Abstract
Magnetic refrigeration has been paid much attention with the view of alternating conventional gas-expansion cooling techniques which use some sort of harmful gases such as ozone-depleting (CFC;chlorofluocarbon), green-house (HCFC;hydrochlorofluocarbon, HFC; hydrofluocarbon) toxic (NH3:ammonia) or flammable (CH3CH2CH3) gases as refrigerant. A concept of the Active Magnetic Regenerator (AMR) cycle and use of magnetocaloric effect at the ferromagnetic transition bring magnetic refrigeration to a successful in room temperature range. We have developed a room temperature magnetic refrigeration apparatus with Halbach-type permanent magnets. The magnitude of magnetic field is 1.1 T at the center of the bore. We have obtained the lowest temperature of 10 degrees below zero, and the maximum temperature span DTspan of 44.2 K by operating AMR cycle using GdY spheres as the magnetic refrigerant. It needs breakthrough of magnetic field changing mechanism or advanced magnetocaloric materials or feasible high-frequency operation toward the practical use of magnetic refrigeration.
