Effect of Phonon Dispersion on Thermal Conduction Across Si/Ge Interfaces

We report finite-volume simulations of the phonon Boltzmann transport equation (BTE) for heat conduction across the heterogeneous interfaces in SiGe superlattices. The diffuse mismatch model incorporating phonon dispersion and polarization is implemented over a wide range of Knudsen numbers. The results indicate that the thermal conductivity of a Si/Ge superlattice is much lower than that of the constitutive bulk materials for superlattice periods in the submicron regime. We report results for effective thermal conductivity of various material volume fractions and superlattice periods. Details of the nonequilibrium energy exchange between optical and acoustic phonons that originate from the mismatch of phonon spectra in silicon and germanium are delineated for the first time. Conditions are identified for which this effect can produce significantly more thermal resistance than that due to boundary scattering of phonons.

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Thermal Transport in Finite-Sized Nanocomposites

Heat Transfer: Volume 1 ◽

10.1115/ht2008-56385 ◽

2008 ◽

Cited By ~ 1

Author(s):

Dhruv Singh ◽

Jayathi Y. Murthy ◽

Timothy S. Fisher

Keyword(s):

Thermal Conductivity ◽

Phonon Transport ◽

Boltzmann Transport ◽

Host Materials ◽

Individual Host ◽

Wide Range ◽

Heterogeneous Interfaces ◽

The Individual ◽

Nanoscale Composites ◽

Bulk Behavior

We report finite volume simulations of the phonon Boltzmann Transport Equation (BTE) for heat conduction in periodic nanowire composites. Models for phonon transport across heterogeneous interfaces are developed, and simulations are performed over a wide range of Knudsen numbers. Conditions are identified under which the thermal conductivity of the composite material is less than the bulk thermal conductivity of the individual host materials and under which the alloy limit of thermal conductivity is recovered. We also compute the length scale needed to achieve bulk behavior in nanoscale composites. The results of this study are expected to inform and improve applications such as thermoelectric devices and flexible macroelectronics.

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Spectral Detail of Phonon Conduction and Scattering in Graphene

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 1 ◽

10.1115/ipack2011-52243 ◽

2011 ◽

Author(s):

Dhruv Singh ◽

Jayathi Y. Murthy ◽

Timothy S. Fisher

Keyword(s):

Thermal Conductivity ◽

Phonon Scattering ◽

Interatomic Potential ◽

Phonon Dispersion ◽

Transition Probabilities ◽

Transition Probability ◽

Phonon Transport ◽

Temperature Perturbation ◽

Boltzmann Transport ◽

Wide Range

This paper examines the thermodynamic and thermal transport properties of the 2D graphene lattice. The interatomic interactions are modeled using the Tersoff interatomic potential and are used to evaluate phonon dispersion curves, density of states and thermodynamic properties of graphene as functions of temperature. Perturbation theory is applied to calculate the transition probabilities for three-phonon scattering. The matrix elements of the perturbing Hamiltonian are calculated using the anharmonic interatomic force constants obtained from the interatomic potential as well. An algorithm to accurately quantify the contours of energy balance for three-phonon scattering events is presented and applied to calculate the net transition probability from a given phonon mode. Under the linear approximation, the Boltzmann transport equation (BTE) is applied to compute the thermal conductivity of graphene, giving spectral and polarization-resolved information. Predictions of thermal conductivity for a wide range of parameters elucidate the behavior of diffusive phonon transport. The complete spectral detail of selection rules, important phonon scattering pathways, and phonon relaxation times in graphene are provided, contrasting graphene with other materials, along with implications for graphene electronics. We also highlight the specific scattering processes that are important in Raman spectroscopy based measurements of graphene thermal conductivity, and provide a plausible explanation for the observed dependence on laser spot size.

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Submicron Heat Transport Model in Silicon Accounting for Phonon Dispersion and Polarization

Journal of Heat Transfer ◽

10.1115/1.1833367 ◽

2004 ◽

Vol 126 (6) ◽

pp. 946-955 ◽

Cited By ~ 125

Author(s):

Sreekant V. J. Narumanchi ◽

Jayathi Y. Murthy ◽

Cristina H. Amon

Keyword(s):

Thermal Conductivity ◽

Phonon Dispersion ◽

Transport Model ◽

Relaxation Times ◽

Thermal Response ◽

Boltzmann Transport ◽

Wide Range ◽

Submicron Scale ◽

Different Temperatures ◽

Finite Volume Approach

In recent years, the Boltzmann transport equation (BTE) has begun to be used for predicting thermal transport in dielectrics and semiconductors at the submicron scale. However, most published studies make a gray assumption and do not account for either dispersion or polarization. In this study, we propose a model based on the BTE, accounting for transverse acoustic and longitudinal acoustic phonons as well as optical phonons. This model incorporates realistic phonon dispersion curves for silicon. The interactions among the different phonon branches and different phonon frequencies are considered, and the proposed model satisfies energy conservation. Frequency-dependent relaxation times, obtained from perturbation theory, and accounting for phonon interaction rules, are used. In the present study, the BTE is numerically solved using a structured finite volume approach. For a problem involving a film with two boundaries at different temperatures, the numerical results match the analogous exact solutions from radiative transport literature for various acoustic thicknesses. For the same problem, the transient thermal response in the acoustically thick limit matches results from the solution to the parabolic Fourier diffusion equation. In the acoustically thick limit, the bulk experimental value of thermal conductivity of silicon at different temperatures is recovered from the model. Experimental in-plane thermal conductivity data for silicon thin films over a wide range of temperatures are also matched satisfactorily.

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Highly Anisotropic Thermal Transport in LiCoO2

10.26434/chemrxiv.8874404.v2 ◽

2019 ◽

Author(s):

Hui Yang ◽

Jia-Yue Yang ◽

Christopher Savory ◽

Jonathan Skelton ◽

Benjamin Morgan ◽

...

Keyword(s):

Thermal Conductivity ◽

Lithium Ion Batteries ◽

Phonon Dispersion ◽

Lithium Ion ◽

Boltzmann Transport ◽

Heat Management ◽

Positive Electrodes ◽

Anharmonic Lattice ◽

Anharmonic Interactions ◽

The Impact

<div>LiCoO2 is the prototype cathode in lithium ion batteries. It adopts a crystal structure with alternating Li+ and CoO2- layers along the hexagonal <0001> axis. It is well established that ionic and electronic conduction is highly anisotropic; however, little is known regarding heat transport. We analyse the phonon dispersion and lifetimes of LiCoO2 using anharmonic lattice dynamics based on quantum chemical force constants. Around room temperature, the thermal conductivity in the hexagonal ab plane of the layered cathode is ≈ 6 times higher than that along the c axis based on the phonon Boltzmann transport. The low thermal conductivity (< 10Wm-1K-1) originates from a combination of short phonon lifetimes associated with anharmonic interactions between the octahedral face-sharing CoO2- networks, as well as grain boundary scattering. The impact on heat management and thermal processes in lithium ion batteries based on layered positive electrodes is discussed.</div>

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Effects of Various Parameters on Nanofluid Thermal Conductivity

Journal of Heat Transfer ◽

10.1115/1.2712475 ◽

2006 ◽

Vol 129 (5) ◽

pp. 617-623 ◽

Cited By ~ 249

Author(s):

Seok Pil Jang ◽

Stephen U. S. Choi

Keyword(s):

Thermal Conductivity ◽

Thermal Behavior ◽

Volume Fraction ◽

Heat Transfer Fluids ◽

New Concepts ◽

Model Predictions ◽

Simplifying Assumptions ◽

Thermal Phenomena ◽

First Time ◽

Good Agreement

The addition of a small amount of nanoparticles in heat transfer fluids results in the new thermal phenomena of nanofluids (nanoparticle-fluid suspensions) reported in many investigations. However, traditional conductivity theories such as the Maxwell or other macroscale approaches cannot explain the thermal behavior of nanofluids. Recently, Jang and Choi proposed and modeled for the first time the Brownian-motion-induced nanoconvection as a key nanoscale mechanism governing the thermal behavior of nanofluids, but did not clearly explain this and other new concepts used in the model. This paper explains in detail the new concepts and simplifying assumptions and reports the effects of various parameters such as the ratio of the thermal conductivity of nanoparticles to that of a base fluid, volume fraction, nanoparticle size, and temperature on the effective thermal conductivity of nanofluids. Comparison of model predictions with published experimental data shows good agreement for nanofluids containing oxide, metallic, and carbon nanotubes.

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Investigation of the novelty of latent functionally thermal fluids as alternative to nanofluids in natural convective flows

Scientific Reports ◽

10.1038/s41598-020-77224-6 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Zoubida Haddad ◽

Farida Iachachene ◽

Eiyad Abu-Nada ◽

Ioan Pop

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Heat Transfer Enhancement ◽

Volume Fraction ◽

Heat Of Fusion ◽

Transfer Enhancement ◽

Maximum Heat ◽

Thermal Fluids ◽

Maximum Heat Transfer ◽

Wide Range

AbstractThis paper presents a detailed comparison between the latent functionally thermal fluids (LFTFs) and nanofluids in terms of heat transfer enhancement. The problem used to carry the comparison is natural convection in a differentially heated cavity where LFTFs and nanofluids are considered the working fluids. The nanofluid mixture consists of Al2O3 nanoparticles and water, whereas the LFTF mixture consists of a suspension of nanoencapsulated phase change material (NEPCMs) in water. The thermophysical properties of the LFTFs are derived from available experimental data in literature. The NEPCMs consist of n-nonadecane as PCM and poly(styrene-co-methacrylic acid) as shell material for the encapsulation. Finite volume method is used to solve the governing equations of the LFTFs and the nanofluid. The computations covered a wide range of Rayleigh number, 104 ≤ Ra ≤ 107, and nanoparticle volume fraction ranging between 0 and 1.69%. It was found that the LFTFs give substantial heat transfer enhancement compared to nanofluids, where the maximum heat transfer enhancement of 13% was observed over nanofluids. Though the thermal conductivity of LFTFs was 15 times smaller than that of the base fluid, a significant enhancement in thermal conductivity was observed. This enhancement was attributed to the high latent heat of fusion of the LFTFs which increased the energy transport within the cavity and accordingly the thermal conductivity of the LFTFs.

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Thermal Conductivity of Metal-Oxide Nanofluids: Particle Size Dependence and Effect of Laser Irradiation

Journal of Heat Transfer ◽

10.1115/1.2427071 ◽

2006 ◽

Vol 129 (3) ◽

pp. 298-307 ◽

Cited By ~ 225

Author(s):

Sang Hyun Kim ◽

Sun Rock Choi ◽

Dongsik Kim

Keyword(s):

Thermal Conductivity ◽

Particle Size ◽

Effective Thermal Conductivity ◽

Laser Irradiation ◽

Volume Fraction ◽

Suspended Particle ◽

Titanium Dioxide Nanoparticles ◽

Size Change ◽

Conductivity Enhancement ◽

Wide Range

The thermal conductivity of water- and ethylene glycol-based nanofluids containing alumina, zinc-oxide, and titanium-dioxide nanoparticles is measured using the transient hot-wire method. Measurements are performed by varying the particle size and volume fraction, providing a set of consistent experimental data over a wide range of colloidal conditions. Emphasis is placed on the effect of the suspended particle size on the effective thermal conductivity. Also, the effect of laser-pulse irradiation, i.e., the particle size change by laser ablation, is examined for ZnO nanofluids. The results show that the thermal-conductivity enhancement ratio relative to the base fluid increases linearly with decreasing the particle size but no existing empirical or theoretical correlation can explain the behavior. It is also demonstrated that high-power laser irradiation can lead to substantial enhancement in the effective thermal conductivity although only a small fraction of the particles are fragmented.

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Highly Anisotropic Thermal Transport in LiCoO2

10.26434/chemrxiv.8874404 ◽

2019 ◽

Author(s):

Hui Yang ◽

Jia-Yue Yang ◽

Christopher Savory ◽

Jonathan Skelton ◽

Benjamin Morgan ◽

...

Keyword(s):

Thermal Conductivity ◽

Lithium Ion Batteries ◽

Phonon Dispersion ◽

Lithium Ion ◽

Boltzmann Transport ◽

Heat Management ◽

Positive Electrodes ◽

Anharmonic Lattice ◽

Anharmonic Interactions ◽

The Impact

<div>LiCoO2 is the prototype cathode in lithium ion batteries. It adopts a crystal structure with alternating Li+ and CoO2- layers along the hexagonal <0001> axis. It is well established that ionic and electronic conduction is highly anisotropic; however, little is known regarding heat transport. We analyse the phonon dispersion and lifetimes of LiCoO2 using anharmonic lattice dynamics based on quantum chemical force constants. Around room temperature, the thermal conductivity in the hexagonal ab plane of the layered cathode is ≈ 6 times higher than that along the c axis based on the phonon Boltzmann transport. The low thermal conductivity (< 10Wm-1K-1) originates from a combination of short phonon lifetimes associated with anharmonic interactions between the octahedral face-sharing CoO2- networks, as well as grain boundary scattering. The impact on heat management and thermal processes in lithium ion batteries based on layered positive electrodes is discussed.</div>

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Simulation of Phonon Transport in Semiconductors Using a Population-Dependent Many-Body Cellular Monte Carlo Approach

Journal of Heat Transfer ◽

10.1115/1.4035042 ◽

2016 ◽

Vol 139 (3) ◽

Cited By ~ 1

Author(s):

Flavio F. M. Sabatti ◽

Stephen M. Goodnick ◽

Marco Saraniti

Keyword(s):

Monte Carlo ◽

Phonon Dispersion ◽

Phonon Transport ◽

Space Distribution ◽

Boltzmann Transport ◽

Many Body ◽

Simulation Code ◽

Conservation Of Energy ◽

Wide Range ◽

Cellular Monte Carlo

A Monte Carlo rejection technique for numerically solving the complete, nonlinear phonon Boltzmann transport equation (BTE) is presented in this work, including three particles interactions. The technique has been developed to explicitly model population-dependent scattering within a full-band cellular Monte Carlo (CMC) framework, to simulate phonon transport in semiconductors, while ensuring conservation of energy and momentum for each scattering event within gridding error. The scattering algorithm directly solves the many-body problem accounting for the instantaneous distribution of the phonons. Our general approach is capable of simulating any nonequilibrium phase space distribution of phonons using the full phonon dispersion without the need of approximations used in previous Monte Carlo simulations. In particular, no assumptions are made on the dominant modes responsible for anharmonic decay, while normal and umklapp scattering are treated on the same footing. In this work, we discuss details of the algorithmic implementation of both the three-particle scattering for the treatment of the anharmonic interactions between phonons, as well as treating isotope and impurity scattering within the same framework. The simulation code was validated by comparison with both analytical and experimental results; in particular, the simulation results show close agreement with a wide range of experimental data such as thermal conductivity as function of the isotopic composition, the temperature, and the thin-film thickness.

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