Heat conduction and its related interdisciplinary areas
从燧人氏钻木取火开始, 人类文明的发展就和“热能”息息相关, 对热现象的认识贯穿整个人类社会发展的历程. 全球约 60%的能源都以废热的形式白白浪费. 热物理的进展对于我国最近强调的 “碳达峰、碳中和”至关重要. 我国力争于 2030年前二氧化碳排放达到峰值, 2060年前实现碳中和.而在利用的和废弃的能源中, 占比最大的都是热能. 关于热能的研究涉及材料、电子器件、生物、能源等诸多学科, 纳米工程的引入为热物理的进展注入了新的活力. 微纳米电子器件、电池中的过热问题会直接影响其性能和使用寿命, 成为 5G、量子计算、芯片、电动汽车等国家战略技术领域目前的研究热点. 人类对于纳米尺度和跨尺度中热物理的认知还是远远不够的. 因此, 物理、工程、材料、电子等多学科的交叉研究将在上述新兴领域大有用武之地.
鉴于热传导问题研究的挑战性与紧迫性, 受编辑部委托特组织本专题, 报道热传导领域最新进展和前沿态势. 陈亮、冯芒老师综述了基于离子阱中离子晶体的热传导的研究进展, 包括一维、二维和三维模型中温度分布和稳态热流的计算方法, 还讨论了无序度对离子晶体热导性的影响; 鲍华老师回顾了金属导热研究的历史, 并对最近十几年来金属导热的研究进行了总结, 特别是对基于第一原理电子-声子耦合模式分析的金属导热机理的研究进行了综述; 唐桂华老师基于宏观热流调控的思想, 提出了非封闭式热斗篷, 并用于高超声速飞行器头锥热防护. 希望本专题对读者了解此前沿领域有所帮助, 为热传导及其相关交叉领域领域的学术交流做一点贡献.
2023, 72 (18): 184401.
doi: 10.7498/aps.72.20230687
Abstract +
The graded thermal conductivity in nanoscale “hot spot” system is a new phenomenon in nanoscale heat conduction. It is found that the thermal conductivity is no longer uniform, and the thermal conductivity gradually increases from the inside to the outside in the radial direction, which no longer obeys Fourier’s law of thermal conductivity. An in-depth understanding of the mechanism of the graded thermal conductivity can provide a theoretical basis for solving engineering problems such as heat dissipation of nanochip. This paper first reviews the new phenomenon of heat conduction recently discovered in nanosystem, then, focuses on the graded thermal conductivity in the “hot spot” system, and expounds the variation law of the graded thermal conductivity in different dimensional systems. According to the changes of atomic vibration mode and phonon scattering, the physical mechanism of the graded thermal conductivity is explained. Finally, the new challenges and opportunities brought by the graded thermal conductivity characteristics of nano “hot spot” to the heat dissipation of nanodevices are summarized, and the future research in this direction is also prospected.
2024, 73 (3): 033701.
doi: 10.7498/aps.73.20231719
Abstract +
Heat transport is one of the most important research topics in physics. Especially in recent years, with the in depth study on single-molecule devices, heat transport in low-dimensional (i.e. one- and two-dimensional) microsystems has received more and more attention. In the research of Fermi-Pasta-Ulam crystals and harmonic crystals, it is widely accepted that heat conduction in low-dimensional system does not follow Fourier’s law. Due to the lack of the equipment that can directly measure heat current, it has been proven to be a challenging task to carry out relevant experiments. Ion crystal in ion trap is located in vacuum and does not exchange energy with the external environment. The crystal structure and temperature can be accurately controlled by electric field and optical field, providing an ideal experimental platform for studying thermal conduction in low-dimensional crystals in classical state or quantum state. Herein we summarize the recent theoretical research on thermal conduction in ion crystals, including the methods of calculating temperature distribution and steady-state heat current in one-dimensional, two-dimensional, and three-dimensional models, as well as the characteristics of heat current and temperature distribution under different ion crystal configurations. Because the nonlinear effect caused by the imbalance among three dimensions hinders the heat transport, the heat current in ion crystal is largest in the linear configuration while smallest in the zig-zag configuration. In addition, we also introduce the influence of disorder on the thermal conductivity of ion crystal, including the influence on the heat current across various ion crystal configurations such as the linear, the zig-zag and the helical configuration. Notably, the susceptibility of ion crystal to disorder increases with crystal size increasing. Specifically, the zig-zag ion crystal configuration exhibits the largest susceptibility to disorder, whereas the linear configuration is least affected. Finally, we provide a concise overview of experimental studies of the heat conduction in low-dimensional systems. Examination of the heat conduction in ion crystal offers a valuable insight into various cooling techniques employed in ion trap systems, including sympathetic cooling, electromagnetically induced transparency cooling, and polarization gradient cooling. Just like macroscopic thermal diodes made by thermal metamaterials, it is possible that the microscopic thermal diodes can also be made in low-dimensional systems.
2024, 73 (3): 037201.
doi: 10.7498/aps.73.20231151
Abstract +
Metal is one of the most widely used engineering materials. In contrast to the extensive research dedicated to their mechanical properties, studies on the thermal conductivity of metals remain relatively rare. The understanding of thermal transport mechanisms in metals is mainly through the Wiedemann-Franz Law established more than a century ago. The thermal conductivity of metal is related to both the electron transport and the lattice vibration. An in-depth understanding of the thermal transport mechanism in metal is imperative for optimizing their practical applications. This review first discusses the history of the thermal transport theory in metals, including the Wiedemann-Franz law and models for calculating phonon thermal conductivity in metal. The recently developed first-principles based mode-level electron-phonon interaction method for determining the thermal transport properties of metals is briefly introduced. Then we summarize recent theoretical studies on the thermal conductivities of elemental metals, intermetallics, and metallic ceramics. The value of thermal conductivity, phonon contribution to total thermal conductivity, the influence of electron-phonon interaction on thermal transport, and the deviation of the Lorenz number are comprehensively discussed. Moreover, the thermal transport properties of metallic nanostructures are summarized. The size effect of thermal transport and the Lorenz number obtained from experiments and calculations are compared. Thermal transport properties including the phonon contribution to total thermal conductivity and the Lorenz number in two-dimensional metals are also mentioned. Finally, the influence of temperature, pressure, and magnetic field on thermal transport in metal are also discussed. The deviation of the Lorenz number at low temperatures is due to the different electron-phonon scattering mechanisms for thermal and electrical transport. The mechanism for the increase of thermal conductivity in metals induced by pressure varies in different kinds of metals and is related to the electron state at the Fermi level. The effect of magnetic field on thermal transport is related to the coupling between the electron and the magnetic field, therefore the electron distribution in the Brillouin zone is an important factor. In addition, this review also looks forward to the future research directions of metal thermal transport theory.
2024, 73 (3): 034401.
doi: 10.7498/aps.73.20231262
Abstract +
The aerodynamic heat of hypersonic vehicle nose cone can reach tens of MW/m2 during flight, which could be transferred to the interior of hypersonic vehicle in the form of conduction and radiation. High efficient thermal insulation technology is of significance in keeping internal electronic components working safely. Thermal metamaterials can regulate the macroscopic heat flow path, and they are developing rapidly and have a wide application prospect in the field of thermal protection. In this work, a non-enclosed point transformation thermal cloak is designed to guide heat flow around hypersonic vehicle nose cone by using the transformation multithermotics, which can control thermal conduction and radiation simultaneously. A multi-layer structure is designed as cloak’s simplified approximation due to the anisotropic parameters. Based on the software COMSOL, the thermal protection characteristics and heat transfer mechanism of the point transformation cloak and multi-layer structure are studied numerically. The results show that heat can flow around the object in the form of conduction and radiation in both point transformation thermal cloak and multi-layer structure, so the heat transferred to the inner area decreases. Comparing with the thermal insulation material, the heating rate of the protected area slows down, and the temperature in the front of the hypersonic vehicle nose cone is significantly reduced. However, the improvement of the thermal protection performance of point transformation cloak and multi-layer structures requires that the solid thermal conductivity and radiative thermal conductivity of the material are lower than those of the original thermal insulation material. To solve this problem, a non-enclosed region transformation thermal cloak is further proposed. The solid thermal conductivity and radiative thermal conductivity of region transformation thermal cloak are non-singular, which could be higher than those of the original thermal insulation material. Numerical simulation results show that the region transformation thermal cloak can guide heat flow around object, so the thermal protection capability is improved significantly. Comparing with the thermal insulation materials, the temperature of the front of the hypersonic vehicle nose cone is reduced by 100 K, and the temperature of the inner central zone of the hypersonic vehicle nose cone is reduced by 10 K. The non-enclosed region transformation thermal cloak provides a new approach to realizing thermal protection and is suitable for complex target areas, showing great application potential in thermal protection.
