Bend Pressure Drop Predictions Using the Euler-Euler Model in Dense Phase Pneumatic Conveying

Pneumatic conveying of powdered and granular materials is a very common transport technology across a broad range of industries, for example, chemicals, cosmetics, pharmaceuticals, and power generation. As the demands of these industries for greater efficiency increases and to comply with environmental regulations there is a need for a more fundamental understanding of the behavior of materials in pneumatic conveying systems. The approach presented in this article is to develop a model of a section of pneumatic conveying line, a horizontal or vertical 90° bend, in the commercial CFD software package FLUENT and to describe the multiphase flow behavior by the mixture or Eulerian method. Models of this type have been used in the past to show qualitative and quantitative agreement between model and experiment. The model results presented were compared with experimental data gathered from an industrial-scale pneumatic conveying test system. Broad qualitative agreement in trends and flow patterns were found. Quantitative comparisons were less uniform, with predictions from around 10% to 90% different from experimental results, depending on conveying conditions and bend orientation.     

Voidage Measurement for a Moving Plug in Dense Phase Pneumatic Conveying Using Two Different Methods

Two simple ways to measure voidage in a moving plug in dense phase pneumatic conveying have been explored, along with voidage behavior and other parameters. The first method (bulk solid method) determines the average voidage for a single plug, by measuring the length and the weight of the plug, while the second method (Ergun's method) determines the voidage along the plug length from plug head to tail by using the Ergun equation. The experiments were performed under different experimental conditions of plug lengths, gas velocities, and materials. The results from both methods showed varying degrees of agreement, depending on the material transported. The measurements also found that the voidage varied only slightly with the plug velocity. However, it did vary more within the plug (e.g., plug head, middle of plug, and plug tail).     

低速高能效的浓相气力输送技术

低速浓相输送装置的出现,解决了物料在输送过程中易破碎、堵塞和磨蚀管道等难题,降低了耗气量。本文中综述了低速浓相输送的几种定义和输送过程中的相图、物料流动形态及相应的判定、影响浓相气力输送特性的因素等技术参数,并介绍了输送过程中经常遇到的堵管和磨损现象以及气力输送过程中的检测和自动控制技术,指出了今后的研究方向。     

粉体性能对浓相气力输送特性的影响

气力输送过程中物料性能是确定输送特性的重要因素,因此,粉料气力输送技术的实现要以对粉料的性能研究为基础。文中对影响气力输送的粉体基本性能及其相关参数做了较全面分析,其中粒子尺寸、粒径分布、形状是影响粉料是否可适用于浓相气力输送的关键参数,其它特性都与这3种特性相关联。介绍了几种应用广泛的粉料气力输送特性分组方法,并进行了简要评述,同时指出了今后的研究方向。     

正压浓相恒压输送系统的DCS控制设计及应用

正压浓相气力输送系统是目前国内火电厂应用最为广泛的气力输送系统,该系统对运行的控制流程要求高、逻辑性强;其关键输送技术指标均采用模拟量进行检测,并实时控制.本文介绍的恒压输送系统,除了以上特点外,其独具的输送压力的动态实时调控功能,更是对控制系统提出更高的要求;阐述了DCS用于正压浓相恒压输送系统的典型设计.     

Stress-Field Modeling and Pressure Drop Prediction for Slug-Flow Pneumatic Conveying in an Aerated Radial Stress Chamber

Slug-flow pneumatic conveying is a full-bore mode of flow within the dense-phase flow regime where bulk materials are transported in the form of slugs at conveying speeds below saltation velocity. The mechanism of slug-flow pneumatic conveying consists of the particles being picked up from the stationary bed in front of a moving slug while the same amount of material is deposited behind the slug. Stress field modeling of the material slug is the first step in developing a prediction model for the pressure drop along a pneumatic conveying line. However, a reliable prediction strongly relies on an accurate assessment of several factors, including the particle properties, pipeline dimensions, and operating conditions. So far, the particle diameter has always been one of the crucial parameters, which is not desirable in regards to the limitations it imposes on the choice of bulk materials. This article focuses on one parameter, the stress transmission coefficient k_w, which relates the lateral wall stress within a slug of material to the axial stress. To date, this parameter could not be measured directly in an aerated material bed and had to be estimated. Inaccuracies within the prediction were therefore unavoidable. A newly designed test chamber now enables the measurement of the lateral and axial stresses within a slug, which leads directly to this stress transmission coefficient. This article outlines the design of the test apparatus and reports on the experimental results. For the two materials tested, an exponential correlation between the pressure on top of the slug (frontal stress) and the stress transmission coefficient was obtained. Calculating the wall friction coefficient leads to a constant value above a certain material-specific air velocity.     

Particle Trajectories in Dilute Phase Pneumatic Conveying

A nonintrusive cross-correlation method to measure the particle velocities in dilute phase pneumatic conveying is described. The cross-correlation function generated gives information about the time it takes for a particle to travel between two optimally placed measurement planes. Experiments and CFD simulations are used to estimate an optimal inter-plane distance for various flow conditions.     

Effect of Dune Formation on Pressure Drop in Horizontal Pneumatic Conveying System

Pneumatic conveying is widely used in industries handling large amount of granular materials to transport the solid particles; however, the process is energy intensive as an instability of flow sets in the transportation line even in the dilute regime, causing large fluctuations in the line pressure drop, the reason of which is not clearly understood. Here, we investigate, both by experiments and by using numerical simulations, the instability transition regimes and identify the reasons of the fluctuations observed in the line pressure drop in a horizontal pneumatic transport system operating at near-saltation conditions. It is observed that the increase in the pressure drop (immediately after the saltation) is accompanied by the formation of distinct dunes. It is also observed that the line pressure drop depends on the axial location of the dune and shows large fluctuations in the regime where the dunes are unstable. Results obtained from the numerical simulations suggest that the increase in the line pressure drop in the presence of dunes is essentially due to the shear stresses at the dune surface which are larger than that for the flows in clean pipe.     

A Pressure Drop Model for Positive Pneumatic Conveying of Flour Through a Vertical Pipeline

A differential equation of motion for gas-flour two-phase flow in a vertical pipe was first derived based on the momentum conservation and by adopting two empirical expressions for the velocity ratio of flour to gas and frictional coefficient between flour and pipe wall, and then a pressure drop model for dilute positive pneumatic conveying of flour through a vertical pipeline was developed by employing the continuity and state equations for gas. The conveying tests were conducted on a positive pneumatic conveying system of flour in a flour mill. Under each of the six different flow conditions, the conveying parameters, such as the flour and gas mass flow rates and the pressure drop between two selected cross sections on the vertical pipeline were measured. The pressure drop between the two selected cross sections was evaluated using the pressure drop model for each of the six flow conditions. The calculated values of pressure drop agree well with the measured data, and it is demonstrated that the model is applicable to vertical positive pneumatic conveying systems of flour.     

Experimental and numerical study of a horizontal-vertical gas-solid two-phase system with self-excited oscillatory flow

To better explore the energy-saving mechanism and flow characteristics of the self-excited oscillatory flow, the experiment is performed by a new self-excited oscillatory flow generator that the 45° oblique sheet is mounted through the pipe axis in a horizontal-vertical closed pneumatic conveying system. The experimental study focuses on the optimum air-velocity and power consumption, and results shows the maximum reduction of the optimum air-velocity and the coefficient of power consumption are approximately 8.2% and 16.4%, respectively. In addition, the CFD-DEM coupled approach is first developed to investigate the interaction of gas-solid flow in terms of the gas turbulent kinetic energy and spatial particle flow characteristics. Compared with the conventional pneumatic conveying, it is found that the optimum air-velocity and power consumption are reduced by the new self-excited oscillatory flow at lower air-velocities. The numerical results show that the approximately symmetric distribution of axial velocity and the intensive tangential velocity is emerged in the self-excited oscillatory flow at upstream. Particles is efficiently dispersed and suspended by the self-exited oscillatory flow reflecting in the smaller particle variation coefficient and the lager particle suspension coefficient. And since the airflow kinetic energy is utilized more fully to promote particles flowing, the spatial particle axial velocity is accelerated and reached early steady state. As a result, the developed numerical model is further explained the mechanism of energy saving with the self-excited oscillatory flow.     

密相气力输灰管道的设计与应用

对气力输灰工程中密相输灰管道的设计和计算确定管内压力和速度的公式进行整理 ,同时可以得到较合理的管径和不同管径的长度。运行参数当已知时 ,给出的计算公式可作为设计的依据     

车轮半自动径,轴向跳动谐波检测仪的研制

本文介绍“车轮半自动径、轴向跳动谐波检测仪”的用途，测量原理及主要技术参数，应用计算机完成了测试数据在线处理及测试过程的自动化。     

Numerical Simulation for Hydrodynamic Analysis and Pressure Drop Prediction in Horizontal Gas-Solid Flows

Two fluid or Eulerian modeling incorporating the kinetic theory for granular particles and accounting for four-way coupling was performed to investigate the hydrodynamics and pressure drop characteristics of gas-solid flows in horizontal pipes. The model was validated by comparison with the experimental data found in literature and the predictions agreed reasonably well with experimental results. It was found that lift force along with particle-wall collision and specularity coefficient play significant role in the simulation of horizontal gas-solid flows. Granular temperature model by Ding and Gidaspow (1990 Ding , J. , and D. Gidaspow . 1990 . A bubbling fluidization model using kinetic theory of granular flow . AIChE Journal 36 ( 4 ): 523 – 538 .[Crossref], [Web of Science ®] , [Google Scholar]) predicts the velocity profiles of both phases accurately. The gas-solid two-phase flow in the horizontal pipe generally has an asymmetric structure in the vertical direction, which is due to the effect of gravity. An extensive investigation was also done to study the effect of various flow parameters like particle properties, gas velocity, and solid concentration on pressure drop prediction. Finally a simplified correlation was proposed for fully developed pressure drop in horizontal gas-solid flows. Unlike the existing correlations, this correlation is valid for a wide range of particle size, pipe diameter, and mass loading.     

An Investigation into Pressure Fluctuations and Improved Modeling of Solids Friction for Dense-Phase Pneumatic Conveying of Powders

The aim of this paper is to investigate into flow mechanism with the help of pressure signal fluctuations analysis and modeling solids friction in case of solids–gas flows for fluidized-dense-phase pneumatic conveying of fine powders. Materials conveyed include fly ash (median particle diameter 30 µm; particle density 2300 kg m^?3; loose-poured bulk density 700 kg m^?3) and white powder (median particle diameter 55 µm; particle density 1600 kg m^?3; loose-poured bulk density 620 kg m^?3). These were conveyed in different flow regimes varying from fluidized-dense-to-dilute phase. To obtain information on the nature of flow inside pipeline, static pressure signals were studied using technique of Shannon entropy. Increase in the values of Shannon entropy along the flow direction through the straight-pipe sections were found for both the powders. However, drop occurred in the Shannon entropy values after the flow through bend(s). Change in slope of straight-pipe pneumatic conveying characteristics along the flow direction is another factor which provided indication regarding change in flow mechanisms along the flow. A new technique for modeling solids friction factor has been developed using a solids volumetric concentration and ratio of particle terminal settling velocity to superficial air velocity by replacing the conventional use of solids loading ratio and Froude number, respectively. The new model format has shown promise for predictions under diameter scale-up conditions.     

渐开线花键压力角及相关参数的测量与计算

通过对渐开线内花键棒间距和渐开线外花键跨棒距的计算公式分别进行微分,推导出压力角的关系式。又分别求得其它结构主参数的测量和计算方法并举例说明。     

Phase Formation and Melt Processing of Yb-123

The formation of Yb-123 has been studied at different temperatures in air and in reduced oxygen partial pressure. It is found that the stability and/or the formation kinetics of Yb-123 phase is a major hurdle in manufacturing phase-pure Yb-123 in air. However, under reduced oxygen partial pressure, Yb-123 forms rapidly and more than 90% phase-pure Yb-123 is achieved within three sintering steps. Rods made from this powder were melt-processed in air and showed a T _c of 90 K. Kinetic studies performed by interrupting the growth during the directional solidification of these rods revealed a growth mechanism similar to that of Y-123 and a maximum growth rate of 7.2 mm/h for a stable planar interface. EPMA of the interface showed the liquid to be rich in barium cuprates with a Ba:Cu ratio of 1:3.     

风电滑环电刷接触压力精密测试技术与试验研究

电刷接触压力是风电滑环性能指标的关键参数,直接影响滑环的接触电阻和寿命。本文针对现有风电滑环刷丝压力测试方法效率低且精度不高的问题,提出了一种快速准确获得风电滑环电刷接触压力的精密测试方法,并设计一套基于AGS—X拉力测试平台的风电滑环刷丝接触压力检测系统,实现了电刷压力的快速准确测量,可进行对刷丝压力的连续测试,结果表明被测滑环电刷接触压力平均值与理论设计值仅相差5mN,各环接触压力测量值波动峰值差小于50mN,并且测试摩擦力矩指标满足其设计和工作要求。     

Effects of Microstructures,Porosity and External Pressure on the Phase Transition of Ferroelectric Ceramics Upon Cooling

A micromechanics-based thermodynamics model is developed to predict the effects of internal stress, microstructures, porosity, and external hydrostatic pressure, on the phase transition of ferroelectric ceramics, with a special reference to the cubictetragonal transformation. The development makes use of the 3-D randomly oriented ellipsoidal inclusions containing an eigenstrain and eigen-polarization to represent the morphology of the transformed domains in the polycrystalline ceramic. The change of Gibbs free energy under a thermo-electro-mechanical loading is then derived at a finite volume concentration of new domains f _p and porosity f _v. This free energy serves to determine the thermodynamic driving force for domain growth, and, together with the resistance force associated with the energy dissipation due to domain wall motion, a kinetic equation is established. This kinetic equation provides the evolution of the tetragonal domains as the temperature passes through the Curie point. The build-up of internal stress in the parent phase is then calculated, and found to increase linearly at the initial stage but becomes nonlinear at the end. This internal stress plays a significant role in hindering the domain growth process. Consistent with some experimental observations, porosity is found to raise the transition temperature, but for BaTiO₃ ceramic external pressure is found to lower it. Applications of the theory to a BaTiO₃ single crystal for the evolution of overall polarization is found to give results that are in good accord with the test data.