Pseudo-laminarization effect of several types of surfactant solutions in small-sized pipe flows

Abstract

Fluid mechanics at a very small scale, particularly micro-flows and nano-flows, have many technical applications, and the elastic properties of small-scale flows are strongly expressed even for dilute aqueous solutions of non-Newtonian fluids. We have investigated the flow properties of water and several types of surfactant solutions with spherical or rod-like micelles. Before the flow property investigations, Newtonian and non-Newtonian viscosities for the test fluids were observed by using a capillary viscosity meter. Pressure drops were experimentally measured, and the frictional coefficient of the pipe was estimated in flows through capillaries ranging from 133 $$\upmu $$ m to 2.87 mm in diameter. For water flow, good agreement was obtained between the experimental results and the predictions for Hagen–Poiseuille flow and the Blasius expression. The flow properties of the spherical micelle surfactant solutions agreed with those of water. However, the rod-like micelle surfactant solutions maintained laminar flows in the transition regions. Thus, a pseudo-laminarization effect for surfactant solutions with rod-like micelles is indicated. A relationship between these experimental results and estimated first normal stress differences is also strongly suggested.