【作者】 帅永；

【导师】 谈和平； 夏新林；

【作者基本信息】 哈尔滨工业大学 ， 工程热物理， 2008， 博士

【摘要】 表面微结构所具有的独特热辐射特性及其对辐射的调控能力为可再生能源利用、国防和航天领域急需的热辐射光谱和方向控制技术的发展提供了机遇。当结构几何尺度与入射波长相当或较之更小时,宏观尺度下的唯象理论已经无法有效考虑和解决这类热辐射传输问题。本文在研究两类典型光学系统的热辐射传输特性的基础上,从宏观和微观角度分析了影响表面热辐射特性和传输规律的因素,研究结果为热辐射的光谱和方向调控技术提供了理论基础。主要研究内容包括以下五个方面。(1)发展了基于辐射交换因子的反向蒙特卡洛辐射传输模型,分析了边界条件和物性参数对蒙特卡洛辐射传输算法的计算效率的影响。算例比较证实了在仅需要了解空间某一小立体角内或某一个小区域内辐射能量时,反向蒙特卡洛算法的计算效率要远远高于正向蒙特卡洛法。(2)开展了辐射交换因子不确定性分析和伪随机数发生器性能检验,给出了单个计算单元辐射交换因子的估计误差、整个系统的辐射交换因子的平均估计误差的表达式,提出了一种能比较充分验证伪随机数发生器性能的辐射对称性检验方法,可以实现不同层次上无限制的比较发生器的优劣。(3)采用表面特性镜漫处理和多级能量分裂等计算技术,分析了成像光学系统中杂散辐射传输、非成像光学系统中太阳能聚集辐射传输,获得了边界条件、物性参数对辐射传输的影响规律。建立了聚集能束矢量特性的描述模型,提出了基于等热流密度面与多次反射的腔式吸收器的梯级设计方法,设计了一种能流均匀性好、效率高的新型腔式吸收器结构。(4)基于电磁涨落耗散理论和格林函数特性,推导了无限大表面、粒子与平面板间的近场热辐射传输的表达式,考察了极化态、粒径、间距、介电常数对近场热辐射传输的影响规律。采用时域有限差分法分析了具有栅栏结构、沟渠结构的硅基材料的表面辐射特性,获得了温度、入射波长对表面BRDF的影响规律。(5)基于四波长BRDF测试平台,测试了柔性金属镀膜表面和微粗糙硬铝表面的反射特性,考察了波长、粗糙结构对表面辐射特性的影响。改进了一套基于CCD相机间接测量聚集能流密度的装置,实现了不同位置误差的碟式聚能器的焦面辐射热流测量,并对实验数据与数值结果进行了比较分析。更多还原

【Abstract】 Surface microstructure provides an opportunity to control the spectral and directional properties in fields of renewable energy, defence and aerospace technologies, because it has unique thermal radiation properties and control ability of radiation. When the geometry size becomes as small as the wavelength or less, phenomenological theories at macroscale level are no longer valid to solve these problems of radiative heat transfer. In this research, two classical optical systems are studied on radiative heat transfer, and the influence factors analysis of surface radiation properties and radiation transfer characteristics are explored from a macro perspective and micro perspective. The results offer a theoretical foundation to control spectral and directional properties of thermal radiation. The scope of present research contains five parts:(1) A backward Monte Carlo radiative transfer model based on the radiative exchange factor is developed, and the effects of boundary conditions and physical parameters on calculation efficiency of Monte Carlo method are presented. In the case of detecting radiation energy at some selected positions and/or given direction, the efficiency of the backward Monte Carlo method (BMCM) is much more efficient than the forward Monte Carlo method (FMCM).(2) An uncertainty analysis of the radiative exchange factor (REF) and randomness properties of pseudorandom number generator (PNG) are investigated. The expressions for the estimation error of a computational element and the average error of the whole system are presented on the REF. A method to test radiation symmetry is proposed to validate the performance of PNGs, and it can be widely used to compare unrestricted the performance of PNGs under several different calculation conditions.(3) Some calculation techniques, such as radiant characteristic coupled with diffusion and specular reflection, multiple splitting technique of radiant energy, are adopted to simulate stray radiation in imaging optical system and radiation characteristics of concentrating solar power in non-imaging optical system. The influence laws of boundary conditions and physical parameters on radiative transfer characteristics are also presented. A model to solve the vectorial field properties of concentrating solar power is developed, and a method on the basis of the concept of equivalent radiation flux and step design with multi-reflection is proposed to design the shape of cavity receiver. Furthermore, a new shape of the cavity receiver with an almost uniform flux distribution and high thermal efficiency takes shape.(4) Based on the fluctuation–dissipation theorem and the Green’s function theory, the expressions of thermal near-field emission from a semi-infinite plane surface and near-field radiative heat transfer between a particle and a plane surface are derived. The effects of polarization, particle size, distance and dielectric constant on near-field radiative heat transfer are investigated. Moreover, the FDTD (Finite Difference Time Domain) method is employed to analyze surface radiation characteristic of Si-based material with barrier structure and ditch structure, and the effects of temperature and incident wavelength on surface BRDF (Bidirectional Reflectance Distribution Function) are obtained.(5) Two typical surfaces, flexible metal surface coating and duralumin with micro-roughness, are measured by means of four band BRDF test platform. More, the effects of roughness and wavelength on surface radiation properties are also studied. A measuring system is developed to measure the focal radiative flux distribution using charge coupled device (CCD) cameras, and a series of flux measurements are performed for target placements at different distances from the dish vertex of a paraboloidal dish solar concentrator. Further, the measured flux distributions are compared with a Monte-Carlo-predicted distribution.更多还原