References of "Machrafi, Hatim"
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See detailEffect of including a gas layer on the gel formation process during the drying of a polymer solution
Rabani, Ramin ULiege; Machrafi, Hatim ULiege; Dauby, Pierre ULiege

in The European Physical Journal E (2017), 40(89), 11579-3

In this paper, we study the influence of the upper gas layer on the drying and gelation of a polymer solution. The gel is formed due to the evaporation of the binary solution into (inert) air. A one ... [more ▼]

In this paper, we study the influence of the upper gas layer on the drying and gelation of a polymer solution. The gel is formed due to the evaporation of the binary solution into (inert) air. A one dimensional model is proposed, where the evaporation flux is more realistically described than in previous studies. The approach is based on general thermodynamic principles. A composition-dependent diffusion coefficient is used in the liquid phase and the local equilibrium hypothesis is introduced at the interface to describe the evaporation process. The results show that the high thickness of the gas layer reduces evaporation, thus leading to longer drying times. Our model is also compared with more phenomenological descriptions of evaporation, for which the mass flux through the interface is described by the introduction of a Peclet number. A global agreement is found for appropriate values of the Peclet numbers and our model can thus be considered as a tool allowing to link the value of the empirical Peclet number to the physics of the gas phase. Finally, in contrast with other models, our approach emphasizes the possibility of very fast gelation at the interface, which could prevent all Marangoni convection during the drying process. [less ▲]

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See detailMicrobial Lipids as Diesel Replacement: Current Challenges and Recent Advances
Machrafi, Hatim ULiege; Minetti, C.; Iorio, C.S.

in Harzevili, Farshad Darvishi; Hiligsmann, Serge (Eds.) Microbial Fuels Technologies and Applications (2017)

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See detailSelf-assembly by multi-drop evaporation of carbon-nanotube droplets on a polycarbonate substrate
Machrafi, Hatim ULiege; Minetti, C.; Dauby, Pierre ULiege et al

in Physica E: Low-Dimensional Systems and Nanostructures (2017), 85

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See detailExperimental investigation of force balance at vapour condensation on a cylindrical fin
Glushchuk, A.; Minetti, C.; Machrafi, Hatim ULiege et al

in International Journal of Heat & Mass Transfer (2017), 108

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See detailThe role of several heat transfer mechanisms on the enhancement of thermal conductivity in nanofluids
Machrafi, Hatim ULiege; Lebon, Georgy ULiege

in Continuum Mechanics & Thermodynamics (2016), 28(5), 1461-1475

A modelling of the thermal conductivity of nanofluids based on extended irreversible thermodynamics is proposed with emphasis on the role of several coupled heat transfer mechanisms: liquid interfacial ... [more ▼]

A modelling of the thermal conductivity of nanofluids based on extended irreversible thermodynamics is proposed with emphasis on the role of several coupled heat transfer mechanisms: liquid interfacial layering between nanoparticles and base fluid, particles agglomeration and Brownian motion. The relative importance of each specific mechanism on the enhancement of the effective thermal conductivity is examined. It is shown that the size of the nanoparticles and the liquid boundary layer around the particles play a determining role. For nanoparticles close to molecular range, the Brownian effect is important. At nanoparticles of the order of 1–100 nm, both agglomeration and liquid layering are influent. Agglomeration becomes the most important mechanism at nanoparticle sizes of the order of 100 nm and higher. The theoretical considerations are illustrated by three case studies: suspensions of alumina rigid spherical nanoparticles in water, ethylene glycol and a 50/50w% water/ethylene glycol mixture, respectively, good agreement with experimental data is observed. © 2016, Springer-Verlag Berlin Heidelberg. [less ▲]

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See detailEffect of volume-fraction dependent agglomeration of nanoparticles on the thermal conductivity of nanocomposites: Applications to epoxy resins, filled by SiO2, AlN and MgO nanoparticles
Machrafi, Hatim ULiege; Lebon, Georgy ULiege; Iorio, C. S.

in Composites Science & Technology (2016), 130

A thermodynamic model for transient heat conduction in ceramic-polymer nanocomposites is proposed. The model takes into account particle's size, particle's volume fraction, and interface characteristics ... [more ▼]

A thermodynamic model for transient heat conduction in ceramic-polymer nanocomposites is proposed. The model takes into account particle's size, particle's volume fraction, and interface characteristics with emphasis on the effect of agglomeration of particles on the effective thermal conductivity of the nanocomposite. The originality of the present work is its basement on extended irreversible thermodynamics, combining nano- and continuum-scales without invoking molecular dynamics. The model is compared to experimental data using the examples of SiO2, AlN and MgO nanoparticles embedded in epoxy resin. The analysis is limited to spherical nanoparticles. The dependence of the degree of agglomeration with respect of the volume fraction of particles is also discussed and a power-law relation is established through a kinetic mechanism and experiments performed in our laboratory. This relation is used in our theoretical model, resulting into a good agreement with experiments. It is shown that the effective thermal conductivity may either increase or decrease with the degree of agglomeration. © 2016 Elsevier Ltd. [less ▲]

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See detailThermal rectifier efficiency of various bulk-nanoporous silicon devices
Machrafi, Hatim ULiege; Lebon, Georgy ULiege; Jou, D.

in International Journal of Heat & Mass Transfer (2016), 97

Our objective is to calculate and to compare the rectifying thermal coefficient of various bulk-porous silicon configurations. We consider successively homogeneous devices involving two- and three ... [more ▼]

Our objective is to calculate and to compare the rectifying thermal coefficient of various bulk-porous silicon configurations. We consider successively homogeneous devices involving two- and three elements and several graded devices characterized by variable porosity and/or size of the pores along the system. The criterion is to obtain rectifying coefficients different from one in order that thermal rectification be as efficient as possible. In that respect, it turns out that the porous-bulk-porous configurations are of little interest, in contrast to the bulk-porous-bulk systems whose rectifying coefficients may be larger than two and comparable to the values of the simpler two-element bulk-porous devices. Graded systems with either a variable porosity or a variable pore size do not exhibit better results. However, when both porosity and pore size are varying along the device, the highest efficiency is obtained. © 2016 Elsevier Ltd. All rights reserved. [less ▲]

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See detailGeneral constitutive equations of heat transport at small length scales and high frequencies with extension to mass and electrical charge transport
Machrafi, Hatim ULiege; Lebon, Georgy ULiege

in Applied Mathematics Letters (2016), 52

A generalized heat transport equation applicable at small length and short time scales is proposed. It is based on extended irreversible thermodynamics with an infinite number of high-order heat fluxes ... [more ▼]

A generalized heat transport equation applicable at small length and short time scales is proposed. It is based on extended irreversible thermodynamics with an infinite number of high-order heat fluxes selected as state variables. Extensions of Fick's and Ohm's laws are also formulated. As a numerical illustration, heat conduction in a rigid body subject to fixed and oscillatory temperature boundary conditions is discussed. © 2015 Elsevier Ltd. [less ▲]

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See detailAn extended thermodynamic model for size-dependent thermoelectric properties at nanometric scales: Application to nanofilms, nanocomposites and thin nanocomposite films
Machrafi, Hatim ULiege

in Applied Mathematical Modelling (2016), 40(3), 2143-2160

A new mathematical model is developed, describing size-dependent subcontinuum thermoelectric properties from an extended thermodynamic point of view. This model takes into account the non-local effects of ... [more ▼]

A new mathematical model is developed, describing size-dependent subcontinuum thermoelectric properties from an extended thermodynamic point of view. This model takes into account the non-local effects of heat transfer through phonons and electrons that are important at nanometric scales. These phenomena are extended to apply also for electric transfer as well as the Seebeck coefficient. This model includes at nanoscale size-dependent electron and phonon thermal conductivities, electric conductivity, Seebeck coefficient and carrier concentrations. We compared nanofilms to nanocomposites and assessed their thermoelectric performances in the form of a figure of merit using as an example Bismuth and BismuthTelluride materials. It appeared that the figure of merit increases considerably for nanofilms and nanocomposites with respect to bulk materials. This is caused by the scattering of phonons and electrons. Our model shows that this scattering effect is not only present at the boundary or particle-matrix interface of the nanosized material, but also within it. The effect of particle size and surface specularity has been investigated, showing that a decreasing value of the particle size and specularity increases the scattering effect and improves the thermoelectric properties. An extension towards thin films of nanocomposite has been presented. © 2015. [less ▲]

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See detailHeat transfer at nanometric scales described by extended irreversible thermodynamics
Machrafi, Hatim ULiege

in Communications in Applied and Industrial Mathematics (2016), 7(2), 177-195

The purpose of this work is to present a study on heat conduction in systems that are composed out of spherical and cylindrical micro-and nanoparticles dispersed in a bulk matrix. Special emphasis is put ... [more ▼]

The purpose of this work is to present a study on heat conduction in systems that are composed out of spherical and cylindrical micro-and nanoparticles dispersed in a bulk matrix. Special emphasis is put on the dependence of the effective heat conductivity on various selected parameters as particle size and also its shape, surface specularity and density, including particle-matrix interaction. The heat transfer at nanometric scales is modelled using extended irreversible thermodynamics, whose main feature is to elevate the heat flux vector to the status of independent variable. The model is illustrated by a Copper-Silicium (Cu-Si) system. It is shown that all the investigated parameters have a considerable influence, the particle size being especially useful to either increase or decrease the effective thermal conductivity. © 2016 Hatim Machrafi, licensee De Gruyter Open. [less ▲]

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See detailAn extended irreversible thermodynamic modelling of size-dependent thermal conductivity of spherical nanoparticles dispersed in homogeneous media
Lebon, Georgy ULiege; Machrafi, Hatim ULiege; Grmela, M.

in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences (2015), 471(2182),

The effective thermal conductivity of nanocomposites constituted by nanoparticles and homogeneous host media is discussed from the point of view of extended irreversible thermodynamics. This formalism is ... [more ▼]

The effective thermal conductivity of nanocomposites constituted by nanoparticles and homogeneous host media is discussed from the point of view of extended irreversible thermodynamics. This formalism is particularly well adapted to the description of small length scales. As illustrations, dispersion of Si nanoparticles in Ge (respectively, SiO2 in epoxy resin) homogeneous matrices is investigated, the nanoparticles are assumed to be spherical with a wide dispersion. Four specific problems are studied: the dependence of the effective thermal conductivity on the volume fraction of particles, the type of phonon scattering at the interface particle-matrix, the radius of the nanoparticles and the temperature. © 2015 The Author(s) Published by the Royal Society. All rights reserved. [less ▲]

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See detailThermal conductivity of tubular nanowire composites based on a thermodynamical model
Lebon, Georgy ULiege; Machrafi, Hatim ULiege

in Physica E: Low-Dimensional Systems and Nanostructures (2015), 71

A formula for the effective heat conductivity of a nanocomposite with cylindrical nanowire inclusions is derived. Both transversal and longitudinal heating along the wires are investigated. Several ... [more ▼]

A formula for the effective heat conductivity of a nanocomposite with cylindrical nanowire inclusions is derived. Both transversal and longitudinal heating along the wires are investigated. Several effects are examined: the volume fraction and sizes of the nanowires, the type of scattering at the particle-matrix interface and temperature. As illustration, silicon nanowires inclusions in a germanium matrix is considered; the results are shown to be in good agreement with other models and numerical solutions of the Boltzmann transport equation. Our main contribution consists of using extended irreversible thermodynamics to cope with the nano dimensions of the wires. © 2015 Elsevier B.V. All rights reserved. [less ▲]

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See detailImportance of wavenumber dependence of Biot numbers in one-sided models of evaporative Marangoni instability: horizontal layer and spherical droplet
Machrafi, Hatim ULiege; Rednikov, Alexey; Colinet, Pierre et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2015), 91

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See detailRelation between convective thermal patterns and heat flux through an evaporating surface via 2D and 3D numerical simulations
Machrafi, Hatim ULiege; Iorio, Carlo; Dauby, Pierre ULiege

in Interfacial Phenomena and Heat Transfer (2014), 2(3), 199-209

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See detailTime-dependent Marangoni-Bénard instability of an evaporating binary-liquid layer including gas transients
Machrafi, Hatim ULiege; Rednikov, A.; Colinet, P. et al

in Physics of Fluids (2013), 25

We are here concerned with Bénard instabilities in a horizontal layer of a binary liquid, considering as a working example the case of an aqueous solution of ethanol with a mass fraction of 0.1. Both the ... [more ▼]

We are here concerned with Bénard instabilities in a horizontal layer of a binary liquid, considering as a working example the case of an aqueous solution of ethanol with a mass fraction of 0.1. Both the solvent and the solute evaporate into air (the latter being insoluble in the liquid). The system is externally constrained by imposing fixed "ambient" pressure, humidity, and temperature values at a certain effective transfer distance above the liquid-gas interface, while the ambient temperature is also imposed at the impermeable rigid bottom of the liquid layer. Fully transient and horizontally homogeneous solutions for the reference state, resulting from an instantaneous exposure of the liquid layer to ambient air, are first calculated. Then, the linear stability of these solutions is studied using the frozen-time approach, leading to critical (monotonic marginal stability) curves in the parameter plane spanned by the liquid layer thickness and the elapsed time after initial contact. This is achieved for different ratios of the liquid and gas thicknesses, and in particular yields critical times after which instability sets in (for given thicknesses of both phases). Conversely, the analysis also predicts a critical thickness of the liquid layer below which no instability ever occurs. The nature of such critical thickness is explained in detail in terms of mass fraction profiles in both phases, as it indeed appears that the most important mechanism for instability onset is the solutal Marangoni one. Importantly, as compared to the result obtained previously under the quasi-steady assumption in the gas phase [H. Machrafi, A. Rednikov, P. Colinet, and P. C. Dauby, Eur. Phys. J. Spec. Top.192, 71 (2011)]10.1140/epjst/e2011-01361-y, it is shown that relaxing this assumption may yield essentially lower values of the critical liquid thickness, especially for large gas-to-liquid thickness ratios. A good-working analytical model is developed for the description of such delicate transient effects in the gas. The analysis reveals that the system considered in this paper is generally highly unstable, the instability setting in even for very small times and liquid thicknesses. © 2013 AIP Publishing LLC. [less ▲]

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See detailEvaporation Rates and Bénard-Marangoni Supercriticality Levels for Liquid Layers Under an Inert Gas Flow
Machrafi, Hatim ULiege; Sadoun, Nacer; Rednikov, Alexey et al

in Microgravity Science and Technology (2013)

Detailed reference viewed: 24 (4 ULiège)