The Influence of Air Permeation on the Flow Properties of Bulk Solids

This paper considers the influence of low air permeation on the flow properties of slightly consolidated bulk solids in steady state flow. A ring shear device was built that enables the powder sample to be permeated during the shear test from below, upwards with flow velocities below the onset of fluidization. Furthermore, a mathematical model predicting the dependence of both the shear stress as well as the location of the shear zone in the shear cell on the aeration degree was developed. This model predicts a reduction of the shear stress with increasing air feed pressure and a sudden displacement of the shear zone from the cover to the bottom of the shear cell for a high degree of aeration. The good agreement between the measured results and the model predictions proves that the influence of the permeation on the flow properties of bulk solids can be traced back to the change of the normal stresses in the shear zone.     

Modeling of Caked Contacts in DEMs

When modeling the caking properties of bulk solids, it is not only necessary to incorporate the yield properties of individual particle contacts, but also to extend them to a many‐particle system. To accomplish this by means of Distinct Element Method (DEM) simulations a contact model for (spherical) particles, including a yield criterion for combined load is proposed. An application to the simulation of a caking test is presented and compared to experiments.     

Product Design of Cohesive Powders – Mechanical Properties,Compression and Flow Behavior

The fundamentals of cohesive powder consolidation and flow behavior are explained using a reasonable combination of particle and continuum mechanics. By the model “stiff particles with soft contacts”, universal models are presented which include the elastic‐plastic and viscoplastic particle contact behavior with adhesion, load‐unload hysteresis and thus energy dissipation, a history‐dependent and a nonlinear adhesion force function. With this as the physical basis, incipient powder consolidation, yield and cohesive steady‐state flow, consolidation and compression functions, compression and preshear works are explained. As an example, the flow properties of an ultrafine limestone powder are shown. These constitutive models are used to evaluate shear cell test results for apparatus design to ensure reliable powder flow. Finally, conclusions are drawn concerning particle stressing, powder handling behavior and product quality assessment in processing industries.     

Model for Gas‐Liquid Flow through Wet Porous Medium

A method involving bubbling of air through a fibrous filter immersed in water has recently been investigated (Agranovski et al. [1]). Experimental results showed that the removal efficiency for ultra‐fine aerosols by such filters was greatly increased compared to dry filters. Nuclear Magnetic Resonance (NMR) imaging was used to examine the wet filter and to determine the nature of the gas flow inside the filter (Agranovski et al. [2]). It was found that tortuous preferential pathways (or flow tubes) develop within the filter through which the air flows and the distribution of air and water inside the porous medium has been investigated. The aim of this paper is to investigate the geometry of the pathways and to make estimates of the flow velocities and particle removal efficiency in such pathways. A mathematical model of the flow of air along the preferred pathways has been developed and verified experimentally. Even for the highest realistic gas velocity the flow field was essentially laminar (Re ≈ 250). We solved Laplace's equation for stream function to map trajectories of particles and gas molecules to investigate the possibility of their removal from the carrier.     

Magnetic Field,Flow Field and Inclusion Collision Growth in a Continuous Caster with EMBR

A three‐dimension mathematical model has been developed to describe the magnetic field, fluid flow and inclusion transport in a continuous caster with electromagnetic brake (EMBR). According to the model, all the governing equations can be expressed as a general differential equation, so a general numerical method was developed to solve these equations. The numerical results agree well with the experimental result. In the continuous caster, the inclusion distributions have ‘M’ shape under the nozzle and ‘W’ shape at the exit, which come from the centrifugal effect and the collision and aggregation among inclusions. The three‐dimensional static magnetic field can effectively damp local flows and affect the inclusion transport in a continuous caster. If EMBR is installed under the nozzle, it can promote the inclusion removal and the inclusion ‘M’ distribution disappears.     

Atomization of Liquids by Two‐phase Gas‐liquid Flow through a Plain‐orifice Nozzle: Flow Regimes inside the Nozzle

Liquids or suspensions are divided into sprays of small droplets by atomization of two‐phase gas‐liquid mixtures. In this way either an equal distribution of the droplets or the generation of large surface areas of the liquid phase are accomplished, leading to increased heat‐ and mass‐transfer. The spatial and time dependency of the mean droplet diameter is a function of the total pressure upstream of the nozzle, the volumetric flow rate of the liquid and the gas, as well as on the flow regime in the nozzle. Thus the radial and axial profile of the void fraction inside the nozzle are measured with an electrical measurement technique. In addition, the flow in the nozzle is imaged by a high‐speed camera. Three flow regimes are identified. These are bubbly flow, plug flow and annular flow. A continuous flow of the emitting spray is observed for bubbly flow and annular flow only. The distribution of the dispersed bubble phase is given by ratio of the isothermic compression energy needed to pressurize the gas mass flow rate from atmospheric pressure up to the total pressure in front of the nozzle, and the potential energy of the supplied liquid mass flow rate.     

不同流场状态对球形氢氧化镍生长粒度的影响

在相同的搅拌桨线速度、晶化时间、化学条件下,采用化学沉淀法分别应用八斜叶涡轮圆盘桨、推进式螺旋桨、Intermig桨分别制备球形氢氧化镍晶体。采用SEM技术考察各个样品的微观形貌,并结合PIV物理模拟技术分析不同桨型状态下反应器内的流场特性,研究表明:采用八斜叶涡轮圆盘桨是样品的球形度最佳,采用Intermig桨时样品的粒度d0.5最大。讨论了不同桨型对球形氢氧化镍晶体松装密度的影响。     

Time Series Modeling of Two‐ and Three‐Phase Flow Boiling Systems with Genetic Programming

The time series of the physical parameters in boiling evaporators with vapor‐liquid (V‐L) two‐phase and vapor‐liquid‐solid (V‐L‐S) three‐phase external natural circulating flows exhibit nonlinear features. Hence, proper system evolution models may be built from the point of view of nonlinear dynamics. In this work, genetic programming (GP) was utilized to find the nonlinear modeling functions necessary to develop global explicit two‐variable iteration models, using wall temperature signals measured from the heated tube in ordinary two‐phase and three‐phase fluidized bed evaporators. The model predictions agree well with the experimental data of the time series, which means that the models established with GP can adequately describe the dynamic evolution behavior of multi‐phase flow boiling systems.     

Device Performance Improvement of Double‐Pass Concentric Circular Mass Exchangers under Uniform Wall Fluxes

A double‐pass concentric circular mass exchanger under uniform wall fluxes is produced by inserting a permeable barrier into a circular tube to improve the device performance. The mathematical formulation was developed theoretically for such double‐pass, forced‐convection, mass‐transfer problems which are referred to as conjugated Graetz problems. The analytical solutions are obtained by the linear superposition of an asymptotic solution and a homogeneous solution which are linear in the axial direction and solved with the use of an eigenfunction expansion in a power series. The analytical results show that the mass‐transfer rate of a double‐pass mass exchanger can be improved compared to that of a single‐pass mass exchanger by suitably adjusting the permeable barrier position. Moreover, the ratio of mass‐transfer efficiency improvement and power consumption increment is also shown to make good economic sense.     

气力流槽的设计计算

气力流槽是一种常用的固体粉料、粒料的输送设备。它适用范围广,结构简单,制造价格低廉。本文从理论上论述了影响气力输送物料流量的各个因素,为设计和使用设备提供了理论依据。     

Validation of Gas Flow Measurement During Ozone Generator Performance Testing

Key measurements for ozone generator efficiency testing include generator power, ozone concentration, and gas flow rate. Accurate gas flow measurement must address numerous issues such as: meter precision, meter calibration, gas density changes due to variations in molecular composition, and gas compression and expansion changes due to variation in temperature and pressure. Preferably, the gas flowmeter for performance testing is one that can be field-verified for accuracy. Orifice-plate, flow-tube and venturi differential pressure flowmeters have these characteristics and have been frequently used to obtain gas flow readings of record during ozone generator performance tests. This paper discusses the importance of field-verification, provides reference equations and example calculations, and presents issues and considerations for quality assurance.     

两级石油化工流程泵的结构设计及应用

对离心式石油化工流程泵的不同结构进行了比较 ,指出了流程泵第 1级采用双吸叶轮、压水室为双涡室结构对于提高汽蚀性能和平衡径向力的重要作用。理论分析、试验结果及工业应用表明 ,采用小叶片出口角 β2 、少叶片数Z和大叶片包角θ的叶轮以及X形分布的两个中间过渡流道 ,能减轻泵的振动 ,提高效率 ,扩大高效区范围     

Simulation of Thermal and Flow Characteristics for Optimum Design of an Automotive Catalytic Converter

In the present work, the effect of a flow maldistribution on the thermal and conversion response of a monolithic catalytic converter is investigated. To achieve this goal, a combined chemical reaction and multidimensional fluid dynamic mathematical model has been developed. The present results show that flow uniformity within the monolith brick has a significant impact on light-off performance of the catalytic converter. In the case of lower flow uniformity, large portions of the monolith remain cold due to locally concentrated high velocities, and CO and HC are unconverted during the warm-up period, which leads to retardation of light-off. It has also been found that the heat-up pattern of the monolith is similar to the flow distribution profile in the early stage of the reaction. It may be concluded that flow maldistribution can cause a significant retardation of the light-off and, hence, can eventually worsen the conversion efficiency of an automotive catalytic converter.     

空气输送流槽的设计计算

空气输送流槽是一种利用压缩空气作为动力来输送物料的装置。本文介绍了空气输送流槽的输送原理和结构,并以炭黑输送为例,提出了设计计算空气输送流槽的简易方法。     

Experimental and Numerical Study of Serpentine Flow Fields for Improving Direct Methanol Fuel Cell Performance

Methanol crossover is an important issue as it affects direct methanol fuel cell (DMFC) performance. But it may be controlled by selecting a proper flow field design. Experiments were carried out to investigate the effect of single, double and triple serpentine flow field configurations on a DMFC with a 25 cm² membrane electrode assembly (MEA) with a constant open ratio. A three dimensional model was also developed for the anode of the DMFC to predict methanol concentration and cell current density distributions. Experimental and model results show that at lower methanol concentrations (0.25–0.5M), single serpentine flow field (SSFF) provides high peak power density, while a double serpentine flow field (DSFF) gives high peak power density at a high methanol concentration (1–2M). Single and double serpentine flow fields exhibit the same peak power density (33 mW cm⁻²) at 1M. But the cell efficiency of double serpentine flow field is 12.5% which is 3.5% point greater than single serpentine flow field. This is attributed to reduced mixed potential. triple serpentine flow field (TSFF) shows the lowest peak power density and cell efficiency, which is attributed to high mass transfer resistance.     

脉动流参数对旋流器分离性能的影响

介绍了脉动实验系统及相关的实验参数,研究了脉动流的一些主要参数对水力旋流器分离性能的影响,详细分析了脉动周期比、流量脉动幅值比和雷诺数等参数对水力旋流器用于细颗粒分离性能的影响。结果表明,在脉动周期比为0.68及流量脉动幅值比为2%左右等条件下,流量的脉动反而会提高水力旋流器的分离效率。