Viscous flow through a bed of settled aggregates: Evolution of tubes void of particles

Observations show that, when a viscous fluid flows vertically through a bed of settled flocculated aggregates, particles are emerged from locations on the upper surface of the bed, as a volcano process, and hollow tubes are created in the bed though the latter remains basically stable. A theoretical model is presented to explain this odd phenomenon from the onset of particle motion to the development of the tubular cavities and the particles' deposits around them. Analytical and numerical calculations are performed to show fluid streamlines and particle trajectories.     

固体颗粒的分散

分析了颗粒在液体中的分散过程,综述了颗粒在液相中的分散原理和分散方法,介绍了几种颗粒分散的评价方法.     

Inhalability of large solid particles

Large particles (10–$\text{150}\text{μm}\text{)}$ with systemic toxicity pose a health risk if inhaled regardless of where they deposit. This research seeks to better define particle inhalability, the fraction of airborne particles that are inhaled as a function of particle size.Measurements of inhalability were made for solid particles using a 1.6×1.6×5-m wind tunnel. Tunnel air velocities were 0.4, 1.0, and $\text{1.6}\text{m}\text{/}\text{s}$. A full-size, full-torso mannequin was used to collect dust entering either the mouth or nose for breathing at minute volumes of 14.2, 20.8, and $\text{37.3}\text{l}$. The mannequin either faced the oncoming wind or rotated slowly $\text{(0.06}\text{rpm}\text{)}$ during sample collection. At the test section, air velocity was uniform to within 10% and aerosol concentration was uniform to within 15% over the central 80% of the cross section.Orientation-averaged inhalability for mouth breathing was higher than the inhalable particulate mass (IPM) sampling criterion for particles smaller than $\text{35}\text{μm}$ and lower than the criterion for larger particles, leveling off at about 30% for particles $\text{>70}\text{μm}$. Facing-the-wind mouth inhalability showed the same trend as the IPM sampling criterion, but the measured values were 25% higher. Wind velocity and breathing pattern had little effect on inhalability for the range of conditions examined here. Orientation-averaged inhalability for nose breathing dropped quickly with particle size reaching less than 10% at $\text{60}\text{μm}$. Facing-the-wind nose inhalability was slightly increased for particles smaller than $\text{60}\text{μm}$ compared to orientation averaged inhalability for nose breathing.     

The mixing of solid particles in a fluidized bed

In this paper a new experimental method, based on the freezing of the fluidized bed by the aid of paraffin wax is used for the determination of the diffusion coefficient of the solid particles. The experimental diffusion coefficients are compared with those given by a theoretical equation. In order to explain the time and spatial dependence of the experimental diffusion coefficient a cinematographic study supplemented by visual observations is also made. One concludes that for small tube diameters a circulation motion of the solid particles takes place which is responsible for the mentioned effect.     

Performance characteristics of a cstr containing immobilised enzyme particles

The effects of internal and external substrate diffusion resistances on the performance of a continuous stirred tank reactor are analysed in this work. Both immobilised enzymatic reactions with and without substrate inhibitions are considered. The substrate conversion for the reaction without substrate inhibition is dependent on four dimensionless parameters: the Thiele modulus, the dimensionless Michaelis constant, the mass transfer Nusselt number and β, which represents a combination of particle hold-up, maximum reaction rate, input substrate concentration and substrate residence time in the continuous stirred tank reactor. For the corresponding reaction with substrate inhibition, the effect of the additional dimensionless inhibition constant on the substrate conversion is also very significant. The substrate conversion generally decreases with decrease in dimensionless parameter β, increase in Thiele modulus and decrease in mass transfer Nusselt number. For the reaction with small Thiele modulus, β and strong substrate diffusion resistances, a multireactor system may be needed if a certain desired substrate conversion is required. The single CSTR model can be extended to describe the multireactor system and the effect of the number of reactors on the substrate conversion for a two- or more reactor system is also examined.     

Transient response of diffusion cell containing a porous solid

Transient response of an adsorbing or non-adsorbing tracer injected as step or square pulse input in a diffusion cell with two flowing streams across the pellet is theoretically investigated in this paper. Exact solutions and the asymptotic solutions in the time domain and in three different limits are obtained by using an integral transform technique and a singular perturbation technique, respectively. Parametric dependence of the concentrations in the top and bottom chambers can be revealed by investigating the asymptotic solutions, which are far simpler than their exact counterpart. In the time domain investigation, it is found that the bottom-chamber concentration is very sensitive to the value of the macropore effective diffusivity. Therefore this concentration could be used to extract diffusivity by fitting in the time domain. The bottom-chamber concentration is also sensitive to flow rate, pellet length chamber volume and the type of input (step and square input).     

The transient response of a CSTR containing immobilized enzyme particles

A mathematical model is formulated for describing the transient substrate response in a continuous flow stirred tank reactor containing immobilized enzyme particles. The model considers the effects of internal and external substrate diffusion resistances as well as the inherent enzyme denaturation. Simulation of the model so formulated using the kinetic and physical parameters which are within the practical operating range, reveals that a substrate response minimum occurs in all the cases under consideration. Such a substrate response minumum is significantly affected by several characteristic dimensionless groups which govern the reactor performance equations. The unsteady state simulation is also extended to two CSTRs in series. It is found that the substrate response characteristics in the second reactor are similar to these in the first except for a much lower substrate concentration level.     

Initiation of divergent detonation in a vacuum containing monofuel particles

The problem of impactless initiation of spherical and cylindrical detonation in a vacuum containing monofuel particles is formulated and solved numerically. Included in discussion are the dynamics and formation characteristics of the reaction zone for the divergent detonation waves with a dispersed structure. Critical initiation energies are determined as a function of the energy from the outside and of the dimensions of the region where that energy is released. Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 5, pp. 66–71, September–October, 1993.     

水力旋流器内固体颗粒的沉降

水力旋流器内固体颗粒的离心沉降是一种复杂的两相流行为。从分析固液体系的相互作用，分别讨论了颗粒的自由沉降、干涉沉降问题，提出了高浓度下水力旋流器内颗粒之间的几种碰撞模式，阐述了旋流器内颗粒沉降的特殊性及其与使流器工作和旋流器结构间的可能联系，并指出了离心沉降本身有待深入研究的若干问题。     

Para-magnetic polyvinylbutyral particles containing activated carbon as a new adsorbent

In this study, a new type of magnetic particle was prepared in a uniform and spherical form for the range of 750 w m <D p <1000 w m from commercially available polyvinylbutyral (Mowital B30H, Hoechst), magnetite, and activated carbon using solvent evaporation technique. Magnetite (D p <5 w m) was successfully embedded in the adsorbent particles. The surface and cross-sectional views of p -magnetic particles were investigated with a Scanning Electron Microscope (SEM). The intensity of magnetization was measured with a vibrating-sample magnetometer. The adsorption studies of phenol and chromium (Cr(VI)) onto the adsorbent particles were carried out batch-wise. The effects of activated carbon and magnetite percentages on the adsorption capacity were investigated, and different initial adsorbate concentration and pH values were examined. Desorption experiments were carried out with different concentrations of NaOH, and it was determined that approximately 95% of adsorbed ions were desorbed. It was concluded that the para-magnetic polyvinylbutyral particles containing activated carbon and magnetite could effectively be used in the adsorption of organic and inorganic pollutants.     

Simultaneous absorption with reaction in a slurry containing fine particles

The simultaneous absorption of two gases accompanied by chemical reaction into a slurry of fine suspended particles was numerically analysed using the model obtained with some extension of the corresponding single gas absorption.Experiments were performed for the simultaneous absorption of sulfur dioxide and carbon dioxide with a plane gas—liquid type stirred tank absorber. The experimental results were satisfactorily elucidated by the proposed model and it is suggested that when accompanied by sulfur dioxide absorption, carbon dioxide may almost be regarded as an inert gas.     

Ignition of a metallized composite solid propellant by a group of hot particles

The solid-state ignition of a metallized composite propellant (ammonium perchlorate + 14% butyl rubber +5% aluminum powder + 6% plasticizer) under local heating by several sources of limited power capacity (dimensions of the hot particle x _p = 4 mm and y _p = 2 mm) was studied by mathematical modeling. For the temperature of the heated steel particles and the distance between them varied in the ranges 700 < T _p < 1500 K and 0.1_{x p} < Δ_x < 1.5xp, respectively, the values of T _p and Δ_x were determined for which the ignition delay corresponds to the initiation of combustion of the composite propellant by a single particle, by a plate at a constant temperature or by several particles. In the region of low initial temperatures of the local sources (T _p < 1100 K), the limiting values Δ_x → 0.1x _p and Δ_x > 1.5x _p, were identified for which the characteristics and mechanism of ignition of the propellant by a group of heated particles can be studied using the “plate–propellant–gas” model and the “single particle–propellant–gas” model, respectively. Decreasing the distance Δx at T _p < 1100 K decreases the induction period to 50% and reduces the minimum initial temperature of the source required to initiate propellant combustion from 830 to 700 K. At T _p > 1100 K, the ignition of the metallized composite solid propellant by a single or several particles can be studied using relatively simple one-dimensional models of condensed material ignition by a plate at constant temperature. The variation in the ignition delay in this case is less than 5%.     

Holdup and flow pattern of solid particles in freeboard of gas—solid fluidized bed with fine particles

The behavior of solid particles suspended in the freeboard of a 12 cm i.d. fluidized bed was studied using FCC particles of which the weight-mean diameter was 65 – 68 μm. The height of the freeboard was 180 cm, and the superficial gas velocity was changed from 15 to 50 cm s^?1.The weight-mean diameter and holdup of solid particles in the freeboard below the TDH vary with the axial position and the gas velocity. The lateral distribution of the solids holdup measured by a capacitance probe is almost flat in the region of r ? 5 cm, but the relative pulse frequency detected by a fiber optic probe indicates that the solids holdup increases greatly in the immediate vicinity of the column wall. The flow patterns of solid particles were measured by a fiber optic probe and a thermal response probe. The steady internal circulation of solid particles is formed in the freeboard below the TDH, and the circulating solids flow rate is much larger than the net entrainment rate of solid particles.