Spectral Radiative Transfer On Surfaces Of The Representative Optical Systems And Microscale Effects

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 When the geometry size becomes as small as the wavelength or less, phenomenological theories at macroscale level are no longer valid to solve these problems of radiative heat transfer.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.