Nanofluids are dispersions of nanometer-size particles in a liquid medium. A number of studies have shown that nanofluids composed of a small volume fraction of metals or metal oxides in a variety of base fluids show anomalous enhancement in the thermal conductivity compared to theoretical predictions. Due to this reason, nanofluids have generated interest as heat transfer fluids for better heat management operations in many applications. One such application is cooling of drill bits in deep drilling operations for oil and gas exploration.

In this work, thermal conductivities of nanofluids were measured using the transient hot-wire method in order to study the effect of parameters such as constituent thermal conductivities, particle size and dispersion state. Measurements tended to drift with time, and a modified procedure is described for minimizing measurement errors. Thermal conductivities of aqueous nanofluids of synthetic nanoclay (Laponite RDŽ) and micellar solutions of anionic and nonionic surfactants were measured. It was found that whereas for Laponite nanofluids thermal conductivity increases with concentration, for surfactants it decreases. These results are also compared and contrasted with those on metal-based nanofluids and with predictions of theoretical models such as the effective medium theory, the model of Hamilton and Crosser and microconvection models.