Slip behavior during pressure driven flow of Laponite suspension

TL;DR

This study examines the slip behavior of Laponite suspension during pressure-driven pipe flow, revealing a universal slip law and unusual pressure-flow relationship, advancing understanding of thixotropic fluid dynamics.

Contribution

It introduces a universal slip law for Laponite suspension flow and demonstrates how slip influences flow behavior under various conditions.

Findings

Steady state flow achieved with pressure drop decreasing as flow rate increases.

Flow results collapse onto a universal curve when accounting for slip.

Slip length varies linearly with flow rate and inversely with tube diameter.

Abstract

We investigate pressure driven pipe flow of Laponite suspension, as a model thixotropic fluid. The tendency of the suspension to age is controlled by addition of sodium chloride salt to vary the ionic strength. We use a syringe pump to prescribe the flow and observe that a steady state flow is obtained. Unusually, the steady state pressure drop required to maintain a constant flow rate decreases with an increase in the flow rate, in qualitative contrast to the expectation for Poiseuille flow. We demonstrate that experimental results obtained by varying the flow rate, salt concentration, and flow geometry (pipe diameter and length) can be collapsed onto a single universal curve that can be rationalized by invoking slip of the suspension at the tube walls. The Laponite suspension exhibits plug-like flow, yielding at the tube walls. Our results suggest that the slip length varies linearly with the flow rate and inversely with the tube diameter.