Upper bound to the thermal conductivity of carbon nanotube pellets (original) (raw)
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Unusually High Thermal Conductivity of Carbon Nanotubes
2000
Combining equilibrium and nonequilibrium molecular dynamics simulations with accurate carbon potentials, we determine the thermal conductivity l of carbon nanotubes and its dependence on temperature. Our results suggest an unusually high value, l ഠ 6600 W͞m K, for an isolated ͑10, 10͒ nanotube at room temperature, comparable to the thermal conductivity of a hypothetical isolated graphene monolayer or diamond. Our results suggest that these high values of l are associated with the large phonon mean free paths in these systems; substantially lower values are predicted and observed for the basal plane of bulk graphite.
…, 2010
The extremely high thermal conductivity of individual carbon nanotubes, predicted theoretically and observed experimentally, has not yet been achieved for large nanotube assemblies. Resistances at tube-tube interconnections and tube-electrode interfaces have been considered the main obstacles for effective electronic and heat transport. Here we show that, even for infinitely long and perfect nanotubes with well-designed tube-electrode interfaces, excessive radial heat radiation from nanotube surfaces and quenching of phonon modes in large bundles are additional processes that substantially reduce thermal transport along nanotubes. Equivalent circuit simulations and an experimental self-heating 3ω technique were used to determine the peculiarities of anisotropic heat flow and thermal conductivity of single MWNTs, bundled MWNTs and aligned, free-standing MWNT sheets. The thermal conductivity of individual MWNTs grown by chemical vapor deposition and normalized to the density of graphite is much lower (κ MWNT = 600 ± 100 W m −1 K −1 ) than theoretically predicted. Coupling within MWNT bundles decreases this thermal conductivity to 150 W m −1 K −1 . Further decrease of the effective thermal conductivity in MWNT sheets to 50 W m −1 K −1 comes from tube-tube interconnections and sheet imperfections like dangling fiber ends, loops and misalignment of nanotubes. Optimal structures for enhancing thermal conductivity are discussed.
The molecular dynamics simulation with the use of the empirical Tersoff potential is applied to study the thermal characteristics of carbon nanotubes (CNTs). A thermal reservoir is devised to control the temperature and to exact the heat flux input. The quantum effect defining the precise temperature from the absolute zero Kelvin and up is included by applying phonon (boson) statistics to the specific heat. At low temperature, the CNT thermal conductivity increases with increasing temperature. After reaching its peak, which is limited by the length of the CNT, it decreases with temperature due to phonon-phonon interactions. The scaling law of thermal conductivity as a function of temperature and length is inferred from the simulation results, allowing prediction for CNTs of much longer length beyond what MD could simulate.
Thermal Conductance of an Individual Single-Wall Carbon Nanotube above Room Temperature
Nano Letters, 2006
The thermal properties of a suspended metallic single-wall carbon nanotube (SWNT) are extracted from its high-bias (I-V) electrical characteristics over the 300-800 K temperature range, achieved by Joule self-heating. The thermal conductance is approximately 2.4 nW/K and the thermal conductivity is nearly 3500 Wm -1 K -1 at room temperature for a SWNT of length 2.6 µm and diameter 1.7 nm. A subtle decrease in thermal conductivity steeper than 1/T is observed at the upper end of the temperature range, which is attributed to secondorder three-phonon scattering between two acoustic modes and one optical mode. We discuss sources of uncertainty and propose a simple analytical model for the SWNT thermal conductivity including length and temperature dependence. *
Investigation of thermal conductivity of single and multi-walled carbon nanotubes
2006
In this paper, the thermal conductivity of single-wall carbon nanotubes is determined by lattice vibrations (phonons) and free elections. The thermal conductivity is modeled up to 8-300 K and the observed deviations in K-T figures are explained in terms of phonon vibrations models. An suitable theoretical model is shown for thermal conductivity behavior with respect to temperature and is generalized for experimental results. This model enables us to calculate the thermal conductivity and the thermal potential energy of single-wall carbon nanotubes. Key word: single-wall carbon nanotube, thermal conductivity, specific heat capacity, thermal potential energy
Temperature Dependent Thermal Properties in Single-Wall Carbon Nano Tubes Based on Phonon Scattering
Engineering International, 2014
Electronic devices and integrated systems are reduced to the size of micron and nanometer level and it becomes particularly important to predict the thermal transport properties of the components. Because of a unique structure and novel properties of carbon nanotubes (CNTs) have attracted significant attention. In this article, thermal transport properties of single wall CNTs (SWCNTs) are introduced. Combining equilibrium and nonequilibrium molecular dynamics with carbon potentials, we have studied the thermal conductivity of carbon nanotubes and its dependence on temperature. Phonon conduction depends on band gaps as well as thermal contact resistance of metallic CNTs, governed by phonon scattering and it shows evidence of 1-D quantization of the phonon band structure. We have studied here the thermal conductivity of single wall nanotubes dependence on chirality structure, dimensions of tubes, defects and vacancies in tubes. We found that the single wall carbon nanotubes have very high thermal conductivity comparable to diamond crystal and in-plane graphite sheet.
Thermal Conductance of Helically Coiled Carbon Nanotubes
Contemporary Materials, 2014
Thermal conductivity is one of the most interesting physical properties of carbon nanotubes. This quantity has been extensively explored experimentally and theoretically using different approaches like: molecular dynamics simulation, Boltzmann-Peierls phonon transport equation, modified wave-vector model etc. Results of these investigations are of great interest and show that carbon- based materials, graphene and nanotubes in particular, show high values of thermal conductivity. Thus, carbon nanotubes are a good candidate for the future applications as thermal interface materials. In this paper we present the results of thermal conductance s of a model of helically coiled carbon nanotubes (HCCNTs), obtained from phonon dispersion relations. Calculation of s of HCCNTs is based on the Landauer theory where phonon relaxation rate is obtained by simple Klemens-like model.
Thermal Transport Measurements of Individual Multiwalled Nanotubes
Physical Review Letters, 2001
The thermal conductivity and thermoelectric power of a single carbon nanotube were measured using a microfabricated suspended device. The observed thermal conductivity is more than 3000 W͞K m at room temperature, which is 2 orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. The temperature dependence of the thermal conductivity of nanotubes exhibits a peak at 320 K due to the onset of umklapp phonon scattering. The measured thermoelectric power shows linear temperature dependence with a value of 80 mV͞K at room temperature.
Thermal conductivity of individual multiwalled carbon nanotubes
… Journal of Thermal …, 2012
Thermal conductivity of individual multiwalled carbon nanotubes (MWCNT) is measured using a pulsed photothermal reflectance technique. Intrinsic thermal conductivity of individual MWCNT with a diameter 150 nm and length 2 mm at room temperature is extracted to be 2586 W/mK. Individual MWCNT is surrounded by SiO 2 , so parallel resistor model is applied in which SiO 2 supportive is treated as a conducting channel that transports heat in parallel with MWCNT.