Hofmeister Anne M
Department of Earth, Environmental, and Planetary Sciences, Washington University, St. Louis, MO 63130, USA.
Materials (Basel). 2024 Sep 11;17(18):4469. doi: 10.3390/ma17184469.
Models of heat transport in solids, being based on idealized elastic collisions of gas molecules, are flawed because heat and mass diffuse independently in solids but together in gas. To better understand heat transfer, an analytical, theoretical approach is combined with data from laser flash analysis, which is the most accurate method available. Dimensional analysis of Fourier's heat equation shows that thermal diffusivity () depends on length-scale, which has been confirmed experimentally for metallic, semiconducting, and electrically insulating solids. A radiative diffusion model reproduces measured thermal conductivity ( = = × density × specific heat) for thick solids from ~0 to >1200 K using idealized spectra represented by 2-4 parameters. Heat diffusion at laboratory temperatures (conduction) proceeds by absorption and re-emission of infrared light, which explains why heat flows into, through, and out of a material. Because heat added to matter performs work, thermal expansivity is proportional to /Young's modulus (i.e., rigidity or strength), which is confirmed experimentally over wide temperature ranges. Greater uptake of applied heat (e.g., generally increasing with or at certain phase transitions) reduces the amount of heat that can flow through the solid, but because = , the rate () must decrease to compensate. Laser flash analysis data confirm this proposal. Transport properties thus depend on heat uptake, which is controlled by the interaction of light with the material under the conditions of interest. This new finding supports a radiative diffusion mechanism for heat transport and explains behavior from ~0 K to above melting.
基于气体分子理想化弹性碰撞的固体热传输模型存在缺陷，因为热量和质量在固体中独立扩散，而在气体中共同扩散。为了更好地理解热传递，将一种分析性的理论方法与激光闪光分析数据相结合，激光闪光分析是目前最精确的方法。对傅里叶热方程进行量纲分析表明，热扩散率（）取决于长度尺度，这已在金属、半导体和电绝缘固体中得到实验证实。一个辐射扩散模型使用由2 - 4个参数表示的理想化光谱，再现了从约0到>1200 K的厚固体的测量热导率（= = ×密度×比热容）。在实验室温度下的热扩散（传导）通过红外光的吸收和重新发射进行，这解释了热量为何流入、通过并流出一种材料。因为添加到物质中的热量会做功，热膨胀系数与/杨氏模量（即刚度或强度）成正比，这在很宽的温度范围内都得到了实验证实。对施加热量的更大吸收（例如，通常随或在某些相变时增加）会减少能够流过固体的热量，但由于 = ，速率（）必须降低以进行补偿。激光闪光分析数据证实了这一观点。传输特性因此取决于热量吸收，而热量吸收在感兴趣的条件下由光与材料的相互作用控制。这一新发现支持了热传输的辐射扩散机制，并解释了从约0 K到熔点以上的行为。
