Shear banding flow behavior around the periodic triangle-shaped pillars in microchannel*

It is known that the shear banding is occurred by using a semi-dilute polymer solution due to the non-uniform shear rate. In this study, we investigated the flow behavior of semi-dilute polymer solution in a microchannel having a triangle-shaped pillar array by µPIV. Using this pillar array, the effect of continuous contraction and expansion flow which shows the periodic non-uniform shear rate on flow behavior, was evaluated. In the experiment, we visualized that the dead zone (DZ) was formed around the pillar due to the shear banding, and its shape changes depending on the Weissenberg number (Wi) and concentration of the solution. Based on the velocity measurement results, both the viscosity and flow type parameter distribution were calculated. It was revealed that the various viscosity distribution appeared inside the DZ, resulting in the complex flow behavior containing both extension and rotation behavior. Moreover, the dominated flow behavior around the pillar array depending on Wi was also investigated.