ChBE Seminar Series: Paul Salipante, Materials Measurement Lab @ NIST
Speaker: Dr. Paul Salipate, Materials Measurement Lab @ NIST
Title: Effect of microfluidic geometry on flow instabilities of wormlike micelle solutions
The pressure driven flow of non-Newtonian fluids through pipes is common in industrial processing and high shear rate rheological measurements. Viscoelastic instabilities can complicate these measurements, especially for fluids with self-assembling microstructures such as wormlike micelle solutions. In this talk, Dr. Salipante will focus on experimental measurements of viscoelastic flow instabilities in microfluidic geometries. Global measurements of flow rate and pressure drop are related to velocity profile measurements using microparticle tracking techniques. He will introduce advancements in using digital holographic particle tracking velocimetry to measure 3-D flow fields with high temporal resolution. This technique is used to measure velocity profiles of a jetting instability of wormlike micelle solutions in rectangular microfluidic channels. At higher flow rates, the velocity profiles are measured and compared to simultaneous slit rheology measurements, where discrepancies between the two measurements arise in channels smaller than 200 µm. He will also show results of flow behavior of wormlike micelle solutions in an axisymmetric capillary constriction, which produces a spatio-temporal instability affecting the flow throughout the fluid system. Velocimetry measurements in the entrance region show a transition to unstable flow above a critical flow rate, where large flow circulations are observed in the tapered geometry. This is further investigated using polarized light microscopy, which shows a rapid breakdown in micelle alignment at the onset of a flow spurt, indicating the importance of rapid micelle structural changes on the fluctuations.
Paul Salipante received his M.S. degree in engineering sciences from Dartmouth College in 2009 and Ph.D. in mechanical engineering from Brown University in 2013. He became a National Research Council research associate at NIST in 2013 and has continued as a mechanical engineer in the Polymers and Complex Fluids group. His research experience includes drop electrohydrodynamics, biomembrane mechanics, microparticle tracking techniques, and viscoelastic instabilities in microfluidics.