Effect of temperature and pHon the electrical conductivity of nanofluids

• Main Authors: Chin-Nan Yeh, 葉晉男
• Other Authors: 李雨
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/fu98zm

碩士 === 國立臺灣大學 === 應用力學研究所 === 106 === Nanofluid is a liquid suspended uniformly and stably with nano particles (1~100 nm). One primary factor for affecting the properties and flow behavior of nanofluid is the agglomeration of particles in fluid, which is closely related to the electric conductivity. The goal of this study is thus to investigate the electrical conductivity of nanofluid through detailed experiments, and extend the previous theoretical model by including the effects of temperature and pH. Three nanofluids were studied, with de-ionized water as base fluid, and Al2O3, SiO2, and TiO2 as suspended particles, respectively. Electrical conductivities and pH’s of nanofluids, as well as the size distributions of particles, the z-average diameters and zeta potentials of particles in nanofluid, were measured for different volume fractions and temperatures. Also studied were the nanofluids at vary pH’s with HCl and NaOH added. The experimental findings are: (1) the electrical conductivities of nanofluids are enhanced significantly from that of the base fluid by one to two orders, and increase as volume fraction and temperature increase, (2) pH’s are different for different nanofluids associated with different dissociation of water, (3) the zeta potentials of particles in nanofluids decrease with temperature, (4) the electrical conductivity increases as the ionic strength of nanofluid increases, but the increase is more obvious at low volume fraction in comparing with that at high volume fraction, probably due to the less absorption of ions on particles at low volume fraction. The present study adopted the theory of electrical conductivity in the literature, which consists of four contributions: that associated with the conductivity of materials at rest according to the Maxwell’s effective medium theory, that associated with the electrophoretic motion of particles, that associated with the electrophoretic motion of H+ ions, and that associated with the electrophoretic motion of OH- ions, and extend the theory by including the effects of temperature, pH and ionic strength. The inputs required for the theory are the pH of nanfluid, the z-average diameter of particles and zeta potential of particles, as well as the ionic strength. For TiO2-water nanofluids, the ratios (r) between the experimental measurement and the theoretical predictions are from 1.07 ~ 1.24 for volume fraction 0.5% ~ 3% and temperature 25oC ~ 55oC. For Al2O3-water nanofluids, r = 0.65 ~ 1.71 for volume fraction 0.5% ~ 3% at 25oC, and r = 1.5 ~ 1.9 at 55oC. For SiO2-water nanofluids, r = 0.48 ~ 1.37 at 25oC, and r = 1.05 ~ 1.89 at 55oC。The theory agrees nicely with the experiment for TiO2-water nanofluids, and farily with the experiment for Al2O3-water and SiO2-water nanofluids. They are better than those predicted using existing theories.