New observations of hydrodynamic instabilities around junctions by using microfluidics
Microfluidics has emerged as a powerful platform of investigating flow instabilities at small lengh scales, as it provides access to regimes of low inertia and high elasticity and allows for the study of purely elastic flow instabilities and elastic turbulence, which occur at low Reynolds numbers but high Weissenberg numbers. By employing a state-of-the-art microfabrication technique (selective laser-induced etching) to fabricate glass microfluidic devices, we create platforms for discovering new insights on flow instabilties of complex fluids, assisted by a number of flow visualization and diagnostic techniques.
In this talk, I will focus on an example of using cross-slot microfluidics to explore how fluid elasticity affects inertial flow instability: Simple fluids often display flow instabilitiesinvolving the production of vortices. However, studying how polymers and vortices interact is challenging because vortices generally fluctuate significantly and polymereffects at low concentrations can be subtle. A better understanding of these interactions is needed to optimize the use of polymer additives in industrial and biomedicalapplications ranging from lab-on-a-chip devices to large pipelines. We fabricated unique glass microfluidic devices containing junctions to make measurements on a single,steady, stationary vortex by direct visualization at high frame rates. By adding increasing amounts of a flexible polymer to water-based solvents, we discovered that theaddition of the polymer is destabilizing and lowers the threshold flow rate needed for vortex formation. At the same time, we found that the polymer significantly reduces thestrength of the resulting vortex. Our discoveries provide new insight regarding the competing effects of inertial and elastic instabilities on vortex formation and dynamics atsmall length scales. If time permits, I will also show some ongoing work of flow around microfluidic cylinders using both polymer and surfactant wormlike micellar solutions.
Prof. Amy Shen
Okinawa Institute of Science and Technology (Japan)
Venerdì 12 Aprile 2019, h 15.00
Sapienza Università di Roma
Facoltà di Ingegneria Civile e Industriale, Via Eudossiana 18
Aula 32
