Nanofluids: suspension of nanoparticles

In these days, nanofluids have attracted many researchers because their characteristics are not matched with predicted ones from theoretical values. Nanofluid is the suspension of nanoparticles whose size is less than 100 nm. In classical theories such as the effective medium theory (EMT), suspension of micro-sized particles increases thermal conductivity and viscosity. However, these micro-sized particles have poor stability, so these particles are settled down. On the other hand, nanoparticles are better stable, and the enhancements of thermal conductivity and viscosity are larger than that of the micro-sized particles. In these reasons, nanofluids are expected to be applied in many areas of industry. For examples, in the heat transfer fluids, nanofluids can increase the efficiency of heat transfer with very small volume fraction less than 10 vol%. In addition to the heat transfer, there are a lot of applications, for instance, lubricants, fuels, and solar systems.

TEM images of Alumina and Zinc Oxide nanoparticles

Thermal conductivity with volume fraction