Effective Thermal Conductivity of Spherical Particulate Nanocomposites: Comparison with Theoretical Models, Monte Carlo Simulations and Experiments

Machrafi, Hatim; Lebon, Georgy

doi:10.1142/s0219581x14500227

Cited by 14 publications

(20 citation statements)

References 22 publications

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“…In contrast, our results disagree with Eucken's approximation and the simplified formula (14), which predict overestimated results, particularly Eucken's approach. This is a clear indication that pore sizes play a decisive role in the calculations of thermal conductivity in nanoporous materials (an observation already well known for nanocomposites [12][13][14]). The hydrodynamic formulation does consider pore size and the ballistic property of the heat transport which is not the case of the simplified formula which express the heat conductivity exclusively as a function of the porosity.…”

Section: Results and Comparison With Other Modelsmentioning

confidence: 64%

“…Comparison between our model and the five other ones expressed by relations (12), to (16) is found in Fig 1, wherein the effective thermal conductivity is plotted as a function of the porosity for a pore radius of 10 nm. Whatever the selected model, the heat conductivity is decreasing with the porosity, this reduction is easily understood owing to the weak thermal conductivity of air enclosed in the pores.…”

Section: Results and Comparison With Other Modelsmentioning

confidence: 95%

“…In a previous paper [12], we have studied the influence of the presence of nano inclusions on the effective thermal conductivity of nanocomposites. Our aim here is to extend, the type of approach made in [12] to nanoporous materials.…”

Section: Heat Conductivity Of Nano-porous Si Devicesmentioning

confidence: 99%

“…Our aim here is to extend, the type of approach made in [12] to nanoporous materials. As in reference [12], the system is simplified by homogenizing the heterogeneous original material with the resulting homogeneous system called the effective medium approach (EMA). This approach was initiated by Nan et al [13] and revisited by Minnich and Chen [14].…”

Section: Heat Conductivity Of Nano-porous Si Devicesmentioning

confidence: 99%

“…Working in analogy with previous works on heat transport in nanocomposites [12,14], represents a dimensionless parameter describing the interaction between the nanopores and the medium; it reads as [14]…”

Section: Heat Conductivity Of Nano-porous Si Devicesmentioning

confidence: 99%

See 4 more Smart Citations

Size and porosity effects on thermal conductivity of nanoporous material with an extension to nanoporous particles embedded in a host matrix

Machrafi

Lebon

2015

Physics Letters A

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Abstract.A formula for the effective thermal conductivity of nanoporous media is derived, following a thermodynamic approach. An extension to nanocomposites composed of a homogeneous matrix wherein porous nanoparticles are dispersed is proposed as well. The originality of the model is that it is based on extended irreversible thermodynamics, a theory specifically designed for sub-scaled systems. Two different situations are discussed, in the first one, nanoporous silicon with spherical porous inclusions of micro, meso and macro-dimension respectively is considered. The description is validated by comparison with experimental data and five other models. Analysis of the results shows an excellent agreement of our theoretical approach with experiments in the whole range of porous radii, from 2 to 100 nm. In the second part of the work, thermal conductivity of porous silicon nanoparticles embedded in a germanium host matrix is investigated. The coupled influence of the pore and nanoparticles sizes is emphasized.Keywords: nanoporous media, thermal conductivity, phonon scattering, extended thermodynamics IntroductionThe effect of porosity is to decrease considerably the thermal conductivity of crystalline materials, as is observed, for instance, in nanoporous silicon [1][2][3][4][5]. This lowering property has been widely exploited with the objective to reinforce thermal insulation in several systems as microsensors, integrated circuits, semiconductor devices. It has therefore fostered an increasing interest during the last decade. Thermal properties of nanoporous media are generally investigated by referring to, for instance, kinetic theory of phonons [3], molecular simulations [5], Monte Carlo simulations [6], two-component materials [7] or hydrodynamic models [8]. In this work, we take a different route and prefer a thermodynamic approach. To be explicit, we will base our study on extended irreversible thermodynamics (EIT) [9,10], which is a formalism specifically dedicated to the treatment of micro and nano systems and highfrequency processes. For the sake of completeness, the present analysis will be compared to other theoretical models and experimental data.Nanoporous materials are generally made out of a homogeneous matrix wherein nanopores are dispersed. In that respect, such systems are similar to nanocomposites, wherein nanoparticles are embedded in a matrix, the difference being that nanoparticles are replaced by nanopores. A great deal of papers have been devoted to the problem of heat transport in nanofluids and nanocomposites, see for instance the review paper by Michaeledis [11]. In particular, the problem of the overall heat conductivity of the system as a function of the volume fraction of the nanoparticles and their size has drawn much attention. Our purpose in the present work is twofold. Firstly, it is the purpose to study the role of porosity and the size of the pores on the heat conductivity of porous systems, like nanoporous silicon, via our thermodynamic formalism. Secondly, we examine, using t...

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Section: Results and Comparison With Other Modelsmentioning

confidence: 64%

Section: Results and Comparison With Other Modelsmentioning

confidence: 95%

Section: Heat Conductivity Of Nano-porous Si Devicesmentioning

confidence: 99%

Section: Heat Conductivity Of Nano-porous Si Devicesmentioning

confidence: 99%

Section: Heat Conductivity Of Nano-porous Si Devicesmentioning

confidence: 99%

See 3 more Smart Citations

Size and porosity effects on thermal conductivity of nanoporous material with an extension to nanoporous particles embedded in a host matrix

Machrafi

Lebon

2015

Physics Letters A

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Phonon Conductivity of Nanoparticles Embedded in Dielectric Material

Singh

Guo

Cid

et al. 2018

Physica Status Solidi (b)

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A theory of the thermal conductivity has been developed for nanomaterials made by embedding nanoparticles in a host dielectric material. The phonon dispersion relation has been calculated using the transfer matrix method in the long-range approximation, where the phonon wavelength is larger than the size of the nanoparticle. We found that these nanomaterials have two phonon branches known as ω þ k -phonon and ω À k -phonon branches. For both phonon branches, the density of states and the phonon velocity are calculated. The thermal conductivity is evaluated with the Kubo formalism and the Green's function method for both ω þ k -phonon and ω À k -phonon branches. It is also found that the density of states, phonon velocity and thermal conductivity for both phonon branches depend on the size of the nanoparticles, spacing between nanoparticles, and the phonon refractive index of the nanoparticles and the host material. In the long wave approximation, expressions of the phonon conductivity, the density of states and the phonon velocity have very simple forms which can be used by experimentalists to explain their experiments or plan new experiments. We have also applied our theory to explain the experimental thermal conductivity data of silica-resin, alumina-resin, AlN-resin and CaO-polyethylene nanomaterials. A good agreement between theory and experiments is achieved. Our results furthermore illustrate that one can fabricate new types of nanomaterials with high and low thermal conductivity by adjusting the refractive index contrast between nanoparticles and the host material. These are very novel and interesting properties and they can be used to fabricate new types of thermal devices.

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The role of several heat transfer mechanisms on the enhancement of thermal conductivity in nanofluids

Machrafi

Lebon

2016

Continuum Mech. Thermodyn.

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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 sizes 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 50/50 w% water/ethylene-glycol mixture, respectively, good agreement with experimental data is observed.

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Effective Thermal Conductivity of Spherical Particulate Nanocomposites: Comparison with Theoretical Models, Monte Carlo Simulations and Experiments

Cited by 14 publications

References 22 publications

Size and porosity effects on thermal conductivity of nanoporous material with an extension to nanoporous particles embedded in a host matrix

Size and porosity effects on thermal conductivity of nanoporous material with an extension to nanoporous particles embedded in a host matrix

Phonon Conductivity of Nanoparticles Embedded in Dielectric Material

The role of several heat transfer mechanisms on the enhancement of thermal conductivity in nanofluids

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