Preparation of controllable nanofluids and research on thermal conductivity

To study the effects of different conditions in the one-step nanofluid preparation on the size of nanoparticles, water-SiO₂ nanofluid was prepared using the sol-precipitation method. The size and size distribution of nanoparticles were measured by transmission electron microscopy (TEM) and laser particle size analyzer, and the stability of the nanofluids was analyzed employing the zeta potential measurement system and long time observation. The thermal conductivity enhancement of nanofluids containing different particle sizes and concentrations were investigated by the laser flash method. The results show that the size of SiO₂ nanoparticles can be controlled in 50-200 nm. The nanofluids prepared by the sol-precipitation method have excellent stability. When the volume fraction of nanofluids is 1.3%, the thermal conductivity of nanofluids containing SiO₂ nanoparticles with average diameter of 70 nm increases 24% compared with the pure water. The enhancement of thermal conductivities is not sensitive to the rising of temperature.