Microscale Acoustic Streaming Flows in Viscoelastic Fluids: Comparison of Experiment and Simulation

Micro-bubble streaming induces vortices of secondary flows around a vibrating bubble in a microfluidic device. It has been applied to micro-scale fluid manipulations such as mixing enhancement, fluid pumping and micro-particle sorting. Although microbubble streaming has been widely investigated both experimentally and numerically in Newtonian fluids, there is little information in the literature on such flows in viscoelastic fluids specifically on the numerical aspect. The Oldroyd-B family of viscoelastic fluids provides a linear constitutive model to describe the behavior of the dilute polymeric solutions based on the dumbbell model. This study focuses on the investigation of the flow around a sessible vibrating micro-bubble attached to the wall of a micro-channel in two cases: a Newtonian fluid and a viscoelastic fluid. In the experimental investigation, aqueous glycerol and dilute solution of polyethylene oxide (PEO) in aqueous glycerol are respectively utilized as the Newtonian and viscoelastic fluids in the micro-channel. The patterns of the flow field at different frequencies are visualized by high-speed imaging and particle-lines. In the numerical solution, finite element method is employed to simulate flow patterns around the vibrating micro-bubble and to probe the effect of the elasticity on how the bubble vibrates. Both numerical and experimental results suggest a significant change in the number and the position of vortices in the steady streaming flow pattern around the micro-bubble.