The preparation and thermal performance research of spherical Ag-H2O nanofluids & applied in heat pipe

Spherical silver-water (Ag-H2O) nanofluids with good suspension (more than 85 days) have been obtained via one-step method in the water phase without any surfactants or additives in the present work. The size-control technique of spherical Ag nanoparticle has been obtained through adjusting the reaction rate and the mechanism of size effect has been studied in detail. It can be found that the faster the reaction rate, the smaller the nucleation density and the smaller the particle size. The thermal conductivity of spherical Ag-H2O nanofluids were higher than H2O even the few Ag nanoparticle incorporation. Based on the preparation of Ag-H2O nanofluids, the effects of particle size, solid content and temperature on the thermal conductivity of spherical Ag-H2O nanofluids were discussed and all the measure was performed in the same condition. The conclusion can be drawn that the thermal conductivity of Ag-H2O nanofluids increases with the content of Ag nanoparticles and temperature increasing and average size of Ag nanoparticles decreasing. The effect mechanism of particle size, temperature and content of Ag nanoparticles has been studied in detail. The Ag-H2O nanofluids were determined to be the Newtonian fluid whose viscosity is close to water and the viscosity increases with the increase of the mass fraction of Ag nanoparticles. The start-up and heat transfer performance of the heat pipe using the spherical Ag-H2O nanofluids have been improved compared to the heat pipe using DI water. It is expected that the spherical Ag-H2O nanofluids with a high thermal conductivity and low viscosity are expected to be new heat transfer fluid.