Abstract
Nanofluid is a fluid of new type that consists of a base liquid with nanocrystalline particles dispersing in it. With the capability of higher thermal conductivity, the nanofluid has received considerable attention in related thermal management laboratories. In the present study, water and ethylene glycol are used as the base liquids respectively. The gold, silver, CuO and Al2O3 nanoparticles are added in the base liquids. Effects of volume fraction and size of nanoparticles on the viscosity and thermal conductivity of nanofluids are investigated by experiment. The thermal conductivity of nanofluids is measured by the steady-state parallel plate and transient hot-wire methods, respectively. Results here include (i) the homemade equipment to measure the effective thermal conductivity (ii) the measurement of thermal conductivity and viscosity (iii) the measurement of properties of nanofluids of various types. The results show that the thermal conductivity of the nanofluid increases with the volume fraction of the nanoparticles. Besides, the thermal conductivity of the nanofluids increases with decreasing the size of nanoparticles. In addition, the acid liquid is found to achieve a better dispersion of the nanoparticles in nanofluids. The better dispersion of nanoparticles also results in a lower viscosity and higher thermal conductivity of nanofluids. For ferrofluids, the thermal conductivity of ferrofluids increases with the strength of applied magnetic field. However, the thermal conductivity of the ferrofluid no longer increases as the applied magnetic field reaches a critical strength. The thermal conductivity of the ferrofluids varies with the direction of the magnetic fields. The data and the experience obtained in this work are significant for the research institutes to further develop the nano-technology.