Role of Adsorbing Moieties on Thermal Conductivity and Associated Properties of Nanofluids

Abstract

We probe the contributions of adsorbing moieties (surface active species) on thermal conductivity (k), rheology, density, contact angle, and refractive index of nanofluids. The role of surface morphology, initial thermal conductivity of solid particles and their number density on thermal property enhancement of nanofluids is also studied. Our studies on a model soft sphere system, consisting of micelles of an average size of 2.5–7 nm with different headgroup charges, show that the thermal conductivity of ionic surfactant micelles follows the effective medium theory of poor thermal conductors, i.e., 1 – 3φ/2 with the interfacial resistance tending to infinity, where φ is the volume fraction. The results suggest that the long alkyl chain group of nonionic surfactant micelles are poor thermal conductors at very low concentrations with large interfacial tension compared to their anionic counterparts. The k measurement in aqueous alumina, silica, and nonaqueous iron oxide nanofluids with particle size in the r...