Active magnetic regenerator performance enhancement using passive magnetic materials

Magnetic refrigeration devices using permanent magnets are currently limited to useful field strengths of less than 2 T, and more practically less than 1.5 T. In this range, the useful magnetocaloric effect is less than 6K and limits the cooling power of active magnetic regenerator (AMR) devices. Maximizing the useful magnetocaloric effect is critical in enabling commercially viable permanent magnet devices, and methods of increasing the net change in magnetic field would be beneficial. It has been shown [O. Peksoy, A. Rowe, J. Magn. Magn. Mater. 288 (2005) 424] that the geometry of a regenerator and the magnetic properties of the refrigerant can alter the local magnetic field, H. This is called demagnetization. A numerical model is used to study demagnetizing effects in a single-material AMR. The use of additional passive magnetic material to reduce demagnetization is examined and suggests that augmenting the effective field, H, is possible. Numerical results are validated with experiments in near room temperature using AMRs consisting of Gd and Gd0.74Tb0.26 adjacent to layers composed of 1010 carbon steel. Experimental data show an increase in the no-load temperature span for certain operating conditions and confirm the beneficial impact of using passive magnetic material to reduce demagnetization effects at low fields. (c) 2007 Elsevier B. V. All rights reserved.