Evidence for enhanced thermal conduction through percolating structures in nanofluids

The unusually large enhancement of thermal conductivity (k/k(f) similar to 4.0, where k and k(f) are the thermal conductivities of the nanofluid and the base fluid, respectively) observed in a nanofluid containing linear chain-like aggregates provides direct evidence for efficient transport of heat through percolating paths. The nanofluid used was a stable colloidal suspension of magnetite (Fe3O4) nanoparticles of average diameter 6.7 nm, coated with oleic acid and dispersed in kerosene. The maximum enhancement under magnetic field was about 48 phi (where phi is the volume fraction). The maximum enhancement is observed when chain-like aggregates are uniformly dispersed without clumping. These results also suggest that nanofluids containing well-dispersed nanoparticles (without aggregates) do not exhibit significant enhancement of thermal conductivity. Our findings offer promising applications for developing a new generation of nanofluids with tunable thermal conductivity.