The Passive Microfluidic Chip Design Based On The Particle-fluid Interaction

The microfluidic system is wildly used in the field of biology, medical science,and environment science. In the past few years, it has gained significant advances. Thepassive microfluidic chips use the interaction between channel wall and hydrodynamicsto control the movement of particle. In this thesis, three types of the passive microflu-idic chips are discussed in succession.The inertia effect on the particle is strong when the Reynolds number is high.Therefore, the inertia lift force can be used for the high through separation and focus-ing. In order to know how to manipulate the particle by the inertia effect, the hypo-stable state mold is proposed which couples the particle movement and fluid field. Inthis thesis, the force on the particle in the2D fluid field is analyzed. And also, the pa-rameter sweep method is used to find the equilibrium position for difference Reynoldsnumbers. Furthermore, the equilibrium position and the force on the particle in the3Dfluid is analyzed based on the method for the2D mold. The mesh only deform in onedirection when the equation is solved to find the equilibrium position. So the meshdistortion can be easily controlled and the computational cost is low.For passive sheathless particles focusing in microfluidics, the equilibrium posi-tions of particles are typically controlled by micro channels with a V-shaped obstaclearray (VOA). The design of the obstacles is mainly based on the distribution of flowstreamlines without considering the existence of particles. We report an experimentallyverified particle trajectory simulation using the arbitrary Lagrangian-Eulerian (ALE)fluid-particle interaction method. The particle trajectory which is strongly influenced by the interaction between the particle and channel wall is systematically analyzed.The numerical experiments show that the streamline is a good approximation of parti-cle trajectory only when the particle locates on the center of the channel in depth. Asthe advantage of fluid-particle interaction method is achieved at a high computationalcost and the streamline analysis is complex, a heuristic dimensionless design objectivebased on the Faxen’s law is proposed to optimize the VOA devices. The optimizedperformance of particle focusing is verified via the experiments and ALE method.The contraction and expansion structure has the capability to twist flow streamlinevia the Dean and inertia effects. In this thesis, the topology optimization method isused to optimize the topology of the contraction and expansion structure. Based on theoptimized topology geometry, the detailed lateral flow structure is simplified based onthe boolean operation. One-layer mixer is designed via sequentially connected lateralstructure and bent channels. The mixing efficiency is optimized via key geometric pa-rameters of designed one-layer mixer. The numerical results illustrate that the proposedmixer has better mixing efficiency than the contraction-expansion mixer in relativelywide range of Re number cases.