A comprehensive model for effective density of nanofluids based on particle clustering and interfacial layer formation

Nanofluids are nanotechnology-based heat transfer liquids, which has dispersed solid phase (nanoparticles) and continuous liquid phase (basefluids). Owing to their superior thermal properties, nanofluids have a lot of potential to be used as coolants in high-density heat flux applications. Thermo-physical properties of nanofluids are influenced by several parameters such as nanoparticle volume fraction, thermo-physical properties of particles and basefluids, temperature, particle size and pH, etc. Several works on theoretically predicting the effective thermo-physical properties of nanofluids, namely the thermal conductivity and viscosity have been reported in literature. Effective density of nanofluids is also an important property that determines the practical applications of nanofluids, but, has received a very less attention among the researchers. In this work, a comprehensive model for predicting the effective density of nanofluids has been proposed. In the present model, aggregation of nanoparticles and interfacial layer formation have been taken into account. Particle size distribution (PSD) analysis has been utilized to calculate the average size and volume fraction of the clusters. The change in volume fraction due to the formation of interfacial layer has also been considered. The density of primary nanoparticles and clusters surrounded by the interfacial layer has been explicitly calculated. Predictions based on the present model are compared with the experimental data of different types of nanofluids taken from literature. It is seen that present model exhibits consistent and close predictions when compared to the widely used mixture rule. Therefore, present model will be helpful in development of real-time heat transfer systems using nanofluids.