Computation of Radiative Properties in One-Dimensional Sphere Packings for Sintering Applications

Rapid sintering is an important manufacturing process. Because of the rapid rise of the powder system to the sintering temperature, thermal gradients are typically induced in the system. This gradient can be important in determining the microstructure of the final product. To obtain the temperature distribution, the radiative properties such as the phase function, as well as the absorption and scattering coefficients, are required. Typically, the conjugate gradient method is utilized to acquire these properties. The method employs a minimization technique on a single-objective function composed of several sets of other parameters. Thus although this method has been shown to be useful in many situations, it may not be suitable for certain configurations. In the current study, another method is developed to compute the radiative properties. The phase function was removed from the objective function and computed separately. In addition, a dual-objective function technique was developed. The results from benchmarking showed the present technique not only to produce more accurate results than the conjugate gradient method, but also to require significantly less computational time.     

空气在煤灰球中的等效扩散系数的实验测定

本文提出了一种测量煤焦粒燃烬时间的方法来确定空气在煤灰球中的等效扩散系数，由于煤焦粒的燃烬时间的测定较准确，因此所得之等效扩散系数较可靠，测量结果表明，空气在煤灰球中的等效扩散系数随煤中灰份的含量的增加呈单调下降的关系，并给出了它们之间的通用关系式。     

Thermal Radiative Properties of Complex Media: Theoretical Prediction Versus Experimental Identification

In many engineering applications and natural phenomena, thermal radiation interacts with complex media composed of dispersed phases that may be of different type: solid/solid, solid/gas, or liquid/gas. Most of them are semitransparent media that emit, absorb, and scatter thermal radiation. Heat transfer by combined radiation with conduction or convection in such media is a problem of high practical importance, mostly in situations where radiation is a dominant mode. Improvement of thermal performance of such materials or of the manufacturing processes that involve these media requires the availability of efficient methods (i) for radiative transfer modeling, and (ii) to predict and to experimentally determine the thermophysical properties intended to feed the models. This paper is focused on radiative properties assessment. After a brief overview of the materials and properties of interest, the emphasis is put on methodology of property investigation combining both theoretical prediction and experimental identification. Examples related to different particulate media are presented, showing recent advances and needs for further investigation.     

煤粉炉内颗粒光学特性实验与数值模型

采用KBr压片吸收谱法对钙基矿物质，炭与飞灰的光学特性进行了实验测定。通过Mie理论分析了钙基矿物质的辐射特性，并分别基于Mie理论、包覆球体模型及等效光学常数理论，结合未燃尽炭的结构模型建立了三种辐射特性计算模型，对不同程度的未燃尽炭的辐射参量进行了计算，并与实验测得的未燃尽炭的辐射特性进行了对比，对三种模型的准确性进行了评判。     

Numerical Investigation of Energy-Efficient Receiver for Solar Parabolic Trough Concentrator

In this paper, a thermal analysis of an energy-efficient receiver for solar parabolic trough concentrator is presented. Various porous receiver geometries are considered for the performance evaluation of a solar parabolic trough concentrator. Numerical models are proposed for a porous energy-efficient receiver for internal heat gain characteristics and heat loss due to natural convection. The internal flow and heat transfer analysis is carried out based on a RNG k-? turbulent model, whereas external heat losses are treated as a laminar natural convection model. The numerical models have been solved using the commercial engineering package, FLUENT. The thermal analysis of the receiver is carried out for various geometrical parameters, such as fin aspect ratio, thickness, and porosity, for different heat flux conditions. The inclusion of porous inserts in tubular receiver of solar trough concentrator enhanced the heat transfer about 17.5% with a pressure penalty of 2 kPa. The Nusselt number correlation is proposed based on the extensive numerical data for internal heat transfer inside the receiver. The proposed model is compared with more well-known natural convection models. A comparative study is carried out with different porous geometries to evolve an optimum configuration of energy-efficient receivers.     

Thermal Analysis of a Volumetric Solar Receiver

The volumetric receiver has received wide attention due to its high thermal efficiency. This paper studied a new type of a solid-liquid composite volumetric receiver. The heat transfer in a solid-liquid composite volumetric solar receiver was analyzed using a one-dimensional unsteady simulation model of the solid-liquid receiver. The model included absorption of the incident solar radiation by the glass window, the silicon carbide porous ceramic heat absorber panel and the water. The results were verified against experimental data for a volumetric receiver and the error did not exceed 10%. It can be used to predict the heat transfer in solid-liquid composite volumetric receivers.     

气体污染物的红外辐射特性

基于 HITRAN Database给出的谱线参数 ,利用逐线计算方法计算了 SO2 ,CO,N2 O,NO,NO2等气体污染物的红外辐射特性 ,给出了总压为 1atm、温度为 2 96K、波数范围 4 0 0～ 80 0 0内气体污染物的吸收系数分布图。为便于比较 ,同时给出了水蒸汽和二氧化碳气体的吸收系数分布图。     

热管式吸热／蓄热器在太阳能发电系统中的研究与应用

介绍了热管式太阳能吸热／蓄热器的工作原理,国内外对其所做的研究,以及在太空发电站中的应用,针对热管式吸热／蓄热器研究方向提出了几点建议。     

Exergy Analysis of Photo-Thermal Interaction Process between Solar Radiation Energy and Solar Receiver

A unified theory of non-equilibrium radiation thermodynamics is always in search as it is meaningful for solar energy utilization. An exergy analysis of photo-thermal interaction process between the solar radiation energy and solar receiver is conducted in this paper. The non-equilibrium radiation thermodynamic system is described. The thermodynamic process of photo-thermal interaction between the solar radiation and solar receiver is introduced. Energy, exergy and entropy equations for the photo-thermal process are provided. Formulas for calculating the optimum receiving temperatures of the solar receiver under both non-concentration and solar concentration conditions are presented. A simple solar receiver is chosen as the calculation example to launch the exergy analysis under non-concentration condition. Furthermore, the effect analysis of solar concentration on the thermodynamic performance of the solar receiver for solar thermal utilization is carried out. The analysis results demonstrate that both the output exergy flux and efficiency of the solar receiver can be improved by increasing the solar concentration ratio during the solar thermal utilization process. The formulas and results provided in this paper may be used as a theoretical reference for the further studies of non-equilibrium radiation thermodynamic theory and solar thermal utilization.     

Experimental Study for the Performance of the Solar Distiller

This article describes the experimental results obtained by the solar distiller by specifying the radiative properties of materials, the analysis of various types of losses in the system and the establishment of the energy assessment of the system being the main question to consider. The experiment was undertaken in Tlemcen-Algeria by working out a solar distiller in order to measure the various temperatures of the system. Salt was added to study the negotiable effect of the salinity of water on solar distillation and it is noted that the production of distilled water decreases with salinity. The distiller is forwarded to a constant global solar flow. Experimental results obtained in heat transfer of natural convection in the pure and simultaneous heat and mass transfer, proven that these phenomena are in the boundary layer. This enables people to admit that the existence of a stagnant zone inside of distiller is called the ＂buffer zones＂.     

可燃材料热辐射点火的实验研究

利用早期特性实验台研究了白松木等固体材料在热辐射条件下热解、着火和燃烧的过程，测定了不同辐射强度下的试样质量损失速率、表面温升和引燃时间的变化规律。为研究材料的可燃性质、非接触条件下火灾蔓延的条件和规律提供实验依据。     

A High-Order-Accurate GPU-Based Radiative Transfer Equation Solver for Combustion and Propulsion Applications

In this article we present a high-order-accurate solver for the radiative transfer equation (RTE) which uses the discontinuous Galerkin (DG) method and is designed for graphics processing units (GPUs). The compact nature of the high-order DG method enhances scalability, particularly on GPUs. High-order spatial accuracy can be used to reduce discretization errors on a given computational mesh, and can also reduce the mesh size needed to achieve a desired error tolerance. Computational efficiency is a key concern in solutions to radiative heat transfer problems, due to potentially large problem sizes created by (a) the presence of participating nongray media in a full-spectrum analysis, (b) the need to resolve a large number of angular directions and spatial extent of the domain for an accurate solution, and (c) potentially large variations in material and flow properties in the domain. We present here a simulation strategy, as well as a set of physical models, accompanied by a number of case studies, demonstrating the accuracy and superior performance in terms of computational efficiency of this approach.     

太阳能柱式吸热器非均匀受热的数值模拟

塔式太阳能热发电站中的吸热器是光热转换的重要设备,其由多根无间隙排列的集热管组成。通常集热管表面接收的太阳辐射能流极不均匀,当水/蒸汽作为集热管内的传热工质时,管内工质状态为复杂的沸腾两相流动,因此研究其受热特性具有重要价值。本文基于Fluent平台,利用VOF(Volume of Fluid)方法,建立了不均匀能流边界条件下水/蒸汽集热管的数值模型。模拟分析呈现了管内汽液两相的流动特性;得到了集热管管内工质和管壁的温度分布和集热管内壁面的努塞尔数分布。     

一种多孔介质太阳能吸热器传热研究

为了研究塔式太阳能多孔介质吸热器的传热传质特性,建立吸热器稳态传热模型,选择适合多孔介质太阳能吸热器的体积对流换热系数模型,采用数值方法求解,并分别分析孔隙密度、孔隙率和入口空气速度对温度场的影响。文中技术可以为同类型太阳能吸热器的设计和改造提供参考。     

Normalization of Various Phase Functions for Radiative Heat Transfer Analysis in a Solar Absorber Tube

Normalization of various phase functions is considered for accurately predicting radiative heat transfer. A solar absorber tube filled with anisotropic scattering working medium is used as an example. Analysis of a previous normalization technique shows that while it does conserve scattered energy exactly after discrete-ordinates method (DOM) discretization, the overall asymmetry factor of the phase function is distorted, leading to substantial changes in overall scattering effect. A new normalization technique that conserves asymmetry factor and scattered energy simultaneously is investigated. The impact of lack of asymmetry factor conservation is analyzed for both the Legendre polynomial and the Henyey–Greenstein phase function approximations. Variations of medium optical thickness, scattering albedo, asymmetry factor, and side-wall emissivity are scrutinized to determine the effects of said parameters on wall heat flux and energy absorbing rate inside the absorber tube. Side-wall heat flux is found to increase with increases in asymmetry factor, optical thickness, and wall emissivity, and with decreases in scattering albedo. Energy absorbing rate profiles are found to depend greatly on optical thickness and scattering albedo.     

Determination of the Radiative Heat Transfer in Transparent Silica Aerogel

Radiative heat transfer in SiO₂ aerogel is determined from the spectral infrared extinction (absorption) E(λ). From E( λ) we derive a temperature dependent Rosse-land mean ē(T) for extinction. A suitable diffusion model for the infrared radiation allows to calculate the temperature dependent radiative loss coefficient k_raa(T). For a 1?cm thick aerogel board and a mean temperature within the insulation of T = 280?K, a value as low as k_rad,? 0.16W/m²K results. Between T = 250 and 450K a good approximation is_rad∞T_α, with α = 5.6.     

燃烧产物辐射特性的误差对炉内辐射传热计算精度的影响

本文用离散坐标法对含吸收散射性介质矩形空腔内的３维辐射传递过程进行了模拟，并编写了相应的数值计算程序。利用该程序分析了介质的吸收系数、散射系数、相函数、光谱特性及壁面灰渣沉积层黑度的不确定性对矩形燃烧室内烟气温度及热流计算精度的影响。结果表明计算精度很大程度上取决于燃烧产物辐射特性的取值精度，特别是壁面灰渣沉积层黑度的取值精度。在煤粉燃烧室中，介质的散射不宜忽略。     

两段式塔式太阳能腔式吸热器设计及性能分析

针对一种新型两段式塔式太阳能热发电的吸热器进行几何设计,建立了呈高斯分布热流密度的条件下吸热器辐射和对流换热以及流动模型,确定了吸热器I和吸热器II受热面蛇形管管道布置方式和几何尺寸,获得了吸热器内部不同位置受热面的热流密度分布情况.结合气液两相传热和流动特点确定了吸热器典型管道内部工质温度、干度、压降和沿管道流程的壁温分布规律.得出两段式塔式太阳能腔式吸热器几何结构的系统化设计流程,并对吸热器进行了热力性能分析.结果表明:两段式塔式太阳能腔式吸热器能够有效减小预热蒸发吸热器的几何尺寸,提高平均辐射热负荷的同时降低吸热器的平均温度,有效提高吸热器的热效率;多管程蛇形管道布置可使出口参数分布更加均匀,避免受热严重不均等安全问题.