Academic Interests
I'm working experimentally with condensed matter and complex physics within the topics
- Porous media physics
- Granular materials
- Fracture and fracture dynamics
- Clay and nano silicates
Teaching
Experimental techniques in condensed matter physics
Experimental methods in physics
Publications
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Reis, Paula Kozlowski Pitombeira; Flekkøy, Eirik Grude; Toussaint, Renaud & Måløy, Knut Jørgen
(2026).
Linear response theory of front back-contraction during a single Haines jump.
Journal of Fluid Mechanics.
ISSN 0022-1120.
1041.
doi:
10.1017/jfm.2026.11960.
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We study the linear response of a fluid–fluid interface in a porous medium subjected to a localised, transient perturbation. A single pore is driven out of mechanical equilibrium by a small displacement, initiating a back-contraction of the interface. Assuming negligible total flow, the interface relaxes with a time- and space-dependent profile h(x,t), modelled for a flat geometry. This set-up reflects conditions achievable experimentally using a localised heterogeneity in pore-throat sizes. We determine the evolving interface shape during the relaxation process, together with the associated pressure and velocity fields, using both analytical calculations and pore-network simulations.
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Thorens, Louison; Rodriguez, Solenn; Taberlet, Nicolas; Bourgoin, Mickael; Måløy, Knut Jørgen & Santucci, Stephane
(2026).
Hybrid magnetic Janssen effect arising from percolating ferromagnetic grain networks.
Soft Matter.
ISSN 1744-683X.
doi:
10.1039/d6sm00069j.
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Xu, Yao; Moura, Marcel; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2026).
A comparison of different image analysis techniques for mapping spatiotemporal pH and carbon dissolution in density-driven convection of CO2 in water.
Advances in Water Resources.
ISSN 0309-1708.
212.
doi:
10.1016/j.advwatres.2026.105296.
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Reis, Paula Kozlowski Pitombeira & Måløy, Knut Jørgen
(2025).
Drainage front width in a three-dimensional random porous medium under gravitational and capillary effects.
Physical Review Research (PRResearch).
7(3).
doi:
10.1103/5bbz-ksds.
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Moura, Marcel; Kern, Vanessa Ruth; Måløy, Knut Jørgen; Carlson, Andreas & Flekkøy, Eirik Grude
(2025).
Droplet spreading in a wedge: a route to fluid rheology for power-law liquids.
Soft Matter.
ISSN 1744-683X.
21(36),
p. 7014–7020.
doi:
10.1039/d5sm00286a.
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Measuring the rheology of liquids typically requires precise control over shear rates and stresses. Here, we describe an alternative route for predicting the characteristic features of a power-law fluid by simply observing the capillary spreading dynamics of viscous droplets in a wedge-shaped geometry. In this confined setting, capillary and viscous forces interact to produce a spreading dynamics described by anomalous diffusion, a process where the front position grows as a power-law in time with an exponent that differs from the value 1/2 found in classical diffusion. We derive a nonlinear diffusion equation that captures this behavior, and we show that the diffusion exponent is directly related to the rheological exponent of the fluid. We verify this relationship by using both experiments and simulations for different power-law fluids. As the predictions are independent from flow-specific details, this approach provides a robust tool for inferring rheological properties from the spreading dynamics.
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Brodin, Joachim Falck; Pierce, James Kevin; Reis, Paula Kozlowski Pitombeira; Rikvold, Per Arne; Moura, Marcel & Jankov, Mihailo
[Show all 7 contributors for this article]
(2025).
Interface instability of two-phase flow in a three-dimensional porous medium.
Physical Review Fluids.
10(6).
doi:
10.1103/hm82-167x.
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We present an experimental study of immiscible, two-phase fluid flow through a three-dimensional porous medium consisting of randomly packed, monodisperse glass spheres. Our experiments combine refractive-index matching and laser-induced fluorescence imaging to resolve the morphology and stability of the moving interface resulting from the injection of one fluid into another. The imposed injection rate sets a balance between gravitational and viscous forces, producing interface morphologies which range from unstable collections of tangled fingers at low rates to stable sheets at high rates. The image data are complemented by time-resolved pressure measurements. We develop a stability criterion for the fluid interface based on the analysis of the 3D images and the pressure data. This criterion involves the Darcy permeability in each of the two phases and the time derivative of the pressure drop across the medium. We observe that the relative permeability encountered by the invading fluid is modified by the imposed flow rate in our experiment, which impacts the two-phase flow dynamics. We show that, in addition to the balance between the relevant forces driving the dynamics, local regions of crystalline order in the beadpack (crystallites) affect the stability of the invading front. This work provides insights into how disorder on multiple length scales in porous media can interact with viscous, capillary, and gravitational forces to determine the stability and dynamics of immiscible fluid interfaces.
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Reis, Paula Kozlowski Pitombeira & Måløy, Knut Jørgen
(2025).
Drainage front width in a three-dimensional random porous medium under gravitational and capillary effects.
http://arxiv.org/abs/cond-mat.
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A theoretical approach to estimating stable drainage front widths in three-dimensional random porous media under gravitational and capillary effects is presented. Based on the frontier of the infinite cluster in gradient percolation, we propose an expression for the 3D front width dependent on the pore-network topology, the distribution of capillary pressure thresholds for the pore throats, the stabilizing capillary pressure gradient, the average pore size, and the correlation length critical exponent from percolation in three dimensions. Theoretical predictions are successfully compared to numerical results obtained with a bond invasion-percolation model for a wide range of drainage flow parameters.
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Khobaib, Khobaib; Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Toussaint, Renaud; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2025).
Gravity stabilized drainage in porous media with controlled disorder.
Physical Review Research (PRResearch).
7(2).
doi:
10.1103/PhysRevResearch.7.023040.
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This work presents an experimental, numerical, and theoretical investigation of slow drainage processes in porous media, focusing on systematic variations in pore-scale disorder. We examine a system comprising a monolayer of cylinders in a quasi-two-dimensional (2D) geometry, where the medium's disorder is controlled via a disorder parameter, 𝜀. By systematically altering 𝜀, we randomly shift the positions of the cylinders and analyze the resulting effects on the gravity stabilized invasion front. Our results show that increasing 𝜀 has a significant impact on the stable width of the invasion front, with this width scaling with the disorder parameter according to an exponent 𝛽=0.57, which closely matches the theoretical value predicted by percolation theory for 2D systems. Additionally, we derive a reciprocal relationship between the dimensionless fluctuation number and the disorder parameter 𝜀. Moreover, we find a correlation between the invasion front width and the size of trapped clusters in the system, and we explore how pore disorder affects the air saturation left behind the invasion front. Both our experimental and numerical findings exhibit exponent values that align with theoretical scaling predictions. This study advances the current understanding of multiphase flows in porous media by specifically addressing the influence of pore-scale disorder on the morphology of invasion fronts.
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Birgisson, Hilmar Yngvi; Xu, Yao; Moura, Marcel; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2025).
Mapping dissolved carbon in space and time: An experimental technique for the measurement of pH and total carbon concentration in density driven convection of CO2 dissolved in water.
Advances in Water Resources.
ISSN 0309-1708.
198.
doi:
10.1016/j.advwatres.2025.104916.
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Abbasov, Rashad; Fahs, Marwan; Younes, Anis; Nowamooz, Hossein; Måløy, Knut Jørgen & Toussaint, Renaud
(2024).
Modeling rainfall-induced landslide using the concept of local factor of safety: Uncertainty propagation and sensitivity analysis.
Computers and geotechnics.
ISSN 0266-352X.
167.
doi:
10.1016/j.compgeo.2024.106102.
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Rainfall-induced landslides (RILS) are commonly investigated using hydro-mechanical models with the concept of local factor of safety. The inputs of these models are usually prone to uncertainties. An uncertainty analysis is required to investigate how uncertainties propagate through the model and impact the predictions. An appropriate strategy for uncertainty propagation analysis is suggested in this work to deal with nonlinearity and high dimensionality of RILS problems. It proceeds by performing a sensitivity analysis in two steps. A screening technique is first applied to eliminate insignificant parameters. Then, a global sensitivity analysis is performed to rank the parameters by order of importance. The Sobol indices are used as sensitivity metrics. The polynomial chaos expansion is used to compute the Sobol indices. The proposed strategy is first applied to a hypothetical benchmark and then to a more realistic configuration where prior knowledge of parameters and type of soil are considered. The results show that, when prior knowledge of soil is available, the most important parameters are the coefficient of cohesion, friction angle and air entry pressure head, respectively. The results also show that 10% uncertainty on these parameters leads to about 20% uncertainty on the prediction of slope stability.
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Thorens, Louison; Måløy, Knut Jørgen; Flekkøy, Eirik Grude; Sandnes, Bjørnar; Bourgoin, Mickaël & Santucci, Stephane F A
(2023).
Capillary washboarding during slow drainage of a frictional fluid.
Soft Matter.
ISSN 1744-683X.
doi:
10.1039/d3sm00717k.
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Numerous natural and industrial processes involve the mixed displacement of liquids, gases and granular materials through confining structures. However, understanding such three-phase flows remains a formidable challenge, despite their tremendous economic and environmental impact. To unveil the complex interplay of capillary and granular stresses in such flows, we consider here a model configuration where a frictional fluid (an immersed sedimented granular layer) is slowly drained out of a horizontal capillary. Analyzing how liquid/air menisci displace particles from such granular beds, we reveal various drainage patterns, notably the periodic formation of dunes, analogous to road washboard instability. Considering the competitive role of friction and capillarity, a 2D theoretical approach supported by numerical simulations of a meniscus bulldozing a front of particles provides quantitative criteria for the emergence of those dunes. A key element is the strong increase of the frictional forces, as the bulldozed particles accumulate and bend the meniscus horizontally. Interestingly, this frictional enhancement with the attack angle is also crucial in small-legged animals' locomotion over granular media.
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Zhang, Dawang; Campbell, James; Eriksen, Jon Alm; Flekkøy, Eirik Grude; Måløy, Knut Jørgen & MacMinn, Christopher W.
[Show all 7 contributors for this article]
(2023).
Frictional fluid instabilities shaped by viscous forces.
Nature Communications.
14(1).
doi:
10.1038/s41467-023-38648-6.
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Multiphase flows involving granular materials are complex and prone to pattern formation caused by competing mechanical and hydrodynamic interactions. Here we study the interplay between granular bulldozing and the stabilising effect of viscous pressure gradients in the invading fluid. Injection of aqueous solutions into layers of dry, hydrophobic grains represent a viscously stable scenario where we observe a transition from growth of a single frictional finger to simultaneous growth of multiple fingers as viscous forces are increased. The pattern is made more compact by the internal viscous pressure gradient, ultimately resulting in a fully stabilised front of frictional fingers advancing as a radial spoke pattern.
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Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Rikvold, Per Arne; Toussaint, Renaud & Flekkøy, Eirik Grude
[Show all 7 contributors for this article]
(2023).
A simplified pore-scale model for slow drainage including film-flow effects.
Advances in Water Resources.
ISSN 0309-1708.
182.
doi:
10.1016/j.advwatres.2023.104580.
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Liquid-filled corners and capillary bridges can establish networks connecting seemingly isolated clusters during drainage in porous media. Coupled with drainage through the bulk of pores and throats, the flow through these networks constitutes a secondary drainage mechanism that can significantly affect fluid configurations and residual saturations. In order to investigate the prevalence of this drainage mechanism, we propose a quasi-static pore-network model based on modifying the trapped-cluster-identification algorithm in an invasion-percolation model. With the modification, wetting-phase connectivity is provided by direct successions of pores and throats, represented by sites and bonds, as well as by chains of interconnected capillary bridges. The advancement of the fluid interface in the porous matrix is determined by the bonds’ invasion thresholds and local capillary pressure values, calculated taking into consideration gravitational effects. With the proposed model, experimentally verified phenomena related to slow drainage in granular porous media are reproduced, showing good qualitative agreement.
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Flekkøy, Eirik Grude; Sandnes, Bjørnar & Måløy, Knut Jørgen
(2023).
Shape of a frictional fluid finger.
Physical Review Fluids.
8(11).
doi:
10.1103/PhysRevFluids.8.114302.
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Frictional fluid dynamics describes the displacement patterns that arise when a confined mixture of liquid and grains are displaced by an immiscible fluid under pressures that are too small to cause drainage into single pores. The flow, which is governed by solid friction and capillary forces, thus bulldozes the grains into compaction fronts which give rise to propagating fingers that eventually interact to create a range of patterns, including labyrinthine ones. We derive an analytic description that successfully reproduces the experimental results for the shape of a single finger as well as the compaction front profile. The theory thus depends on only one fitting parameter.
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Brodin, Joachim Falck; Moura, Marcel; Toussaint, Renaud; Måløy, Knut Jørgen & Rikvold, Per Arne
(2022).
Visualization by optical fluorescence of two-phase flow in a three-dimensional porous medium.
Journal of Physics: Conference Series (JPCS).
ISSN 1742-6588.
2241.
doi:
10.1088/1742-6596/2241/1/012004.
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Abstract Slow flow of a single fluid through a porous medium is well understood on a macroscopic level through Darcy’s law, a linear relation between flow rate and a combination of pressure differences, viscosity, and gravitational forces. Two-phase flow is complicated by the interface separating the fluids, but understanding of two-dimensional, two-phase flow has been obtained from experiments using transparent cells. In most three-dimensional media, however, visual observation is difficult. Here, we present preliminary results of experiments on a model medium consisting of randomly packed glass spheres, in which one fluorescent liquid invades another. By refractive index matching and scanning with a sheet-shaped laser beam, we obtain slices of the flow patterns, which we combine into three-dimensional pictures. We observe a compact region of invading fluid, surrounded by finger-like protrusions. The compact region becomes more dominant with increasing invader flow rate. The patterns are theoretically analyzed in terms of the interplay between gravitational, viscous, and capillary forces.
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Brodin, Joachim Falck; Rikvold, Per Arne; Moura, Marcel; Toussaint, Renaud & Måløy, Knut Jørgen
(2022).
Competing Gravitational and Viscous Effects in 3D Two-Phase Flow Investigated With a Table-Top Optical Scanner.
Frontiers in Physics.
10.
doi:
10.3389/fphy.2022.936915.
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We present experiments and theory describing the transition from viscosity-stabilized flow to gravitationally unstable fingering for two-phase flow in a cubic box, filled with a synthetic porous medium. Observation is made possible by the use of our newly developed table-top 3D scanner based on optical index matching and laser-induced fluorescence, which is described in detail. In the experiment, a more dense, more viscous fluid injected at a fixed flow rate from a point source at the top of the flow cell displaces a less viscous, less dense fluid. We observe a stable invasion zone near the inlet, which increases in size with increasing flow rates, and presents initially a close to hemispherical shape. At later times, the invasion front transits to an unstable mode and a fingering flow regime. The transition occurs at a predicted critical radius, Rc, corresponding to the zero of the combined viscous and gravitational pressure gradient.
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Vincent-Dospital, Tom Yannick Yves; Moura, Marcel; Toussaint, Renaud & Måløy, Knut Jørgen
(2022).
Stable and unstable capillary fingering in porous media with a gradient in grain size.
Communications Physics.
5(1).
doi:
10.1038/s42005-022-01072-1.
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Multiphase flows in complex porous networks occur in many natural processes and engineering applications. We present an analytical, experimental and numerical investigation of slow drainage in porous media that exhibit a gradient in grain size. We show that the effect of such structural gradient is similar to that of an external force field on the obtained drainage patterns, when it either stabilises or destabilises the invasion front. For instance, gravity can enhance or reverse the drainage pattern in graded porous media. In particular, we show that the width of stable drainage fronts scales both with the spatial gradient of the necessary pressure for pore invasion and with the local distribution of this (disordered) threshold. The scaling exponent results from percolation theory and is − 0.57 for 2D systems. Overall, introducing a dimensionless Fluctuation number, we propose a unifying theory for the up-scaling of dual immiscible fluid flows covering most classical scenarii.
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Campbell, James; Sandnes, Bjørnar; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2022).
Dynamics of Dendritic Ice Freezing in Confinement.
Crystal Growth & Design.
ISSN 1528-7483.
22(4),
p. 2433–2440.
doi:
10.1021/acs.cgd.1c01488.
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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 thermally conductive glass are used alone and in combination, at temperatures between −10.6 and −4.8 °C, with separations between 17 and 135 μm wide. No effect of confinement was detected for propagation on glass surfaces, but a possible slowing of propagation speed was seen between insulating plates. The pattern of dendritic growth was also studied, with a change from curving to straight dendrites being strongly associated with a switch from a glass to a plastic substrate.
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Eriksen, Fredrik Kvalheim; Moura, Marcel; Jankov, Mihailo; Turquet, Antoine Leo & Måløy, Knut Jørgen
(2022).
Transition from viscous fingers to compact displacement during unstable drainage in porous media.
Physical Review Fluids.
7(1).
doi:
10.1103/PhysRevFluids.7.013901.
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We describe a crossover from the viscous fingering instability to a compact invasion regime during viscously unstable drainage of porous media, and we investigate the underlying mechanisms of this compact fluid displacement. The study is based on a series of drainage experiments in a radial porous Hele-Shaw cell where we systematically vary the viscosity of the defending (wetting) fluid and the overpressure of the invading (nonwetting) fluid to map out the resulting invasion structures as a function of viscosity ratio and injection pressure. We show that above a threshold of injection pressure and viscosity ratio a more stable and compact invasion structure emerges within the viscous fingering patterns, i.e., a roughly circular displacement with viscous fingers on the outside. The onset of the stable displacement is found to begin at a rather low viscosity ratio M between the invading and defending fluids, i.e., when M≥10−3 for injection pressures of 3–5 kPa. We find that the ratio between the length of the outer fingers and the size of the compact invasion scales with the viscosity ratio and approaches a more or less constant value during growth, resulting in structures with proportionate growth and larger compact invasions for higher viscosity ratios. As opposed to the viscous fingering instability, we describe rich ganglion dynamics within the compact invasion structures and show that the pressure gradient is not screened by the outer fingers.
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Thorens, Louison; Viallet, Maud; Måløy, Knut Jørgen; Bourgoin, Mickael & Santucci, Stephane
(2021).
Discharge of a 2D magnetic silo.
The European Physical Journal Conferences.
ISSN 2101-6275.
249,
p. 03017–03017.
doi:
10.1051/epjconf/202124903017.
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We investigate experimentally the discharge of a 2D-silo, a Hele-Shaw cell, filled with a mono layer of ferromagnetic grains submitted to an external magnetic field B perpendicular to the cell plane. In this case the magnetic pair interactions are repulsive. We show that the granular flow rate decreases systematically with the amplitude of the external magnetic field applied. Interestingly, while the output flow rate remains constant during an experiment, we reveal very large spatio-temporal fluctuations of the packing density within the cell, particularly evident for magnetic field of high amplitudes.
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Vincent-Dospital, Tom; Cochard, Alain; Santucci, Stephane; Måløy, Knut Jørgen & Toussaint, Renaud
(2021).
Thermally activated intermittent dynamics of creeping crack fronts along disordered interfaces.
Scientific Reports.
11.
doi:
10.1038/s41598-021-98556-x.
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Abstract We present a subcritical fracture growth model, coupled with the elastic redistribution of the acting mechanical stress along rugous rupture fronts. We show the ability of this model to quantitatively reproduce the intermittent dynamics of cracks propagating along weak disordered interfaces. To this end, we assume that the fracture energy of such interfaces (in the sense of a critical energy release rate) follows a spatially correlated normal distribution. We compare various statistical features from the obtained fracture dynamics to that from cracks propagating in sintered polymethylmethacrylate (PMMA) interfaces. In previous works, it has been demonstrated that such an approach could reproduce the mean advance of fractures and their local front velocity distribution. Here, we go further by showing that the proposed model also quantitatively accounts for the complex self-affine scaling morphology of crack fronts and their temporal evolution, for the spatial and temporal correlations of the local velocity fields and for the avalanches size distribution of the intermittent growth dynamics. We thus provide new evidence that an Arrhenius-like subcritical growth is particularly suitable for the description of creeping cracks.
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Vincent-Dospital, Tom; Toussaint, Renaud & Måløy, Knut Jørgen
(2021).
Heat Emitting Damage in Skin: A Thermal Pathway for Mechanical Algesia.
Frontiers in Neuroscience.
ISSN 1662-4548.
15.
doi:
10.3389/fnins.2021.780623.
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Mechanical pain (or mechanical algesia) can both be a vital mechanism warning us for dangers or an undesired medical symptom important to mitigate. Thus, a comprehensive understanding of the different mechanisms responsible for this type of pain is paramount. In this work, we study the tearing of porcine skin in front of an infrared camera, and show that mechanical injuries in biological tissues can generate enough heat to stimulate the neural network. In particular, we report local temperature elevations of up to 24°C around fast cutaneous ruptures, which shall exceed the threshold of the neural nociceptors usually involved in thermal pain. Slower fractures exhibit lower temperature elevations, and we characterise such dependency to the damaging rate. Overall, we bring experimental evidence of a novel—thermal—pathway for direct mechanical algesia. In addition, the implications of this pathway are discussed for mechanical hyperalgesia, in which a role of the cutaneous thermal sensors has priorly been suspected. We also show that thermal dissipation shall actually account for a significant portion of the total skin's fracture energy, making temperature monitoring an efficient way to detect biological damages.
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Vincent-Dospital, Tom; Toussaint, Renaud; Cochard, Alain; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2021).
Thermal dissipation as both the strength and weakness of matter. A material failure prediction by monitoring creep.
Soft Matter.
ISSN 1744-683X.
17(15),
p. 4143–4150.
doi:
10.1039/d0sm02089c.
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In any domain involving some stressed solids, that is, from seismology to general engineering, the strength of matter is a paramount feature to understand. We here discuss the ability of a simple thermally activated sub-critical model, which includes the auto-induced thermal evolution of cracks tips, to predict the catastrophic failure of a vast range of materials. It is in particular shown that the intrinsic surface energy barrier, for breaking the atomic bonds of many solids, can be easily deduced from the slow creeping dynamics of a crack. This intrinsic barrier is however higher than the macroscopic load threshold at which brittle matter brutally fails, possibly as a result of thermal activation and of a thermal weakening mechanism. We propose a novel method to compute this macroscopic energy release rate of rupture, Ga, solely from monitoring slow creep, and we show that this reproduces the experimental values within 50% accuracy over twenty different materials, and over more than four decades of fracture energy.
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Vehel, Victor Levi dit; Hatani, Tokahiro; Vanel, Loïc; Måløy, Knut Jørgen & Ramos, Osvanny
(2021).
Dilation as a precursor in a continuous granular fault.
The European Physical Journal Conferences.
ISSN 2101-6275.
249.
doi:
10.1051/epjconf/202124915006.
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We analyze the dilation of the system in a cylindrical granular fault consisting of one single layer of disks submitted to both normal pressure and continuous and slow shear, which results in intermittent and sudden energy release events that reproduce the main laws of seismicity. The dilation of the system can be separated into two parts: a smooth increase of dilation, plus sudden changes both contracting and dilating the medium, which are correlated to abrupt jumps -both positive and negative- in the measured resisting torque. We explain the four possible (and existing) general scenarios combining those two variables: dilation jumps and torque jumps, thanks to the assumption of an optimal local angle in the direction of force chains, and each reorganization of the structure as a replacement of the force chain holding most of the applied stress. The average rate of increase of global dilation varies monotonically with the size of the energy release event, making dilation a plausible candidate to predict catastrophic events in such earthquake-like systems.
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Thorens, Louison; Måløy, Knut Jørgen; Santucci, Stephane & Bourgoin, Mickael
(2021).
Tamming the Janssen effect.
The European Physical Journal Conferences.
ISSN 2101-6275.
249,
p. 08004–08004.
doi:
10.1051/epjconf/202124908004.
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We investigate both experimentally and theoretically the apparent mass of a ferromagnetic granular assembly filling a cylindrical container and submitted to a magnetic field B , aligned vertically along the silo. We show that the mass of the ferromagnetic granular column depends strongly on the applied magnetic field. Notably, our measurements deviate strongly from the exponential saturation of the measured mass as a function of the true mass of the grain packing, as predicted by Janssen [H.A. Janssen, Vereins Eutscher Ingenieure Zeitschrift, 1045 (1895)]. In particular, the measured mass of tall columns decreases systematically as the amplitude of the magnetic field increases. We rationalize our experimental findings by considering the induced magnetic dipole-dipole interactions within the whole packing. We show the emergence of a global magnetic radial force along the walls of the silos, fully determined by the external magnetic field. The resulting tunable frictional interactions allows a full control of the effective mass of the ferromagnetic granular column.
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Måløy, Knut Jørgen; Moura, Marcel; Hansen, Alex; Flekkøy, Eirik Grude & Toussaint, Renaud
(2021).
Burst Dynamics, Upscaling and Dissipation of Slow Drainage in Porous Media.
Frontiers in Physics.
9.
doi:
10.3389/fphy.2021.796019.
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We present a theoretical and experimental investigation of drainage in porous media. The study is limited to stabilized fluid fronts at moderate injection rates, but it takes into account capillary, viscous, and gravitational forces. In the theoretical framework presented, the work applied on the system, the energy dissipation, the final saturation and the width of the stabilized fluid front can all be calculated if we know the dimensionless fluctuation number, the wetting properties, the surface tension between the fluids, the fractal dimensions of the invading structure and its boundary, and the exponent describing the divergence of the correlation length in percolation. Furthermore, our theoretical description explains how the Haines jumps’ local activity and dissipation relate to dissipation on larger scales.
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Thorens, Louison; Måløy, Knut Jørgen; Santucci, Stephane & Bourgoin, Mickael
(2021).
Magnetic Janssen effect.
Nature Communications.
12.
doi:
10.1038/s41467-021-22722-y.
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Abstract A pile of grains, even when at rest in a silo, can display fascinating properties. One of the most celebrated is the Janssen effect, named after the pioneering engineer who explained the pressure saturation at the bottom of a container filled with corn. This surprising behavior arises because of frictional interactions between the grains through a disordered network of contacts, and the vessel lateral walls, which partially support the weight of the column, decreasing its apparent mass. Here, we demonstrate control over frictional interactions using ferromagnetic grains and an external magnetic field. We show that the anisotropic pairwise interactions between magnetized grains result in a radial force along the walls, whose amplitude and direction is fully determined by the applied magnetic field. Such magnetic Janssen effect allows for the fine tuning of the granular column apparent mass. Our findings pave the way towards the design of functional jammed materials in confined geometries, via a further control of both their static and dynamic properties.
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Xu, Le; Szymczak, Piotr; Toussaint, Renaud; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2020).
Dissolution phase diagram in radial geometry.
Frontiers in Physics.
8.
doi:
10.3389/fphy.2020.00369.
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Fractures play an important role as flow paths in porous media. When an undersaturated reactive fluid is flowing in a fracture, the dissolution process will alter the flow paths locally. Dissolution patterns grow slowly, but they may lead to a dramatic reorganization of the flow. Here, we study dissolution in a radial geometry, which is relevant for a number of practical applications, e.g., the acidization of oil reservoirs. Different dissolution patterns are presented in a phase diagram with the Péclet and Damköhler numbers as parameters. We also analyze quantitatively the density of wormholes and the relation between the aperture roughness and the ramified patterns.
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Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Toussaint, Renaud
(2020).
Intermittent Dynamics of Slow Drainage Experiments in Porous Media: Characterization Under Different Boundary Conditions.
Frontiers in Physics.
7.
doi:
10.3389/fphy.2019.00217.
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The intermittent dynamics of slow drainage flows in a porous medium is studied experimentally. This kind of two-phase flow is characterized by a rich burst activity and our setup allows us to characterize those bursts directly via images of the flow and pressure measurements. Two different boundary conditions were analyzed: controlled withdrawal rate (CWR) and controlled imposed pressure (CIP). We have characterized geometrical and statistical properties of the bursts from images and pressure measurements. We have shown that in spite of leading to similar final invasion patterns, some dynamical features of the invasion differ considerably between the CWR and CIP boundary conditions. In particular, their pressure signatures are very distinct, which then translates into very distinct features on the power spectrum density of the pressure signals. A fully integrable analytical framework is presented which successfully describes the scaling features of the power spectrum for the CIP case.
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Vincent-Dospital, Tom; Toussaint, Renaud; Santucci, Stephane; Vanel, Loïc; Bonamy, Daniel & Hattali, Lamine
[Show all 9 contributors for this article]
(2020).
How heat controls fracture: the thermodynamics of creeping and avalanching cracks.
Soft Matter.
ISSN 1744-683X.
16(41),
p. 9590–9602.
doi:
10.1039/D0SM01062F.
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While of paramount importance in material science, the dynamics of cracks still lacks a complete physical explanation. The transition from their slow creep behavior to a fast propagation regime is a notable key, as it leads to full material failure if the size of a fast avalanche reaches that of the system. We here show that a simple thermodynamics approach can actually account for such complex crack dynamics, and in particular for the non-monotonic force-velocity curves commonly observed in mechanical tests on various materials. We consider a thermally activated failure process that is coupled with the production and the diffusion of heat at the fracture tip. In this framework, the rise in temperature only affects the sub-critical crack dynamics and not the mechanical properties of the material. We show that this description can quantitatively reproduce the rupture of two different polymeric materials (namely, the mode I opening of polymethylmethacrylate (PMMA) plates, and the peeling of pressure sensitive adhesive (PSA) tapes), from the very slow to the very fast fracturing regimes, over seven to nine decades of crack propagation velocities. In particular, the fastest regime is obtained with an increase of temperature of thousands of kelvins, on the molecular scale around the crack tip. Although surprising, such an extreme temperature is actually consistent with different experimental observations that accompany the fast propagation of cracks, namely, fractoluminescence (i.e., the emission of visible light during rupture) and a complex morphology of post-mortem fracture surfaces, which could be due to the sublimation of bubbles.
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Vincent-Dospital, Tom; Toussaint, Renaud; Cochard, Alain; Måløy, Knut Jørgen & Flekkøy, Eirik Grude
(2020).
Thermal weakening of cracks and brittle-ductile transition of matter: A phase model.
PHYSICAL REVIEW MATERIALS.
4(2).
doi:
10.1103/PhysRevMaterials.4.023604.
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We present a model for the thermally activated propagation of cracks in elastic matrices. The propagation is considered as a subcritical phenomenon, the kinetics of which is described by an Arrhenius law. In this law, we take the thermal evolution of the crack front into account, assuming that a portion of the released mechanical energy is transformed into heat in a zone surrounding the tip. We show that such a model leads to a two-phase crack propagation: the first phase at low velocity in which the temperature elevation is of little effect and the propagation is mainly governed by the mechanical load and by the toughness of the medium, and the second phase in which the crack is thermally weakened and propagates at greater velocity. We illustrate, with numerical simulations of mode I cracks propagating in thin disordered media, how such a dual behavior can explain the usual stick-slip in brittle fracturing. In addition, we predict the existence of a limiting ambient temperature above which the weakened phase ceases to exist and we propose this critical phenomenon as a novel explanation for the brittle-ductile transition of solids.
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Ayaz, Atta-Ul-Monem; Toussaint, Renaud; Schäfer, Gerhard & Måløy, Knut Jørgen
(2020).
Gravitational and Finite-Size Effects On Pressure Saturation Curves During Drainage.
Water Resources Research.
ISSN 0043-1397.
56(10).
doi:
10.1029/2019WR026279.
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We experimentally and numerically study the influence of gravity and finite-size effects on the pressure-saturation relationship in a given porous medium during slow drainage. The effect of gravity is systematically varied by tilting the system relative to the horizontal configuration. The use of a quasi two-dimensional porous media allows for direct spatial monitoring of the saturation. Exploiting the fractal nature of the invasion structure, we obtain a relationship between the final saturation and the Bond number SFnw = Bo0.097 using percolation theory. Moreover, the saturation, pressure, and Bond number are functionally related, allowing for pressure-saturation curves to collapse onto a single master curve, parameterized by the representative elementary volume size and by the Bond and capillary numbers. This allows to upscale the pressure-saturation curves measured in a laboratory to large representative elementary volumes used in reservoir simulations. The large-scale behavior of these curves follows a simple relationship, depending on Bond and capillary numbers, and on the flow direction. The size distribution of trapped defending fluid clusters is also shown to contain information on past fluid flow and can be used as a marker of past flow speed and direction.
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Olsen, Kristian Stølevik; Flekkøy, Eirik Grude; Angheluta, Luiza; Campbell, James; Måløy, Knut Jørgen & Sandnes, Bjørnar
(2019).
Geometric universality and anomalous diffusion in frictional fingers.
New Journal of Physics.
21(6).
doi:
10.1088/1367-2630/ab25bf.
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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 checked using updated numerical simulation algorithms for frictional fingers. We also propose a theoretical model for anomalous diffusion in these patterns, and discuss the role of diffusion as a tool to classify geometry.
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Turquet, Antoine Leo; Toussaint, Renaud; Eriksen, Fredrik Kvalheim; Daniel, Guillaume; Lengline, Oliver & Flekkøy, Eirik Grude
[Show all 7 contributors for this article]
(2019).
Source localization of microseismic emissions during pneumatic fracturing.
Geophysical Research Letters.
ISSN 0094-8276.
46(7),
p. 3726–3733.
doi:
10.1029/2019GL082198.
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Localization of signals is a widely applied technique used in different areas of science telecommunication, medicine, or seismology. In this work, we study microseismic emissions due to stick‐slip events during pneumatic fracture in a transparent setup at laboratory scale and apply a localization method “Estimated Source Energy Homogeneity.” The seismic location results are compared with the image correlation results for displacement maps corresponding to the event times. We have observed (using optics and acoustics) that the movement starts inside the porous medium and progresses toward the channel tips, eventually causing channels to grow further. This finding could be of interest in understanding fluid‐induced earthquake nucleation processes. Similar to in‐site applications of pneumatic or fluid‐related fracturing, it shows that the area influenced extends beyond the fracture tips. This also shows why even after the end of pumping, we may get earthquakes, such as in the Basel case (Haring et al., 2008, https://doi.org/10.1016/j.geothermics.2008.06.002).
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Flekkøy, Eirik Grude; Moura, Marcel & Måløy, Knut Jørgen
(2019).
Dynamics of the Fluctuating Flying Chain.
Frontiers in Physics.
7,
p. 1–15.
doi:
10.3389/fphy.2019.00187.
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A chain which is made to flow from a container, forms a striking arch that rises well above the container top. This phenomenon is caused by the well known Mould effect and is explained by a supply of momentum from the container, causing an upwards kick. Here we introduce a theory that allows for dynamic fluctuations of the chain and compare with corresponding simulations and experiments. The predictions for the chain velocity and fountain height agree well with experiments. We also explore the underlying mechanism for this momentum transfer for different chain models and find that it depends subtly on the nature of the chain as well as on the container.
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Moura, Marcel; Flekkøy, Eirik Grude; Måløy, Knut Jørgen; Schäfer, Gerhard & Toussaint, Renaud
(2019).
Connectivity enhancement due to film flow in porous media.
Physical Review Fluids.
4(9).
doi:
10.1103/PhysRevFluids.4.094102.
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We study the effects of connectivity enhancement due to film flow phenomena on the drainage of an artificial porous medium and the relative influence of gravity for such effects. The medium is initially fully saturated with a liquid (wetting phase), which is displaced by air (nonwetting phase). Our setup allows us to directly visualize the dynamics of the flow and, in particular, to pinpoint which pore invasion events are due to film flow phenomena. We have observed the formation of an active zone behind the liquid-air interface, inside which film flow drainage events are more likely to occur. Understanding the basic mechanisms of film flow in artificial porous media is of relevance for the analysis of real three-dimensional porous systems, in which gravity cannot be neglected and film flow is bound to be present.
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Lherminier, Sébastien; Planet, Ramon; Vehel, V Levy Dit; Simon, Gilles; Vanel, Loïc & Måløy, Knut Jørgen
[Show all 7 contributors for this article]
(2019).
Continuously Sheared Granular Matter Reproduces in Detail Seismicity Laws.
Physical Review Letters.
ISSN 0031-9007.
122(21),
p. 218501-1–218501-6.
doi:
10.1103/PhysRevLett.122.218501.
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We introduce a shear experiment that quantitatively reproduces the main laws of seismicity. By continuously and slowly shearing a compressed monolayer of disks in a ringlike geometry, our system delivers events of frictional failures with energies following a Gutenberg-Richter law. Moreover, foreshocks and aftershocks are described by Omori laws and interevent times also follow exactly the same distribution as real earthquakes, showing the existence of memory of past events. Other features of real earthquakes qualitatively reproduced in our system are both the existence of a quiescence preceding some main shocks, as well as magnitude correlations linked to large quakes. The key ingredient of the dynamics is the nature of the force network, governing the distribution of frictional thresholds.
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Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Pierce, Kevin; Måløy, Knut Jørgen & Linga, Gaute
(2026).
Secondary imbibition in 2D porous media: The role of flow direction in trapping.
Full text in Research Archive
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Reis, Paula Kozlowski Pitombeira; Flekkøy, Eirik Grude; Toussaint, Renaud & Måløy, Knut Jørgen
(2026).
Linear Response Theory of Front-Back Contraction During a Single Haines Jump.
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Reis, Paula Kozlowski Pitombeira & Måløy, Knut Jørgen
(2026).
A Theoretical Model for Stable Drainage Fronts in 3D Porous Media.
Full text in Research Archive
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Moura, Marcel; Hansen, Alex; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2026).
POROUS MATTER: PoreLab's sci-art adventures in Romania.
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Xu, Yao; Moura, Marcel; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2025).
Quantification for density-driven convection of CO2 in water.
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Lanza, Federico; Linga, Gaute; Barras, Fabian; Khobaib, Khobaib; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2025).
From Carbopol to magma: challenges in complex flows through porous and confined media.
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Moura, Marcel; Kern, Vanessa Ruth; Olsen, Pål Eivind; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude
(2025).
Complex fluids in confinement: spreading in a wedge and instabilities in textured lifted Hele-Shaw cells.
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Moura, Marcel; Kern, Vanessa Ruth; Olsen, Pål Eivind; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude
(2025).
Fluidos complexos em confinamento: espalhamento em cunha e instabilidades em células de Hele-Shaw texturizadas.
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Reis, Paula Kozlowski Pitombeira & Måløy, Knut Jørgen
(2025).
Drainage fronts in two and three-dimensional random porous media under gravitational and capillary effects.
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Reis, Paula Kozlowski Pitombeira & Måløy, Knut Jørgen
(2025).
Numerical investigation of invasion-front characteristics during stable drainage in a three-dimensional porous medium.
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Kern, Vanessa Ruth; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude
(2024).
Linking anomalous diffusion and rheology for a droplet spreading in a corner: A rheometer for power-law liquids.
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Moura, Marcel; Hansen, Alex; Måløy, Knut Jørgen & Flekkøy, Eirik Grude
(2024).
POROUS MATTER: Our sci-art adventures in Romania.
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Moura, Marcel; Kern, Vanessa Ruth; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude
(2024).
Linking anomalous diffusion and rheology for a droplet spreading in a corner: A rheometer for power-law liquids.
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Moura, Marcel; Hansen, Alex; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2024).
POROUS MATTER: PoreLab's sci-art adventures in Romania.
Full text in Research Archive
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Moura, Marcel; Eriksen, Fredrik Kvalheim; Jankov, Mihailo; Turquet, Antoine Leo; Hansen, Alex & Måløy, Knut Jørgen
(2024).
Experiments on transient and steady-state flows in porous media: the transition from viscous fingers to compact displacement during unstable drainage flows.
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Reis, Paula Kozlowski Pitombeira; Vincent-Dospital, Tom Yannick Yves; Toussaint, Renaud & Måløy, Knut Jørgen
(2024).
Modeling drainage in porous media with stratified gradient in pore sizes.
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Brodin, Joachim Falck; Rikvold, Per Arne; Moura, Marcel; Pierce, James Kevin; Toussaint, Renaud & Måløy, Knut Jørgen
(2023).
Experimental investigation of two phase flow with a table top optical scanner: the competition between viscous and gravitational effects under different boundary conditions.
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Khobaib, Khobaib; Reis, Paula Kozlowski Pitombeira; Jankov, Mihailo; Moura, Marcel & Måløy, Knut Jørgen
(2023).
Experimental studies of slow drainage in porous media: Effect of the randomness of the porous medium on the fluid flow.
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Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Rikvold, Per Arne; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2023).
A simplified pore-scale model for drainage including film flow effects.
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Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Rikvold, Per Arne; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2023).
A modified-invasion-percolation model for drainage in quasi-2D porous media.
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Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Rikvold, Per Arne; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2023).
A simplified pore-scale model for slow drainage including film-flow effects.
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Moura, Marcel; Måløy, Knut Jørgen & Hansen, Alex
(2023).
Experiments on the motion of liquids and gases through porous materials.
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Moura, Marcel; Eriksen, Fredrik Kvalheim; Jankov, Mihailo; Turquet, Antoine Leo & Måløy, Knut Jørgen
(2022).
Transition from viscous Fingers to compact displacement during unstable drainage in porous media.
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Moura, Marcel; Eriksen, Fredrik Kvalheim; Jankov, Mihailo; Turquet, Antoine Léo & Måløy, Knut Jørgen
(2022).
Transition from viscous fingers to compact displacement during unstable drainage in porous media.
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Moura, Marcel; Vincent-Dospital, Tom Yannick Yves; Måløy, Knut Jørgen & Flekkøy, Eirik Grude
(2022).
Watching paint dry and the making of the non-Newtonian doughnut.
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Moura, Marcel; Brodin, Joachim Falck; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Rikvold, Per Arne
(2022).
Capillary pumping – the spreading of pollution in porous media.
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Moura, Marcel; Eriksen, Fredrik Kvalheim; Jankov, Mihailo; Turquet, Antoine Léo & Måløy, Knut Jørgen
(2022).
Transition from viscous fingers to compact displacement during unstable drainage in porous media.
Full text in Research Archive
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Moura, Marcel; Vincent-Dospital, Tom Yannick Yves; Måløy, Knut Jørgen & Flekkøy, Eirik Grude
(2022).
Watching paint dry and the making of the non-Newtonian doughnut.
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Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Rikvold, Per Arne
(2022).
Pore-scale modeling of film flow effects during gas-liquid drainage.
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Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Toussaint, Renaud
(2021).
Coffee is for drinking, tea is for porous media science: intermittent burst dynamics in slow drainage experiments in porous media.
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Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude; Schäfer, Gerhard & Toussaint, Renaud
(2020).
Thin film flow: fluid transport via thin liquid films in slow porous media flows.
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Rikvold, Per Arne; Brodin, Joachim Falck; Moura, Marcel Nascimento de & Måløy, Knut Jørgen
(2020).
Visualization of Two-phase Flow in a Three-dimensional Porous Medium.
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Rikvold, Per Arne; Brodin, Joachim Falck; Moura, Marcel Nascimento de & Måløy, Knut Jørgen
(2020).
Visualization of Two-phase Flow in a Three-dimensional Porous Medium.
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Brodin, Joachim Falck; Måløy, Knut Jørgen; Moura, Marcel; Toussaint, Renaud & Rikvold, Per Arne
(2020).
An experimental study of the interplay between viscous, capillary and gravitational forces in two-phase flow in a three-dimensional porous medium.
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We study the interplay between viscous, capillary and gravitational forces in two-phase flow in a threedimensional
porous medium, with the use of an optical scanner based on index-matched medium and fluorescent
fluids. A more viscous, denser, fluid is injected into a less viscous, less dense fluid in a 3D porous
medium, comprised of randomly packed glass beads of uniform size. We tune the injection rate over 10 experiments.
Experience from the 2D scenario suggests that with a slow injection rate capillary and gravitational
forces will dominate, and we should observe an unstable displacement and fingering. Conversely, with a high
injection rate, viscous forces will dominate, leading to a more stable displacement and a narrower invasion
front. How do the 2D findings hold up in the 3D scenario? We confirm the qualitative findings from the 2D
experiments and establish a clear regime change, from unstable to stable displacement. We seek to derive a
dimensionless number to quantify the relevant balance of forces and consider this number in relation to the
invasion pattern. We characterize the invasion by Minkowski-functionals and fractal dimensions and seek
relations between the found geometries and the derived dimensionless numbers.
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Turquet, Antoine Leo; Toussaint, Renaud; Eriksen, Fredrik Kvalheim; Flekkøy, Eirik Grude & Måløy, Knut Jørgen
(2020).
Reverse Engineering Earthquakes using Lab-scale Replicas: Application to Mw5. 5 2017 Pohang Earthquake.
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Måløy, Knut Jørgen; Eriksen, Jon Alm; Flekkøy, Eirik Grude; Toussaint, Renaud; Galland, Olivier & Sandnes, Bjørnar
(2019).
Pattern formation of frictional fingers in a gravitational potential.
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Brodin, Joachim Falck; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Moura, Marcel Nascimento de
(2025).
Stable and unstable invasion in two-phase flow in three-dimensional porous media.
Universitetet i Oslo.
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The thesis centers on three research papers [1–3], investigating the dynamics of two-phase flow in porous media using an custum built optical 3D scanner in lab experiments. We study cases where a more viscous, denser fluid is injected into a less viscous, lighter fluid from above at constant flow rates. The focus is on the transition from stabilized invasion at high flow rates to instability at lower rates, with emphasis on dynamics and structure near the transition. The first two papers examine injection from a single point source near the top of the invasion cell. Initially, the invading fluid expands spherically, occupying adjacent pores. High local velocity ensures that capillary pressure overcomes pore-throat thresholds, even in narrow passages. The front area grows as it advances and the local flow velocity at the front decreases, reducing capillary pressure. Downward protrusions gain additional capillary pressure from the hydrostatic column, favoring penetration in these regions. When the local flow rate is sufficiently low, the hydrostatic pressure build up in the protrusions is larger than the loss of viscous pressure as compared to the lagging front. At this stage, the invasion body transitions from a compact sphere to downward-extending branches, in what we label fingering. We derive a theoretical prediction for a flow-rate-dependent critical radius for this transition and compare it with experiments, finding good agreement. In the third paper, we modify the experiment to initiate invasion as a horizontal sheet, spanning the cross section of the cell. We analyze the transition to instability as a function of flow rate. A stability criterion for the fluid interface is developed based on pressure data, incorporating flow-velocity dependent two-phase permeability and the time derivative of the pressure drop. We observe that the invading fluid’s relative permeability varies with flow rate. We measure the effects of heterogeneities in the porous media caused by regions of crystalline structures with low local permeability. We label this effect pinning and derive a methodology to measure how the front geometry can be decomposed as a sum of fingering and pinning. Together, the work elucidates how multiscale disorder in porous media interacts with viscous, capillary, and gravitational forces to shape immiscible fluid interface stability and dynamics.
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Kristiansen, Kim Roger; Kjelstrup, Signe & Måløy, Knut Jørgen
(2024).
Thermal Driving Forces Across Membrane Systems: Energy Conversion and Water Purification.
Norges teknisk-naturvitenskapelige universitet.
ISSN 9788232680375.
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Among the energy sources used to fuel our modern industrialized society, industrial waste heat is among the most abundant and untapped. Wherever energy conversion from high-grade sources occurs, a fraction of this energy is lost in the form of low-grade heat energy. More than half of this heat energy is dissipated in media at temperatures below the atmospheric boiling point of water, where operation of traditional energy conversion methods is limited. In this work, we have focused on the application of thermal driving forces in membrane systems designed to convert low-grade heat energy into high-grade energy and to produce potable water in order to address the increasing scarcity of both high-grade energy and potable water. We have studied two different types of membrane system for this purpose: one is designed to simultaneously produce potable water and mechanical energy, while another is designed to convert heat into electrical energy. In our studies on the pressure-retarded membrane distillation (PRMD) process, most of the work revolved around the formulation of a non-equilibrium thermodynamics approach to generalize the already-existing models found in the membrane distillation (MD) literature. The rationale behind this was that membranes required for a feasible PRMD process would require conditions where effects not captured by traditional models may be important. By means of kinetic theory, a model was formulated to capture effects that cannot be neglected as membrane pores approach the nanometer scale. The findings in this work were combined with the development of a systematic non-equilibrium thermodynamics approach to decompose the transport coefficients of the membrane system on a macroscopic scale. In this framework, connections were made from physical models on the microscopic scale to measurable effects on the macroscopic scale. By means of appropriate approximations, we showed correspondence to the traditional MD models and demonstrated conditions under which the additional effects captured by the systematic non-equilibrium thermodynamics approach would be significant. Such conditions include nanoscale pore sizes and superhydrophobic membrane surfaces, both conditions beneficial for the performance of the PRMD process. A flow cell system was designed and built in order to obtain accurate flow measurements in response to tightly controlled temperatures and pressures across membranes. The apparatus was successfully commissioned with isobaric MD measurements, and measurements on the pressure-retarded process is planned as future work. Based on data from these measurements, further predictions were made on the potential of the PRMD process. It was found that the mechanical power density of PRMD could well approach values found in commercial pressure-retarded osmosis (PRO) if membranes are properly designed specifically for high PRMD performance. We highlight that the PRMD process has potable water as byproduct, and the pressure can be adjusted to regulate the balance between the production of mechanical energy and potable water. We also studied the potential for conversion of heat to electrical energy by means of thermogalvanic cells. We started the work by designing a flow cell to provide accurate measurements of the Seebeck coefficients of ion-exchange membranes. The experimental work combined with the theoretical developments allowed us to demonstrate a systematic approach to describe the coupled transport phenomena. A review paper was published where several results from the literature were all interpreted within the same theoretical framework. We concluded that more systematic work is needed to correlate the structural and chemical properties of ion-exchange membranes to their performance as components in thermogalvanic cells. To ensure that such studies are well-designed and that the results are correctly interpreted, the theoretical framework and conventions in the field need to be standardized. A perspective article was formulated as an attempt to set the record straight on the connections between different conventions used within non-equilibrium thermodynamics descriptions of thermogalvanic systems. We highlighted potential pitfalls where one would interpret a measured quantities to relate to purely theoretical non-measurables, and made recommendations for a standardized approach that makes only reference to measurable quantities. This work has contributed towards clarifying and standardizing theoretical descriptions of non-isothermal membrane systems, and provided new insights that can help direct the development of membrane systems both for the PRMD process and for thermogalvanic systems such as non-isothermal reverse electrodialysis. The methodology is presented in a transparent manner intended to provide the reader with the insight required to apply the same methodology to systems not specifically investigated in this work.
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Olsen, Kristian Stølevik & Måløy, Knut Jørgen
(2021).
Active and passive Brownian particles in complex environments.
Universitetet i Oslo.
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In his annus mirabilis, Albert Einstein published several important works that would strongly affect the future of physics. Among these was a work on Brownian motion – the random motion of small particles suspended in a liquid due to thermal fluctuations, as discovered by Robert Brown almost a century earlier. Today, stochastic modeling akin to that of Brownian motion is one of the main tools used to understand the complex motion of particles is disordered or otherwise non-trivial media on small scales. Applications range from the almost trivial, like a drop of dye slowly spreading in a stationary fluid, to the more complex, like cells migrating through the extra-cellular matrix or bacteria moving in a disordered media. In this thesis the stochastic dynamics of both passive (like the drop of dye) or active (like the bacterium) is studied in different complex environments. The interplay between a complex medium or a geometric confinement and the dynamics of active particles has become a field of great interest in recent years, with hopes of constructing biology-inspired machines and micro-robotics performing tasks like drug delivery.
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Published
Nov. 4, 2010 12:27 PM
- Last modified
Nov. 11, 2025 10:47 AM
