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Evaluation of different particle-actuation modes in molecular dynamics and their impact on nanoscale flow behaviors

An accurate understanding of nanoscale gas transport mechanism is a fundamental concern in many engineering applications, which remains as a research challenge currently. Two particle-actuation modes, namely force-driven and pressure-driven methods, are evaluated and compared by molecular dynamics simulations of flows in nano-channels focusing on the characteristics of gas adsorption and slip velocity behaviours. The force-driven method may lead to unphysical properties when fluid inhomogeneities are significant since all fluid molecules are subjected to a same external force. By contrast, fluid molecules move forwards through the central part of the flow domain as a predominate pathway in a pressure-driven method. Results show that there is a significant difference between the two methods at smooth or small rough wall conditions, while the results tend to be consistent as roughness increases. The density distribution is uniform along the flow direction in force-driven cases, while adsorbed gas density increases in pressure-driven cases, leading to a smaller slip velocity near the outlet region. The effects of fluid wettability strength on solid surfaces and system temperature on gas adsorption and flow behaviours are also investigated and analyzed. This study is helpful for better understanding nanoscale gas dynamics and has many practical implications, such as the shale gas production.