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

[0001]This application claims Paris Convention priority of DE 10 2006 006 326.0 filed Feb. 11, 2006 the complete disclosure of which is hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]The invention concerns 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 a working fluid and a heat storage medium are provided for the regenerative cyclic process.[0003]A device of this type has been disclosed in the document “A multi-stage continuous-duty adiabatic demagnetization refrigerator” (P. J. Shirron et al., Adv. Cry. Eng., Vol. 45B, page 1629). It combines a regenerative, cyclic gas refrigeration process with magnetic cooling by using a Gifford-McMahon gas refrigerator for precooling several, series-connected magnetic cold stages in orde...

AI Technical Summary

Benefits of technology

[0013]The advantage of an inventive device compared to conventional devices consists in that the apparative expense is greatly reduced. The advantages of the inventive device compared to prior art may be explained by means of example by the arrangement of the document “Performance testing of a 4 K active magnetic regenerative refrigerator” (S. F. Kral et al., Adv. Cry. Eng., Vol. 45A, page 329). When the working fluid of a cooler of a regenerative cyclic process, e.g. of the Gifford-McMahon cooler that is used in the conventional device is used in accordance with the invention as a heat transfer fluid of the magnetocaloric cold stage, both may be advantageously transported via the same drive mechanism. In the same way, the inventive use of the active material of the magnetocaloric cold stage as a regenerator material in the Gifford-McMahon cooler represents a simplification of the apparatus. Moreover, the inventive combined process is thermo-dynamically more efficient than a conventional regenerative gas cycle alone (as used e.g. for a gas refrigerator in a pulse tube cooler or Gifford-McMahon cooler). The cooling or heating performance may be increased without considerably increasing the volume of the machine, thereby increasing the power density. Moreover, an existing external magnetic field (as described e.g. in the patent document U.S. 2002 / 0002830A1) is not disturbing, but even advantageous, since it can be utilized for the magnetocaloric cycle.

[0031]The inventive method is essentially advantageous when the heat is transported within a superconducting magnet configuration, wherein the superconducting magnet configuration is part of an apparatus for magnetic resonance (MR), in particular, for nuclear magnetic resonance imaging (MRI) or nuclear magnetic resonance spectroscopy (NMR) or is part of an apparatus for ion cyclotron resonance spectroscopy (ICR) or for electron spin resonance (ESR, EPR). In this fashion, such an apparatus can be cooled efficiently and in a user-friendly fashion. Compared to conventional cooling using liquid cryogens, the user friendliness of the apparatus and the cooling costs can be reduced, in particular, when the price for cryogens increases in the near future.

Problems solved by technology

Since there are always two independent cooling mechanisms in the conventional devices of this type, the apparative expense is relatively large.

An external magnetic field is thereby undesired in this case.

Moreover, a pulse tube cooler does not work very efficiently in contrast to magnetic coolers, with the consequence that the operating costs for cooling the magnet system are relatively high.

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