Abstract
Three-phase suspensions, of liquid that suspends dispersed solid particles and gas bubbles, are common in both natural and industrial settings. Their rheology is poorly constrained, particularly for high total suspended fractions (≳0.5). We use a dam-break consistometer to characterize the rheology of suspensions of (Newtonian) corn syrup, plastic particles and CO2 bubbles. The study is motivated by a desire to understand the rheology of magma and lava. Our experiments are scaled to the volcanic system: they are conducted in the non-Brownian, non-inertial regime; bubble capillary number is varied across unity; and bubble and particle fractions are 0 ≤ ϕ gas ≤ 0.82 and 0 ≤ ϕ solid ≤ 0.37, respectively. We measure flow-front velocity and invert for a Herschel-Bulkley rheology model as a function of , , and the capillary number. We find a stronger increase in relative viscosity with increasing in the low to intermediate capillary number regime than predicted by existing theory, and find both shear-thinning and shear-thickening effects, depending on the capillary number. We apply our model to the existing community code for lava flow emplacement, PyFLOWGO, and predict increased viscosity and decreased velocity compared with current rheological models, suggesting existing models may not adequately account for the role of bubbles in stiffening lavas.
Highlights
Two-phase liquid–solid and liquid–gas suspensions are important across nature and industry.royalsocietypublishing.org/journal/rspa Proc
We invert for a Herschel–Bulkley rheology using a depth-integrated one-dimensional forward model [39] and the probabilistic ensemble Kalman filter approach
Our results show good agreement with existing literature for particle-bearing suspensions with a strongly nonlinear increase in viscosity with increasing particle fraction, development of yield stresses at particle fractions φsolid 0.35, and development of shear-thinning behaviour at particle fractions φsolid 0.39
Summary
Two-phase liquid–solid (particle) and liquid–gas (bubble) suspensions are important across nature and industry. The only systematic experimental study, which was limited to φsolid 0.5, φgas 0.3 and low capillary number [17], found that the rheology was well described by a simple convolution of existing two-phase rheology models in which the liquid and bubbles were treated as an effective medium that suspended the particles. Magma (and lava, which is its subaerial counterpart) is a natural three-phase suspension, composed of a molten silicate liquid (melt) that suspends a variable fraction of solid particles (crystals) and gas bubbles. We conduct experiments in which bubbles are grown in situ via a chemical reaction, and analysed using a dam-break consistometer This approach circumvents both problems, allowing us to investigate samples with bubble fractions (0 ≤ φgas ≤ 0.8) and particle fractions (0 ≤ φsolid ≤ 0.37) that span the most relevant ranges for natural magma and lava.
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