Simultaneous measurements of thermal conductivity and thermal diffusivity of nanofluids using 3ω method
A 3ω method was developed for the simultaneous determination of thermal conductivity and thermal diffusivity of nanofluids.The principle was presented in the frequency domain.The 3ω system was established by using a Pt wire as the heater and sensor.The system was calibrated by using water with known properties.The thermal oscillation signals satisfied the heat conduction equations well in frequency domain.It showed that the micro-convection effect of the liquid could be reduced effectively by periodical heating.The multi-spherical Brownian motion(MSBW) model was used to predict the thermal conductivities of nanofluids.The thermal conductivity and thermal diffusivity of TiO2/water and Al2O3/water at different temperatures were proved to increase linearly with the temperature at a low volume fraction.The results showed that temperature dependence played an important role in the enhancement of thermal transport in nanofluids.At 18—65℃,the enhancement of heat transfer for nanofluids was mainly due to the thermal conductivity increment of water and the micro-convection effect.