Application of Dynamic Light Scattering to Characterize Nanoparticle Agglomeration in Alumina Nanofluids and its Effect on Thermal Conductivity.

摘要

Nanoparticles dispersed in base fluids have shown that they have increased thermal conductivity and increased heat transfer potential. In practical applications, these particles agglomerate in nanofluid to form aggregates, as opposed to completely dispersing in the base fluid. The resulting nanofluid has a size distribution of aggregated nanoparticles at different length scales. The mechanism that causes the enhanced thermal characteristics in nanofluids has not been widely researched in terms of particle interactions and experimental characterization of aggregate size distribution. This study reports nanofluid characterization by Dynamic Light Scattering (DLS) measurements at dilute and regular particle concentrations. In this study, the resulting size distribution data was used to determine thermal conductivity enhancement by mechanisms of aggregation and liquid layering around nanoparticles using fractal models. These thermal conductivity results were compared with results based on the Maxwell model, which signified a completely dispersed nanofluid. It was determined by this study that nanoparticle aggregation results in the formation of percolation clusters and liquid layers that cause the thermal conductivity of dilute and regular nanofluids to increase 2.5 fold compared to results using a well-dispersed nanofluid. It was also determined that liquid layering did not significantly contribute to enhancement in thermal conductivity of the nanofluid, in addition to percolation clusters. The study concluded that the near-linear relationship between particle concentration and thermal conductivity is preserved for nanofluids that are well dispersed, and for nanofluids with significant particle interactions to aggregate and form percolating clusters.