scholarly journals A Thermal Transport Study of Branched Carbon Nanotubes with Cross and T-Junctions

2021 ◽  
Vol 11 (13) ◽  
pp. 5933
Author(s):  
Wei-Jen Chen ◽  
I-Ling Chang
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Thermal Management ◽  
Thermal Transport ◽  
Topological Defects ◽  
Branch Length ◽  
Phonon Transport ◽  
Heat Current ◽  
Transport Mechanisms ◽  
Non Equilibrium Molecular Dynamics

This study investigated the thermal transport behaviors of branched carbon nanotubes (CNTs) with cross and T-junctions through non-equilibrium molecular dynamics (NEMD) simulations. A hot region was created at the end of one branch, whereas cold regions were created at the ends of all other branches. The effects on thermal flow due to branch length, topological defects at junctions, and temperature were studied. The NEMD simulations at room temperature indicated that heat transfer tended to move sideways rather than straight in branched CNTs with cross-junctions, despite all branches being identical in chirality and length. However, straight heat transfer was preferred in branched CNTs with T-junctions, irrespective of the atomic configuration of the junction. As branches became longer, the heat current inside approached the values obtained through conventional prediction based on diffusive thermal transport. Moreover, directional thermal transport behaviors became prominent at a low temperature (50 K), which implied that ballistic phonon transport contributed greatly to directional thermal transport. Finally, the collective atomic velocity cross-correlation spectra between branches were used to analyze phonon transport mechanisms for different junctions. Our findings deeply elucidate the thermal transport mechanisms of branched CNTs, which aid in thermal management applications.

scholarly journals The Atomistic Study on Thermal Transport of the Branched Cnt

2020 ◽  
Vol 36 (5) ◽  
pp. 721-727 ◽  
Author(s):  
Wei-Jen Chen ◽  
I-Ling Chang
Keyword(s):  
Heat Flow ◽  
Thermal Management ◽  
Thermal Transport ◽  
Tensile Strain ◽  
Branch Length ◽  
Phonon Transport ◽  
Dynamics Simulation ◽  
Thermal Circuit ◽  
Non Equilibrium Molecular Dynamics ◽  
Atomistic Study

ABSTRACTIn this research, the thermal transport behavior of the branched carbon nanotube (CNT) with T-junction was investigated using non-equilibrium molecular dynamics simulation. Both symmetric and asymmetric temperature-controlled simulations were imposed to evaluate how the heat flowed inside the branched CNT with three branches of equal length and same chirality. The branch length and strain effects on the heat flow were examined. In addition, the simulated heat flow was compared with the prediction made by conventional thermal circuit calculation based on diffusive phonon transport. The heat was observed to flow straight rather than sideway inside the branched CNT with T-junction under the asymmetric temperature setup; this finding contradicts the conventional thermal circuit calculation. There are two possible explanations for this phenomenon. One is ballistic phonon transport and the other is phonons have different interactions or scattering with the defective atomic configurations at the T-junction. Moreover, the tensile strain could tune the heat flow, a finding that might be useful in thermal management applications.

scholarly journals The Integrated Component-System Optimization of a Typical Thermal Management System by Combining Empirical and Heat Current Methods

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6347
Author(s):  
Junhong Hao ◽  
Youjun Zhang ◽  
Nian Xiong
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Thermal Management ◽  
Management System ◽  
Optimal Allocation ◽  
Current Method ◽  
Heat Current ◽  
Component System ◽  
Minimum Pressure ◽  
Thermal Management System

Integration of modeling and optimization of a thermal management system simultaneously depends on heat transfer performance of the components and the topological characteristics of the system. This paper introduces a heat current method to construct the overall heat current layout of a typical double-loop thermal management system. We deduce the system heat transfer matrix as the whole system constraint based on the overall heat current layout. Moreover, we consider the influences of structural and operational parameters on the thermal hydraulic performances of each heat exchanger by combining the empirical correlations of the heat transfer and pressure drop. Finally, the minimum pressure drop is obtained by solving these optimal governing equations derived by the Lagrange multiplier method considering the physical constraints and operational conditions. The optimization results show that the minimum pressure drop reduces about 8.1% with the optimal allocation of mass flow rates of each fluid. Moreover, the impact analyses of structural and operating parameters and boundary conditions on the minimum and optimal allocation present that the combined empirical correlation-heat current method is feasible and significant for achieving integrated component-system modeling and optimization.

Pump-Probe Experimental Study of Phonon Reflectivity at an Interface and Phonon Relaxation Time

2005 ◽  
Author(s):  
Ronggui Yang ◽  
Xiaoyuan Chen ◽  
Aaron Schmidt ◽  
Gang Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Management ◽  
Thermal Transport ◽  
Size Effects ◽  
Energy Transport ◽  
Quantum Size Effects ◽  
Pump Probe ◽  
Sensor Development ◽  
Quantum Size ◽  
Phonon Relaxation Time

Heat transfer in nanostructures differs significantly from that in macrostructures because of classical and quantum size effects on energy carriers, i.e., phonons, electrons, and photons [1–3]. Understanding thermal transport in nanostructures is of fundamental importance to a variety of technologies, including thermal management of nanoelectronics and optoelectronics, energy conversion, nanofabrication, and sensor development. A better understanding of the energy transport at nanoscale calls for both simulations and experimental techniques on thermal transport in nanostructures.

scholarly journals Thermal Transport in Nonlinear Unsteady Colloidal Model by Considering the Carbon Nanomaterials Length and Radius

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2448
Author(s):  
Syed Tauseef Mohyud-Din ◽  
Adnan ◽  
T. Abdeljawad ◽  
Umar Khan ◽  
Naveed Ahmed ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Thermal Transport ◽  
Carbon Nanomaterials ◽  
Colloidal Suspension ◽  
Velocity Slip ◽  
Shear Stresses ◽  
Medical Sciences ◽  
Multiwalled Carbon ◽  
Walled Carbon Nanotubes

Thermal transport analysis in colloidal suspension is significant from industrial, engineering, and technological points of view. It has numerous applications comprised in medical sciences, chemical and mechanical engineering, electronics, home appliances, biotechnology, computer chips, detection of cancer cells, microbiology, and chemistry. The carbon nanomaterials have significant thermophysical characteristics that are important for thermal transport. Therefore, the thermal transport in H2O composed by single and multiwalled carbon nanotubes is examined. The length and radius of the nanomaterials is in range of 3 μm ≤ L* ≤ 70 μm and 10 nm ≤ d ≤ 40 nm, respectively. The problem is modelled over a curved stretching geometry by inducing the velocity slip and thermal jump conditions. The coupling of Runge-Kutta (RK) and shooting technique is adopted for the solution. From the analysis it is perceived that the heat transfer at the surface drops for stretching. The heat transfer rate prevailed for Single walled carbon nanotubes SWCNTs-H2O colloidal suspension. The suction and stretching of the surface resist the shear stresses and more shear stress trends are investigated for larger curvature.

scholarly journals Modeling of Subcontinuum Thermal Transport Across Semiconductor-Gas Interfaces

2008 ◽  
Author(s):  
Dhruv Singh ◽  
Xiaohui Guo ◽  
Alina Alexeenko ◽  
Jayathi Y. Murthy ◽  
Timothy S. Fisher
Keyword(s):  
Heat Transfer ◽  
Boltzmann Equation ◽  
Thermal Transport ◽  
Phonon Transport ◽  
Interface Temperature ◽  
Molecular Flow ◽  
Parallel Plates ◽  
Thermal Interface ◽  
The Boltzmann Equation ◽  
Gas Molecules

A physically rigorous computational algorithm is developed and applied to calculate sub-continuum thermal transport in structures containing semiconductor-gas interfaces. The solution is based on a finite volume discretization of the Boltzmann equation for gas molecules (in the gas phase) and phonons (in the semiconductor). A partial equilibrium is assumed between gas molecules and phonons at the interface of the two media, and the degree of this equilibrium is determined by the accommodation coefficients of gas molecules and phonons on either side of the interface. Energy balance is imposed to obtain a value of the interface temperature. The problem of heat transfer between two parallel plates is investigated. A range of transport regimes is studied, varying from ballistic phonon transport and free molecular flow to continuum heat transfer in both gas and solid. In particular, the thermal interface resistance (or temperature slip) at a gas-solid interface is extracted in the mesoscopic regime where a solution of the Boltzmann equation is necessary. This modeling approach is expected to find applications in the study of heat conduction through microparticle beds, gas flows in microchannel heat sinks and in determining gas gap conductance in thermal interface materials.

Topics of Heat Transfer Related to Single-Walled Carbon Nanotubes

2007 ◽  
Author(s):  
Shigeo Maruyama
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Heat Conduction ◽  
Single Walled Carbon Nanotubes ◽  
Phonon Transport ◽  
Hot Water ◽  
Single Walled Carbon ◽  
Stationary Heat ◽  
Stationary Heat Conduction ◽  
Walled Carbon Nanotubes

Using an alcohol catalytic CVD method shown to produce high-quality single-walled carbon nanotubes (SWNTs), films of vertically aligned (VA-)SWNTs were synthesized on quartz substrates. The VA-SWNTs can be removed from the substrate and transferred onto an arbitrary surface—without disturbing the vertical alignment—using a hot-water assisted technique. This ability makes experimental measurements of the anisotropic properties of SWNTs considerably less challenging. A series of molecular dynamics simulations have been performed to investigate a variety of heat conduction characteristics of SWNTs. Investigations of stationary heat conduction identifies diffusive-ballistic heat conduction regime in a wide range of nanotube-lengths. Furthermore, studies on non-stationary heat conduction show that the extensive ballistic phonon transport gives rise to wave-like non-Fourier heat conduction. Finally, several case studies are presented for SWNT heat transfer in more practical situations.

Interfacial Thermal Conductance and Thermal Rectification Across In-Plane Graphene/h-BN Heterostructures With Different Bonding Types

2019 ◽  
Author(s):  
Ting Liang ◽  
Ping Zhang ◽  
Peng Yuan ◽  
Man Zhou ◽  
Siping Zhai
Keyword(s):  
Thermal Management ◽  
Thermal Transport ◽  
Strain Distribution ◽  
Hexagonal Boron Nitride ◽  
Thermal Conductance ◽  
Interfacial Stress ◽  
Thermal Rectification ◽  
Nanoelectronic Devices ◽  
Interfacial Thermal Conductance ◽  
Non Equilibrium Molecular Dynamics

Abstract The in-plane graphene/hexagonal boron nitride (Gr/h-BN) heterostructures have received extensive attention in recent years due to their excellent physical properties and the development potential of next-generation nanoelectronic devices. Generally, different bonding types between Gr and h-BN are considered in different non-equilibrium molecular dynamics (NEMD) simulations studies. However, which type of bonding is most conducive to interface thermal transport is still very confusing. In this work, we investigate the interfacial thermal conductance (ITC) and the thermal rectification (TR) in five different bonding types of in-plane Gr/h-BN heterostructures by using NEMD simulations. It is found that the ITC depends strongly on the bonding strength and arrangement of different atoms across the boundary. Among the five different bonding types of heterostructures, the C-N bonded heterojunction exhibits the highest ITC due to its stronger interfacial bonding. The analyses on the strain distribution indicated that a low interfacial stress level at the interface junction, may facilitate the heat conduction, thus leading to a higher ITC. In addition, we found that TR occurs in all five bonded heterostructures, and the C-B bonded heterojunction possesses the highest TR factor. The present study is of significance for understanding the thermal transport behavior of Gr/h-BN heterostructures and promoting their future applications in thermal management and thermoelectric devices.

An overview of phonon-based heat conduction models and their solution

2016 ◽  
Vol 26 (3/4) ◽  
pp. 916-949 ◽  
Author(s):  
V.M Wheeler ◽  
K K Tamma
Keyword(s):  
Heat Transfer ◽  
Thin Films ◽  
Heat Conduction ◽  
Thermal Transport ◽  
Phonon Transport ◽  
Random Motion ◽  
Comprehensive Overview ◽  
Content Type ◽  
The Subject ◽  
Numerical Discretization

Purpose – The purpose of this paper is to provide an overview and some recent advances in the models, analysis and simulation of thermal transport of phonons as related to the field of microscale/macroscale heat conduction in solids. The efforts focus upon a fairly comprehensive overview of the subject matter from a unified standpoint highlighting the various approximations inherent in the thermal models. Subsequently, the numerical formulations and illustrations using the current state-of-the-art are provided. Design/methodology/approach – This paper is dedicated to the approximate solution to the relaxation time phonon Boltzmann equation (BE). While original contributions are pointed out and addressed appropriately, the efforts and contributions will be focussed on a relatively complete overview highlighting the field from one unified standpoint and clearly stating all assumptions that go into the approximations inherent to existing models. The contents will be divided as follows: In the first section the authors will give an overview of semi-classical phonon transport physics. Then the authors will discuss the equation of phonon radiative transport (EPRT) and its approximations—the ballistic-diffusive approximation (BDA) and the new heat equation (NHE). Next the authors derive and discuss the C-F model. A numerical discretization method valid for all models is then presented followed by results to numerical simulations and discussion. Findings – From a unified treatment based on the introduction of an energy distribution function, the authors have derived the EPRT and its two well-known approximations: BDA and NHE. For completeness and to provide a vehicle for a general numerical discretization approach, the authors have also included analysis of the C-F model and the parabolic and hyperbolic descriptions of heat transfer along with it. The approximation of angular dependence of phonons in radiation-like descriptions of transport has been given special attention. The assumption of isotropy was found to be of paramount importance in the formulation of position space models for phononic thermal transport. For the thin film problem considered here, the NHE along with the proper boundary condition appears to be the best choice to approximate the phonon BE. Not only does it provide predictions that are in excellent agreement with EPRT, it does not require the discretization of phase space making it far more computationally efficient. Originality/value – The authors hope this work will help dispel the idea that since Fourier’s law describes diffusion (under limiting assumptions) and it has shown to be ineffective in describing heat transfer for very thin films, that diffusion cannot describe heat transfer in thin films and one should look to a radiative description instead. If one considers diffusion in the sense of random motion, as invisaged by the original builders of the subject (Smoluchowski, Einstein, Ornstein et al.), instead of a temperature gradient, the idea that diffusion can govern thermal transport at this scale is not surprising. Indeed, the NHE is essentially a diffusion equation that describes the motion of particles up to the point of true randomness (isotropy) as well as thereafter.

scholarly journals Thermal Characterization and Modelling of AlGaN-GaN Multilayer Structures for HEMT Applications

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2363 ◽  
Author(s):  
Lisa Mitterhuber ◽  
René Hammer ◽  
Thomas Dengg ◽  
Jürgen Spitaler
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Phonon Transport ◽  
Thermal Design ◽  
High Electron ◽  
Transport Mechanisms ◽  
Von Karman ◽  
Hemt Structure ◽  
Von Kármán ◽  
Thermal Conductivities

To optimize the thermal design of AlGaN-GaN high-electron-mobility transistors (HEMTs), which incorporate high power densities, an accurate prediction of the underlying thermal transport mechanisms is crucial. Here, a HEMT-structure (Al0.17Ga0.83N, GaN, Al0.32Ga0.68N and AlN on a Si substrate) was investigated using a time-domain thermoreflectance (TDTR) setup. The different scattering contributions were investigated in the framework of phonon transport models (Callaway, Holland and Born-von-Karman). The thermal conductivities of all layers were found to decrease with a temperature between 300 K and 773 K, due to Umklapp scattering. The measurement showed that the AlN and GaN thermal conductivities were a magnitude higher than the thermal conductivity of Al0.32Ga0.68N and Al0.17Ga0.83N due to defect scattering. The layer thicknesses of the HEMT structure are in the length scale of the phonon mean free path, causing a reduction of their intrinsic thermal conductivity. The size-effect of the cross-plane thermal conductivity was investigated, which showed that the phonon transport model is a critical factor. At 300 K, we obtained a thermal conductivity of (130 ± 38) Wm−1K−1 for the (167 ± 7) nm thick AlN, (220 ± 38) Wm−1K−1 for the (1065 ± 7) nm thick GaN, (11.2 ± 0.7) Wm−1K−1 for the (423 ± 5) nm thick Al0.32Ga0.68N, and (9.7 ± 0.6) Wm−1K−1 for the (65 ± 5) nm thick Al0.17Ga0.83N. Respectively, these conductivity values were found to be 24%, 90%, 28% and 16% of the bulk values, using the Born-von-Karman model together with the Hua–Minnich suppression function approach. The thermal interface conductance as extracted from the TDTR measurements was compared to results given by the diffuse mismatch model and the phonon radiation limit, suggesting contributions from inelastic phonon-scattering processes at the interface. The knowledge of the individual thermal transport mechanisms is essential for understanding the thermal characteristics of the HEMT, and it is useful for improving the thermal management of HEMTs and their reliability.

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