Effect of the particle temperature on lift force of nanoparticle in a shear rarefied flow*

Su, Junjie; Wang, Jun

doi:10.1088/1674-1056/abf351

Cited by 2 publications

(1 citation statement)

References 48 publications

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“…上述理论均基于气体分子与颗粒之间的刚体碰撞假设建立模型, 此假设对于微米量级的大颗粒来说是适用的, 但是当颗粒的尺寸逐渐降低到亚微米或纳米量级时, 刚体碰撞模型可能不再适用 [24][25][26] .…”

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Simulation study of drag force characteristics of nanoparticles in transition regime

Liu,

Zhang,

Wang

et al. 2024

Acta Phys. Sin.

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The transport properties of nanoparticles in gases have a widely practical application, including aerosol science, combustion, and micro- and nanoscale fabrication. A nanoparticle moving in a fluid is expected to experience a drag force, which determines the transport property of the particle. According to the Einstein relationship, the diffusion coefficient of a particle is inversely proportional to the drag force coefficient. However, in the transition regime, it is usually difficult to evaluate the drag force of suspended particles. A typical method is to extend the asymptotic solution of the free molecular or continuum limit to the transition regime. Based on gas kinetic theory, Li and Wang proposed a theoretical expression for drag force on nanoparticles in the free molecular regime, which is then extended to the entire range of Knudsen number following a semi-empirical approach. For nanoparticles, it is necessary to verify the theoretical predictions since the gas-particle non-rigid-body interactions have to be taken into account. In the present paper, the drag force on nanoparticles in the transition regime is investigated by using molecular dynamics (MD) simulations. To evaluate the drag force, a harmonic potential is employed to the nanoparticle to constrain its Brownian motion in our MD simulations. In the steady state, the drag force can be obtained by the balance between the drag and harmonic forces. It is found that the gas-particle non-rigid-body interactions have a significant influence on the drag force of nanoparticles. For weak gas-solid couplings, the MD simulation results could agree well with the prediction of Li-Wang theory. However, for strong couplings, there exists significant discrepancy between the MD simulation results and the theoretical results. Due to the gas-solid intermolecular interactions, gas molecules can be adsorbed on the nanoparticle surface, and after a time period, they may re-emit from the surface when they gained sufficient kinetic energy. Therefore, an adsorption-desorption equilibrium and an adsorption layer can be established on the particle surface. The adsorption layer enlarges the collision cross-sectional area and enhances the momentum transfer between gas molecules and the particle, and thus the drag. This can explain the inconsistent between the theoretical results and MD simulations. In this work, we introduce an adsorption ratio to evaluate the thickness of the adsorption layer. Then, the effective particle radius can be defined by the sum of particle radius and the thickness of the adsorption layer. By using the effective particle radius, the simulation values agree with the theoretical predictions much better. The results of this work provide insights for the application of nanoparticles in aerosol science.

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Simulation study of drag force characteristics of nanoparticles in transition regime

Liu,

Zhang,

Wang

et al. 2024

Acta Phys. Sin.

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Thermophoresis of nanoparticles in the transition regime

Liu

Wang

2023

Physics of Fluids

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The thermophoresis of nanoparticles suspended in gas is investigated in the transition regime by molecular dynamics simulations. It is found that there exists significant discrepancy between the simulation results and the theoretical predictions for the thermophoretic force, which is attributed to the adsorption of gas molecules on nanoparticles and the gas–particle non-rigid body collisions. By using the effective particle radius, the simulation results and Talbot et al.'s equation could agree with each other in the transition regime. In addition, the effect of the finite system size of the molecular dynamics simulations is non-negligible, and the simulation results modified by effective particle radius can coincide with Phillips' equation quite well. Therefore, for particles of a few nanometers, the non-rigid body collision effect and the adsorption of gas molecules and the effective radius of the nanoparticle under strong gas–particle coupling should be taken into account in the theoretical model. The investigation presented in this paper provides guidance for the application of nanoparticles in aerosol science.

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Effect of the particle temperature on lift force of nanoparticle in a shear rarefied flow*

Cited by 2 publications

References 48 publications

Simulation study of drag force characteristics of nanoparticles in transition regime

Simulation study of drag force characteristics of nanoparticles in transition regime

Thermophoresis of nanoparticles in the transition regime

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