With the discovery of the magnetocaloric effect, utilizing magnetocaloric materials in cycles to generate cooling power began. The magnetocaloric effect is a physical phenomenon observed in some magnetic materials where the temperature of the material increases and decreases with application and removal of magnetic field. Usually the adiabatic temperature change observed in magnetocaloric materials is too small for room temperature refrigeration. A solution to this problem is to use magnetocaloric materials in an active magnetic regenerator (AMR) cycle. In this study a detailed numerical model is developed, validated, and used to improve our understanding of AMR systems. A one dimensional, time dependent model is used to study the performance of an active magnetic regenerator. Parameters related to device configuration such as external heat leaks and demagnetization effects are included. Performance is quantified in terms of cooling power and second law efficiency for a range of displaced fluid volumes and operating frequencies. Simulation results show that a step change model for applied field can be effectively used instead of full field wave form if the flow weighted average low and high field values are used. This is an important finding as it can greatly reduce the time required to solve the numerical problem. In addition, the effects of external losses on measured AMR performance are quantified. The performance of eight cases of known magnetocaloric material (including first order MnFeP1-xAsx and second order materials Gd, GdDy, Tb) and 15 cases of hypothetical materials are considered. Using a fixed regenerator matrix geometry, magnetic field, and flow waveforms, the maximum exergetic cooling power of each material is identified. Several material screening metrics such as RCP and RC are tested and a linear correlation is found between RCPMax and the maximum exergetic cooling power. The sensitivity of performance to variations in the hot side and cold side temperatures from the conditions giving maximum exergetic power are determined. The impact of 2 K variation in operating temperature is found to reduce cooling power up to 20 % for a second order material, but can reduce cooling power up to 70% with a first order material. A detailed numerical analysis along with experimental measurements are used to study the behavior of typical first order material (MnFeP1-xSix samples) in an AMR. For certain operating conditions, it is observed that multiple points of equilibrium (PE) exist for a fixed heat rejection temperature. Stable and unstable PEs are identified and behavior of these points are analysed. The impacts of heat loads, operating conditions and configuration losses on the number of PEs are discussed and it is shown that the existence of multiple PEs can affect the performance of an AMR significantly. Thermal hysteresis along with multiple PEs are considered as the main factors that contribute to the temperature history dependent performance behavior of FOMs when used in an AMR. / Graduate / 0548 / iniknia@uvic.ca

Le domaine du refroidissement est en constante expansion, le système actuel est basé sur la compression/décompression des fluides. Face aux problèmes environnementaux et économiques que ce système présente (natures des fluides frigorigènes et leurs recyclages, nuisances sonores et vibratoires, réglementations contraignantes), de nouvelles solutions techniques alternatives émergent. Ainsi ce travail de thèse porte sur de nouveaux systèmes de refroidissement basés sur les effets électrocalorique et magnétocalorique, respectivement présents dans des films minces de polymère fluoré et dans des composites à matrice polymère et à charges magnétocaloriques. A travers des caractérisations physico-chimiques, électriques, électrocaloriques et magnétocaloriques ces travaux se proposent d’identifier l’origine de l’effet électrocalorique dans des films minces de terpolymère P(VDF-TrFE-CTFE) ferroélectrique relaxeur, mais également d’étudier l’influence de la dispersion des particules magnétocaloriques La(Fe,Si)H dans une matrice polymère de poly(propylène) sur le phénomène magnétocalorique. De plus, dans le cadre de cette thèse, un appareil de mesure directe de l’effet électrocalorique a été développé avec le Dr. Basso de l’INRIM de Turin. La comparaison avec la méthode de mesure indirecte permet d’aborder ce phénomène d’un point de vue thermodynamique afin de faire le point sur la validité des hypothèses thermodynamiques utilisées dans le cas d’un polymère ferroélectrique relaxeur. / The cooling sector is in constant expansion, the current system is based on the compression/decompression of fluids. In front of environmental and economic problems of this system (nature of frigorigen fluids and their recycling, noise and vibration issues, restrictive regulations), new alternative technological solutions emerge. Thus this thesis provides new cooling systems based on the magnetocaloric and electrocaloric effects respectively present in thin films of fluoropolymer and composites with polymer matrix and magnetocaloric loads. Through physicochemical, electrical, electrocaloric and magnetocaloric characterizations, this work intends to identify the origin of electrocaloric effect in thin terpolymer films P(VDF-TrFE-CTFE) which is a ferroelectric relaxor, but also to study the influence of the magnetocaloric particles La(Fe,Si)H dispersion in a polymer matrix of poly(propylene) on the magnetocaloric phenomenon. In addition, as part of this thesis, a direct measurement device of the electrocaloric effect was developed with Dr. Basso from the INRIM of Turin. The comparison with the indirect measurement method comes up with this phenomenon from a thermodynamic point of view to take stock of the validity of thermodynamic assumptions used in the case of a ferroelectric polymer relaxor.