Laminar-turbulent transition in polymer solutions through micro-tubes

Experiments are performed to characterize laminar-turbulent transition for the flow of polymer solutions through micro-tubes of size ~400µm using micro-PIV and dye stream visualization techniques. Using small diameter tubes enable us to probe high elasticity number. We observe that addition of small amounts of polymer (50ppm-100ppm) delays transition to turbulence as compared to a Newtonian fluid whereas addition of larger amounts of polymer (500ppm-800ppm) causes an early transition. It is observed that addition of polymer decreases velocity fluctuations in the post-transition regime irrespective of the concentration of polymer added for polyacrylamide solutions which may be linked to the drag reduction phenomena. The phenomena was corroborated by using a different polymer of a different molecular weight. Transition Re observed in our experiments (by varying polymer concentration, with tubes of different diameters and by using two different polymers) shows a remarkable data collapse.