Impact of Thermodiffusion on Temperature Fields in Stationary Nanofluids

The research community has reported a large variety of at times contradictory thermal conductivity enhancements for nanofluids. Some of the differences may result from thermodiffusion, which is the coupled transport of heat and nanoparticles in a temperature gradient. Thermodiffusion can influence the apparent conductivity observed in a given experimental setup. This work explores the potential impact of thermodiffusion on the inconsistencies of the previous results and on the observed temperature dependence of the thermal conductivity enhancement. The thermal conductivity variation with temperature is captured using infrared microscopy. The thermal conductivity distribution varies significantly over the temperature range 27 – 73°C. This work also explores the potential impact of aggregation, gravitational separation, and thermodiffusion on the time-evolution of the thermal conductivity. For 1 percent by volume aluminum oxide in deionized water, this work finds a thermal conductivity enhancement of between 1 and 15 percent depending on temperature and time, which corresponds to an enhancement factor of between 1 and 15. For 0.2 percent by volume carbon nanotubes in silicone oil, this work finds a thermal conductivity enhancement of 8 percent with no dependence on temperature, which corresponds to an enhancement factor of 40.