Experimental Study of Viscosity of Titanium Oxide Nanofluids
Date Issued
2014
Date
2014
Author(s)
Yeh, Hshing-I
Abstract
Nanofluid is a liquid suspended with uniformly distributed and stable nano-sized particles. The heat conductivity of nanofluid is substantially higher than that of its base fluid and the classical theoretical prediction according to the literature, but the mechanisms are still not fully understood. Such a heat conductivity enhancement implies that nanofluids can be applied to heat exchangers. However, the pumping power of nanofluids in heat exchanger depends on its viscosity, which is also one of the major topics of nanofluid research, and is also the goal of the present thesis. The nanofluids of the present study are made by introducing TiO2 nano particles into de-ionized water or glycerol. Viscosity measurements were performed and the results are summarized as follows: (i) Nanofluids are Newtonian fluids in the parameter ranges of the present study. (ii) The viscosity of nanofluid increases as the particle’s volume fraction increases, as the particle size decreases, and as the temperature decreases. On the other hand, the relative viscosity (the ratio between the nanofluid viscosity and the base fluid viscosity) remains essentially invariant with temperature, implying that the temperature variation of nanofluid viscosity is qualitatively similar to that of base fluid. However, the relative viscosity of nanofluid is larger for case with smaller particles and with less viscous base fluid, because of the stronger Brownian effect. Also the relative viscosity is larger for higher volume fraction as more particles participates the Brownain effect. (iii) The nanofluid viscosity increases with the base fluid electric conductivity, and reaches its maximum value (about 240 times the viscosity of the base fluid) at an electric conductivity corresponds to the isoelectric point (when pH = 6 approximately). The viscosity decreases rapidly as the pH value increases further above the isoelectric point. The above phenomena can be explained by the particle agglomeration effect associated with the weakening of the Coulomb’s repulsive force between electric double layers of two particles. (iv) The viscosity decreases slightly as times goes by. Such an aging effect becomes moderate at higher volume fraction. For example, the viscosity decreases about 10% after a week for a nanofluid with volume fraction 4%.
Subjects
二氧化鈦
奈米流體
黏度
導電率
布朗運動
電雙層
Type
thesis
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