Department of Physics, Technical University of Denmark, DTU Physics Building 309, DK-2800 Kongens Lyngby, Denmark.
Lab Chip. 2012 Nov 21;12(22):4617-27. doi: 10.1039/c2lc40612h.
We present a numerical study of the transient acoustophoretic motion of microparticles suspended in a liquid-filled microchannel and driven by the acoustic forces arising from an imposed standing ultrasound wave: the acoustic radiation force from the scattering of sound waves on the particles and the Stokes drag force from the induced acoustic streaming flow. These forces are calculated numerically in two steps. First, the thermoacoustic equations are solved to first order in the imposed ultrasound field taking into account the micrometer-thin but crucial thermoviscous boundary layer near the rigid walls. Second, the products of the resulting first-order fields are used as source terms in the time-averaged second-order equations, from which the net acoustic forces acting on the particles are determined. The resulting acoustophoretic particle velocities are quantified for experimentally relevant parameters using a numerical particle-tracking scheme. The model shows the transition in the acoustophoretic particle motion from being dominated by streaming-induced drag to being dominated by radiation forces as a function of particle size, channel geometry, and material properties.
颗粒对声波散射产生的声辐射力和诱导声流产生的斯托克斯阻力。这些力通过两步数值计算得到。首先，在施加的超声波场中求解热声方程，考虑到靠近刚性壁的微米级但至关重要的热粘性边界层。其次，将所得一阶场的乘积用作时均二阶方程中的源项，由此确定作用在颗粒上的净声力。使用数值粒子跟踪方案，根据实验相关参数对声致颗粒速度进行量化。该模型展示了颗粒在声致运动中从以流致阻力为主到以辐射力为主的转变，其取决于颗粒尺寸、通道几何形状和材料性质。
