Investigation of fiber motion near solid boundaries in simple shear flow

In this paper, fiber motion near a planar wall was investigated using a planar shear flow apparatus. Fibers were placed (one at a time) perpendicular to the flow direction at various locations throughout the flow field. The location and orientation of each fiber versus time was measured, using an image processing system, until the fiber aligned with the flow direction. When the centroid of the fiber was located at distances greater than a fiber length from the wall, Jeffery's equations governing particle motion were verified. For distances less than a fiber length and greater than a fiber diameter from the wall, the fiber experienced an increased rate of rotation. In this regime, the motion of the fiber could be described by Jeffery's equations if an increased effective shear rate was used. The effective shear rate was found to increase logarithmically with decreasing separation distance. The wall effect was higher for longer aspect ratio fibers and was also a function of orientation; fibers oriented perpendicular to the wall rotated faster than those oriented parallel to the wall at the same separation distance. Once the fiber aligned with the flow direction, it ceased to rotate within the field of view. In this orientation, the wall had a stabilizing effect on the fiber. In efforts to relate the increase in shear rate to the aspect ratio of the fiber and the separation distance between the fiber and a solid wall, a translation model based on the work of De Mestre and Russel was explored. This model allows one to quantify the increase in shear rate experienced by the fiber due to the presence of a wall or obstruction in the flow field. However, the model has its limitations and care should be taken when applying this model outside its realm of validity. When compared to experimental data, the translation model provides a very good estimate of the increased shear rate experienced by the fiber when it is located less than 2/3 of a fiber length from a planar wall. Received: 20 April 2000 Accepted: 28 September 2000     

Velocity and concentration profiles in uniform sediment-laden flow

This paper presents a theoretical model for computing the velocity and sediment concentration profiles in a uniform sediment-laden flow carrying all fine, medium and coarse sediments. The proposed model essentially includes the effect of sediment concentration in total turbulent shear stress and eddy diffusivity in addition to the modified mixing length derived by Umeyama and Gerritsen [J. Hydr. Engng., ASCE, 118 (2) (1992) 229–245] applied to Hunt’s diffusion equation. Numerical solution of coupled differential equations for velocity and sediment concentration is carried out. The theoretical results show quite good agreement with the experimental data.     

Random copolymers at a selective interface: Many chains with excluded volume interactions

We investigate numerically, using the bond-fluctuation model, the adsorption of many random AB-copolymers with excluded volume interactions at the interface between two solvents. We find two regimes, controlled by the total number of polymers. In the first (dilute) regime, the copolymers near the interface extend parallel to it, while in the second regime they extend perpendicular to it. The density at the interface and the density in the bulk depend differently on the total number of copolymers: In the first regime the density at the interface increases more rapidly than in the bulk, whereas the opposite is true in the second regime. Received 4 March 1998 and Received in final form 22 September 1998     

纸浆纤维悬浮液物性参数对流动特性的影响

分析了纸浆的物性参数对两相流动模拟的影响，这些物性参数主要包括浆流种类、纤维的尺寸等参数，通过Phoen—ics软件的模拟得出结论，对于同类型的纸浆而言，随着浓度的增大，流体的速度梯度增大，剪切应力增大，径向浓度差增大；对于不同类型的纸浆，木浆的剪切应力大于同样浓度草浆的剪切应力；管道中浓度分布呈中心高，壁面低的单调递减趋势，很不均匀；对于不同类型的纸浆，草浆的径向浓度差小于木浆的径向浓度差．     

DC conductivity of a suspension of insulating particles with internal rotation

We analyse the consequences of Quincke rotation on the conductivity of a suspension. Quincke rotation refers to the spontaneous rotation of insulating particles dispersed in a slightly conducting liquid and subject to a high DC electric field: above a critical field, each particle rotates continuously around itself with an axis pointing in any direction perpendicular to the DC field. When the suspension is subject to an electric field lower than the threshold one, the presence of insulating particles in the host liquid decreases the bulk conductivity since the particles form obstacles to ion migration. But for electric fields higher than the critical one, the particles rotate and facilitate ion migration: the effective conductivity of the suspension is increased. We provide a theoretical analysis of the impact of Quincke rotation on the apparent conductivity of a suspension and we present experimental results obtained with a suspension of PMMA particles dispersed in weakly conducting liquids.     

Simulation of particle settling in rotating and non-rotating flows of non-Newtonian fluids

Finite element solutions are presented for the flow of Newtonian and non-Newtonian fluids around a sphere falling along the centreline of a cylindrical tube. Both rotating and stationary tube scenarios are considered. Calculations are reported for three different inelastic constitutive models that manifest shear-thinning, extension-thickening and their combination. The influence of inertia and these various forms of viscous response are examined for their influence upon the drag on the settling particle and the structure of the flow. Simulations are performed by employing a semi-implicit time marching Taylor–Galerkin/pressure-correction finite element algorithm, a fractional-staged scheme of second-order-accuracy. © 1998 John Wiley & Sons, Ltd.     

The basic character of five two‐phase flow model equation sets

Three test problems were simulated using five different two‐phase flow model equation sets from the open literature. The test problems chosen were a fluidized bed, a batch settling, and a horizontal jet impingement on a vertical wall. These three problems demonstrate an important cross‐section of physical phenomena, such as fluidized bed voidage oscillations, phase separation, countercurrent flow, and jet formation. The dispersed flow regime is selected for all three problems. The study was performed to assess the basic character of the five‐field equation sets responding to the same initial and boundary conditions and using the same finite difference numerical scheme. The general performance of the five equation sets was found to be similar, even though one of them was ill posed as an initial‐value problem. Broad trends are the same and quantitative differences could be assessed by examining the fine structure of the results. None of the equation sets could be entirely rejected on the basis of producing physically impossible or unacceptable results. Copyright © 2000 John Wiley & Sons, Ltd.     

Porous SiO2 nanoparticles containing ruthenium or sulfur compounds: Sonochemical producing and sonoluminescence in aqueous suspensions

Aqueous suspensions of silicon dioxide porous nanoparticles (average size 10–30 nm, average pore size 5.8 nm) were obtained via ultrasonic dispersing. As was shown through recording SiO molecular lines in a moving single-bubble sonoluminescence spectrum, these nanoparticles penetrate into the bubble and then undergo decay. Similarly, suspensions of SiO₂ nanoparticles, the pores of which were saturated with ruthenium dodecacarbonyl or elemental sulfur, were obtained by impregnation of the initial powder with solutions of these reagents in chloroform followed by evaporation of the solvent. Single-bubble sonoluminescence spectra of these suspensions contain more intense lines of Ru or S and Sⁿ⁺ as compared with the SiO lines. This also proves the involvement of water insoluble ruthenium and sulfur compounds into bubble sonoluminescent reactions in the heterogenic aqueous medium. Using the method of comparing the experimentally obtained and computer simulated luminescent spectra, we determined the effective electronic temperature T_e^Ru, which was 9000 ± 500 K, in non-equilibrium plasma of a bubble levitating in the ultrasonic field.     

Mass cultivation of catharanthus roseus cells using a nonmechanically agitated bioreactor

Batch suspension cultures ofCatharanthus roseus G. Don were grown in a 5 L LKB Ultraferm fermenter, converted to operate as an airlift bioreactor, to test the suitability of such a system for the mass culture of plant cells. Results show that the airlift system has considerable merits as a culture vessel for such a purpose, including: conversion rates of carbohydrate substrate to cell mass equivalent to > 50% under optimum conditions. (Operating under these conditions, growth rates of approximately 0.4 d^-1 are typical). In the absence of the mechanical shear normally associated with mechanically driven bioreactors, the gently agitated environment of the airlift vessel proves to be an ideal system for the growth of fragile plant cells. Use of a nozzle sparger reduces the possibility of a high mass transfer coefficient, except at very high gassing rates, thereby eliminating any interference with the growth rate caused by high rates of gaseous exchange.     

稀土掺杂聚苯撑ER流体的研究

选用CeCl4和FeCl3等对自制的对苯撑进行掺杂,将制得的高介电聚苯撑粉末加入到硅油中得到电流变体流体,测量了在电场作用下粘度和漏电流密度,以及相关的物理常数。讨论了电场强度、粒子浓度与粘度和漏电流密度的关系,粘度变化的响应速度和恢复时间,并探讨了其相关机制。