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Start Over Descriptor "Effective medium approximation" Publisher elsevier
7 results on '"Effective medium approximation"'

1. Estimating the universal scaling of gas diffusion in coarse-textured soils

Author

J. Valdes-Abellan, D. Benavente, B. Ghanbarian, P. Moldrup, E. Arthur, T. Norgaard, and L. Wollesen de Jonge

Subjects
Soil gas diffusion, Soil water retention curve, Van Genuchten model, Percolation theory, Effective medium approximation, Science
Abstract

Gas diffusion, D, in partially saturated soils, constitutes a critical topic in soil sciences. However, it is a complex process and this limits its characterization and estimation. In this study, we analyzed and parameterized the soil gas diffusion using a combination of percolation theory (PT) and the effective-medium approximation (EMA). Here, we selected 126 coarse-textured soils with measurements including sand, silt, and clay content, bulk density, organic matter, porosity, soil water content measured at different pressure heads and saturation-dependent gas diffusion. First, we adopted the van Genuchten model, fit it to the soil water retention curve (SWRC), optimized its parameters, and determined the water content at the inflection point. Second, the parameters of the universal scaling law from PT and EMA were optimized by directly fitting the model to the saturation-dependent gas diffusion data. Those parameters are (1) the critical air-filled porosity, εc, (2) the crossover air-filled porosity, εx, at which the gas movement behavior changes from the percolation theory domain to the EMA domain; and (3) the average pore coordination number, z. Next, a multiple linear regression analysis (MLRA) was applied to link εc, εx and z to other soil parameters, such as soil textural and/or hydraulic properties. Uncertainties in our results were evaluated using a jack-knife resampling technique, which involved applying the MLRA more than 7000 times. Results revealed that the most accurate estimations were obtained when both soil textural and hydraulic properties were used simultaneously. However, the use of only soil textural parameters presents practical advantages, as it provides excellent estimations for εx and z, although not for εc. The latter is a critical parameter in the application of the PT and EMA to gas diffusion that requires both the soil basic properties and water saturation curve properties to be correctly estimated.

Published
2024
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2. Effect of interfacial thermal resistance and nanolayer on estimates of effective thermal conductivity of nanofluids

Author

Masoud Bozorg Bigdeli, Eliodoro Chiavazzo, Pietro Asinari, Shahin Mohammadnejad, Matteo Fasano, and Ali Khodayari

Subjects
ENTROPY GENERATION, Materials science, Nanolayer, Kapitza resistance, 020209 energy, Nanoparticle, 02 engineering and technology, Effective medium approximation, Nanofluid, ENHANCEMENT, Thermal conductivity, SOLAR COLLECTOR, HEAT-TRANSFER, Thermal engineering, 0202 electrical engineering, electronic engineering, information engineering, WATER, Interfacial thermal resistance, Composite material, Engineering (miscellaneous), Nanoscopic scale, Fluid Flow and Transfer Processes, Science & Technology, 021001 nanoscience & nanotechnology, Thermal conduction, PARTICLE-SIZE, MODEL, Nanolayer, Kapitza resistance, Nanofluid, Effective medium approximation, Thermal conductivity, MULTISCALE SIMULATION APPROACH, LAYER, lcsh:TA1-2040, Physical Sciences, Heat transfer, Thermodynamics, 0210 nano-technology, lcsh:Engineering (General). Civil engineering (General)
Abstract

© 2018 The Authors. Colloidal suspensions of nanoparticles (nanofluids) are materials of interest for thermal engineering, because their heat transfer properties are typically enhanced as compared to the base fluid one. Effective medium theory provides popular models for estimating the overall thermal conductivity of nanofluids based on their composition. In this article, the accuracy of models based on the Bruggeman approximation is assessed. The sensitivity of these models to nanoscale interfacial phenomena, such as interfacial thermal resistance (Kapitza resistance) and fluid ordering around nanoparticles (nanolayer), is considered for a case study consisting of alumina nanoparticles suspended in water. While no significant differences are noticed for various thermal conductivity profiles in the nanolayer, a good agreement with experiments is observed with Kapitza resistance ≈ 10-9 m2K/W and sub-nanometer nanolayer thickness. These results confirm the classical nature of thermal conduction in nanofluids and highlight that future studies should rather focus on a better quantification of Kapitza resistance at nanoparticle-fluid interfaces, in order to allow bottom up estimates of their effective thermal conductivity. ispartof: CASE STUDIES IN THERMAL ENGINEERING vol:12 pages:454-461 status: published

Published
2018

3. Prediction of gas permeability of block-segregated polymeric membranes by an effective medium model

Author

Ángel Marcos-Fernández, Laura Palacio, Mónica de la Viuda, Antonio Hernández, Angel E. Lozano, Alberto Tena, and Pedro Prádanos

Subjects
Materials science, Ethylene oxide, Effective Medium Approximation, Gas separation, Percolation, Filtration and Separation, BPDA, Biochemistry, Amorphous solid, chemistry.chemical_compound, Membrane, chemistry, Chemical engineering, Copoly(ether-imide) membrane, Phase segregation, Diamine, Polymer chemistry, Volume fraction, Copolymer, General Materials Science, Thermal treatment, Physical and Theoretical Chemistry
Abstract

Producción Científica, A complete series of aliphatic aromatic copoly(ether-imide)s, based on aromatic dianhydrides (BPDA, BKDA or PMDA) and mixtures of an aromatic diamine (ODA) and an aliphatic diamine terminated poly(ethylene oxide) PEO(2000) (Mw=2000 g/mol) or PEO(6000) (Mw= 6000 g/mol), has been synthesized using different PEO contents. Cast films of these copolymers have been thermally treated to ensure the segregation of the linear PEO chains from the aromatic portion of these copoly(ether-imide)s. Gas permeability (O2, N2, CO2 and CH4) of membranes, made from these copolymers with different proportions of PEO, were compared with the predictions of various electrical or thermal conductivity models adapted to gas permeability. Several of these models, from Maxwell-Garnett to percolation theory, proved to be inaccurate. Nevertheless, the model based on the Effective Medium Approximation (EMA) is proved here to succeed in predicting the main features of the experimental results for all mixture proportions, taking as the starting point the sole input of pure homopolymer permeabilities. Specifically, this later method was able to calculate the volume fraction for the maximum increase of permeability, a common feature for all the studied segregated copolymer membranes. The model was even able to predict the permeabilities of a three phase system consisting in the aromatic (BKDA-ODA) phase plus a mixture of amorphous PEO(6000) and crystalline PEO(6000)., Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13)

Published
2014

4. Prediction of gas permeability of block-segregated polymeric membranes by an effective medium model

Author

Tena Matías, Alberto and Tena Matías, Alberto

Abstract

Producción Científica, A complete series of aliphatic aromatic copoly(ether-imide)s, based on aromatic dianhydrides (BPDA, BKDA or PMDA) and mixtures of an aromatic diamine (ODA) and an aliphatic diamine terminated poly(ethylene oxide) PEO(2000) (Mw=2000 g/mol) or PEO(6000) (Mw= 6000 g/mol), has been synthesized using different PEO contents. Cast films of these copolymers have been thermally treated to ensure the segregation of the linear PEO chains from the aromatic portion of these copoly(ether-imide)s. Gas permeability (O2, N2, CO2 and CH4) of membranes, made from these copolymers with different proportions of PEO, were compared with the predictions of various electrical or thermal conductivity models adapted to gas permeability. Several of these models, from Maxwell-Garnett to percolation theory, proved to be inaccurate. Nevertheless, the model based on the Effective Medium Approximation (EMA) is proved here to succeed in predicting the main features of the experimental results for all mixture proportions, taking as the starting point the sole input of pure homopolymer permeabilities. Specifically, this later method was able to calculate the volume fraction for the maximum increase of permeability, a common feature for all the studied segregated copolymer membranes. The model was even able to predict the permeabilities of a three phase system consisting in the aromatic (BKDA-ODA) phase plus a mixture of amorphous PEO(6000) and crystalline PEO(6000)., Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13)

Published
2014

5. Prediction of gas permeability of block-segregated polymeric membranes by an effective medium model

Author

Tena, Alberto, Viuda, Monica de la, Palacio, Laura, Prádanos, Pedro, Marcos-Fernández, Ángel, Lozano López, Ángel Emilio, Hernández, Antonio, Tena, Alberto, Viuda, Monica de la, Palacio, Laura, Prádanos, Pedro, Marcos-Fernández, Ángel, Lozano López, Ángel Emilio, and Hernández, Antonio

Abstract

A complete series of aliphatic aromatic copoly(ether-imide)s, based on aromatic dianhydrides (BPDA, BKDA or PMDA) and mixtures of an aromatic diamine (ODA) and an aliphatic diamine terminated poly(ethylene oxide) PEO(2000) (Mw=2000. g/mol) or PEO(6000) (Mw=6000. g/mol), has been synthesized using different PEO contents. Cast films of these copolymers have been thermally treated to ensure the segregation of the linear PEO chains from the aromatic portion of these copoly(ether-imide)s.Gas permeability (O2, N2, CO2 and CH4) of membranes, made from these copolymers with different proportions of PEO, were compared with the predictions of various electrical or thermal conductivity models adapted to gas permeability. Several of these models, from Maxwell-Garnett to percolation theory, proved to be inaccurate. Nevertheless, the model based on the Effective Medium Approximation (EMA) is proved here to succeed in predicting the main features of the experimental results for all mixture proportions, taking as the starting point the sole input of pure homopolymer permeabilities. Specifically, this later method was able to calculate the volume fraction for the maximum increase of permeability, a common feature for all the studied segregated copolymer membranes. The model was even able to predict the permeabilities of a three phase system consisting in the aromatic (BKDA-ODA) phase plus a mixture of amorphous PEO(6000) and crystalline PEO(6000). © 2013 Elsevier B.V.

Published
2014

6. Electromagnetic absorption in anisotropic photonic crystal of alumina cylinders

Author

José Sánchez-Dehesa, Jorge Carbonell, Arkady Krokhin, Jesús Arriaga, and Ludmila Gumen

Subjects
Alumina, ESTADISTICA E INVESTIGACION OPERATIVA, Physics::Optics, Rod, Electromagnetism, Dielectric tensors, Anisotropic photonic crystal, Anisotropy, Condensed matter physics, Effective Medium Approximation, Metamaterial, Surfaces and Interfaces, Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Unit cells, Imaginary parts, Modeling and Simulation, Numerical results, Permittivity, Materials science, Plane wave expansion method, Experimental measurements, Experimental studies, Angular dependence, Biomaterials, TECNOLOGIA ELECTRONICA, Analytical expressions, Photonic crystals, Optics, Dielectric rods, TEORIA DE LA SEÑAL Y COMUNICACIONES, Alumina rods, Real part, Electromagnetic wave absorption, Electrical and Electronic Engineering, Photonic crystal, business.industry, Effective permittivity, Photonic crytals, Microwave reflection, Electromagnetic absorption, Dissipative system, business, Low loss, Long-wavelength limits
Abstract

[EN] We present a theoretical and experimental study of the effective permittivity of a photonic crystal (PC) made of parallel dielectric rods in the long-wavelength limit. Using the plane-wave expansion method we derive an analytical expression for the imaginary part of the dielectric tensor. Angular dependence of the dissipative part of permittivity turns out to be more complicated than that for the real part. In particular, it exhibits stronger anisotropy for a PC with rectangular unit cell. Theoretical and numerical results are compared to the experimental measurements of microwave reflection and transmission through a PC fabricated from low-loss alumina rods. A good agreement between the theory and experiment was obtained in the limit where the effective medium approximation is valid. © 2011 Elsevier B.V., This work was supported by the Ministerio de Ciencia e Innovación of Spain under contracts TEC 2007-67239, TEC 2010-19751 and CONSOLIDER CSD2008-00066, by the US Department of Energy through the Grant No. DE-FG02-06ER46312, and by the Office of Naval Research through the Grant No. 000140910554. L.G. acknowledges the support by CONACyT (Mexico) and A.K. acknowledges the support by the Ministerio de Educación of Spain Contract No. SAB2009-00009. Authors thank F. Cervera for technical help.

Published
2011

7. Electromagnetic absorption in anisotropic photonic crystal of alumina cylinders

Author

Universitat Politècnica de València. Departamento de Estadística e Investigación Operativa Aplicadas y Calidad - Departament d'Estadística i Investigació Operativa Aplicades i Qualitat, Universitat Politècnica de València. Departamento de Ingeniería Electrónica - Departament d'Enginyeria Electrònica, Universitat Politècnica de València. Grupo de Fenómenos Ondulatorios (GFO), Ministerio de Ciencia e Innovación, U.S. Department of Energy, Ministerio de Educación y Ciencia, Office of Naval Research, Carbonell Olivares, Jorge, Sánchez-Dehesa Moreno-Cid, José, Arriaga, J., Gumen, L., Krokhin, A., Universitat Politècnica de València. Departamento de Estadística e Investigación Operativa Aplicadas y Calidad - Departament d'Estadística i Investigació Operativa Aplicades i Qualitat, Universitat Politècnica de València. Departamento de Ingeniería Electrónica - Departament d'Enginyeria Electrònica, Universitat Politècnica de València. Grupo de Fenómenos Ondulatorios (GFO), Ministerio de Ciencia e Innovación, U.S. Department of Energy, Ministerio de Educación y Ciencia, Office of Naval Research, Carbonell Olivares, Jorge, Sánchez-Dehesa Moreno-Cid, José, Arriaga, J., Gumen, L., and Krokhin, A.

Abstract

[EN] We present a theoretical and experimental study of the effective permittivity of a photonic crystal (PC) made of parallel dielectric rods in the long-wavelength limit. Using the plane-wave expansion method we derive an analytical expression for the imaginary part of the dielectric tensor. Angular dependence of the dissipative part of permittivity turns out to be more complicated than that for the real part. In particular, it exhibits stronger anisotropy for a PC with rectangular unit cell. Theoretical and numerical results are compared to the experimental measurements of microwave reflection and transmission through a PC fabricated from low-loss alumina rods. A good agreement between the theory and experiment was obtained in the limit where the effective medium approximation is valid. © 2011 Elsevier B.V.

Published
2011

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