scholarly journals Temperature Distribution through a Nanofilm by Means of a Ballistic-Diffusive Approach

Inventions ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 2 ◽  
Author(s):  
Hatim Machrafi
Keyword(s):  
Heat Transport ◽  
Temperature Jump ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Behavior Changes ◽  
Heat Management ◽  
Qualitative Comparison ◽  
Microelectronic Devices ◽  
Order Of Magnitude ◽  
Non Local

As microelectronic devices are important in many applications, their heat management needs to be improved, in order to prolong their lifetime, and to reduce the risk of damage. In nanomaterials, heat transport shows different behaviors than what can be observed at macroscopic sizes. Studying heat transport through nanofilms is a necessary tool for nanodevice thermal management. This work proposes a thermodynamic model incorporating both ballistic, introduced by non-local effects, and diffusive phonon transport. Extended thermodynamics principles are used in order to develop a constitutive equation for the ballistic behavior of heat conduction at small-length scales. Being an irreversible process, the present two-temperature model contains a one-way transition of ballistic to diffusive phonons as time proceeds. The model is compared to the classical Fourier and Cattaneo laws. These laws were not able to present the non-locality that our model shows, which is present in cases when the length scale of the material is of the same order of magnitude or smaller than the phonon mean free path, i.e., when the Knudsen number K n ≤ O ( 1 ) . Moreover, for small K n numbers, our model predicted behaviors close to that of the classical laws, with a weak temperature jump at both sides of the nanofilm. However, as K n increases, the behavior changes completely, the ballistic component becomes more important, and the temperature jump at both sides of the nanofilms becomes more pronounced. For comparison, a model using Fourier’s and Cattaneo’s laws with an effective thermal conductivity has shown, with reasonable qualitative comparison for small Knudsen numbers and large times.

scholarly journals Non-local effects in radial heat transport in silicon thin layers and graphene sheets

2011 ◽  
Vol 468 (2141) ◽  
pp. 1217-1229 ◽  
Author(s):  
A. Sellitto ◽  
D. Jou ◽  
J. Bafaluy
Keyword(s):  
Heat Transport ◽  
Local Equilibrium ◽  
Mean Free Path ◽  
Thin Layers ◽  
Graphene Sheets ◽  
Fourier Law ◽  
Local Effects ◽  
Radial Heat ◽  
Non Local ◽  
The Mean

We explore non-local effects in radially symmetric heat transport in silicon thin layers and in graphene sheets. In contrast to one-dimensional perturbations, which may be well described by means of the Fourier law with a suitable effective thermal conductivity, two-dimensional radial situations may exhibit a more complicated behaviour, not reducible to an effective Fourier law. In particular, a hump in the temperature profile is predicted for radial distances shorter than the mean-free path of heat carriers. This hump is forbidden by the local-equilibrium theory, but it is allowed in more general thermodynamic theories, and therefore it may have a special interest regarding the formulation of the second law in ballistic heat transport.

Transient, Sub-Continuum, Heat Conduction in Irregular Geometries

2022 ◽  
Vol 0 (0) ◽  
Author(s):  
Saad Bin Mansoor ◽  
Bekir S. Yilbas
Keyword(s):  
Intensity Distribution ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Geometric Feature ◽  
Shape Effect ◽  
Film Material ◽  
Irregular Shapes ◽  
Frequency Independent ◽  
Order Of Magnitude ◽  
The Mean

Abstract Phonon transfer in irregular shapes is important for assessing the influence of shape effect on thermal transport characteristics of low-scale films. It becomes critical for evaluating the contribution of the scattering phonons to the phonon intensity distribution inside the film. Hence, the sub-continuum ballistic-diffusive model is incorporated to formulate the phonon transport in an irregular geometry of low-size film adopting the transient, frequency-independent, equation of phonon radiative transfer. The discrete ordinate method is used in the numerical discretization of the governing transport equation. It is demonstrated that the geometric feature of the film influences the phonon intensity distribution within the film material. The transport characteristics obtained from the Fourier and the ballistic-diffusive models are markedly different in their spatial and temporal behavior. This is true when the device sizes are of the same order of magnitude as the mean-free path of the heat carriers.

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.

scholarly journals Design aspects of Bi2Sr2CaCu2O8+δ THz sources: optimization of thermal and radiative properties

2021 ◽  
Author(s):  
Mikhail M Krasnov ◽  
Natalia D Novikova ◽  
Roger Cattaneo ◽  
Alexey A Kalenyuk ◽  
Vladimir M Krasnov
Keyword(s):  
Experimental Data ◽  
Power Efficiency ◽  
Open Space ◽  
Radiation Power ◽  
Impedance Matching ◽  
Dipole Antenna ◽  
Radiative Properties ◽  
Heat Management ◽  
Order Of Magnitude ◽  
Thz Sources

Impedance matching and heat management are important factors influencing performance of THz sources. In this work we analyze thermal and radiative properties of such devices based on mesa structures of a layered high-temperature superconductor Bi2Sr2CaCu2O8+δ. Two types of devices are considered, containing either a conventional large single crystal, or a whisker. We perform numerical simulations for various geometrical configurations and parameters and make a comparison with experimental data for the two types of devices. It is demonstrated that the structure and the geometry of both the superconductor and the electrodes are playing important roles. In crystal-based devices an overlap between the crystal and the electrode leads to appearance of a large parasitic capacitance, which shunts THz emission and prevents impedance matching with open space. The overlap is avoided in whisker-based devices. Furthermore, the whisker and the electrodes form a turnstile (crossed-dipole) antenna facilitating good impedance matching. This leads to more than an order of magnitude enhancement of the radiation power efficiency in whisker-based, compared to crystal-based devices. These results are in good agreement with presented experimental data.

A model for non-local electron heat transport

2009 ◽  
Vol 49 (7) ◽  
pp. 075025 ◽  
Author(s):  
A.K. Wang ◽  
H. Wang ◽  
H.B Jiang ◽  
Z.T Wang
Keyword(s):  
Heat Transport ◽  
Local Electron ◽  
Electron Heat ◽  
Non Local

scholarly journals Direct observation of large electron–phonon interaction effect on phonon heat transport

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Jiawei Zhou ◽  
Hyun D. Shin ◽  
Ke Chen ◽  
Bai Song ◽  
Ryan A. Duncan ◽  
...  
Keyword(s):  
Heat Transport ◽  
Phonon Scattering ◽  
Crystalline Silicon ◽  
Substantial Reduction ◽  
Phonon Transport ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Exciting Electron ◽  
Energy Conversion Devices ◽  
The Impact

AbstractAs a foundational concept in many-body physics, electron–phonon interaction is essential to understanding and manipulating charge and energy flow in various electronic, photonic, and energy conversion devices. While much progress has been made in uncovering how phonons affect electron dynamics, it remains a challenge to directly observe the impact of electrons on phonon transport, especially at environmental temperatures. Here, we probe the effect of charge carriers on phonon heat transport at room temperature, using a modified transient thermal grating technique. By optically exciting electron-hole pairs in a crystalline silicon membrane, we single out the effect of the phonon–carrier interaction. The enhanced phonon scattering by photoexcited free carriers results in a substantial reduction in thermal conductivity on a nanosecond timescale. Our study provides direct experimental evidence of the elusive role of electron–phonon interaction in phonon heat transport, which is important for understanding heat conduction in doped semiconductors. We also highlight the possibility of using light to dynamically control thermal transport via electron–phonon coupling.

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.

scholarly journals The Theory of Extended and Expanding Atmospheres

1973 ◽  
Vol 51 ◽  
pp. 148-170
Author(s):  
Karl-Heinz Böhm
Keyword(s):  
Theoretical Study ◽  
Transfer Problem ◽  
Mechanical Energy ◽  
Radiation Force ◽  
Mean Free Path ◽  
Stellar Radius ◽  
Order Of Magnitude ◽  
Acceleration Of Gravity ◽  
Expanding Atmospheres ◽  
Radiative Acceleration

(A) The possibilities and the difficulties of a theoretical study of extended atmospheres in binaries are briefly discussed.(B) We try to summarize and discuss critically the present status of the theory of three types of extended atmospheres (i.e. atmospheres in which the average photon mean-free-path is the same order of magnitude or larger than the stellar radius):(1) Extended atmospheres in hydrostatic and in grey or non-grey radiative equilibrium.(2) Dynamic (expanding) atmospheres which occur if the radiative acceleration is slightly smaller than the acceleration of gravity.(3) Stellar coronae which are formed in the presence of a mechanical energy flux.In (1) we study the importance of the ‘forward peaking’ of the radiation field in the outer layers of the atmosphere. The possibilities for the solution of the non-grey transfer problem in an extended atmosphere are discussed.In (2) we pay special attention to Marlborough's and Roy's (1970) result that the atmospheric gas cannot be accelerated directly to supersonic velocities by the action of the radiation force.In (3) the large differences in the coronal properties of stars of different chemical composition are emphasized. We draw attention to the partially unexplored but probably very interesting properties of coronae of helium-rich stars.

Coupling Between Phonons and Fluid Particles in Water/Carbon Nanotube Systems

2009 ◽  
Author(s):  
A. J. H. McGaughey ◽  
J. A. Thomas ◽  
J. Turney ◽  
R. M. Iutzi
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Carbon Nanotube ◽  
Relaxation Times ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Dynamics Simulation ◽  
Spectral Energy ◽  
Total Thermal Conductivity ◽  
Phonon Modes

We investigate thermal transport in water/carbon nanotube (CNT) composite systems using molecular dynamics simulations. Carbon-carbon interactions are modeled using the second-generation REBO potential, water-water interactions are modeled using the TIP4P potential, and carbon-water interactions are modeled using a Lennard-Jones potential. The thermal conductivities of empty and water-filled CNTs with diameters between 0.83 nm and 1.66 nm are predicted using molecular dynamics simulation and a direct application of the Fourier law. For empty CNTs, the thermal conductivity decreases with increasing CNT diameter. As the CNT length approaches 1 micron, a length-independent thermal conductivity is obtained, indicative of diffusive phonon transport. When the CNTs are filled with water, the thermal conductivity decreases compared to the empty CNTs and transitions to diffusive phonon transport at shorter lengths. To understand this behavior, we calculate the spectral energy density of the empty and water-filled CNTs and calculate the mode-specific group velocities, relaxation times, and thermal conductivity. For the empty 1.10 nm diameter CNT, we show that the acoustic phonon modes account for 65 percent of the total thermal conductivity. This behavior is attributed to their long mean-free paths. When the CNT is filled with water, interactions with the water molecules shorten the acoustic mode mean-free path and lower the overall CNT thermal conductivity.

scholarly journals Two-dimensional phonon hydrodynamics in narrow strips

2015 ◽  
Vol 471 (2182) ◽  
pp. 20150376 ◽  
Author(s):  
A. Sellitto ◽  
I. Carlomagno ◽  
D. Jou
Keyword(s):  
Heat Flow ◽  
Heat Transport ◽  
Knudsen Number ◽  
Slip Flow ◽  
Transport Equations ◽  
Two Dimensional ◽  
Non Local

Heat flow along two-dimensional strips as a function of the Knudsen number is examined in two different versions of heat-transport equations with non-local terms, with or without heat slip flow. In both of them, a parabolic heat profile corresponding to the Poiseuille phonon flow may appear in some domains of temperature, or of the Knudsen number, in the transition from the Fourier regime to the ballistic one. The influence of the slip heat flow on such a transition is discussed.

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