有限体积法解多场耦合下散射性非灰介质内的辐射换热

将有限体积法与谱带模型结合 ,求解了吸收、散射性非灰介质内的耦合换热 .经与光线踪迹法、离散传递法的计算结果比较表明 :提出的数值方法具有较高的精度 ;有限体积法适合辐射导热的多场耦合计算 ;对非灰介质建议选用谱带模型 ;并应考虑折射率对传热的影响     

微粒散射对半透明流体层光谱吸收特性的影响

通过数值模拟分析了微粒散射对半透明流体层光谱吸收特性的影响 .采用MonteCarlo法模拟辐射能被半透明流体和微粒的吸收与散射以及在半透明镜反射面处的折射、反射和不透明漫反射壁面处的反射过程 ,用H -G相函数考虑了微粒的各向同性、前向及后向散射几种典型的散射分布 .模拟了各种散射分布下含微粒水层对垂直入射辐射的光谱吸收率及水层内部的吸收分布 ,分析了散射分布、吸收因子、衰减系数和反照率等对半透明流体层吸收特性的影响     

散射介质中辐射全交换面积的求解方法

在辐射交换面积叠加方法基础上,从辐射传热机理出发,定义了散射热流密度并给出矩阵表达式,用于分析介质的散射特性,推导出各向同性散射介质参与条件下辐射全交换面积各分量矩阵以及总矩阵的合成,所得结果与Noble方法完全一致。并模拟研究了介质的散射对辐射热交换的影响。该方法物理意义明确,推导过程简便,便于理解与分析,有利于准确求解各向同性散射介质参与的辐射换热问题。     

用蒙特卡罗方法预测液固两相体系中颗粒的超声衰减

为研究高浓度颗粒两相流中超声复散射现象并建立颗粒表征模型,从单颗粒弹性散射理论出发,采用蒙特卡罗方法预测不同粒度、浓度及超声频率下玻璃微珠/水颗粒两相体系中颗粒的超声衰减特性.在颗粒体积浓度低于1%时,蒙特卡罗方法与基于单散射理论的ECAH模型吻合较好,随颗粒体积浓度和颗粒尺寸增加,声的衰减呈非线性变化,二者差异增加.利用该方法预测颗粒半径为35和90μm的液固两相体系随浓度衰减变化的结果与文献实验值基本一致.蒙特卡罗方法可用于50%固相体积浓度范围内超声衰减计算并为超声法颗粒测量提供理论模型基础.     

HTI介质射线追踪正演

常规的地震勘探都是建立在各向同性的介质模型假设之上的,但是实际地层普遍是各向异性的。在各向异性介质中,由于地震波的相速度和群速度之间的差异,使得地震响应变得复杂。本文根据HTI(具有水平对称轴的横向各向同性)介质中地震波的运动学特征,应用射线追踪方法,计算了介质中地震波的旅行时,并合成了反射P波地震记录,同时观测到P波旅行时、振幅等地震响应既随入射角变化又随方位角呈周期性变化,这为之后HTI介质方位特性分析提供了基础。研究结果表明:对于HTI介质,应用射线追踪方法进行地震正演收敛快,精度高,地震波运动学特征计算准确,值得推广。     

HTI介质射线追踪正演

常规的地震勘探都是建立在各向同性的介质模型假设之上的,但是实际地层普遍是各向异性的。在各向异性介质中,由于地震波的相速度和群速度之间的差异,使得地震响应变得复杂。本文根据HTI(具有水平对称轴的横向各向同性)介质中地震波的运动学特征,应用射线追踪方法,计算了介质中地震波的旅行时,并合成了反射P波地震记录,同时观测到P波旅行时、振幅等地震响应既随入射角变化又随方位角呈周期性变化,这为之后HTI介质方位特性分析提供了基础。研究结果表明:对于HTI介质,应用射线追踪方法进行地震正演收敛快,精度高,地震波运动学特征计算准确,值得推广。     

6-苄氨基嘌呤-纳米银-十二烷基磺酸钠体系共振光散射光谱研究及分析应用

研究了标题化合物共振光散射的增强效应.在pH为4.5的酸性介质中,纳米银-十二烷基磺酸钠在350 nm处共振光散射增强与6-苄氨基嘌呤浓度呈线性关系,据此建立了一种测定6-苄氨基嘌呤的共振光散射法.测定的线性范围为2.0×10-8～1.0×10-5mol/L,检出限为2.8 ×10-9mol/L.该法简便、快速、选择性...     

升温条件下多孔介质内气泡的生长和聚并行为

设计了两种横向和纵向喉道宽度比值(w_h∶w_z)分别为1.48∶1和1∶1的各向异性和各向同性多孔介质微流体芯片,以CO₂为气体,二甲基硅油为液体,采用可视化实验,系统地研究了升温条件下多孔介质结构对气泡生长和聚并规律的影响。结果表明,温度升高引起的传质生长是气泡突破喉道的动力。单个气泡在多孔介质内生长方向的选择依赖于喉道的门阙压力,气泡倾向于突破门阙压力小的喉道。随着温度的升高,气泡侵入和突破喉道速度加快。在各向异性多孔介质中,气泡倾向于在横向生长时与其他气泡发生聚并,而在各向同性多孔介质中,气泡更易发生纵向聚并。当多个气泡存在于各向异性多孔介质内时,气泡的初始分布会显著影响气泡间的生长和聚并过程;在各向同性多孔介质内时,影响则较小。各向异性多孔介质在实际工程应用过程中更易实现气泡流型调控。     

烃源岩地震声速模型:Gassmann模型与Backus平均(二)

烃源岩被描述为由伊利石和有机介质(干酪根、油、气)组成的横向各向同性多孔介质。油气混合物的弹性体积模量由KusterToksoz干酪根混合流体不饱和模型计算而得。假设油是包含在干酪根基质中的。一般我们运用Backus平均和Gassmann方程所描述的含有固体孔隙填充的各向异性介质模型来计算页岩的地震波速。在后一种方法中(Gassmann),干燥的岩石弹性常数是由Krief各向异性方程计算得到。本文进一步解释页岩地震波速计算过程,通过wood平均的流体模型计算出的混合流体饱和度,计算最终页岩地震横纵波速。     

二氧化钛的相对散射力

介绍了相对散射力的概念，并对比分析了国内外部分金红石型二氧化钛的相对散射力。研究了煅烧时间、粒度及粒度分布、介质中的分散性以及后处理包膜等因素对金红石型二氧化钛在一定颜料体积浓度(PVC)下的相对散射力的影响。     

SCATTERING EFFECTS IN A FURNACE SLAB

The major mode of heat transfer in industrial combustion furnaces is that of radiation. The effects of radiative scattering are therefore of great importance in furnace design. This study investigates the behavior of both anisotropic and isotropic scattering using a computer-simulated model of a typical combustion furnace

The furnace model employed is based on the zoning method of Hottel and the Monte-Carlo statistical approach. To study scattering effects, subroutines to simulate isotropic and anisotropic scattering have been added on to the model developed in earlier work with non-scattering mediums. Anisotropic scattering distributions studied include both forward and backward skewed profiles

To simplify the three-dimensional model, a three by four meter slab of a semi-infinite furnace is studied. Each stab is rectangular in shape, containing twelve cubical zones and incorporating a single burner. Model results are presented in the form of temperature contours and total surface heat fluxes for different scattering albedoes and profiles.     

Textures of ethyl cellulose–dichloroacetic acid mesomorphic solution

Textures of the ethyl cellulose (EC)-dichloroacetic acid (DCA) mesomorphic solution were studied systematically by polarizing microscopy and small-angle light scattering. It was found that with increasing polymer concentration, the mesophase could show a disklike texture, an oil streak texture, a pseudoisotropic texture, and an iridescent planar texture. Within the mesophase the ordering degree is different in different zones. The phase transition between anisotropic and isotropic phases could also be accomplished by changing temperature. With increasing temperature the mesophase with the lower degree of order could first transform to the isotropic phase and the phase transition from an anisotropic phase with a higher degree of order to the isotropic one could take place only at the higher temperature. A disklike texture was also observed during the phase transition between the anisotropic and isotropic phases when the solution was heated and it was probably a basic texture in polymer cholesteric liquid crystals.     

Isotropic and anisotropic microporosity development upon chemical activation of carbon fibers, revealed by microbeam small-angle X-ray scattering

A sub-micrometer size beam (0.5 μm diameter) in a position-resolved small angle X-ray scattering set-up (μSAXS) has been used for the characterization of chemically activated carbon fibers (ACF). These materials have been prepared from isotropic carbon fibers (pitch carbon fibers) and anisotropic carbon fibers (PAN-based carbon fibers) by chemical activation with KOH and NaOH. The μSAXS experimental set-up made it possible to analyze different regions of a single fiber across its diameter and to distinguish the structural features already existing in the raw fibers or being created during the activation process. The results showed that depending on the precursor, the chemical activation process produces isotropic or anisotropic development of porosity. It was observed that chemically ACF prepared from isotropic carbon fibers present an isotropic development of the porosity and that a high micropore volume is developed not only in the external region of the fiber, but also in the core. On the other hand, in the case of anisotropic PAN-based carbon fibers the existence of two regions with different structure was detected by μSAXS measurements across the fiber diameter: an anisotropic external ring and a more isotropic fiber core. The results showed that these two regions remain after chemical activation and that the activating agents are reaching the fiber core. It seems that the more isotropic fiber core is activated easier by NaOH than KOH.     

Light scattering studies on crystallization in polyethylene terephthalate

The light scattering from the spherulites of polyethylene terephthalate grown near the glass transition temperature has been investigated. The Hv scattering profiles can be reproduced by the sum of the ideal spherulite scattering with the distribution of spherulite radius and the isotropic scattering from randomly oriented crystallites. The ratio of optical anisotropies in the isotropic scattering to the ideal spherulite scattering is obtained by the method established to eliminate the effects of the number density of spherulites and the coefficient depending on the experimental conditions. It is found that the anisotropy ratio is almost independent of the crystallization time and of temperature above 106 °C, while it is larger at a crystallization temperature of 103 °C. The spherulitic structure is discussed in terms of the anisotropy ratio.     

Pore-scale modelling of diffusion in unconsolidated porous structures

A deterministic pore-scale model is used to predict the diffusivity ratio of unconsolidated porous media in which the diffusion process can be regarded as isotropic. The pore-scale model is based on a rectangular representative unit cell concept. A porosity-based weighted average of the two-dimensional and three-dimensional pore-scale models is proposed as a convenient model to predict the effective diffusion coefficient of isotropic systems. The diffusivity ratio of two-dimensionally staggered and non-staggered arrays of anisotropic solid rectangles is computed numerically and an existing weighted average model is applied to verify the numerical data. A particular case of a staggered array of solid squares, for which this weighted average model is no longer adequate, is outlined and the weighted average pore-scale model is proposed instead to predict the diffusivity ratio. The newly proposed pore-scale model and the present numerical results compare favourably with numerical data, experimental data and other predictive measures reported in the literature.     

An attempt to simulate the bowing phenomenon in tenter with simple models

The bowing phenomenon throughout a tenter was experimentally observed with a pilot plant of successive biaxial stretching. The observed results were compared with simulated ones, by which the deformation behaviors of film in a tenter were predicted, with the assumption that the film was homogeneous isotropic, homogeneous anisotropic, heterogeneous isotropic, or heterogeneous anisotropic for a two-dimensional elastic body with an FEM. Comparatively good agreement between the simulated and observed results was obtained for a heterogeneous anisotropic elastic body with an initial mesh, involving in advance a plastic deformation part. © 1993 John Wiley & Sons, Inc.     

Characterization of pore distribution in activated carbon fibers by microbeam small angle X-ray scattering

In the present work, the results corresponding to the first experiments done with single activated carbon fibers (ACFs) at the microfocus beamline (ID13) in the ‘European Synchrotron Radiation Facility’ (Grenoble) are presented. The experiments done with CO₂ and steam ACFs have demonstrated the suitability of this technique to characterize a single ACF. The experiments show that scattering intensity increases with the burn-off degree, which agrees with SAXS experiments carried out using bigger amounts of fibers. Moreover, the two-dimensional scattering patterns show that, in this type of ACFs, the porosity development during the activation process is isotropic. In addition, it has been demonstrated that the use of an X-ray microbeam of 2 μm diameter allows the characterization of different regions of the same fiber with microscopic position resolution. The scans across the fiber diameter are the first direct proof for the previous results obtained by our research group. Thus, in the case of CO₂ ACFs, the scattering is high in different regions across the fiber diameter, confirming that CO₂ activation takes place within the fibers, generating a quite homogeneous development of porosity. On the other hand, in the case of steam ACFs, the scattering is much higher in the external zones of the fibers than in the bulk, which means that steam focuses the activation in the outer parts of the fibers.