Flow fluctuations in wormlike micelle fluids

Published

October 22, 2018

Author(s)

Paul NMN Salipante, Steven Meek, Steven D Hudson

Abstract

We investigate the unstable flow of wormlike micelle solutions in pressure driven capillary flow, with a focus on the effect of entrance geometry on the fluid fluctuations. The flow is measured at different points in the capillary using particle image velocimetry while simultaneously measuring the pressure drop across the entire capillary. The fluctuations are characterized by rapid flow rate jumps that correspond with a decrease in the pressure drop followed by a longer recovery period. Velocimetry measurements in the entrance region show a transition to unstable flow above a critical flow rate, where large flow circulations are observed in the tapered geometry and localized jets are observed in an abrupt contraction. The transition to this unstable flow is shown to occur at a similar dimensionless extension rate normalized by the micelle relaxation time. A rapid breakdown in micelle alignment is observed in polarized light microscopy at the onset of the flow rate jump, indicating the importance of rapid micelle structural changes on the fluctuations. We characterize the system by analyzing the power spectral densities and develop a dynamical systems model to describe the relationship between pressure and flow rate.

Citation

Soft Matter

Volume

14

Issue

44

Pub Type

Journals

Download Paper

https://doi.org/10.1039/c8sm01649f

Keywords

flow instabilities, rheology

Citation

, P. , Meek, S. and , S. (2018), Flow fluctuations in wormlike micelle fluids, Soft Matter, [online], https://doi.org/10.1039/c8sm01649f (Accessed March 6, 2025)