Abstract
Nanoparticle deposition in microchannel devices inducing contaminant clogging is a serious barrier to the application of micro-electro-mechanical systems (MEMS). For micro-scale gas flow fields with a high Knudsen number (Kn) in the microchannel, gas rarefaction and velocity slip cannot be ignored. Furthermore, the mechanism of nanoparticle transport and deposition in the microchannel is extremely complex. In this study, the compressible gas model and a second-order slip boundary condition have been applied to the Burnett equations to solve the flow field issue in a microchannel. Drag, Brownian, and thermophoretic forces are concerned in the motion equations of particles. A series of numerical simulations for various particle sizes, flow rates, and temperature gradients have been performed. Some important features such as reasons, efficiencies, and locations of particle deposition have been explored. The results indicate that the particle deposition efficiency varies more or less under the actions of forces such as Brownian force, thermophoretic force, and drag force. Nevertheless, different forces lead to different particle motions and deposition processes. Brownian or thermophoretic force causes particles to move closer to the wall or further away from it. The drag force influence of slip boundary conditions and gas rarefaction changes the particles’ residential time in the channel. In order to find a way to decrease particle deposition on the microchannel surface, the deposition locations of different sizes of particles have been analyzed in detail under the action of thermophoretic force.
Highlights
As one of the most promising technologies in this field, the microfluidic system has attracted widespread attention in recent years
The main goal of this study is to discover the principle of nanoparticle deposition on the microchannel surface
Discussion and full-field gas speed increased along the exit direction
Summary
As one of the most promising technologies in this field, the microfluidic system has attracted widespread attention in recent years. The transportation, diffusion, and deposition of aerosol particles in microchannels are the common gas–solid two-phase flow problems in MEMS devices, such as microreactors [1], filters [2], and micromixers [3]. The micro-scale gas flow field in a microchannel with a high Knudsen number (Kn) begins to deviate from the thermodynamic equilibrium due to insufficient molecular collisions. Kn is a dimensionless parameter of the relative sizes of the gas mean free path (λ) and the characteristic scale of the microchannel geometry. When 10 ≤ Kn ≤ 10, the flow regime is in the transition regime [4].
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