| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 103 === Nanofluid is a liquid suspended stably with nano sized particles. It was found in the literature that the thermal conductivity of nanofluid increases as the volume fraction of particles increases, and the increase is substantially greater than that predicted by the classical theory. A large amount of effort was thus spent in studying the behind physics and chemistry, and various effects, including the electric double layer, particle agglomeration, and Brownian motion, were studied. The thermal conductivity of nanofluids with different monometer diameters (14, 22, <50 and <100nm) and volume fractions were measured in the present study using transient hot disk method. It was found that the effect of monomer diameter is small, and the detailed constituent of particles could have effort on thermal conductivity. Effect of electric conductivity and pH were also studied by adding different amount of KCl and NaOH into the nanofluids. The thermal conductivity increases as the electric conductivity increases, but tends to fltten out at large value. As for the effect of pH, the thermal conductivity attains its maximum around pH=6 (the isoelectric point), which can explained by the particle agglomeration effect associated with the weakening of the repulsive double layer force, and was supported by a viscosity measurement ; the nanofluid viscosity increases 2 folds in comparing with that of the base fluid at pH=6. The aging effect is insignificant when the volume fraction is low and is minor at large volume fractions. The above results are qualitatively similar to those in literature, but here we employed a different method for measuring the thermal conductivity, and provided results for a boarder ranges of parameters.
|
|---|
