Drag-reduction behavior of an unusual nonionic surfactant in a circular pipe turbulent flow

The Alkyl Polyglucoside (APG) is a nonionic surfactant with no toxicity and with high biodegradability, its drag-reduction behavior in a circular pipe flow is measured, and the rheological characteristics are investigated with a rheometer with a cone-plate flow cell. From the measured results, the APG is shown to have a high drag-reduction capacity, whose shear viscosity is shear-ratedependent at high concentrations, while its solution at concentrations with drag-reduction effects is non-viscoelastic as verified by zero relaxation time in the relaxation process of the shear stress, which contradicts the general viewpoint that there is a correlation between the viscoselastic characteristics and the turbulent drag reduction for the drag-reduction surfactant. However, the APG solution is birefringent as observed through a birefringent test, which indicates that there are rod-shaped micelles in the solution under the shearing flow. The higher extensional viscosity inferred from the extensional phenomenon observed in the measurements of the shear viscosity could be responsible for the drag reduction property of this nonionic surfactant.