Differential study on the thermal-physical properties of metal and its oxide nanoparticle-formed nanofluids: Molecular dynamics simulation investigation of argon-based nanofluids

The influence of nanoparticle shape, volume fraction, and temperature on the thermal properties of nanofluids plays a pivotal role in engineering applications. However, there remains a considerable lack of systematic research comprehensively considering these factors to study the similarities and differences in the thermal properties of nanofluids composed of metals and their oxides and to conduct in-depth analyses of their internal mechanisms and characteristics. In this study, molecular dynamics simulations were conducted, employing reversing perturbation non-equilibrium molecular dynamics and non-equilibrium molecular dynamics methods. The thermal conductivity and viscosity of Al-Ar and Al2O3-Ar nanofluids were thoroughly investigated under the various influencing factors. Results reveal that under identical conditions, the thermal conductivity of Al-Ar nanofluid surpasses that of Al2O3-Ar nanofluid, exemplified by values such as 0.1832 W/m K (Al-Ar, 1.5%, cylinder, 86 K) versus 0.17745 W/m K (Al2O3-Ar, 1.5%, cylinder, 86 K). Furthermore, the viscosity of Al-Ar nanofluid is lower than that of Al2O3-Ar nanofluid, demonstrated by values such as 0.0004882 Pa S (Al-Ar nanofluid, 86 K, 2.5%, platelets) compared to 0.008975 Pa S (Al2O3-Ar nanofluid, 86 K, 2.5%, platelets). Subsequently, this study analyzed the difference in thermal conductivity between the two nanofluids from the perspective of microscale interface heat conduction by comparing the phonon density of states curves of Al, Ar, and Al2O3 in the two nanofluids for overlap. Subsequently, through radial distribution function analysis, the viscosity difference between Al-Ar and Al2O3-Ar nanofluids is explained based on nanofluid-solid interface and microstructural considerations. This research addresses the comprehensive lack of comparative studies on the thermal properties of nanofluids formed by metals and their oxides. The internal mechanisms underlying the thermal property differences of nanofluids formed by metals and their oxides were revealed from a microscopic perspective, which holds significant implications for the engineering applications of nanofluids.