Drag on two nonuniformly structured flocs moving along the axis of a cylindrical tube

The boundary effect on the drag on two identical, nonuniformly structured flocs moving along the axis of a cylindrical tube filled with a Newtonian fluid is investigated at a small to medium larger Reynolds number. A two-layer model is adopted to simulate various possible structures of a floc, and the flow field inside is described by Darcy–Brinkman model. The results of numerical simulation reveal that a convective flow is present in the rear region of a floc when Reynolds number is on the order of 40. The presence of the tube wall and/or the porous structure of a floc has the effect of reducing that convective flow. For a fixed level of the volume-average permeability of a floc, the influence of the tube wall on the drag depends upon floc structure; the influence on a nonuniformly structured floc is more significant than that on a uniformly structured floc. The more nonuniform the floc structure, the more appreciable the deviation of the drag coefficient–Reynolds number curve from a Stokes’-law-like relation becomes. The smaller the volume-average permeability of a floc and/or the smaller the separation distance between the two flocs, the greater is the deviation, but the presence of the tube wall has the effect of reducing that deviation.     

硅的原子吸收光谱分析进展

对近十年来用原子吸收光谱法测定硅的情况进行评述．重点介绍用石墨炉测定硅时，为了避免硅与石墨炉中碳形成难熔碳化硅影响测定硅的灵敏度而使用的各种化学改进剂，涂层石墨管和一些新的实验技术．引用参考文献４２篇．     

用原子捕获技术提高火焰原子吸收光谱法的灵敏度

采用简易的石英原子捕获器，使Ｃｕ，Ａｇ，Ａｕ，Ｚｎ，Ｃｄ，Ｐｂ，Ｓｂ，Ｂｉ等易挥发元素在空气－乙炔火焰原子吸收光谱法中的灵敏度提高了３～５倍，并有较好的精密度，相对标准偏差在１％左右，方法中用此技术测定了标准物质中Ｐｂ、Ｃｄ的含量，获得了满意的结果，它较之石墨炉原子吸收光地具有快速，简便的特点，具有较大的实用价值。     

用选择离子流动管质谱测定汽油和柴油蒸汽成分

采用选择离子流动管质谱(SIFT／MS)装置，以H30^ 、N0^ 为初始离子对汽油和柴油蒸汽进行了研究，质谱分析表明，汽油和柴油主要由C—H化合物组成，包括烷烃、环烷烃、烯烃、炔烃、二烯烃以及芳香烃。在这几种成分中，烷烃都占有最大的比例；汽油蒸汽和柴油蒸汽最大的区别是柴油蒸汽中长链大分子的挥发性C—H化合物所占的比例远远高于汽油蒸汽。文中还给出了以H30^ 、N0^ 为初始离子所得到的汽油蒸汽的质谱图，以及汽油、柴油蒸汽中各种成分的定量分析结果。     

旋流煤粉燃烧的一维综合数值模拟

发展了综合考虑气－固两相旋流流动，气相燃烧，颗粒相变与燃烧及两相辐射传热的旋流煤粉燃烧－维数学模型，给出了气－固两相能量方程中颗粒相就源项的计算表达式，应用这一模型对涡旋燃烧炉环形通道内多组工况的旋流气体燃烧和煤粉燃烧进行了数值模拟，计算得到的炉内温度分布和燃烧效率与实验数据基本相符，表明本文建立的模型可用于旋流煤粉燃烧的一维综合数值模拟。     

The effect of gas injection on a thermal argon plasma flow in a water-cooled tube

The effect of gas injection on an atmospheric thermal argon plasma flow in a water-cooled tube was investigated experimentally and numerically. The injection gas is argon, helium, or nitrogen. The static pressure with helium injection increases greatly because of its high thermal conductivity, while little increase occurs for nitrogen injection because of the dissociation. The increasing rate of the static pressure depends on the ratio of the momentum term to the viscosity term. The heat flux to the tube wall with gas injection changes less than that without injection. The numerical results showed variations similar to the experimental ones.     

Modeling of plasma jets with superimposed vortex flow

This work is concerned with analytical studies of thermal plasma jets, which are finding increasing interest for thermal plasma processing. A two-dimensional model for turbulent plasma jets with superimposed vortex flow has been developed, incorporating multiple time scales for velocity and temperature fluctuations and a density-weighted averaging for the density fluctuation effect. Results show that adding swirl to the flow field for confined and free jets induces strong axial and radial pressure gradients near the nozzle exit, causing a rapid decay of the axial velocity with increasing distance from the nozzle. Comparisons with cold flow show similar trends close to the nozzle exit, but further downstream, the axial velocities increase again, especially for larges swirl numbers. Comparisons of theoretical predictions based on the present model with available experimental data are, in general, in reasonable agreement.     

The effect of a coriolis force on Taylor-Couette flow

Taylor-Couette flow subject to a Coriolis force is studied experimentally and numerically. In the experiment, the Couette apparatus is mounted on a turntable with the axis of the cylinders orthogonal to the rotation vector of the turntable. The Coriolis force stabilizes the fluid against the onset of Taylor vortices and alters the velocity fields, both above and below the transition from the initial flow. At small dimensionless turntable frequencies, the transition yields time-independent Taylor vortices which are tilted with respect to the cylinder axis. At larger there is a direct transition to turbulence. We determine the first-order correction to the classical Couette initial flow, to account for the effects of the Coriolis force, by expanding in powers of. We present numerical results for the axial velocity (the only nonvanishing correction term to order) in the infinite-cylinder approximation.     

C12簇及其碳管烷C12H12的理论研究

C60和C70等碳笼烯的发现及其在新物质、新材料等研究领域中的重要性，激励人们去探索合成更多新型多面体碳簇化合物与碳元素类似物[1，2]．最近，两类新型多面体碳管笼烯的设想提出来了[3，4]应用HMO和MNDO方法对其稳定性变化规律、结构和成键特征进行了讨论.关于多苯的vanderWaals簇实验上已有广泛的调查[5，6]，理论上对其二聚物（C6H6）。的不同几何构型与稳定性进行了深入的研究[7]．本文采用abinitio计算有效势（effectivecorePotential）方法，对C12碳管元素簇和C12H12，碳管烷的平衡结构、稳定性和价键特征进行了理论预测．1…     

Influence of the variable wall thickness of the sample tubes and a quartz Dewar on the EPR signal intensity in a single TE102 and double TE104 rectangular cavity

The response of a single TE₁₀₂ and double TE₁₀₄ rectangular cavity to the insertion of samples contained in tubes with variable wall thickness and a quartz Dewar into the cavity has been analyzed. A direct, indirect, and concurrent (positive or negative) “lens effect” inside the double TE₁₀₄ rectangular cavity is discussed. The experimental dependence of the EPR signal intensity on the wall thickness of the sample tube, δ, for the line-like samples with identical length of the sample material column, L=30 mm, recorded in the microwave cavity showed a directly proportional increase of the relative “lens effect” with the increase of the wall thickness of the tube in the interval, δ∈<0.1 mm, >0.5 mm. The insertion of the variable-temperature double-wall quartz Dewar (home-built, resonant frequency shift, ca. −300 MHz) into the single TE₁₀₂ rectangular cavity showed the same relative “lens effect”, with ca. 1.5-time increase of the EPR signal intensity, for a point-like sample and the line-like samples with material columns of diameter of 1 and 1.3 mm, and wall thickness of the sample tubes, δ∈<0.1 mm, >0.5 mm. The increased effect of the Dewar arises because the active volume of the quartz Dewar tube walls is always much more larger than the active volume of the sample tube wall. In the case of the double TE₁₀₄ rectangular cavity, the insertion of the quartz Dewar: (i) into the same cavity, in which the sample is present, caused a direct “lens effect”, with ca. 1.8-fold increase of the EPR signal intensity; however, (ii) into the complementary cavity, in which the sample is absent, caused an indirect “lens effect”, with ca. 0.6-fold decrease of the EPR signal intensity. With the Dewar and sample in one cavity and a large empty sample tube in the complementary cavity, a concurrent (positive or negative) “lens effect” can be observed. Thus, the possible increase/decrease of the EPR signal intensity depends on the volume ratio of the quartz Dewar tube walls and large sample tube wall inserted into the double TE₁₀₄ rectangular cavity. Each of the above phenomena may be a significant source error in quantitative EPR spectrometry unless the samples to be compared in the quantitative EPR analysis are contained in sample tubes having the same wall thickness and each EPR spectra should be recorded inside an identical quartz Dewar.