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

这项建议提出了一项旨在建立干燥预测理论的理论和实验工作计划。在理论框架和实验测量中都考虑了局域非均质性的影响。理论分析基于大尺度平均法和考虑局部非均质性影响的闭合方案。实验研究利用核磁共振成像(NMRI)来量化多孔介质中的非均质性，并测量干燥过程中的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大范围饱和度空间偏差的实验值。反过来，这些将与闭合计算的预测进行比较。大尺度平均方法的关键特征是速度和浓度出现大尺度空间偏差，并且存在能够预测这些空间偏差的闭合方案。在以往对多孔介质中输运现象的所有研究中，理论和实验都是根据测量和预测的有效输运系数进行比较的。随着NMRI的使用，PI能够将比较扩展到有效传输系数的水平之外，并在计算和测量的大尺度空间偏差之间进行直接比较。干燥过程是非常广泛的工程和科学从业者感兴趣的，他们关心最终或中间产品中的水分传输。其中一些应用如下：在农产品、油漆和油墨、木材、凝胶、土壤、催化剂颗粒和泡沫中。这项调查应使人们能够更好地了解这一重要的运输过程。

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.