On the flow characteristics of nanofluids by experimental approach and molecular dynamics simulation

Employing nanofluids is a novel way to enhance heat transfer. However, the micro-flow enhancement due to the adding of nanoparticles, which is one of the key mechanisms behind heat transfer enhancement in nanofluids, still lacks experimental observation and a microscale-level understanding. The aim of this work was to experimentally research flow characteristics of nanofluids and to explore the microscopic mechanism for micro-flow enhancement by molecular dynamics simulation. Utilizing a wavy-walled tube, the experiment measured flow characteristics and took flow visualization photos of nanofluids in different flow regimes. In addition, internal flow characteristics of nanofluids were simulated by MD method and statistically analyzed. The measuring results for frictional resistance showed that compared to that of de-ionized water the frictional resistance of nanofluids increases slightly in laminar and transition flow regimes, and shows no obvious increase in turbulent regime, which indicates no additional pump work is needed and is advantageous to engineering application. The visualization experiment results showed at the same Reynolds number the adding of nanoparticles causes more homogeneous longitudinal mixing and enhances mass transferring of nanofluids, which indicates the micro-flow in nanofluids is enhanced. And the MD simulation results showed the microscopic mechanism for micro-flow enhancement is mainly because the irregular micro-motions of nanoparticles enhance momentum exchange and increase the intensity of turbulence. The present work suggests the mechanism of micro-flow enhancement in nanofluids, which is the basis of proposing suitable theory to mathematically describe flow of nanofluids.

► We apply flow visualization to analyze flow characteristics of nanofluids.
► We use a wavy-walled tube for convenient comparison of flow patterns.
► We combine flow test with molecular dynamics simulation to reveal enhanced micro-flow mechanism in nanofluids.
► We propose the irregular micro-motions of nanoparticles as the mechanism for micro-flow enhancement in nanofluids.