Imperial College London

Professor Omar K. Matar

Faculty of EngineeringDepartment of Chemical Engineering

Vice-Dean (Education), Faculty of Engineering
 
 
 
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Contact

 

+44 (0)20 7594 9618o.matar Website

 
 
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Assistant

 

Miss Nazma Mojid +44 (0)20 7594 3918

 
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Location

 

506ACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

264 results found

Pavlidis D, Xie Z, Percival JR, Gomes JLMA, Pain CC, Matar OKet al., 2014, Two- and three-phase horizontal slug flow simulations using an interface-capturing compositional approach, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 67, Pages: 85-91, ISSN: 0301-9322

Journal article

Xie Z, Pavlidis D, Percival JR, Gomes JLMA, Pain CC, Matar OKet al., 2014, Adaptive unstructured mesh modelling of multiphase flows, International Journal of Multiphase Flow, Vol: 67, Pages: 104-110, ISSN: 0301-9322

© 2013 Elsevier Ltd. Multiphase flows are often found in industrial and practical engineering applications, including bubbles, droplets, liquid film and waves. An adaptive unstructured mesh modelling framework is employed here to study interfacial flow problems, which can modify and adapt anisotropic unstructured meshes to better represent the underlying physics of multiphase problems and reduce computational effort without sacrificing accuracy. The numerical framework consists of a mixed control volume and finite element formulation, a 'volume of fluid'-type method for the interface capturing based on a compressive control volume advection method and second-order finite element methods. The framework also features a force-balanced algorithm for the surface tension implementation, minimising the spurious velocities often found in such flows. Numerical examples of the Rayleigh-Taylor instability and a rising bubble are presented to show the ability of this adaptive unstructured mesh modelling framework to capture complex interface geometries and also to increase the efficiency in multiphase flow simulations.

Journal article

Percival JR, Pavlidis D, Xie Z, Gomes JLM, Sakai M, Shigeto Y, Takahashi H, Matar OK, Pain CCet al., 2014, Control volume finite element modelling of segregation of sand and granular flows in fluidized beds, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 67, Pages: 191-199, ISSN: 0301-9322

Journal article

Xie Z, Pavlidis D, Percival JR, Gomes JLMA, Pain CC, Matar OKet al., 2014, Adaptive unstructured mesh modelling of multiphase flows, International Journal of Multiphase Flow, Vol: 67, Pages: 104-110, ISSN: 0301-9322

© 2013 Elsevier Ltd. Multiphase flows are often found in industrial and practical engineering applications, including bubbles, droplets, liquid film and waves. An adaptive unstructured mesh modelling framework is employed here to study interfacial flow problems, which can modify and adapt anisotropic unstructured meshes to better represent the underlying physics of multiphase problems and reduce computational effort without sacrificing accuracy. The numerical framework consists of a mixed control volume and finite element formulation, a 'volume of fluid'-type method for the interface capturing based on a compressive control volume advection method and second-order finite element methods. The framework also features a force-balanced algorithm for the surface tension implementation, minimising the spurious velocities often found in such flows. Numerical examples of the Rayleigh-Taylor instability and a rising bubble are presented to show the ability of this adaptive unstructured mesh modelling framework to capture complex interface geometries and also to increase the efficiency in multiphase flow simulations.

Journal article

Zadrazil I, Matar OK, Markides CN, Phase-locked measurements of gas-liquid horizontal flows, American Physical Society - Division of Fluid Dynamics

A flow of gas and liquid in a horizontal pipe can be described in terms of various flow regimes, e.g. wavy stratified, annular or slug flow. These flow regimes appear at characteristic gas and liquid Reynolds numbers and feature unique wave phenomena. Wavy stratified flow is populated by low amplitude waves whereas annular flow contains high amplitude and long lived waves, so called disturbance waves, that play a key role in a liquid entrainment into the gas phase (droplets). In a slug flow regime, liquid-continuous regions travel at high speeds through a pipe separated by regions of stratified flow. We use a refractive index matched dynamic shadowgraphy technique using a high-speed camera mounted on a moving robotic linear rail to track the formation and development of features characteristic for the aforementioned flow regimes. We show that the wave dynamics become progressively more complex with increasing liquid and gas Reynolds numbers. Based on the shadowgraphy measurements we present, over a range of conditions: (i) phenomenological observations of the formation, and (ii) statistical data on the downstream velocity distribution of different classes of waves.

Conference paper

Kovalchuk NM, Trybala A, Starov V, Matar O, Ivanova Net al., 2014, Fluoro- vs hydrocarbon surfactants: Why do they differ in wetting performance?, ADVANCES IN COLLOID AND INTERFACE SCIENCE, Vol: 210, Pages: 65-71, ISSN: 0001-8686

Journal article

Kuchin IV, Matar OK, Craster RV, Starov VMet al., 2014, Influence of the Disjoining Pressure on the Equilibrium Interfacial Profile in Transition Zone Between a Thin Film and a Capillary Meniscus, Colloids and Interface Science Communications, Vol: 1, Pages: 18-22, ISSN: 2215-0382

The behaviour of liquid layers on solid substrates depends on a number of factors, the most important of which is the action of surface forces in the vicinity of the three phase contact line. The equilibrium interfacial (gas/liquid) profile in the transition zone between the thin flat film and the spherical part of a meniscus is determined by the combined action of the disjoining/conjoining and capillary pressures. The disjoining/conjoining pressure is considered to include the electrostatic, van der Waals and structural components. The Poisson–Boltzmann equation is also solved with various boundary conditions to calculate the electrostatic component of the disjoining/conjoining pressure. Wetting conditions are considered and the interfacial profile is determined for various parameters governing the surface interactions, as well as the ratio between the disjoining/conjoining and capillary pressures.

Journal article

Che Z, Fang F, Percival J, Pain C, Matar O, Navon IMet al., 2014, An ensemble method for sensor optimisation applied to falling liquid films, International Journal of Multiphase Flow, Vol: 67, Pages: 153-161, ISSN: 1879-3533

Multiphase flow problems are often extremely complex due to their strong nonlinearity. To study multiphase flow, it is important to simulate or measure key parameters accurately, such as pressure drops and flow rates. Therefore, it is essential to place the sensors at the locations with high impact, and to avoid locations with low impact, where impact is determined by a function such as one of the key variables like pressure drop or flow rate. In this paper, an ensemble method is used to optimise sensor locations for falling film problems based on an importance map. The importance map can identify the important regions according to a target function. The sensor locations are selected based on the importance map, the variation of the variables, and the costs of performing the measurements. We demonstrate the approach by applying data assimilation and show that the optimised sensor locations can significantly improve the data assimilation results. Through sensitivity analysis, sensor optimisation, and data assimilation, this study, for the first time, provides a systematic linkage between the experiments and the models for falling film problems. It also presents a new goal or target based method for sensor placement. This method can be extended to other complex multiphase flow problems.

Journal article

Wray AW, Papageorgiou DT, Craster RV, Sefiane K, Matar OKet al., 2014, Electrostatic Suppression of the "Coffee Stain Effect", LANGMUIR, Vol: 30, Pages: 5849-5858, ISSN: 0743-7463

Journal article

Karapetsas G, Sahu KC, Sefiane K, Matar OKet al., 2014, Thermocapillary-Driven Motion of a Sessile Drop: Effect of Non-Monotonic Dependence of Surface Tension on Temperature, LANGMUIR, Vol: 30, Pages: 4310-4321, ISSN: 0743-7463

Journal article

Xie Z, Pavlidis D, Percival JR, Gomes JLMA, Pain CC, Matar OKet al., 2014, Adaptive unstructured mesh modelling of multiphase flows, International Journal of Multiphase Flow, ISSN: 0301-9322

Multiphase flows are often found in industrial and practical engineering applications, including bubbles, droplets, liquid film and waves. An adaptive unstructured mesh modelling framework is employed here to study interfacial flow problems, which can modify and adapt anisotropic unstructured meshes to better represent the underlying physics of multiphase problems and reduce computational effort without sacrificing accuracy. The numerical framework consists of a mixed control volume and finite element formulation, a 'volume of fluid'-type method for the interface capturing based on a compressive control volume advection method and second-order finite element methods. The framework also features a force-balanced algorithm for the surface tension implementation, minimising the spurious velocities often found in such flows. Numerical examples of the Rayleigh-Taylor instability and a rising bubble are presented to show the ability of this adaptive unstructured mesh modelling framework to capture complex interface geometries and also to increase the efficiency in multiphase flow simulations.

Journal article

Zadrazil I, Matar OK, Markides CN, 2014, An experimental characterization of downwards gas-liquid annular flow by laser-induced fluorescence: Flow regimes and film statistics, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 60, Pages: 87-102, ISSN: 0301-9322

Journal article

Theodorakis PE, Müller EA, Craster RV, Matar OKet al., 2014, Insights into surfactant-assisted superspreading, Current Opinion in Colloid & Interface Science, ISSN: 1359-0294

Journal article

Kusuma JN, Matar OK, Sahu KC, 2014, Numerical simulations of miscible channel flow with chemical reactions, CURRENT SCIENCE, Vol: 106, Pages: 841-852, ISSN: 0011-3891

Journal article

Gherase D, Conroy D, Matar OK, Blackmond DGet al., 2014, Experimental and Theoretical Study of the Emergence of Single Chirality in Attrition-Enhanced Deracemization, CRYSTAL GROWTH & DESIGN, Vol: 14, Pages: 928-937, ISSN: 1528-7483

Journal article

Saenz PJ, Valluri P, Sefiane K, Karapetsas G, Matar OKet al., 2014, On phase change in Marangoni-driven flows and its effects on the hydrothermal-wave instabilities, PHYSICS OF FLUIDS, Vol: 26, ISSN: 1070-6631

Journal article

Angeli P, Azzopardi BJ, Hewakandamby B, Hewitt GF, Pain CC, Simmons MJH, Matar OKet al., 2014, Multi-scale exploration of multiphase physics in flows (MEMPHIS): A framework for the next-generation predictive tools for multiphase flows, Pages: 231-238

Copyright © American Institute of Chemical Engineers. All rights reserved. In this paper, we outline the framework that we are developing as part of the Multi-scale Exploration of Multiphase PHysIcs in flowS (MEMPHIS) programme to create the next generation modelling tools for complex multiphase flows. These flows are of central importance to microfluidics, oil-and-gas, nuclear, and biomedical applications, and every processing and manufacturing technology. This framework involves the establishment of a transparent linkage between input and prediction to allow systematic error-source identification, and, optimal, modeldriven experimentation, to maximise prediction accuracy. The framework also involves massivelyparallelisable numerical methods, capable of running efficiently on 105-106 core supercomputers, with optimally-adaptive, three-dimensional resolution, and sophisticated multi-scale physical models. The overall aim of this framework is to provide unprecedented resolution of multi-scale, multiphase phenomena, thereby minimising the reliance on correlations and empiricism.

Conference paper

Kuchin IV, Matar OK, Craster RV, Starov VMet al., 2014, Modeling the effect of surface forces on the equilibrium liquid profile of a capillary meniscus, SOFT MATTER, Vol: 10, Pages: 6024-6037, ISSN: 1744-683X

Journal article

Ibarra R, Markides CN, Matar OK, 2014, A review of liquid-liquid flow patterns in horizontal and slightly inclined pipes, Multiphase Science and Technology, Vol: 26, Pages: 171-198, ISSN: 0276-1459

© 2014 by Begell House, Inc. This paper presents a review of the co-current flow of two immiscible liquids in horizontal and slightly inclined pipes. Liquid-liquid flows are present in a wide variety of industrial processes, such as chemicals, pharmaceuticals, and food processing. However, this phenomenon is mainly studied in the oil industry, especially in the analysis of oil-water mixtures encountered in long transportation pipelines from the wellhead to the processing facility. The hydrodynamic behavior of liquid-liquid flows is more complex than that of gas-liquid flows because of density ratio, viscosity ratio, interfacial forces, and pipe wettability. This means that a significant number of different flow patterns can be obtained from different fluid properties and pipe characteristics. Furthermore, the flow pattern classification of liquid-liquid flows is arbitrary and several researchers use their own classification, complicating comparison and analysis of flow pattern maps. In this paper, a unified flow pattern classification for liquid-liquid flow is proposed. This classification enables the direct comparison of flow pattern maps for further analysis.

Journal article

Angeli P, Azzopardi BJ, Hewakandamby B, Hewitt GF, Pain CC, Simmons MJH, Matar OKet al., 2014, The next-generation predictive tools for multiphase flows, Pages: 221-228

In this paper, we outline the framework that we are developing as part of the Multi-scale Exploration of Multiphase PHysIcs in flowS (MEMPHIS) programme to create the next generation modelling tools for complex multiphase flows. These flows are of central importance to microfluidics, oil-and-gas, nuclear, and biomedical applications, and every processing and manufacturing technology. This framework involves the establishment of a transparent linkage between input and prediction to allow systematic error-source identification, and, optimal, modeldriven experimentation, to maximise prediction accuracy. The framework also involves massivelyparallelisable numerical methods, capable of running efficiently on 105-106 core supercomputers, with optimally-adaptive, three-dimensional resolution, and sophisticated multi-scale physical models. The overall aim of this framework is to provide unprecedented resolution of multi-scale, multiphase phenomena, thereby minimising the reliance on correlations and empiricism.

Conference paper

Purvis JA, Mistry RD, Markides CN, Matar OKet al., 2013, An experimental investigation of fingering instabilities and growth dynamics in inclined counter-current gas-liquid channel flow, PHYSICS OF FLUIDS, Vol: 25, ISSN: 1070-6631

Journal article

Wray AW, Papageorgiou DT, Matar OK, 2013, Electrostatically controlled large-amplitude, non-axisymmetric waves in thin film flows down a cylinder, Journal of Fluid Mechanics, Vol: 736, ISSN: 1469-7645

We examine the dynamics of a thin film flowing under gravity down the exterior of a vertically aligned inner cylinder, with a co-aligned, concentric cylinder acting as an outer electrode; the space between the outer cylinder and the film is occupied by an inviscid gas. The stability of the interface is studied when it is subjected to an electric field, applied by imposing a potential difference between the two cylinders. Leaky-dielectric theory is used in conjunction with asymptotic reduction, in the large-conductivity limit, to derive a single, two-dimensional evolution equation for the interfacial location, which accounts for gravity, capillarity, and electrostatic effects. A linear stability analysis is carried out which shows that non-axisymmetric modes become more dominant with increasing electric field strength. Our fully two-dimensional numerical solutions of the evolution equation demonstrate qualitative agreement between the trends observed in the nonlinear regime and those predicted by linear theory. These numerical solutions also show that, depending on the electric field strength and the relative proximity of the outer electrode, the interface either remains spatially uniform, or exhibits either axisymmetric or, importantly, non-axisymmetric travelling waves. The effect of wave formation on the interfacial area is investigated in connection with the use of electric fields to control thin film flows to enhance heat and mass transfer rates.

Journal article

Zadrazil I, Matar OK, Markides CN, Slug front gas entrainment in gas-liquid two-phase horizontal flow using hi-speed slug-tracking, American Physical Society - Division of Fluid Dynamics

A gas-liquid flow regime where liquid-continuous regions travel at high speeds (i.e. slugs) through a pipe separated by regions of stratified flow (i.e. elongated bubbles) is referred to as a ``slug flow.'' This regime is characterised by the turbulent entrainment of gas into the slug front body. We use a high-speed camera mounted on a moving robotic linear rail to track the formation of naturally occurring slugs over 150 pipe diameters. We show that the dynamics of the slugs become progressively more complex with increasing liquid and gas Reynolds numbers. Based on the slug- tracking visualization we present, over a range of conditions: (i) phenomenological observations of the formation and development of slugs, and (ii) statistical data on the slug velocity and gas entrainment rate into the slug body.

Conference paper

Heiles B, Zadrazil I, Matar OK, The effect of surfactant on stratified and stratifying gas-liquid flows, American Physical Society - Division of Fluid Dynamics

We consider the dynamics of a stratified/stratifying gas-liquid flow in horizontal tubes. This flow regime is characterised by the thin liquid films that drain under gravity along the pipe interior, forming a pool at the bottom of the tube, and the formation of large-amplitude waves at the gas-liquid interface. This regime is also accompanied by the detachment of droplets from the interface and their entrainment into the gas phase. We carry out an experimental study involving axial- and radial-view photography of the flow, in the presence and absence of surfactant. We show that the effect of surfactant is to reduce significantly the average diameter of the entrained droplets, through a tip-streaming mechanism. We also highlight the influence of surfactant on the characteristics of the interfacial waves, and the pressure gradient that drives the flow.

Conference paper

Zadrazil I, Matar OK, Markides CN, On the Frequency of Large Waves in Vertical Gas-Liquid Annular Flow, American Institute of Chemical Engineers

Conference paper

Wray AW, Papageorgiou DT, Matar OK, 2013, Electrified coating flows on vertical fibres: enhancement or suppression of interfacial dynamics, JOURNAL OF FLUID MECHANICS, Vol: 735, Pages: 427-456, ISSN: 0022-1120

Journal article

Zhao Y, Markides CN, Matar OK, Hewitt GFet al., 2013, Disturbance wave development in two-phase gas-liquid upwards vertical annular flow, International Journal of Multiphase Flow, Vol: 55, Pages: 111-129, ISSN: 0301-9322

Disturbance waves are of central importance in annular flows. Such waves are characterised by their large amplitudes relative to the mean film thickness, their high translation velocities relative to the mean film speed, and their circumferential coherence. The present paper is concerned with the existence, development and translation of disturbance waves in upwards, gas–liquid annular flows. Experiments are described, which featured simultaneous high-frequency film thickness measurements from multiple conductance probes positioned circumferentially and axially along a vertical pipe, these measurements were aimed at studying the three-dimensional development of these interfacial structures as a function of distance from the tube inlet. From the results, it is found that disturbance waves begin to appear and to achieve their circumferential coherence from lengths as short as 5–10 pipe diameters downstream of the liquid injection location; this coherence gradually strengthens with increasing distance from the inlet. It is further shown that the spectral content of the entire interfacial wave activity shifts to lower frequencies with increasing axial distance from the inlet, with the peak frequency levelling off after approximately 20 pipe diameters. Interestingly, on the other hand, the frequency of occurrence of the disturbance waves first increases away from the inlet as these waves form, reaches a maximum at a length between 7.5 and 15 pipe diameters that depends on the flow conditions, and then decreases again. This trend becomes increasingly evident at higher gas and/or liquid flow-rates. Both wave frequency measures increase monotonically at higher gas and/or liquid flow-rates.

Journal article

Saenz PJ, Valluri P, Sefiane K, Karapetsas G, Matar OKet al., 2013, Linear and nonlinear stability of hydrothermal waves in planar liquid layers driven by thermocapillarity, PHYSICS OF FLUIDS, Vol: 25, ISSN: 1070-6631

Journal article

Karapetsas G, Sahu KC, Matar OK, 2013, Effect of Contact Line Dynamics on the Thermocapillary Motion of a Droplet on an Inclined Plate, LANGMUIR, Vol: 29, Pages: 8892-8906, ISSN: 0743-7463

Journal article

Zadrazil I, Markides CN, Hewitt GF, Matar OKet al., Structure and Velocity Profiles in Downwards Gas-Liquid Annular Flow, 8th International Conference on Multiphase Flow

The downwards co-current gas-liquid annular flows inside a vertically oriented pipe have been experimentally investigated.The measurements and characterisation were performed using advanced optical non-intrusive laser-based techniques, namelyLaser Induced Fluorescence, and Particle Image/Tracking Velocimetry. The investigated conditions were in the range of ReL =306 – 1,532 and ReG = 0 – 84,600. Temporal film thickness time traces were constructed using the Laser Induced Fluorescenceimages. Based on these, the wave frequency was evaluated using direct wave counting approach and power spectral densityanalysis. Additionally, qualitative PIV observations revealed the presence of recirculation zones within a wave front ofdisturbance waves.

Conference paper

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