Study Of Surface Radiative Properties And Radiative Intensity With Directional High Resolution

Increasing the efficiency of the present energy system and developing renewable energy source are two important ways to solve the energy problem coming up today. Coal will be the main energy source in China for a long time. To operate power plant boilers more securely and economically will be a good way to increase energy utility efficiency. In power plant boiler which is a high temperature system, radiation is a main heat transfer mode. Calculation of radiative heat transfer is very important for boiler design. Furthermore, radiative transfer calculation is the precondition of inverse analysis process, such as temperature detection inside boilers.Developing a numerical method that can calculate directional high resolution intensity efficiently and can be applied to most cases is very important in inverse analysis and is attempted in this study. The DRESOR (Distributions of Ratios of Energy Scattered Or Reflected) method proposed by my workgroup is extended to solve the transient radiative transport in non-uniform scattering media. The transport process of a short pulse in the media is analyzed. The reflectance signal shows a dual peak phenomenon which can be used to identify the interface between two different scattering media. The existence condition for the dual peak phenomenon is analyzed in detail. The iterative DRESOR method is proposed based on the traditional DRESOR method. The directional high resolution intensity calculated by DRESOR method is substituted into the integral radiative transfer equation and updated directional intensity can be gotten. After several iterations, the calculation error can be reduced to 0.02% for this method, while the calculation error of DRESOR method is about 4%. The iterative DRESOR method can achieve much better accuracy without much time increase comparing with DRESOR method. An improved discrete ordinates method is also proposed in this study. Intensity with directional high resolution is calculated by DOS+ISW (Discrete Ordinates Scheme with Infinitely Small Weights) method, which can calculate intensity very efficiently. The intensity can be used to calculate radiative integral quantities, such as heat flux, incident radiation etc.. Ray effects caused by non-uniform emission of boundaries and media are investigated in present study. It shows this method can mitigate both of them effectively by comparing the results with those of benchmark solutions given in references.Additionally, the influence of different medium and boundary conditions on radiative transport is examined by the methods mentioned above. The temperature and reflectivity of the boundaries can affect the radiative equilibrium status and emission of the radiative system obviously. When the temperature of the boundaries is equal to that of the medium, or the boundaries are total reflection surfaces, the emission at the boundary are equal to that of blackbody. The influence of boundaries with different reflection modes (specular reflection or diffuse reflection) on radiative intensity and radiative flux in one dimensional system with one emissive boundary is also investigated. Directional intensity is influenced obviously, especially in the zone near the boundary with changed reflection mode. The influence of different reflection modes of emissive boundary or non-emissive boundary on radiative flux is different. The influence of different reflection modes of the emissive boundary on transmittance and reflectance is negligible. Different reflection modes of the non-emissive boundary also have little effect on the transmittance, but they obviously influence the reflectance. The influence of non-emissive boundary reflection modes on reflectance under different conditions (different optical thickness, scattering albedo, and different scattering phase function) is also examined. This provides information for researchers or engineers to determine if the boundaries can be simply considered as diffuse reflectors.Thermophotovoltaic devices have been considered as energy conversion systems, which allow recycling the wasted heat as well as enhancing the conversion efficiency. Solar energy is a very clean energy source, as a renewable energy it attracts a growing interest from the world. Proper spectrum selective surfaces can enhance the energy conversion efficiency, either in thermophotovoltaic or solar energy applications. The Finite Difference Time Domain (FDTD) method is applied to analyze several different patterned surfaces in this study, including simple and complex grating doped silicon structures. The influence of small features (nano-scale) on spectrum properties of patterned surfaces is given. The small feature can shift the spectrum absorptance peak to longer wavelength and the shifted distance depends on the position arrangement and the size of the small features. This is useful for quality estimation in micro/nano-structure producing industry, also can be used for tailoring surface spectrum properties. The FDTD method is also used to calculate two dimensional silicon rough surfaces. Comparisons between the experimental results and results calculated by the FDTD method show that this method has a good accuracy. Geometry optics ray tracing method is applied to calculate the reflection properties of road surfaces. Results show that when the incident angle is large the reflected light only exists in a very small span of solid angle and the reflection direction is around specular and off-specular reflection direction. The pavement surface acts like a mirror surface due to the strong reflection from large incident angle. This can be used to explain highway mirage phenomenon.