Drag coefficient and settling velocity for particles of cylindrical shape

Solid particles of cylindrical shape play a significant role in many separations processes. Explicit equations for the drag coefficient and the terminal velocity of free-falling cylindrical particles have been developed in this work. The developed equations are based on available experimental data for falling cylindrical particles in all flow regimes. The aspect ratio (i.e., length-over-diameter ratio) has been used to account for the particle shape. Comparisons with correlations proposed by other researchers using different parameters to account for the geometry are presented. Good agreement is found for small aspect ratios, and increasing differences appear when the aspect ratio increases. The aspect ratio of cylindrical particles satisfactorily accounts for the geometrical influence on fluid flow of settling particles.     

Drag Correlation of Drop Motion on Fibers

The objective of this article is to correlate a drag coefficient to the Reynolds number for axial motion of barrel drops on fibers. This work includes effects of vibration-induced motion of droplets and coalescence. The study of motion of drops is important to understand the drainage behavior of droplets. Drainage of liquid helps to eliminate moisture from media samples before applying thermal energy and hence reducing the drying cost. A significant amount of literature describes the mechanisms of droplet capture, coalescence, and drainage from filter media and models are developed at a scale that accounts for the liquid held in the filter through averaged parameters such as saturation. Few papers discuss the motion of individual drops attached to fibers.

The study of drop motion on fibers is of scientific and economic interest for many possible applications like printing, coatings, drug delivery and release, and filters to remove or neutralize harmful chemicals or particulates from air streams. Gas convection–induced drop motion in fibrous materials occurs in coalescing filters, clothes dryers, textile manufacturing, convection ovens, and dewatering of filter cakes. Droplet removal can significantly reduce drying costs by reducing the free moisture contained in fibrous materials prior to applying thermal drying techniques.

In this article, the experimental drag coefficient versus Reynolds number data are compared for 1-D and 3-D cylindrical drop models. The results show that 1-D models are inadequate to predict the drag coefficient but do show the same general trends.     

Drag Correlation of Drop Motion on Fibers

The objective of this article is to correlate a drag coefficient to the Reynolds number for axial motion of barrel drops on fibers. This work includes effects of vibration-induced motion of droplets and coalescence. The study of motion of drops is important to understand the drainage behavior of droplets. Drainage of liquid helps to eliminate moisture from media samples before applying thermal energy and hence reducing the drying cost. A significant amount of literature describes the mechanisms of droplet capture, coalescence, and drainage from filter media and models are developed at a scale that accounts for the liquid held in the filter through averaged parameters such as saturation. Few papers discuss the motion of individual drops attached to fibers.

The study of drop motion on fibers is of scientific and economic interest for many possible applications like printing, coatings, drug delivery and release, and filters to remove or neutralize harmful chemicals or particulates from air streams. Gas convection-induced drop motion in fibrous materials occurs in coalescing filters, clothes dryers, textile manufacturing, convection ovens, and dewatering of filter cakes. Droplet removal can significantly reduce drying costs by reducing the free moisture contained in fibrous materials prior to applying thermal drying techniques.

In this article, the experimental drag coefficient versus Reynolds number data are compared for 1-D and 3-D cylindrical drop models. The results show that 1-D models are inadequate to predict the drag coefficient but do show the same general trends.     

New simple correlation formula for the drag coefficient of non-spherical particles

A simple correlation formula for the standard drag coefficient (i.e. a single stationary particle in a uniform flow) of arbitrary shaped particles is established using a large number of experimental data from the literature and a comprehensive numerical study [A. Hölzer, M. Sommerfeld, IUTAM Symposium on Computational Approaches to Multiphase Flow, Springer, 2006]. This new correlation formula accounts for the particle orientation over the entire range of Reynolds numbers up to the critical Reynolds number. Such a correlation may be easily used in the frame of Lagrangian computations where also the particle orientation along the trajectory is computed.     

Comparison of formulas for drag coefficient and settling velocity of spherical particles

Two formulas are proposed for explicitly evaluating drag coefficient and settling velocity of spherical particles, respectively, in the entire subcritical region. Comparisons with fourteen previously-developed formulas show that the present study gives the best representation of a complete set of historical data reported in the literature for Reynolds numbers up to 2 × 10⁵.     

马来酸酐－醋酸异丙酯二元固液平衡的测定和关联

马来酸酐－醋酸异丙酯二元固液平衡的测定和关联陈新志侯虞钧（浙江大学化工系，杭州３１００２７）关键词固液平衡活度系数１引言相平衡数据在化工生产和研究中占有重要的地位。流体相平衡已得到了广泛的研究，并积累了大量的数据，与之相应的实验方法也较为完善，同时...     

Effects of surface-active agents on mass transfer of a solute into single buoyancy driven drops in solvent extraction systems

Numerical simulation was made of transient mass transfer to a surfactant contaminated buoyancy-driven drop controlled by appreciable resistance in both liquid phases. For this purpose, the momentum equations were formulated and solved in a boundary-fitted orthogonal coordinate system. On the basis of resolved hydrodynamics of the contaminated drop, the transient mass transfer was formulated and solved in the same coordinate system. In order to check the applicability of the numerical scheme, single drop extraction experiments were conducted in a totally closed droplet file column with the terminal effect efficiently eliminated. The MIBK-acetic acid-water system was used with small quantities of SDS (sodium dodecyl sulphate), Triton X-100, or Tween 80 introduced into the continuous phase. For these experimental cases, the flow field and the drag coefficient of a contaminated drop were simulated first. The numerical prediction of the drag coefficient is found in good agreement with the corresponding experimental data. It illustrates that the behavior of a drop approaches that of a rigid sphere and that about 100 times higher bulk concentration of SDS than that of Triton X-100 is required for the same extent contamination of a MIBK drop of the same size. Then the information of the flow field of a contaminated MIBK drop was used in simulating the transient mass transfer of solute into the drop. The resulted extraction fraction and overall mass transfer coefficient are in reasonable coincidence with the experimental data. Both numerical results and experimental data show that overall mass transfer coefficient of a heavily contaminated drop is only about one third of that in the pure system. This can be explained well by the distribution of the local Sherwood number, which drops down abruptly along the rear stagnant surface. Also the interfacial resistance of adsorbed surfactant was incorporated in the mass transfer model and then estimated by the least square fitting the simulation with data. The numerical results also show that Tween 80 presents obvious interfacial resistance on the acetic acid diffusing across the interface, whereas SDS and Triton X-100 show no interfacial resistance. It is suggested that the numerical simulation can be resorted in some solvent extraction systems containing surfactants to conduct numerical experiments and parametric study.     

固体硫化剂在工业中的应用（上）

探讨了固体硫化剂应用于裂硫汽油加氢装置二段催化剂预硫化新工艺,介绍了固体硫化剂的预硫化机理及工艺流程。     

Computational fluid dynamics (CFD) modeling of spouted bed: Assessment of drag coefficient correlations

In the computational fluid dynamics (CFD) modeling of gas-solids two-phase flows, drag force is the only accelerating force acting on particles and thus plays an important role in coupling two phases. To understand the influence of drag models on the CFD modeling of spouted beds, several widely used drag models available in literature were reviewed and the resulting hydrodynamics by incorporating some of them into the CFD simulations of spouted beds were compared. The results obtained by the different drag models were verified using experimental data of He et al. [He, Y.L., Lim, C.J., Grace, J.R., Zhu, J.X., Qin, S.Z., 1994a. Measurements of voidage profiles in spouted beds. Canadian Journal of Chemical Engineering 72 (4), 229-234; He, Y.L., Qin, S.Z., Lim, C.J., Grace, J.R., 1994b. Particle velocity profiles and solid flow patterns in spouted beds. Canadian Journal of Chemical Engineering 72 (8), 561-568.] The quantitative analyses showed that the different drag models led to significant differences in dense phase simulations. Among the different drag models discussed, the Gidaspow (1994. Multiphase Flow and Fluidization, Academic Press, San Diego.) model gave the best agreement with experimental observation both qualitatively and quantitatively. The present investigation showed that drag models had critical and subtle impacts on the CFD predictions of dense gas-solids two-phase systems such as encountered in spouted beds.     

Drag on two coaxial rigid spheres moving along the axis of a cylinder filled with Carreau fluid

The boundary effect on the drag on two identical, rigid spheres moving along the axis of a long cylinder filled with a Carreau fluid for Reynolds number ranges from 0.1 to 40 is investigated. The influences of the key parameters of the problem under consideration, including the separation distance between two spheres, the relaxation time constant and the power-law index of a Carreau fluid, the Reynolds number, and the ratios (radius of sphere/radius of cylinder), on the drag acting on two spheres are investigated. We show that the boundary effect for the present case is more significant than that for the corresponding Newtonian fluid. The presence of the cylinder has the effect of enhancing the convective motion in the rear part of a sphere, thereby forming wakes and a reverse flow field, and this phenomenon is enhanced by the shear-thinning nature of a fluid. If the boundary effect is insignificant, the shear-thinning nature of a fluid has the effect of reducing the deviation of the ln(drag coefficient)-ln(Reynolds number) curve from a Stokes'-law-like relation. On the other hand, if it is significant, this deviation has a local minimum as the shear-thinning nature of a fluid varies.     

评估固体推进剂压强温度系数的方法

提出了目前评价压强温度系数所存在的问题,较系统地分析了压强温度系数的变化规律,建立了参比压强温度系数的计算方法。     

单体自增溶原位固相接枝法合成三单体接枝物PE-g-（GMA／St／BA）的研究

采用单体自增溶原位固相接枝技术合成PE—g-（GMA＋St＋BA）的三单体固相接枝物，采用傅立叶变红外光谱分析接枝物的结构，并探讨单体配比、单体总质量、引发剂用量等反应条件对接枝率和凝胶率的影响。结果表明，当三种单体的配比GMA／St/BA（质量比）：6／6／2，BPO用量为2phr，单体的总用量在50phr左右时，接枝率较高；苯乙烯能降低凝胶含量，BPO为2phr时凝胶含量较低。     

Unsteady motion of a single bubble in highly viscous liquid and empirical correlation of drag coefficient

The unsteady motion of single bubbles rising freely in a quiescent liquid with high viscosity was measured using a CCD (charge coupled device) camera. Sequences of the recorded frames were digitized and analyzed using image analysis software and the measurements of the acceleration and steady motion of bubbles were obtained. The total drag coefficient was calculated from the accelerating motion to the steady motion with the added mass force and history force included. In virtue of dimensional analysis, the total drag coefficient of single bubbles is correlated as a function of the acceleration number, Archimedes number and Reynolds number based on the equivalent bubble diameter. The proposed correlation represents very well the experimental data of the total drag force in a wide range covering both unsteady accelerating motion and steady motion. The combined added mass and history force coefficient accounting for the accelerating effect on single bubbles was evaluated and correlated.     

Solid Phase Enhanced Direct Spectrofluorometric Determination of Polychlorinated Biphenyls (PCBs) in Natural Waters

A method of detection of PCBs in water, based on extraction/concentration with chips cut from an SPE disk-shaped C18 inverse phase coupled with a fluorescence detection and quantification directly on the phase has been evaluated. Experiments were performed with PCBs congeners IUPAC N° 3, 35, 67 and 169. Within the experimental conditions used : Hitachi F-4500 fluorometer, band-paths: 2.5 nm and extraction time: 60 min. the limits of detection were estimated to be respectively : 0.07, 0.4, 0.3 and 0.2 ppb. These values are within the range of PCB concentrations found in highly polluted waters and thus confer some interest to the method. However its sensitivity is not sufficient for application to moderately polluted natural water and the method needs some further improvements. Moreover, fluorescence quenching by humic substances was shown to substantially affect PCB's fluorescence intensity and must be taken into consideration for quantitative analysis.     

SO_4~(2-)/M_xO_y型固体超强酸催化剂的改性研究

SO42-/MxOy型固体超强酸催化剂具有不腐蚀设备、易分离、制备简单等优点,作为一类新型的绿色催化材料,在合成工业上有广泛的应用前景。但是这种催化剂也存在易积炭、稳定性差、价格昂贵等缺点,因此对SO42-/MxOy型固体超强酸催化剂的改性研究已成为国内外研究的热点。本文主要介绍了SO42-/MxOy型固体超强酸催化剂的改性研究。     

CFD modeling of pressure drop and drag coefficient in fixed and expanded beds

The aim of this study is computational fluid dynamic (CFD) simulation of the single-phase pressure drop in fixed and expanded beds. A fixed bed with a column to particle diameter ratio (D/d_p) of 5 and having 151 particles arranged in 8 layers was taken as a computational geometrical model. In the case of expanded beds, 0.605 voidage bed consisted of 105 particles and 0.783 voidage bed consisted of 55 particles. Simulations were performed in the creeping, transition and turbulent flow regimes, where Reynolds number (d_pV_Lρ_L/μ_L) was varied from 0.1 to 10,000. The deviations from Ergun's equation due to the wall effects, which are important in D/d_p < 10 beds, were well explained by the CFD simulations. Thus, an increase in the pressure drop was observed due to the wall friction in the creeping flow, whereas, in turbulent regime a decrease in the pressure drop was observed due to the channeling near the wall. Energy balance has been established through the CFD predicted values of energy dissipation rates (viscous as well as turbulent).     

填料塔气液传质参数研究（Ⅱ）──气膜传质系数

用拟一级快速化学反应吸收法测定了拉西环填料塔的气膜传质系数，并得出其无因次表达式。     

Determination of effective diffusion coefficient and interfacial mass transfer coefficient of bovine serum albumin (BSA) adsorption into porous polyethylene membrane by microscope FTIR-mapping study

Here, a new method for simultaneous determination of diffusion coefficient D and interfacial mass transfer coefficient (or convective mass transfer coefficient) k was proposed for bovine serum albumin (BSA) adsorption into porous polymeric membranes. The experimental data for BSA concentration at different membrane depth and different time were determined from FTIR-mapping measurements. Then the diffusion coefficient D and interfacial mass transfer coefficient k were estimated from the calculated dimensionless concentration data at different time and membrane depth by a trial-and-error method based on the diffusion equation initiated in this paper. The diffusion coefficient D and interfacial mass transfer coefficient k evaluated in this manner are respectively: and . The theoretical concentration values calculated from the determined parameters were compared with experimental reading from FTIR mappings, which showed a good agreement between them, especially for the case of a relatively long-time adsorption.     

固相法改性粘土及其在聚氯乙烯中的应用

首先采用固相法对粘土进行有机化插层改性,制得有机粘土,再通过熔融插层法制备聚氯乙烯/有机粘土复合材料。XRD表明固相法改性粘土可以与聚氯乙烯形成纳米复合材料。利用DSC研究了纳米复合材料的玻璃化转变温度,结果显示:聚氯乙烯/有机粘土纳米复合材料的玻璃化转变温度高于纯聚氯乙烯。