Hybrid heat pump / refrigerator with magnetic cooling stage

Abstract

A device for transporting heat from a cold reservoir to a warm reservoir, in which at least two cyclic processes are employed for transporting heat thereby absorbing work, of which at least one is a regenerative cyclic process, and at least one is a magnetocaloric cyclic process, wherein the regenerative cyclic process has a working fluid and a heat storage medium, is characterized in that the heat storage medium of the regenerative cyclic process comprises a magnetocaloric material for the magnetocaloric cyclic process, wherein the magnetocaloric material is in a regenerator area with a cold end and a warm end, the working fluid of the regenerative cyclic process additionally serving as a heat transfer fluid for the magnetocaloric cyclic process. This produces a compact device with low apparative expense, wherein the power density and also the efficiency of the device are increased. The device may advantageously be used for cooling a superconducting magnet configuration.

Description

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a shows a schematic construction of a device for transporting heat from a cold reservoir to a warm reservoir in a regenerative, cyclic process in accordance with Stirling (prior art);

FIG. 1 b shows a schematic construction of a device for transporting heat from a cold reservoir to a warm reservoir in a magnetocaloric cyclic process (prior art);

FIG. 1 c shows a schematic construction of an inventive device for transporting heat from a cold reservoir to a warm reservoir;

FIG. 2 a shows the different process phases in a device for transporting heat from a cold reservoir to a warm reservoir in a regenerative, cyclic process in accordance with Stirling (prior art);

FIG. 2 b shows the different process phases in a device for transporting heat from a cold reservoir to a warm reservoir in a magnetocaloric cyclic process (prior art);

FIG. 2 c shows the different process phases in an inventive device for transporting heat from a cold reservoir to a warm reservoir;

FIG. 3 shows an embodiment of an inventive device for cooling a superconducting magnet system;

FIG. 4 shows the process phases III->IV and VI->I in an inventive device for transporting heat from a cold reservoir to a warm reservoir with volume elements of the working fluid;

FIG. 5 a shows all process phases of an inventive device for a first volume element of the working fluid in a temperature-entropy diagram (T-S diagram);

FIG. 5 b shows all process phases of an inventive device for any volume element of the working fluid in a temperature-entropy diagram (T-S diagram);

FIG. 5 c shows all process phases of an inventive device for a last volume element of the working fluid in a temperature-entropy diagram (T-S diagram); and

FIG. 6 shows the power increase and the exergetic efficiency in dependence on the pressure ratio for an exemplary inventive hybrid Stirling refrigerator.

Claims

1. A device for transporting heat from a cold reservoir to a warm reservoir using at least two cyclic processes for transporting the heat, thereby absorbing work, the device comprising: means for transporting heat via a working fluid in a regenerative cyclic process;means for exchanging heat via a magnetocaloric material in a magnetocaloric cyclic process;means for storing heat with the magnetocaloric material during said regenerative cyclic process; andmeans for transferring heat with the working fluid during said magnetocaloric cyclic process.

2. The device of claim 1, wherein said regenerative cyclic process has a heat storage medium comprising said magnetocaloric material, said magnetocaloric material being disposed in a regenerator area having a cold end and a warm end, wherein said working fluid of said regenerative cyclic process additionally serves as a heat transfer fluid for said magnetocaloric cyclic process.

3. The device of claim 2, wherein a cold reservoir has a temperature which is below ambient temperature, and a warm reservoir has a temperature which is at or above ambient temperature.

4. The device of claim 2, wherein said regenerative cyclic process is based on a Stirling, a Vuilleumier, a Gifford-McMahon, or a pulse tube gas cycle.

5. The device of claim 2, wherein said magnetocaloric material comprises different components with different Curie temperatures which are disposed next to each other in layers at said regenerator area in order of decreasing Curie temperature, wherein a component of said magnetocaloric material with a highest Curie temperature is disposed at said warm end and a component of said magnetocaloric material with a lowest Curie temperature is disposed at said cold end of said regenerator area.

6. The device of claim 2, further comprising means for providing a magnetic field and/or for shielding a magnetic background field to provide and/or shield a magnetic field at least at a location of said magnetocaloric material.

7. The device of claim 6, wherein said means for providing a magnetic field and/or shielding a magnetic background field comprise a permanent magnet.

8. The device of claim 6, wherein said means for providing a magnetic field and/or shielding a magnetic background field comprise a magnet coil winding with a normally conducting and/or a superconducting wire.

9. The device of claim 6, wherein a magnetic shielding of soft magnetic material is provided for shielding said magnetic background field.

10. A superconducting magnet configuration comprising the device for transporting heat from a cold reservoir to a warm reservoir of claim 1.

11. The superconducting magnet configuration of claim 10, wherein the superconducting magnet configuration is part of an apparatus for magnetic resonance (MR), nuclear magnetic resonance imaging (MRI), or nuclear magnetic resonance spectroscopy (NMR).

12. The superconducting magnet configuration of claim 10, wherein the superconducting magnet configuration is part of an apparatus for ion cyclotron resonance spectroscopy (ICR) or electron spin resonance (ESR, EPR).

13. A method for transporting heat from a cold reservoir to a warm reservoir using at least two cyclic processes for transporting the heat, thereby absorbing work, the method comprising the steps of: a) transporting heat via a working fluid in a regenerative cyclic process;b) exchanging heat via a magnetocaloric material in a magnetocoleric cyclic process;c) storing heat with the magnetocaloric material during step a); andd) transferring heat with the working fluid during step b).

14. The method of claim 13, wherein the working fluid passes through a compression phase, a phase of heat release, an expansion phase and a heat absorbing phase in the regenerative cyclic process.

15. The method of claim 13, wherein a field strength of a magnetic field is periodically varied at least at a location of the magnetocaloric material.

16. The method of claim 15, wherein the field strength is varied through cyclic change of a relative position of the magnetocaloric material relative to a permanent magnet.

17. The method of claim 15, wherein the field strength is varied by changing a current flow in a normally conducting and/or superconducting magnet coil.

18. The method of claim 13, wherein a strength of a magnetic field shielding in a magnetic background field is varied periodically at least at a location of the magnetocaloric material.

19. The method of claim 13, wherein, in the regenerative cyclic process, a heat absorbing phase and a compression phase are executed with a high magnetic field in the magnetocaloric material, and a heat release phase and expansion phase are executed with a low magnetic field in the magnetocaloric material.