Investigation of Thermal Properties of Nanofluids and the Application of Ferrofluids on Transformers
Date Issued
2010
Date
2010
Author(s)
Tsai, Tsung-Han
Abstract
The thermal conductivity of nanofluids and the application of ferrofluids are investigated. With respect to the first topic, the effect of the viscosity of base fluids on the thermal conductivity of nanofluids is discussed. Experimental results reveal an obvious enhancement on thermal conductivity of nanofluids with low viscous base fluids. The measured thermal conductivity of low viscous nanofluids markedly exceeds that predicted by Maxwell prediction model. As the viscosity of the base fluid increases, the measured thermal conductivity of the nanofluid gradually approaches the value predicted by Maxwell prediction model, indicating that the viscosity of nanofluids influences their thermal conductivity, and the Brownian motion of suspended particles importantly enhances the thermal conductivity of nanofluids. Moreover, while the first topic is investigated, some special properties of ferrofluid are found. Therefore, a new application is derived. With respect to the second topic, ferrofluids and bulk Fe3O4 are applied as the magnetic cores of transformers. The transformers used in this thesis are constructed on a capillary or on a wafer. The performance of transformers with different magnetic cores is measured and simulated. Although Fe3O4 increases the inductance and coupling coefficient, it also increases the resistance owing to a lag between the external magnetic field and the magnetization of the material. Finally, a new process for fabricating a solid magnetic core is proposed, in which ferrofluids are used to deliver ferro-nanoparticles into microchannels. A transformer with a solid magnetic core outperforms the same transformer that with an air core below a frequency of 4 MHz.
Subjects
Thermal conductivity
nanofluids
Brownian motion
ferrofluids
transformers
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