scholarly journals Non-equilibrium temperatures and heat transport in nanosystems with defects, described by a tensorial internal variable

2016 ◽  
Vol 7 (2) ◽  
pp. 81-97 ◽  
Author(s):  
Liliana Restuccia
Keyword(s):  
Heat Flux ◽  
Heat Transport ◽  
Energy Flux ◽  
Constitutive Relations ◽  
Internal Variable ◽  
Nonequilibrium Steady States ◽  
Solid Matrix ◽  
Isotropic Case ◽  
External Energy ◽  
Non Equilibrium

AbstractThe paper deals with the meaning of non-equilibrium temperatures in nanosystems with an internal variable, describing defects inside them, and implications on heat transport. In equilibrium all definitions of temperature lead to the same value, but in nonequilibrium steady states they lead to different values, giving information on different degrees of freedom. We discuss the caloric and entropic non-equilibrium temperatures and the relations among them, in defective nanosystems (crystals with dislocations or porous channels, carbon nanotubes in a solid matrix and so on), crossed by an external energy flux. Here, we present a model for nanocrystals with dislocation defects submitted to an external energy flux. The dislocations may have a strong influence on the effective thermal conductivity, and their own dynamics may be coupled in relevant way to the heat flux dynamics. In the linear case the constitutive relations, the rate equations for the internal variable and the heat flux are worked out and a generalized telegraphic heat equation is derived in the anisotropic and isotropic case, describing the thermal disturbances with finite velocity.

scholarly journals Phonon heat transport in cavity-mediated optomechanical nanoresonators

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Cheng Yang ◽  
Xinrui Wei ◽  
Jiteng Sheng ◽  
Haibin Wu
Keyword(s):  
Heat Flux ◽  
Heat Transport ◽  
Nonequilibrium Steady States ◽  
Strong Coupling Regime ◽  
Equilibrium System ◽  
Heat Engines ◽  
Universal Bound ◽  
Long Range Interactions ◽  
Steady State Heat ◽  
Non Equilibrium

Abstract The understanding of heat transport in nonequilibrium thermodynamics is an important research frontier, which is crucial for implementing novel thermodynamic devices, such as heat engines and refrigerators. The convection, conduction, and radiation are the well-known basic ways to transfer thermal energy. Here, we demonstrate a different mechanism of phonon heat transport between two spatially separated nanomechanical resonators coupled by the cavity-enhanced long-range interactions. The single trajectory for thermalization and non-equilibrium dynamics is monitored in real-time. In the strong coupling regime, the instant heat flux spontaneously oscillates back and forth in the nonequilibrium steady states. The universal bound on the precision of nonequilibrium steady-state heat flux, i.e. the thermodynamic uncertainty relation, is verified in such a temperature gradient driven far-off equilibrium system. Our results give more insight into the heat transfer with nanomechanical oscillators, and provide a playground for testing fundamental theories in non-equilibrium thermodynamics.

Statistical Mechanics of Thermotransport of a Heavy Impurity in an Insulating Solid

1971 ◽  
Vol 26 (1) ◽  
pp. 10-17 ◽  
Author(s):  
A. R. Allnatt
Keyword(s):  
Heat Flux ◽  
Time Correlation ◽  
Three Dimensions ◽  
Time Correlation Functions ◽  
Single Vacancy ◽  
One Dimensional ◽  
Enthalpy Of Activation ◽  
Heavy Impurity ◽  
The One ◽  
Non Equilibrium

AbstractA kinetic equation is derived for the singlet distribution function for a heavy impurity in a lattice of lighter atoms in a temperature gradient. In the one dimensional case the equation can be solved to find formal expressions for the jump probability and hence the heat of transport, q*. for a single vacancy jump of the impurity, q* is the sum of the enthalpy of activation, a term involving only averaging in an equilibrium ensemble, and two non-equilibrium terms in­volving time correlation functions. The most important non-equilibrium term concerns the cor­relation between the force on the impurity and a microscopic heat flux. A plausible extension to three dimensions is suggested and the relation to earlier isothermal and non-isothermal theories is indicated

scholarly journals ANALYSIS OF HEAT TRANSFER IN BUILDING PARTITIONS WITH THE USE OF COMPUTATIONAL FLUID DYNAMICS TOOLS

2020 ◽  
Vol 10 (3) ◽  
pp. 48-51
Author(s):  
Arkadiusz Urzędowski ◽  
Joanna Styczeń ◽  
Magdalena Paśnikowska-Łukaszuk
Keyword(s):  
Heat Flux ◽  
Heat Transport ◽  
Outer Wall ◽  
Single Family ◽  
Ansys Fluent ◽  
Structural Wall ◽  
Contact Points ◽  
Temperature Distributions ◽  
Building Walls ◽  
Family House

The article presents the mechanisms of heat exchange in building partitions along with a description of the phenomena occurring there. The methods of heat transport on selected examples of the construction of sandwich building walls were presented and discussed. A review of the methods allowing to determine the heat flux value by means of analytical methods and simulations based on numerical analyzes was carried out. The methodology of solving thermal problems has been presented, indicating the complexity of the phenomena occurring at the contact points of surfaces, for which the correct characteristics should be selected in more than one selected form of determining temperature distributions. Heat transport simulation was performed in ANSYS Fluent 2020 R2 software. The value of the heat flux density flowing through the outer wall of a single-family house located in Lublin, Poland was analytically determined. Three different structural wall solutions were adopted: one, two and three-layer. The obtained results were presented in a tabular manner, allowing for a clear verification of the correctness of the calculations performed with both selected methods.

Non-equilibrium heat transport of copper-silver alloy films by femtosecond laser with double pump beams

Optik ◽  
2019 ◽  
Vol 176 ◽  
pp. 114-118
Author(s):  
Xiaofang Xu ◽  
Fengfeng Yang ◽  
Xiaoliang Li ◽  
Yongfeng Gao
Keyword(s):  
Femtosecond Laser ◽  
Heat Transport ◽  
Silver Alloy ◽  
Alloy Films ◽  
Non Equilibrium

Experimental Validation of Non-Fourier Thermal Response in Porous Media

2001 ◽  
Author(s):  
A. G. Agwu Nnanna ◽  
K. T. Harris ◽  
A. Haji-Sheikh
Keyword(s):  
Heat Flux ◽  
Porous Media ◽  
Experimental Validation ◽  
Thermal Response ◽  
Lag Time ◽  
Equation Model ◽  
Thermal Parameters ◽  
Solid Matrix ◽  
Microscale Model ◽  
Short Time

Abstract An experimental validation of non-Fourier behavior in porous media due to short time thermal perturbation is presented. The governing energy equation is formulated based on the two-equation model and the non-Fourier model. This formulation leads to the emergence of four thermal parameters: lag-time in heat flux τq, lag-time τt in temperature due to interstitial heat transfer coefficient h, and lag-time in the transient response of the temperature gradient τx in the heat flux equation. These parameters account for the microstructural thermal interaction between the fluid and neighboring solid matrix as well as the delay time needed for both phases to approach thermal equilibrium. An experimental verification of the microscale model was performed under standard laboratory conditions. The values of the aforementioned thermal parameters were determined to compute the fluid and solid temperatures. Results predicted from three models (classical Fourier, non-Fourier, and experimental) were compared. It indicates an excellent agreement between the non-Fourier and the experimental model, and a significant deviation of Fourier prediction from the experimental results.

Non-equilibrium heat transport of electron in Cu films irradiated by three femtosecond laser beams

2019 ◽  
Vol 48 (2) ◽  
pp. 206001
Author(s):  
许孝芳 Xu Xiaofang ◽  
李晓良 Li Xiaoliang ◽  
王庆伟 Wang Qingwei ◽  
杨逢逢 Yang Fengfeng ◽  
高永锋 Gao Yongfeng ◽  
...  
Keyword(s):  
Femtosecond Laser ◽  
Heat Transport ◽  
Laser Beams ◽  
Cu Films ◽  
Non Equilibrium

Non-equilibrium natural convection in a differentially-heated nanofluid cavity partially filled with a porous medium

2019 ◽  
Vol 29 (8) ◽  
pp. 2524-2544 ◽  
Author(s):  
Mikhail A. Sheremet ◽  
Ioan Pop ◽  
A. Cihat Baytas
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Natural Convection ◽  
Volume Fraction ◽  
Good Control ◽  
Solid Matrix ◽  
Content Type ◽  
Practical Applications ◽  
Nanofluid Viscosity ◽  
Non Equilibrium

Purpose This study aims to numerically analyze natural convection of alumina-water nanofluid in a differentially-heated square cavity partially filled with a heat-generating porous medium. A single-phase nanofluid model with experimental correlations for the nanofluid viscosity and thermal conductivity has been considered for the description of the nanoparticles transport effect in the present study. Local thermal non-equilibrium approach for the porous layer with the Brinkman-extended Darcy model has been used. Design/methodology/approach Dimensionless governing equations formulated using stream function, vorticity and temperature have been solved by the finite difference method. The effects of the Rayleigh number, Ostrogradsky number, Nield number and nanoparticles volume fraction on nanofluid flow, heat and mass transfer have been analyzed. Findings It has been revealed that the dimensionless heat transfer coefficient at the fluid/solid matrix interface can be a very good control parameter for the convective flow and heat transfer intensity. The present results are original and new for the study of non-equilibrium natural convection in a differentially-heated nanofluid cavity partially filled with a porous medium. Originality/value The results of this paper are new and original with many practical applications of nanofluids in the modern industry.

scholarly journals The Interaction of Rotation with Convection

1970 ◽  
Vol 4 ◽  
pp. 30-36
Author(s):  
Bernard R. Durney
Keyword(s):  
Heat Flux ◽  
Angular Momentum ◽  
Heat Transport ◽  
Differential Rotation ◽  
Initial Value Problem ◽  
List Type ◽  
Reynolds Stresses ◽  
Initial Value ◽  
Convective Cells ◽  
Flux Difference

AbstractThe equations for a rotating convective spherical shell are solved in the Herring approximation as an initial value problem. The main results are (1)The most unstable modes (those that maximize the heat flux) correspond to convective cells stretching from pole to pole.(2)The calculations of the Reynolds stresses show transport of angular momentum towards the equator. That is, differential rotation sets in with equatorial acceleration.(3)The convective heat transport is maximum at the equator. This would give rise to an equator-pole flux difference.(4)If convection is non-axisymmetric (as in the most unstable modes) there are no time independent solutions. The time dependence is oscillatory and of the form ωt + mφ.

Heat controlling in the mass-graded harmonic lattices with double-well on-site potential

2018 ◽  
Vol 32 (20) ◽  
pp. 1850217
Author(s):  
Peng Kong ◽  
Zhengzheng Wei ◽  
Tao Hu ◽  
Yi Tang
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Power Spectrum ◽  
Molecular Dynamics Simulations ◽  
Heat Transport ◽  
Nonequilibrium Molecular Dynamics ◽  
Thermal Rectification ◽  
Average Temperature ◽  
New Type ◽  
Dynamics Simulations

Using nonequilibrium molecular dynamics simulations, we investigate thermal rectification in mass-graded lattices with a new type on-site potential which has a physical picture of the double-well. By adjusting the ratio of harmonic on-site potential and anharmonic on-site potential, we could obtain the optimal heat transport and the best thermal rectification. In addition, we observe the reversal thermal rectification by changing the ratio of on-site potential and analyzes the mechanism of thermal rectification through the power spectrum. At last, we also study the heat flux and thermal rectification in a different case of average temperature and mass gradient.

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