纤维聚合物复合材料的有效湿扩散系数

根据纤维聚合物复合材料的微观结构, 建立了基于复合材料单胞模型的湿扩散计算方法, 研究了不同温度和不同体积分数下纤维聚合物复合材料的湿扩散性能。假设纤维是不可渗透的, 并在聚合物基体中均匀分布, 计算了不同温度不同体积分数下复合材料的有效湿扩散系数。结果表明: 复合材料的有效湿扩散系数随温度的升高而增大, 随纤维体积分数的增大而减小; 在相同温度、 相同体积分数下, 正六边形排列的纤维复合材料的湿扩散系数比正方形的略大。计算结果及经验公式与Gueribiz曲线基本一致, 说明用单胞模型计算复合材料的湿扩散性能是非常有效的, 有助于理解纤维复合材料的湿扩散机制和性能。      

微乳化乙醇柴油热物性计算与分析

车用清洁型微乳化油是内燃机的理想代用燃料之一．微乳化油热物性参数难以计算,从而影响在内燃机上对它的定量计算研究．以微乳化乙醇柴油为例,用经验公式计算其蒸发焓、生成焓、液体比热容、导热率和微乳化油蒸气的扩散系数,分析了温度和压力以及不同溶醇量对热物性参数的影响规律,为微乳化油热物性参数的计算提供一种工程方法．结果表明：随着温度的增加,微乳化乙醇柴油蒸发焓、导热率降低,定压比热容和微乳化油蒸气扩散系数增加;随着压力增加,微乳化油蒸气扩散系数降低;随着混合燃料中乙醇含量的增加,定压比热容和混合气扩散系数均增大,蒸发焓减小;乙醇含量对混合燃料导热率的影响与燃料温度有关,在一定温度下乙醇含量效应发生逆转;微乳化乙醇柴油中乙醇含量增加有利于燃料蒸发．     

用恒热流法测定多孔介质的热质迁移特性参数

设计了一种测定多孔介质热质迁移特性的实验装置。通过测定该装置中多孔介质的局部温含量和温度，结合恒热流下一维半无限大多孔介质热质迁移微分方程的解，得到了石英砂、玻璃珠等多孔介质的质扩散系数、热质扩散系数、名义热扩散系数、名义导热系数等热质迁移特性参数以及这些参数随湿含量、温度的变化。此外，还讨论了加热功率、初始湿含量等因素对测量的影响。     

石膏基复合相变材料热湿参数的实验

研究了相变微胶囊掺入建筑石膏制备石膏基复合相变材料的热湿性能。通过饱和盐溶液、传热传湿模拟试验、等效导热测试等方法对石膏基复合相变材料进行性能测试,并且采用微积分和数学拟合方法对测试结果进行分析。结果表明,石膏基复合相变材料具有良好的储热含湿性能,研究首次提出石膏基复合相变材料的表面质交换系数、湿扩散系数、相变因子等重要参数,为石膏基复合相变材料的节能效果计算提供重要依据。     

蒸发冷却设备蒸发水损失的计算与分析

参照冷却塔蒸发水损失的计算方法,总结5种蒸发冷却设备的蒸发水损失计算方法。选取3个实际测试的设备进行计算,将计算结果与实际测试结果进行对比分析。结果表明:利用空气进出口的含湿量差和机组处理的风量计算的结果与实际测试结果相差较小,建议利用此方法计算蒸发水损失。     

直接蒸发冷却式空调机用热湿交换材料的研究进展

介绍了直接蒸发冷却式地温空调机的原理和特点;综述了直接蒸发冷却式地温空调机用纸质、金属质、泡沫陶瓷质和其它材质热湿交换材料及其应用的最新研究进展;预测泡沫陶瓷将是空调机热湿交换材料的主要发展方向。     

直接蒸发冷却式空调机用热湿交换材料的研究进展

介绍了直接蒸发冷却式水源热泵空调机的原理和特点;综述了直接蒸发冷却式水源热泵空调机用纸质、金属质、泡沫陶瓷质和其它材质热湿交换材料及其应用的最新研究进展;预测泡沫陶瓷将是空调机热湿交换材料的主要发展方向。     

考虑纤维/基体界面相的复合材料湿扩散模型

通过类比复合材料湿扩散与热传导的控制方程以及边界条件,以Halpin & Tsai模型为基础,发展了一个考虑了纤维/基体界面相的三相复合材料湿扩散模型,并研究了纤维界面随机损伤对湿扩散的影响。建立了纤维周期排布、随机排布、界面相损伤随机分布3种细观有限元模型。用上述模型分析了单向复合材料横向有效湿扩散系数（TEMDUC）随纤维和界面相体积分数、湿扩散性能以及界面相损伤率变化的规律,理论预测与有限元计算结果一致。研究发现：界面相或纤维相的扩散系数存在一个临界值,当扩散系数小于该临界值时,TEMDUC随纤维体积分数的增大而减小;反之,TEMDUC随纤维体积分数的增大而增大,此临界值的大小与纤维体积含量无关。研究还发现纤维界面损伤率相同的条件下,其分布的随机性对复合材料的有效湿扩散系数影响不大。     

兰州地区蒸发冷却技术在办公建筑中的应用分析

对蒸发冷却空调系统在兰州地区的适用性进行了分析。本文以兰州市某办公建筑为模型,计算了其逐时冷负荷,并在焓湿图上分析了分别采用常规空调和蒸发冷却空调的送风过程。计算结果表明:在兰州地区办公建筑非常适合采用一级直接蒸发冷却空调系统,节能、环保、空气品质好。     

湿膜加湿器热质交换过程分析

湿膜加湿器是利用直接蒸发加湿的工作原理,对空气进行加湿,只消耗风机和循环水泵的电耗,具有结构简单和节省能源的优点。本文根据热质交换理论对湿膜加湿的传质过程进行了理论分析,建立了湿膜加湿器的传热、传质微分方程,得出影响加湿量的主要因素,并讨论了它们的影响趋势。     

Numerical solution of an inverse diffusion problem for the moisture transfer coefficient in a porous material

On the basis of the solution of a nonlinear diffusion equation with initial and boundary conditions, a transfer coefficient of moisture in a sample of a porous material is found by minimization of a functional, which expresses error of the calculated profile of moisture concentration in well defined time moments from their experimental values for the defined moisture transfer coefficient. In this case the transfer coefficient as opposed to previous studies is found as a sum of a power function and an exponential function of the moisture concentration. The exponent of the power function depends on time. Thus, a more accurate coincidence of the calculated profiles of the moisture concentration to their experimental profiles is gained in comparison to the investigations performed by other authors. The exponential term provides a good coincidence of the mentioned profiles for big times nearby the boundary of the sample, where the moisture evaporation to the atmosphere takes place.     

Moisture Transfer Tests in Blister Package Testing

Lactose and dicalcium phosphate tablets have been made by six different manufacturing-methods. These two types of tablet were packaged in blister packs and subjected to accelerated moisture tests. Methods are described whereby the diffusion coefficient of the blister film can be calculated from the moisture absorption curves. It is shown that the excipient effect (plasticizer) in the film increases the diffusion coefficient by at least an order of magnitude over and above the pure polymer. It is shown that, except for extruded granules, tablets made by the various methods exhibited approximately the same moisture absorption characteristics. The effects of this absorption on the hardness of the tablets are variable and demonstrate the necessity of adapting the formula and the manufacturing procedure to the particular blister.     

Moisture absorption in unfilled and glass-filled, cross-linked polyester

The moisture uptake characteristics of unfilled and filled lyester resin at 60°C are reported. The objective was to determine the influence of filler on the moisture uptake properties of unfilled polymer. Diffusivity in the filled polyester is lower than in the plain resin. However, the filled resin absorbs significantly more water than unfilled polyester. Tensile load was found to have no effect on the water uptake in plain polyester. However, moisture absorption was affected by tensile load in 20% (by volume) bead-filled polyester and in SMC-R65. Increasing load increased the diffusion coefficient in SMC-R65. Combining rules predicted the diffusion coefficient in unloaded SMC-R65, but could not account for changes in diffusivity caused by tensile loading. In bead-filled polyester, the diffusion coefficient was accurately predicted when microstructural effects were accounted for.     

Investigation of the processes of impregnation and drying of granular silica gel

The process of capillary impregnation and drying of silica gel grains in the acousto-convective drier of the ITPM of the Siberian branch of the Russian Academy of Sciences has been investigated experimentally. Two methods for humidifying a material with developed surface and internal structures have been considered. A comparison of these methods has been made and the influence of the impregnation rate on the geometry of silica gel grains has been analyzed. Silica gel grains were dried by three methods: microwave, convective, and acousto-convective. The dependence of the drying rate and the quality of the dried material on the chosen drying method has been shown. To describe the moisture extraction, we propose a mathematical model based on a two-dimensional diffusion equation written in the cylindrical system of coordinates. The moisture distribution in cylindrical samples consisting of silica gel grains has been obtained numerically for various values of the initial moisture content with the use of certain diffusion coefficients and the dependence of the moisture transfer coefficient on the frequency of acousto-convective action.     

非饱和土中温度引起水分迁移的光滑粒子法数值模拟

基于光滑粒子法(Smoothed particle hydrodynamics,SPH)的基本原理,尝试着对给出的非饱和土中水热耦合问题进行数值模拟。首先,采用基于SPH算法自行编制的程序对抛物型偏微分方程进行求解,并与解析解做出对比。计算结果表明,SPH算法用来数值模拟抛物型偏微分方程是可行的及有效的,这就为进一步采用SPH算法计算非饱和土在温度作用下的水分迁移问题提供了理论依据。然后,对非饱和土介质中热能传输以及水分迁移的规律进行了数值计算,其中重点计算了不同热扩散系数、温度诱致的水分扩散系数、等温条件下的水分扩散系数和热源条件下的体积含水率和温度分布的特点,并对其演化过程和机理进行分析,从而将SPH算法的应用范围作了扩展。     

Longitudinal shrinkage-moisture relations in softwood

Data have been presented on the axial dimensional changes of wood under zero load, both in equilibrium and non-equilibrium humidity conditions. The results support the idea of differing energy levels of moisture bonding, and suggest the division of sorbed moisture into two components: the first is a high-energy moisture that is associated with dimensional changes and shows very little hysteresis, and the second is a lower-energy moisture that is not associated with dimensional changes and shows considerable hysteresis. Diffusion of the first moisture component obeys Fick's laws with a concentration-dependent diffusion coefficient, whilst the hysteresis and the very slow approach to equilibrium of the second component makes the application of Fick's laws difficult or impossible. The addition of the two effects in diffusion measurements based on mass change alone could explain the difficulties normally encountered in the analysis of moisture diffusion in wood. No statistically significant effect of stress on the diffusion coefficient could be detected. Some results on very thin pieces show a strain reversal during the approach to moisture equilibrium, as predicted by some previous workers and attributed to the relaxation of internal stresses.     

Numerical analysis of moisture vapor diffusion in asphalt mixtures using digital images

The presence of moisture in asphalt mixtures is detrimental to their performance, e.g., softening the asphalt binder and weakening the aggregate-binder bond. One of the mechanisms of moisture transport, and the focus of this study, is molecular diffusion. Moisture diffusion occurs in response to a concentration gradient. The objective of this study was to estimate the diffusion coefficient of moisture vapor in asphalt mixtures by using finite element (FE) and finite difference (FD) numerical algorithms that employ digital images to discretize the composite. X-ray computed tomography was used to characterize the microstructure of laboratory-prepared specimens and provide the required three-dimensional digital images, which were segmented into three phases: air voids, a mixture of asphalt binder and the fine aggregate fraction, and coarse aggregates. Individual diffusion coefficients were assigned to each phase and the effective diffusion coefficient for the composite was computed using the numerical algorithms. The outcome was compared against experimental values. The effective diffusion coefficient for the asphalt mixtures obtained using the FD method showed closer agreement with the experimental data, while the FE results overestimated the experimental measurements in all cases.     

The Prediction of the Emissivity and Thermal Conductivity of Powder Beds

The present study attempts to understand drying characteristics of rubber wood sawdust in a tray dryer as it is the simplest and oldest of the dryers known commercially. An increase in temperature, flow rate of the heating medium, and initial moisture content was found to increase the drying rate. However, an increase in the particle diameter and bed height was found to reduce the drying rate. The increase in drying rate with temperature and moisture content was attributed to increase in the diffusion coefficient, while the increase due to the flow rate is attributed to reduction in the external mass transfer resistance during early stages of drying while the drying rate was high. An increase in bed height as well as particle size increases the diffusion path length for moisture, which contributes to the reduction in drying rate. The experimental data were modeled using Fick's diffusion equation, and the effective diffusivity coefficient was evaluated by minimizing the error between the experimental data and the prediction using the model equation. The effective diffusion coefficient was found to increase with increase in temperature, initial moisture content, and the flow rate of the heating medium, while it was found to decrease with increase in particle size. The diffusion coefficient was not found to vary with the bed height/solid loading. The effective diffusion coefficient was found to vary within 9.1 × 10^?9to 22 × 10^?9 m²/min. The standard deviation of error between the experimental data and prediction using the model, using the estimated effective diffusivity coefficient, was found to be less than 0.07 for the entire set of data, indicating the appropriateness of the model in predicting drying kinetics.     

热固性树脂中孔隙形成条件的定量测试方法与影响因素

根据热固性树脂基复合材料的热压成型特点和扩散形成孔隙机制 , 建立了一种离线的孔隙形成条件量测试方法 , 可实现孔隙率2树脂压力变化关系的定量测定。采用该方法研究了两类环氧树脂体系固化过程中胶温度、 相对湿度、 树脂压力等条件对孔隙形态和分布的影响 , 并与修正的 Kardos气泡模型的理论计算结果进了对比分析。结果表明: 所建立的测试方法可以模拟热压工艺条件离线测定水汽形成孔隙情况 , 结果重复性好不同条件下树脂压力与孔隙率的关系均呈指数衰减的变化规律 ; 凝胶温度和相对湿度对孔隙率影响显著; 树脂类明显影响孔隙率大小和形态分布。研究结果为热压工艺复合材料孔隙缺陷的控制提供了重要的测试方法和验依据。      

Determination of moisture distributions in porous building materials by neutron transmission analysis

The movement of moisture inside building structures can affect them in important ways, causing physical and chemical damage. Therefore the study of moisture transport in porous building materials is highly relevant to a better understanding of the durability of building structures made of porous materials. The moisture transport can be described phenomenologically by a diffusion equation using a moisture content dependent moisture transfer coefficient. To determine the transfer coefficient in a given material, the experimental quantitative measurement of the time and space dependent moisture distribution in the material is necessary. Neutron radiography provides a highly sensitive non-destructive method for the detection of the presence of water and provides high spatial resolution. A new neutron transmission analysis technique has been developed and optimized for the study of moisture in building materials to extract the quantitative information from the experimental data. Typically, moisture contents down to a few mg/cm³ can be detected at a spatial resolution of 1 mm. As an application example, the determination of the time and space dependent moisture distribution in a brick sample and the subsequent determination of the moisture transfer coefficient are presented.