Jader R. Barbosa
Date of publication
ABCM-EMBRAER Award 2016 best doctoral thesis
The research on alternative technologies aims at the development of environmentally-friendly thermal systems with a lower energy consump-tion. In this context, magnetic refrigeration at near-room temperature stands out as a promising alternative technology for the development of refrigeration systems.
The present thesis advances theoretical and experimental analyses of passive and active magnetic regenerators aiming at applications in re-frigeration systems. The study of passive regenerators will provide the basis for the assessment of the active matrices. Therefore, the thesis work was carried out along two research fronts. The ﬁrst is concerned with the study of the thermal-hydraulic performance of passive regen-erators through an evaluation of their eﬀectiveness and viscous losses. The second front is dedicated to the evaluation of active magnetic re-generators as part of a refrigeration cycle, by means of an analysis of the system cooling capacity, temperature diﬀerence between the ther-mal reservoirs and coeﬃcient of performance.
Both fronts have experimental and numerical approaches. In the ex-perimental part, an apparatus for the evaluation of passive and active magnetic regenerators was designed and built. Diﬀerent matrix ge-ometries (parallel plates, pin arrays and packed beds of spheres) were evaluated in terms of their thermal performances. In the numerical analysis, a mathematical model based on the ﬁnite volume method was developed to solve the transient one-dimensional forms of the mo-mentum equation for the ﬂuid ﬂow through the porous matrix and the energy equations for the ﬂuid and solid phases. Diﬀerent types of losses were included in the model, such as the internal demagnetizing ﬁeld, heat transfer to the surroundings, axial heat conduction and void volume losses. Finally, a methodology to optimize passive and active regenerators based on the Entropy Generation Minimization theory was proposed and implemented in the numerical model.
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