Prof. V Shankar's Talk

Nov 02, 2017 - 17:00

Nov 02, 2017 - 18:00

Room 118 Chemical Engg Dept

Seminars

Prof. V Shankar IIT Kanpur

Abstract: Laminar flow of Newtonian fluids in a tube/pipe becomes unstable at a Reynolds number ∼ 2000 but linear stability analysis predicts that the flow is always stable at all Reynolds number to infinitesimal disturbances. However when flow of viscoelastic polymer solutions is considered earlier experiments have observed all the three possibilities due to addition of the polymer: no effect a delay or an advancement in the Reynolds number for the onset of transition. We carry out experiments to characterize the onset of transition in the flow of polymer solutions in microtubes (of diameters 390 and 470 μm). Two different polymer (polyacrylamide and polyethylene oxide) solutions at varying concentrations are considered and the transition is characterized using micro-PIV measurements as well as dye-stream visualization. By considering tubes of such small diameters the present experiments probe (hitherto unexplored) regimes of high elasticity number E = λν/R 2 where λ is the longest relaxation time of the polymer solution ν is the kinematic viscosity and R is the tube radius. Our results show that for small concentrations of the added polymer there is a transition delay but at sufficiently large concentrations the Re for transition can be as low as 800. We show that the data for transition Re for solutions of two different polymers of varying polymer concentration different tube diameters collapse well according to the scaling relation Re c ∝ (E(1 − β)) −1/2 where β is the ratio of solvent to solution viscosity. We also carry out linear stability analyses for the pressure-driven flow of viscoelastic Oldroyd-B fluids through rigid tubes and channels. This talk will discuss the results from our theoretical analysis and their relevance to experimental observations.Bio: V. Shankar is currently the Sajani Kumar Roy Chair Professor and Head Department of Chemical Engineering IIT Kanpur. He obtained his B.Tech in Electrochemical Engineering from the Central Electrochemical Research Institute Karaikudi and his Masters and PhD in Chemical Engineering from the Indian Institute of Science Bangalore. After a post-doctoral stint at the University of Minnesota Minneapolis he joined IIT Kanpur in 2002 where he currently leads a group working in the general area of stability of fluid flows with focus on fluids with complex rheology and in flow past deformable solid surfaces. His group uses a combination of theory computation and experiments to understand and unravel new physical phenomena in such systems. Note: The seminar is mandatory for those enrolled in CL 702/704.