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Thesis
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Fundamental and applied studies of magnetically controllable fluids and elastomers
Borbáth, Tünde
2012-09-28
Abstract: ABSTRACT The thesis analyses and characterizes the most fascinating soft magnetic materials: high magnetization magnetic nanofluids, nano-micro structured composite magnetic fluids and magnetorheological elastomers in order to get a deep knowledge of these materials and their applicability. It reviews several criteria for obtaining high magnetization magnetic nanofluids with long-term colloidal stability even in a high intensity strongly nonuniform magnetic field. One of the main directions was to understand the structure formation of magnetic particles in such materials which influences their physical properties. The thesis introduces a new way to investigate the microstructure of iron particle (1-10 μm) suspensions in magnetic nanofluids. By using X-ray microcomputed tomography coupled with tools for digital image processing, it offers, for the first time, real three-dimensional images about the inner particle structure in a fluidic environment. Such measurements offer both qualitative and quantitative information. Results summarized in the thesis evidence a high influence of the magnetic field gradient on the distribution of the micron sized iron particles dispersed in magnetic nanofluids. By using the same technique, systematic investigations of structure formation of magnetic particles embedded in elastomer have been conducted in order to understand the field dependence of the main characteristics of the columnar structures in magnetorheological elastomers. The final part of the thesis focuses on technical applications. It investigates the influence of the properties of different magnetizable fluids on the operating parameters of leakage-free rotating seals with magnetic fluids. Constructive details, numerical simulation of magnetic fields in sealing systems and concrete examples are discussed. The main differences between magnetic nanofluids and nano-micro composite magnetic fluids regarding to the usage in diverse seal systems are synthetized, as well as the influence of their properties on the operating parameters. A custom designed experimental bench for testing different operating parameters of leakage-free rotating seals with magnetic fluids is presented. The thesis summarizes several experimental results about the sealing capacity and the influence of the magnetic fluid viscosity on the seal temperature at different rotational speeds and on the breakaway torque of the seal. It was demonstrated that a composite magnetic fluid can assure even 20 times better sealing capabilities than a magnetic nanofluid with moderate saturation magnetization. However, high magnetization magnetic nanofluids, especially which have high vacuum oil carrier liquid, can significantly affect the temperature and the breakaway torque of the magnetofludic rotating seals. Moreover, this part highlights the potential of using magnetic controllable fluids and elastomers in magnetorheological devices with a much longer life-time and better performance.
Keyword(s): Fluide magnetice -- Teză de doctorat ; Nanofluide magnetice -- Teză de doctorat ; Elastomeri magnetoreologici -- Teză de doctorat
OPAC: See record in BC-UPB Web OPAC
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Notice créée le 2016-05-12, modifiée le 2016-05-13
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