Effects of surfactant on thermal conductivity of aqueous silica nanofluids

Abstract In this study, the effects of several surfactants on the TC of Silica/deionized water (DI water) nanofluids are investigated. The nanofluid used in this study was prepared using a two-step method. TEM, XRD, and Zeta Potential analysis confirmed the size of the nanoparticles used in the nanofluid as well as the stability and the type of nanofluid. The effects of three types of surfactant, i.e., cetyl trimethyl ammonium bromide (CTAB), sodium lauryl sulfate (SLS), and polysorbate 20 (PS20) as cationic, anionic, and nonionic surfactants, respectively were studied on TC of the nanofluid. Results demonstrated that the TC of the nanofluid increased by increasing either temperature or volumetric concentration for all the surfactants. Furthermore, the anionic and nonionic surfactants resulted in the highest and lowest TCs, respectively (anionic > cationic > nonionic). For all the surfactants, the ratio of the variations in Relative Thermal Conductivity (RTC) to temperature was increased by a rise in nanoparticle concentration. A similar trend was observed for the slop of the variations in RTC to nanoparticle concentration by increasing the temperature. The anionic and nonionic surfactants resulted in the highest and lowest ratios, respectively (anionic > cationic > nonionic).