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

270 results found

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

Zadrazil I, Matar OK, Markides CN, 2013, On the frequency of large waves in vertical gas-liquid annular flows

Conference paper

Zadrazil I, Hewitt GF, Matar OK, Markides CNet al., Wave Structure and Velocity Profiles in Downwards Gas-Liquid Annular Flows, American Physical Society, American Physical Society - Division of Fluid Dynamics

A downwards flow of gas in the core of a vertical pipe, and of liquid in the annulus between the pipe wall and the gas phase is referred to as a ``downwards annular flow'' (DAF). DAFs are conventionally described in terms of short-lived, small-amplitude ``ripples,'' and large-amplitude, high-speed ``disturbances.'' We use a combination of Laser Induced Fluorescence (LIF), Particle Image and Tracking Velocimetry (PIV, PTV) to study DAFs. We demonstrate through these techniques that the liquid films become progressively more complex with increasing liquid Reynolds number (ReL), while a similar increase of complexity is observed for increasing gas Reynolds number (ReG). Disturbance waves are observed for low and high ReL, and ripples for intermediate ReL. Additionally, a high degree of rolling breakdown of disturbance waves is observed in falling films at the highest ReL, which is a source of bubble entrainment into the film body. Our results will comprise: (i) statistical data on film thickness, and (ii) wave frequency, velocity, wavelength. In addition, a qualitative (e.g. re-circulation zones) and quantitative (e.g. mean/rms velocity profiles) velocity characterisation of the film flows will be presented.

Conference paper

Zadrazil I, Markides CN, Naraigh LO, Matar OKet al., Dynamics of Turbulent Falling Films, American Physical Society - Division of Fluid Dynamics

The dynamics of laminar falling films have received considerable attention over the past several decades. In contrast, turbulent falling films have been the subject of far fewer studies. We seek to redress this balance by studying the stability of falling films which have already undergone a transition from a laminar to a turbulent flow regime. We derive a uniform-film base-state for this flow by assuming the averaged turbulent velocity field to be steady and fully-developed, and by employing a modified version of mixing-length theory. The latter features an interpolation function for the eddy viscosity, and van Driest-type functions for turbulence-damping near the wall and interface regions. The predicted base-state streamwise velocity component is in good agreement with experimental data. A linear stability analysis of this base-state is then carried out by solving a modified version of the Orr-Sommerfeld equation. Our results suggest that the unstable mode is a long-wave one. This provides motivation for the derivation of long-wave equations for the nonlinear evolution of the film.

Conference paper

Zhao Y, Zadrazil I, Markides CN, Matar OK, Hewitt GFet al., Wave structure in Upwards Gas-Liquid Annular Flows, American Physical Society - Division of Fluid Dynamics

A two-phase flow system in a vertical pipe in which the liquid around the pipe periphery is lifted by the gas core is referred to as an ``upwards annular flow'' (UAF). UAFs have a complex interfacial structure, which consists of short-lived, small-amplitude ``ripple'' waves, and large amplitude, high-speed ``disturbances'' waves. Two sets of flush-mounted electrically conducting probes together with axial view photography were used to study UAFs. The overall wave frequency decreased with increasing distance from the inlet until saturation. Disturbance waves were observed over a wide range (both low and high) of liquid Reynolds numbers, ReL, while ripples were observed at lower ReL. Disturbance ``bursts,'' which are a source of liquid entrainment into the gas core, were also observed, with increasing frequency at progressively higher ReL. The waves appeared more chaotic near the inlet, which hindered the formation of the correlated waves. As the small (ripple) waves coalesced into bigger waves with increasing distance from the inlet, the waves became more coherent around the pipe periphery. The results that will be presented comprise: (i) statistical film thickness data, and (ii) wave, frequency, velocity, and wavelength.

Conference paper

Conroy DT, Craster RV, Matar OK, Cheng L-J, Chang H-Cet al., 2012, Nonequilibrium hysteresis and Wien effect water dissociation at a bipolar membrane, PHYSICAL REVIEW E, Vol: 86, ISSN: 1539-3755

Journal article

Zadrazil I, Markides CN, Matar OK, Naraigh LO, Hewitt GFet al., Characterisation of Downwards Co-Current Gas-Liquid Annular Flows, Turbulence, Heat and Mass Transfer 7, Publisher: Begell House

The hydrodynamic characteristics of downwards co-current two-phase (gas-liquid) flows inside avertical tube (ID = 32 mm) have been investigated experimentally. Advanced optical techniques, namely LaserInduced Fluorescence and Particle Tracking Velocimetry, were utilised for the characterisation of these flowsover a wide range of gas and liquid superficial velocities (U_G = 0 – 34 m/s and U_L = 0.034 – 0.182 m/s),corresponding to Reynolds numbers Re_G = 0 – 84,600 and Re_L = 1,230 – 6,130. A flow regime map, whichcontains a previously unreported flow regime, is constructed based on the flow observations. The quantitativeanalysis of the liquid films allows the generation of film thickness, wave frequency, bubble size, bubblefrequency and velocity profile data. It was found that the different observed flow regimes posses a characteristiccombination of the investigated quantitative parameters. A model, based on modified mixing-length theory, wasused to predict the liquid film velocity profiles and good agreement was found with the experimental results.

Conference paper

Karapetsas G, Matar OK, Valluri P, Sefiane Ket al., 2012, Convective Rolls and Hydrothermal Waves in Evaporating Sessile Drops, LANGMUIR, Vol: 28, Pages: 11433-11439, ISSN: 0743-7463

Journal article

Conroy DT, Matar OK, Craster RV, Papageorgiou DTet al., 2012, Compound viscous thread with electrostatic and electrokinetic effects, JOURNAL OF FLUID MECHANICS, Vol: 701, Pages: 171-200, ISSN: 0022-1120

Journal article

Wray AW, Matar O, Papageorgiou DT, 2012, Non-linear waves in electrified viscous film flow down a vertical cylinder, IMA JOURNAL OF APPLIED MATHEMATICS, Vol: 77, Pages: 430-440, ISSN: 0272-4960

Journal article

Spandagos C, Goudoulas TB, Luckham PF, Matar OKet al., 2012, Surface Tension-Induced Gel Fracture. Part 2. Fracture of Gelatin Gels, LANGMUIR, Vol: 28, Pages: 8017-8025, ISSN: 0743-7463

Journal article

Spandagos C, Goudoulas TB, Luckham PF, Matar OKet al., 2012, Surface Tension-Induced Gel Fracture. Part 1. Fracture of Agar Gels, LANGMUIR, Vol: 28, Pages: 7197-7211, ISSN: 0743-7463

Journal article

Mavromoustaki A, Matar OK, Craster RV, 2012, Dynamics of a climbing surfactant-laden film II: Stability, JOURNAL OF COLLOID AND INTERFACE SCIENCE, Vol: 371, Pages: 121-135, ISSN: 0021-9797

Journal article

Mavromoustaki A, Matar OK, Craster RV, 2012, Dynamics of a climbing surfactant-laden film - I: Base-state flow, JOURNAL OF COLLOID AND INTERFACE SCIENCE, Vol: 371, Pages: 107-120, ISSN: 0021-9797

Journal article

Wray AW, Matar OK, Papageorgiou, Non-linear waves in electrified viscous film flow down a vertical cylinder, Ima Journal of Applied Mathematics, ISSN: 1464-3634

Journal article

Matar OK, 2012, PATTERN FORMATION IN EVAPORATING DROPS WITH AND WITHOUT NANOPARTICLES, 9th International Conference on Nanochannels, Microchannels and Minichannels, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 599-606

Conference paper

Karapetsas G, Craster RV, Matar OK, 2011, Surfactant-driven dynamics of liquid lenses, PHYSICS OF FLUIDS, Vol: 23, ISSN: 1070-6631

Journal article

Mavromoustaki A, Matar OK, Craster RV, 2011, Shock-wave solutions in two-layer channel flow. II. Linear and nonlinear stability, PHYSICS OF FLUIDS, Vol: 23, ISSN: 1070-6631

Journal article

Sahu KC, Matar OK, 2011, Three-dimensional convective and absolute instabilities in pressure-driven two-layer channel flow, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 37, Pages: 987-993, ISSN: 0301-9322

Journal article

Naraigh LO, Spelt PDM, Matar OK, Zaki TAet al., 2011, Interfacial instability in turbulent flow over a liquid film in a channel, INTERNATIONAL JOURNAL OF MULTIPHASE FLOW, Vol: 37, Pages: 812-830, ISSN: 0301-9322

Journal article

Sileri D, Sahu KC, Matar OK, 2011, Two-fluid pressure-driven channel flow with wall deposition and ageing effects, JOURNAL OF ENGINEERING MATHEMATICS, Vol: 71, Pages: 109-130, ISSN: 0022-0833

Journal article

Conroy DT, Matar OK, Craster RV, Papageorgiou DTet al., 2011, Breakup of an electrified, perfectly conducting, viscous thread in an AC field, PHYSICAL REVIEW E, Vol: 83, ISSN: 2470-0045

Journal article

Karapetsas G, Craster RV, Matar OK, 2011, On surfactant-enhanced spreading and superspreading of liquid drops on solid surfaces, JOURNAL OF FLUID MECHANICS, Vol: 670, Pages: 5-37, ISSN: 0022-1120

Journal article

Conroy DT, Matar OK, Craster RV, Papageorgiou DTet al., 2011, Breakup of an electrified viscous thread with charged surfactants, PHYSICS OF FLUIDS, Vol: 23, ISSN: 1070-6631

Journal article

Macchietto S, Hewitt GF, Coletti F, Crittenden BD, Dugwell DR, Galindo A, Jackson G, Kandiyoti R, Kazarian SG, Luckham PF, Matar OK, Millan-Agorio M, Muller EA, Paterson W, Pugh SJ, Richardson SM, Wilson DIet al., 2011, Fouling in Crude Oil Preheat Trains: A Systematic Solution to an Old Problem, HEAT TRANSFER ENGINEERING, Vol: 32, Pages: 197-215, ISSN: 0145-7632

Journal article

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