【作者】 程强；

【导师】 周怀春；

【作者基本信息】 华中科技大学 ， 热能工程， 2007， 博士

【摘要】 辐射强度空间高方向分辨率分布对于反演辐射传热系统内光学参数和源项等理论问题,以及解决大尺寸燃烧系统(如燃煤锅炉和大型加热设备)内燃烧可视化等实际问题具有重要价值。本文提出一种求解辐射传递方程的新方法——DRESOR法(Distribution of Ratio of Energy Scattered by the medium Or Reflected by the boundary surface,被介质散射或被壁面反射的能量分布份额)。具体工作如下:首先给出DRESOR法求解辐射传递方程的具体推导过程,建立了采用基于蒙特卡洛法的DRESOR法求解辐射传递方程的基本原理和方法。在具有不同边界条件的各向同性一维灰性平行平板系统中验证了DRESOR法求解辐射传递方程的有效性和准确性。通过验证发现DRESOR法一些有吸引力的优点,例如辐射强度对不同发射源的线性可加性和求解的辐射强度自动满足边界条件等,这些特点使得DRESOR法便于采用并行计算研究复杂辐射传热系统和处理复杂的边界条件。用前向蒙特卡洛法和逆向蒙特卡洛法在处理辐射源是平行光入射并且需要计算任意很小区域和很小立体角内的入射辐射问题时,它们的计算效率非常低。本文中用基于蒙特卡洛法的DRESOR法处理这类问题,在各向同性散射平行平板中求解有平行光入射的辐射传递问题。在研究中,整个4π空间立体角被离散成13087个小立体角,通过DRESOR法可以计算得到系统内任意位置处的辐射强度在如此之多离散方向上的值,进而得到任意位置处探测器在不同接收角下接收的辐射热流,其值和相关文献中结果吻合很好。在充满颗粒云和燃烧气固颗粒混合物的高温系统中各向异性散射是一个基本特征。本文用DRESOR法在具有不同边界条件的一维灰性平行平板中处理各向异性散射问题。通过研究发现:介质的散射并不是不能改变介质中能量的大小,实际上,更强的散射使得能量有更多的机会被介质吸收,从而间接地改变了能量的大小;同时一个有趣的现象被发现:散射介质中的散射特性使得边界辐射强度不能达到同温度下黑体的辐射强度值,即使是光学厚度趋于无限大。目前在一些应用领域,例如短激光脉冲对金属的加工、小尺度系统传热、遥感测量、激光治疗等,需要考虑瞬态辐射传递对事物特性变化的影响。本文用DRESOR法在散射、吸收、无发射的一维平行平板中,处理不同周期和波形的序列脉冲平行入射条件下瞬态辐射传递问题。通过在系统内计算一单位入射辐射能对介质的DRESOR数分布,就能计算任意波形序列脉冲入射辐射在系统内的瞬态分布特性,简便的计算方式说明DRESOR法处理序列脉冲入射问题的优势。同时,用DRESOR法还考察了不同波形平行入射、壁面反射、介质散射率、光学厚度、各向异性散射等条件对辐射能传播及瞬态辐射分布的影响。本文将DRESOR法求解辐射传递问题扩展到二维矩形系统。在二维各向同性散射介质中DRESOR法可以在半球空间立体角内提供6658个方向分辨率的辐射强度分布。在二维各向异性散射辐射传递研究问题中发现,前向散射能有效提高辐射能量穿过介质的能力,使对面边界出射辐射强度最大;后向散射对辐射传递起阻碍作用,使对面边界出射辐射强度最小。最后,本文用能够给出辐射强度在高方向分辨率上分布的DRESOR法建立辐射成像装置中辐射图像信息和三维不规则加热炉内温度分布的定量关系,这是炉内燃烧可视化监测系统的关键技术之一。用建立的这种辐射成像计算关系式,结合三维温度场重建技术,在武汉钢铁(集团)公司一个工业加热炉内开展了三维温度场检测试验研究。为了对用DRESOR法建立的辐射成像计算关系式和系统检测的三维温度分布进行验证。在工业炉内进行了火嘴调试试验和在线实时运行试验。通过试验证明,本系统能准确直观的反映不同工况下,炉内温度分布及板坯温度分布的变化情况,和热电偶最大测温误差在40 C以内,相对误差在5%以内,证明该系统能够满足工业炉在线检测炉内板坯上表面及空间三维温度分布的要求。更多还原

【Abstract】 The radiative intensity distribution with high directional resolution meets lots of demands in many numerical simulations to estimate the radiative parameters and radiation source and practical applicaitions to measure temperature distribution by radiative image processing techniques in the large-scale combustion systems such as pulverized-coal-fired boiler and industrial heat equipments. A new method called DRESOR (Distribution of Ratio of Energy Scattered by the medium Or Reflected by the boundary surface, DRESOR) method is developed to solve the radiative transfer eqution. The detailed description is as below.First the detailed deduce process of the DRESOR method to sovling the radiative transfer equation was given. The fundamental principle and technique of the DRESOR method based on the Monte Carlo method was also built. The method was applied to a gray absorbing, emitting, isotropically scattering, gray, plane-parallel medium with diffusely or specularly reflecting boundaries. And validation results demonstrated its accuracy. Some attractive features, such as the additivity of intensity for different emitting sources and automatically meeting the boundary conditions, make the present method feasible in dealing with complicated radiative transfer problems by parallel computation.Forward and backward Monte Carlo methods may become inefficient when radiant source is collimated and radiation onto a small, arbitrary spot and onto a small, arbitrary direction cone is desired. In this paper, the DRESOR method was formulated to study the radiative heat transfer process in an isotropically scattering layer exposed to collimated radiation. As the whole 4πsolid angle space was uniformly divided into 13087 discrete solid angles, the intensity at some point in up to such discrete directions was given. The radiation fluxes incident on a detector inside the layer for varying acceptance angles were also got, which agreed well with those in literature.It is well known that anisotropic scattering is usually a basic feature in high-temperature systems, which are filled with particles cloud as well as the combustion gases–particles mixtures. The DRESOR method was proposed to deal with the anisotropic scattering, emitting, absorbing, plane-parallel media with different boundary conditions. An attractive phenomenon is observed that the scattering of the medium makes the intensity at boundary can not reach the blackbody emission capability with the same temperature, even if the optical thickness tends to very large. It is also revealed that the scattering of the medium does not mean it can not alter the magnitude of the energy; actually, stronger scattering causes the energy to have more chance to be absorbed by the medium, and indirectly changes the energy magnitude in the medium.In many application areas, such as short laser pulse processing of metal, heat transfer in microstructures, remote sensing and medical diagnosis et al., the effect of transient heat transfer on the charecteristic change of meterial should be considerd. The time-dependent DRESOR method was utilized to solve the transient radiative transfer in a one-dimensional slab filled with an absorbing, scattering and non-emitting medium and exposed to collimated incident serial-pulse with different shape and width. In the DRESOR method, by calculating the time-dependent DRESOR values for a unit short-pulse radiation incident into a scattering media, the solution of intensity can be got by integral with DRESOR values for a serial of incident pulse with different shape and width. So there is no obvious difficulty for solution of the transient radiation transfer process with different shape and width incident serial-pulse, even in the anisotropic scattering medium. The influences of the pulse shape and width, reflectivity of the boundary, the scattering albedo, the optical thickness and anisotropic scattering on the transient radiative transfer were investigated.The DRESOR method was developed to solve the radiative transfer equation in a 2-D, anisotropic/isotropic scattering, rectangular enclosure. Radiative intensity with highly directional resolution in 6658 directions in the hemisphere space at the boundary of the enclosure was provided by the DRESOR method. It was found that in the anisotropic scattering media, the largest boundary intensity occurs with the largest forward scattering capability, and the smallest one with the largest backward scattering capability.Finally, quantified relationship between the radiation temperature image and the temperature distribution in the irregular 3-D industrial heat furnace was built by the DRESOR method, which can give the intensity distributions with high direction resolution. Based on this relationship and 3-D temperature reconstruction technology, a 3-D temperature mesurement test was carried out in a industrail heat furnace of Wuhan iron steel company. To validate calculation relationship of the radiation image and correctness of measured temperature, a burner combustion regulating test and an on-line monitoring test were conducted. The tests confirmed that the system could accurately and intuitively display the temperature change inside the furnace. The error between the temperature measured by thermocouples and the present system were less than 40 C , and relative error was less than 5%. The results demonstrated that the 3-D temperature measurement system could on-line and availably provide top surface of billets and full-scale temperature distributions in the furnace.更多还原