Drag-reduction of a nonionic surfactant aqueous solution and its rheological characteristics

Abstract

In order to develop turbulent drag-reducing technology by using an environmentally friendly additive in a water-transporting system, the drag reducing characteristics in a non-ionic surfactant (Oleyldimethylamineoxide, ODMAO) dilute aqueous solution flowing in a circular pipe of 5 mm diameter have been experimentally investigated with an air-driven fluid resistance test device. The rheological characteristics of the solution have also been examined by a rheometer with a cone-plate flow cell. The results show that the ODMAO solutions are drag-reducing when concentration is 400 ppm or higher, that the critical Reynolds number corresponding to the maximum drag reduction rate increases with both concentration and temperature, and that the maximum drag reduction rate can reach up to 70% in the straight pipe. At low shear rates, the shear viscosity of ODMAO solutions with a relatively high drag-reduction behaves similarly to Newtonian fluids; at above a certain critical shear rate, it is firstly shear-thickening, then shear-thinning. Such shear-rate-dependent characteristics of the shear viscosity are attributed to the different transitions of micellar network structure induced by different shear rates. Relaxation of shear stress after removing an applied constant shear rate at which the solution is in the SIS (shear-induced structure) state is found to be well expressed by a 2-step Maxwell model with a tail relaxation time much shorter than that for a drag-reducing cationic surfactant, which indicates that for the ODMAO solution, a viscoelasticity as strong as a drag-reducing cationic surfactant is not needed to realize turbulent drag-reduction.