粗糙表面近场辐射换热的梯度有效介质模型
Near-field radiative heat transfer between rough surfaces modeled using effective media with gradient distribution of dielectric function
摘要：
粗糙表面间近场辐射换热（NFRHT）在近场能源利用的工程实践中广泛存在，需要对其进行深入研究，特别是从物理机理的角度进行研究。本文建立了一个有效的多层模型来研究碳化硅（SiC）随机粗糙表面之间的非均匀热变形。利用有效介质理论（EMT），得到了各层的有效介电函数，沿介质深度形成了介电函数的梯度分布。分析了有效介电函数对表面声子极化激元（SPhP）的影响，结果表明，SiC填充率小的有效层的SPhP共振频率比SiC体材料低。从介电函数的梯度分布SPhPs的耦合产生新的表面模式，占主导地位的NFRHT。对均方根高度（RMS height，σ）影响的研究表明，随着σ的增大，局域态密度（LDOS）和谱热流密度的峰值均发生红移，而峰值频率以下的谱热流密度增大。这可以归因于粗糙层内SPhPs的耦合。研究还发现，平均间距粗糙表面间的总净热通量大于光滑表面间的总净热通量，且随σ的增大而增大，这为NFRHT的强化提供了一种新的途径。本文的工作为粗糙表面间非线性摩擦传热的模拟和理解提供了参考。
英文摘要：
Near-field radiative heat transfer (NFRHT) between rough surfaces, due to its widespread presence in engineering practice of near-field energy utilization, requires indepth studies, especially from the perspective of physical mechanism. In this paper, an effective multilayer model is built to approach the NFRHT between random rough surfaces of silicon carbide (SiC). Using the effective medium theory (EMT), the effective dielectric function of each layer is obtained, which forms a gradient distribution of dielectric function along the depth of the medium. The influence of the effective dielectric function on surface phonon polaritons (SPhPs) is analyzed, showing that the effective layers with small filling fraction of SiC feature lower SPhP resonance frequencies than SiC bulk. The coupling of SPhPs from the gradient distribution of dielectric function produces new surface modes that dominates the NFRHT. Investigation on the effect of root mean square height (RMS height, σ) reveals that the peaks of local density of states (LDOS) and spectral heat flux are red-shifted as σ increases, while the spectral heat flux below the peak frequency gets larger. This can be attributed to the coupling of SPhPs inside the rough layer. We also found the total net heat flux between rough surfaces separated by an average distance exceeds that between smooth plates and increases with increasing σ, which offer a new way to enhance NFRHT. This work provides a reference for the simulation and understanding of the NFRHT between rough surfaces.
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