Controlling the heat flow: now it is possible

We discuss the problem of heat conduction in 1D nonlinear chains in relation to the dynamical properties of the system. We provide convincing numerical evidence for the validity of Fourier law of heat conduction in linear mixing systems. Therefore, deterministic diffusion and normal heat transport which are usually associated with full hyperbolicity, actually take place in systems without exponential instability. We then show that, acting on the parameter which controls the strength of the on site potential inside a segment of the chain, we induce a transition from conducting to insulating behavior in the whole system. The control of heat conduction by nonlinearity opens the possibility to propose new devices such as a thermal rectifier.     

Normal heat conduction in a chain with a weak interparticle anharmonic potential

We analytically study heat conduction in a chain with an interparticle interaction V(x)= lambda[1-cos(x)] and harmonic on-site potential. We start with each site of the system connected to a Langevin heat bath, and investigate the case of small coupling for the interior sites in order to understand the behavior of the system with thermal reservoirs at the boundaries only. We study, in a perturbative analysis, the heat current in the steady state of the one-dimensional system with a weak interparticle potential. We obtain an expression for the thermal conductivity, compare the low and high temperature regimes, and show that, as we turn off the couplings with the interior heat baths, there is a "phase transition": Fourier's law holds only at high temperatures.     

Heat Conduction in the α−β Fermi–Pasta–Ulam Chain

Recent simulation results on heat conduction in a one-dimensional chain with an asymmetric inter-particle interaction potential and no onsite potential found non-anomalous heat transport in accordance to Fourier’s law. This is a surprising result since it was long believed that heat conduction in one-dimensional systems is in general anomalous in the sense that the thermal conductivity diverges as the system size goes to infinity. In this paper we report on detailed numerical simulations of this problem to investigate the possibility of a finite temperature phase transition in this system. Our results indicate that the unexpected results for asymmetric potentials is a result of insufficient chain length, and does not represent the asymptotic behavior.     

Effects of fullerene coalescence on the thermal conductivity of carbon nanopeapods

The heat conduction and its dependence on fullerene coalescence in carbon nanopeapods (CNPs) have been investigated by equilibrium molecular dynamics simulations. The effects of fullerene coalescence on the thermal conductivity of CNPs were discussed under different temperatures. It is shown that the thermal conductivity of the CNPs decreases with the coalescence of encapsulated fullerene molecules. The thermal transmission mechanism of the effect of fullerene coalescence was analysed by the mass transfer contribution, the relative contributions of phonon oscillation frequencies to total heat current and the phonon vibrational density of states (VDOS). The mass transfer in CNPs is mainly attributed to the motion of encapsulated fullerene molecule and it gets more restricted with the coalescence of the fullerene. It shows that the low-frequency phonon modes below 20 THz contribute mostly to thermal conductivity in CNPs. The analysis of VDOS demonstrates that the dominating contribution to heat transfer is from the inner fullerene chain. With the coalescence of fullerene, the interfacial heat transfer between the CNT and fullerene chain is strengthened; however, the heat conduction of the fullerene chain decreases more rapidly at the same time.     

Heat conduction from a spherical nano-particle: status of modeling heat conduction in laser-induced incandescence

Laser-induced incandescence (LII) of nano-second pulsed laser heated nano-particles has been developed into a popular technique for characterizing concentration and size of particles suspended in a gas and continues to draw increased research attention. Heat conduction is in general the dominant particle cooling mechanism after the laser pulse. Accurate calculation of the particle cooling rate is essential for accurate analysis of LII experimental data. Modelling of particle conduction heat loss has often been flawed. This paper attempts to provide a comprehensive review of the heat conduction modelling practice in the LII literature and an overview of the physics of heat conduction loss from a single spherical particle in the entire range of Knudsen number with emphasis on the transition regime. Various transition regime models developed in the literature are discussed with their accuracy evaluated against direct simulation Monte Carlo results under different particle-to-gas temperature ratios. The importance of accounting for the variation of the thermal properties of the surrounding gas between the gas temperature and the particle temperature is demonstrated. Effects of using these heat conduction models on the inferred particle diameter or the thermal accommodation coefficient are also evaluated. The popular McCoy and Cha model is extensively discussed and evaluated. Based on its superior accuracy in the entire transition regime and even under large particle-to-gas temperature ratios, the Fuchs boundary-sphere model is recommended for modeling particle heat conduction cooling in LII applications. PACS 44.05.+e; 44.10.+i; 47.45.-n; 61.46.Df; 78.70.-g     

Size Dependent Heat Conduction in One-Dimensional Diatomic Lattices

We study the size dependency of heat conduction in one-dimensional diatomic FPU-β lattices and establish that for low dimensional material,contribution from optical phonons is found more effective to the thermal conductivity and enhance heat transport in the thermodynamic limit N →∞.For the finite size,thermal conductivity of 1D diatomic lattice is found to be lower than 1D monoatomic chain of the same size made up of the constituent particle of the diatomic chain.For the present 1D diatomic chain,obtained value of power divergent exponent of thermal conductivity0.428±0.001 and diffusion exponent 1.2723 lead to the conclusions that increase in the system size,increases the thermal conductivity and existence of anomalous energy diffusion.Existing numerical data supports our findings.     

From compact point defects to extended structures in silicon

We show that in contrast to the 1d Frenkel-Kontorova (FK) chain known to obey the Fourier law of heat conduction and several 2d models which show logarithmic dependence of conductivity on system size, a scalar 2d FK lattice with commensurate structure exhibits anomalous heat conduction, whose thermal conductivity displays a power law behavior. The dependence of thermal gradient on bulk temperature and noise correlation is critically analyzed. A dynamical contribution to conductivity when the system attains a nonequilibrium steady state of thermal conduction has been identified.     

The stationary state and the heat equation for a variant of Davies' model of heat conduction

We study a variant of Davies' model of heat conduction, consisting of a chain of (classical or quantum) harmonic oscillators, whose ends are coupled to thermal reservoirs at different temperatures, and where neighboring oscillators interact via intermediate reservoirs. In the weak coupling limit, we show that a unique stationary state exists, and that a discretized heat equation holds. We give an explicit expression of the stationary state in the case of two classical oscillators. The heat equation is obtained in the hydrodynamic limit, and it is proved that it completely describes the macroscopic behavior of the model.     

Intriguing heat conduction of a chain with transverse motions

We study heat conduction in a one-dimensional chain of particles with longitudinal as well as transverse motions. The particles are connected by two-dimensional harmonic springs together with bending angle interactions. Using equilibrium and nonequilibrium molecular dynamics, three types of thermal conducting behaviors are found: a logarithmic divergence with system sizes for large transverse coupling, 1/3 power law at intermediate coupling, and 2/5 power law at low temperatures and weak coupling. The results are consistent with a simple mode-coupling analysis of the same model. We suggest that the 1/3 power-law divergence should be a generic feature for models with transverse motions.     

Influence of the experimental conditions on the specific heat critical behaviour of TGS

Using a conduction calorimeter the specific heat critical behaviour of a TGS crystal has been measured. The ranges of the deviations from the classical behaviour below and above the transition point are 1 and 20 K respectively. These deviations seem to be well related to LK theory predictions. In a range of 0.1 K below the transition point thermal hysteresis appears which does not depend on the measuring temperature rate. The same behaviour is obtained with the sample at atmospheric pressure and under a high vacuum.     

微结构气体夹层的导热和辐射比较

气体夹层作为散热或绝热机构在微传感器、微驱动器等微器件中是经常出现的。通常认为,气体夹层的导热是微结构表面间热量传递的主要方式,而表面间的热辐射可以忽略不计。本文比较了不同尺度和温度下电介质材料表面间导热和辐射换热的相对强弱,发现当辐射表面间距离只有十几个纳米的时候,辐射换热会大大强于导热。根据不同尺度和温度下导热和辐射相对强弱的不同,对微结构中电介质材料表面间热传递的主要方式进行了划分。     

高热流密度器件热控制实验研究

高热流密度热控制或高性能服务器的冷却处理方式已受到广泛关注,其CPU散热量持续增高导致了能量分布的不均匀.本文对计算机服务器CPU的耗能量、冷却效果等进行了实验研究.提出通过采用导热板扩大CPU散热面积,以及采用高导热相变设备,如新型热管式散热器来解决高热流密度器件能耗的处理办法.研究结果证实,对高热流密度器件依靠增大外界气流的速度来改善散热器的冷却性能并不明显,采用高效热管散热器强化芯片传热可满足大型计算机服务器CPU的冷却要求.     

含有格点势的一维Fibonacci链热传导性质的研究

用传输矩阵的方法,研究了格点势(on-site势)对一维Fibonacci链的热传导性质(透射系数、Lyapunov指数及热导率κ)的影响.研究结果表明:当固定原子质量比和力作用常数比时,随着格点势的增大,低频区域的透射系数减小,对应的Lyapunov指数增大,透射谱向高频方向移动.同时,格点势越大,同样大小的体系对应的κ越小,当格点势足够大时,κ会趋近零.在热导率κ对振动频率ω²作图中,κ呈现台阶式缓慢上升的趋势,且在高频     

Normal heat conductivity of the one-dimensional lattice with periodic potential of nearest-neighbor interaction

The process of heat conduction in a chain with a periodic potential of nearest-neighbor interaction is investigated by means of molecular dynamics simulation. It is demonstrated that the periodic potential of nearest-neighbor interaction allows one to obtain normal heat conductivity in an isolated one-dimensional chain with conserved momentum. The system exhibits a transition from infinite to normal heat conductivity with the growth of its temperature. The physical reason for normal heat conductivity is the excitation of high-frequency stationary localized rotational modes. These modes absorb the momentum and facilitate locking of the heat flux.     

Simultaneous measurement of thermal and dielectric properties in a conduction calorimeter: Application to the lock-in transition in Rb2ZnCl4 single crystal

A device for simultaneous measurement of thermal properties (specific heat, latent heat and related properties) and electric properties (such as permittivity, dielectric spectroscopy) based on conduction calorimetry is explained. The device is used to study the commensurate-incommensurate (lock-in) phase transition in Rb₂ZnCl₄ single crystal. This transition is found to be first-order. Thermal and dielectric anomalies are discussed.     

基于热质运动概念的普适导热定律

根据爱因斯坦的质能等效关系式,热能具有的等效质量称为热质,从而在固态和气态介质中分别建立了声子气质量和热子气质量的概念.应用牛顿定律建立了含有驱动力、阻力和惯性力的热质(声子气或热子气)运动的动量守恒方程.由于热量在介质中的传递本质上就是热质(声子气和热子气)在介质中的运动,所以热质动量守恒方程就是普适的导热定律,能够统一描述各种条件下的导热规律.当热流密度不是很大从而热质惯性力可以忽略时,热质动量守恒方程就退化为傅里叶导热定律,这表明傅里叶导热定律是特殊条件下的导热定律,对于微纳尺度条件下的导热,热流密度可以极高,由速度空间变化引起的惯性力不能忽略,在稳态导热情况下也将出现非傅里叶导热,此时在计算或者实验中不能用热流密度除温度梯度求导热系数.在超快速加热条件下,必需考虑惯性力,与基于CV导热模型的波动方程相比,普适的导热定律增加了因速度空间变化引起的惯性力项,所以在介质中热波叠加时不会出现产生负温度的非物理现象,表明基于热质运动概念的普适导热定律更为合理. 关键词： 傅里叶导热定律 普适导热定律 热质运动 非傅里叶导热     

Derivation of the modification heating conduction equation of a kind of laser thermal effect by quantum mechanics

The Fourier equation of heat conduction predicts a paradox that the effect of a thermal impulse (e.g. the thermal effect in pulse laser) in an infinite medium; i.e., a thermal impulse is propagated in an infinite velocity. In order to solve the thermal transport paradox, C. W. Ulbrich and M. Chester have proposed the modification heat conduction equation respectively from different macroscopic viewpoint. This paper derived the modification heat conduction equation according to phonon model and quantum mechanics from microscopic viewpoint.     

Temperature dependence of heat conduction coefficient in nanotube/nanowire networks

Studies on heat conduction are so far mainly focused on regular systems such as the one-dimensional(1D) and twodimensional(2D) lattices where atoms are regularly connected and temperatures of atoms are homogeneously distributed.However, realistic systems such as the nanotube/nanowire networks are not regular but heterogeneously structured, and their heat conduction remains largely unknown. We present a model of quasi-physical networks to study heat conduction in such physical networks and focus on how the network structure influences the heat conduction coefficient κ. In this model,we for the first time consider each link as a 1D chain of atoms instead of a spring in the previous studies. We find that κ is different from link to link in the network, in contrast to the same constant in a regular 1D or 2D lattice. Moreover, for each specific link, we present a formula to show how κ depends on both its link length and the temperatures on its two ends.These findings show that the heat conduction in physical networks is not a straightforward extension of 1D and 2D lattices but seriously influenced by the network structure.     

Dependence of the thermal conductivity of a polymer chain on its tension

The heat transfer along a finite polyethylene macromolecule with fixed ends has been simulated. It has been shown that the thermal flux arising in the chain essentially depends on the distance between its ends. The thermal flux along the chain increases due to its stretching and decreases when its ends become closer to each other. There is a critical value for the approach of the ends at which the coil-globule transition begins. Upon a closer approach, a globule in the chain is formed and, upon a smaller approach, the chain always freely bends in space. It is at this critical approach of the ends that the tension in the chain and heat transfer along it are the weakest. Making the ends more remote or closer, one can change the thermal flux by more than two orders of magnitude. This effect is connected with the strong dependence of the morphology of the polymer chain on its tension. In nanotechnologies, such a polymer molecule with a variable distance between its fixed ends can be used as a regulated phonon resistor, i.e., as a phonon rheostat.     

热超构材料：几何结构、工作机制与新奇性质

因为在热保护、热探测和热管理领域存在重要的应用价值,自由操控宏观热流一直是人类的 一个梦想。热超构材料正是为此目的应运而生,它是电磁超构材料在热学领域的延伸。在此,我将 综述该领域自2008 年诞生以来取得的若干研究进展,其将主要包括以下新奇热现象或功能器件： 热隐身;热聚集;热旋转;宏观热二极管;热伪装;热透明;热晶体;环境温差中零能耗保温;宏 观热网络中反常热传导;热对流隐身、聚集、伪装;热辐射制冷。我将介绍与之相关的微观或宏观 传热机制,这些机制可以通过以下理论或方法来理解或阐述：变换热学理论、Laplace 方程、热声 子能带理论、相变理论、变换热对流理论、热辐射制冷理论。我也将介绍这些材料从基础研究到工 业应用的发展前景。