scholarly journals Quasi-Ballistic Heat Transfer From Metal Nanostructures on Sapphire

2011 ◽  
Author(s):  
Austin Minnich ◽  
Gang Chen
Keyword(s):  
Heat Transfer ◽  
Heat Transport ◽  
Free Path ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Minimum Size ◽  
Metal Nanostructures ◽  
Fourier’S Law ◽  
Length Scales ◽  
Fourier's Law

Quasi-ballistic phonon transport, where heat transfer does not obey Fourier’s law, occurs when length scales become comparable to the phonon mean free path (MFP). Understanding this regime of heat transport is of fundamental interest, as the manner in which the heat transport deviates from Fourier’s law reveals important information about the phonon mean free path distribution. While ultrafast techniques can provide the time resolution to observe heat transfer in this regime, the minimum size of the heated region is restricted by diffraction to approximately 1 μm, which is larger than phonon MFPs in many materials. To circumvent this limit, we study heat transfer from metallic dot arrays with sub-micron diameters on sapphire fabricated using electron beam lithography. We describe heat transfer models which allow us to determine how the heat transfer in sapphire deviates from Fourier’s law at these small length scales. Our results indicate that quasi-ballistic transport occurs in sapphire when length scales are on the order of hundreds of nanometers.

THREE-DIMENSIONAL PHONON TRANSPORT SIMULATION FOR NANO/MICROSTRUCTURED MATERIALS

2008 ◽  
Vol 07 (02n03) ◽  
pp. 103-112 ◽  
Author(s):  
A. SAKURAI ◽  
S. MARUYAMA ◽  
A. KOMIYA ◽  
K. MIYAZAKI
Keyword(s):  
Radiative Transfer ◽  
Heat Transport ◽  
Characteristic Length ◽  
Transport Phenomena ◽  
Three Dimensional ◽  
Phonon Transport ◽  
Discrete Ordinates ◽  
Complex Geometries ◽  
Transport Mechanisms ◽  
Length Scales

The Discrete Ordinates Radiation Element Method (DOREM), which is radiative transfer code, is applied for solving phonon transport of nano/microscale materials. The DOREM allows phonon simulation with multi-dimensional complex geometries. The objective of this study is to apply the DOREM to the nano/microstructured materials. It is confirmed that significant changes of the heat transport phenomena with different characteristic length scales and geometries are observed. This study also discusses further variations for understanding of heat transport mechanisms.

Heat Conduction in Nanostructured Materials Predicted by Phonon Bulk Mean Free Path Distribution

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Giuseppe Romano ◽  
Jeffrey C. Grossman
Keyword(s):  
Free Path ◽  
Nanostructured Materials ◽  
Thermal Transport ◽  
High Efficiency ◽  
Theoretical Models ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Computational Effort ◽  
Boltzmann Transport ◽  
Computational Framework

We develop a computational framework, based on the Boltzmann transport equation (BTE), with the ability to compute thermal transport in nanostructured materials of any geometry using, as the only input, the bulk cumulative thermal conductivity. The main advantage of our method is twofold. First, while the scattering times and dispersion curves are unknown for most materials, the phonon mean free path (MFP) distribution can be directly obtained by experiments. As a consequence, a wider range of materials can be simulated than with the frequency-dependent (FD) approach. Second, when the MFP distribution is available from theoretical models, our approach allows one to include easily the material dispersion in the calculations without discretizing the phonon frequencies for all polarizations thereby reducing considerably computational effort. Furthermore, after deriving the ballistic and diffusive limits of our model, we develop a multiscale method that couples phonon transport across different scales, enabling efficient simulations of materials with wide phonon MFP distributions length. After validating our model against the FD approach, we apply the method to porous silicon membranes and find good agreement with experiments on mesoscale pores. By enabling the investigation of thermal transport in unexplored nanostructured materials, our method has the potential to advance high-efficiency thermoelectric devices.

Fourier's law of heat transfer and its implication to cell motility

Biosystems ◽  
2005 ◽  
Vol 81 (1) ◽  
pp. 19-24 ◽  
Author(s):  
Tomoaki Kawaguchi ◽  
Hajime Honda ◽  
Kuniyuki Hatori ◽  
Ei-ichi Imai ◽  
Koichiro Matsuno
Keyword(s):  
Heat Transfer ◽  
Cell Motility ◽  
Fourier’S Law ◽  
Fourier's Law

Thermal Transport Property of Silicon Membranes With Asymmetric Porous Structure

2015 ◽  
Author(s):  
Harutoshi Hagino ◽  
Koji Miyazaki
Keyword(s):  
Thermal Conductivity ◽  
Free Path ◽  
Thermal Conduction ◽  
Transport Theory ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Boundary Scattering ◽  
Rectification Effect ◽  
Thermal Rectification ◽  
Asymmetric Pores

The size effect on thermal conduction due to phonon boundary scattering in films was studied as controlling heat conduction. Thermal rectifier was proposed as a new heat control concept by a ballistic rectifier relies on asymmetric scattering of phonons in asymmetric linear structure. We focus on the thermal rectification effect in membrane with asymmetric pores. We discussed on the thermal rectification effect from the calculation and thermal conductivity measurement of asymmetric structured membrane. Thermal conduction was calculated by using radiation calculation of ANSYS Fluent based on Boltzmann transport theory which is development of equation of phonon radiative transfer from view point of phonon mean free path and boundary scattering condition. In-plane thermal conductivities of free standing membranes with microsized asymmetric pores were measured by periodic laser heating measurement. From the result of calculation, phonons were transition to ballistic transport in the membranes with asymmetric shaped pores and thermal rectification effect was obtained on the condition of specular scattering because of the asymmetric back-scattering of ballistic phonons from asymmetric structure. The thermal rectification effect was increased with decreasing thickness of membrane shorter and shorter than mean free path of phonon. From the result of measurements, we were able to confirm the reduction of thermal conductivity based on ballistic phonon transport theory, but the strong thermal rectification effect was not confirmed.

Translation-rotation coupling and heat transfer in orientationally-disordered phase of CCl4

Open Physics ◽  
2006 ◽  
Vol 4 (2) ◽  
Author(s):  
Oleg Pursky ◽  
Vyacheslav Konstantinov
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Free Path ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Mobility Edge ◽  
Total Thermal Resistance ◽  
Disordered Phase ◽  
Diffusive Modes

AbstractThe isochoric thermal conductivity of an orientationally-disordered phase of CCl4 is analysed within a model in which heat is transferred by phonons and above the phonon mobility edge by ”diffusive” modes migrating randomly from site to site. The mobility edge ω0 is found from the condition that the phonon mean-free path cannot become smaller than half the phonon wavelength. The contributions of phonon-phonon, one-, and two-phonon scattering to the total thermal resistance of solid CCl4 are calcualted under the assumption that the different scattering mechanisms contribute additively. An increase in the isochoric thermal conductivity with temperature is explained by suppression of phonon scattering at rotational excitations due to a decrease in correlation in the rotation of neighbouring molecules.

scholarly journals Theoretical studies on electron and radiation preheatings

1989 ◽  
Vol 7 (3) ◽  
pp. 487-493 ◽  
Author(s):  
K. Mima ◽  
H. Takabe ◽  
A. Nishiguchi ◽  
Y. Kihara ◽  
S. Nakai
Keyword(s):  
Surface Layer ◽  
Kinetic Energy ◽  
Laser Pulse ◽  
Heat Transport ◽  
Free Path ◽  
Coupling Efficiency ◽  
Mean Free Path ◽  
Theoretical Studies ◽  
Hollow Shell ◽  
Electron Heat

In order to enhance the coupling efficiency, a low Z ablator is generally used for ICF targets. The ablator thickness is appropriately chosen so it is burned out by the end of a laser pulse. Then all of the implosion kinetic energy is contained in the DT fuel. However, a small amount of preheating degrades the compression in a hollow shell, DT fueled target implosion. In this paper, we investigate the preheating level of the fuel shell by Fokker–Planck simulations of the electron heat transport.From the analysis, it is found that a thick surface layer of a laser irradiated low-Z target is preheated by Maxwellian tail electrons which have a long mean free path. Hence, we propose that the target be precompressed by a tailored pulse, in order to increase the shell ρΔR at the laser peak.

Non-Fourier Heat Conduction in Carbon Nanotubes

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Hai-Dong Wang ◽  
Bing-Yang Cao ◽  
Zeng-Yuan Guo
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Heat Flux ◽  
Heat Conduction ◽  
Thermal Inertia ◽  
Energy Relation ◽  
Fourier’S Law ◽  
Fourier Heat Conduction ◽  
Fourier's Law

Fourier’s law is a phenomenological law to describe the heat transfer process. Although it has been widely used in a variety of engineering application areas, it is still questionable to reveal the physical essence of heat transfer. In order to describe the heat transfer phenomena universally, Guo has developed a general heat conduction law based on the concept of thermomass, which is defined as the equivalent mass of phonon gas in dielectrics according to Einstein’s mass–energy relation. The general law degenerates into Fourier’s law when the thermal inertia is neglected as the heat flux is not very high. The heat flux in carbon nanotubes (CNTs) may be as high as 1012 W/m2. In this case, Fourier’s law no longer holds. However, what is estimated through the ratio of the heat flux to the temperature gradient by molecular dynamics (MD) simulations or experiments is only the apparent thermal conductivity (ATC); which is smaller than the intrinsic thermal conductivity (ITC). The existing experimental data of single-walled CNTs under the high-bias current flows are applied to study the non-Fourier heat conduction under the ultrahigh heat flux conditions. The results show that ITC and ATC are almost equal under the low heat flux conditions when the thermal inertia is negligible, while the difference between ITC and ATC becomes more notable as the heat flux increases or the temperature drops.

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