Light scattering coatings: Theory and solar applications

We report on the recent theoretical advances in the field of light scattering by coatings or foils. Methods for computing all the parameters in the four-flux and two-flux radiative transfer theories have been devised. The four-flux theory is applied to the optical properties of white paints and pigmented polymer foils. Nocturnal dew collection by pigmented foils has been investigated in Dodoma, Tanzania, over a period of five months.     

基于图像光散射法的超低排放烟尘在线测量方法

针对超低排放烟尘在线实时监测问题,提出了基于图像传感器的在线实时测量烟尘质量浓度和粒度的新型光散射方法,并搭建实验装置对低质量浓度的烟尘颗粒进行测量。结果表明:低质量浓度下散射光强与烟尘质量浓度成正比;该方法能够满足超低排放烟尘浓度在线实时监测的要求,并能同时测量烟尘颗粒的平均粒径。     

颗粒粒径分布光散射反演问题的一种随机算法

颗粒粒径分布的光散射测量是燃烧光学诊断研究中一个非常重要的内容。本文根据粒子在Ｍａｒｋｏｖ链上的游动模型提出一种从光散射数据反演颗粒粒径分布的随机算法,对粒径分布进行了数值模拟。计算的结果表明该算法抗噪能力强,允许噪信比可达２０％;算法对颗粒粒径分布参数不敏感,可适合于极窄、极宽和各种颗粒粒径分布形式;该算法编程简单,易于计算机实现,可望用于颗粒粒径分布光散射在线测量的反演计算。     

How Heat and Mass Recovery Strategies Impact the Performance of Adsorption Desalination Plant: Theory and Experiments

A prototype adsorption desalination facility is experimentally studied, and the performance tests are conducted with and without the heat and mass recovery procedures. The experiments show that practical and yet effective methods could yield a significant boost to the specific daily water production and performance ratio of the desalination plant by 15.7% and 42.5%, respectively.     

激光散射理论在汽轮机蒸汽湿度及水滴直径测量中的应用

蒸汽湿度的存在不但降低汽轮机组的运行效率,而且会引起严重的叶片水蚀,给汽轮机组的经济性和安全性带来很大的危害.根据激光散射理论和Mie散射理论,利用半导体激光器发射出三个不同波长的光能够在线测出汽轮机末级蒸汽湿度及水滴颗粒大小和分布,为监控和减少湿蒸汽对汽轮机的危害提供最直接的数据.图5表1参11     

烟颗粒光散射Muller矩阵测量与尺寸、形状参数的研究

对烟颗粒光散射Muller矩阵及其测量原理、测量方法进行了说明,并对依据此测量方法建立的烟颗粒光散射实验平台进行了介绍.根据烟颗粒形状具有分形结构,以及该类颗粒光散射的特点,提出了用光散射Muller矩阵测量烟颗粒回转半径与分形维数的方法,并利用该方法对棉绳阴燃烟颗粒的同转半径进行了测量,结果表明棉绳阴燃烟颗粒的回转半径大致在200-300 nm.     

Source Distribution Based on Mie's Scattering Theory for Heat Conduction in Nanoparticle Subject to Ultrashort Laser Irradiation

The objective of this paper is to find a more appropriate source term for heat conduction in a nanoparticle subject to ultrashort laser irradiation. Monte Carlo simulation based on Mie's theory is used to investigate the heat source distribution in a single nanoparticle subject to ultrashort laser irradiation. The results show that when the particulate radius is much smaller than the wavelength, the source distribution is similar to that of blackbody sphere. However, if the radius is comparable to or greater than the wavelength, more photons will bypass the particle which makes the source distribution different.     

Heat transfer from small objects in microgravity: Experiments and analysis

Heat transfer over a sub-millimeter spheroidal solid is of interest in many engineering processes. One important mechanism of heat transfer in the above processes is natural convection which leads to heat transfer rates many times larger than that of pure conduction. Despite the huge literature devoted to natural convection heat transfer rates over spheres (and to a smaller extent over spheroids) there is not a generally accepted correlation especially for small Rayleigh numbers. Existing correlations for external geometries predict a progressively increasing contribution of natural convection to heat transfer with respect to gravity (starting from zero gravity). To test the validity of these correlations, experiments are performed for the estimation of heat transfer rates at low gravity. Heat pulses are given to a miniature thermistor with a nearly spheroidal shape immersed in a liquid and its thermal response is registered during heating in parabolic flights. The contribution of natural convection to heat transfer is undoubtedly estimated from runs in which acceleration varies from 0 to 1.8 g. Surprisingly enough, the experiments showed that the Rayleigh number must take a minimum value before non-negligible effect of natural convection on heat transfer appears (existence of a threshold Rayleigh number). In the absence of natural convection (below Ra_thr) the experimental thermal response curves can be successfully described by approximating solutions of the transient heat conduction equation for the spheroidal geometry of the thermistor. Apparently, additional research is needed regarding the natural convection around sub-millimeter objects for small Rayleigh numbers.     

The solar hardening of steels: Experiments and predictions

A method of hardening steels with a solar furnace has been developed. Initial trials were conducted with a plain carbon steel to measure the thermal transients which could be expected, and from the results a simple thermal model was developed to predict what would be needed to achieve hardening. The consequent improvements in the process allowed the surface of low-alloy steel to be hardened. To predict more exactly the reaction of steels to solar irradiation, a thermochemical model was developed. It uses a finite difference method to calculate the thermal transient induced by the solar beam, and a calculation of its kinetic strength to predict how much austenite will form. A comparison of the cooling curve with the TTT diagram of the steels then allows the percentage f martensite and hardness to be predicted. Comparison with experimental results showed that the predicted case depth and hardness were within 10% of the measured values. It is/suggested that this method could also be applied to other, more common hardening processes.     

Adsorption of hydrogen isotopes in the zeolite NaX: Experiments and simulations

Among the different methods to separate hydrogen isotopes one is based on the physisorption at low temperature (below 100 K) where quantum effects induce a particular behavior. In the present work, we study the adsorption of single H₂ and D₂ on the zeolite NaX by combining experiments (manometry) from 30 to 150 K and molecular dynamics simulations at 40 and 77 K. Simulations also include the adsorption analysis for T₂. Adsorption on NaX membranes is simulated and quantum corrections are introduced by using the well-known Feynman–Hibbs approach into the interaction potentials. Experimental adsorption isotherms are reproduced by using the Toth equation and it is shown that the adsorption capacity increases with the molecular weight of the isotopes. Isosteric enthalpies evidence a heterogeneous adsorption process with two type of hydrogen isotopes differently linked to the zeolitic structure. The calculated pair distribution functions at high loadings exhibit a liquid-like structuration in the supercages of NaX, which may explain the different adsorption capacities for H₂, D₂ and T₂ and the heterogeneity of the adsorption process.     

Dynamics of a Natural Circulation Loop: Analysis and Experiments

A dynamic one-dimensional model of a simple rectangular natural circulation loop with tube bundles in the two vertical legs has been simulated. A supporting experimental study using water at atmospheric pressure as the working fluid has been conducted to obtain data to verify the model. Good agreement was obtained between the predicted and measured mixed-mean fluid temperatures and surface temperatures of the tube bundle as well as the loop piping and insulation temperatures at several locations around the system. A number of different simulations and tests have been performed and are discussed. In general, at steady state there was less than 7% deviation between the model predictions and the test data, which indicates that the one-dimensional model is capable of predicting the transient temperature response of the loop structural components and of the circulating fluid.     

Air heat exchangers with long heat pipes: Experiments and predictions

This paper presents measurements and predictions of a heat pipe-equipped heat exchanger with two filling ratios of R134a, 19% and 59%. The length of the heat pipe, or rather thermosyphon, is long (1.5 m) as compared to its diameter (16 mm). The airflow rate varied from 0.4 to 2.0 kg/s. The temperatures at the evaporator side of the heat pipe varied from 40 to 70 °C and at the condenser part from 20 to 50 °C. The measured performance of the heat pipe has been compared with predictions of two pool boiling models and two filmwise condensation models. A good agreement is found. This study demonstrates that a heat pipe equipped heat exchanger is a good alternative for air–air exchangers in process conditions when air–water cooling is impossible, typically in warmer countries.     

不同水的衰减系数对受激布里渊散射放大受激拉曼散射的影响

为了深一步研究水中受激布里渊散射(SBS)和受激拉曼散射(SRS)特性关系,分析了单模激光泵浦下不同水的衰减系数对SBS放大后向受激拉曼散射(BSRS)的影响.由于SBS阈值与水的衰减系数有关,当激发并放大的SBS作为一个新的激发源去激发并增强SRS时,水的衰减系数就会影响SRS的放大效应.实验结果表明,水的衰减系数越小,SBS输出能量越高,同时BSRS的能量也越大.     

Experiments and Modelling of Coal Devolatilization

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Encapsulated phase change materials for thermal energy storage: Experiments and simulation

In the present study, encapsulated phase change materials (PCMs) were used for the storage of thermal energy. Both experiments and simulation were performed to evaluate the characteristics of encapsulated PCMs. Tests were conducted in a packed bed to determine the performance of the encapsulated PCM. In the preparation of encapsulated PCMs, the coacervation technique was used. The performance of the encapsulated PCM was evaluated in terms of encapsulation ratio, hydrophilicity, and energy storage capacity. The experiments were designed, based on surface response method, to optimize the processing conditions. It was found that a higher coating to paraffin ratio led to a higher paraffin encapsulation ratio. The hydrophilicity value of encapsulated paraffin depended mainly on the ratio of paraffin to coating. The higher the ratio, the lower was its product hydrophilicity. When the paraffin to coating ratio was constant, the higher concentration of HCHO led to a lower hydrophilicity of the product. The encapsulated paraffin has shown large energy storage and release capacity (20–90 J g^?1) during its phase changes depending on different ratios of paraffin to coating. Thermal cyclic test showed that encapsulated paraffin kept its geometrical profile and energy storage capacity even after 1000 cycles of operation. In the experiments and simulation of fluid heating process in encapsulated PCM charged packed bed, results showed that Eulerian granular multiphase model in FLUENT 4.47 is suitable for simulation of such a system. Copyright © 2002 John Wiley & Sons, Ltd.     

基于石墨烯电极的聚合物太阳能电池光学减反层的研究

石墨烯薄膜具有低阻且在可见光谱区具有高透过率,可应用于聚合物太阳能电池透明电极。本文基于时域有限差分分析方法（FDTD）,研究了石墨烯太阳能电池的反射损耗及光吸收特性,并通过在玻璃基板与石墨烯间添加氧化镍层（NiO）进行光学减反射。理论分析表明：优化的NiO /石墨烯透明电极结构,能够成为氧化铟锡（ITO）的良好替代电极。     

Scattering of electromagnetic radiation in particulate laden fluids

The main purposes of this article are to introduce the reader to the theoretical treatment of light scattering, and to build on previous reviews by incorporating recent literature. The paper begins with the very basic concepts of wave propagation and radiation, and then reviews the fundamental terminology and theories of scattering by spheres and non-spherical particles, including the integral formulation of the problem. A number of approximate methods of solution are discussed, and in the final section the principles behind the diagnostic applications of scattering are reviewed with emphasis on recent developments.