The DRESOR Method Solving The Radiative Transfer Equation With Its Application

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.