Particle manipulation by attractive and repulsive forces in 2-D streaming flows

Microfluidics;Experimental Fluid Mechanics;Streaming flows

Raju, David Vijay ; Hilgenfeldt ; Sascha

关键词: Microfluidics;    Experimental Fluid Mechanics;    Streaming flows;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/101102/RAJU-THESIS-2018.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

In this piece of work, we have attempted to study the variation in the trajectory of microparticles as they move in flows which are characterized by the superposition of microbubble streaming and transport flows. Our experimental setup uses steady streaming flow generated by ultrasonically driven semi-cylindrical microbubble combined with Poiseuille flow. Previous experiments have shown instances of particles being repelled from the surface of the interface. Theoretical predictions suggest that particles that are not density matched may experience attractive forces which may cause them to be attracted toward the surface of the interface.We can modify the previous experiments by lowering the strength of the streaming flow which allows for a relatively larger variety of particle trajectories. Experiments are conducted to study the effect of density mismatch, particle size and fluid viscosity. In this work, we also emphasize the importance of a new parameter which is the minimum surface to surface distance between the particle and the interface (quantity denoted by h_min). In order to see the net effect of these forces on a microparticle we utilize a method that uses a few small particle trajectories to interpolate the entire flow field, which is then used to see the relative behavior of a particle.We also comment on the development of asymptotic solutions to the Maxey Riley equations which allow us to predict the experimental behavior of a particle. We develop both a purely radial version which assists in making qualitative predictions as well as a 2-D analog which provides quantitative estimates of particle behavior in experiments.We see a number of novel results from these experiments. Firstly, we show conclusive evidence of the presence of attractive forces on micro-particles in this flow field. Secondly, we show that the key parameter in the determination of the nature of the net force on the particle i.e. attraction vs repulsion is the value of h_min. Finally, we show that there is a very systematic way in which the attractive behavior varies with h_min , density mismatch and particle size. As a general rule it is seen that attractive behavior is most apparent in large particles which are denser than the fluid and have a value of h_min which is of the order of particle radius. It is seen that these results are qualitatively and semi-quantitatively consistent with the predictions obtained from both the purely radial and 2-D versions of the developed theory.