Bjornar Sandnes

Swansea University | SWAN · Centre for Complex Fluid Processing

Multiphase flows in deformable porous materials are important in numerous geological and geotechnical applications; however, the complex flow behavior makes subsurface transport processes difficult to control—or even characterize. Here, we study gas-driven (pneumatic) fracturing of a wet unconsolidated granular packing confined in a Hele-Shaw cell,...

Fluid flow in transforming porous rocks, fracture networks, and granular media is subject to considerable current interdisciplinary research activity in Physics, Earth Sciences, and Engineering. Examples of natural and engineered processes include hydrocarbon recovery, carbon dioxide geo-sequestration, soil drying and wetting, pollution remediation...

We study experimentally the flow and patterning of a granular suspension displaced by air inside a narrow tube. The invading air-liquid interface accumulates a plug of granular material that clogs the tube due to friction with the confining walls. The gas percolates through the static plug once the gas pressure exceeds the pore capillary entry pres...

Granular flows such as landslides, debris flows and avalanches are systems of particles with a large range of particle sizes that typically segregate while flowing. The physical mechanisms responsible for this process, however, are still poorly understood, and there is no predictive framework for ascertaining the segregation behaviour of a given sy...

Pattern-forming processes in simple fluids and suspensions have been studied extensively, and the basic displacement structures, similar to viscous fingers and fractals in capillary dominated flows, have been identified. However, the fundamental displacement morphologies in frictional fluids and granular mixtures have not been mapped out. Here we c...

We use high-speed photography to observe the dendritic freezing of ice between two closely spaced parallel plates. Measuring the propagation speeds of dendrites, we investigate whether there is a confinement-induced thermal influence upon the speed beyond that provided by a single surface. Plates of thermally insulating plastic and moderately therm...

Silo discharge has been extensively studied for decades although questions remain regarding the nature of the velocity field, particularly for submerged systems. In this work, fluid-driven granular drainage was performed in a quasi-two-dimensional silo with grains submerged in fluid. While the observed Gaussian velocity profiles were generally cons...

Fluid-driven grain flow through a confined channel filled with non-buoyant grains is herein observed to exist in three regimes according to total imposed flow rate. (1) At low imposed flow rates, no grain flow occurs as the fluid stress is insufficient to mobilise the grains and Darcy flow is observed. (2) At a sufficient imposed flow rate, grains...

Confined fluid-driven granular flows are present in a plethora of natural and industrial settings yet even the most fundamental of these are not completely understood. While widely-studied grain flows such as bed load and density-matched Poiseuille flow have been observed to exhibit exponential and Bingham style velocity profiles respectively, this...

Recent theoretical and experimental work suggests a frictionless-frictional transition with increasing inter-particle pressure explains the extreme solid-like response of discontinuous shear thickening suspensions. However, analysis of macroscopic discontinuous shear thickening flow in geometries other than the standard rheometry tools remain scarc...

The motion of a capillary interface across a deformable granular material in a confined geometry shows the complex interplay between viscous forces, solid friction, and capillary forces. In a horizontal quasi-one-dimensional geometrical confinement, a millifluidic tube, the displacement of a three-phase flow consisting of two fluids and a mobile gr...

Frictional finger trees are patterns emerging from non-equilibrium processes in particle-fluid systems. Their formation share several properties with growth algorithms for minimum spanning trees (MSTs) in random energy landscapes. We propose that the frictional finger trees are indeed in the same geometric universality class as the MSTs, which is c...

Using high-speed imaging and digital image correlation, we study the granular motion and deformation caused by pneumatic fracturing of a wet granular packing in a Hele-Shaw cell subject to a constant injection of air. These pneumatic fractures form patterns of conductive pathways whose form is determined by a complex interplay between pressure, cap...

Aligned finger structures, with a characteristic width, emerge during the slow drainage of a liquid-granular mixture in a tilted Hele-Shaw cell. A transition from vertical to horizontal alignment of the finger structures is observed as the tilting angle and the granular density are varied. An analytical model is presented, demonstrating that the al...

Commercial aluminosilicate proppant particles have been coated with Ca-Si oxides, with the aim to provide an in-situ increase in the angularity (decrease in Krumbein roundness value) to facilitate their immobilization. Ca-Si oxide systems have been synthesized via sol-gel, cured, and sintered at 1200 °C using (a) CaCO3, (b) CaCO3 + orthosilicic aci...

An experimental observation of the structuring of a granular suspension under the progress of a gas/liquid meniscus in a narrow tube is reported here. The granular material is moved and compactifies as a growing accumulation front. The frictional interaction with the confining walls increases until the pore capillary entry pressure is reached. The...

Aligned finger structures, with a characteristic width, emerges during the slow drainage of a liquid/granular mixture in a tilted Hele-Shaw cell. A transition from vertical to horizontal alignment of the finger structures is observed as the tilting angle and the granular density are varied. An analytical model is presented, demonstrating that the a...

Experiments on confined two-phase flow systems, involving air and a dense suspension, have revealed a diverse set of flow morphologies. As the air displaces the suspension, the beads that make up the suspension can accumulate along the interface. The dynamics can generate "frictional fingers" of air coated by densely packed grains. We present here...

Understanding how gasses escape from particle-rich suspensions has important applications in nature and industry. Motivated by applications such as outgassing of crystal-rich magmas, we map gas migration patterns in experiments where we vary (1) particle fractions and liquid viscosity (10–500 Pa s), (2) container shape (horizontal parallel plates a...

In both nature and engineering, loosely packed granular materials are often compacted inside confined geometries. Here, we explore such behaviour in a quasi-two dimensional geometry, where parallel rigid walls provide the confinement. We use the discrete element method to investigate the stress distribution developed within the granular packing as...

Submerged granular material exhibits a wide range of behavior when the saturating fluid is slowly displaced by a gas phase. In confined systems, the moving interface between the invading gas and the fluid/grain mixture can cause beads to jam, and induce intermittency in the dynamics. Here, we study the stability of layers of saturated jammed beads...

Dissipative interactions between grains often lead to instabilities and pattern formation in flows involving granular materials. This is especially so in wet granular flows, where viscous and capillary forces add to the complex dynamics. In a recent study we found an extraordinary diversity in the flow behaviour of wet granular material displaced b...

When a compressible gas displaces a granular mixture in a quasi 2D space, friction causes stick slip motion. A localized slip event at the interface allows expansion of the compressed gas and a sudden forward motion of the front. The reservoir volume of gas determines the available elasticity in the system, and thereby the size of the expansion. La...

From landslides to oil and gas recovery to the squeeze of a toothpaste tube, flowing complex fluids are everywhere around us in nature and engineering. That is not to say, though, that they are always well understood. The dissipative interactions, through friction and inelastic collisions, often give rise to nonlinear dynamics and complexity manife...

Here we shall investigate the displacement of wet granular mixtures and deformable porous media by an invading gas. The experiment is straight forward: a mixture of grains and fluid is loaded into the gap between two glass plates, followed by injection of gas at constant rate. As it turns out, the resulting dynamics is far from simple. Several forc...

This paper addresses the scar tissue maturation process that occurs stepwise, and calls for reliable classification. The structure of collagen imaged by nonlinear optical microscopy (NLOM) in post-burn hypertrophic and mature scar, as well as in normal skin, appeared to distinguish these maturation steps. However, it was a discrimination analysis,...

Remarkable shapes and patterns appear in multiphase flow experiments with frictional fluids. Here we explore the rich dynamics, and map the emerging morphologies in a phase diagram.

While pattern-forming processes in simple fluids and suspensions have been studied extensively, and the basic displacement structures, like viscous fingers and fractals in capillary dominated flows, have been identified, the fundamental displacement morphologies in frictional fluids and granular mixtures have not been mapped out. Here we add Coulom...

We introduce a retroemitter (REM) device comprising a planar glass bead set placed on a luminescent material substrate, which converges an excitation beam into a set of foci (voxels). The in-voxel emission is collimated by the beads, and propagates upstream over the long range, unlike the out-of-voxel emission spreading in all angles. The REM signa...

This movie shows the displacement dynamics for the two experiments presented in Fig. 2. At low filling fraction f the injected air invades the granular fluid mixture in a creeping fingering fashion, while a transition to stick slip bubble formation is seen at high f. The injection rate and the volume of air contained in the syringe was the same in...

This movie shows examples of the types of displacement dynamics that emerge at different injection rates, starting with stick slip bubbles at low rate (q = 0.03 ml/min), followed by "temporal intermittency" where periods of continuous motion are interrupted by occasional jamming (0.3 ml/min), "Coral" growth (0.1 ml/min) and destabilized viscous fin...

The effects of non-ablative infrared (IR) laser treatment of collagenous tissue have been commonly interpreted in terms of collagen denaturation spread over the laser-heated tissue area. In this work, the existing model is refined to account for the recently reported laser-treated tissue heterogeneity and complex collagen degradation pattern using...

A branching labyrinth of granular material emerges when a confined granular fluid system is slowly drained. From a series of experiments, simulations and theoretical modeling, we explain the mechanism for the pattern formation in terms of the forces involved. We further show that the granular fluid system undergoes a series of transitions whereby n...

Random labyrinthine patterns have been shown to emerge during slow drainage of granular‐fluid systems in two‐dimensional confinement. We investigate this process under the influence of a gravitational field; that is to say in a tilted system. The isotropy of the labyrinthine pattern is broken. Instead the system is drained from one side, and a fron...

A study was conducted to investigate the properties of weakly bound clusters of single-digit nanodiamonds (SND) using spectrally and temporally resolved luminescence detection, electron paramagnetic resonance (EPR) spectroscopy, and transmission electron microscopy (SEM). Nitrogen-vacancy (NV) centers were created in diamonds by high-energy proton...

When a droplet of silica particles suspended in water dries out on a horizontal surface, one can observe an emerging pattern of interconnected stripes of sedimented mass. From experimental observations and numerical simulations we find that the mechanism for the pattern formation is a combination of meniscus shape perturbations caused by pinned par...

Experiments on granular-fluid systems in confined geometries have been shown to produce labyrinth patterns. This is the case when the fluid from a particle/fluid dispersion in a Hele-Shaw cell is slowly withdrawn, resembling a drying process. Based on a model of capillary and friction forces, we present a, simulator that reproduces the experimental...

We present a new pattern formation process where labyrinthine structures emerge during slow drainage of a confined granular-fluid mixture. Capillary and frictional forces govern the process, and the resulting pattern has a characteristic wavelength that is a function of both the initial volume fraction of granular material in the mixture, and also...

Flexing a metallic disk triggers the crystallization of the supercooled sodium acetate solution contained in commercial heat pads. Many mechanisms have been proposed to explain the apparent nucleation of crystalline material. In this paper a simple experiment is described that demonstrates that nucleation is triggered by preserving seed crystals cl...

Pattern forming processes are abundant in nature. Here, we report on a particular pattern forming process. Upon withdrawal of fluid from a particle-fluid dispersion in a Hele-Shaw cell, the particles are shown to be left behind in intriguing mazelike patterns. The particles, initially being uniformly spread out in a disc, are slowly pulled inwards...

Abstract: Collagen is the most abundant protein in connective animal tissue. Due to its helical structure and high degree of polarizability, collagen effectively generates second harmonic photons at double the excitation frequency [1]. Structural changes occur in collagen due to aging and pathological conditions, and also in response to recently in...

A random, labyrinthine pattern emerges during slow drainage of a granular-fluid system in two-dimensional confinement. Compacted grains are pushed ahead of the fluid-air interface, which becomes unstable due to a competition between capillary forces and the frictional stress mobilized by grain-grain contact networks. We reproduce the pattern format...

Thermal energy can be stored in supercooled liquids where the material is in thermal equilibrium with its surroundings. The stored latent heat of fusion is released by triggering the crystallization of the supercooled substance. In this study, enthalpy-temperature curves including the effect of supercooling are measured for some well known supercoo...

We study the diffision of water in weakly-hydrated samples of the smectite clay Na-fluorohectorite, The quasi one-dimensional samples are dry compounds of nano-layered particles consisting of -80 silicate platelets. Water diffises into a sample through the mesoporosity in between the particles, and can subsequently intercalate into the adjacent par...

We performed synchrotron X-ray scattering studies of the dynamics of the water intercalation front in a Na-Fluorohectorite clay. Like other smectite clays, fluorohectorite particles can swell due to intercalation of successive water layers. Monitoring the intensities of Bragg peaks of the known 1- and 2-water-layer hydration states at different pos...

A calorimetric method is applied to determine the solar system performance by in-situ measured data. The heat store is interpreted as a calorimeter and the information on charge and discharge is extracted from the shape analysis of the heat store’s temperature profile. The method is applicable to any heating system which includes a heat store. In t...

A polymer solar heat collector was combined with single-crystal silicon PV cells in a hybrid energy-generating unit that simultaneously produced low temperature heat and electricity. The PV/T unit was tested experimentally to determine its thermal and photovoltaic performance, in addition to the interaction mechanisms between the PV and thermal ene...

The key objective of this study was to compare tracer-based methods that measure bioturbation and irrigation rates with predictive models based on benthic community parameters such as animal size and abundance. The individual parameters of each model were investigated separately to assess their relative influence on model output. An important aspec...

The influence of faunal activity and particle type on sediment-mixing processes of the particle-bound, organic contaminant di(2-ethylhexyl) phthalate (DEHP) were examined over a 48 d experimental period with natural box-cosm sediments. A dual-labelling radiotracer technique using C-14-DEHP and Cr-51 determined the fate and utilization of DEHP assoc...