测量含湿多孔介质局部含湿量的针型电容法

发展了一种能够测量含湿多孔介质局部含湿量的针型电容法。通过采用针型电容传感器和能够测量微小电容变化的测量电路，采取减少介质损耗的有效措施，使测量的灵敏度，稳定性和空间分辨率均达到了较高的程度。实验结果表明，针型电容法灵敏度高，线性度好，可为含湿多孔介质局部含湿量的测量提供一种测试手段。     

参数估计法测定多孔介质热湿迁移特性的实验研究

设计了基于参数估计法测定多孔介质热湿迁移特性的实验测试装置，在多孔介质局部含湿量和温度的实验测试数据基础上的波动通过参数估计算法得到了砂土的热湿迁移特必数据，此外，还对参数估计算法中的几个问题进行了分析探讨。     

同时测定含湿多孔介质热湿迁移特性的参数估计法

将含湿多孔介质瞬态温度场和湿度场的理论解与测量介质中某些点处的温度值和湿度值相结合，提出了一种同时测定含湿多孔介质热湿迁移特性的参数估计法。它可以通过一次实验获得多个迁移特性的数据，为发展多孔介质热湿迁移特性综合测量装置奠定了基础。     

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。     

多孔介质质扩散系数的参数估计方法及测定方法

提出一种在第三类边界条件下,通过使数值计算的湿分蒸发与规律实测值之间的最佳逼近,以瞬态确定计算多孔介质质扩散系数的参数估计方法。设计并制造了对流蒸发实验装置。在假设质扩散系数为含湿量线性函数的情况下,对石膏板和水泥板的质扩散系数进行了测量和计算。测试及计算方法简单可行,测定时间较稳态方法大大缩短,因此比较实用。     

液氮在多孔介质体系中传热特性实验研究

为研究液氮在煤体内的传导机制,构建了基于玻璃棉的多孔介质体系,进行了液氮在多孔介质体系中的传热模拟实验。采用热电偶和数据采集器获取了多孔介质内温度场的动态分布,探讨了注液氮量对液氮传热特性的影响。结果表明,液氮在多孔介质体系中形成冷量集中区,呈现局部降温效果;冷量集中区以垂直向下移动为主,移动速度受注液氮量的影响较小。研究为液氮防灭煤火技术实践提供理论基础。     

基于COMSOL的纸浆模塑干燥模拟及验证

目的 研究采用COMSOL Multiphysics模拟纸浆模塑干燥效率及厚度变化的可行性。方法 基于多孔介质理论,应用有限元仿真软件COMSOL Multiphysics建立纸浆模塑干基含水率随时间变化的热湿、水分流动、非等温流动多物理场耦合模型,考虑干燥中含湿多孔介质的湿空气热对流及多孔基体的热传导,模拟在热板加热条件下纸浆模塑的干燥效率和厚度的变化,并与实验结果进行比较。结果 模型内域探针所得模拟结果与实验结果具有良好的一致性,在干燥后期厚度预测误差范围为0.4%～7.7%,干燥效率预测差异值最低为4.3%。结论 采用COMSOL Multiphysics模拟纸浆模塑干燥过程可行。     

瞬态高强加热条件下含湿多孔介质传热传质模型研究

提出了瞬态高强加热下含湿多孔介质传热传质的新模型，模型包括的水分种类齐全、水分迁移机制全面，假设条件相对较少，考虑了非Fourier传热效应和非Fick传质效应。新模型通过具体的分区分析得到简化并更加实用。     

饱和多孔介质中动力渗流耦合分析的Biot-Cosserat连续体模型与应变局部化有限元模拟

提出了适用于饱和多孔介质中应变局部化分析及动力渗流耦合分析的Biot-Cosserat连续体模型。基于饱和多孔介质动力渗流耦合分析的Biot理论,将固体骨架看作Cosserat连续体,并考虑旋转惯性,建立了饱和多孔介质动力渗流耦合分析的Biot-Cosserat连续体模型。基于Galerkin加权余量法,对所发展的模型推导了以固体骨架广义位移(包含旋转)及孔隙水压力为基本未知量的有限元公式。利用所发展的数值模型,对包含压力相关弹塑性固体骨架材料的饱和多孔介质进行了动力渗流耦合分析与应变局部化有限元模拟,结果表明,所发展的两相饱和多孔介质动力渗流耦合分析的Biot-Cosserat连续体模型能保持饱和两相介质应变局部化问题的适定性及模拟饱和多孔介质中由应变软化引起的应变局部化现象的有效性。     

保温多孔材料含湿传热过程分析模型

基于粗宏观表征体元RMV(representative macroscopic volume),考虑孔隙中含有湿分的情况,建立了多孔介质传热的黑箱、灰箱、白箱模型。根据建立的"三箱"模型和传热过程分析,推导出了导热系数的公式。以岩棉为例,通过所建模型数值计算并讨论了孔隙率、含湿率、孔隙通道分布系数和迂曲度对导热系数的影响效果。结果发现,孔隙率和孔隙通道分布系数与导热系数呈负相关关系,含湿率和迂曲度与导热系数呈正相关关系。结论可为提高材料的保温性能提供相应的思路和方法。     

Linear viscoelastic behavior of porous media with non-uniform saturation

Heterogeneous moisture distribution is usually observed in partially saturated porous media in the form of saturation patches. Such local heterogeneity can significantly influence the macroscopic hydro-mechanical and acoustic behavior of porous media. In this paper, a linear viscoporoelastic model is presented that can be used to address the effects of local fluid flow in the heterogeneously saturated porous media subjected to a small perturbation. The effects of local flow are characterized using the notion of capillary relaxation. The complex, frequency-dependent material properties characterizing the viscoporoelastic behavior are derived. A rigorous procedure is presented to evaluate the material parameters. The proposed model describes well the effects of patchy saturation on the dispersion and attenuation of the compressional wave in partially saturated rocks. It is found that at high saturation the effects of local gas-pressure redistribution are not negligible. A procedure is proposed to determine the capillary relaxation times using acoustic data. The proposed model provides an alternative methodology to characterize the effects of patchy saturation on the acoustic behavior of partially saturated porous media.     

High mobility of SDBS-dispersed single-walled carbon nanotubes in saturated and unsaturated porous media

Knowledge of the mobility of carbon nanotubes (CNTs) in porous media is very important to assess their impacts on the environment. In this study, a series of laboratory experiments were conducted to explore the transport mechanisms of sonication shortened, sodium dodecylbenzene sulfonate (SDBS) dispersed single-walled nanotubes (SWNTs) in both saturated and unsaturated sand columns. Laboratory columns packed with quartz sand with different combinations of moisture content and grain-size distribution were used to examine the breakthrough behavior of the SDBS-dispersed SWNTs. Bubble column experiments were also conducted to study the interactions between the SDBS-dispersed SWNTs and the air-water interface. Packed-column experimental results showed that the SDBS-dispersed SWNTs were highly mobile for most of the experimental conditions tested. The surface deposition of the SWNTs in the sand columns was low because all the interactive surfaces were negatively charged. Physical trapping was not observed for the SWNTs in the saturated porous media of different grain-size distributions because the SWNTs might orient parallel to the streamlines in flow to reduce their retention. Retention of the SWNTs in unsaturated porous media occurred only at a very low moisture content (<0.10). Otherwise, reduction in moisture content showed little impact on the retention and transport of the SWNTs in unsaturated porous media. Findings from the bubble-column experiments confirmed that the SDBS-dispersed SWNTs did not attach to the air-water interface. A mathematical model based on the advection-dispersion equation coupled with reaction-rate laws successfully described the retention and transport of the SDBS-dispersed SWNTs in both water-saturated and unsaturated columns.     

An acoustic method for soil moisture measurement

The paper deals with the problem of measuring the moisture of agricultural soils by an accurate, on-site, real-time method. The idea is to estimate the moisture by measuring the speed of sound in the medium: the main issue is therefore to determine a precise relationship between the two quantities. To this purpose, the Brutsaert's model for elastic waves in porous media is applied, taking into consideration different kinds of soil of common interest in agriculture. The authors have derived the speed-moisture curves, the conditions for the actual validity of the curves, and the suitable sound frequency for performing the measurement, for a wide range of agricultural soils in different physical conditions. The paper results are therefore the basis to realize an inexpensive and accurate moisture sensor for farmers.     

On the measurement of thermal conductivity in moist porous materialsMesure de la conduction thermique des matériaux poreux humides

A new method for simultaneous measurement of both conduction and diffusion in a moist porous material has been developed. The experiments are carried out during the moistening process in such a way that the local thermal conductivity and the local diffusion flux may be determined as a function of the continuously increasing moisture content. First results show, for example, that the moisture distribution in the individual pores can have a significant effect on the thermal conductivity of moist porous materials.     

Determination of moisture content of concrete by microwave-resonance method

The moisture content of concrete is one of its important properties. A new method of measuring the moisture content of concrete and other building materials is described. The method is based on the measurement of the dielectric constant at microwave frequencies. Studies on concrete have shown that a linear relation exists between the evaporable water content of concrete and the instrument reading. The main advantages of this method are i) it is nondestructive, ii) rapid response of the instrument, iii) humidity gradients in the specimen can be studied iv) measurements are independent of the dielectric losses and the conductivity of the material, v) sharp resonance peak of the microwaves allows very accurate measurements.     

Determination of Moisture Diffusivity as a Function of Both Moisture and Temperature

The effect of moisture and temperature on liquid water transport in porous media was studied. Specimens of autoclaved aerated concrete were subjected to one-sided water penetration in isothermal conditions at temperatures of 20 °C, 40 °C, 60 °C, and 80 °C. After specified time intervals, moisture profiles were determined gravimetrically. The moisture diffusivity was calculated for a particular temperature as a function of moisture content, using an inverse analysis. The results demonstrate the dependence of the moisture diffusivity on the moisture content and the temperature of the samples. The moisture diffusivity for high moisture content can be as much as one order of magnitude greater than for the lowest moisture content studied. The moisture diffusivity was found to increase by as much as a factor of two when the temperature is increased from 20 °C to 80 °C.     

Application of resistance strain gauges on a wet surface

The application of strain gauges to determine the stress on wet and porous media such as rock has been examined. Weldable strain gauges have not been considered. Special consideration has been. given to different methods of water protection. For unbonded strain gauges tested under water a logarithmic dependence between time and resistivity has been found. Several kinds of moisture protection have been tried on the material side as well as on the back side of selected strain gauges. The bonding and the stability of the gauges under load in water has been examined.