Drag Reduction on a Polymer Gel Surface.

We investigated the hydrogel of poly (vinyl alcohol) (PVA) which possesses elastic behavior similar to the blood vessel. In this study, drag reduction on the polymer hydrogel tube surface was experimentally investigated at steady flow condition. A transparent PVA hydrogel tube was prepared from the solution of PVA, dimethyl sulfoxide (DMSO) and water by repetitive cooling method and the surface of the hydrogel tube was modified with poly (acrylic-acid) (PAA). Monodisperse polystyrene particles (7.21 μm in diameter) were used as a tracer of fluid flow and the flow was observed by CCD camera under a microscope. The wall shear stress (WSS) was determined from near-wall velocity gradient obtained by particle-tracking (PT) method and drag reduction was calculated from the WSS. Microscopic investigations have shown that the drag reduction on the hydrogel surface depends on the chemical nature of the hydrogel surface, which was varied with changing pH of flow liquid. Maximum drag reduction was obtained with water (flow), when the PAA of modified surface is in the dissociated condition.