Critical evaluation of coupling particle size distribution with the shrinking core model

The shrinking core model (SCM) is widely used to model fluid-solid reactions such as the leaching of metals from minerals. In most cases, however, the particle size distribution (PSD) of the solid material was disregarded. In this paper the erroneous shift in the control regime when neglecting PSD was quantified and the dependence of the shift on the coefficients of variation (CV) and the type of PSD was analysed. By coupling the SCM with a Gamma PSD, it was found that neglecting the PSD would shift the control regime from chemical reaction to inert/ash layer diffusion, when the CV was between 0.7 and 1.2. For a system controlled by liquid film diffusion, neglect of the PSD, would shift the control regime to chemical reaction when CV is between 0.3 and 0.7 or to inert/ash layer diffusion when CV is greater (0.9-1.5). It was therefore postulated that some researchers had unknowingly made invalid conclusions about the control regime due to the neglect of PSD. However, an inert/ash layer diffusion-controlled process was insensitive to the neglect of PSD. When CV<0.3, neglect of the PSD would not cause any erroneous shifts, irrespective of the control regime. Experimental data confirmed the observation. For a given CV, the deviation in the fraction reacted from the mono-PSD increases with CV and decreases with time. The maximum deviation, which occurs at the beginning, is about 10% with a gamma PSD of CV=0.3. The percent deviation is dependent of the type of PSDs. Gamma PSD gives the lowest deviation while Gaudin-Schuhmann results in the largest deviation (maxi. ∼19%, with CV=0.3) in the first half of dissolution process. Log-normal distribution gives a larger deviation than gamma but quickly approaches the latter with time. The deviation for Rosin-Rammler is between log-normal and Gaudin-Schuhmann. For systems with CV less than 0.3, the SCM can be fairly used without considering PSD. When CV is greater than 0.3, particularly in the early stage of a dissolution process with a PSD other than gamma, PSD should be included to avoid substantial errors.     

Flow regime, hydrodynamics, floc size distribution and sludge properties in activated sludge bubble column, air-lift and aerated stirred reactors

This paper presents a comparative study how reactor configuration, sludge loading and air flowrate affect flow regimes, hydrodynamics, floc size distribution and sludge solids-liquid separation properties. Three reactor configurations were studied in bench scale activated sludge bubble column reactor (BCR), air-lift reactor (ALR) and aerated stirred reactor (ASR). The ASR demonstrated the highest capacity of gas holdup and resistance, and homogeneity in flow regimes and shearing forces, resulting in producing large numbers of small and compact flocs. The fluid dynamics in the ALR created regularly directed recirculation forces to enhance the gas holdup and sludge flocculation. The BCR distributed a high turbulent flow regime and non-homogeneity in gas holdup and mixing, and generated large numbers of larger and looser flocs. The sludge size distributions, compressibility and settleability were significantly influenced by the reactor configurations associated with the flow regimes and hydrodynamics.     

MACROPROCESS OF PARTICLE FORMATION IN SUSPENSION POLYMERIZATION OF STYRENE WITH INORGANIC STABILIZER SYSTEM

The macroprocess of particle formation from suspension droplets of styrene in a pdymerizationsystem was investigated.Inorganic hydroxyapatite or its mixture with polyvinyl alcohol as thepolymerization system was used.Those items such as the effects of the Weight fraction of dispersed-phase,the amount of the inorganic stabilizer and the agitation speed on the breakup and coalescence of thetransient dispersed drops etc.Were examined.Results showd that the dynamic behavior of the transi-ent polymer droplets changed in the presence of the suspension stabilizer during the reaction.     

离网型太阳能光伏发电系统设计研究

离网型太阳能光伏发电系统是太阳能光伏发电系统的重要组成。它具有灵活度高、分布广、项目成本低等优点。本文主要对现有离网光伏发电系统设计过程进行分析。     

实时数据仓库中一种改进的数据流更新算法

为实现数据仓库中数据的高效集成,针对数据偏斜分布现象,提出一种改进的数据流更新算法EH-JOIN。该算法对传统散列连接方法进行改进,利用索引将部分频繁使用的主数据存储在内存中,解决了高速数据流下的磁盘频繁访问问题。实验结果表明,与MESHJOIN算法和R-MESHJOIN算法相比,EH-JOIN算法的服务速率在磁盘存储关系集保持适当大小时分别提高了96%和81%,在内存大小不同时提高了57%和48%。     

湿浸法制备活性组分非均匀分布负载型催化剂过程的计算机模拟

对活性组分非均匀分布的负载型催化剂的湿浸法制备过程进行了计算机模拟,其模拟程度可适用于任意多个活性组分的浸渍。发现单组分浸渍时,通过控制浸渍时间可获得活性组分由薄到厚的蛋壳型分布和均匀分布,但通过预浸渍吸附至一定分布后,再在空白溶液中浸渍洗脱,控制洗脱条件也可获得蛋黄、蛋白型的分布;加入竞争吸附剂,进行双组分及多组分浸渍,通过控制浸渍溶液性质及浸渍时间可获得各种类型的活性组分分布,诸如蛋壳型、蛋白型、蛋黄型和均匀型。通过对制备过程参数(如竞争吸附剂的选择、各组分有效扩散系数、初始浓度、吸脱附速率常数等)与活性组分分布形式之间关系的分析,可实现对任一分布形式的催化剂的制备过程参数的优化。这对实际制备催化剂具有指导意义。     

胶层厚度对拉伸试样应力分布影响的数值分析

运用弹塑性有限元法研究了胶层厚度对承受拉伸载荷的对接接头胶层内应力分布的影响．三维有限元法数值分析的结果表明，随胶层厚度减小，胶层中正应力SZ与剪应力SYZ的分布趋于均匀；而对正应力SY而言，胶层厚度为0．15mm时，其边缘峰值应力最低。     

Dipole moments of copolymers in relation to the distribution of polar monomer unit sequences

A method for evaluating the dipole moments of copolymers in relation to the distribution of polar unit sequences is proposed. Experimental data on the synthesis and dipole moments of styrene-p-chlorostyrene and styrene-p-methoxystyrene copolymers were used to calculate the effective dipole moment of a polar unit in a copolymer. For this purpose, we assumed the following effective moment values for the corresponding polar unit sequences along the copolymer chains: when both of the nearest neighbours are polar, μ_PP, when one of the nearest neighbours is polar and the other is non-polar, μ_PS, and when both of the nearest neighbours are non-polar, μ_SS. The relative magnitudes of μ_SS, μ_PS and μ_PP calculated for both copolymers reflect the influence of dipole-dipole interactions on the effective dipole moment of a polar unit in a copolymer molecule.     

一种高效的网格资源监测算法ACTC的改进算法

资源监控是网格计算的关键组成部分。资源监控算法既要保证网格系统中资源信息高保真度又要考虑资源信息在网络传输中的负担最低。ACTC算法就是为实现以上目的而被提出,但是算法中对资源信息更新量的动态门槛值(d_threshold)计算方式不合理,有可能导致算法演变成低级的单纯依靠时间敏感机制(TSM)来发送资源更新通知,并且算法中遗漏了一些极端情况的考虑。提出了新的d_threshold计算公式和限制条件,进行性能改进和完善,并对改进前后两算法进行实验对比。实验表明,改进后算法提高了资源信息准确性,并使监控系统     

多维超几何分布的最可能成功数

超几何分布是一种重要的离散型概率分布,本文利用反证法以及比较法求出了三维超几何分布的最可能成功次数,并在此基础上,求出了多维超几何分布的最可能成功次数.