Jaime A. L. Cadena
Date of publication
CAPES Award Thesis 2016 Engineering III area
Magnetic refrigeration is an emerging cooling technology for applications at room-temperature. The magnetocaloric effect (MCE) is the thermal response of a magnetic material when subjected to a changing magnetic field. Magnetic refrigeration harvests the MCE in a regenerative thermodynamic cycle to transfer heat from a lowtemperature environment to a high-temperature one by means of magneticworkinanactivemagneticregenerator(AMR).Inthisthesis, several aspects of this technology were analyzed with contributionsonfourresearchfronts.First,atemperaturecontrolledfacility wasconstructedtoimprovethedirectmeasurementsoftheMCEby means of the adiabatic temperature change, ΔTad. Measurements of the benchmark magnetocaloric material gadolinium (Gd), and one of the most promising magnetic refrigerants, MnFe(P,As), were investigated. Second, a magnetic circuit with a 2-pole rotor-stator configuration with high magnetic flux regions of approximately 1 T was designed aiming at an efficient use of the Nd-Fe-B permanent magnets. A novel method to optimize the magnetic circuit was proposed by employing a magnet wedge concept. Third, a novel rotary magnetic refrigerator was designed and built at the Federal UniversityofSantaCatarina(UFSC)usingtheoptimizedrotarymagnetic circuitandastationaryAMRcomposedby8pairsbedspackedwith 1.7 kg of Gd spheres. Two low-friction rotary valves were developed to synchronize the hydraulic and magnetic cycles and positioned at the hot end to avoid heat generation in the cold end. The last part of this thesis comprised an experimental and thermodynamic performance analysis of the rotary magnetic cooler prototype developed atthe TechnicalUniversity ofDenmark(DTU). Adetailedstudyof the losses external to the regenerator and a methodology to breakdown the COP and the motor power was developed to quantify the efficiencyimprovementsofthesystemandthemajorlosses. Theperformance of both magnetic refrigerators were evaluated in terms of there generator temperature span, coefficient of performance (COP) and the overallsecond-law efficiency (η2nd) as a function of different operating conditions.
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