Percolation Effects on the Thermal Conductivity of 3D Nanotube Composites

2008 ◽  
Author(s):  
Satish Kumar ◽  
Muhammad A. Alam ◽  
Jayathi Y. Murthy
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Thermal Transport ◽  
Three Dimensional ◽  
Linear Response Theory ◽  
Critical Parameters ◽  
Conductivity Ratio ◽  
Interfacial Resistance ◽  
Numerical Predictions ◽  
Nanotube Composites

We analyze thermal transport in three-dimensional (3D) nano-composites composed of carbon nanotube (CNT) dispersions to investigate percolation effects on the effective thermal conductivity of these composites. Thermal transport simulations for the randomly distributed nanotubes inside the host substrate are based on the diffusive Fourier conduction theory. The numerical model incorporates the effect of substrate-CNT conductivity ratio and the interfacial resistance due to tube-tube and tube-substrate contact, which are the most critical parameters governing thermal transport properties. Numerical predictions of effective thermal conductivity are in excellent agreement with the linear response theory and effective medium approximation (EMA) when assumptions of theory are incorporated in the model. The trends for the variation of effective thermal conductivity with increasing nanotube density are in broad agreement with previous experimental observations. Our numerical results also show that the onset of thermal percolation is gradual and largely dependent on the tube-to-substrate conductivity ratio and interfacial resistance at tube-tube and tube-substrate contact.

Numerical Model for Thermal Transport in 3-D Nanotube Composites

2007 ◽  
Author(s):  
Satish Kumar ◽  
Jayathi Y. Murthy
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Finite Volume ◽  
Thermal Transport ◽  
Three Dimensional ◽  
Finite Volume Scheme ◽  
Interfacial Resistance ◽  
Volume Scheme ◽  
Numerical Predictions ◽  
Nanotube Composites

The effective thermal conductivity of three dimensional (3-D) nanocomposites composed of carbon nanotube (CNT) dispersions is computed using Fourier conduction theory. The random ensemble of nanotubes is generated numerically and each nanotube is discretized using a finite volume scheme. The background substrate mesh is also discretized using a finite volume scheme. We incorporate all parameters crucial for thermal transport studies, i.e. tube aspect ratio, tube density, composite sample size, substrate-CNT conductivity ratio and the interfacial resistance due to tube-tube and tube-substrate contact. Two-dimensional (thin film) nanocomposites are also simulated for comparison. Numerical predictions of effective thermal conductivity are in excellent agreement with the effective medium approximation (EMA) for both 2-D and 3-D nanocomposites at low tube densities, but depart significantly from EMA predictions when tube-tube interaction becomes significant. It is found that the effect of tube-tube contact on effective thermal conductivity is more significant for 2-D composites than 3-D composites. Hence percolation effects may play a more significant role in thermal transport in 2-D nano-composites.

Constructing Three-dimensional Nano-crystalline Diamond Network within Polymer Composites for Enhanced Thermal Conductivity

Nanoscale ◽  
2021 ◽  
Author(s):  
Shaoyang Xiong ◽  
Yue Qin ◽  
Linhong Li ◽  
Guoyong Yang ◽  
Maohua Li ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Polymer Composites ◽  
Thermal Performance ◽  
Thermal Transport ◽  
High Performance ◽  
Rapid Development ◽  
Electronic Devices ◽  
Three Dimensional ◽  
Nano Crystalline ◽  
Enhanced Thermal Conductivity

In order to meet the requirement of thermal performance with the rapid development of high-performance electronic devices, constructing a three-dimensional thermal transport skeleton is an effective method for enhancing thermal...

Brownian-Motion-Based Convective-Conductive Model for the Effective Thermal Conductivity of Nanofluids

2005 ◽  
Vol 128 (6) ◽  
pp. 588-595 ◽  
Author(s):  
Ravi Prasher ◽  
Prajesh Bhattacharya ◽  
Patrick E. Phelan
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Particle Sizes ◽  
Brownian Movement ◽  
Liquid Temperature ◽  
Interfacial Resistance ◽  
Conduction Model ◽  
Order Of Magnitude ◽  
Base Liquid ◽  
Good Agreement

Here we show through an order-of-magnitude analysis that the enhancement in the effective thermal conductivity of nanofluids is due mainly to the localized convection caused by the Brownian movement of the nanoparticles. We also introduce a convective-conductive model which accurately captures the effects of particle size, choice of base liquid, thermal interfacial resistance between the particles and liquid, temperature, etc. This model is a combination of the Maxwell-Garnett (MG) conduction model and the convection caused by the Brownian movement of the nanoparticles, and reduces to the MG model for large particle sizes. The model is in good agreement with data on water, ethylene glycol, and oil-based nanofluids, and shows that the lighter the nanoparticles, the greater the convection effect in the liquid, regardless of the thermal conductivity of the nanoparticles.

Numerical Simulations of Thermal Transport in Random Porous Materials and Powder Systems Using the Smoothed Particle Hydrodynamics Method

2017 ◽  
Author(s):  
Deepak Shah ◽  
Alexey N. Volkov
Keyword(s):  
Thermal Conductivity ◽  
Porous Materials ◽  
Effective Thermal Conductivity ◽  
Smoothed Particle Hydrodynamics ◽  
Thermal Transport ◽  
Thermal Contact Conductance ◽  
Powder Bed ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Powder Particles

A numerical method to solve thermal transport problems in powder bed systems and porous materials with finite thermal contact conductance at interfaces between individual powder particles or grains is developed based on the Smoothed Particle Hydrodynamics approach. The developed method is applied to study the effective thermal conductivity of two-dimensional random powder bed systems with binary distribution of powder particles radii. The effects of particle size distribution parameters, density parameter, and effective interface area between particles on the effective thermal conductivity are studied. It is found that at finite Biot number, which characterizes the ratio of the interfacial conductance to the conductance of the bulk powder material, the effective thermal conductivity of porous samples increases with increasing fraction of particles of larger size.

Numerical Simulation of Heat and Mass Transfer in Metal Hydride Hydrogen Accumulators of Different Complex Designs

2010 ◽  
Author(s):  
Dmitriy Lazarev ◽  
Valeriy Artemov ◽  
Georgiy Yankov ◽  
Konstantin Minko
Keyword(s):  
Thermal Conductivity ◽  
Mass Transfer ◽  
Effective Thermal Conductivity ◽  
Heat And Mass Transfer ◽  
Metal Hydride ◽  
Solid Phase ◽  
Three Dimensional ◽  
Calculated Data ◽  
Sorption Rate ◽  
Gas Admixtures

A three-dimensional mathematical model of unsteady heat and mass transfer in porous hydrogen-absorbing media, accounting for presence of “passive” gas admixtures, is developed. New technique for evaluation of effective thermal conductivity of porous medium, which consists of microparticles, is suggested. Effect of “passive” gas admixtures on heat and mass transfer and sorption rate in metal hydride reactor is analyzed. It is shown that decrease of effective thermal conductivity and partial hydrogen pressure under decrease of hydrogen concentration effect on the hydrogen sorption rate considerably. It is disclosed that an intensive 3D natural convection takes place in a gas volume of reactor under certain conditions. Numerical analysis of heat and mass transfer in metal-hydride reactor of hydrogen accumulation systems was done. Sorption of hydrogen in cylindrical reactors with external cooling and central supply of hydrogen are analyzed including reactors with finned active volume and tube-shell reactor with external and internal cooling cartridge matrix. Unsteady three dimensional temperature and concentration fields in solid phase are presented. Integral curves representing the dynamic of sorption and desorption are calculated. Data on efficiency of considered reactors are presented and compared.

scholarly journals Third-order thermo-mechanical properties for packs of Platonic solids using statistical micromechanics

2015 ◽  
Vol 471 (2177) ◽  
pp. 20150060 ◽  
Author(s):  
A. Gillman ◽  
G. Amadio ◽  
K. Matouš ◽  
T. L. Jackson
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Three Dimensional ◽  
Adaptive Methods ◽  
Shape Effect ◽  
Third Order ◽  
Recent Letter ◽  
Penetrable Spheres ◽  
First Time

Obtaining an accurate higher order statistical description of heterogeneous materials and using this information to predict effective material behaviour with high fidelity has remained an outstanding problem for many years. In a recent letter, Gillman & Matouš (2014 Phys. Lett. A 378, 3070–3073. ()) accurately evaluated the three-point microstructural parameter that arises in third-order theories and predicted with high accuracy the effective thermal conductivity of highly packed material systems. Expanding this work here, we predict for the first time effective thermo-mechanical properties of granular Platonic solid packs using third-order statistical micromechanics. Systems of impenetrable and penetrable spheres are considered to verify adaptive methods for computing n -point probability functions directly from three-dimensional microstructures, and excellent agreement is shown with simulation. Moreover, a significant shape effect is discovered for the effective thermal conductivity of highly packed composites, whereas a moderate shape effect is exhibited for the elastic constants.

State of the art of thermal characterization of electronic components using computational fluid dynamic tools

2017 ◽  
Vol 27 (11) ◽  
pp. 2433-2450 ◽  
Author(s):  
Eric Monier-Vinard ◽  
Brice Rogie ◽  
Valentin Bissuel ◽  
Najib Laraqi ◽  
Olivier Daniel ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Numerical Model ◽  
Effective Thermal Conductivity ◽  
Three Dimensional ◽  
Computation Time ◽  
Printed Wiring Board ◽  
Electronic Components ◽  
Content Type ◽  
Three Dimensional Representation ◽  
Wiring Board

Purpose Latest Computational Fluid Dynamics (CFDs) tools allow modeling more finely the conjugate thermo-fluidic behavior of a single electronic component mounted on a Printed Wiring Board (PWB). A realistic three-dimensional representation of a large set of electric copper traces of its composite structure is henceforth achievable. The purpose of this study is to confront the predictions of the fully detailed numerical model of an electronic board to a set of experiment results to assess their relevance. Design/methodology/approach The present study focuses on the case of a Ball Grid Array (BGA) package of 208 solder balls that connect the component electronic chip to the Printed Wiring Board. Its complete geometrical definition has to be coupled with a realistic board layers layout and a fine description of their numerous copper traces to appropriately predict the way the heat is spread throughout that multi-layer composite structure. The numerical model computations were conducted on four CFD software then compare to experiment results. The component thermal metrics for single-chip packages are based on the standard promoted by the Joint Electron Device Engineering Council (JEDEC), named JESD-51. The agreement of the numerical predictions and measurements has been done for free and forced convection. Findings The present work shows that the numerical model error is lower than 2 per cent for various convective boundary conditions. Moreover, the establishment of realistic numerical models of electronic components permits to properly apprehend multi-physics design issues, such as joule heating effect in copper traces. Moreover, the practical modeling assumptions, such as effective thermal conductivity calculation, used since decades, for characterizing the thermal performances of an electronic component were tested and appeared to be tricky. A new approach based on an effective thermal conductivity matrix is investigated to reduce computation time. The obtained numerical results highlight a good agreement with experimental data. Research limitations/implications The study highlights that the board three-dimensional modeling is mandatory to properly match the set of experiment results. The conventional approach based on a single homogenous layer using effective thermal conductivity calculation has to be banned. Practical implications The thermal design of complex electronic components is henceforth under increasing control. For instance, the impact of gold wire-bonds can now be investigated. The three-dimensional geometry of sophisticated packages, such as in BGA family, can be imported with all its internal details as well as those of its associated test board to build a realistic numerical model. The establishment of behavioral models such as DELPHI Compact Thermal Models can be performed on a consistent three-dimensional representation with the aim to minimize computation time. Originality/value The study highlights that multi-layer copper trace plane discretization could be used to strongly reduce computation time while conserving a high accuracy level.

Evaporation, Condensation, and Flow in an Idealized Micro Heat Pipe

2002 ◽  
Author(s):  
Jin Zhang ◽  
Harris Wong
Keyword(s):  
Thermal Conductivity ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Three Dimensional ◽  
Heat Pipes ◽  
Rigorous Analysis ◽  
Evaporation And Condensation ◽  
Micro Heat Pipe ◽  
Complicated Geometry ◽  
Micro Heat Pipes

Micro heat pipes have been used in cooling micro electronic components. However their effective thermal conductivity is low compared with that of conventional heat pipes. Due to the complexity of the coupled heat and mass transport, and to the complicated three-dimensional bubble geometry inside micro heat pipes, there is a lack of rigorous analysis. As a result, the relatively low effective thermal conductivity remains unexplained. We have conceptualized an idealized micro heat pipe that eliminates the complicated geometry, but retains the essential physics. Given the simplified geometry, many effects can be studied, such as thermocapillary flow, and evaporation and condensation physics. In this talk, we will present the flow field induced by evaporation.

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