Summary
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 ofthisthesiscomprisedanexperimentalandthermodynamicperformance 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 theregeneratortemperaturespan,coefficientofperformance(COP) andtheoverallsecond-lawefficiency(η2nd)asafunctionofdifferent operating conditions.
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