Current problems in the modelling of chemical reactors

Modelling of chemical reactors is reviewed with an emphasis on process development and scale-up. A distinction is made between modelling of chemical kinetics, of rate processes in volume elements and of whole reactors. Examples are mainly taken from papers presented at the Sixth International Symposium on Chemical Reaction Engineering. Special attention is given to the modelling of single phase reactors, fixed beds, trickle beds, fluid beds, and gas bubble reactors.     

Internal relative humidity distribution in high-performance cement paste due to moisture diffusion and self-desiccation

This investigation was carried out to study internal relative humidity (IRH) distribution of cement paste made with different water / cement ratios (w / c) and mineral admixtures in isothermal drying conditions. IRH changes in cement paste resulting from self-desiccation and moisture diffusion, respectively, at different ages were studied. The change laws of IRH in cement paste resulting from combining moisture diffusion with self-desiccation were discussed. The results indicate that IRH reduction of cement paste with w / c higher than 0.4 is mainly affected by moisture diffusion. However, IRH reduction of cement paste with w / c no higher than 0.4 is controlled by both moisture diffusion and self-desiccation. With the decrease of w / c, IRH reduction of cement paste resulting from self-desiccation increases, and IRH reduction resulting from moisture diffusion decreases at a given age. IRH decrement of cement paste incorporated with silica fume and ground blast-furnace slag is higher than that of control paste. w / c and the distance to the exposed surface play a significant role in IRH change resulting from moisture diffusion in isothermal drying condition. Change laws of IRH in cement paste with silica fume due to moisture diffusion considering self-desiccation are different from those in cement paste without silica fume.     

极限电流型氧传感器的实验研究

本实验用8mol%Y_2O_3-ZrO_2固体电解质制成了极限电流型氧传感器,并测定了氧在0.23～28.70mol%,温度在550～800℃范围时,传感器的输出特性,观察到该传感器有较好的稳定性和电压电流特性曲线。实验验证了极限电流值与氧摩尔分数和温度的关系。     

DIFFUSION AND REACTION OF BENZENE HYDROGENATION OVER POROUS Ni/γ-Al_2O_3 CATALYST

The macro-kinetics of benzene hydrogenation over porous Ni/γ-Al_2O_3 catalyst was measured with asingle-pellet diffusion reactor.Based on the dusty-gas model,the differential equations by taking into account ofthe variation of effective diffusivities with the composition were derived to describe the diffusion and reactionprocesses of reacting species over porous catalyst.Using the tortuosity factors determined under the condition ofsteady physical diffusion,the global reaction rates were calculated by solving the equations,and the results are ingood agreement with the experimental data obtained.     

大面积水域浓度场测试方法及系统研究

针对大面积水域浓度场难以实现实时测量、测量精度不高等问题,采用了一种多通道荧光测试系统和方法。首先,基于单色光诱导荧光检测浓度(LIF)原理,使用探头获取离散点的浓度参数。然后,经总线或通信网络技术,将数百个测点连接起来。最后,通过数据总线或网络将采集的数据输送到中央测控计算机中,处理离散的数据后形成完整的浓度场。在恒定流浓度场中的试验结果表明,污染物测量相对误差均值不超过5%,单次测量相对误差最高值为8.33%,传感器线性度不超过5%,可检测的荧光素钠溶液浓度分辨率为0.001 ppm,系统测量稳定、精度较高。相较于其他浓度测量方法,该系统具有测量面积大、实时测量的优势,可为水污染防治等领域提供可靠的技术支撑。     

硫酸装置布朗扩散型纤维除雾器的现场测试

开发了一种用于布朗扩散型纤维除雾器的便携式现场测试装置，用这套装置可在现场测定纤维床阻力，从而对元件制造水平进行评价和比较，或在维修期间预测清洗后元件的操作性能。介绍便携式现场测试装置的设备布局、安装和运行，并对整体充填、平行缠绕、斜交叉缠绕纤维床及同心组合纤维床进行比较。此外，论述了硫酸装置工艺气体压降的价值。     

Stochastic defect diffusion model for relaxation effects in crystalline polyethylene

It is suggested that some relaxation processes observed in crystalline polyethylene are consequences of the diffusive motion of a particular defect called a point dislocation or twist dispiration loop along the polyethylene stems in lamellar crystals. The motion of the defect, characterized by a diffusion coefficient and a mobility, is described by solutions of the Smoluchowski diffusion equation with boundary conditions that constrain the defect to move along routes that produce experimentally observable results. The fact that passage of the defect causes both a 180° rotation of the chain and moves an extra CH₂ group in the direction of the chain axis is important to the interpretation of the data according to this model. The diffusion coefficient for a defect is estimated to be around 2 × 10^?9 cm² s^?1 at 70°C. This value is shown to be reasonable both from the viewpoint of detailed computer modelling of defect motion and contemporary ideas about scaling.     

Application of pulse methods to the determination of the electrochemical characteristics of lithium intercalates

The transfer processes proceeding in insertion electrodes with surface control on the application of a potential or current step are considered theoretically. The theoretical relationships have been verified by the determination of the kinetic and diffusion parameters of electrochemical lithium intercalation into thin carbon films. The overall electrode polarization is divided, both theoretically and experimentally, into the kinetic component, related to hindered ion transfer in the passive surface layer, and the diffusion one, related to decelerated lithium diffusion in the carbon matrix. The polarization dependence of kinetic current is shown to obey the same regularities that the current-potential function of the lithium electrode. The concentration dependences of the surface layer parameters and the diffusion coefficient of lithium in carbon have been determined.     

Water sorption of poly(vinyl alcohol)/ poly(diallyldimethylammonium chloride) interpenetrating polymer network hydrogels

Temperature‐responsive interpenetrating polymer network (IPN) hydrogels constructed with poly(vinyl alcohol) and poly(diallyldimethylammonium chloride) using the sequential IPN method were studied. The characteristics of IPN hydrogels were investigated using the dynamic vapor sorption system. IPN hydrogels exhibited a relatively high sorption ratio, 180–360% at room temperature. The sorption ratio of hydrogels depended on temperature. Diffusion coefficients were calculated according to the Fickian Law at several temperatures. The apparent activation energy was 5.43 kJ mol^?1, which corresponds to typical diffusion processes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1389–1392, 2003     

User experience and personal innovativeness: An empirical study on the Enterprise Resource Planning systems

Although user experience and personal innovativeness are two important factors in new technology adoption, there has been no prior study to test these factors with the Enterprise Resource Planning (ERP) adoption. This paper investigates moderating roles of user experience on the relationship between the personal innovativeness and the ERP adoption motivations. This issue is important because if the user has more experience with the systems then the power of influence of personal innovativeness on ERP adoption motivation would be different. Thus, this paper tests these important insights of ERP systems adoption with the two different field samples with high (more than three years) and low (less than three years) user experience, based on the innovation diffusion theory, self determination theory, and different types of motivations such as intrinsic and extrinsic motivations. The findings, based on the PLS analysis of the model using 107 ERP end users, show that there are clear moderating effects of user experience—such as impacts of personal innovativeness on ERP systems adoption motivations are higher in case of low user experience samples, as expected. Academic and practical implications are discussed in the paper based on these empirical findings.