Analysis of factors influencing thermal conductivity and viscosity in different kinds of surfactant solutions

Addition of surfactants into the fluids is often used to minimize particle aggregation and improve dispersion behavior of nanofluids. However, they also affect the physical characteristics of liquids, such as, thermal conductivity and viscosity. In this paper, the thermal conductivity and viscosity of several common used surfactant solutions are investigated experimentally, with regard to the effect of critical factors such as concentration, temperature and pH value. The results show that the thermal conductivity ratios of surfactant solutions keep stable after a certain concentration. Compared with non-ionic surfactants, the ionic surfactants are more sensitive to temperature. With the increase of temperature, the thermal conductivities of three ionic surfactants gradually approach the value of pure water. Both strong alkaline and acidic mediums go against the improvement of thermal conductivity of surfactant solutions. The zero-shear viscosity of polyvinylpyrrolidone (PVP) solution at 4.0 wt% is about twice than that of water, while the viscosity of an ionic surfactant does not increase noticeably at low concentration. Therefore, an appropriate combined treatment addressing concentration, temperature and pH is recommended to improve the thermal conductivity and viscosity of the base fluid and thereby for practical applications of nanofluids. (C)2011 Elsevier Inc. All rights reserved.