离散发热器件基于(火积)耗散率最小和最高温度最小的构形优化比较

建立了导热基座上圆柱体离散发热器件的三维湍流散热模型,基于构形理论,考虑空气变物性及可压缩性和黏性耗散,研究了器件材料的热导率、热源强度和流体流速对器件最高温度、基于(火积)耗散定义的当量热阻和平均Nu数的影响.结果表明:在总发热功率一定的条件下,以器件最高温度和当量热阻为性能指标进行热设计,均存在最优热源强度分布使得散热性能最优.当各热源强度相同且热源热导率小于基座热导率时,提高热源热导率可明显改善散热性能;将热源热导率沿流动方向从低到高布置可降低器件最高温度,而将热源热导率均匀布置可使当量热阻最小.所得结果可为实际热设计中不同材质和不同发热率的电子器件最优布置提供理论支撑.     

碳纳米管和碳化硅纳米管热导率的分子动力学研究

采用Tersoff势测试和研究了反向非平衡分子动力学中的Müller-Plathe法和Jund法在一维纳米管热传导中的应用.在相同的模拟步数中,Müller-Plathe法可以得到很好的结果,热导率在交换频率大于50时对参数的选择并不敏感.然而,Jund法并不能得到良好的线性温度梯度,其热导率在一定程度上依赖于选择的热流大小.在此基础上,运用Müller-Plathe法进一步研究了碳纳米管和碳化硅纳米管的长度、直径和温度对热导率的影响.结果表明,无论是碳纳米管还是碳化硅纳米管,其长度、直径和温度对热导率的影响是一致的.只要长度增加,纳米管的热导率相应增大,但增长速率不断降低.直径对热导率的影响很大程度上还取决于温度,在高温时,直径对热导率几乎没有影响.除此之外,纳米管的热导率随着温度的增加总体上也是不断降低的,但峰值现象的出现还受纳米管长度的影响.     

快速来流条件下低温平板常物性霜层一维干模态结霜模拟研究

在快速来流条件下低温平板结霜实验观测的基础上,提出了该种结霜条件下的一维结霜模型。在准稳态的假设前提下,构建了动态结霜的能量方程和质量方程,进行了常物性霜层一维模拟,模拟结果与结霜实验结果吻合较好。进行了单因素变化的一维干模态结霜模拟分析,研究了冷板温度、来流速度、来流湿度、来流温度、霜层密度和霜层热导率等因素变化对结霜的影响规律。在所模拟的参数范围内,来流温度、霜层密度对结霜厚度的影响较小,来流速度、来流湿度、冷板温度和霜层热导率对结霜厚度的影响较大。     

一维二元非对角关联无序体系跳跃电导特性

在单电子紧束缚无序模型基础上，建立了一维二元关联无序体系电子跳跃输运直流电导模型，并推导了其直流电导公式，通过计算其直流电导率，探讨了格点能量无序度、非对角关联及温度、外场对体系跳跃电导的影响.计算结果表明，一维二元无序体系的直流电导率随着格点能量无序度的增大而减小；当引入非对角关联时，体系出现退局域化现象，从而使体系的直流电导率增大；温度对体系的电子输运的影响表现为体系的直流电导率随温度的升高而增大；在外加电场的调制下，体系的直流电导率在强场区随电场强度增加而增长很快，呈现出非欧姆定律特性，但在弱场区外场的作用不明显. 关键词： 二元无序体系 跳跃电导 格点能量无序度 非对角关联     

基于界面原子混合的材料导热性能

构造了界面具有原子混合的硅锗(Si/Ge)单界面和超晶格结构.采用非平衡分子动力学模拟研究了界面原子混合对于单界面和超晶格结构热导率的影响,重点研究了界面原子混合层数、环境温度、体系总长以及周期长度对不同晶格结构热导率的影响.结果表明:由于声子的“桥接”机制,2层和4层界面原子混合能提高单一界面和少周期数的超晶格的热导率,但是在多周期体系中,具有原子混合时的热导率要低于完美界面时的热导率;界面原子混合会破坏超晶格中声子的相干性输运,一定程度引起热导率降低;完美界面超晶格具有明显的温度效应,而具有原子混合的超晶格热导率对温度的敏感性较低.     

一维二元非对角关联无序体系交流跳跃电导特性

在单电子紧束缚无序模型基础上，建立了一维二元非对角关联无序体系电子跳跃输运交流电导模型，并推导了其交流电导公式，通过计算其交流电导率，探讨了格点能量无序度、格点原子组分、非对角关联及温度、外场对体系交流跳跃电导的影响.计算结果表明，一维二元非对角关联无序体系的交流电导率随格点能量无序度的增大而减小.同时，体系中两种原子的组分的变化实际代表着体系成分无序程度的变化，因而对其交流电导率的影响很大，表现为随A类原子含量p的增加而先减小后增大.当引入非对角关联时，体系出现退局域化现象，电子波函数由局 关键词： 二元无序体系 交流跳跃电导 格点能量无序度 非对角关联     

准一维多链无序体系跳跃电导特性

在单电子紧束缚近似下,建立了准一维多链无序体系直流、交流电子跳跃输运模型,通过计算探讨了无序模式、维度效应、温度及外场对其直流、交流电导率的影响.计算结果表明:准一维多链无序体系的直流、交流电导率随着格点能量无序度的增大而减小,非对角无序具有增强体系电子输运能力的作用.随着链数的增加,体系的直流、交流电导率增大,但格点能量无序度较小时,维度效应的影响不明显.在对角无序情况下准一维多链无序体系的交流电导率随温度的升高而增大,而在非对角无序模式下却随温度的升高而减小,但对于直流情况,体系的直流电导率随温度的升     

La_(2-x)Sr_xCuO_4单晶的各向异性热导率的测量

采用加热器和温差电偶搭建了低温热导率的稳态法测量装置,并研究了高温超导材料La_(2-x)Sr_xCuO_4(x=0.01~0.04)单晶的各向异性热导率.实验发现:热导率随温度的变化存在明显的声子峰,并且随着Sr掺杂量的增大,声子热导率逐渐被压制,声子峰的强度也逐渐变弱,该现象来源于掺杂引起的晶格无序度的增强.对于欠掺杂的样品,a方向的热导率总是比b方向的大,这可能源于自旋/电荷沿a轴方向形成准一维的条纹状分布,而准一维的条纹结构会对b方向传导的声子产生额外的散射作用.     

不同周期结构硅锗超晶格导热性能研究

构造了均匀、梯度、随机3种不同周期分布的硅/锗(Si/Ge)超晶格结构.采用非平衡分子动力学(NEMD)方法模拟了硅/锗超晶格在3种不同周期分布下的热导率,并研究了样本总长度和温度对热导率的影响.模拟结果表明:梯度和随机周期Si/Ge超晶格的热导率明显低于均匀周期结构超晶格;在不同的周期结构下,声子分别以波动和粒子性质输运为主;均匀周期超晶格热导率具有显著的尺寸效应和温度效应,而梯度、随机周期Si/Ge超晶格的热导率对样本总长度和温度的依赖性较小.     

微观下的热

<正>在日常生活中,热传导现象很常见。宏观上热传导被看作能量在温度梯度场下的扩散行为,而这一输运过程取决于傅里叶定律给出的材料热导率。由傅里叶定律与能量守恒定律所衍生出的热传导方程,则描绘了温度在时间与空间中的分布。但是,这个宏观热传导方程留下了很多未解之谜。例如,为什么金刚石具有极高的热导率,而和它     

Influences of Structure Disorder and Temperature on Properties of Proton Conductivity in Hydrogen-Bond Molecular Systems

The dynamic properties of proton conductivity along hydrogen-bonded molecular systems,for example,ice crystal,with structure disorder or damping and finite temperatures exposed in an externally applied electric-field have been numerically studied by Runge-Kutta way in our Soliton model.The results obtained show that the proton-soliton is very robust against the structure disorder including the fluctuation of the force constant and disorder in the sequence of masses and thermal perturbation and damping of medium,the velocity of its conductivity increases with increasing of the externally applied electric-field and decreasing of the damping coefficient of medium,but the proton-soliton disperses for quite great fluctuation of the force constant and damping coefficient.In the numerical simulation we find that the proton-soliton in our model is thermally stable in a large region of temperature of T ≤ 273 K under influences of damping and externally applied electric-field in ice crystal.This shows that our model is available and appropriate to ice.     

纳米ZnO／石蜡复合相变材料的热物理性质研究

本文通过将纳米氧化锌（ZnO）颗粒加入熔融的石蜡（PW）并进行搅拌和超声制备了一种纳米ZnO／PW复合相变储能材料。为使纳米氧化锌在基体物质中分散均匀,在制备过程中使用了搅拌和超声以制备均匀的复合材料。使用扫描电镜观察其微观结构表明氧化锌在石蜡中分散良好。对所得ZnO／PW复合相变材料的相变温度、相变焓及导热系数等热物...     

Molecular Dynamics Simulation of Thermal Conductivity in Si--Ge Nanocomposites

Thermal conductivity of nanocomposites is calculated by molecular dynamics （MD） simulation. The effect of size on thermal conductivity of nanowire composites and the temperature profiles are studied. The results indicate that the thermal conductivity of nanowire composites could be much lower than alloy value; the thermal conductivity is slightly dependent on temperature except at very low temperature.     

相变微胶囊的热导率测量

提出应用3ω谐波探测技术进行脲醛树脂-石蜡相变微胶囊的等效热导率测量方法。测试了跨越相变温度区间的微胶囊等效热导率,分析了等效热导率随温度的变化关系。在其相变温度区间内,热导率存在极大值,该极值点对应的温度与其相变温度峰值一致。同样温度下,降温时的等效热导率略小于升温,这主要是由降温时相变材料的过冷引起。     

Effect of dispersion on the phonon focusing and anisotropy of thermal conductivity of silicon single crystals in the boundary scattering regime

The effect of dispersion on the focusing of thermal phonons and on the thermal conductivity of silicon single crystals in the boundary scattering regime has been investigated. Analysis of the spectra of acoustic modes obtained for silicon single crystals from inelastic neutron scattering data has demonstrated that, upon transition from long-wavelength phonons to short-wavelength phonons, the directions of their focusing change. With an increase in temperature, this leads to a change in the anisotropy of thermal conductivity of phonons with different polarizations and, consequently, to a change in the anisotropy of the total thermal conductivity. Analysis of the temperature dependence of the thermal conductivity has revealed that the presence of extended flattened sections in the spectrum of short-wavelength transverse phonons indicates anomalously low values of the group velocity and, accordingly, a significant decrease in the contribution from these phonons to the thermal conductivity with increasing temperature. The contribution from longitudinal phonons to the thermal conductivity also significantly increases even at temperatures higher than 110 K and becomes dominant.     

Tunneling states in amorphous ferromagnets

A model of an amorphous ferromagnet in which a certain number of atoms forms two-level systems is considered. Relaxation time of such systems due to the interaction with spin waves is calculated and it is shown that this time can be comparable to the phonon relaxation time. The spin wave damping in such ferromagnet is determined and the magnetic contribution to the thermal conductivity is calculated.     

Transport of electron thermal energy in high temperature plasmas

The nature of the anomalous transport of electron thermal energy in existing experiments on magnetically confined toroidal plasmas is discussed and a new form of the relevant electron thermal conductivity, that is consistent with the observed temperature profiles, is presented.     

氮化硅纳米薄膜非平衡热导率实验研究

3ω实验方法是一种可以对薄膜热导率进行瞬时测量的方法。根据3ω方法测试原理,搭建了薄膜导热系数测试平台,并且分别测试低频率段和高频段薄膜与基底的温升以及薄膜热导率。测试结果表明:Si3N4薄膜的热导率随温度的升高而增大;高频段下,热导率受频率影响大,误差大;在低频段下薄膜热导率与频率变化基本无关;基于电子与声子的局部热平衡运输方程假设,S i3N4薄膜的热导率具有极度非平衡性;通过比较电阻、热导率与温度的关系可以看出加热器的尺寸大小会影响薄膜的热导率,最佳加热器的宽度选用20μm左右。     

Thermoelectric transport in holographic quantum matter under shear strain

We study thermoelectric transport under shear strain in two spatial dimensional quantum matter using the holographic duality.General analytic formulae for the DC thermoelectric conductivities subjected to finite shear strain are obtained in terms of black hole horizon data.Off-diagonal terms in the conductivity matrix also appear at zero magnetic field,resembling an emergent electronic nematicity,which cannot nevertheless be identified with the presence of an anomalous Hall effect.For an explici...     

Temperature and concentration dependences of thermal conductivity of solid solutions of gadolinium and dysprosium sulfides

Thermal conductivity of a number of solid solutions of gadolinium and dysprosium sulfides has been studied experimentally within the temperature range 80-400 K. The work offers the data on thermal conductivity coefficient and lattice thermal conductivity of the studied samples. It was found that replacement of gadolinium ions by dysprosium ions leads to significant decrease of the samples?? thermal conductivity and changes its temperature dependence character due to the resonance scattering of phonons by paramagnetic ions of dysprosium. Influence of this mechanism of phonon scattering conditions the area of anomalous change observed on the concentration dependence of thermal conductivity coefficient.