Study on Preparation of Silver/ Titanium Dioxide Composite Nano-fluids Assisted with Ultraviolet Irradiation and It's Property
| Autor: | Chun-Yung Chen, 陳雋永 |
|---|---|
| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 Adding solid particle can be used to improve the thermal conductivity of the working fluid. But in the fluid containing the particles size in the micron scale, it will cause mechanical wear, high pressure drop and particle aggregation during forced heat convective process. This problem can be overcome through dispersing and stabilizing nanoparticles with higher heat transfer properties in the fluid. This study disperses titanium dioxide (P25) in ethylene glycol that can be used as a solvent and reducing agent for silver ions to synthesize silver nanoparticles. With ultraviolet light irradiation, silver ion can also be reduced with photocatalyzed reaction. We add sodium hydroxide to synthesize silver nano particles more quickly and having more crystal nuclei to grow. To understand lattice structure of silver nanoparticles prepared in alkaline environment, we use XRD to analyze silver nanoparticles prepared in different alkaline concentration. From the results, although sodium hydroxide and silver ions react to produce silver oxide,the product would finally reduce to silver after UV irradiation.The content of silver oxide nanoparticles in composite nanoparticles is very low, and silver crystal size is about 11-22 nm analyzed by Scherrer equation. Analyzing property of nanofluid prepared by titanium dioxide adsorbed with sodium hydroxide on the surface, we can get the following conclusions: (1) From transmission electron microscopy, preparing composite nanoparticle with 0.00067M titanium dioxide suspension, silver nanoparticle, which size is about 5-10 nm, is observed on the surface of silver / titanium dioxide composite nanoparticle which size is 20-70 nm and its critical dimesion conform to the regulation of nanoscale. (2) With viscosity analysis, we learned that the amount of silver nanoparticles have greater influence on viscosity;for example, adsorbing 0.005M silver nanoparticles on the surface of titanium dioxide in different concentration, the viscosity of 0.25M titanium dioxide with alkali on the surface reduce from 21cp to 17cp, and the concentration of 0.05M reduce from 17cp to 16cp.The result shows whether high or low concentration of titanium dioxide, hydroxide would be consumed in the process of preparing silver / titanium dioxide composite nanoparticles, and viscosity of titanium dioxide suspension adsorbed with sodium hydroxide decrease significantly. (3) Thermal conductivity coefficient increase with the solid content of titanium dioxide in ethylene glycol;for instance, thermal conductivity coefficient of 1 vol% titanium dioxide suspension increase 2.7% than ethylene glycol which thermal conductivity coefficient is 0.253(W/m‧k). Fixing solid content of titanium dioxide suspension at 0.1 vol%,thermal conductivity coefficient is 3.5% greater when adding 10% mole ratio of silver nanoparticles on titanium dioxide than pure titanium dioxide suspension which thermal conductivity coefficient is 0.256(W/m‧k); in other words, titanium dioxide modified by silver nanoparticles on the surface would increase thermal conductivity coefficient of nanofluid significantly;comparing experimental data and the results of Maxwell model,we get the results that low concentration of titanium dioxide nanofluid which volume concentration is 0.1 vol% is closer to theotectical value. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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