Dependence of particle size on the effective thermal diffusivity and conductivity of nanofluids: role of base fluid properties

Effect of nanoparticle size on effective thermal diffusivity and conductivity of polymeric and water based nanofluids are investigated following thermal wave interference technique. Two sets of nanofluids, prepared by dispersing TiO₂ nanoparticles, with average sizes in the range 5–100?nm, in polyvinyl alcohol and water show opposing particle size dependences. Variations are explained invoking effective medium theory, including size of nanoparticles, molecular weight of base fluid and effects associated with it.