UCLA

Microfluidic devices are tiny circuits that flow fluids instead of electrons. Because they are inexpensive and portable, microfluidic devices are ideal for use in areas where medical resources are scarce. Inertial microfluidic devices represent a new direction in microfluidic device design in which high flow speeds are used to exert nonlinear inertial effects on the fluid and on fluid-suspended particles. While inertial microfluidic devices are finding applications in fields such as fluid mixing, particle filtration, flow cytometry (the counting, sorting, and analyzing of cells), the devices are built with essentially no theoretical input due to a lack of models for the nonlinear inertial effects.

Why is there so little theory for inertial microfluidic devices? While there are many numerical methods for simulating inertial migration, because most devices have multiple moving boundaries and rely on three-dimensional effects, simulations are computationally intensive. In many cases, the computational time far exceeds the time needed to build and test a device experimentally. In contrast, asymptotic studies of inertial migration are only valid in limited cases, such as vanishingly small particle sizes.

This thesis is concerned with developing a theory for inertial effects in microfluidic devices for a wide range of complicated geometries. This theory is achieved through the combination of both asymptotic and numerical methods. First, a theory is developed for the inertial lift force on a particle in a square channel. Second, this theory for the inertial lift force is validated against experiment. Third, a theory is developed for the formation of particle chains in a rectangular channel. Finally, a theory is developed for the number of focusing positions in a given channel.