| Summary: | 碩士 === 國立中央大學 === 機械工程學系 === 102 === The transient hot-wire method (THW) is widely used for measuring the thermal conductivity of fluids, due to its fast measurement, less convectioneffect, and relatively simple set up. In recent years, nanofluids and biological fluids have drawn attention in thermal transport applications. The high-cost or diffcult-to-produce samples draw the need of defeloping miniaturized devices to measure fluid samples in small quantity. In this study, we develop a micro-THW device to measure the thermal conductivity of fluid with micro-litter volume using MEMS (micro-electromechanical system) fabrication techniques. Numerical simulations are performed to assist the geometric design and evaluation of the measuremnt errors.
First, we study the effect of the heating line geometry, and find the length-to-width ratio of the heating-line cross-section affects the measurung time interval selection. With the appropriate design of the outer boundary of the testing domain, we can obtain the right data selection of the measurements. Furthermore, the end effect has a close relation to the length of the heating-line, which can be alleviated by increasing the length of the heating-line. In the case when two media are present in the measurement, we find that the measured thermal conductivity is the arithmetic mean of the meadia and the influence of end effects is dominated by the one with lower thermal diffusivity. Different current measurements are tested, and it is found that the error increases as the current increas, which should be taken into account for high-accuracy measurements. Finally, we measure the thermal conductivity of water and glycerin with different concentration. The measured results are around 5% deiated from the literature value.
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