EFFECTIVE DIFFUSION COEFFICIENT OF ACTIVE SOLVENTS IN COMPOSITE POLYMERIC MATERIALS

A method and a device for determination of the effective diffusion coefficient of active solvents in composite polymeric materials (CPM) based on cellulose derivatives are proposed and examined. This method accounts for anomalous mass transfer phenomena, considerable shrinkage and changes of sorption capacity of the CPM specimen allowing selection of the rational technological regime. Results of experimental studies on diffusion of acetone and ethanol in cellulose nitrate with various degrees of substitution are given as examples.     

THE INFLUENCE OF AIR TEMPERATURE ON EFFECTIVE DIFFUSION COEFFICIENT OF MOISTURE IN THE FALLING RATE PERIOD

ABSTRACT

The convection drying of spheres of Al-Ni catalyst and thin clay plate was investigated on a laboratory scale. The aim of the investigation was to determine the mechanism of moisture transfer within the firm sample skeleton.

By measuring the mass loss and the surface temperature of the samples during the drying process, basic dependencies necessary to describe the process kinetics was obtained. Found functional dependencies show high level of correlation with experimental data. Exponential model parameters are dependent of air temperature and velocity, and the type of the examined material.

The applicability of the chosen model to describe the drying kinetics is proven regardless of drying material origin and geometry, The comparison of different drying experiment and determination of the average diffusional coefficient at given experimental conditions is enabled.     

多孔氧化铝中气体的有效扩散系数

在两种氧化铝中 ,分别采用C₂H₄ 、Ar和CO₂ 进行了两组分和三组分的Wicke -Kallenbach定态扩散实验 .由尘气模型和Stefan -Maxwell方程建立起的扩散通量方程 ,对实验结果加以处理 ,得到了两组分扩散的有效扩散系数及三组分扩散的虚拟两组分有效扩散系数 .同时 ,针对过渡区扩散推出了等温下两组分扩散的有效扩散系数为常数应满足的基本条件 ,所得结论和实验结果相吻合 .而对三组分扩散中的虚拟两组分有效扩散系数不能按照常数处理 .此外 ,无论是两组分或三组分扩散 ,对每一种氧化铝而言 ,有着相近的曲折因子 ,从而证实了曲折因子是与多孔介质结构密切相关的参数     

分子吸附对聚乙烯醇在氧化铝粉末压缩体中扩散系数的影响

利用氧化铝粉末压缩球状体和Ｆｉｃｋ第二扩散定律,系统地研究了聚乙烯醇在多孔介质和实验系统ｐＨ值为８．４０±０．２条件下的扩散行为,以及聚乙烯醇在球体外表面吸附对扩散系数的影响．实验结果和相应计算得到的扩散系数表明：发生在氧化铝表面的分子吸附,不仅导致扩散平衡状态时的Ｍｔ（聚乙烯醇在时间ｔ的扩散量）高于理论计算值Ｍ∞,而且使实验初始阶段计算的扩散系数远大于其它过程扩散系数．由分子吸附产生的实验误差和扩散系数计算误差,可通过修正浓度分配系数Ｋ,或者直接从Ｍｔ中去除可能存在的吸附量得到解决．     

UNIFAC模型在非理想多组分扩散系数计算中的应用

引　言对于非理想体系的多组分扩散 ,由于各组分分子之间存在强烈的相互作用而导致许多“奇异”的扩散现象 ,如渗透扩散、扩散障碍和反向扩散等[1] ,进行扩散通量计算必须考虑热力学非理想性对扩散的影响 .基于不可逆热力学理论的多组分扩散的Max well Stefan方程采用热力学因子矩阵Γ描述非理想性对扩散的影响 ,已经广泛用于单相内扩散、相际传质、催化剂和吸附剂内扩散以及膜分离等有关扩散过程的研究[2 ,3 ] .估计热力学因子的主要困难在于各组分活度系数对组成导数的计算 .目前应用较成熟的活度系数模型 ,如基于局部组成概念的Wilson…