Effect of particle shape on suspension stability and thermal conductivities of water-based bohemite alumina nanofluids

The suspension stability and thermal conductivity of water-based bohemite alumina nanofluids created using nanoparticles of various shapes (brick, platelet, and blade) at concentrations from 0.3 vol% to 7.0 vol% were theoretically and experimentally investigated. To quantitatively examine the effect of nanoparticle shape on suspension stability, this study uses the laser-scattering method rather than the zeta-potential measurement or the sedimentation test because both the zeta-potential and sedimentation tests cannot systematically represent the suspension stability of nanofluids. Using the DLVO (Derjaguin and Landau, Verwey and Overbeek) theory, we explain why the suspension stability varies with nanoparticle shape despite similar volume fraction of nanoparticles, pH, and temperature. The thermal conductivities are also measured by the transient hot wire method, which was developed in house. Experimental data are compared with theoretical results predicted by the Hamilton-Crosser model, which considers the effect of nanoparticle shape. It is shown that the model cannot predict nanofluids thermal conductivity relative to nanoparticle shape. Finally it is clearly shown that the thermal conductivity of nanofluids strongly depends on the suspension stability of bohemite alumina with various shapes.