magnetocaloric regenerator units, wherein the magnetic shieldings are in a second position without displaying the magnetic poles. According to the example shown in FIG. 2b the magnetic field generated between the magnetic poles (21a) and (21b) acts through the windows (23a) and (24a) on the magnetocaloric materials (1) to (7) contained in the magnetocaloric unit (12a). In this example only one first position exists. According to the example shown in FIG. 3b the magnetic field acts on the magnetocaloric material (1) to (7) contained in the magnetocaloric units (12a), (12b) and (12c) through the six windows in the magnetic shieldings (23) and (24) from which only the three windows (23a), (23b) and (23c) of the outer hollow cylinder are shown. In this example of the present invention the magnetocaloric shielding can take three first positions and three second positions, which are alternating attained by successive concurrent rotation of the magnetic shieldings (23) and (24) about the rotational axis of the magnetic shieldings after every 60° rotation.

(6) This embodiment of the present invention has the advantage that more than one arrangement of magnetocaloric materials, i.e. that more than one magnetocaloric unit can be placed within one magnetic unit leading to a better utilization of the magnetic unit.

(7) According to this embodiment of the present invention the two magnetic shieldings are preferably moved with the same angular frequency to ensure that each shielding will be at the same time in a first position and in a second position, respectively.

(8) In FIGS. 1b, 2b, and 3b the rotational axis for the rotational movement of the magnetic shielding(s) is displayed, too.

(9) In all embodiments of the present invention the area of the at least one window preferably is larger than the area taken by the magnetocaloric material contained within the magnetocaloric material unit when the magnetic shielding is in a second position and it is looked along the magnetic field lines of the magnetic field acting on the magnetocaloric material produced by the magnetic unit. This shape of the window has the advantage that the magnetic field lines are not disturbed or bypassed by the magnetic shielding so that the magnetocaloric material is completely and evenly exposed to the magnetic field.

(10) An important feature for the performance of the magnetocaloric regenerator unit is the heat transfer from and to the magnetocaloric material unit. The heat transfer is preferably performed by a heat transfer medium passing through the magnetocaloric material unit.

(11) The three-dimensional form of the individual different magnetocaloric materials contained in the magnetocaloric material unit can be selected as desired. They may be packed beds of particles of the magnetocaloric materials. Alternatively, they may be stacked plates or shaped bodies which have continuous channels through which the heat exchange medium can flow. Suitable geometries are described below.

(12) A packed bed composed of magnetocaloric material particles is a highly efficient material geometry which allows optimal operation of the magnetocaloric material unit. The individual material particles may have any desired form. The material particles are preferably in spherical form, pellet form, sheet form or cylinder form. The material particles are more preferably in spherical form. The diameter of the material particles, especially of the spheres, is 50 μm to 1 mm, more preferably 200 to 400 μm. The material particles, especially spheres, may have a size distribution. The porosity of the packed bed is preferably in the range from 30 to 45%, more preferably from 36 to 40%. The size distribution is preferably narrow, such that predominantly spheres of one size are present. The diameter preferably differs from the mean diameter by not more than 20%, more preferably by not more than 10%, especially by not more than 5%.

(13) Material particles, especially spheres with the above dimensions, used as a packed bed in the magnetocaloric units give high heat transfer coefficients between solid and a fluid used as heat exchanger fluid, the pressure drop being small to low. This allows an improved coefficient of performance (COP) of the packed bed. The high heat transfer coefficient allows the packed beds to be operated at higher frequencies than customary, and hence allows greater energy extraction.

(14) For the particular operating conditions, the performance of the packed bed can be optimized by using material particles, especially spheres, of different diameter. A lower diameter, especially sphere diameter, leads to a higher coefficient of heat transfer and hence allows better heat exchange. This, however, is associated with a higher pressure drop through the packed bed. Conversely, the use of larger material particles, especially spheres, leads to slower heat transfer, but to lower pressure drops.

(15) The movement resistance of the packed bed of magnetocaloric material can be achieved by any suitable measures. For example, the vessel in which the packed bed of magnetocaloric material(s) is present can be closed on all sides. This can be done, for example, using a mesh cage. In addition, it is possible to join the individual material particles to one another, for example by surface melting of the material particles in the packed bed or by sintering the material particles to one another in the packed bed. The surface melting or sintering should be effected such that the interstices between the material particles are very substantially preserved.

(16) The formation of the packed bed by magnetocaloric material particles in sheet, cylinder, pellet or sphere form or similar form is advantageous, since a large ratio of surface to mass is achieved therewith. This achieves an improved heat transfer rate coupled with relatively low pressure drop.

(17) The magnetocaloric material can be present as shaped body, too. The shaped body may be a block of magnetocaloric material, in which case two opposite end sides of the block have entry and exit orifices for a fluid which are connected by continuous channels which run through the entire monolith. The continuous channels allow a liquid heat transfer medium to flow through, such as water, water/alcohol mixtures, water/salt mixtures or gases such as air or noble gases. Preference is given to using water or water/alcohol mixtures, in which case the alcohol may be a mono- or polyhydric alcohol. For example, the alcohols may be glycols.

(18) If the magnetocaloric material is present in form of a shaped body, the shaped body preferably has continuous channels with a cross-sectional area of the individual channels in the range from 0.001 to 0.2 mm.sup.2 and a wall thickness of 50 to 300 μm, a porosity in the range from 10 to 60% and a ratio of surface to volume in the range from 3000 to 50 000 m.sup.2/m.sup.3.

(19) Alternatively, the magnetocaloric material unit may comprise or be formed from a plurality of parallel sheets of the different magnetocaloric materials with a sheet thickness of 0.1 to 2 mm, preferably 0.5 to 1 mm, and a plate separation (interstice) of 0.01 to 1 mm, preferably 0.05 to 0.2 mm. The number of sheets may, for example, be 5 to 100, preferably 10 to 50.

(20) The shaped body is produced, for example, by extrusion, injection molding or molding of the magnetocaloric material.

(21) The beds of the individual materials, or stacks of plates or shaped bodies of the individual materials, are combined to give a magnetocaloric material unit, either by bonding them directly to one another or stacking them one on top of another, or separating them from one another by intermediate thermal and/or electrical insulators.

(22) The different magnetocaloric materials with different Curie temperatures contained in the magnetocaloric material unit may be selected from any suitable magnetocaloric materials. In the meantime a wide variety of possible magnetocaloric materials and their preparation are known to the person skilled in the art.

(23) The magnetocaloric cascades may be prepared by a process, which comprises subjecting powders of the particular the magnetocaloric materials to shaping to form the magnetocaloric materials and subsequently packing the magnetocaloric materials to form the magnetocaloric cascade.

(24) Preferred magnetocaloric materials for use in the inventive magnetocaloric regenerator unit are selected from (1) compounds of the general formula (I)
(A.sub.yB.sub.1-y).sub.2+dC.sub.wD.sub.xE.sub.z  (I)
where A: is Mn or Co, B: is Fe, Cr or Ni, C, D and E: at least two of C, D and E are different, have a non-vanishing concentration and are selected from P, B, Se, Ge, Ga, Si, Sn, N, As and Sb, where at least one of C, D and E is Ge, As or Si, d: is a number in the range from −0.1 to 0.1, w, x, y, z: are numbers in the range from 0 to 1, where w+x+z=1; (2) La- and Fe-based compounds of the general formulae (II) and/or (III) and/or (IV)
La(Fe.sub.xAl.sub.1-x).sub.13H.sub.y or La(Fe.sub.xSi.sub.1-x).sub.13H.sub.y  (II)
where x: is a number from 0.7 to 0.95, y: is a number from 0 to 3, preferably from 0 to 2;
La(Fe.sub.xAl.sub.yCo.sub.z).sub.13 or La(Fe.sub.xSi.sub.yCo.sub.z).sub.13  (III)
where x: is a number from 0.7 to 0.95, y: is a number from 0.05 to 1−x, z: is a number from 0.005 to 0.5; and
LaMn.sub.xFe.sub.2-xGe  (IV)
where x: is a number from 1.7 to 1.95; (3) Heusler alloys of the MnT.sub.tT.sub.p type where T.sub.t is a transition metal and T.sub.p is a p-doping metal having an electron count per atom e/a in the range from 7 to 8.5; (4) Gd- and Si-based compounds of the general formula (V)
Gd.sub.5(Si.sub.xGe.sub.1-x).sub.4  (V)
where x is a number from 0.2 to 1; (5) Fe.sub.2P-based compounds; (6) manganites of the perovskite type; (7) compounds which comprise rare earth elements and are of the general formulae (VI) and (VII)
Tb.sub.5(Si.sub.4-xGe.sub.x)  (VI)
where x: is 0, 1, 2, 3, 4;
XTiGe  (VII)
where X: is Dy, Ho, Tm; and (8) Mn- and Sb- or As-based compounds of the general formulae (VIII), (IX), (X), and (XI)
Mn.sub.2-xZ.sub.xSb  (VIII)
Mn.sub.2Z.sub.xSb.sub.1-x  (IX)
where Z: is Cr, Cu, Zn, Co, V, As, Ge, x: is from 0.01 to 0.5,
Mn.sub.2-xZ.sub.xAs  (X) and
Mn.sub.2Z.sub.xAs.sub.1-x  (XI)
where Z: is Cr, Cu, Zn, Co, V, Sb, Ge, x: is from 0.01 to 0.5.

(25) It has been found in accordance with the invention that the aforementioned magnetocaloric materials can be used advantageously in the inventive magnetocaloric regenerator.

(26) Particular preference is given in accordance with the invention to the metal-based materials selected from compounds (1), (2) and (3), and also (5).

(27) Materials particularly suitable in accordance with the invention are described, for example, in WO 2004/068512 A1, Rare Metals, Vol. 25, 2006, pages 544 to 549, J. Appl. Phys. 99,08Q107 (2006), Nature, Vol. 415, Jan. 10, 2002, pages 150 to 152 and Physica B 327 (2003), pages 431 to 437.

(28) Magnetocaloric materials of general formula (I) are described in WO 2004/068512 A1 and WO 2003/012801 A1. Preference is given to magnetocaloric materials selected from at least quaternary compounds of the general formula (I) wherein C, D and E are preferably identical or different and are selected from at least one of P, As, Ge, Si, Sn and Ga. More preferred are magnetocaloric materials selected from at least quaternary compounds of the general formula (I) which, as well as Mn, Fe, P and optionally Sb, additionally comprise Ge or Si or As or both Ge and Si or both Ge and As or both Si and As, or each of Ge, Si and As. The material preferably has the general formula MnFe(P.sub.wGe.sub.xSi.sub.z) wherein x is preferably a number in the range from 0.3 to 0.7, w is less than or equal to 1−x and z corresponds to 1−x−w. The material preferably has the crystalline hexagonal Fe.sub.2P structure. Examples of suitable materials are MnFeP.sub.0.45 to 0.7, Ge.sub.0.55 to 0.30 and MnFeP.sub.0.5 to 0.70(Si/Ge).sub.0.5 to 0.30. (Si/Ge) means, that only one of Si and Ge may be present or both.

(29) Also preferred at least 90% by weight, more preferably at least 95% by weight, of component A is Mn. More preferably at least 90% by weight, more preferably at least 95% by weight, of B is Fe. Preferably at least 90% by weight, more preferably at least 95% by weight, of C is P. Preferably at least 90% by weight, more preferably at least 95% by weight, of D is Ge. Preferably at least 90% by weight, more preferably at least 95% by weight, of E is Si.

(30) Suitable compounds are additionally Mn.sub.1+xFe.sub.1-xP.sub.1-yGe.sub.y with x in the range from −0.3 to 0.5, y in the range from 0.1 to 0.6. Likewise suitable are compounds of the general formula Mn.sub.1+xFe.sub.1-xP.sub.1-yGe.sub.y-zSb.sub.z with x in the range from −0.3 to 0.5, y in the range from 0.1 to 0.6 and z less than y and less than 0.2. Also suitable are compounds of the formula Mn.sub.1+xFe.sub.1-xP.sub.1-yGe.sub.y-zSi.sub.z with x in the range from 0.3 to 0.5, y in the range from 0.1 to 0.66, z less than or equal to y and less than 0.6.

(31) Especially useful magnetocaloric materials of general formula (I) exhibiting a small thermal hysteresis of the magnetic phase transition are described in WO 2011/111004 and WO 2011/083446 having the general formula
(Mn.sub.xFe.sub.1-x).sub.2+zP.sub.1-ySi.sub.y
where

(32) 0.20≦x≦0.40

(33) 0.4≦y≦0.8

(34) −0.1≦z≦0.1

(35) or

(36) 0.55≦x<1

(37) 0.4≦y≦0.8

(38) −0.1≦z≦0.1.

(39) Suitable Fe.sub.2P-based compounds originate from Fe.sub.2P and FeAs.sub.2, and obtain optionally Mn and P. They correspond, for example, to the general formulae MnFe.sub.1-xCo.sub.xGe, where x=0.7-0.9, Mn.sub.5-xFe.sub.xSi.sub.3 where x=0-5, Mn.sub.5Ge.sub.3-xSi.sub.x where x=0.1-2, Mn.sub.5Ge.sub.3-xSb.sub.x where x=0-0.3, Mn.sub.2-xFe.sub.xGe.sub.2 where x=0.1-0.2, Mn.sub.3-xCo.sub.xGaC where x=0-0.05. A description of magnetocaloric Fe.sub.2P-based compounds may be found in E. Brueck et al., J. Alloys and Compounds 282 (2004), pages 32 to 36.

(40) Preferred La- and Fe-based compounds of the general formulae (II) and/or (III) and/or (IV) are La(Fe.sub.0.90Si.sub.0.10).sub.13, La(Fe.sub.0.89Si.sub.0.11).sub.13, La(Fe.sub.0.880Si.sub.0.120).sub.13, La(Fe.sub.0.877Si.sub.0.123).sub.13, LaFe.sub.11.8Si.sub.1.2, La(Fe.sub.0.88Si.sub.0.12).sub.13H.sub.0.5, La(Fe.sub.0.88Si.sub.0.12).sub.13H.sub.1.0, LaFe.sub.11.7Si.sub.1.3H.sub.1.1, LaFe.sub.11.57Si.sub.1.43H.sub.1.3, La(Fe.sub.0.88Si.sub.0.12)H.sub.1.5, LaFe.sub.11.2Co.sub.0.7Si.sub.1.1, LaFe.sub.11.5Al.sub.1.5C.sub.0.1, LaFe.sub.11.5Al.sub.1.5C.sub.0.2, LaFe.sub.11.5Al.sub.1.5C.sub.0.4, LaFe.sub.11.5Al.sub.1.5Co.sub.0.5, La(Fe.sub.0.94Co.sub.0.06).sub.11.83Al.sub.1.17, La(Fe.sub.0.92Co.sub.0.08).sub.11.83Al.sub.1.17.

(41) Suitable manganese-comprising compounds are MnFeGe, MnFe.sub.0.9Co.sub.0.1Ge, MnFe.sub.0.8Co.sub.0.2Ge, MnFe.sub.0.7Co.sub.0.3Ge, MnFe.sub.0.6Co.sub.0.4Ge, MnFe.sub.0.5Co.sub.0.5Ge, MnFe.sub.0.4Co.sub.0.6Ge, MnFe.sub.0.3Co.sub.0.7Ge, MnFe.sub.0.2Co.sub.0.8Ge, MnFe.sub.0.15Co.sub.0.85Ge, MnFe.sub.0.1Co.sub.0.9Ge, MnCoGe, Mn.sub.5Ge.sub.2.5Si.sub.0.5, Mn.sub.5Ge.sub.2Si, Mn.sub.5Ge.sub.1.5Si.sub.1.5, Mn.sub.5GeSi.sub.2, Mn.sub.5Ge.sub.3, Mn.sub.5Ge.sub.2.9Sb.sub.0.1, Mn.sub.5Ge.sub.2.8Sb.sub.0.2, Mn.sub.5Ge.sub.2.7Sb.sub.0.3, LaMn.sub.1.9Fe.sub.0.1Ge, LaMn.sub.1.85Fe.sub.0.15Ge, LaMn.sub.1.8Fe.sub.0.2Ge, (Fe.sub.0.9Mn.sub.0.1).sub.3C, (Fe.sub.0.8Mn.sub.0.2).sub.3C, (Fe.sub.0.7Mn.sub.0.3).sub.3C, Mn.sub.3GaC, MnAs, (Mn, Fe)As, Mn.sub.1+δAs.sub.0.8Sb.sub.0.2, MnAs.sub.0.75Sb.sub.0.25, Mn.sub.1.1As.sub.0.75Sb.sub.0.25, Mn.sub.1.5As.sub.0.75Sb.sub.0.25.

(42) Heusler alloys suitable in accordance with the invention are, for example, Ni.sub.2MnGa, Fe.sub.2MnSi.sub.1-xGe.sub.x with x=0-1 such as Fe.sub.2MnSi.sub.0.5Ge.sub.0.5, Ni.sub.52.9Mn.sub.22.4Ga.sub.24.7, Ni.sub.50.9Mn.sub.24.7Ga.sub.24.4, Ni.sub.55.2Mn.sub.18.6Ga.sub.26.2, Ni.sub.51.6Mn.sub.24.7Ga.sub.23.8, Ni.sub.52.7Mn.sub.23.9Ga.sub.23.4, CoMnSb, CoNb.sub.0.2Mn.sub.0.8Sb, CoNb.sub.0.4Mn.sub.0.6SB, CoNb.sub.0.6Mn.sub.0.4Sb, Ni.sub.50Mn.sub.35Sn.sub.15, Ni.sub.50Mn.sub.37Sn.sub.13, MnFeP.sub.0.45As.sub.0.55, MnFeP.sub.0.47As.sub.0.53, Mn.sub.1.1Fe.sub.0.9P.sub.0.47As.sub.0.53, MnFeP.sub.0.89-XSi.sub.XGe.sub.0.11, X=0.22, X=0.26, X=0.30, X=0.33.

(43) Additionally suitable are Fe.sub.90Zr.sub.10, Fe.sub.82Mn.sub.8Zr.sub.10, Co.sub.66Nb.sub.9Cu.sub.1Si.sub.12B.sub.12, Pd.sub.40Ni.sub.22.5Fe.sub.17.5P.sub.20, FeMoSiBCuNb, Gd.sub.70Fe.sub.30, GdNiAl, NdFe.sub.12B.sub.6GdMn.sub.2.

(44) Manganites of the perovskite type are, for example, La.sub.0.6Ca.sub.0.4MnO.sub.3, La.sub.0.67Ca.sub.0.33MnO.sub.3, La.sub.0.8Ca.sub.0.2MnO.sub.3, La.sub.0.7Ca.sub.0.3MnO.sub.3, La.sub.0.958Li.sub.0.025Ti.sub.0.1Mn.sub.0.9O.sub.3, La.sub.0.65Ca.sub.0.35Ti.sub.0.1Mn.sub.0.9O.sub.3, La.sub.0.799Na.sub.0.199MnO.sub.2.97, La.sub.0.88Na.sub.0.099Mn.sub.0.977O.sub.3, La.sub.0.877K.sub.0.096Mn.sub.0.974O.sub.3, La.sub.0.65Sr.sub.0.35Mn.sub.0.95Cn.sub.0.05O.sub.3, La.sub.0.7Nd.sub.0.1Na.sub.0.2MnO.sub.3, La.sub.0.5Ca.sub.0.3Sr.sub.0.2MnO.sub.3.

(45) Heusler alloys of the MnT.sub.tT.sub.p type where T.sub.t is a transition metal and T.sub.p is a p-doping metal having an electron count per atom e/a in the range from 7 to 8.5 are described are described in Krenke et al., Physical review B72, 014412 (2005).

(46) Gd- and Si-based compounds of the general formula (V)
Gd.sub.5(Si.sub.xGe.sub.1-x).sub.4
where x is a number from 0.2 to 1

(47) are, for example, Gd.sub.5(Si.sub.0.5Ge.sub.0.5).sub.4, Gd.sub.5(Si.sub.0.425Ge.sub.0.575).sub.4, Gd.sub.5(Si.sub.0.45Ge.sub.0.55).sub.4, Gd.sub.5(Si.sub.0.365Ge.sub.0.635).sub.4, Gd.sub.5(Si.sub.0.3Ge.sub.0.7).sub.4, Gd.sub.5(Si.sub.0.25Ge.sub.0.75).sub.4.

(48) Compounds comprising rare earth elements are Tb.sub.5(Si.sub.4-xGe.sub.x) with x=0, 1, 2, 3, 4 or XTiGe with X=Dy, Ho, Tm, for example Tb.sub.5Si.sub.4, Tb.sub.5(Si.sub.3Ge), Tb(Si.sub.2Ge.sub.2), Tb.sub.5Ge.sub.4, DyTiGe, HoTiGe, TmTiGe.

(49) Mn- and Sb- or As-based compounds of the general formulae (VIII) to (XI) preferably have the definitions of z=0.05 to 0.3, Z=Cr, Cu, Ge, Co.

(50) The magnetocaloric materials used in accordance with the invention can be produced in any suitable manner.

(51) The magnetocaloric materials are produced, for example, by solid phase reaction of the starting elements or starting alloys for the material in a ball mill, subsequent pressing, sintering and heat treatment under inert gas atmosphere and subsequent slow cooling to room temperature. Such a process is described, for example, in J. Appl. Phys. 99, 2006, 08Q107.

(52) Processing via melt spinning is also possible. This makes possible a more homogeneous element distribution which leads to an improved magnetocaloric effect; cf. Rare Metals, Vol. 25, October 2006, pages 544 to 549. In the process described there, the starting elements are first induction-melted in an argon gas atmosphere and then sprayed in the molten state through a nozzle onto a rotating copper roller. There follows sintering at 1000° C. and slow cooling to room temperature.

(53) In addition, reference may be made to WO 2004/068512 A1 for the production. However, the materials obtained by these processes frequently exhibit high thermal hysteresis. For example, in compounds of the Fe.sub.2P type substituted by germanium or silicon, large values for thermal hysteresis are observed within a wide range of 10 K or more.

(54) The thermal hysteresis can be reduced significantly and a large magnetocaloric effect can be achieved when the metal-based materials are not cooled slowing to ambient temperature after the sintering and/or heat treatment, but rather are quenched at a high cooling rate. This cooling rate is at least 100 K/s. The cooling rate is preferably from 100 to 10 000 K/s, more preferably from 200 to 1300 K/s. Especially preferred cooling rates are from 300 to 1000 K/s.

(55) The quenching can be achieved by any suitable cooling processes, for example by quenching the solid with water or aqueous liquids, for example cooled water or ice/water mixtures. The solids can, for example, be allowed to fall into ice-cooled water. It is also possible to quench the solids with subcooled gases such as liquid nitrogen. Further processes for quenching are known to those skilled in the art. What is advantageous here is controlled and rapid cooling.

(56) The rest of the production of the magnetocaloric materials is less critical, provided that the last step comprises the quenching of the sintered and/or heat-treated solid at the inventive cooling rate.

(57) A further aspect of the present invention refers to the use of at least one magnetic shielding comprising at least one window as described above for operating a magnetocaloric device containing at least one magnetocaloric material by varying the magnetic field used to exploit the magnetocaloric effect by moving the at least one magnetic shielding between at least one first position and at least one second position thereby insulating the magnetocaloric material contained in the magnetocaloric material unit from the magnetic field as the magnetic shielding is in a first position and allowing the magnetic field to act on the magnetocaloric material through the at least one window as the magnetic shielding is in a second position.

(58) Another aspect of the present invention is a process of operating a magnetocaloric device containing at least one magnetocaloric material wherein the varying magnetic field used to exploit the magnetocaloric effect is produced by moving at least one magnetic shielding comprising at least one window as described above between at least one first position and at least one second position thereby insulating the magnetocaloric material contained in the magnetocaloric material unit from the magnetic field as the magnetic shielding is in a first position and allowing the magnetic field to act on the magnetocaloric material through the at least one window as the magnetic shielding is in a second position.

(59) The inventive magnetocaloric regenerators are preferably used in refrigeration systems like fridges, freezers and wine coolers, climate control units including air condition, and heat pumps. The present invention therefore provides refrigeration systems like fridges, freezers and wine coolers, climate control units including air condition, and heat pumps comprising an inventive magnetocaloric regenerator unit as described above.