Lai Tsz Wai, Tennakoon Thilhara, Chan Ka Chung, Liu Chun-Ho, Chao Christopher Yu Hang, Fu Sau Chung
Department of Building Environment and Energy Engineering, The Hong Kong Polytechnic University, Hong Kong, China.
Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China.
Ultrasonics. 2024 Jan;136:107126. doi: 10.1016/j.ultras.2023.107126. Epub 2023 Jul 27.
Acoustophoresis is an effective technique for particle manipulation. Acoustic radiation force scales with particle volume, enabling size separation. Yet, isolating sub-micron particles remains a challenge due to the acoustic streaming effect (ASE). While some studies confirmed the focusing ability of ASE, others reported continuous stirring effects. To investigate the parameters that influence ASE-induced particle motion in a microchannel, this study examined the effect of microchannel height and particle size. We employed standing surface acoustic wave (SSAW) to manipulate polystyrene particles suspended in the water-filled microchannel. The results show that ASE can direct particles as small as 0.31 µm in diameter to the centre of the streaming vortices, and increasing the channel height enhances the focusing effect. Smaller particles circulate in the streaming vortices continuously, with no movement towards the centres. We also discovered that when the channel height is at least 0.75 the fluid wavelength, particles transitioning from acoustic radiation-dominated to ASE-dominated share the same equilibrium position, which differs from the pressure nodes and the vortices' centres. The spatial distance between particles in different categories can lead to particle separation. Therefore, ASE is a potential alternative mechanism for sub-micron particle sorting when the channel height is accurately adjusted.
声泳是一种有效的粒子操控技术。声辐射力与粒子体积成正比，可实现尺寸分离。然而，由于声流效应（ASE），分离亚微米级粒子仍然是一项挑战。虽然一些研究证实了ASE的聚焦能力，但其他研究报告了持续搅拌效应。为了研究影响微通道中ASE诱导粒子运动的参数，本研究考察了微通道高度和粒子尺寸的影响。我们采用表面驻波（SSAW）来操控悬浮在充满水的微通道中的聚苯乙烯粒子。结果表明，ASE可将直径小至0.31 µm的粒子引导至流场涡旋的中心，增加通道高度可增强聚焦效果。较小尺寸的粒子在流场涡旋中持续循环，不会向中心移动。我们还发现，当通道高度至少为流体波长的0.75倍时，从声辐射主导转变为ASE主导的粒子具有相同的平衡位置，这与压力节点和涡旋中心不同。不同类别粒子之间的空间距离可导致粒子分离。因此，当通道高度精确调整时，ASE是亚微米级粒子分选的一种潜在替代机制。
