Degassing cascades in a shear-thinning viscoelastic fluid

TL;DR

This study investigates the periodic degassing behavior of a shear-thinning viscoelastic fluid under constant air flow, revealing how pressure signals and cascades relate to the fluid's rheological properties.

Contribution

It provides the first detailed experimental analysis of degassing cascades in shear-thinning viscoelastic fluids and links pressure dynamics to fluid relaxation times.

Findings

Periodic bubble cascades occur independently of flow rate.

Pressure thresholds and flow dynamics are described by a Maxwell model.

Monitoring cascades reveals the fluid's relaxation time.

Abstract

We report the experimental study of the degassing dynamics through a thin layer of shear-thinning viscoelastic fluid (CTAB/NaSal solution), when a constant air flow is imposed at its bottom. Over a large range of parameters, the air is periodically released through series of successive bubbles, hereafter named {\it cascades}. Each cascade is followed by a continuous degassing, lasting for several seconds, corresponding to an open channel crossing the fluid layer. The periodicity between two cascades does not depend on the injected flow-rate. Inside one cascade, the properties of the overpressure signal associated with the successive bubbles vary continuously. The pressure threshold above which the fluid starts flowing, fluid deformation and pressure drop due to degassing through the thin fluid layer can be simply described by a Maxwell model. We point out that monitoring the evolution inside the cascades provides a direct access to the characteristic relaxation time associated with the fluid rheology.