Study On Regulative Characteristics And Directional Transfer Of Surface Thermal Radiation

As one kind of heat transfer mechanism, thermal radiation can be found in many technical fields, such as the thermal engineering, power and propulsion, solar energy utilization, chemical engineering, material manufacturing, as well as the thermal control and thermal protection of space vehicles. It usually combines with the thermal conduction or the thermal convection by various ways to transport heat. On the other hand, thermal radiation is the electromagnetic wave caused by thermal effects. As the visible and infrared signals, it has been widely used in optical measurement, infrared detection and remote sensing technologies. In those applications, its propagating process is a kind of directional transfer behavior of the radiative energy characterized by spectral feature and given spatial distribution, which takes place in complex background and disturbing environment. The involved geometric structure, radiative properties and temperature field are usually complicated. Therefore, an investigation on the regulative characteristics of thermal radiation and the directional transfer is valuable to engineering application and theory development.In this thesis, two kinds of technical fields including the high temperature thermal protection and the spaceborne infrared detection are taken to be the main application backgrounds. The regulative characteristics of thermal radiation for high temperature material and the directional transfer of radiation in spaceborne infrared detection are investigated by the analysis of mechanism model, the development of calculation method and the numerical simulation.The Monte Carlo method to solve radiation heat transfer is improved. Aiming at characteristic of directional radiation transfer in spaceborne infrared detection caused by the complex system, the tremendous variety of geometric scale and the multi-source radiation, numerical method of forward-backward bidirectional calculation is put forward on the basis of Monte Carlo simulation. By comparing with typical cases, superiority of this method is verified with respect to traditional Monte Carlo method. Considering the different grid requirement between the thermal radiation calculation and the heat conduction solution of high temperature ceramic material, a local radiative grid method for thermal source term of radiative exchange is developed. By calculation and comparison, its applicability and effects of relevant parameter are analyzed. The calculating model of the ceramics surface emissivity in high temperature is constructed, including the temperature field in medium subjected to aeroheating as well as the reflection and refraction of the interfaces. Base on this model, the backward Monte Carlo method is used to simulate the thermal emission of the surface in isothermal ceramics. Moreover, the control volume method is combined with the bidirectional Monte Carlo method and the spectral band model to solve the temperature field of coupled heat transfer in ceramics. The effects of emissivity of surface radiation, material property, surface status as well as the effects of aeroheating are discussed.Base on above calculation method and characteristic research of surface radiation, two sorts of transporting models are put forward to regulate thermal radiation of high temperature surface from heat transport and redistribution and coupled mechanism in the thermal protection structure. The control volume method is combined with the local radiative grid method and the Monte Carlo simulation to investigate the regulative characteristics of surface thermal radiation under various conditions and main factors. The forward-backward bidirectional calculation with subsection is used to simulate the directional propagating processes in the multi-spectral infrared system for remote sensing of the earth-atmosphere, the spaceborne optical measurement system to detect moving objects in space and solar energy concentrator. The effects of the geometric structure, the radiative properties of surfaces and the temperature field as well as that of the background and environment are discussed.By the investigation, the numerical methods for thermal radiation regulating of high temperature surface and that for the directional transfer of radiation are obtained. The obtained knowledge on the emission and the regulative characteristics of surface thermal radiation is of theoretical support to the surface radiation characteristics, heat transport and redistribution and direction control of the radiation transfer systems. The understanding to radiation heat transfer of the high temperature thermal protection and the infrared detecting provides necessary base and theory reference.