Role of Thermal-Interaction Between Aggregated Particles in Thermal Conductivity Enhancement of Nanofluids

This study investigates the role of thermal-interaction (TI) between aggregated particles (APs) on the enhanced thermal conductivity of nanofluids. With the assumption of configurations of linear chain-like aggregates in the direction transverse to the thermal flux, two-dimensional heat conduction is considered for estimation of the effective thermal conductivity of regular arrays, which is separated into three components, namely, no thermal-interaction (NTI) effect, longitudinal thermal-interaction (LTI) effect, and transverse thermal-interaction (TTI) effect. We have obtained a solution to the 1D confine case of APs, and a thermal analysis is carried out for different confine systems to investigate their relatively quantitative assessments of thermal contribution to the enhanced effective thermal conductivity using the first-order approximation. We show that these effects are represented as a function of ϕ (where ϕ is the volume fraction of APs) for engineering purposes. It is also found that TI contribution to the enhanced thermal conduction reaches up to around 87.5% when APs contact with each other and that TTI has an important role in the range 0.3785 ≤ ϕ ≤ 0.7031 due to the confine effect of field-variation caused by transversely bidirectional thermal-interactions. When ϕ > 0.7031, LTI effect again plays key role in heat conduction in nanofluid systems owing to closed packing of APs. Consequently, to achieve energy-efficient heat transfer nanofluids that are required in many industrial applications, both APs' distribution configuration and APs' volume fraction have to be considered in the thermal analysis of nanofluids.