EAGER: Modeling and Characterization of Mesoscale Nondiffusive Heat Transfer

#1637370Ma，Yanbao随着微/纳/光电子器件和结构尺寸的不断减小，热传输的操纵和控制正成为许多纳米技术发展的瓶颈。 虽然宏观尺度传热中的热导率是一种材料性质，与样品尺寸和加热方法无关，但在微/纳米系统中测量的热导率可能取决于样品尺寸和非稳态加热的频率。尺寸依赖性或频率依赖性的热导率表明傅立叶定律的故障来描述微/纳米系统中的非扩散热传递。本项目开发的统一非扩散-扩散模型将为微/纳米系统的热管理提供强有力的理论和数值设计工具，这对于突破纳米技术的发展瓶颈至关重要。综合研究和教育计划将鼓励更多来自传统上代表性不足的社区的妇女和学生进入STEM职业生涯，并参与UC默塞德拟议的研究活动。 声子是绝缘体和半导体中的主要热载体。傅立叶分解？s定律是由于当特征长度尺度变得与声子的平均自由程（MFP）相当或甚至比其小得多时，存在显著的弹道热传导。目前，有两个主要的技术障碍，在理解非扩散传热：（a）缺乏实用的中尺度非扩散传热模型，可应用于实验数据分析;（B）缺乏特设的参数来表征非扩散传热的独特功能。因此，目前大多数非扩散传热的研究集中在傅立叶定律的框架内的有效导热系数（ETC）的预测和测量，但这些提供的独特功能的非扩散传热的洞察力很少。虽然分子尺度模型可以描述几个纳米的热传导，傅立叶定律描绘了几十微米或更大的宏观尺度的热传递，但在分子尺度和宏观尺度之间的热传导模型中存在差距。声子玻尔兹曼输运方程（BTE）被认为是填补这一空白，但它是昂贵的，以解决这么多的未知参数。因此，实用和计算成本低廉的中尺度非扩散传热模型是必不可少的，以弥补这一差距，描述传热的声子长度尺度从几十纳米到几十微米。 该项目的研究目标是开发和验证一个中尺度非扩散传热（包括弹道和弹道扩散）模型，以阐明无法用热导率表征的独特功能。该项目的成功不仅将通过发展高保真统一的非扩散-扩散多尺度传热模型来弥合宏观尺度和分子尺度模型之间的热传导理论的差距，而且还将为在傅立叶定律框架之外研究非扩散传热的独特特性开辟新的途径。

#1637370Ma, YanbaoWith continuous decrease in the size of micro-/nano-/optoelectronic devices and structures, the manipulation and control of heat transport is becoming a bottleneck for the development of many nanotechnologies. While thermal conductivity in macroscale heat transfer is a material property and independent of the sample size and heating method, the measured thermal conductivity in micro-/nanosystem may depend on the sample size and the frequency in unsteady heating. The size-dependent or frequency-dependent thermal conductivity indicates the breakdown of Fourier's law to describe nondiffusive heat transfer in micro-/nanosystems. The unified nondiffusive-diffusive model to be developed in this project will provide powerful theoretical and numerical design tools for thermal management in micro/nanosystems that is crucial for breaking the developmental bottleneck of nanotechnologies. The integrated research and education plan will encourage more women and students from traditionally underrepresented communities to enter STEM careers and participate in the proposed research activities at UC Merced. Phonons are the dominant heat carriers in insulators and semiconductors. The breakdown of Fourier?s law is due to the fact that there is significant ballistic heat conduction when the characteristic length scale becomes comparable to or even much smaller than the mean-free-path (MFP) of phonons. Currently, there are two major technical barriers in understanding nondiffusive heat transfer: (a) a lack of practical mesoscale nondiffusive heat transfer models that can be applied to experimental data analysis; and (b) a lack of ad hoc parameters to characterize the unique features of nondiffusive heat transfer. Consequently, most current studies of nondiffusive heat transfer focus on the predictions and measurements of effective thermal conductivity (ETC) within the framework of Fourier's law, but these provide little insight on the unique features of nondiffusive heat transfer. Although molecular scale models can describe heat conduction over a few nanometers, and Fourier's law delineates macroscale heat transfer over tens of microns or larger, a gap exists in heat conduction models between the molecular scale and the macroscale. The phonon Boltzmann transport equation (BTE) was supposed to fill this gap, but it is prohibitively expensive to solve with so many unknown parameters. Therefore, practical and computationally inexpensive mesoscale nondiffusive heat transfer models are indispensable to bridge this gap to describe heat transfer by phonons over length scales ranging from tens of nanometers to tens of microns. The research objective for this project is to develop and validate a mesoscale nondifussive heat transfer (including ballistic and ballistic-diffusive) model to elucidate unique features that cannot be characterized by thermal conductivity. The success of this project will not only bridge the gap in heat conduction theories between macroscale and molecular scale models by developing high-fidelity unified nondiffusive-diffusive models for multiscale heat transfer, but also open up new venues to study unique features of nondiffusive heat transfer outside the framework of Fourier's law.