Dispersion behavior and thermal conductivity characteristics of Al 2 O 3 –H 2 O nanofluids Dongsheng Zhu a , Xinfang Li a, * , Nan Wang a , Xianju Wang a,b , Jinwei Gao a , Hua Li a a Key Lab of Enhanced Heat Transfer and Energy Conservation, Ministry of Education, School of Chemical and Energy Engineering, South China University of Technology, Guangzhou, Guangdong 510641, China b Navy Arms of Services Command Academy, Guangzhou, Guangdong 510431, China Received 20 July 2007; accepted 28 December 2007 Available online 8 January 2008 Abstract Nanofluid is a kind of new engineering material consisting of solid nanoparticles with sizes typically of 1–100 nm suspended in base fluids. In this study, Al 2 O 3 –H 2 O nanofluids were synthesized, their dispersion behaviors and thermal conductivity in water were inves- tigated under different pH values and different sodium dodecylbenzenesulfonate (SDBS) concentration. The sedimentation kinetics was determined by examining the absorbency of particle in solution. The zeta potential and particle size of the particles were measured and the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was used to calculate attractive and repulsive potentials. The thermal conduc- tivity was measured by a hot disk thermal constants analyser. The results showed that the stability and thermal conductivity enhance- ments of Al 2 O 3 –H 2 O nanofluids are highly dependent on pH values and different SDBS dispersant concentration of nano-suspensions, with an optimal pH value and SDBS concentration for the best dispersion behavior and the highest thermal conductivity. The absolute value of zeta potential and the absorbency of nano-Al 2 O 3 suspensions with SDBS dispersant are higher at pH 8.0. The calculated DLVO interparticle interaction potentials verified the experimental results of the pH effect on the stability behavior. The Al 2 O 3 –H 2 O nanofluids with an ounce of Al 2 O 3 have noticeably higher thermal conductivity than the base fluid without nanoparticles, for Al 2 O 3 nanoparticles at a weight fraction of 0.0015 (0.15 wt%), thermal conductivity was enhanced by up to 10.1%. Ó 2008 Elsevier B.V. All rights reserved. PACS: 82.70.K; 47.17 Keywords: Nanofluid; Alumina nanoparticle; Dispersion and stability; Zeta potential; Absorbency; Thermal conductivity 1. Introduction Recently, due to the development of nanotechnology and surface science, many researches on nanofluids have been carried out actively. Nanofluid is a kind of new engi- neering material consisting of solid nanoparticles with sizes typically of 1–100 nm suspended in base fluids. It cannot only solve the problems such as sedimentation, cohesion and corrosion which happen conventionally in heteroge- neous solid/liquid mixture with millimeter or micrometer particles, but also increase the thermal performance of base fluids remarkably [1–9]. Choi [1], Das et al. [4], Xuan et al. [5], Eastman et al. [6,7] and Lee et al. [8] who found great enhancement of thermal conductivity (5–60%) over the vol- ume fraction range of 0.1–5%. Patel et al. [10] concluded that 5–21% enhancement of the thermal conductivity of nanofluids for water with citrate in the temperature range 30–60 °C at a very low loading of 0.00026 vol% of Ag par- ticles. For a loading of 0.011% of Au particles, the improvement of thermal conductivity was around 7–14%. Kumar et al. [11] reported an enhanced thermal conductiv- ity of about 20% for a nanofluid of only 0.00013% Au nanoparticles in water. Since such an anomalous enhance- ment is expected to have wide applications in thermal engi- neering, nanofluids have received considerable attention in 1567-1739/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2007.12.008 * Corresponding author. Tel.: +86 20 87114568; fax: +86 20 87114185. E-mail address: xtulxf@163.com (X. Li). www.elsevier.com/locate/cap www.kps.or.kr Available online at www.sciencedirect.com Current Applied Physics 9 (2009) 131–139