Magnetocaloric refrigerator

Abstract

The invention is for an apparatus and method for a refrigerator and a heat pump based on the magnetocaloric effect (MCE) offering a simpler, lighter, robust, more compact, environmentally compatible, and energy efficient alternative to traditional vapor-compression devices. The subject magnetocaloric apparatus alternately exposes a suitable magnetocaloric material to strong and weak magnetic field while switching heat to and from the material by a mechanical commutator using a thin layer of suitable thermal interface fluid to enhance heat transfer. The invention may be practiced with multiple magnetocaloric stages to attain large differences in temperature. Key applications include thermal management of electronics, as well as industrial and home refrigeration, heating, and air conditioning. The invention offers a simpler, lighter, compact, and robust apparatus compared to magnetocaloric devices of prior art. Furthermore, the invention may be run in reverse as a thermodynamic engine, receiving low-level heat and producing mechanical energy.

What is claimed is: 
     
         1 . A magneto-caloric refrigerator (MCR) comprising: a magneto-caloric effect (MCE) material, a means for generating magnetic field, a first heat commutator, a second heat commutator, and a thermal interface fluid (TIF);
 a) said MCE material being arranged to be in close proximity to said first heat commutator thereby forming a first gap therebetween;   b) said MCE material being arranged to be in close proximity to said second heat commutator thereby forming a second gap therebetween;   c) said TIF being arranged to substantially fill said first gap and said second gap;   d) said means for generating magnetic field arranged to produce a region of weak magnetic field and a region of strong magnetic field;   e) said first heat commutator comprising a first thermally conducting core;   f) said second heat commutator comprising a second thermally conducting core;   g) said MCE material being arranged to be in motion relative to each said first thermally conducting core and said second thermally conducting core;   h) said motion causing said MCE material to be alternately exposed to a weak magnetic field and to a strong magnetic field;   i) said MCE material being arranged to be in good thermal communication with said first thermally conducting core by means of said TIF when said MCE material is exposed to a weak magnetic field; and   j) said MCE material being arranged to be in good thermal communication with said second thermally conducting core by means of said TIF when said MCE material is exposed to a strong magnetic field.   
     
     
         2 . The MCR of  claim 1 , wherein said motion is causing said TIF to flow in a shear flow regime. 
     
     
         3 . The MCR of  claim 1 , wherein said first thermally conducting core is thermally coupled to a heat reservoir at a first temperature, said second thermally conducting core is thermally coupled to a heat reservoir at a second temperature, and said second temperature is higher than said first temperature. 
     
     
         4 . The MCR of  claim 1 , wherein said TIF is selected from the family consisting of liquid metal, gallium-based liquid metal alloy, gallium-indium-tin liquid metal alloy, gallium-indium-tin-zinc liquid metal alloy, nanofluid, and nanofluid substantially comprising carbon nanotubes. 
     
     
         5 . The MCR of  claim 1 , wherein said MCE material is formed as a disk arranged to rotate about its axis of rotational symmetry. 
     
     
         6 . The MCR of  claim 1 , wherein said means for generating magnetic field is selected from the family consisting of a permanent magnet, electromagnet, and superconducting coil. 
     
     
         7 . The MCR of  claim 1 , wherein said first gap and said second gap are each selected to be between about 50 and about 500 micrometers wide. 
     
     
         8 . A staged magnetocaloric refrigerator (MCR) comprising a plurality of MCR stages;
 a) each said MCR stage comprising a magnetocaloric effect (MCE) material, a first thermally conducting core, a second thermally conducting core, a means for producing a region of strong magnetic field and a region of weak magnetic field, and a thermal interface fluid (TIF);   b) within each said MCR stage, said first thermally conducting core of that MCR stage being arranged to be in a good thermal communication by means of said TIF with a portion of said MCE material of that stage when said portion of said MCE material of that stage is immersed in a weak magnetic field;   c) within each said MCR stage, said second thermally conducting core of that MCR stage being arranged to be in a good thermal communication by means of said TIF with a portion of said MCE material of that MCR stage when said portion of said MCE material of that MCR stage is immersed in a strong magnetic field;   d) the thermally conducting core of the first MCR stage being thermally coupled to a lower heat reservoir;   e) for each subsequent said MCR stage, the first thermally conducting core of that MCR stage being coupled to the second thermally conducting core of the preceding MCR stage; and   f) said second thermally conducting core of the last MCR stage being thermally coupled to an upper heat reservoir.   
     
     
         9 . The staged MCR of  claim 8 , wherein the temperature of said lower heat reservoir is substantially lower than the temperature of said upper heat reservoir. 
     
     
         10 . The staged MCR of  claim 8 , wherein within each said MCR stage said MCE material of that MCR stage is arranged to be in motion relative to each said first thermally conducting core of that MCR stage and said second thermally conducting core of that MCR stage. 
     
     
         11 . The staged MCR of  claim 10 , wherein said motion is causing said TIF to flow in a shear flow regime. 
     
     
         12 . The staged MCR of  claim 8 , wherein within each said MCR stage, said first thermally conducting core of that MCR stage and said MCE material of that MCR stage are arranged to form a first gap therebetween and said first gap is substantially filled with said TIF; and said second thermally conducting core of that MCR stage and said MCE material of that MCR stage are arranged to form a second gap therebetween and said second gap is substantially filled with said TIF. 
     
     
         13 . The staged MCR of  claim 8 , wherein said TIF has a thermal conductivity of at least 1 watt/meter—degree Kelvin. 
     
     
         14 . The staged MCR of  claim 8 , wherein said TIF is selected from the family consisting of liquid metal, gallium-based liquid metal alloy, gallium-indium-tin liquid metal alloy, gallium-indium-tin-zinc liquid metal alloy, nanofluid, and nanofluid substantially comprising carbon nanotubes. 
     
     
         15 . The staged MCR of  claim 1 , wherein said means for producing said region of strong magnetic field is selected from the family consisting of a permanent magnet, electromagnet, and superconducting coil. 
     
     
         16 . The staged MCR of  claim 1 , wherein said thermal communication comprises a flow of heat through said TIF flowing in s shear flow regime. 
     
     
         17 . A method for pumping heat comprising the steps of:
 a) providing a magnetocaloric effect (MCE) material;   b) providing a first thermal conductor at a first temperature;   c) providing a second thermal conductor at a second temperature;   d) arranging said MCE material to be in close proximity of said first conductor with a first gap therebetween;   e) arranging said MCE material to be in close proximity of said second conductor with a second gap therebetween;   f) substantially filling said first gap and said second gap with a thermal interface fluid (TIF);   g) moving said MCE material with respect to said first thermal conductor;   h) moving said MCE material with respect to said second thermal conductor;   i) flowing said TIF in said first and said second gap in a shear flow regime;   j) exposing said MCE material to a weak magnetic field;   k) forming a good thermal communication between said MCE material and said first thermal conductor through said TIF;   l) exposing said MCE material to a strong magnetic field;   m) forming a good thermal communication between said MCE material and said second thermal conductor through said TIF.   
     
     
         18 . The method of  claim 17 , wherein said second temperature is higher than said first temperature. 
     
     
         19 . The method of  claim 17 , wherein said steps of (j) exposing said MCE material to a weak magnetic field and (k) forming a good thermal communication between said MCE material and said first thermal conductor through said TIF, are performed concurrently. 
     
     
         20 . The method of  claim 17 , wherein said steps of (l) exposing said MCE material to a strong magnetic field and (m) forming a good thermal communication between said MCE material and said second thermal conductor through said TIF, are performed concurrently.