Effect of geometrical shape of the working substance Gadolinium on the performance of a regenerative magnetic Brayton refrigeration cycle

• Published in: Journal of magnetism and magnetic materials Vol. 326; pp. 103 - 107
• Main Authors: Diguet, Gildas, Lin, Guoxing, Chen, Jincan
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-01-2013; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Demagnetizing; Demagnetizing field; Entropy; Exact sciences and technology; Gadolinium; Magnetic entropy; Magnetic fields; Magnetic materials; Magnetic properties and materials; Magnetic refrigeration; Magnetically ordered materials: other intrinsic properties; Magnetocaloric effect, magnetic cooling; Physics; Refrigeration; Refrigerators; Thermodynamic performance; Thermodynamics; Magnetic refrigeration; Demagnetizing field; Magnetic entropy; Thermodynamic performance; Magnetic refrigerators; Geometrical shape; Mean field approximation; Magnetocaloric effects; Magnetic field effects; Gadolinium; Exchange interactions
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2012.08.044

Based on Mean Field Theory (MFT), the entropy of magnetic material Gadolinium (Gd), which is a function of the local magnetic field and temperature, is calculated and analyzed. This local magnetic field is the sum of the applied field H0 plus the exchange field HW=λM and the demagnetizing field Hd=−NM, where the demagnetizing factor N depends on the shape of magnetic materials. Hereby, the impacts of the demagnetizing factor N on the magnetic entropy, magnetic entropy change and main thermodynamics performance of a regenerative magnetic Brayton refrigeration cycle using Gd as the working substance are investigated and evaluated in detail. The results obtained underline the importance of the shape of the working substance used in magnetic refrigerators for room-temperature application; elongated materials provide better thermodynamics performance such as higher COP and net heat absorption. It is pointed out that for low external fields, the magnetic refrigerator ceased to be functional if flat materials were used.
► Gd entropy is calculated as a function of temperature and internal magnetic field. ► Magnetic Brayton cycle properties generally depend on the demagnetizing factor. ► Redundant heat transfer is highly sensitive to the demagnetizing factor. ► The net cooling quantity is highly sensitive to the demagnetizing factor. ► Coefficient of performance is dependant to the magnetic material shape.