Acoustic Streaming Flows Induced by Microbubbles in Viscoelastic Fluids: Fundamentals and Applications to Micro-Rheometry

University Of Missouri-Columbia, Columbia MO

Investigators

Abstract

Adding minute amounts of polymers into water can turn the solution into a weakly elastic fluid, which exhibit both viscous, liquid-like, and elastic, solid-like behaviors. The elastic behavior is due to stretching and coiling of polymers under flow. Even weak elasticity can have a profound effect on fluid behaviors, which are essential in many industrial applications, ranging from spraying and pesticide deposition to drag reduction in piping flows. To achieve the desired outcomes in those applications, it is critical to accurately measure the fluid viscosity and elasticity. While viscosity is easy to measure, the elasticity of weakly elastic fluids has been challenging to measure. One potential method to measure elasticity is to use steady flows caused by a micro-sized bubble that is vibrating in an acoustic field. The flow patterns that are induced by the bubble will change depending on the acoustic frequency and the fluid properties, allowing inferring of the fluid elasticity. The principal aim of this award is to provide a deep understanding of the key factors governing the microbubble induced flows in a viscoelastic fluid. This award will also incorporate significant educational activities, which disseminate applications of microfluidics as well as concept of viscoelastic fluids through undergraduate research projects, engagement of minority and underrepresented students into research, and outreach modules that are aimed at middle and high school students. Accurate measurement of relaxation times of low-viscosity elastic fluids is still a challenging task. This award will tackle this challenge by using acoustically driven microbubbles. The steady streaming flows arising from the bubble are shown to depend on the driving acoustics and fluid elasticity, suggesting feasible microbubble-based rheometry devices for measuring small relaxation times. In this research, the PIs will combine experiments, simulations, and theoretical modeling to elucidate the interplay between elasticity and acoustic streaming flows by: 1) conducting systematic experiments to characterize the bubble dynamics and streaming flow behavior, 2) deriving appropriate theory based on the asymptotic method to understand the interaction of the fluid elasticity and acoustic oscillations, 3) establishing numerical models to accurately predict the flow patterns, by validating the simulations with the outcome of Task 1, and 4) engineering novel rheometer-on-a-chip devices using the developed models in task 3. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.