Validation of a Method of Determination of Apparent Diffusivity Versus Composition in Solids

A method is presented for computing the values of apparent diffusivity in solids with respect to the concentration of the diffusing substance (water or sodium chloride). This method does not require any assumption upon the mathematical relationship between diffusivity and concentration. It can be applied to experimental measurements of local concentration versus position within the solid (profiles) with relatively few measurements (circa 10) and a mathematical smoothing of the experimental data by using an artificial neural network model. The method was first validated on simulated data obtained by using a constant diffusivity value and on experimental profiles when the relation between diffusivity and concentration was given. It was then applied to original experimental moisture profiles obtained by putting gelatin gels with different initial moisture contents into contact for up to 14 days. The method was also successfully applied to five sets of experimental moisture and sodium chloride profiles taken from the literature and obtained from different food products. Apparent diffusivities calculated by our method were found in agreement with those obtained by authors using different numerical methods to compute the diffusivity values.     

基于连续性扩散流的湿地表面水流动力学模型

受表面密生植被的影响,湿地表面流总是处于高阻力、低流速状态。湿地表面流的水流动力学方程中,其水流加速度项相对于地表高密度植被造成的高阻力项相比,可以忽略。由此,以水流连续性方程和忽略加速度项的水流动力学方程为基础,构建基于连续性扩散流的湿地表面流动力学模型。该模型是一个抛物型偏微分方程,相对于描述一般径流流态的圣维南双曲型偏微分方程组而言,其求解过程相对容易。模型中的表面流流量采用修正的曼宁方程描述,表面糙率采用已有经验公式,数值计算方法采用六点差分格式。模拟结果表明,该模型能够体现湿地表面流的高阻力、低流速特征。水深越浅,水流模式变化越慢,水深越大,表面流受植被阻力越小,水流模式变化越快。     

以不同PAN系炭纤维布制备燃料电池气体扩散层之研究

采用石墨化PAN系炭纤维布制备了高分子电解质燃料电池气体扩散层。通过电学实验、X-ray绕射与元素分析考察了所制气体扩散层的性能。结果表明：随热处理温度的升高，气体扩散层的电阻率降低，L2增加，d（x）2减小。高温处理后的炭纤维布作为高分子电解质燃料电池气体扩散层显示了较高的电池效能。     

聚酰亚胺渗透汽化膜的研究(Ⅰ)膜的制备和结构对动态吸附特性的影响

以2种二酐，3种二胺为单体，两步法制备了6种不同结构的聚酰亚胺均质膜，通过红外光谱和元素分析证实了其重复单元的分子结构，测定了这几种膜的物理性质和对水蒸气的动态吸附性能，并计算出其反常扩散指数dw。实验表明，随着聚合物二胺单元分子结构的变化，按MDA、ODA、PDA的顺序，密度逐渐变大，链间距逐渐减小，链堆砌变得紧密，水蒸气在膜中的吸附和扩散也变慢，并出现从正常扩散到反常扩散的过渡现象。     

离心式高炉鼓风机扩压叶片断裂事故分析及处理

通过高炉鼓风机扩压叶片断裂事故，从化学分析、物理检验，结合使用情况对扩压叶片断裂原因进行了详细分析，并提出了改进措施。     

Al-Cu双金属复合结构的扩散连接试验研究

应用扩散连方法进行了Al-Cu双金属复合结构的试验研究，比较了不同的焊接工艺，材料组合以及母材状态情况Al合金与Cu的连接性，观察了接头区域的微观组织结构，研究表明，固相扩散连接是一种适用于异种材料连接的有效方法，通过在连接区域形成Al-Cu金属间化合物，达到Al和Cu的有效连接，材料组合，母材原始状态以及连接工艺参数对Al合金与Cu的扩散连接存在着明显的影响。表面镀Ni工艺不但能够有效阻止Al和Cu之间形成脆性相，而且Al和Ni之间形成了良好的扩散连接，改善了接头性能。     

Copper(II) removal from aqueous solutions by fly ash

The removal of Cu(II) by adsorption on fly ash has been found to be concentration, pH and temperature dependent. The kinetics of adsorption indicates the process to be diffusion controlled. The Langmuir constants have been calculated at different temperatures, and the adsorption has been found to be endothermic (ΔH = 15.652 kcal mol^?1). The maximum removal is observed at pH 8.0, and variation in adsorption with pH has been explained on the basis of surface ionisation and complexation.     

EXPERIMENTAL INVESTIGATIONS ON LONGITUDINAL DISPERSION CHARACTERISTICS OF TIDAL RIVERS

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Influence of adsorption on the measurement of diffusion coefficients by Taylor dispersion

The effect of adsorption on the measurement of diffusion coefficients by the Taylor dispersion technique is investigated by modifying the governing equation to account for reversible, nonequilibrium adsorption. The resulting two-dimensional equations are solved by an explicit finite-difference technique. Experimental data for the acridine carbon dioxide system indicated that acridine adsorbs on the walls on the tubing and these data were investigated with this model. The influence of carious parameters including the number of sites and the rates of adsorption desorption was investigated by conducting a parametric sensitivity analysis on the model. It was found that adsorption of the solute on the wall of the tubing could produce an error as high as 35% on the measured diffusion coefficient compared to the actual diffusion coellicient. Examination of the influence of each of the parameters will enable Inure investigators to reduce the effect of adsorption in the measurement of diffusion coefficients by Taylor dispersion.