Obstructed viscoplastic flow in a Hele-Shaw cell

Abstract

Experiments are conducted exploring the flow of Carbopol past obstacles in a narrow slot and compared with predictions of a model based on the Herschel-Bulkley constitutive law and the conventional Hele-Shaw approximation. Although Carbopol is often assumed to be a relatively simple yield-stress fluid, the flow pattern around an obstacle markedly lacks the fore-aft symmetry expected theoretically. Such asymmetry has been observed previously for viscoplastic flows past obstacles in unconfined geometries, but the narrowness of the Hele-Shaw cell ensures that the stress state is very different, placing further constraints on the underlying origin. The asymmetry is robust, as demonstrated by varying the shape and number of the obstacles, the surfaces of the cell walls, and the steadiness of the flow rate. The results suggest that rheological hysteresis near the yield point may be the cause of the asymmetry.

Atypical plug formation in internal elastoviscoplastic fluid flows over a non-smooth topology

“…The incoming flow at the upstream of the cavity/aperture was studied before in a similar geometry as in Daneshi et al [6]. They showed that the velocity at the upstream of the channel is unidirectional and fully developed such that its cross-wise velocity profile matches the analytical one obtained from the Poiseuille flow of a Herschel-Bulkley fluid.…”

“…Direct visualization of the flow using state-of-the-art imaging devices was exploited to characterize the velocity fields and yielding surfaces developing around the cavity and aperture [6,25]. For each of these geometries, the details of the experimental setup including the channel geometry and its fabrication as well as the visualization techniques employed to monitor the flow are explained in the following subsections.…”

“…This material has been widely used in many visualization experiments and rheological studies [7,35]. Carbopol gels of two different concentrations 0.060 (wt/wt%) and 0.075 (wt/wt%) were prepared according to the procedure explained in our previous works [6,25]. The rheological curves and parameters of the fluids were measured using a rotational rheometer (MCR501, Anton Paar) with an angular resolution of 0.01 mrad and a torque resolution of 0.1 nN m. A parallel plate geometry with the diameter of 50 mm was used for the rheological measurements with a ramp rate of 0.05 P a/s.…”

“…Yield-stress fluids are characterized by a transition from solid-like to fluid-like behaviour above a threshold, τ y -the yield stress. This implies a co-existence of a liquid and solid phase, which may cause the material to plug small apertures in a pressure driven flow [5,6]. Beside the yield stress, these materials exhibit complex properties such as elasticity and thixotropy [7][8][9] which further complicate their flow features and our understanding of solid-liquid transition.…”

Fully turbulent flows of viscoplastic fluids in a rectangular duct

“…By far the most widely used polymer additive is Carbopol [34]. When correctly mixed, it provides a clear solution which is ideal for visualization and laser velocimetry experiments [35,25,36,8], while exhibiting little viscoelastic behaviour beyond the yielding point and negligible thixotropy [35,34,37], with only the yield stress and shear-thinning as dominant characteristics. Thus, Carbopol solutions have been considered to be very close to an ideal viscoplastic fluid and are also used in our study.…”