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Certain paramagnetic materials, like gadolinium alloys, heat up when placed in a magnetic field and cool down when the field is removed. In a magnetic refrigeration system this process takes the place of the compressor that is used in a normal vapor compression system. Specifically, a regenerator bed made with porous magnetocaloric material is employed. Water flows through the regenerator bed and move heat to or from the system's heat exchangers.
Most magnetocaloric materials exhibit a large magnetocaloric effect over a narrow temperature range that is centered on their Curie temperatures. Early magnetocaloric materials typically had very low Curie temperatures and their use was limited to low temperature cryogenic cooler applications. However, newer families of magnetocaloric alloys and hydrides are now being developed at the Ames Research Laboratory and other laboratories. These new materials have higher Curie temperatures which make them practical for use in comfort cooling and refrigerator applications.
Also many of these new alloys and hydrides can have their compositions varied slightly to produce adjustable Curie temperatures. By layering a regenerative bed with several magnetocaloric materials with different Curie temperatures, one can extend the effective temperature range in which the magnetocaloric effect is useful.
As part of this project, researchers at the University of Wisconsin-Madison conducted analytical studies, using the model coupled with the DOE/ORNL heat pump design model, to predict the performance of a magnetic refrigeration system with a gadolinium-erbium regenerator in comfort cooling and refrigeration applications. These studies predicted that magnetic refrigeration systems can operate more efficiently than current baseline vapor compression systems if the regenerator is adequately large. The challenge now is to find more advanced magnetocaloric materials that are economical and allow design of more compact regenerator beds.
As more advanced magnetocaloric materials are developed, the numerical model developed in this project will allow researchers to analytically determine the efficiency and performance limits of magnetic refrigeration systems using those materials.
An executive summary of the report can be downloaded at www.arti-research.org/research/completed/exec-summaries/10075-es.pdf. The entire final report can be downloaded at www.arti--research.org/research/completed/finalreports/10075-final.pdf.
The Air-Conditioning and Refrigeration Technology Institute is a not-for-profit organization established by the Air-Conditioning and Refrigeration Institute (ARI) to undertake scientific research in the public interest.
Publication date: 07/04/2005