Pressure Loss of Viscoelastic Surfactant Solutions under the Flow in a Packed Bed of Particles

The objective of this study is to examine the property of pressure loss under the flow of surfactant solutions in a packed bed of particles. Three mixtures of CTAB and NaSal in distilled water were used as test fluids. The flow property of surfactant solution in the packed bed was expressed by a wall shear stress and an apparent shear rate, which were defined in a model channel for a packed bed. The flow curve, a plot of the shear stress versus the shear rate, shows a sigmoidal shape. The first bending point in flow curve occurs because of the sudden increase in shear stress, which looks like the shear-thickening in shear viscosity. However, the surfactant solutions in the packed bed was affected by a stretch deformation due to a converging-diverging flow. We estimated an apparent elongational viscosity by means of the difference in pressure loss between the packed bed and the capillary flow data. As a result, it is found that the obtained elongational property demonstrates a significant change, that is the transition from a stretch-thickening property to stretch-thinning one with the increase in stretch rate. It is considered that the property of elongational viscosity for surfactant solutions is closely related to the transition of micellar network structure.