Moisture Transport in Unconsolidated Porous Media During Drying: Use of Nuclear Magnetic Resonance Imaging as an Experimental Probe

这一建议提出了一个计划的理论和实验工作，直接对干燥的预测理论。在理论框架和实验测量中都考虑了局部异质性的影响。理论分析基于大规模平均方法和考虑局部异质性影响的封闭方案。实验研究利用核磁共振成像（NMRI）来量化多孔介质的非均质性，并测量干燥过程中局部体积平均饱和度。确定局部体积平均饱和度的空间变化将提供饱和度大尺度空间偏差的实验值。这些结果又将与闭合计算的预测结果进行比较。大尺度平均方法的关键特征是速度和浓度的大尺度空间偏差的出现，以及可以预测这些空间偏差的封闭方案的存在。在以往对多孔介质中输运现象的研究中，理论和实验都是根据实测和预测的有效输运系数进行比较的。利用NMRI， PI可以开展有效输运系数水平以外的比较，直接比较计算和测量的大尺度空间偏差。干燥过程是一个非常广泛的工程和科学实践者感兴趣的过程，他们关心最终或中间产品中的水分输送。其中一些应用如下：农产品、油漆和油墨、木材、凝胶、土壤、催化剂颗粒和泡沫。这项调查将使人们对这一重要的运输过程有更深入的了解。

This proposal presents a program of theoretical and experimental work directed toward a predictive theory of drying. The influence of local heterogeneities is incorporated into both the theoretical framework and the experimental measurements that were proposed. The theoretical analysis is based on the method of large-scale averaging and a closure scheme that incorporates the effect of local heterogeneities. The experimental studies make use of nuclear magnetic resonance imaging (NMRI) to both quantify the heterogeneities in a porous medium and to measure the local volume averaged saturation during drying. Determination of the spatial variation of the local volume averaged saturation will provide experimental values of the large-scale spatial deviation of the saturation. These in turn, will be compared with predictions from the closure calculations. The key feature of the method of large-scale averaging is the appearance of large-scale spatial deviations in the velocity and concentration, and the existence of a closure scheme that can predict these spatial deviations. In all previous studies of transport phenomena in porous media, theory and experiment have been compared in terms of measured and predicted effective transport coefficients. With the use of NMRI, the PI's are in a position to develop the comparison beyond the level of the effective transport coefficients and make a direct comparison between calculated and measured large-scale spatial deviations. The process of drying is of interest to a very wide range of engineering and scientific practitioners who are concerned with moisture transport in final or intermediate products. Some of these applications are given as follows: in agricultural products, paints and inks, wood, gels, soils, catalyst pellets, and foams. This investigation should permit a greater understanding of this important transport process.