Rheology of three-phase suspensions determined via dam-break experiments

Area of Science:

• Rheology
• Volcanology
• Fluid Dynamics

Background:

• Three-phase suspensions (liquid, solid particles, gas bubbles) are prevalent in nature and industry.
• The rheology of these complex fluids, especially at high solid fractions, is not well understood.
• Understanding magma and lava rheology is critical for predicting volcanic eruption behavior.

Purpose of the Study:

• To characterize the rheology of three-phase suspensions under volcanic conditions.
• To investigate the influence of gas bubbles and solid particles on suspension viscosity.
• To develop an improved rheological model for magma and lava flow.

Main Methods:

• Used a dam-break consistometer to study suspensions of corn syrup, plastic particles, and CO2 bubbles.
• Conducted experiments in the non-Brownian, non-inertial regime, varying bubble and particle fractions.
• Measured flow-front velocity and inverted data to fit a Herschel-Bulkley rheology model.

Main Results:

• Observed a greater increase in relative viscosity with increasing particle fraction than predicted by theory, particularly at low to intermediate bubble capillary numbers.
• Identified both shear-thinning and shear-thickening behaviors dependent on the capillary number.
• The developed model predicts increased viscosity and decreased flow velocity for lava, compared to existing models.

Conclusions:

• Gas bubbles play a significant role in stiffening magmas and lavas.
• Current rheological models may underestimate the impact of bubbles on lava flow emplacement.
• Accurate rheological models incorporating bubble effects are needed for improved volcanic hazard assessment.