Synergetic Effect of Wall-Slip and Compressibility During Startup Flow of Complex Fluids

TL;DR

This paper investigates how wall-slip, compressibility, and thixotropy interact during the startup flow of complex fluids, revealing a new mechanism where wall-slip facilitates gel degradation, supported by experiments and simulations.

Contribution

It introduces a combined rheological and slip-based model to explain the synergistic effects during flow startup of structured fluids.

Findings

Wall-slip facilitates gel degradation during startup.

A new flow-startup mechanism involving pressure propagation.

Experimental and numerical simulations support the findings.

Abstract

The present letter explains the synergetic effect of wall-slip, compressibility, and thixotropy in a pressurized flow startup operation of various structured fluids. Opposite to the intuition, experimental and numerical simulations suggest that the wall-slip (adhesive failure) is facilitating gel degradation (cohesive failure), revealing a new flow-startup mechanism. The thixotropic rheological model includes structural degradation kinetics at the bulk. Whereas, a static slip-based model addresses the near-wall phenomenon. The near-wall transient variations in axial velocity or strain evolution, and the initial pressure propagation mechanism along the axis of the circular pipe explain the essence of the aforementioned synergy.