Intermittent outgassing through a non-Newtonian fluid

TL;DR

This study investigates how gas intermittently flows through a non-Newtonian fluid, revealing spontaneous regime changes similar to volcanic degassing, with statistical analysis of regime durations showing power-law behavior.

Contribution

It provides experimental evidence of intermittent gas flow regimes in non-Newtonian fluids and analyzes their statistical properties, linking them to natural volcanic phenomena.

Findings

Bubbles and flues alternate spontaneously in the flow.

Flue lifespan follows a power-law distribution.

The power-law exponent depends on fluid properties.

Abstract

We report an experimental study of the intermittent dynamics of a gas flowing through a column of a non-Newtonian fluid. In a given range of the imposed constant flow rate, the system spontaneously alternates between two regimes: bubbles emitted at the bottom either rise independently one from the other or merge to create a winding flue which then connects the bottom air entrance to the free surface. The observations are reminiscent of the spontaneous changes in the degassing regime observed on volcanoes and suggest that, in the nature, such a phenomenon is likely to be governed by the non-Newtonian properties of the magma. We focus on the statistical distribution of the lifespans of the bubbling and flue regimes in the intermittent steady state. The bubbling regime exhibits a characteristic time whereas, interestingly, the flue lifespan displays a decaying power-law distribution. The associated exponent, which is significantly smaller than the value 1.5 often reported experimentally and predicted in some standard intermittency scenarios, depends on the fluid properties and can be interpreted as the ratio of two characteristic times of the system.